use std::sync::Arc;
use std::sync::OnceLock;

use crate::compact::CompactedHistoryMetadata;
use crate::compact::CompactionAnalyticsAttempt;
use crate::compact::CompactionAnalyticsDetails;
use crate::compact::InitialContextInjection;
use crate::compact::build_compaction_initial_context;
use crate::compact::compaction_status_from_result;
use crate::compact::insert_initial_context_before_last_real_user_or_summary;
use crate::compact_model_fallback::record_model_fallback;
use crate::compact_model_fallback::should_retry_with_current_model;
use crate::compact_remote_history::HistoryItemGroup;
use crate::compact_remote_history::history_item_groups;
use crate::context::world_state::WorldState;
use crate::context_manager::ContextManager;
use crate::context_manager::estimate_item_token_count;
use crate::hook_runtime::PostCompactHookOutcome;
use crate::hook_runtime::PreCompactHookOutcome;
use crate::hook_runtime::run_post_compact_hooks;
use crate::hook_runtime::run_pre_compact_hooks;
use crate::responses_metadata::CompactionTurnMetadata;
use crate::session::session::Session;
use crate::session::step_context::StepContext;
use crate::session::turn_context::TurnContext;
use codex_analytics::CompactionImplementation;
use codex_analytics::CompactionPhase;
use codex_analytics::CompactionReason;
use codex_analytics::CompactionTrigger;
use codex_history::ResponseItemEnvelope;
use codex_protocol::error::CodexErr;
use codex_protocol::error::Result as CodexResult;
use codex_protocol::items::ContextCompactionItem;
use codex_protocol::items::TurnItem;
use codex_protocol::models::BaseInstructions;
use codex_protocol::models::FunctionCallOutputBody;
use codex_protocol::models::FunctionCallOutputPayload;
use codex_protocol::models::ResponseItem;
use codex_protocol::protocol::EventMsg;
use codex_protocol::protocol::TurnStartedEvent;
use codex_rollout_trace::CompactionCheckpointTracePayload;
use codex_utils_output_truncation::approx_token_count;
use tokio_util::sync::CancellationToken;

#[path = "compact_remote_request.rs"]
mod request;
use request::RemoteCompactAttempt;
use request::run_remote_compact_attempt;

const CONTEXT_WINDOW_TRUNCATED_OUTPUT_MESSAGE: &str =
    "Output exceeded the available model context and was truncated";

pub(crate) async fn run_inline_remote_auto_compact_task(
    sess: Arc<Session>,
    step_context: Arc<StepContext>,
    fallback_step_context: Option<Arc<StepContext>>,
    turn_state: Arc<OnceLock<String>>,
    initial_context_injection: InitialContextInjection,
    reason: CompactionReason,
    phase: CompactionPhase,
) -> CodexResult<()> {
    let compaction_metadata = CompactionTurnMetadata::new(
        CompactionTrigger::Auto,
        reason,
        CompactionImplementation::ResponsesCompact,
        phase,
    );
    run_remote_compact_task_inner(
        &sess,
        &step_context,
        fallback_step_context.as_ref(),
        Some(turn_state),
        initial_context_injection,
        compaction_metadata,
    )
    .await?;
    Ok(())
}

pub(crate) async fn run_remote_compact_task(
    sess: Arc<Session>,
    turn_context: Arc<TurnContext>,
) -> CodexResult<()> {
    // Standalone compaction is its own request boundary, so it captures a fresh step.
    let step_context = sess
        .capture_step_context(Arc::clone(&turn_context), &CancellationToken::new())
        .await?;
    let start_event = EventMsg::TurnStarted(TurnStartedEvent {
        turn_id: turn_context.sub_id.clone(),
        trace_id: turn_context.trace_id.clone(),
        started_at: turn_context.turn_timing_state.started_at_unix_secs().await,
        model_context_window: turn_context.model_context_window(),
        collaboration_mode_kind: turn_context.mode(),
    });
    sess.send_event(&turn_context, start_event).await;

