import type { SqliteDatabase } from '../../infrastructure/database/database.js';

/**
 * Reconciles jobs that the console still believes are in flight.
 *
 * Every job is executed inside the request that created it, so a row left in `running` after a
 * crash can never finish on its own. The official Hub exposes the same capability on its command
 * ledger; here it closes the loop against our own job table instead of a remote queue.
 *
 * `queued` rows never reached a transport, so they are cancelled. `running` and `cancelling` rows
 * may or may not have reached the device, so they become `unknown-result`, which is the only
 * honest terminal state for an interrupted write.
 *
 * The service also owns operator cancellation, which the published contract promises on
 * `POST /api/v1/jobs/{jobId}/cancel`. Both paths share one rule: a job only ever moves from an
 * active state to a terminal one, and every write is guarded by the active state, so a cancel
 * racing an in-flight executor loses cleanly instead of overwriting a real result.
 */

const DISPATCHED_STATUSES = new Set(['running', 'cancelling']);
const QUEUED_STATUSES = new Set(['queued']);
const ACTIVE_STATUSES = new Set([...DISPATCHED_STATUSES, ...QUEUED_STATUSES]);
const ACTIVE_PLACEHOLDERS = '?, ?, ?';

/** On-demand sweeps leave a margin so a slow batch in another request is never clobbered. */
export const DEFAULT_RECONCILE_GRACE_MS = 15 * 60 * 1000;

export interface JobReconcileResult {
  /** Jobs closed by this sweep. */
  readonly interrupted: number;
  /** Jobs still considered in flight once the sweep finished. */
  readonly pending: number;
}

export interface JobReconcileSummary {
  readonly pending: number;
  readonly dispatched: number;
  readonly queued: number;
  readonly oldestCreatedAt: string | null;
}

export interface JobReconcileOptions {
  readonly db: SqliteDatabase;
  readonly now?: () => Date;
}

export type JobCancelErrorCode = 'NOT_FOUND' | 'NOT_CANCELLABLE';

export class JobCancelError extends Error {
  constructor(
    readonly code: JobCancelErrorCode,
    message: string,
  ) {
    super(message);
    this.name = 'JobCancelError';
  }
}

const CANCEL_RESULT_CODE = 'CANCELLED_BY_OPERATOR';

const isActiveStatus = (status: unknown): status is string =>
  typeof status === 'string' && ACTIVE_STATUSES.has(status);

export class JobReconcileService {
  readonly #db: SqliteDatabase;
  readonly #now: () => Date;

  constructor(options: JobReconcileOptions) {
    this.#db = options.db;
    this.#now = options.now ?? (() => new Date());
  }

  summary(olderThanMs = 0): JobReconcileSummary {
    const cutoff = this.#cutoff(olderThanMs);
    const rows = this.#db
      .prepare(
        'SELECT status, created_at FROM jobs WHERE status IN (?,?,?) AND created_at <= ? ORDER BY created_at ASC, id ASC',
      )
      .all('queued', 'running', 'cancelling', cutoff) as Array<{
      status: unknown;
      created_at: unknown;
    }>;
    let dispatched = 0;
    let queued = 0;
    for (const row of rows) {
      if (typeof row.status === 'string' && DISPATCHED_STATUSES.has(row.status)) dispatched += 1;
      else if (typeof row.status === 'string' && QUEUED_STATUSES.has(row.status)) queued += 1;
    }
    const oldest = rows[0]?.created_at;
    return {
      pending: rows.length,
      dispatched,
      queued,
      oldestCreatedAt: typeof oldest === 'string' ? oldest : null,
    };
  }

  reconcile(olderThanMs = DEFAULT_RECONCILE_GRACE_MS): JobReconcileResult {
    const cutoff = this.#cutoff(olderThanMs);
    const closedAt = this.#now().toISOString();
    const interrupted = this.#db.transaction((): number => {
      const rows = this.#db
        .prepare(
          'SELECT id, status FROM jobs WHERE status IN (?,?,?) AND created_at <= ? ORDER BY created_at ASC, id ASC',
        )
        .all('queued', 'running', 'cancelling', cutoff) as Array<{
        id: unknown;
        status: unknown;
      }>;
      const closeItems = this.#db.prepare(
        `UPDATE job_items SET status = ?, result_code = ?, finished_at = ?, updated_at = ?
          WHERE job_id = ? AND status IN ('queued','running','cancelling')`,
      );
      const closeAttempts = this.#db.prepare(
        "UPDATE job_attempts SET status = ?, finished_at = ? WHERE job_id = ? AND status = 'running'",
      );
      const closeJob = this.#db.prepare(
        'UPDATE jobs SET status = ?, finished_at = ?, updated_at = ? WHERE id = ? AND status IN (?,?,?)',
      );
      let count = 0;
      for (const row of rows) {
        if (typeof row.id !== 'string' || !isActiveStatus(row.status)) continue;
        const dispatched = DISPATCHED_STATUSES.has(row.status);
        const finalStatus = dispatched ? 'unknown-result' : 'cancelled';
        const resultCode = dispatched ? 'INTERRUPTED' : 'NEVER_DISPATCHED';
        closeItems.run(finalStatus, resultCode, closedAt, closedAt, row.id);
        closeAttempts.run(finalStatus, closedAt, row.id);
        closeJob.run(finalStatus, closedAt, closedAt, row.id, 'queued', 'running', 'cancelling');
        count += 1;
      }
      return count;
    })();
    return { interrupted, pending: this.summary().pending };
  }

  #cutoff(olderThanMs: number): string {
    if (!Number.isFinite(olderThanMs) || olderThanMs < 0) {
      throw new RangeError('olderThanMs must be a non-negative finite number');
    }
    return new Date(this.#now().getTime() - olderThanMs).toISOString();
  }

  /** Requests cancellation of a job that has not reached a terminal state yet. */
  cancel(jobId: string): void {
    if (typeof jobId !== 'string' || jobId.length === 0 || jobId.length > 128) {
      throw new JobCancelError('NOT_FOUND', 'Job was not found');
    }
    const closedAt = this.#now().toISOString();
    const changed = this.#db.transaction((): boolean => {
      const row = this.#db.prepare('SELECT status FROM jobs WHERE id = ?').get(jobId) as
        | { status: unknown }
        | undefined;
      if (!row) throw new JobCancelError('NOT_FOUND', 'Job was not found');
      if (!isActiveStatus(row.status))
        throw new JobCancelError('NOT_CANCELLABLE', 'Job already reached a terminal state');
      this.#db
        .prepare(
          `UPDATE job_items SET status = 'cancelled', result_code = ?, finished_at = ?, updated_at = ?
            WHERE job_id = ? AND status IN ('queued', 'running', 'cancelling')`,
        )
        .run(CANCEL_RESULT_CODE, closedAt, closedAt, jobId);
      this.#db
        .prepare(
          "UPDATE job_attempts SET status = 'cancelled', finished_at = ? WHERE job_id = ? AND status = 'running'",
        )
        .run(closedAt, jobId);
      const updated = this.#db
        .prepare(
          `UPDATE jobs SET status = 'cancelled', finished_at = ?, updated_at = ?
            WHERE id = ? AND status IN (${ACTIVE_PLACEHOLDERS})`,
        )
        .run(closedAt, closedAt, jobId, 'queued', 'running', 'cancelling');
      return updated.changes === 1;
    })();
    if (!changed)
      throw new JobCancelError('NOT_CANCELLABLE', 'Job already reached a terminal state');
  }
}