use std::fmt::Write as _;
use std::io::Write;
use std::sync::Arc;

use anyhow::{Context as _, Result};
use assistant_settings::AssistantSettings;
use assistant_tool::{ActionLog, Tool, ToolWorkingSet};
use chrono::{DateTime, Utc};
use collections::{BTreeMap, HashMap, HashSet};
use fs::Fs;
use futures::future::Shared;
use futures::{FutureExt, StreamExt as _};
use git;
use gpui::{App, AppContext, Context, Entity, EventEmitter, SharedString, Task, WeakEntity};
use language_model::{
    LanguageModel, LanguageModelCompletionEvent, LanguageModelRegistry, LanguageModelRequest,
    LanguageModelRequestMessage, LanguageModelRequestTool, LanguageModelToolResult,
    LanguageModelToolUseId, MaxMonthlySpendReachedError, MessageContent, PaymentRequiredError,
    Role, StopReason, TokenUsage,
};
use project::git_store::{GitStore, GitStoreCheckpoint};
use project::{Project, Worktree};
use prompt_store::{
    AssistantSystemPromptContext, PromptBuilder, RulesFile, WorktreeInfoForSystemPrompt,
};
use serde::{Deserialize, Serialize};
use settings::Settings;
use util::{maybe, post_inc, ResultExt as _, TryFutureExt as _};
use uuid::Uuid;

use crate::context::{attach_context_to_message, ContextId, ContextSnapshot};
use crate::thread_store::{
    SerializedMessage, SerializedMessageSegment, SerializedThread, SerializedToolResult,
    SerializedToolUse,
};
use crate::tool_use::{PendingToolUse, ToolUse, ToolUseState};

#[derive(Debug, Clone, Copy)]
pub enum RequestKind {
    Chat,
    /// Used when summarizing a thread.
    Summarize,
}

#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Serialize, Deserialize)]
pub struct ThreadId(Arc<str>);

impl ThreadId {
    pub fn new() -> Self {
        Self(Uuid::new_v4().to_string().into())
    }
}

impl std::fmt::Display for ThreadId {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", self.0)
    }
}

#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy, Serialize, Deserialize)]
pub struct MessageId(pub(crate) usize);

impl MessageId {
    fn post_inc(&mut self) -> Self {
        Self(post_inc(&mut self.0))
    }
}

/// A message in a [`Thread`].
#[derive(Debug, Clone)]
pub struct Message {
    pub id: MessageId,
    pub role: Role,
    pub segments: Vec<MessageSegment>,
}

impl Message {
    pub fn push_thinking(&mut self, text: &str) {
        if let Some(MessageSegment::Thinking(segment)) = self.segments.last_mut() {
            segment.push_str(text);
        } else {
            self.segments
                .push(MessageSegment::Thinking(text.to_string()));
        }
    }

    pub fn push_text(&mut self, text: &str) {
        if let Some(MessageSegment::Text(segment)) = self.segments.last_mut() {
            segment.push_str(text);
        } else {
            self.segments.push(MessageSegment::Text(text.to_string()));
        }
    }

    pub fn to_string(&self) -> String {
        let mut result = String::new();
        for segment in &self.segments {
            match segment {
                MessageSegment::Text(text) => result.push_str(text),
                MessageSegment::Thinking(text) => {
                    result.push_str("<think>");
                    result.push_str(text);
                    result.push_str("</think>");
                }
            }
        }
        result
    }
}

#[derive(Debug, Clone)]
pub enum MessageSegment {
    Text(String),
    Thinking(String),
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct ProjectSnapshot {
    pub worktree_snapshots: Vec<WorktreeSnapshot>,
    pub unsaved_buffer_paths: Vec<String>,
    pub timestamp: DateTime<Utc>,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct WorktreeSnapshot {
    pub worktree_path: String,
    pub git_state: Option<GitState>,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct GitState {
    pub remote_url: Option<String>,
    pub head_sha: Option<String>,
    pub current_branch: Option<String>,
    pub diff: Option<String>,
}

#[derive(Clone)]
pub struct ThreadCheckpoint {
    message_id: MessageId,
    git_checkpoint: GitStoreCheckpoint,
}

#[derive(Copy, Clone, Debug)]
pub enum ThreadFeedback {
    Positive,
    Negative,
}

pub enum LastRestoreCheckpoint {
    Pending {
        message_id: MessageId,
    },
    Error {
        message_id: MessageId,
        error: String,
    },
}

impl LastRestoreCheckpoint {
    pub fn message_id(&self) -> MessageId {
        match self {
            LastRestoreCheckpoint::Pending { message_id } => *message_id,
            LastRestoreCheckpoint::Error { message_id, .. } => *message_id,
        }
    }
}

/// A thread of conversation with the LLM.
pub struct Thread {
    id: ThreadId,
    updated_at: DateTime<Utc>,
    summary: Option<SharedString>,
    pending_summary: Task<Option<()>>,
    messages: Vec<Message>,
    next_message_id: MessageId,
    context: BTreeMap<ContextId, ContextSnapshot>,
    context_by_message: HashMap<MessageId, Vec<ContextId>>,
    system_prompt_context: Option<AssistantSystemPromptContext>,
    checkpoints_by_message: HashMap<MessageId, ThreadCheckpoint>,
    completion_count: usize,
    pending_completions: Vec<PendingCompletion>,
    project: Entity<Project>,
    prompt_builder: Arc<PromptBuilder>,
    tools: Arc<ToolWorkingSet>,
    tool_use: ToolUseState,
    action_log: Entity<ActionLog>,
    last_restore_checkpoint: Option<LastRestoreCheckpoint>,
    pending_checkpoint: Option<ThreadCheckpoint>,
    initial_project_snapshot: Shared<Task<Option<Arc<ProjectSnapshot>>>>,
    cumulative_token_usage: TokenUsage,
    feedback: Option<ThreadFeedback>,
}

