use crate::handlers::HandlerRegistry;
use chrono::Utc;
use serde_json::Value;
use sqlx::{PgPool, Row};
use std::sync::Arc;
use tokio::sync::Semaphore;
use tracing::{error, info, warn};
use uuid::Uuid;

/// Hent og prosesser jobber i en uendelig loop.
/// Semaphore begrenser antall samtidige jobber.
pub async fn run(
    pool: PgPool,
    registry: Arc<HandlerRegistry>,
    max_concurrent: usize,
    poll_interval_secs: u64,
) -> anyhow::Result<()> {
    let semaphore = Arc::new(Semaphore::new(max_concurrent));
    let interval = std::time::Duration::from_secs(poll_interval_secs);

    loop {
        // Vent til en slot er ledig
        let permit = semaphore.clone().acquire_owned().await?;

        // Forsøk å hente en jobb
        let job = claim_job(&pool).await;

        match job {
            Ok(Some(job)) => {
                let pool = pool.clone();
                let registry = registry.clone();

                tokio::spawn(async move {
                    let _permit = permit; // holdes til jobben er ferdig
                    process_job(&pool, &registry, job).await;
                });
            }
            Ok(None) => {
                drop(permit);
                tokio::time::sleep(interval).await;
            }
            Err(e) => {
                error!(error = %e, "Feil ved henting av jobb");
                drop(permit);
                tokio::time::sleep(interval).await;
            }
        }
    }
}

#[derive(Debug)]
struct Job {
    id: Uuid,
    workspace_id: Uuid,
    job_type: String,
    payload: Value,
    attempts: i16,
    max_attempts: i16,
}

/// Claim neste jobb med FOR UPDATE SKIP LOCKED.
async fn claim_job(pool: &PgPool) -> anyhow::Result<Option<Job>> {
    let row = sqlx::query(
        r#"
        UPDATE job_queue SET
            status = 'running',
            started_at = now(),
            attempts = attempts + 1
        WHERE id = (
            SELECT id FROM job_queue
            WHERE status IN ('pending', 'retry')
                AND scheduled_for <= now()
            ORDER BY priority DESC, scheduled_for ASC
            LIMIT 1
            FOR UPDATE SKIP LOCKED
        )
        RETURNING id, workspace_id, job_type, payload, attempts, max_attempts
        "#,
    )
    .fetch_optional(pool)
    .await?;

    Ok(row.map(|r| Job {
        id: r.get("id"),
        workspace_id: r.get("workspace_id"),
        job_type: r.get("job_type"),
        payload: r.get("payload"),
        attempts: r.get("attempts"),
        max_attempts: r.get("max_attempts"),
    }))
}

/// Prosesser en jobb: dispatch til handler, oppdater status.
async fn process_job(pool: &PgPool, registry: &HandlerRegistry, job: Job) {
    info!(
        job_id = %job.id,
        job_type = %job.job_type,
        workspace_id = %job.workspace_id,
        attempt = job.attempts,
        "Starter jobb"
    );

    let handler = registry.get(&job.job_type);

    let result = match handler {
        Some(handler) => handler.handle(pool, &job.workspace_id, &job.id, &job.payload).await,
        None => {
            warn!(job_type = %job.job_type, "Ukjent jobbtype — ingen handler registrert");
            Err(anyhow::anyhow!("Ukjent jobbtype: {}", job.job_type))
        }
    };

    match result {
        Ok(result_data) => {
            info!(job_id = %job.id, "Jobb fullført");
            let _ = sqlx::query(
                r#"
                UPDATE job_queue SET
                    status = 'completed',
                    result = $1,
                    completed_at = now()
                WHERE id = $2
                "#,
            )
            .bind(&result_data)
            .bind(job.id)
            .execute(pool)
            .await;
        }
        Err(e) => {
            error!(job_id = %job.id, error = %e, "Jobb feilet");

            if job.attempts < job.max_attempts {
                // Retry med eksponentiell backoff: 30s × 2^(attempts-1)
                let backoff_secs = 30i64 * 2i64.pow((job.attempts - 1) as u32);
                let scheduled_for = Utc::now() + chrono::Duration::seconds(backoff_secs);

                info!(
                    job_id = %job.id,
                    next_retry = %scheduled_for,
                    backoff_secs,
                    "Setter opp retry"
                );

                let _ = sqlx::query(
                    r#"
                    UPDATE job_queue SET
                        status = 'retry',
                        error_msg = $1,
                        scheduled_for = $2
                    WHERE id = $3
                    "#,
                )
                .bind(format!("{e}"))
                .bind(scheduled_for)
                .bind(job.id)
                .execute(pool)
                .await;
            } else {
                warn!(job_id = %job.id, attempts = job.attempts, "Maks forsøk nådd — permanent feil");

                let _ = sqlx::query(
                    r#"
                    UPDATE job_queue SET
                        status = 'error',
                        error_msg = $1,
                        completed_at = now()
                    WHERE id = $2
                    "#,
                )
                .bind(format!("{e}"))
                .bind(job.id)
                .execute(pool)
                .await;
            }
        }
    }
}