    let compaction_metadata = CompactionTurnMetadata::new(
        CompactionTrigger::Manual,
        CompactionReason::UserRequested,
        CompactionImplementation::ResponsesCompact,
        CompactionPhase::StandaloneTurn,
    );
    run_remote_compact_task_inner(
        &sess,
        &step_context,
        /*fallback_step_context*/ None,
        /*turn_state*/ None,
        InitialContextInjection::DoNotInject,
        compaction_metadata,
    )
    .await?;
    Ok(())
}

async fn run_remote_compact_task_inner(
    sess: &Arc<Session>,
    step_context: &Arc<StepContext>,
    fallback_step_context: Option<&Arc<StepContext>>,
    turn_state: Option<Arc<OnceLock<String>>>,
    initial_context_injection: InitialContextInjection,
    compaction_metadata: CompactionTurnMetadata,
) -> CodexResult<()> {
    let turn_context = &step_context.turn;
    let trigger = compaction_metadata.trigger();
    let reason = compaction_metadata.reason();
    let implementation = compaction_metadata.implementation();
    let phase = compaction_metadata.phase();
    let mut analytics_details = CompactionAnalyticsDetails {
        active_context_tokens_before: Some(sess.get_total_token_usage().await),
        ..Default::default()
    };
    let attempt = CompactionAnalyticsAttempt::begin(
        sess.as_ref(),
        turn_context.as_ref(),
        trigger,
        reason,
        implementation,
        phase,
    )
    .await;
    let pre_compact_outcome = run_pre_compact_hooks(sess, turn_context, trigger).await;
    match pre_compact_outcome {
        PreCompactHookOutcome::Continue => {}
        PreCompactHookOutcome::Stopped => {
            let error = CodexErr::TurnAborted;
            attempt
                .track(
                    sess.as_ref(),
                    codex_analytics::CompactionStatus::Interrupted,
                    Some(&error),
                    analytics_details,
                )
                .await;
            return Err(error);
        }
    }
    let result = run_remote_compact_task_inner_impl(
        sess,
        step_context,
        fallback_step_context,
        turn_state,
        initial_context_injection,
        compaction_metadata,
        &mut analytics_details,
    )
    .await;
    let status = compaction_status_from_result(&result);
    let codex_error = result.as_ref().err();
    if result.is_ok() {
        let post_compact_outcome = run_post_compact_hooks(sess, turn_context, trigger).await;
        if let PostCompactHookOutcome::Stopped = post_compact_outcome {
            attempt
                .track(sess.as_ref(), status, codex_error, analytics_details)
                .await;
            return Err(CodexErr::TurnAborted);
        }
    }
    attempt
        .track(sess.as_ref(), status, codex_error, analytics_details)
        .await;
    if let Err(err) = result {
        sess.track_turn_codex_error(turn_context, &err);
        let event = EventMsg::Error(
            err.to_error_event(Some("Error running remote compact task".to_string())),
        );
        sess.send_event(turn_context, event).await;
        return Err(err);
    }
    Ok(())
}