impl Thread {
    pub fn new(
        project: Entity<Project>,
        tools: Arc<ToolWorkingSet>,
        prompt_builder: Arc<PromptBuilder>,
        cx: &mut Context<Self>,
    ) -> Self {
        Self {
            id: ThreadId::new(),
            updated_at: Utc::now(),
            summary: None,
            pending_summary: Task::ready(None),
            messages: Vec::new(),
            next_message_id: MessageId(0),
            context: BTreeMap::default(),
            context_by_message: HashMap::default(),
            system_prompt_context: None,
            checkpoints_by_message: HashMap::default(),
            completion_count: 0,
            pending_completions: Vec::new(),
            project: project.clone(),
            prompt_builder,
            tools: tools.clone(),
            last_restore_checkpoint: None,
            pending_checkpoint: None,
            tool_use: ToolUseState::new(tools.clone()),
            action_log: cx.new(|_| ActionLog::new()),
            initial_project_snapshot: {
                let project_snapshot = Self::project_snapshot(project, cx);
                cx.foreground_executor()
                    .spawn(async move { Some(project_snapshot.await) })
                    .shared()
            },
            cumulative_token_usage: TokenUsage::default(),
            feedback: None,
        }
    }

    pub fn deserialize(
        id: ThreadId,
        serialized: SerializedThread,
        project: Entity<Project>,
        tools: Arc<ToolWorkingSet>,
        prompt_builder: Arc<PromptBuilder>,
        cx: &mut Context<Self>,
    ) -> Self {
        let next_message_id = MessageId(
            serialized
                .messages
                .last()
                .map(|message| message.id.0 + 1)
                .unwrap_or(0),
        );
        let tool_use =
            ToolUseState::from_serialized_messages(tools.clone(), &serialized.messages, |_| true);

        Self {
            id,
            updated_at: serialized.updated_at,
            summary: Some(serialized.summary),
            pending_summary: Task::ready(None),
            messages: serialized
                .messages
                .into_iter()
                .map(|message| Message {
                    id: message.id,
                    role: message.role,
                    segments: message
                        .segments
                        .into_iter()
                        .map(|segment| match segment {
                            SerializedMessageSegment::Text { text } => MessageSegment::Text(text),
                            SerializedMessageSegment::Thinking { text } => {
                                MessageSegment::Thinking(text)
                            }
                        })
                        .collect(),
                })
                .collect(),
            next_message_id,
            context: BTreeMap::default(),
            context_by_message: HashMap::default(),
            system_prompt_context: None,
            checkpoints_by_message: HashMap::default(),
            completion_count: 0,
            pending_completions: Vec::new(),
            last_restore_checkpoint: None,
            pending_checkpoint: None,
            project,
            prompt_builder,
            tools,
            tool_use,
            action_log: cx.new(|_| ActionLog::new()),
            initial_project_snapshot: Task::ready(serialized.initial_project_snapshot).shared(),
            // TODO: persist token usage?
            cumulative_token_usage: TokenUsage::default(),
            feedback: None,
        }
    }

    pub fn id(&self) -> &ThreadId {
        &self.id
    }

    pub fn is_empty(&self) -> bool {
        self.messages.is_empty()
    }

    pub fn updated_at(&self) -> DateTime<Utc> {
        self.updated_at
    }

    pub fn touch_updated_at(&mut self) {
        self.updated_at = Utc::now();
    }

    pub fn summary(&self) -> Option<SharedString> {
        self.summary.clone()
    }

    pub fn summary_or_default(&self) -> SharedString {
        const DEFAULT: SharedString = SharedString::new_static("New Thread");
        self.summary.clone().unwrap_or(DEFAULT)
    }

    pub fn set_summary(&mut self, summary: impl Into<SharedString>, cx: &mut Context<Self>) {
        self.summary = Some(summary.into());
        cx.emit(ThreadEvent::SummaryChanged);
    }

    pub fn message(&self, id: MessageId) -> Option<&Message> {
        self.messages.iter().find(|message| message.id == id)
    }

    pub fn messages(&self) -> impl Iterator<Item = &Message> {
        self.messages.iter()
    }

    pub fn is_generating(&self) -> bool {
        !self.pending_completions.is_empty() || !self.all_tools_finished()
    }

    pub fn tools(&self) -> &Arc<ToolWorkingSet> {
        &self.tools
    }

    pub fn pending_tool(&self, id: &LanguageModelToolUseId) -> Option<&PendingToolUse> {
        self.tool_use
            .pending_tool_uses()
            .into_iter()
            .find(|tool_use| &tool_use.id == id)
    }

    pub fn tools_needing_confirmation(&self) -> impl Iterator<Item = &PendingToolUse> {
        self.tool_use
            .pending_tool_uses()
            .into_iter()
            .filter(|tool_use| tool_use.status.needs_confirmation())
    }

    pub fn checkpoint_for_message(&self, id: MessageId) -> Option<ThreadCheckpoint> {
        self.checkpoints_by_message.get(&id).cloned()
    }

    pub fn restore_checkpoint(
        &mut self,
        checkpoint: ThreadCheckpoint,
        cx: &mut Context<Self>,
    ) -> Task<Result<()>> {
        self.last_restore_checkpoint = Some(LastRestoreCheckpoint::Pending {
            message_id: checkpoint.message_id,
        });
        cx.emit(ThreadEvent::CheckpointChanged);
        cx.notify();

