//! Generic dependent fetch queue for resource events, MR closes, and MR diffs.
//!
//! Provides enqueue, claim, complete, fail (with exponential backoff), and
//! stale lock reclamation operations against the `pending_dependent_fetches` table.

use std::collections::HashMap;

use rusqlite::Connection;

use super::error::Result;
use super::time::now_ms;

/// A pending job from the dependent fetch queue.
#[derive(Debug)]
pub struct PendingJob {
    pub id: i64,
    pub project_id: i64,
    pub entity_type: String,
    pub entity_iid: i64,
    pub entity_local_id: i64,
    pub job_type: String,
    pub payload_json: Option<String>,
    pub attempts: i32,
}

/// Enqueue a dependent fetch job. Idempotent via UNIQUE constraint (INSERT OR IGNORE).
///
/// Returns `true` if actually inserted (not deduped).
pub fn enqueue_job(
    conn: &Connection,
    project_id: i64,
    entity_type: &str,
    entity_iid: i64,
    entity_local_id: i64,
    job_type: &str,
    payload_json: Option<&str>,
) -> Result<bool> {
    let now = now_ms();
    let changes = conn.execute(
        "INSERT OR IGNORE INTO pending_dependent_fetches
         (project_id, entity_type, entity_iid, entity_local_id, job_type, payload_json, enqueued_at)
         VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7)",
        rusqlite::params![project_id, entity_type, entity_iid, entity_local_id, job_type, payload_json, now],
    )?;

    Ok(changes > 0)
}

/// Claim a batch of jobs for processing.
///
/// Atomically sets `locked_at` on the claimed jobs. Only claims jobs where
/// `locked_at IS NULL` and `(next_retry_at IS NULL OR next_retry_at <= now)`.
pub fn claim_jobs(conn: &Connection, job_type: &str, batch_size: usize) -> Result<Vec<PendingJob>> {
    if batch_size == 0 {
        return Ok(Vec::new());
    }

    let now = now_ms();

    // Find available jobs
    let mut select_stmt = conn.prepare_cached(
        "SELECT id, project_id, entity_type, entity_iid, entity_local_id, job_type, payload_json, attempts
         FROM pending_dependent_fetches
         WHERE job_type = ?1
           AND locked_at IS NULL
           AND (next_retry_at IS NULL OR next_retry_at <= ?2)
         ORDER BY enqueued_at ASC
         LIMIT ?3",
    )?;

    let jobs: Vec<PendingJob> = select_stmt
        .query_map(
            rusqlite::params![job_type, now, batch_size as i64],
            |row| {
                Ok(PendingJob {
                    id: row.get(0)?,
                    project_id: row.get(1)?,
                    entity_type: row.get(2)?,
                    entity_iid: row.get(3)?,
                    entity_local_id: row.get(4)?,
                    job_type: row.get(5)?,
                    payload_json: row.get(6)?,
                    attempts: row.get(7)?,
                })
            },
        )?
        .collect::<std::result::Result<Vec<_>, _>>()?;

    // Lock the claimed jobs
    if !jobs.is_empty() {
        let ids: Vec<String> = jobs.iter().map(|j| j.id.to_string()).collect();
        let placeholders = ids.join(",");
        conn.execute(
            &format!(
                "UPDATE pending_dependent_fetches SET locked_at = ?1 WHERE id IN ({placeholders})"
            ),
            rusqlite::params![now],
        )?;
    }

    Ok(jobs)
}

/// Mark a job as complete (DELETE the row).
pub fn complete_job(conn: &Connection, job_id: i64) -> Result<()> {
    conn.execute(
        "DELETE FROM pending_dependent_fetches WHERE id = ?1",
        rusqlite::params![job_id],
    )?;

    Ok(())
}

/// Mark a job as failed. Increments attempts, sets next_retry_at with exponential
/// backoff, clears locked_at, and records the error.
///
/// Backoff: 30s * 2^(attempts-1), capped at 480s.
pub fn fail_job(conn: &Connection, job_id: i64, error: &str) -> Result<()> {
    let now = now_ms();

    // Get current attempts
    let current_attempts: i32 = conn
        .query_row(
            "SELECT attempts FROM pending_dependent_fetches WHERE id = ?1",
            rusqlite::params![job_id],
            |row| row.get(0),
        )
        .unwrap_or(0);

    let new_attempts = current_attempts + 1;
    let backoff_ms: i64 = (30_000i64 * (1i64 << (new_attempts - 1).min(4))).min(480_000);
    let next_retry = now + backoff_ms;

    conn.execute(
        "UPDATE pending_dependent_fetches
         SET attempts = ?1, next_retry_at = ?2, locked_at = NULL, last_error = ?3
         WHERE id = ?4",
        rusqlite::params![new_attempts, next_retry, error, job_id],
    )?;

    Ok(())
}

/// Reclaim stale locks (locked_at older than threshold).
///
/// Returns count of reclaimed jobs.
pub fn reclaim_stale_locks(conn: &Connection, stale_threshold_minutes: u32) -> Result<usize> {
    let threshold_ms = now_ms() - (i64::from(stale_threshold_minutes) * 60 * 1000);

    let changes = conn.execute(
        "UPDATE pending_dependent_fetches SET locked_at = NULL WHERE locked_at < ?1",
        rusqlite::params![threshold_ms],
    )?;

    Ok(changes)
}

/// Count pending jobs by job_type (for stats/progress).
pub fn count_pending_jobs(conn: &Connection) -> Result<HashMap<String, usize>> {
    let mut stmt = conn.prepare_cached(
        "SELECT job_type, COUNT(*) FROM pending_dependent_fetches GROUP BY job_type",
    )?;

    let mut counts = HashMap::new();
    let rows = stmt.query_map([], |row| {
        let job_type: String = row.get(0)?;
        let count: i64 = row.get(1)?;
        Ok((job_type, count as usize))
    })?;

    for row in rows {
        let (job_type, count) = row?;
        counts.insert(job_type, count);
    }

    Ok(counts)
}