use std::sync::Arc;
use std::{fmt::Display, future::Future};

use tokio::sync::Mutex;

use super::session::{MessagePersistSnapshot, Session};
use crate::bus::ChatMessage;
use crate::storage::StorageError;
use crate::{providers::Usage, session::TurnController};

async fn persist_added_messages(
    snapshots: Vec<Option<MessagePersistSnapshot>>,
) -> Result<(), StorageError> {
    let mut storage = None;
    let mut session_id = None;
    let mut messages = Vec::new();
    let mut final_meta = None;

    for snapshot in snapshots.into_iter().flatten() {
        let (snapshot_storage, snapshot_session_id, message, meta) = snapshot;
        if let Some(ref expected) = session_id
            && expected != &snapshot_session_id
        {
            return Err(StorageError::Serialization(
                "attempted to persist messages from different sessions in one turn".to_string(),
            ));
        }
        storage = Some(snapshot_storage);
        session_id = Some(snapshot_session_id);
        messages.push(message);
        final_meta = Some(meta);
    }

    let (Some(storage), Some(session_id), Some(final_meta)) = (storage, session_id, final_meta)
    else {
        return Ok(());
    };
    storage
        .persist_message_batch_with_retry(&session_id, &messages, &final_meta)
        .await
}

pub(super) async fn append_persisted_messages(
    session: &Arc<Mutex<Session>>,
    messages: Vec<ChatMessage>,
) -> Result<(), StorageError> {
    append_persisted_messages_with_meta(session, messages)
        .await
        .map(|_| ())
}

enum VersionPolicy {
    Advance,
    PreserveForOwnedTurn(String),
}

/// Persist a message emitted as a side effect of the currently active Turn
/// without invalidating that same Turn's captured session version.
///
/// The task-local Turn ID is revalidated while holding the session lock. If it
/// no longer owns the target session, the write advances `state_version` like
/// any unrelated mutation so stale model work is still rejected.
pub(super) async fn append_active_turn_message(
    session: &Arc<Mutex<Session>>,
    message: ChatMessage,
    turn_id: String,
) -> Result<(), StorageError> {
    append_persisted_messages_inner(
        session,
        vec![message],
        VersionPolicy::PreserveForOwnedTurn(turn_id),
    )
    .await
    .map(|_| ())
}

pub(super) async fn append_persisted_messages_with_meta(
    session: &Arc<Mutex<Session>>,
    messages: Vec<ChatMessage>,
) -> Result<Vec<crate::storage::message::MessageMeta>, StorageError> {
    append_persisted_messages_inner(session, messages, VersionPolicy::Advance).await
}

async fn append_persisted_messages_inner(
    session: &Arc<Mutex<Session>>,
    messages: Vec<ChatMessage>,
    version_policy: VersionPolicy,
) -> Result<Vec<crate::storage::message::MessageMeta>, StorageError> {
    if messages.is_empty() {
        return Ok(Vec::new());
    }

    let persistence_lock = { session.lock().await.persistence_lock.clone() };
    let _persistence_guard = persistence_lock.lock().await;
    let message_ids: Vec<_> = messages.iter().map(|message| message.id.clone()).collect();
    let (snapshots, advance_state_version): (Vec<Option<MessagePersistSnapshot>>, bool) = {
        let mut guard = session.lock().await;
        let advance_state_version = match &version_policy {
            VersionPolicy::Advance => true,
            VersionPolicy::PreserveForOwnedTurn(turn_id) => !guard.owns_active_turn(turn_id),
        };
        let snapshots = messages
            .into_iter()
            .map(|message| {
                guard.add_message_in_memory_with_version(message, true, advance_state_version)
            })
            .collect();
        (snapshots, advance_state_version)
    };
    let committed = snapshots
        .iter()
        .flatten()
        .map(|(_, _, message, _)| message.clone())
        .collect();

    if let Err(error) = persist_added_messages(snapshots).await {
        session
            .lock()
            .await
            .rollback_message_suffix_with_version(&message_ids, advance_state_version);
        return Err(error);
    }
    Ok(committed)
}

