/**
 * 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 { 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, transaction } from "../db/connection.ts";
import { closeUserSockets } from "./ws-service.ts";

import { hashPassword } from "../lib/password.ts";
import { linkAttachments } from "./attachment-service.ts";
import { LIKE, likePattern } from "../lib/like.ts";
import { parseRows } from "../model/rows.ts";
import { isEmailEnabled, sendEmail } from "./email-service.ts";
import { renderWelcomeEmail } from "../mail/welcome.ts";
import {
  RENAME_LIMITS,
  USERNAME_RE,
  VALIDATION,
} from "../../shared/validation.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`;

/**
 * Throws a 409 when `username` is, in any case, the name or a former name of
 * an account other than `exceptUserId`. A former name stays its user's for
 * good, so that old links and old @mentions can't be taken over.
 */
function assertUsernameAvailable(
  username: string,
  exceptUserId?: string,
): void {
  const row = db.prepare(
    `SELECT id FROM users WHERE lower(username) = lower(?) AND id != ?
     UNION ALL
     SELECT user_id FROM user_aliases
      WHERE lower(username) = lower(?) AND user_id != ?
     LIMIT 1;`,
  ).get(username, exceptUserId ?? "", username, exceptUserId ?? "");
  if (row) {
    throw new APIException(409, "Username already exists");
  }
}

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

  assertUsernameAvailable(request.username);
  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 or the address while the hash is
    // computed; the unique indexes are the real guard.
    throw uniqueViolationToConflict(err);
  }

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

/**
 * Emails `user` the welcome message, if email is configured. The register
 * route calls it once the account exists, and doesn't wait: a slow or failing
 * SMTP server mustn't hold up the sign-up, so a failure is only logged.
 */
export function sendWelcomeEmail(user: User): void {
  if (!isEmailEnabled()) return;
  sendEmail({ to: user.email, ...renderWelcomeEmail(user.username) })
    .catch((err) => console.error("[register] welcome email failed:", err));
}

/**
 * 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(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` now, in any case, with their hash and
 * email. Signing in takes it: a former name doesn't sign in.
 *
 * @throws {APIException} 404 when there is no such user.
 */
export function getUserByUsername(username: string): User {
  const userRow = db.prepare(
    `${USER_SELECT} WHERE lower(u.username) = lower(?)`,
  ).get(username);

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

  return userRowToApi(userRow);
}

/**
 * Returns the user who is or was named `username`, in any case: a page or an
 * API path naming a user by a former name reaches them, and the caller sends
 * the client on to the current one.
 *
 * @throws {APIException} 404 when nobody is or was.
 */
export function resolveUsername(username: string): User {
  const alias = db.prepare(
    `SELECT user_id FROM user_aliases WHERE lower(username) = lower(?);`,
  ).get(username) as { user_id: string } | undefined;
  return alias ? getUserById(alias.user_id) : getUserByUsername(username);
}

/**
 * Returns the user an API path's key names: `@name` by their name, current or
 * former ({@link resolveUsername}), anything else by their id. Every route
 * under `/api/users/:key` resolves its key with it.
 *
 * @throws {APIException} 404 when there is no such user.
 */
export function resolveUserKey(key: string): User {
  return key.startsWith("@") ? resolveUsername(key.slice(1)) : getUserById(key);
}

/**
 * Renames user `userId` to `username`, for `PATCH /api/me` and, by a
 * moderator, `PATCH /api/users/:key/username`, and returns them renamed. The
 * old name becomes an alias of theirs for good, so `/@old/…` still reaches
 * them and nobody else may take it; a change of case alone leaves none, since
 * names are looked up in any case. Taking back a former name of one's own is
 * allowed. Their dumps' and playlists' slugs belong to their id, so their
 * paths follow the new name. Unless `exempt` (a moderator), a user may change
 * names once in `RENAME_LIMITS.USERNAME`'s window.
 *
 * @throws {APIException} 400 when `username` isn't a valid name, 404 when
 * there is no such user, 409 when the name is or was someone else's, 429 when
 * the user changed names too recently.
 */
export function renameUser(
  userId: string,
  username: string,
  exempt: boolean,
): User {
  if (!USERNAME_RE.test(username)) {
    throw new APIException(
      400,
      `Username must be ${VALIDATION.USERNAME_MIN}–${VALIDATION.USERNAME_MAX} characters and contain only letters, numbers, or underscores`,
    );
  }
  const user = getUserById(userId);
  if (username === user.username) return user;

  const now = new Date();
  transaction(() => {
    assertUsernameAvailable(username, userId);
    if (username.toLowerCase() !== user.username.toLowerCase()) {
      const { count, windowMs } = RENAME_LIMITS.USERNAME;
      const recent = (db.prepare(
        `SELECT COUNT(*) AS n FROM user_aliases WHERE user_id = ? AND created_at > ?;`,
      ).get(userId, new Date(now.getTime() - windowMs).toISOString()) as {
        n: number;
      }).n;
      if (!exempt && recent >= count) {
        throw new APIException(
          429,
          `A username can only be changed once every ${
            windowMs / 86_400_000
          } days`,
        );
      }
      db.prepare(
        `DELETE FROM user_aliases WHERE user_id = ? AND lower(username) = lower(?);`,
      ).run(userId, username);
      db.prepare(
        `INSERT INTO user_aliases (username, user_id, created_at) VALUES (?, ?, ?);`,
      ).run(user.username, userId, now.toISOString());
    }
    db.prepare(`UPDATE users SET username = ?, updated_at = ? WHERE id = ?;`)
      .run(username, now.toISOString(), userId);
  });
  return getUserById(userId);
}

/**
 * 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(409, "Email already in use");
  }
}

/**
 * Returns `err` as a 409 when it is SQLite's unique violation on a username or
 * an email, and as it is otherwise.
 */
function uniqueViolationToConflict(err: unknown): unknown {
  if (!(err instanceof Error) || !err.message.includes("UNIQUE")) return err;
  return err.message.includes("email")
    ? new APIException(409, "Email already in use")
    : new APIException(409, "Username already exists");
}

/**
 * Returns the user whose email is `email`, in any case, or null, for
 * `requestPasswordReset`.
 */
export function getUserByEmail(email: string): User | null {
  const userRow = db.prepare(
    `${USER_SELECT} WHERE lower(u.email) = lower(?)`,
  ).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?q=`). 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(likePattern(query, "prefix"), 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 = likePattern(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 parseRows(rows, isUserRow, userRowToApi).map(toPublicUser);
}

/**
 * Applies `request` to user `userId` and returns the updated user. It trusts
 * `request`: the routes pick the fields a caller may change. The username
 * changes through {@link renameUser} alone, which keeps the old one as an
 * alias, so a `username` here is ignored. 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, username: _, ...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);

  let userResult;
  try {
    userResult = db.prepare(
      `UPDATE users SET password_hash = ?, role = ?, description = ?, email = ?, updated_at = ? WHERE id = ?`,
    ).run(
      updatedUserRow.password_hash,
      updatedUserRow.role,
      updatedUserRow.description,
      updatedUserRow.email,
      now.toISOString(),
      updatedUserRow.id,
    );
  } catch (err) {
    throw uniqueViolationToConflict(err);
  }

  if (userResult.changes === 0) {
    throw new APIException(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, "user", userId);
  }

  return updatedUser;
}

/**
 * Records that user `userId` now has an avatar of type `mime`, once
 * `PUT /api/me/avatar` 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(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/:key/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),
  }));
}