        let project = self.project.read(cx);
        let restore = project
            .git_store()
            .read(cx)
            .restore_checkpoint(checkpoint.git_checkpoint.clone(), cx);
        cx.spawn(async move |this, cx| {
            let result = restore.await;
            this.update(cx, |this, cx| {
                if let Err(err) = result.as_ref() {
                    this.last_restore_checkpoint = Some(LastRestoreCheckpoint::Error {
                        message_id: checkpoint.message_id,
                        error: err.to_string(),
                    });
                } else {
                    this.truncate(checkpoint.message_id, cx);
                    this.last_restore_checkpoint = None;
                }
                this.pending_checkpoint = None;
                cx.emit(ThreadEvent::CheckpointChanged);
                cx.notify();
            })?;
            result
        })
    }

    fn finalize_pending_checkpoint(&mut self, cx: &mut Context<Self>) {
        let pending_checkpoint = if self.is_generating() {
            return;
        } else if let Some(checkpoint) = self.pending_checkpoint.take() {
            checkpoint
        } else {
            return;
        };

        let git_store = self.project.read(cx).git_store().clone();
        let final_checkpoint = git_store.read(cx).checkpoint(cx);
        cx.spawn(async move |this, cx| match final_checkpoint.await {
            Ok(final_checkpoint) => {
                let equal = git_store
                    .read_with(cx, |store, cx| {
                        store.compare_checkpoints(
                            pending_checkpoint.git_checkpoint.clone(),
                            final_checkpoint.clone(),
                            cx,
                        )
                    })?
                    .await
                    .unwrap_or(false);

                if equal {
                    git_store
                        .read_with(cx, |store, cx| {
                            store.delete_checkpoint(pending_checkpoint.git_checkpoint, cx)
                        })?
                        .detach();
                } else {
                    this.update(cx, |this, cx| {
                        this.insert_checkpoint(pending_checkpoint, cx)
                    })?;
                }

                git_store
                    .read_with(cx, |store, cx| {
                        store.delete_checkpoint(final_checkpoint, cx)
                    })?
                    .detach();

                Ok(())
            }
            Err(_) => this.update(cx, |this, cx| {
                this.insert_checkpoint(pending_checkpoint, cx)
            }),
        })
        .detach();
    }

    fn insert_checkpoint(&mut self, checkpoint: ThreadCheckpoint, cx: &mut Context<Self>) {
        self.checkpoints_by_message
            .insert(checkpoint.message_id, checkpoint);
        cx.emit(ThreadEvent::CheckpointChanged);
        cx.notify();
    }

    pub fn last_restore_checkpoint(&self) -> Option<&LastRestoreCheckpoint> {
        self.last_restore_checkpoint.as_ref()
    }

    pub fn truncate(&mut self, message_id: MessageId, cx: &mut Context<Self>) {
        let Some(message_ix) = self
            .messages
            .iter()
            .rposition(|message| message.id == message_id)
        else {
            return;
        };
        for deleted_message in self.messages.drain(message_ix..) {
            self.context_by_message.remove(&deleted_message.id);
            self.checkpoints_by_message.remove(&deleted_message.id);
        }
        cx.notify();
    }

    pub fn context_for_message(&self, id: MessageId) -> Option<Vec<ContextSnapshot>> {
        let context = self.context_by_message.get(&id)?;
        Some(
            context
                .into_iter()
                .filter_map(|context_id| self.context.get(&context_id))
                .cloned()
                .collect::<Vec<_>>(),
        )
    }

    /// Returns whether all of the tool uses have finished running.
    pub fn all_tools_finished(&self) -> bool {
        // If the only pending tool uses left are the ones with errors, then
        // that means that we've finished running all of the pending tools.
        self.tool_use
            .pending_tool_uses()
            .iter()
            .all(|tool_use| tool_use.status.is_error())
    }

    pub fn tool_uses_for_message(&self, id: MessageId, cx: &App) -> Vec<ToolUse> {
        self.tool_use.tool_uses_for_message(id, cx)
    }

    pub fn tool_results_for_message(&self, id: MessageId) -> Vec<&LanguageModelToolResult> {
        self.tool_use.tool_results_for_message(id)
    }

    pub fn tool_result(&self, id: &LanguageModelToolUseId) -> Option<&LanguageModelToolResult> {
        self.tool_use.tool_result(id)
    }

    pub fn message_has_tool_results(&self, message_id: MessageId) -> bool {
        self.tool_use.message_has_tool_results(message_id)
    }

    pub fn insert_user_message(
        &mut self,
        text: impl Into<String>,
        context: Vec<ContextSnapshot>,
        git_checkpoint: Option<GitStoreCheckpoint>,
        cx: &mut Context<Self>,
    ) -> MessageId {
        let message_id =
            self.insert_message(Role::User, vec![MessageSegment::Text(text.into())], cx);
        let context_ids = context.iter().map(|context| context.id).collect::<Vec<_>>();
        self.context
            .extend(context.into_iter().map(|context| (context.id, context)));
        self.context_by_message.insert(message_id, context_ids);
        if let Some(git_checkpoint) = git_checkpoint {
            self.pending_checkpoint = Some(ThreadCheckpoint {
                message_id,
                git_checkpoint,
            });
        }
        message_id
    }

    pub fn insert_message(
        &mut self,
        role: Role,
        segments: Vec<MessageSegment>,
        cx: &mut Context<Self>,
    ) -> MessageId {
        let id = self.next_message_id.post_inc();
        self.messages.push(Message { id, role, segments });
        self.touch_updated_at();
        cx.emit(ThreadEvent::MessageAdded(id));
        id
    }

    pub fn edit_message(
        &mut self,
        id: MessageId,
        new_role: Role,
        new_segments: Vec<MessageSegment>,
        cx: &mut Context<Self>,
    ) -> bool {
        let Some(message) = self.messages.iter_mut().find(|message| message.id == id) else {
            return false;
        };
        message.role = new_role;
        message.segments = new_segments;
        self.touch_updated_at();
        cx.emit(ThreadEvent::MessageEdited(id));
        true
    }

    pub fn delete_message(&mut self, id: MessageId, cx: &mut Context<Self>) -> bool {
        let Some(index) = self.messages.iter().position(|message| message.id == id) else {
            return false;
        };
        self.messages.remove(index);
        self.context_by_message.remove(&id);
        self.touch_updated_at();
        cx.emit(ThreadEvent::MessageDeleted(id));
        true
    }