async fn run_remote_compact_task_inner_impl(
    sess: &Arc<Session>,
    step_context: &Arc<StepContext>,
    fallback_step_context: Option<&Arc<StepContext>>,
    turn_state: Option<Arc<OnceLock<String>>>,
    initial_context_injection: InitialContextInjection,
    compaction_metadata: CompactionTurnMetadata,
    analytics_details: &mut CompactionAnalyticsDetails,
) -> CodexResult<()> {
    let turn_context = &step_context.turn;
    let context_compaction_item = ContextCompactionItem::new();
    let compaction_id = context_compaction_item.id.clone();
    // Use the UI compaction item ID as the trace compaction ID so protocol lifecycle events,
    // endpoint attempts, and the installed history checkpoint all have one join key.
    let compaction_trace = sess.services.rollout_thread_trace.compaction_trace_context(
        turn_context.sub_id.as_str(),
        compaction_id.as_str(),
        turn_context.model_info().slug.as_str(),
        turn_context.provider.info().name.as_str(),
    );
    let compaction_item = TurnItem::ContextCompaction(context_compaction_item);
    sess.emit_turn_item_started(turn_context, &compaction_item)
        .await;
    let attempt = run_remote_compact_attempt(
        sess,
        step_context,
        turn_state.clone(),
        &compaction_trace,
        compaction_metadata,
        analytics_details,
    )
    .await;
    let (attempt, compaction_turn_context) = match attempt {
        Ok(attempt) => (attempt, turn_context),
        Err(error) => {
            let Some(fallback_step_context) = fallback_step_context else {
                return Err(error);
            };
            if !should_retry_with_current_model(&error) {
                return Err(error);
            }
            sess.set_last_known_step_context(fallback_step_context)
                .await;
            let fallback_turn_context = &fallback_step_context.turn;
            let fallback_compaction_trace =
                sess.services.rollout_thread_trace.compaction_trace_context(
                    fallback_turn_context.sub_id.as_str(),
                    compaction_id.as_str(),
                    fallback_turn_context.model_info().slug.as_str(),
                    fallback_turn_context.provider.info().name.as_str(),
                );
            let fallback_result = run_remote_compact_attempt(
                sess,
                fallback_step_context,
                turn_state,
                &fallback_compaction_trace,
                compaction_metadata,
                analytics_details,
            )
            .await;
            record_model_fallback(
                &sess.services.session_telemetry,
                turn_context.model_info().slug.as_str(),
                fallback_turn_context.model_info().slug.as_str(),
                compaction_metadata.reason(),
                compaction_metadata.implementation(),
                fallback_result.as_ref().err(),
            );
            match fallback_result {
                Ok(attempt) => (attempt, fallback_turn_context),
                Err(_) => return Err(error),
            }
        }
    };
    let RemoteCompactAttempt {
        new_history,
        trace_input_history,
    } = attempt;
    let (new_window_number, new_window_ids) = sess.advance_auto_compact_window().await;
    let (new_history, world_state_baseline) =
        process_compacted_history(sess.as_ref(), new_history, &initial_context_injection).await;

    let reference_context_item = match initial_context_injection {
        InitialContextInjection::DoNotInject => None,
        InitialContextInjection::BeforeLastUserMessage { .. } => {
            Some(compaction_turn_context.to_turn_context_item())
        }
    };
    // Install is the semantic boundary where the compact endpoint's output becomes live
    // thread history. Keep it distinct from the later inference request so the reducer can
    // still represent repeated developer/context prefix items exactly as the model saw them.
    if let Some(trace_input_history) = trace_input_history.as_deref() {
        compaction_trace.record_installed(&CompactionCheckpointTracePayload {
            input_history: trace_input_history,
            replacement_history: &new_history,
        });
    }
    // Legacy `/responses/compact` returns provider-normalized items without a stable link to their
    // original envelopes, so it does not preserve harness metadata. Compaction-trigger/v2 does.
    let new_history = new_history
        .into_iter()
        .map(ResponseItemEnvelope::new)
        .collect();
    sess.replace_compacted_history(
        new_history,
        reference_context_item,
        world_state_baseline,
        CompactedHistoryMetadata {
            message: String::new(),
            window_number: new_window_number,
            window_ids: new_window_ids,
            compaction_response_id: None,
        },
    )
    .await;
    sess.recompute_token_usage(compaction_turn_context).await;

    sess.emit_turn_item_completed(compaction_turn_context, compaction_item)
        .await;
    Ok(())
}

pub(crate) async fn process_compacted_history(
    sess: &Session,
    compacted_history: Vec<ResponseItem>,
    initial_context_injection: &InitialContextInjection,
) -> (Vec<ResponseItem>, Option<Arc<WorldState>>) {
    let compacted_history = compacted_history
        .into_iter()
        .map(ResponseItemEnvelope::new)
        .collect();
    let (compacted_history, world_state_baseline) =
        process_annotated_compacted_history(sess, compacted_history, initial_context_injection)
            .await;
    (
        compacted_history
            .into_iter()
            .map(ResponseItemEnvelope::into_item)
            .collect(),
        world_state_baseline,
    )
}

