/**
 * Reads and writes the `users` table. Its `User`s carry the password hash and
 * email, so a route strips them with `toPublicUser` or `toSelfUser` before
 * answering. `routes/users.ts` is its main caller; `lib/auth.ts` checks every
 * token against {@link getSessionState}.
 *
 * @module
 */

import { APIErrorCode } from "../../shared/api.ts";
import { APIException } from "../lib/api-exception.ts";
import type {
  Invitee,
  PublicUser,
  RegisterUserRequest,
  Role,
  UpdateUserRequest,
  UserSuggestion,
} from "../../shared/user.ts";
import {
  isUserRow,
  toPublicUser,
  type User,
  userApiToRow,
  userRowToApi,
} from "../model/user.ts";
import { db } from "../db/connection.ts";
import { closeUserSockets, disconnectUser } from "./ws-service.ts";

import { hashPassword } from "../lib/jwt.ts";
import { linkAttachments } from "./attachment-service.ts";

/** Selects full `UserRow`s from `users u`, with the inviter's name joined. */
const USER_SELECT =
  `SELECT u.id, u.username, u.password_hash, u.role, u.created_at, u.updated_at, u.avatar_mime, u.description, u.invited_by, u.email,
          i.username as invited_by_username
   FROM users u
   LEFT JOIN users i ON i.id = u.invited_by`;

/**
 * Creates a user with the `user` role, invited by `inviterId`, for
 * `POST /api/users/register`. The caller has validated `request` and claimed
 * the invite.
 *
 * @throws {APIException} 400 when the username is taken, 409 when the email
 * is.
 */
export async function createUser(
  request: RegisterUserRequest,
  inviterId: string | null,
): Promise<User> {
  const userId = crypto.randomUUID();
  const createdAt = new Date();

  const existingUser = db.prepare(
    "SELECT id FROM users WHERE username = ?;",
  ).get(request.username);

  if (existingUser) {
    throw new APIException(
      APIErrorCode.VALIDATION_ERROR,
      400,
      "Username already exists",
    );
  }

  assertEmailAvailable(request.email);

  const passwordHash = await hashPassword(request.password);

  try {
    db.prepare(
      `INSERT INTO users (id, username, password_hash, role, created_at, invited_by, email)
        VALUES (?, ?, ?, ?, ?, ?, ?);`,
    ).run(
      userId,
      request.username,
      passwordHash,
      "user",
      createdAt.toISOString(),
      inviterId,
      request.email,
    );
  } catch (err) {
    // A parallel sign-up can take the name while the hash is computed; the
    // UNIQUE constraint is the real guard. Emails have no such constraint.
    if (err instanceof Error && err.message.includes("UNIQUE")) {
      throw new APIException(
        APIErrorCode.VALIDATION_ERROR,
        400,
        "Username already exists",
      );
    }
    throw err;
  }

  return {
    id: userId,
    username: request.username,
    passwordHash,
    role: "user",
    createdAt,
    email: request.email,
  };
}

/**
 * Returns user `userId`, with their hash and email.
 *
 * @throws {APIException} 404 when there is no such user.
 */
export function getUserById(userId: string): User {
  const userRow = db.prepare(
    `${USER_SELECT} WHERE u.id = ?`,
  ).get(userId);

  if (!userRow || !isUserRow(userRow)) {
    throw new APIException(APIErrorCode.NOT_FOUND, 404, "User not found");
  }

  return userRowToApi(userRow);
}

/**
 * Returns the user's live role and their last password change, before which
 * their tokens don't count, or undefined when the user is gone. `lib/auth.ts`
 * checks every session and media token against it.
 */
export function getSessionState(
  userId: string,
): { role: Role; tokensValidAfter: string | null } | undefined {
  const row = db.prepare(
    `SELECT role, tokens_valid_after FROM users WHERE id = ?;`,
  ).get(userId) as
    | { role: Role; tokens_valid_after: string | null }
    | undefined;
  return row && {
    role: row.role,
    tokensValidAfter: row.tokens_valid_after,
  };
}

/**
 * Returns the user named `username`, with their hash and email. The name
 * matches case-sensitively.
 *
 * @throws {APIException} 404 when there is no such user.
 */
export function getUserByUsername(username: string): User {
  const userRow = db.prepare(
    `${USER_SELECT} WHERE u.username = ?`,
  ).get(username);

  if (!userRow || !isUserRow(userRow)) {
    throw new APIException(APIErrorCode.NOT_FOUND, 404, "User not found");
  }

  return userRowToApi(userRow);
}

/**
 * Throws a 409 when an account other than `exceptUserId` has `email`, in any
 * case. Password resets are looked up by email, so an address must belong to
 * one account only.
 */
function assertEmailAvailable(email: string, exceptUserId?: string): void {
  const row = db.prepare(
    `SELECT id FROM users WHERE lower(email) = lower(?) AND id != ?;`,
  ).get(email, exceptUserId ?? "");
  if (row) {
    throw new APIException(
      APIErrorCode.VALIDATION_ERROR,
      409,
      "Email already in use",
    );
  }
}

/**
 * Returns the user whose email is exactly `email`, or null, for
 * `requestPasswordReset`. Unlike the uniqueness check, it is case-sensitive.
 */
export function getUserByEmail(email: string): User | null {
  const userRow = db.prepare(
    `${USER_SELECT} WHERE u.email = ?`,
  ).get(email);

  if (!userRow || !isUserRow(userRow)) return null;
  return userRowToApi(userRow);
}