    /// Returns the representation of this [`Thread`] in a textual form.
    ///
    /// This is the representation we use when attaching a thread as context to another thread.
    pub fn text(&self) -> String {
        let mut text = String::new();

        for message in &self.messages {
            text.push_str(match message.role {
                language_model::Role::User => "User:",
                language_model::Role::Assistant => "Assistant:",
                language_model::Role::System => "System:",
            });
            text.push('\n');

            for segment in &message.segments {
                match segment {
                    MessageSegment::Text(content) => text.push_str(content),
                    MessageSegment::Thinking(content) => {
                        text.push_str(&format!("<think>{}</think>", content))
                    }
                }
            }
            text.push('\n');
        }

        text
    }

    /// Serializes this thread into a format for storage or telemetry.
    pub fn serialize(&self, cx: &mut Context<Self>) -> Task<Result<SerializedThread>> {
        let initial_project_snapshot = self.initial_project_snapshot.clone();
        cx.spawn(async move |this, cx| {
            let initial_project_snapshot = initial_project_snapshot.await;
            this.read_with(cx, |this, cx| SerializedThread {
                version: SerializedThread::VERSION.to_string(),
                summary: this.summary_or_default(),
                updated_at: this.updated_at(),
                messages: this
                    .messages()
                    .map(|message| SerializedMessage {
                        id: message.id,
                        role: message.role,
                        segments: message
                            .segments
                            .iter()
                            .map(|segment| match segment {
                                MessageSegment::Text(text) => {
                                    SerializedMessageSegment::Text { text: text.clone() }
                                }
                                MessageSegment::Thinking(text) => {
                                    SerializedMessageSegment::Thinking { text: text.clone() }
                                }
                            })
                            .collect(),
                        tool_uses: this
                            .tool_uses_for_message(message.id, cx)
                            .into_iter()
                            .map(|tool_use| SerializedToolUse {
                                id: tool_use.id,
                                name: tool_use.name,
                                input: tool_use.input,
                            })
                            .collect(),
                        tool_results: this
                            .tool_results_for_message(message.id)
                            .into_iter()
                            .map(|tool_result| SerializedToolResult {
                                tool_use_id: tool_result.tool_use_id.clone(),
                                is_error: tool_result.is_error,
                                content: tool_result.content.clone(),
                            })
                            .collect(),
                    })
                    .collect(),
                initial_project_snapshot,
            })
        })
    }

    pub fn set_system_prompt_context(&mut self, context: AssistantSystemPromptContext) {
        self.system_prompt_context = Some(context);
    }

    pub fn system_prompt_context(&self) -> &Option<AssistantSystemPromptContext> {
        &self.system_prompt_context
    }

    pub fn load_system_prompt_context(
        &self,
        cx: &App,
    ) -> Task<(AssistantSystemPromptContext, Option<ThreadError>)> {
        let project = self.project.read(cx);
        let tasks = project
            .visible_worktrees(cx)
            .map(|worktree| {
                Self::load_worktree_info_for_system_prompt(
                    project.fs().clone(),
                    worktree.read(cx),
                    cx,
                )
            })
            .collect::<Vec<_>>();

        cx.spawn(async |_cx| {
            let results = futures::future::join_all(tasks).await;
            let mut first_err = None;
            let worktrees = results
                .into_iter()
                .map(|(worktree, err)| {
                    if first_err.is_none() && err.is_some() {
                        first_err = err;
                    }
                    worktree
                })
                .collect::<Vec<_>>();
            (AssistantSystemPromptContext::new(worktrees), first_err)
        })
    }

    fn load_worktree_info_for_system_prompt(
        fs: Arc<dyn Fs>,
        worktree: &Worktree,
        cx: &App,
    ) -> Task<(WorktreeInfoForSystemPrompt, Option<ThreadError>)> {
        let root_name = worktree.root_name().into();
        let abs_path = worktree.abs_path();

        // Note that Cline supports `.clinerules` being a directory, but that is not currently
        // supported. This doesn't seem to occur often in GitHub repositories.
        const RULES_FILE_NAMES: [&'static str; 5] = [
            ".rules",
            ".cursorrules",
            ".windsurfrules",
            ".clinerules",
            "CLAUDE.md",
        ];
        let selected_rules_file = RULES_FILE_NAMES
            .into_iter()
            .filter_map(|name| {
                worktree
                    .entry_for_path(name)
                    .filter(|entry| entry.is_file())
                    .map(|entry| (entry.path.clone(), worktree.absolutize(&entry.path)))
            })
            .next();

        if let Some((rel_rules_path, abs_rules_path)) = selected_rules_file {
            cx.spawn(async move |_| {
                let rules_file_result = maybe!(async move {
                    let abs_rules_path = abs_rules_path?;
                    let text = fs.load(&abs_rules_path).await.with_context(|| {
                        format!("Failed to load assistant rules file {:?}", abs_rules_path)
                    })?;
                    anyhow::Ok(RulesFile {
                        rel_path: rel_rules_path,
                        abs_path: abs_rules_path.into(),
                        text: text.trim().to_string(),
                    })
                })
                .await;
                let (rules_file, rules_file_error) = match rules_file_result {
                    Ok(rules_file) => (Some(rules_file), None),
                    Err(err) => (
                        None,
                        Some(ThreadError::Message {
                            header: "Error loading rules file".into(),
                            message: format!("{err}").into(),
                        }),
                    ),
                };
                let worktree_info = WorktreeInfoForSystemPrompt {
                    root_name,
                    abs_path,
                    rules_file,
                };
                (worktree_info, rules_file_error)
            })
        } else {
            Task::ready((
                WorktreeInfoForSystemPrompt {
                    root_name,
                    abs_path,
                    rules_file: None,
                },
                None,
            ))
        }
    }

