import { eq, and, desc, asc, sql } from 'drizzle-orm';
import { type LibSQLDatabase } from 'drizzle-orm/libsql';
import type * as schema from '../schema/index';
import { queueItems, contentItems, channels } from '../schema/index';
import type { QueueItem, QueueStatus } from '../../types/index';

// ── Types ──

/** Fields needed to create a new queue item. */
export interface CreateQueueItemData {
  contentItemId: number;
  priority?: number;
  maxAttempts?: number;
}

/** Optional fields when updating queue item status. */
export interface UpdateQueueItemFields {
  error?: string | null;
  startedAt?: string | null;
  completedAt?: string | null;
  attempts?: number;
}

type Db = LibSQLDatabase<typeof schema>;

// ── Repository Functions ──

/**
 * Insert a new queue item. Returns the created row.
 */
export async function createQueueItem(
  db: Db,
  data: CreateQueueItemData
): Promise<QueueItem> {
  const result = await db
    .insert(queueItems)
    .values({
      contentItemId: data.contentItemId,
      priority: data.priority ?? 0,
      maxAttempts: data.maxAttempts ?? 3,
    })
    .returning();

  return mapRow(result[0]);
}

/** Get a queue item by ID. Returns null if not found. */
export async function getQueueItemById(
  db: Db,
  id: number
): Promise<QueueItem | null> {
  const rows = await db
    .select()
    .from(queueItems)
    .where(eq(queueItems.id, id))
    .limit(1);

  return rows.length > 0 ? mapRow(rows[0]) : null;
}

/** Get queue items by status, ordered by priority DESC then createdAt ASC. */
export async function getQueueItemsByStatus(
  db: Db,
  status: QueueStatus
): Promise<QueueItem[]> {
  const rows = await db
    .select({
      id: queueItems.id,
      contentItemId: queueItems.contentItemId,
      status: queueItems.status,
      priority: queueItems.priority,
      attempts: queueItems.attempts,
      maxAttempts: queueItems.maxAttempts,
      error: queueItems.error,
      startedAt: queueItems.startedAt,
      completedAt: queueItems.completedAt,
      createdAt: queueItems.createdAt,
      updatedAt: queueItems.updatedAt,
      contentTitle: contentItems.title,
      channelName: channels.name,
    })
    .from(queueItems)
    .leftJoin(contentItems, eq(queueItems.contentItemId, contentItems.id))
    .leftJoin(channels, eq(contentItems.channelId, channels.id))
    .where(eq(queueItems.status, status))
    .orderBy(desc(queueItems.priority), asc(queueItems.createdAt));

  return rows.map(mapJoinedRow);
}

/** Get all queue items ordered by priority DESC then createdAt ASC. */
export async function getAllQueueItems(
  db: Db
): Promise<QueueItem[]> {
  const rows = await db
    .select({
      id: queueItems.id,
      contentItemId: queueItems.contentItemId,
      status: queueItems.status,
      priority: queueItems.priority,
      attempts: queueItems.attempts,
      maxAttempts: queueItems.maxAttempts,
      error: queueItems.error,
      startedAt: queueItems.startedAt,
      completedAt: queueItems.completedAt,
      createdAt: queueItems.createdAt,
      updatedAt: queueItems.updatedAt,
      contentTitle: contentItems.title,
      channelName: channels.name,
    })
    .from(queueItems)
    .leftJoin(contentItems, eq(queueItems.contentItemId, contentItems.id))
    .leftJoin(channels, eq(contentItems.channelId, channels.id))
    .orderBy(desc(queueItems.priority), asc(queueItems.createdAt));

  return rows.map(mapJoinedRow);
}

/**
 * Get pending queue items ordered by priority DESC then createdAt ASC.
 * Optional limit to constrain the result set (for concurrency control).
 */
export async function getPendingQueueItems(
  db: Db,
  limit?: number
): Promise<QueueItem[]> {
  let query = db
    .select()
    .from(queueItems)
    .where(eq(queueItems.status, 'pending'))
    .orderBy(desc(queueItems.priority), asc(queueItems.createdAt));

