import {
  APIErrorCode,
  APIException,
  type ChatMessage,
} from "../model/interfaces.ts";
import { chatMessageRowToApi, db, isChatMessageRow } from "../model/db.ts";

export const MAX_CHAT_LENGTH = 2000;
const DEFAULT_LIMIT = 50;
const MAX_LIMIT = 100;

const SELECT_COLS =
  `m.id, m.user_id, m.body, m.created_at, m.updated_at,
  u.username as author_username, u.avatar_mime as author_avatar_mime`;

function fetchMessage(id: string): ChatMessage {
  const row = db.prepare(
    `SELECT ${SELECT_COLS} FROM chat_messages m JOIN users u ON m.user_id = u.id WHERE m.id = ?;`,
  ).get(id);
  if (!row || !isChatMessageRow(row)) {
    throw new APIException(APIErrorCode.NOT_FOUND, 404, "Message not found");
  }
  return chatMessageRowToApi(row);
}

export function createChatMessage(userId: string, body: string): ChatMessage {
  const trimmed = body.trim();
  if (!trimmed) {
    throw new APIException(
      APIErrorCode.VALIDATION_ERROR,
      400,
      "Message cannot be empty",
    );
  }
  if (trimmed.length > MAX_CHAT_LENGTH) {
    throw new APIException(
      APIErrorCode.VALIDATION_ERROR,
      400,
      `Message exceeds ${MAX_CHAT_LENGTH} characters`,
    );
  }
  const id = crypto.randomUUID();
  const createdAt = new Date().toISOString();
  db.prepare(
    `INSERT INTO chat_messages (id, user_id, body, created_at) VALUES (?, ?, ?, ?);`,
  ).run(id, userId, trimmed, createdAt);
  return fetchMessage(id);
}

function getMessageOwner(id: string): string {
  const row = db.prepare(`SELECT user_id FROM chat_messages WHERE id = ?;`).get(
    id,
  ) as { user_id: string } | undefined;
  if (!row) {
    throw new APIException(APIErrorCode.NOT_FOUND, 404, "Message not found");
  }
  return row.user_id;
}

// Owners may edit their own messages; moderators may edit any.
export function updateChatMessage(
  id: string,
  body: string,
  requestingUserId: string,
  canModerate: boolean,
): ChatMessage {
  const ownerId = getMessageOwner(id);
  if (ownerId !== requestingUserId && !canModerate) {
    throw new APIException(
      APIErrorCode.UNAUTHORIZED,
      401,
      "Not authorized to edit this message",
    );
  }
  const trimmed = body.trim();
  if (!trimmed) {
    throw new APIException(
      APIErrorCode.VALIDATION_ERROR,
      400,
      "Message cannot be empty",
    );
  }
  if (trimmed.length > MAX_CHAT_LENGTH) {
    throw new APIException(
      APIErrorCode.VALIDATION_ERROR,
      400,
      `Message exceeds ${MAX_CHAT_LENGTH} characters`,
    );
  }
  db.prepare(`UPDATE chat_messages SET body = ?, updated_at = ? WHERE id = ?;`)
    .run(trimmed, new Date().toISOString(), id);
  return fetchMessage(id);
}

// Deletion is a moderation action only (owners can edit but not delete).
export function deleteChatMessage(id: string, canModerate: boolean): void {
  if (!canModerate) {
    throw new APIException(
      APIErrorCode.UNAUTHORIZED,
      401,
      "Not authorized to delete this message",
    );
  }
  getMessageOwner(id); // 404s if the message doesn't exist
  db.prepare(`DELETE FROM chat_messages WHERE id = ?;`).run(id);
}

/**
 * Returns up to `limit` most recent messages in ascending (display) order.
 * When `before` (a message created_at ISO string) is given, returns the page
 * of older messages immediately preceding it — used for "load older" history.
 */
export function getRecentChatMessages(
  limit = DEFAULT_LIMIT,
  before?: string,
): ChatMessage[] {
  const capped = Math.min(Math.max(limit, 1), MAX_LIMIT);
  const rows = before
    ? db.prepare(
      `SELECT ${SELECT_COLS} FROM chat_messages m JOIN users u ON m.user_id = u.id
       WHERE m.created_at < ? ORDER BY m.created_at DESC LIMIT ?;`,
    ).all(before, capped)
    : db.prepare(
      `SELECT ${SELECT_COLS} FROM chat_messages m JOIN users u ON m.user_id = u.id
       ORDER BY m.created_at DESC LIMIT ?;`,
    ).all(capped);

  if (!rows.every(isChatMessageRow)) {
    throw new APIException(
      APIErrorCode.SERVER_ERROR,
      500,
      "Malformed chat message data",
    );
  }
  // Newest-first from SQL; reverse to ascending for display.
  return rows.map(chatMessageRowToApi).reverse();
}