/// Installs already-annotated remote compaction output without dropping its metadata sidecar.
pub(crate) async fn process_annotated_compacted_history(
    sess: &Session,
    compacted_history: Vec<ResponseItemEnvelope>,
    initial_context_injection: &InitialContextInjection,
) -> (Vec<ResponseItemEnvelope>, Option<Arc<WorldState>>) {
    // Mid-turn compaction is the only path that must inject initial context above the last user
    // message in the replacement history. Pre-turn compaction instead injects context after the
    // compaction item, but mid-turn compaction keeps the compaction item last for model training.
    let (initial_context, world_state_baseline) =
        build_compaction_initial_context(sess, initial_context_injection).await;

    let compacted_history = history_item_groups(compacted_history)
        .filter(|group| should_keep_compacted_history_item(&group.source.item))
        .flat_map(HistoryItemGroup::into_items)
        .collect();
    (
        insert_initial_context_before_last_real_user_or_summary(compacted_history, initial_context),
        world_state_baseline,
    )
}

/// Returns whether an item from remote compaction output should be preserved.
///
/// Called while processing the model-provided compacted transcript, before we
/// append fresh canonical context from the current session.
///
/// We drop:
/// - `developer` messages because remote output can include stale/duplicated
///   instruction content.
/// - non-user-content `user` messages (session prefix/instruction wrappers),
///   while preserving real user messages and persisted hook prompts.
///
/// This intentionally keeps:
/// - `assistant` messages (future remote compaction models may emit them)
/// - `user`-role warnings that parse as `TurnItem::UserMessage` and compaction-generated summary
///   messages. Legacy warning fragments are filtered by `parse_turn_item` before they reach this
///   check.
pub(crate) fn should_keep_compacted_history_item(item: &ResponseItem) -> bool {
    match item {
        ResponseItem::Message { role, .. } if role == "developer" => false,
        ResponseItem::Message { role, .. } if role == "user" => {
            matches!(
                crate::event_mapping::parse_turn_item(item),
                Some(TurnItem::UserMessage(_) | TurnItem::HookPrompt(_))
            )
        }
        ResponseItem::Message { role, .. } if role == "assistant" => true,
        ResponseItem::Message { .. } => false,
        ResponseItem::AgentMessage { .. } => true,
        ResponseItem::Compaction { .. } | ResponseItem::ContextCompaction { .. } => true,
        ResponseItem::CompactionTrigger { .. } => false,
        ResponseItem::AdditionalTools { .. }
        | ResponseItem::Reasoning { .. }
        | ResponseItem::LocalShellCall { .. }
        | ResponseItem::FunctionCall { .. }
        | ResponseItem::ToolSearchCall { .. }
        | ResponseItem::FunctionCallOutput { .. }
        | ResponseItem::ToolSearchOutput { .. }
        | ResponseItem::CustomToolCall { .. }
        | ResponseItem::CustomToolCallOutput { .. }
        | ResponseItem::WebSearchCall { .. }
        | ResponseItem::ImageGenerationCall { .. }
        | ResponseItem::Other => false,
    }
}

pub(crate) fn trim_function_call_history_to_fit_context_window(
    history: &mut ContextManager,
    turn_context: &TurnContext,
    base_instructions: &BaseInstructions,
) -> (usize, i64) {
    let Some(context_window) = turn_context.model_context_window() else {
        return (0, 0);
    };
    // Keep the unclamped total so replacing an item cannot lose an overflow hidden by i64
    // saturation in the normal history estimator.
    let base_tokens =
        i128::try_from(approx_token_count(&base_instructions.text)).unwrap_or(i128::MAX);
    let original_items = history.annotated_items();
    let mut estimated_tokens = history_item_groups(original_items.iter().map(|item| &item.item))
        .map(|group| group.estimated_token_count())
        .fold(base_tokens, i128::saturating_add);
    let initial_estimated_tokens = i64::try_from(estimated_tokens).unwrap_or(i64::MAX);
    let mut rewritten_items = Vec::new();
    let mut consumed_items: usize = 0;

