//! The transactional seam's SQLite arm — `begin_tx`, the
//! [`SqliteTxHandle`] (the writer-slot lease, ADR-007), and all eleven
//! transaction-handle methods (ten `*_tx` ops plus `commit`) (`sqlite-engine-seam-tx`).
//!
//! `begin_tx` acquires the writer slot and opens `BEGIN IMMEDIATE` on
//! the acquired connection; the handle owns connection + slot. Every
//! op round-trips the `spawn_blocking` seam to that connection —
//! holding the handle across `await` points parks the writer, which
//! is the design (WAL single-writer, honest).
//!
//! Drop = rollback (ADR-021 §4): dropping the handle without commit
//! issues `ROLLBACK` (ignoring failure — no panic may escape drop) and
//! releases the writer slot; a panic unwinding through any scope
//! holding the handle reaches the same rollback. The no-ghosts
//! property holds through the RAII path.
//!
//! Errors: substrate errors map to
//! [`Error::Database`](alkstore::Error::Database) with the source chain
//! preserved (ADR-008 §5); `encode_payload`'s typed `Codec` error
//! propagates from the enqueue/publish paths (ADR-023 §1). Every
//! name-bearing method validates at the entry point, before any round
//! trip (ADR-008 §4) — the commit-atomic path cannot bypass it.

use serde_json::Value;
use std::sync::Arc;

use alkstore::{BoxedFuture, EnqueueOpts, Error, Job, Result, StreamEvent, TxHandle};
use alkstore::{validate_local_name, validate_shared_name};

use crate::queue::job_from_json;
use crate::resolution::{
    outbox_backing_queue_name, outbox_default_stamps, plain_queue_default_stamps,
    resolve_enqueue_opts, stamps_with_override,
};
use crate::seam::{blocking, sqlite_error};
use crate::stream::stream_events_from_json_page;
use crate::substrate::{
    Writer, enqueue, get_job, stream_get_offset, stream_publish, stream_read_since,
    stream_save_offset,
};

/// The caller-held SQLite transaction handle: the writer-slot lease.
/// Constructed only through [`crate::SqliteStore`]'s `begin_tx` —
/// never held across an engine `Store` trait object (the trait is what
/// consumers see).
pub struct SqliteTxHandle {
    conn: Option<rusqlite::Connection>,
    writer: Arc<Writer>,
    reopen: Arc<dyn Fn() -> Result<rusqlite::Connection> + Send + Sync>,
    /// This store's commit-fault arm (`sqlite-commit-error-arm`) —
    /// read once per commit by the test-only fault branch; dead in
    /// production builds.
    #[cfg(test)]
    commit_fault: crate::seam::commit_fault::Flag,
}

impl std::fmt::Debug for SqliteTxHandle {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("SqliteTxHandle")
            .field("open", &self.conn.is_some())
            .finish_non_exhaustive()
    }
}

impl SqliteTxHandle {
    pub(crate) fn begin(
        writer: Arc<Writer>,
        reopen: Arc<dyn Fn() -> Result<rusqlite::Connection> + Send + Sync>,
        #[cfg(test)] commit_fault: crate::seam::commit_fault::Flag,
    ) -> BoxedFuture<'static, Result<Box<dyn TxHandle + Send>>> {
        Box::pin(async move {
            let writer2 = writer.clone();
            let conn = blocking(move || {
                let conn = writer2.acquire().ok_or_else(|| {
                    alkstore::Error::database(std::io::Error::other(
                        "the store is closed: writer slot unavailable",
                    ))
                })?;
                match conn.execute_batch("BEGIN IMMEDIATE").map_err(sqlite_error) {
                    Ok(()) => Ok(conn),
                    Err(e) => {
                        writer2.release(conn);
                        Err(e)
                    }
                }
            })
            .await?;
            Ok(Box::new(SqliteTxHandle {
                conn: Some(conn),
                writer,
                reopen,
                #[cfg(test)]
                commit_fault,
            }) as _)
        })
    }

