import type { Handler } from 'hono';
import { getUserById, updateUser, OWNER_USER_ID } from 'officerdb';
import argon2 from 'argon2';
import * as errors from '@@/custom-errors';
import { validatePassword } from '../auth/validate-password';

// The owner resetting somebody else's platform password.
//
// Named for what it is, and NOT to be confused with `api/auth/reset-password.ts`, which is the
// token-from-an-email flow the person runs themselves. This one is the owner acting on another account,
// and the only thing the two share is the column they write.
//
// ── Why the platform generates it rather than the owner typing one ──
//
// Because the failure this exists to fix is "I created the account and forgot to copy the password down".
// An owner-typed reset can lose it exactly the same way on the second attempt. A generated one is shown
// once, in a dialog built to be copied, and is never recoverable afterwards — which is the honest state,
// since only the argon2 hash is stored.
//
// ── The Linux account is deliberately untouched ──
//
// A member's Linux account has no password and never had one: `ensureOsUser` runs `useradd` with no `-p`,
// so it is created password-locked. Nothing needs one — their terminal runs through `setpriv`, which does
// not authenticate; their SSH access is the key the owner pasted; `su - <member>` as root does not ask.
// And machine-setup sets `PasswordAuthentication no`, so a Linux password could not be used to log in even
// if it existed. Setting one here would be creating a new way in, not repairing a lost one.

/**
 * Characters the generated password is built from.
 *
 * Split by class because `validatePassword` requires ALL FOUR — twelve characters, a lowercase, an
 * uppercase, a digit and a special. A uniform draw over the union satisfies that only with high
 * probability, and "the reset button fails once a month" is a worse bug than it looks, because it happens
 * to somebody who is already locked out.
 *
 * The specials are a subset of the class `validatePassword` accepts, chosen to survive being copied,
 * pasted, quoted in a shell and read aloud: no quotes, no backslash, no backtick.
 */
const CLASSES = ['abcdefghijkmnopqrstuvwxyz', 'ABCDEFGHJKLMNPQRSTUVWXYZ', '23456789', '!@#$%^&*()-_=+'] as const;

const PASSWORD_LENGTH = 20;

/** Uniform over `alphabet` by rejection sampling — `% n` on a byte biases the first characters. */
function pick(alphabet: string): string {
  const max = 256 - (256 % alphabet.length);
  const byte = new Uint8Array(1);
  for (;;) {
    crypto.getRandomValues(byte);
    if (byte[0]! < max) return alphabet[byte[0]! % alphabet.length]!;
  }
}

/**
 * A password that satisfies `validatePassword` by construction, not by luck.
 *
 * One character from each class first, the remainder from the union, then shuffled — otherwise the first
 * four positions would always be lower, upper, digit, special, which is a pattern worth not having.
 *
 * Fisher-Yates with the same rejection sampling, for the same reason.
 *
 * `l`, `I`, `1`, `O` and `0` are absent from the alphabets above. This gets read off a screen and typed
 * somewhere else often enough that the ambiguous pairs are worth losing.
 */
export function generatePassword(length = PASSWORD_LENGTH): string {
  const union = CLASSES.join('');
  const chars = CLASSES.map((cls) => pick(cls));
  while (chars.length < length) chars.push(pick(union));

  for (let i = chars.length - 1; i > 0; i--) {
    const bound = i + 1;
    const max = 256 - (256 % bound);
    const byte = new Uint8Array(1);
    let j: number;
    do {
      crypto.getRandomValues(byte);
    } while (byte[0]! >= max);
    j = byte[0]! % bound;
    [chars[i], chars[j]] = [chars[j]!, chars[i]!];
  }

  const password = chars.join('');
  // Generated then CHECKED against the same validator every other path uses. If the rules ever gain a
  // requirement the alphabets above do not cover, this throws here — at the one call site, loudly — rather
  // than minting passwords the login form would go on to reject.
  validatePassword(password);
  return password;
}

export const resetUserPasswordHandler: Handler = async function (ctx) {
  const id = Number(ctx.req.param('id'));
  if (!Number.isInteger(id) || id < 1) throw errors.BAD_REQUEST('Invalid user id');

  // The owner has `PUT /auth/change-password`, which asks for the current one. Resetting themselves from
  // here would sign them out of the session they are doing it from, for no gain.
  if (id === OWNER_USER_ID) {
    throw errors.BAD_REQUEST('Change your own password from Settings, which asks for the current one.');
  }

  const existing = await getUserById(id);
  if (!existing) throw errors.NOT_FOUND('User not found');

  const password = generatePassword();

  // `passwordChangedAt: new Date()` is what signs them out everywhere. `userMiddleware` refuses any token
  // whose `iat` predates it, so every session they have — browser, phone, an agent holding a token —
  // stops at the next request. That is the point: a reset happens because the old password was lost or
  // leaked, and leaving live sessions behind would defeat both reasons.
  //
  // It also overwrites the null that `create-user.ts` leaves to mean "the owner chose this, not them".
  // Nothing reads that; the only consumer of this column is the token check above.
  await updateUser(id, { password: await argon2.hash(password), passwordChangedAt: new Date() });

  // Returned exactly once. Only the hash is stored, so there is no second chance to fetch it and the UI
  // says so — which is the whole reason it is generated rather than typed.
  return ctx.json({ email: existing.email, password });
};
