use std::sync::Arc;
use std::sync::atomic::AtomicU64;

use async_channel::Receiver;
use async_channel::Sender;
use codex_async_utils::OrCancelExt;
use codex_protocol::protocol::ApplyPatchApprovalRequestEvent;
use codex_protocol::protocol::Event;
use codex_protocol::protocol::EventMsg;
use codex_protocol::protocol::ExecApprovalRequestEvent;
use codex_protocol::protocol::Op;
use codex_protocol::protocol::SessionSource;
use codex_protocol::protocol::SubAgentSource;
use codex_protocol::protocol::Submission;
use codex_protocol::user_input::UserInput;
use tokio_util::sync::CancellationToken;

use crate::AuthManager;
use crate::codex::Codex;
use crate::codex::CodexSpawnOk;
use crate::codex::SUBMISSION_CHANNEL_CAPACITY;
use crate::codex::Session;
use crate::codex::TurnContext;
use crate::config::Config;
use crate::error::CodexErr;
use codex_protocol::protocol::InitialHistory;

/// Start an interactive sub-Codex conversation and return IO channels.
///
/// The returned `events_rx` yields non-approval events emitted by the sub-agent.
/// Approval requests are handled via `parent_session` and are not surfaced.
/// The returned `ops_tx` allows the caller to submit additional `Op`s to the sub-agent.
pub(crate) async fn run_codex_conversation_interactive(
    config: Config,
    auth_manager: Arc<AuthManager>,
    parent_session: Arc<Session>,
    parent_ctx: Arc<TurnContext>,
    cancel_token: CancellationToken,
    initial_history: Option<InitialHistory>,
) -> Result<Codex, CodexErr> {
    let (tx_sub, rx_sub) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);
    let (tx_ops, rx_ops) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);

    let CodexSpawnOk { codex, .. } = Codex::spawn(
        config,
        auth_manager,
        initial_history.unwrap_or(InitialHistory::New),
        SessionSource::SubAgent(SubAgentSource::Review),
    )
    .await?;
    let codex = Arc::new(codex);

    // Use a child token so parent cancel cascades but we can scope it to this task
    let cancel_token_events = cancel_token.child_token();
    let cancel_token_ops = cancel_token.child_token();

    // Forward events from the sub-agent to the consumer, filtering approvals and
    // routing them to the parent session for decisions.
    let parent_session_clone = Arc::clone(&parent_session);
    let parent_ctx_clone = Arc::clone(&parent_ctx);
    let codex_for_events = Arc::clone(&codex);
    tokio::spawn(async move {
        let _ = forward_events(
            codex_for_events,
            tx_sub,
            parent_session_clone,
            parent_ctx_clone,
            cancel_token_events.clone(),
        )
        .or_cancel(&cancel_token_events)
        .await;
    });

    // Forward ops from the caller to the sub-agent.
    let codex_for_ops = Arc::clone(&codex);
    tokio::spawn(async move {
        forward_ops(codex_for_ops, rx_ops, cancel_token_ops).await;
    });

    Ok(Codex {
        next_id: AtomicU64::new(0),
        tx_sub: tx_ops,
        rx_event: rx_sub,
    })
}

/// Convenience wrapper for one-time use with an initial prompt.
///
/// Internally calls the interactive variant, then immediately submits the provided input.
pub(crate) async fn run_codex_conversation_one_shot(
    config: Config,
    auth_manager: Arc<AuthManager>,
    input: Vec<UserInput>,
    parent_session: Arc<Session>,
    parent_ctx: Arc<TurnContext>,
    cancel_token: CancellationToken,
    initial_history: Option<InitialHistory>,
) -> Result<Codex, CodexErr> {
    // Use a child token so we can stop the delegate after completion without
    // requiring the caller to cancel the parent token.
    let child_cancel = cancel_token.child_token();
    let io = run_codex_conversation_interactive(
        config,
        auth_manager,
        parent_session,
        parent_ctx,
        child_cancel.clone(),
        initial_history,
    )
    .await?;

    // Send the initial input to kick off the one-shot turn.
    io.submit(Op::UserInput { items: input }).await?;

    // Bridge events so we can observe completion and shut down automatically.
    let (tx_bridge, rx_bridge) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);
    let ops_tx = io.tx_sub.clone();
    let io_for_bridge = io;
    tokio::spawn(async move {
        while let Ok(event) = io_for_bridge.next_event().await {
            let should_shutdown = matches!(
                event.msg,
                EventMsg::TaskComplete(_) | EventMsg::TurnAborted(_)
            );
            let _ = tx_bridge.send(event).await;
            if should_shutdown {
                let _ = ops_tx
                    .send(Submission {
                        id: "shutdown".to_string(),
                        op: Op::Shutdown {},
                    })
                    .await;
                child_cancel.cancel();
                break;
            }
        }
    });