/**
 * Returns up to `limit` users whose name starts with `query`, for the editor's
 * @mention suggestions (`GET /api/users/search`). An empty query returns none.
 */
export function searchUsers(
  query: string,
  limit: number,
): UserSuggestion[] {
  if (!query) return [];
  const rows = db.prepare(
    `SELECT id, username, avatar_mime FROM users WHERE username LIKE ? ORDER BY username LIMIT ?;`,
  ).all(`${query}%`, limit) as {
    id: string;
    username: string;
    avatar_mime: string | null;
  }[];
  return rows.map((r) => ({
    id: r.id,
    username: r.username,
    avatarMime: r.avatar_mime,
  }));
}

/**
 * Returns up to `limit` users whose name or description contains `query`, for
 * the `/search` page (`GET /api/search`). They are already public profiles.
 */
export function searchUsersGlobal(query: string, limit: number): PublicUser[] {
  if (!query.trim()) return [];
  const pattern = `%${query}%`;
  const rows = db.prepare(
    `${USER_SELECT} WHERE (u.username LIKE ? OR u.description LIKE ?) ORDER BY u.username LIMIT ?;`,
  ).all(pattern, pattern, limit);
  return rows.filter(isUserRow).map(userRowToApi).map(toPublicUser);
}

/**
 * Returns every user. Nothing calls it.
 *
 * @throws {APIException} 404 when a row doesn't parse as a user.
 */
export function listUsers(): User[] {
  const userRows = db.prepare(
    `${USER_SELECT}`,
  ).all();

  if (!userRows || !userRows.every(isUserRow)) {
    throw new APIException(APIErrorCode.NOT_FOUND, 404, "No user found");
  }

  return userRows.map(userRowToApi);
}

/**
 * Applies `request` to user `userId` and returns the updated user. It trusts
 * `request`: the routes pick the fields a caller may change. A new password
 * also ends every session opened before it and closes the user's sockets, so
 * the caller must issue fresh tokens if the user is to stay signed in. A
 * `description` of null keeps the current one.
 *
 * @throws {APIException} 404 when there is no such user, 409 when the new
 * email belongs to another account.
 */
export async function updateUser(
  userId: string,
  request: UpdateUserRequest,
): Promise<User> {
  const user = getUserById(userId);

  const { password, description, email, ...requestFields } = request;
  if (email !== undefined && email !== user.email) {
    assertEmailAvailable(email, userId);
  }

  const now = new Date();
  const updatedUser: User = {
    ...user,
    passwordHash: password ? await hashPassword(password) : user.passwordHash,
    ...requestFields,
    description: description ?? user.description,
    email: email ?? user.email,
    updatedAt: now,
  };

  const updatedUserRow = userApiToRow(updatedUser);

  const userResult = db.prepare(
    `UPDATE users SET username = ?, password_hash = ?, role = ?, description = ?, email = ?, updated_at = ? WHERE id = ?`,
  ).run(
    updatedUserRow.username,
    updatedUserRow.password_hash,
    updatedUserRow.role,
    updatedUserRow.description,
    updatedUserRow.email,
    now.toISOString(),
    updatedUserRow.id,
  );

  if (userResult.changes === 0) {
    throw new APIException(APIErrorCode.NOT_FOUND, 404, "User not found");
  }

  if (password) {
    db.prepare(`UPDATE users SET tokens_valid_after = ? WHERE id = ?;`).run(
      now.toISOString(),
      userId,
    );
    closeUserSockets(userId, "Password changed");
  }

  if (updatedUser.description) {
    linkAttachments(updatedUser.description, userId);
  }

  return updatedUser;
}

/**
 * Records that user `userId` now has an avatar of type `mime`, once
 * `POST /api/avatars/me` has written the file. It bumps `updated_at`, which
 * the client uses to reload the image.
 *
 * @throws {APIException} 404 when there is no such user.
 */
export function updateUserAvatar(userId: string, mime: string): void {
  const result = db.prepare(
    `UPDATE users SET avatar_mime = ?, updated_at = ? WHERE id = ?`,
  ).run(mime, new Date().toISOString(), userId);

  if (result.changes === 0) {
    throw new APIException(APIErrorCode.NOT_FOUND, 404, "User not found");
  }
}

/**
 * Returns everyone `userId` invited, and everyone they invited in turn, eleven
 * levels deep at most, in sign-up order, for the profile page's invite tree
 * (`GET /api/users/:username/invitees`).
 */
export function getInviteTree(userId: string): Invitee[] {
  const rows = db.prepare(`
    WITH RECURSIVE tree AS (
      SELECT id, username, avatar_mime, invited_by, created_at, 0 AS depth
      FROM users
      WHERE invited_by = ?
      UNION ALL
      SELECT u.id, u.username, u.avatar_mime, u.invited_by, u.created_at, t.depth + 1
      FROM users u
      INNER JOIN tree t ON u.invited_by = t.id
      WHERE t.depth < 10
    )
    SELECT * FROM tree ORDER BY created_at;
  `).all(userId) as {
    id: string;
    username: string;
    avatar_mime: string | null;
    invited_by: string;
    created_at: string;
  }[];

  return rows.map((r) => ({
    id: r.id,
    username: r.username,
    avatarMime: r.avatar_mime ?? undefined,
    invitedById: r.invited_by,
    createdAt: new Date(r.created_at),
  }));
}

/**
 * Deletes user `userId` and disconnects their sockets. Nothing calls it.
 *
 * @throws {APIException} 404 when there is no such user.
 */
export function deleteUser(userId: string): void {
  disconnectUser(userId);

  const result = db.prepare(
    `DELETE FROM users WHERE id = ?;`,
  ).run(userId);

  if (result.changes === 0) {
    throw new APIException(APIErrorCode.NOT_FOUND, 404, "User not found");
  }
}