    /// The private bridge: every op routes through the same connection
    /// via `spawn_blocking`. The connection crosses the seam inside an
    /// RAII [`ConnLease`]: a future cancelled mid-op drops the lease,
    /// which closes the connection (SQLite rolls back the uncommitted
    /// transaction) and replenishes the writer slot with a fresh
    /// connection — the lease cannot leak, and the slot stays
    /// grantable. If `commit`/drop already consumed the handle (`conn`
    /// taken), the op fails closed with `Closed` — one-shot handles
    /// cannot op past their terminal transition.
    fn with_conn<T, F>(&mut self, f: F) -> BoxedFuture<'_, Result<T>>
    where
        T: Send + 'static,
        F: FnOnce(&rusqlite::Connection) -> Result<T> + Send + 'static,
    {
        let Some(conn) = self.conn.take() else {
            return Box::pin(async { Err(Error::Closed) });
        };
        let writer = self.writer.clone();
        let reopen = self.reopen.clone();
        let fut = blocking(move || {
            let lease = ConnLease {
                conn: Some(conn),
                writer: writer.clone(),
                reopen: reopen.clone(),
            };
            let out = match lease.conn() {
                Some(conn) => f(conn),
                None => Err(Error::database(std::io::Error::other(
                    "the store is closed: writer slot unavailable",
                ))),
            };
            Ok((out, lease))
        });
        Box::pin(async move {
            let (out, lease) = fut.await?;
            self.conn = lease.release();
            out
        })
    }
}

/// The writer connection inside the `with_conn` bridge: an RAII guard
/// so the connection crossing `spawn_blocking` always has an owner
/// that accounts for the writer slot. Handled normally, the future's
/// completion defuses the guard (`release`) and the connection returns
/// to the handle; on a mid-op-future cancellation the guard drops
/// instead — dropping the connection (its uncommitted transaction
/// rolls back at the SQLite layer) and replenishing the writer slot
/// with a fresh connection, so the next lease proceeds.
struct ConnLease {
    conn: Option<rusqlite::Connection>,
    writer: std::sync::Arc<Writer>,
    reopen: Arc<dyn Fn() -> Result<rusqlite::Connection> + Send + Sync>,
}

impl ConnLease {
    fn conn(&self) -> Option<&rusqlite::Connection> {
        self.conn.as_ref()
    }

    fn release(mut self) -> Option<rusqlite::Connection> {
        self.conn.take()
    }
}

impl Drop for ConnLease {
    fn drop(&mut self) {
        if let Some(conn) = self.conn.take() {
            if let Err(rollback) = conn.execute_batch("ROLLBACK") {
                eprintln!(
                    "alkstore: error: rollback on a cancelled transaction op \
                     left the connection in an unknown state: {rollback}"
                );
            }
            drop(conn);
            if let Ok(fresh) = (self.reopen)() {
                self.writer.release(fresh);
            }
        }
    }
}

impl TxHandle for SqliteTxHandle {
    fn enqueue_tx<'a>(
        &'a mut self,
        queue: &str,
        opts: EnqueueOpts,
        payload: Value,
    ) -> BoxedFuture<'a, Result<i64>> {
        if let Err(e) = validate_shared_name(queue) {
            return Box::pin(async move { Err(e) });
        }
        let queue = queue.to_string();
        self.with_conn(move |conn| {
            let bytes = alkstore::encode_payload(&payload)?;
            let resolved = resolve_enqueue_opts(conn, &opts)?;
            let stamps = stamps_with_override(plain_queue_default_stamps(), &opts);
            enqueue(
                conn,
                &queue,
                std::str::from_utf8(&bytes)
                    .map_err(|e| Error::Codec(format!("row payload must be utf-8: {e}")))?,
                resolved.run_at,
                opts.priority,
                resolved.expires_at,
                stamps,
            )
            .map_err(sqlite_error)
        })
    }