    // For one-shot usage, return a closed `tx_sub` so callers cannot submit
    // additional ops after the initial request. Create a channel and drop the
    // receiver to close it immediately.
    let (tx_closed, rx_closed) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);
    drop(rx_closed);

    Ok(Codex {
        next_id: AtomicU64::new(0),
        rx_event: rx_bridge,
        tx_sub: tx_closed,
    })
}

async fn forward_events(
    codex: Arc<Codex>,
    tx_sub: Sender<Event>,
    parent_session: Arc<Session>,
    parent_ctx: Arc<TurnContext>,
    cancel_token: CancellationToken,
) {
    while let Ok(event) = codex.next_event().await {
        match event {
            Event {
                id: _,
                msg: EventMsg::SessionConfigured(_),
            } => continue,
            Event {
                id,
                msg: EventMsg::ExecApprovalRequest(event),
            } => {
                // Initiate approval via parent session; do not surface to consumer.
                handle_exec_approval(
                    &codex,
                    id,
                    &parent_session,
                    &parent_ctx,
                    event,
                    &cancel_token,
                )
                .await;
            }
            Event {
                id,
                msg: EventMsg::ApplyPatchApprovalRequest(event),
            } => {
                handle_patch_approval(
                    &codex,
                    id,
                    &parent_session,
                    &parent_ctx,
                    event,
                    &cancel_token,
                )
                .await;
            }
            other => {
                let _ = tx_sub.send(other).await;
            }
        }
    }
}

/// Forward ops from a caller to a sub-agent, respecting cancellation.
async fn forward_ops(
    codex: Arc<Codex>,
    rx_ops: Receiver<Submission>,
    cancel_token_ops: CancellationToken,
) {
    loop {
        let op: Op = match rx_ops.recv().or_cancel(&cancel_token_ops).await {
            Ok(Ok(Submission { id: _, op })) => op,
            Ok(Err(_)) | Err(_) => break,
        };
        let _ = codex.submit(op).await;
    }
}

/// Handle an ExecApprovalRequest by consulting the parent session and replying.
async fn handle_exec_approval(
    codex: &Codex,
    id: String,
    parent_session: &Session,
    parent_ctx: &TurnContext,
    event: ExecApprovalRequestEvent,
    cancel_token: &CancellationToken,
) {
    // Race approval with cancellation and timeout to avoid hangs.
    let approval_fut = parent_session.request_command_approval(
        parent_ctx,
        parent_ctx.sub_id.clone(),
        event.command,
        event.cwd,
        event.reason,
        event.risk,
    );
    let decision = await_approval_with_cancel(
        approval_fut,
        parent_session,
        &parent_ctx.sub_id,
        cancel_token,
    )
    .await;

    let _ = codex.submit(Op::ExecApproval { id, decision }).await;
}

/// Handle an ApplyPatchApprovalRequest by consulting the parent session and replying.
async fn handle_patch_approval(
    codex: &Codex,
    id: String,
    parent_session: &Session,
    parent_ctx: &TurnContext,
    event: ApplyPatchApprovalRequestEvent,
    cancel_token: &CancellationToken,
) {
    let decision_rx = parent_session
        .request_patch_approval(
            parent_ctx,
            parent_ctx.sub_id.clone(),
            event.changes,
            event.reason,
            event.grant_root,
        )
        .await;
    let decision = await_approval_with_cancel(
        async move { decision_rx.await.unwrap_or_default() },
        parent_session,
        &parent_ctx.sub_id,
        cancel_token,
    )
    .await;
    let _ = codex.submit(Op::PatchApproval { id, decision }).await;
}

/// Await an approval decision, aborting on cancellation.
async fn await_approval_with_cancel<F>(
    fut: F,
    parent_session: &Session,
    sub_id: &str,
    cancel_token: &CancellationToken,
) -> codex_protocol::protocol::ReviewDecision
where
    F: core::future::Future<Output = codex_protocol::protocol::ReviewDecision>,
{
    tokio::select! {
        biased;
        _ = cancel_token.cancelled() => {
            parent_session
                .notify_approval(sub_id, codex_protocol::protocol::ReviewDecision::Abort)
                .await;
            codex_protocol::protocol::ReviewDecision::Abort
        }
        decision = fut => {
            decision
        }
    }
}