    pub fn send_to_model(
        &mut self,
        model: Arc<dyn LanguageModel>,
        request_kind: RequestKind,
        cx: &mut Context<Self>,
    ) {
        let mut request = self.to_completion_request(request_kind, cx);
        request.tools = {
            let mut tools = Vec::new();
            tools.extend(self.tools().enabled_tools(cx).into_iter().map(|tool| {
                LanguageModelRequestTool {
                    name: tool.name(),
                    description: tool.description(),
                    input_schema: tool.input_schema(),
                }
            }));

            tools
        };

        self.stream_completion(request, model, cx);
    }

    pub fn to_completion_request(
        &self,
        request_kind: RequestKind,
        cx: &App,
    ) -> LanguageModelRequest {
        let mut request = LanguageModelRequest {
            messages: vec![],
            tools: Vec::new(),
            stop: Vec::new(),
            temperature: None,
        };

        if let Some(system_prompt_context) = self.system_prompt_context.as_ref() {
            if let Some(system_prompt) = self
                .prompt_builder
                .generate_assistant_system_prompt(system_prompt_context)
                .context("failed to generate assistant system prompt")
                .log_err()
            {
                request.messages.push(LanguageModelRequestMessage {
                    role: Role::System,
                    content: vec![MessageContent::Text(system_prompt)],
                    cache: true,
                });
            }
        } else {
            log::error!("system_prompt_context not set.")
        }

        let mut referenced_context_ids = HashSet::default();

        for message in &self.messages {
            if let Some(context_ids) = self.context_by_message.get(&message.id) {
                referenced_context_ids.extend(context_ids);
            }

            let mut request_message = LanguageModelRequestMessage {
                role: message.role,
                content: Vec::new(),
                cache: false,
            };

            match request_kind {
                RequestKind::Chat => {
                    self.tool_use
                        .attach_tool_results(message.id, &mut request_message);
                }
                RequestKind::Summarize => {
                    // We don't care about tool use during summarization.
                }
            }

            if !message.segments.is_empty() {
                request_message
                    .content
                    .push(MessageContent::Text(message.to_string()));
            }

            match request_kind {
                RequestKind::Chat => {
                    self.tool_use
                        .attach_tool_uses(message.id, &mut request_message);
                }
                RequestKind::Summarize => {
                    // We don't care about tool use during summarization.
                }
            };

            request.messages.push(request_message);
        }

        if !referenced_context_ids.is_empty() {
            let mut context_message = LanguageModelRequestMessage {
                role: Role::User,
                content: Vec::new(),
                cache: false,
            };

            let referenced_context = referenced_context_ids
                .into_iter()
                .filter_map(|context_id| self.context.get(context_id))
                .cloned();
            attach_context_to_message(&mut context_message, referenced_context);

            request.messages.push(context_message);
        }

        self.attach_stale_files(&mut request.messages, cx);

        request
    }

    fn attach_stale_files(&self, messages: &mut Vec<LanguageModelRequestMessage>, cx: &App) {
        const STALE_FILES_HEADER: &str = "These files changed since last read:";

        let mut stale_message = String::new();

        for stale_file in self.action_log.read(cx).stale_buffers(cx) {
            let Some(file) = stale_file.read(cx).file() else {
                continue;
            };

            if stale_message.is_empty() {
                write!(&mut stale_message, "{}", STALE_FILES_HEADER).ok();
            }

            writeln!(&mut stale_message, "- {}", file.path().display()).ok();
        }

        if !stale_message.is_empty() {
            let context_message = LanguageModelRequestMessage {
                role: Role::User,
                content: vec![stale_message.into()],
                cache: false,
            };

            messages.push(context_message);
        }
    }

    pub fn stream_completion(
        &mut self,
        request: LanguageModelRequest,
        model: Arc<dyn LanguageModel>,
        cx: &mut Context<Self>,
    ) {
        let pending_completion_id = post_inc(&mut self.completion_count);

        let task = cx.spawn(async move |thread, cx| {
            let stream = model.stream_completion(request, &cx);
            let initial_token_usage =
                thread.read_with(cx, |thread, _cx| thread.cumulative_token_usage.clone());
            let stream_completion = async {
                let mut events = stream.await?;
                let mut stop_reason = StopReason::EndTurn;
                let mut current_token_usage = TokenUsage::default();

                while let Some(event) = events.next().await {
                    let event = event?;