    fn publish_tx<'a>(&'a mut self, stream: &str, payload: Value) -> BoxedFuture<'a, Result<i64>> {
        let stream = stream.to_string();
        Box::pin(async move { self.publish_with_key_tx(&stream, None, payload).await })
    }

    fn publish_with_key_tx<'a>(
        &'a mut self,
        stream: &str,
        key: Option<String>,
        payload: Value,
    ) -> BoxedFuture<'a, Result<i64>> {
        if let Err(e) = validate_shared_name(stream) {
            return Box::pin(async move { Err(e) });
        }
        let key = match key {
            Some(k) if k.is_empty() || k.trim().is_empty() => {
                return Box::pin(async move { Err(Error::InvalidName { name: k }) });
            }
            other => other,
        };
        let stream = stream.to_string();
        self.with_conn(move |conn| {
            let bytes = alkstore::encode_payload(&payload)?;
            stream_publish(
                conn,
                &stream,
                key.as_deref(),
                std::str::from_utf8(&bytes)
                    .map_err(|e| Error::Codec(format!("row payload must be utf-8: {e}")))?,
            )
            .map_err(sqlite_error)
        })
    }

    fn notify_tx<'a>(&'a mut self, channel: &str, payload: Value) -> BoxedFuture<'a, Result<()>> {
        if let Err(e) = validate_shared_name(channel) {
            return Box::pin(async move { Err(e) });
        }
        let channel = channel.to_string();
        self.with_conn(move |conn| {
            let bytes = alkstore::encode_payload(&payload)?;
            conn.query_row(
                "SELECT notify(?1, ?2)",
                rusqlite::params![
                    channel,
                    String::from_utf8(bytes).map_err(|e| Error::Codec(format!(
                        "notify payload must be utf-8 text: {e}"
                    )))?,
                ],
                |_| Ok(()),
            )
            .map_err(sqlite_error)
        })
    }

    fn save_offset_tx<'a>(
        &'a mut self,
        stream: &str,
        consumer: &str,
        offset: i64,
    ) -> BoxedFuture<'a, Result<()>> {
        if let Err(e) = validate_shared_name(stream) {
            return Box::pin(async move { Err(e) });
        }
        if let Err(e) = validate_local_name(consumer) {
            return Box::pin(async move { Err(e) });
        }
        let stream = stream.to_string();
        let consumer = consumer.to_string();
        self.with_conn(move |conn| {
            stream_save_offset(conn, &consumer, &stream, offset)
                .map(|_| ())
                .map_err(sqlite_error)
        })
    }

    fn get_job_tx<'a>(
        &'a mut self,
        queue: &str,
        job_id: i64,
    ) -> BoxedFuture<'a, Result<Option<Job>>> {
        if let Err(e) = validate_shared_name(queue) {
            return Box::pin(async move { Err(e) });
        }
        let queue = queue.to_string();
        self.with_conn(move |conn| {
            let row = get_job(conn, job_id).map_err(sqlite_error)?;
            let Some(json) = row else {
                return Ok(None);
            };
            let value: serde_json::Value = serde_json::from_str(&json)
                .map_err(|e| Error::Codec(format!("job row must be json: {e}")))?;
            if value["queue"].as_str() != Some(queue.as_str()) {
                return Ok(None);
            }
            job_from_json(&value)
        })
    }

    fn get_offset_tx<'a>(
        &'a mut self,
        stream: &str,
        consumer: &str,
    ) -> BoxedFuture<'a, Result<i64>> {
        if let Err(e) = validate_shared_name(stream) {
            return Box::pin(async move { Err(e) });
        }
        if let Err(e) = validate_local_name(consumer) {
            return Box::pin(async move { Err(e) });
        }
        let stream = stream.to_string();
        let consumer = consumer.to_string();
        self.with_conn(move |conn| {
            stream_get_offset(conn, &consumer, &stream).map_err(sqlite_error)
        })
    }