    for group in history_item_groups(original_items.iter().map(|item| &item.item))
        .collect::<Vec<_>>()
        .into_iter()
        .rev()
    {
        if i64::try_from(estimated_tokens).unwrap_or(i64::MAX) <= context_window {
            break;
        }
        let group_item_count = 1 + usize::from(group.attached_notice.is_some());
        let source_index = original_items
            .len()
            .saturating_sub(consumed_items.saturating_add(group_item_count));
        let Some(rewritten_item) = original_items
            .get(source_index)
            .and_then(rewritten_output_for_context_window)
        else {
            break;
        };
        estimated_tokens = estimated_tokens
            .saturating_sub(group.estimated_token_count())
            .saturating_add(i128::from(estimate_item_token_count(&rewritten_item.item)));
        consumed_items += group_item_count;
        rewritten_items.push(rewritten_item);
    }

    let rewritten_outputs = rewritten_items.len();
    if rewritten_outputs > 0 {
        let retained_len = original_items.len() - consumed_items;
        let mut items = original_items[..retained_len].to_vec();
        items.extend(rewritten_items.into_iter().rev());
        history.replace_annotated(items);
    }

    let final_estimated_tokens = i64::try_from(estimated_tokens).unwrap_or(i64::MAX);
    let estimated_deleted_tokens = initial_estimated_tokens.saturating_sub(final_estimated_tokens);
    (rewritten_outputs, estimated_deleted_tokens)
}

fn rewritten_output_for_context_window(
    envelope: &ResponseItemEnvelope,
) -> Option<ResponseItemEnvelope> {
    let item = match &envelope.item {
        ResponseItem::FunctionCallOutput {
            id,
            call_id,
            name,
            namespace,
            output,
            internal_chat_message_metadata_passthrough: metadata,
        } => ResponseItem::FunctionCallOutput {
            id: id.clone(),
            call_id: call_id.clone(),
            name: name.clone(),
            namespace: namespace.clone(),
            output: truncated_output_payload(output),
            internal_chat_message_metadata_passthrough: metadata.clone(),
        },
        ResponseItem::CustomToolCallOutput {
            id,
            call_id,
            name,
            output,
            internal_chat_message_metadata_passthrough: metadata,
        } => ResponseItem::CustomToolCallOutput {
            id: id.clone(),
            call_id: call_id.clone(),
            name: name.clone(),
            output: truncated_output_payload(output),
            internal_chat_message_metadata_passthrough: metadata.clone(),
        },
        ResponseItem::ToolSearchOutput {
            id,
            call_id,
            status,
            execution,
            internal_chat_message_metadata_passthrough: metadata,
            ..
        } => ResponseItem::ToolSearchOutput {
            id: id.clone(),
            call_id: call_id.clone(),
            status: status.clone(),
            execution: execution.clone(),
            tools: Vec::new(),
            internal_chat_message_metadata_passthrough: metadata.clone(),
        },
        _ => return None,
    };
    Some(ResponseItemEnvelope {
        item,
        metadata: envelope.metadata.clone(),
    })
}

fn truncated_output_payload(output: &FunctionCallOutputPayload) -> FunctionCallOutputPayload {
    FunctionCallOutputPayload {
        body: FunctionCallOutputBody::Text(CONTEXT_WINDOW_TRUNCATED_OUTPUT_MESSAGE.to_string()),
        success: output.success,
    }
}

#[cfg(test)]
#[path = "compact_remote_metadata_tests.rs"]
mod metadata_tests;