                    thread.update(cx, |thread, cx| {
                        match event {
                            LanguageModelCompletionEvent::StartMessage { .. } => {
                                thread.insert_message(
                                    Role::Assistant,
                                    vec![MessageSegment::Text(String::new())],
                                    cx,
                                );
                            }
                            LanguageModelCompletionEvent::Stop(reason) => {
                                stop_reason = reason;
                            }
                            LanguageModelCompletionEvent::UsageUpdate(token_usage) => {
                                thread.cumulative_token_usage =
                                    thread.cumulative_token_usage.clone() + token_usage.clone()
                                        - current_token_usage.clone();
                                current_token_usage = token_usage;
                            }
                            LanguageModelCompletionEvent::Text(chunk) => {
                                if let Some(last_message) = thread.messages.last_mut() {
                                    if last_message.role == Role::Assistant {
                                        last_message.push_text(&chunk);
                                        cx.emit(ThreadEvent::StreamedAssistantText(
                                            last_message.id,
                                            chunk,
                                        ));
                                    } else {
                                        // If we won't have an Assistant message yet, assume this chunk marks the beginning
                                        // of a new Assistant response.
                                        //
                                        // Importantly: We do *not* want to emit a `StreamedAssistantText` event here, as it
                                        // will result in duplicating the text of the chunk in the rendered Markdown.
                                        thread.insert_message(
                                            Role::Assistant,
                                            vec![MessageSegment::Text(chunk.to_string())],
                                            cx,
                                        );
                                    };
                                }
                            }
                            LanguageModelCompletionEvent::Thinking(chunk) => {
                                if let Some(last_message) = thread.messages.last_mut() {
                                    if last_message.role == Role::Assistant {
                                        last_message.push_thinking(&chunk);
                                        cx.emit(ThreadEvent::StreamedAssistantThinking(
                                            last_message.id,
                                            chunk,
                                        ));
                                    } else {
                                        // If we won't have an Assistant message yet, assume this chunk marks the beginning
                                        // of a new Assistant response.
                                        //
                                        // Importantly: We do *not* want to emit a `StreamedAssistantText` event here, as it
                                        // will result in duplicating the text of the chunk in the rendered Markdown.
                                        thread.insert_message(
                                            Role::Assistant,
                                            vec![MessageSegment::Thinking(chunk.to_string())],
                                            cx,
                                        );
                                    };
                                }
                            }
                            LanguageModelCompletionEvent::ToolUse(tool_use) => {
                                if let Some(last_assistant_message) = thread
                                    .messages
                                    .iter()
                                    .rfind(|message| message.role == Role::Assistant)
                                {
                                    thread.tool_use.request_tool_use(
                                        last_assistant_message.id,
                                        tool_use,
                                        cx,
                                    );
                                }
                            }
                        }

                        thread.touch_updated_at();
                        cx.emit(ThreadEvent::StreamedCompletion);
                        cx.notify();
                    })?;

                    smol::future::yield_now().await;
                }

                thread.update(cx, |thread, cx| {
                    thread
                        .pending_completions
                        .retain(|completion| completion.id != pending_completion_id);

                    if thread.summary.is_none() && thread.messages.len() >= 2 {
                        thread.summarize(cx);
                    }
                })?;

                anyhow::Ok(stop_reason)
            };

            let result = stream_completion.await;

            thread
                .update(cx, |thread, cx| {
                    thread.finalize_pending_checkpoint(cx);
                    match result.as_ref() {
                        Ok(stop_reason) => match stop_reason {
                            StopReason::ToolUse => {
                                cx.emit(ThreadEvent::UsePendingTools);
                            }
                            StopReason::EndTurn => {}
                            StopReason::MaxTokens => {}
                        },
                        Err(error) => {
                            if error.is::<PaymentRequiredError>() {
                                cx.emit(ThreadEvent::ShowError(ThreadError::PaymentRequired));
                            } else if error.is::<MaxMonthlySpendReachedError>() {
                                cx.emit(ThreadEvent::ShowError(
                                    ThreadError::MaxMonthlySpendReached,
                                ));
                            } else {
                                let error_message = error
                                    .chain()
                                    .map(|err| err.to_string())
                                    .collect::<Vec<_>>()
                                    .join("\n");
                                cx.emit(ThreadEvent::ShowError(ThreadError::Message {
                                    header: "Error interacting with language model".into(),
                                    message: SharedString::from(error_message.clone()),
                                }));
                            }

                            thread.cancel_last_completion(cx);
                        }
                    }
                    cx.emit(ThreadEvent::DoneStreaming);

                    if let Ok(initial_usage) = initial_token_usage {
                        let usage = thread.cumulative_token_usage.clone() - initial_usage;

                        telemetry::event!(
                            "Assistant Thread Completion",
                            thread_id = thread.id().to_string(),
                            model = model.telemetry_id(),
                            model_provider = model.provider_id().to_string(),
                            input_tokens = usage.input_tokens,
                            output_tokens = usage.output_tokens,
                            cache_creation_input_tokens = usage.cache_creation_input_tokens,
                            cache_read_input_tokens = usage.cache_read_input_tokens,
                        );
                    }
                })
                .ok();
        });

        self.pending_completions.push(PendingCompletion {
            id: pending_completion_id,
            _task: task,
        });
    }

    pub fn summarize(&mut self, cx: &mut Context<Self>) {
        let Some(provider) = LanguageModelRegistry::read_global(cx).active_provider() else {
            return;
        };
        let Some(model) = LanguageModelRegistry::read_global(cx).active_model() else {
            return;
        };

        if !provider.is_authenticated(cx) {
            return;
        }

        let mut request = self.to_completion_request(RequestKind::Summarize, cx);
        request.messages.push(LanguageModelRequestMessage {
            role: Role::User,
            content: vec![
                "Generate a concise 3-7 word title for this conversation, omitting punctuation. Go straight to the title, without any preamble and prefix like `Here's a concise suggestion:...` or `Title:`"
                    .into(),
            ],
            cache: false,
        });

        self.pending_summary = cx.spawn(async move |this, cx| {
            async move {
                let stream = model.stream_completion_text(request, &cx);
                let mut messages = stream.await?;

                let mut new_summary = String::new();
                while let Some(message) = messages.stream.next().await {
                    let text = message?;
                    let mut lines = text.lines();
                    new_summary.extend(lines.next());