    fn read_since_tx<'a>(
        &'a mut self,
        stream: &str,
        offset: i64,
        limit: i64,
    ) -> BoxedFuture<'a, Result<Vec<StreamEvent>>> {
        if let Err(e) = validate_shared_name(stream) {
            return Box::pin(async move { Err(e) });
        }
        let stream = stream.to_string();
        self.with_conn(move |conn| {
            if limit <= 0 {
                return Ok(Vec::new());
            }
            let page = stream_read_since(conn, &stream, offset, limit).map_err(sqlite_error)?;
            stream_events_from_json_page(&page, stream)
        })
    }

    fn read_from_consumer_tx<'a>(
        &'a mut self,
        stream: &str,
        consumer: &str,
        limit: i64,
    ) -> BoxedFuture<'a, Result<Vec<StreamEvent>>> {
        if let Err(e) = validate_shared_name(stream) {
            return Box::pin(async move { Err(e) });
        }
        if let Err(e) = validate_local_name(consumer) {
            return Box::pin(async move { Err(e) });
        }
        let stream = stream.to_string();
        let consumer = consumer.to_string();
        self.with_conn(move |conn| {
            if limit <= 0 {
                return Ok(Vec::new());
            }
            let from = stream_get_offset(conn, &consumer, &stream).map_err(sqlite_error)?;
            let page = stream_read_since(conn, &stream, from, limit).map_err(sqlite_error)?;
            stream_events_from_json_page(&page, stream)
        })
    }

    fn outbox_enqueue_tx<'a>(
        &'a mut self,
        outbox: &str,
        opts: EnqueueOpts,
        payload: Value,
    ) -> BoxedFuture<'a, Result<i64>> {
        if let Err(e) = validate_shared_name(outbox) {
            return Box::pin(async move { Err(e) });
        }
        let outbox = outbox.to_string();
        self.with_conn(move |conn| {
            let bytes = alkstore::encode_payload(&payload)?;
            let resolved = resolve_enqueue_opts(conn, &opts)?;
            let stamps = stamps_with_override(outbox_default_stamps(), &opts);
            enqueue(
                conn,
                &outbox_backing_queue_name(&outbox),
                std::str::from_utf8(&bytes)
                    .map_err(|e| Error::Codec(format!("row payload must be utf-8: {e}")))?,
                resolved.run_at,
                opts.priority,
                resolved.expires_at,
                stamps,
            )
            .map_err(sqlite_error)
        })
    }

    fn commit(mut self: Box<Self>) -> BoxedFuture<'static, Result<()>> {
        let Some(conn) = self.conn.take() else {
            return Box::pin(async { Err(Error::Closed) });
        };
        let writer = self.writer.clone();
        let writer_reopen = self.reopen.clone();
        #[cfg(test)]
        let commit_fault = self.commit_fault.clone();
        Box::pin(async move {
            blocking(move || {
                #[cfg(test)]
                let committed = if crate::seam::commit_fault::take(&commit_fault) {
                    Err(crate::seam::commit_fault::failure())
                } else {
                    conn.execute_batch("COMMIT")
                };
                #[cfg(not(test))]
                let committed = conn.execute_batch("COMMIT");
                match committed.map_err(sqlite_error) {
                    Ok(()) => {
                        writer.release(conn);
                        Ok(())
                    }
                    Err(e) => {
                        drop(conn);
                        if let Ok(fresh) = (writer_reopen)() {
                            writer.release(fresh);
                        }
                        Err(e)
                    }
                }
            })
            .await
        })
    }
}

impl Drop for SqliteTxHandle {
    fn drop(&mut self) {
        if let Some(conn) = self.conn.take() {
            match conn.execute_batch("ROLLBACK") {
                Ok(()) => self.writer.release(conn),
                Err(rollback) => {
                    eprintln!(
                        "alkstore: error: rollback on a dropped transaction handle \
                         left the connection in an unknown state: {rollback}"
                    );
                    drop(conn);
                    if let Ok(fresh) = (self.reopen)() {
                        self.writer.release(fresh);
                    }
                }
            }
        }
    }
}