/// Publish `Completed` only after the supplied durable write succeeds.
///
/// Keeping this ordering in one helper makes the user-visible terminal status
/// impossible to publish optimistically before SQLite commits.
pub(super) async fn finalize_turn_after_persistence<F, T, E>(
    controller: &TurnController,
    usage: Option<Usage>,
    persistence: F,
) -> Result<T, E>
where
    F: Future<Output = Result<T, E>>,
    E: Display,
{
    controller.begin_finalizing();
    match persistence.await {
        Ok(value) => {
            controller.complete(usage);
            Ok(value)
        }
        Err(error) => {
            controller.fail(format!("failed to persist turn: {error}"));
            Err(error)
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::config::LLMProviderConfig;
    use crate::memory::MemoryManager;
    use crate::session::{TurnController, TurnStatus};
    use crate::tools::ToolRegistry;
    use std::collections::HashMap;
    use std::path::PathBuf;

    #[tokio::test]
    async fn completed_is_published_only_after_persistence_succeeds() {
        let (controller, _emitter, receiver) = TurnController::start("session", "message");
        let persisted = Arc::new(std::sync::atomic::AtomicBool::new(false));
        let persisted_in_future = persisted.clone();

        let result: Result<(), String> =
            finalize_turn_after_persistence(&controller, None, async move {
                assert_eq!(receiver.borrow().status, TurnStatus::Running);
                assert_eq!(
                    receiver.borrow().phase,
                    crate::session::TurnPhase::Finalizing
                );
                persisted_in_future.store(true, std::sync::atomic::Ordering::SeqCst);
                Ok(())
            })
            .await;

        assert!(result.is_ok());
        assert!(persisted.load(std::sync::atomic::Ordering::SeqCst));
        assert_eq!(controller.snapshot().status, TurnStatus::Completed);
    }

    #[tokio::test]
    async fn persistence_failure_never_publishes_completed() {
        let (controller, _emitter, _receiver) = TurnController::start("session", "message");
        let result: Result<(), &str> =
            finalize_turn_after_persistence(&controller, None, async { Err("database down") })
                .await;

        assert_eq!(result, Err("database down"));
        let snapshot = controller.snapshot();
        assert_eq!(snapshot.status, TurnStatus::Failed);
        assert_eq!(
            snapshot.error.as_deref(),
            Some("failed to persist turn: database down")
        );
    }

    #[tokio::test]
    async fn active_turn_side_effect_does_not_invalidate_its_session_version() {
        let dir = tempfile::tempdir().unwrap();
        let storage = Arc::new(
            crate::storage::Storage::new(&dir.path().join("memory.db"))
                .await
                .unwrap(),
        );
        let memory_manager = Arc::new(MemoryManager::new(
            storage,
            "test".to_string(),
            "test".to_string(),
        ));
        let config = LLMProviderConfig {
            provider_type: "openai".to_string(),
            name: "test".to_string(),
            base_url: "http://127.0.0.1".to_string(),
            api_key: "test".to_string(),
            extra_headers: HashMap::new(),
            model_id: "test".to_string(),
            temperature: None,
            max_tokens: None,
            model_extra: HashMap::new(),
            max_tool_iterations: 1,
            token_limit: 8_192,
            workspace_dir: PathBuf::from("."),
            input_types: vec!["text".to_string(), "image".to_string()],
            price_input_per_million: None,
            price_output_per_million: None,
        };
        let session = Arc::new(Mutex::new(
            Session::new(
                crate::session::UnifiedSessionId::new("cli_chat", "chat", "dialog"),
                config,
                Arc::new(ToolRegistry::new()),
                None,
                String::new(),
                "test".to_string(),
                memory_manager,
            )
            .await
            .unwrap(),
        ));
        let base_version = session.lock().await.state_version_for_test();

        session.lock().await.set_active_turn_for_test("turn-1");
        append_active_turn_message(
            &session,
            ChatMessage::assistant("sent screenshot"),
            "turn-1".to_string(),
        )
        .await
        .unwrap();

        {
            let guard = session.lock().await;
            assert_eq!(guard.state_version_for_test(), base_version);
            assert_eq!(guard.get_history().len(), 1);
        }

        append_active_turn_message(
            &session,
            ChatMessage::assistant("late screenshot"),
            "stale-turn".to_string(),
        )
        .await
        .unwrap();

        let guard = session.lock().await;
        assert_eq!(guard.state_version_for_test(), base_version + 1);
        assert_eq!(guard.get_history().len(), 2);
    }
}