                    // Stop if the LLM generated multiple lines.
                    if lines.next().is_some() {
                        break;
                    }
                }

                this.update(cx, |this, cx| {
                    if !new_summary.is_empty() {
                        this.summary = Some(new_summary.into());
                    }

                    cx.emit(ThreadEvent::SummaryChanged);
                })?;

                anyhow::Ok(())
            }
            .log_err()
            .await
        });
    }

    pub fn use_pending_tools(
        &mut self,
        cx: &mut Context<Self>,
    ) -> impl IntoIterator<Item = PendingToolUse> {
        let request = self.to_completion_request(RequestKind::Chat, cx);
        let messages = Arc::new(request.messages);
        let pending_tool_uses = self
            .tool_use
            .pending_tool_uses()
            .into_iter()
            .filter(|tool_use| tool_use.status.is_idle())
            .cloned()
            .collect::<Vec<_>>();

        for tool_use in pending_tool_uses.iter() {
            if let Some(tool) = self.tools.tool(&tool_use.name, cx) {
                if tool.needs_confirmation()
                    && !AssistantSettings::get_global(cx).always_allow_tool_actions
                {
                    self.tool_use.confirm_tool_use(
                        tool_use.id.clone(),
                        tool_use.ui_text.clone(),
                        tool_use.input.clone(),
                        messages.clone(),
                        tool,
                    );
                } else {
                    self.run_tool(
                        tool_use.id.clone(),
                        tool_use.ui_text.clone(),
                        tool_use.input.clone(),
                        &messages,
                        tool,
                        cx,
                    );
                }
            } else if let Some(tool) = self.tools.tool(&tool_use.name, cx) {
                self.run_tool(
                    tool_use.id.clone(),
                    tool_use.ui_text.clone(),
                    tool_use.input.clone(),
                    &messages,
                    tool,
                    cx,
                );
            }
        }

        pending_tool_uses
    }

    pub fn run_tool(
        &mut self,
        tool_use_id: LanguageModelToolUseId,
        ui_text: impl Into<SharedString>,
        input: serde_json::Value,
        messages: &[LanguageModelRequestMessage],
        tool: Arc<dyn Tool>,
        cx: &mut Context<'_, Thread>,
    ) {
        let task = self.spawn_tool_use(tool_use_id.clone(), messages, input, tool, cx);
        self.tool_use
            .run_pending_tool(tool_use_id, ui_text.into(), task);
    }

    fn spawn_tool_use(
        &mut self,
        tool_use_id: LanguageModelToolUseId,
        messages: &[LanguageModelRequestMessage],
        input: serde_json::Value,
        tool: Arc<dyn Tool>,
        cx: &mut Context<Thread>,
    ) -> Task<()> {
        let run_tool = tool.run(
            input,
            messages,
            self.project.clone(),
            self.action_log.clone(),
            cx,
        );

        cx.spawn({
            async move |thread: WeakEntity<Thread>, cx| {
                let output = run_tool.await;

                thread
                    .update(cx, |thread, cx| {
                        let pending_tool_use = thread
                            .tool_use
                            .insert_tool_output(tool_use_id.clone(), output);

                        cx.emit(ThreadEvent::ToolFinished {
                            tool_use_id,
                            pending_tool_use,
                            canceled: false,
                        });
                    })
                    .ok();
            }
        })
    }

    pub fn attach_tool_results(
        &mut self,
        updated_context: Vec<ContextSnapshot>,
        cx: &mut Context<Self>,
    ) {
        self.context.extend(
            updated_context
                .into_iter()
                .map(|context| (context.id, context)),
        );

        // Insert a user message to contain the tool results.
        self.insert_user_message(
            // TODO: Sending up a user message without any content results in the model sending back
            // responses that also don't have any content. We currently don't handle this case well,
            // so for now we provide some text to keep the model on track.
            "Here are the tool results.",
            Vec::new(),
            None,
            cx,
        );
    }

    /// Cancels the last pending completion, if there are any pending.
    ///
    /// Returns whether a completion was canceled.
    pub fn cancel_last_completion(&mut self, cx: &mut Context<Self>) -> bool {
        let canceled = if self.pending_completions.pop().is_some() {
            true
        } else {
            let mut canceled = false;
            for pending_tool_use in self.tool_use.cancel_pending() {
                canceled = true;
                cx.emit(ThreadEvent::ToolFinished {
                    tool_use_id: pending_tool_use.id.clone(),
                    pending_tool_use: Some(pending_tool_use),
                    canceled: true,
                });
            }
            canceled
        };
        self.finalize_pending_checkpoint(cx);
        canceled
    }

    /// Returns the feedback given to the thread, if any.
    pub fn feedback(&self) -> Option<ThreadFeedback> {
        self.feedback
    }

    /// Reports feedback about the thread and stores it in our telemetry backend.
    pub fn report_feedback(
        &mut self,
        feedback: ThreadFeedback,
        cx: &mut Context<Self>,
    ) -> Task<Result<()>> {
        let final_project_snapshot = Self::project_snapshot(self.project.clone(), cx);
        let serialized_thread = self.serialize(cx);
        let thread_id = self.id().clone();
        let client = self.project.read(cx).client();
        self.feedback = Some(feedback);
        cx.notify();

        cx.background_spawn(async move {
            let final_project_snapshot = final_project_snapshot.await;
            let serialized_thread = serialized_thread.await?;
            let thread_data =
                serde_json::to_value(serialized_thread).unwrap_or_else(|_| serde_json::Value::Null);

            let rating = match feedback {
                ThreadFeedback::Positive => "positive",
                ThreadFeedback::Negative => "negative",
            };
            telemetry::event!(
                "Assistant Thread Rated",
                rating,
                thread_id,
                thread_data,
                final_project_snapshot
            );
            client.telemetry().flush_events();

            Ok(())
        })
    }

    /// Create a snapshot of the current project state including git information and unsaved buffers.
    fn project_snapshot(
        project: Entity<Project>,
        cx: &mut Context<Self>,
    ) -> Task<Arc<ProjectSnapshot>> {
        let git_store = project.read(cx).git_store().clone();
        let worktree_snapshots: Vec<_> = project
            .read(cx)
            .visible_worktrees(cx)
            .map(|worktree| Self::worktree_snapshot(worktree, git_store.clone(), cx))
            .collect();

        cx.spawn(async move |_, cx| {
            let worktree_snapshots = futures::future::join_all(worktree_snapshots).await;

            let mut unsaved_buffers = Vec::new();
            cx.update(|app_cx| {
                let buffer_store = project.read(app_cx).buffer_store();
                for buffer_handle in buffer_store.read(app_cx).buffers() {
                    let buffer = buffer_handle.read(app_cx);
                    if buffer.is_dirty() {
                        if let Some(file) = buffer.file() {
                            let path = file.path().to_string_lossy().to_string();
                            unsaved_buffers.push(path);
                        }
                    }
                }
            })
            .ok();