  if (limit !== undefined) {
    query = query.limit(limit) as typeof query;
  }

  const rows = await query;
  return rows.map(mapRow);
}

/**
 * Update a queue item's status and optional fields. Sets updatedAt to now.
 * Returns updated item or null if not found.
 */
export async function updateQueueItemStatus(
  db: Db,
  id: number,
  status: QueueStatus,
  updates?: UpdateQueueItemFields
): Promise<QueueItem | null> {
  const setData: Record<string, unknown> = {
    status,
    updatedAt: sql`(datetime('now'))`,
  };

  if (updates?.error !== undefined) setData.error = updates.error;
  if (updates?.startedAt !== undefined) setData.startedAt = updates.startedAt;
  if (updates?.completedAt !== undefined) setData.completedAt = updates.completedAt;
  if (updates?.attempts !== undefined) setData.attempts = updates.attempts;

  const result = await db
    .update(queueItems)
    .set(setData)
    .where(eq(queueItems.id, id))
    .returning();

  return result.length > 0 ? mapRow(result[0]) : null;
}

/**
 * Count queue items grouped by status.
 * Returns a record with counts for each QueueStatus value.
 */
export async function countQueueItemsByStatus(
  db: Db
): Promise<Record<QueueStatus, number>> {
  const rows = await db
    .select({
      status: queueItems.status,
      count: sql<number>`count(*)`,
    })
    .from(queueItems)
    .groupBy(queueItems.status);

  const counts: Record<string, number> = {
    pending: 0,
    downloading: 0,
    completed: 0,
    failed: 0,
    cancelled: 0,
  };

  for (const row of rows) {
    counts[row.status] = Number(row.count);
  }

  return counts as Record<QueueStatus, number>;
}

/** Delete a queue item by ID. Returns true if a row was deleted. */
export async function deleteQueueItem(
  db: Db,
  id: number
): Promise<boolean> {
  const result = await db
    .delete(queueItems)
    .where(eq(queueItems.id, id))
    .returning({ id: queueItems.id });

  return result.length > 0;
}

/**
 * Get a queue item by content item ID (for dedup checking before enqueue).
 * Returns the queue item or null if no entry exists for this content item.
 */
export async function getQueueItemByContentItemId(
  db: Db,
  contentItemId: number
): Promise<QueueItem | null> {
  const rows = await db
    .select()
    .from(queueItems)
    .where(eq(queueItems.contentItemId, contentItemId))
    .limit(1);

  return rows.length > 0 ? mapRow(rows[0]) : null;
}

// ── Row Mapping ──

/** Map a plain queue_items row (no JOINs). Used by CRUD operations that don't need display names. */
function mapRow(row: typeof queueItems.$inferSelect): QueueItem {
  return {
    id: row.id,
    contentItemId: row.contentItemId,
    status: row.status as QueueStatus,
    priority: row.priority,
    attempts: row.attempts,
    maxAttempts: row.maxAttempts,
    error: row.error,
    startedAt: row.startedAt,
    completedAt: row.completedAt,
    createdAt: row.createdAt,
    updatedAt: row.updatedAt,
  };
}

/** Joined row shape from explicit `.select({...})` with LEFT JOIN content_items and channels. */
interface JoinedQueueRow {
  id: number;
  contentItemId: number;
  status: string;
  priority: number;
  attempts: number;
  maxAttempts: number;
  error: string | null;
  startedAt: string | null;
  completedAt: string | null;
  createdAt: string;
  updatedAt: string;
  contentTitle: string | null;
  channelName: string | null;
}

/** Map a joined queue row (with content title and channel name from LEFT JOINs). */
function mapJoinedRow(row: JoinedQueueRow): QueueItem {
  return {
    id: row.id,
    contentItemId: row.contentItemId,
    status: row.status as QueueStatus,
    priority: row.priority,
    attempts: row.attempts,
    maxAttempts: row.maxAttempts,
    error: row.error,
    startedAt: row.startedAt,
    completedAt: row.completedAt,
    createdAt: row.createdAt,
    updatedAt: row.updatedAt,
    contentTitle: row.contentTitle ?? null,
    channelName: row.channelName ?? null,
  };
}