            Arc::new(ProjectSnapshot {
                worktree_snapshots,
                unsaved_buffer_paths: unsaved_buffers,
                timestamp: Utc::now(),
            })
        })
    }

    fn worktree_snapshot(
        worktree: Entity<project::Worktree>,
        git_store: Entity<GitStore>,
        cx: &App,
    ) -> Task<WorktreeSnapshot> {
        cx.spawn(async move |cx| {
            // Get worktree path and snapshot
            let worktree_info = cx.update(|app_cx| {
                let worktree = worktree.read(app_cx);
                let path = worktree.abs_path().to_string_lossy().to_string();
                let snapshot = worktree.snapshot();
                (path, snapshot)
            });

            let Ok((worktree_path, snapshot)) = worktree_info else {
                return WorktreeSnapshot {
                    worktree_path: String::new(),
                    git_state: None,
                };
            };

            let repo_info = git_store
                .update(cx, |git_store, cx| {
                    git_store
                        .repositories()
                        .values()
                        .find(|repo| repo.read(cx).worktree_id == snapshot.id())
                        .and_then(|repo| {
                            let repo = repo.read(cx);
                            Some((repo.branch().cloned(), repo.local_repository()?))
                        })
                })
                .ok()
                .flatten();

            // Extract git information
            let git_state = match repo_info {
                None => None,
                Some((branch, repo)) => {
                    let current_branch = branch.map(|branch| branch.name.to_string());
                    let remote_url = repo.remote_url("origin");
                    let head_sha = repo.head_sha();

                    // Get diff asynchronously
                    let diff = repo
                        .diff(git::repository::DiffType::HeadToWorktree, cx.clone())
                        .await
                        .ok();

                    Some(GitState {
                        remote_url,
                        head_sha,
                        current_branch,
                        diff,
                    })
                }
            };

            WorktreeSnapshot {
                worktree_path,
                git_state,
            }
        })
    }

    pub fn to_markdown(&self, cx: &App) -> Result<String> {
        let mut markdown = Vec::new();

        if let Some(summary) = self.summary() {
            writeln!(markdown, "# {summary}\n")?;
        };

        for message in self.messages() {
            writeln!(
                markdown,
                "## {role}\n",
                role = match message.role {
                    Role::User => "User",
                    Role::Assistant => "Assistant",
                    Role::System => "System",
                }
            )?;
            for segment in &message.segments {
                match segment {
                    MessageSegment::Text(text) => writeln!(markdown, "{}\n", text)?,
                    MessageSegment::Thinking(text) => {
                        writeln!(markdown, "<think>{}</think>\n", text)?
                    }
                }
            }

            for tool_use in self.tool_uses_for_message(message.id, cx) {
                writeln!(
                    markdown,
                    "**Use Tool: {} ({})**",
                    tool_use.name, tool_use.id
                )?;
                writeln!(markdown, "```json")?;
                writeln!(
                    markdown,
                    "{}",
                    serde_json::to_string_pretty(&tool_use.input)?
                )?;
                writeln!(markdown, "```")?;
            }

            for tool_result in self.tool_results_for_message(message.id) {
                write!(markdown, "**Tool Results: {}", tool_result.tool_use_id)?;
                if tool_result.is_error {
                    write!(markdown, " (Error)")?;
                }

                writeln!(markdown, "**\n")?;
                writeln!(markdown, "{}", tool_result.content)?;
            }
        }

        Ok(String::from_utf8_lossy(&markdown).to_string())
    }

    pub fn action_log(&self) -> &Entity<ActionLog> {
        &self.action_log
    }

    pub fn project(&self) -> &Entity<Project> {
        &self.project
    }

    pub fn cumulative_token_usage(&self) -> TokenUsage {
        self.cumulative_token_usage.clone()
    }

    pub fn deny_tool_use(&mut self, tool_use_id: LanguageModelToolUseId, cx: &mut Context<Self>) {
        let err = Err(anyhow::anyhow!(
            "Permission to run tool action denied by user"
        ));

        self.tool_use.insert_tool_output(tool_use_id.clone(), err);

        cx.emit(ThreadEvent::ToolFinished {
            tool_use_id,
            pending_tool_use: None,
            canceled: true,
        });
    }
}

#[derive(Debug, Clone)]
pub enum ThreadError {
    PaymentRequired,
    MaxMonthlySpendReached,
    Message {
        header: SharedString,
        message: SharedString,
    },
}

#[derive(Debug, Clone)]
pub enum ThreadEvent {
    ShowError(ThreadError),
    StreamedCompletion,
    StreamedAssistantText(MessageId, String),
    StreamedAssistantThinking(MessageId, String),
    DoneStreaming,
    MessageAdded(MessageId),
    MessageEdited(MessageId),
    MessageDeleted(MessageId),
    SummaryChanged,
    UsePendingTools,
    ToolFinished {
        #[allow(unused)]
        tool_use_id: LanguageModelToolUseId,
        /// The pending tool use that corresponds to this tool.
        pending_tool_use: Option<PendingToolUse>,
        /// Whether the tool was canceled by the user.
        canceled: bool,
    },
    CheckpointChanged,
}

impl EventEmitter<ThreadEvent> for Thread {}

struct PendingCompletion {
    id: usize,
    _task: Task<()>,
}