import { closeSync, constants, fstatSync, openSync, readFileSync } from "node:fs";
import { createHash } from "node:crypto";
import { refuse } from "./errors.mjs";
import { ID_PATTERN } from "./vocabulary.mjs";

export function isPlainObject(value) {
  return typeof value === "object" && value !== null && !Array.isArray(value);
}

export function requireObject(value, where) {
  if (!isPlainObject(value)) refuse(`${where} must be a JSON object`);
  return value;
}

export function rejectUnknownKeys(object, allowed, where) {
  for (const key of Object.keys(object)) {
    if (!allowed.includes(key)) refuse(`unsupported ${where} key: ${JSON.stringify(key)}`);
  }
}

export function requireId(value, where) {
  if (typeof value !== "string" || !ID_PATTERN.test(value)) {
    refuse(`${where} must match ${ID_PATTERN} (got ${JSON.stringify(value)})`);
  }
  return value;
}

export function requireString(value, where, { max = 200 } = {}) {
  if (typeof value !== "string" || value.trim().length === 0 || value.length > max || value.includes("\0")) {
    refuse(`${where} must be a non-empty string of at most ${max} characters`);
  }
  return value;
}

export function requirePositiveInt(value, where) {
  if (!Number.isSafeInteger(value) || value < 1) refuse(`${where} must be a positive integer (got ${JSON.stringify(value)})`);
  return value;
}

// A list of distinct strings, each checked by `check`.
export function requireDistinctList(value, where, check, { nonEmpty = false } = {}) {
  if (!Array.isArray(value)) refuse(`${where} must be an array`);
  if (nonEmpty && value.length === 0) refuse(`${where} must not be empty`);
  const seen = new Set();
  for (const item of value) {
    check(item);
    if (seen.has(item)) refuse(`duplicate entry in ${where}: ${JSON.stringify(item)}`);
    seen.add(item);
  }
  return [...seen];
}

// Calendar date YYYY-MM-DD that exists (2026-02-30 refuses).
export function requireDate(value, where) {
  if (typeof value !== "string" || !/^\d{4}-\d{2}-\d{2}$/.test(value)) refuse(`${where} must be a date YYYY-MM-DD (got ${JSON.stringify(value)})`);
  const d = new Date(`${value}T00:00:00Z`);
  if (Number.isNaN(d.getTime()) || d.toISOString().slice(0, 10) !== value) refuse(`${where} is not a real date: ${value}`);
  return value;
}

// Read a JSON file that must be a regular file, not a symbolic link.
// Missing or not a regular file is 4; unparseable is 2. One descriptor,
// opened without following a link, serves every check and the read.
// `checkStat` sees that descriptor's stat before the read, so the file
// can't be swapped between the check and the read.
export function readJsonFile(file, what, checkStat) {
  let fd;
  try {
    fd = openSync(file, constants.O_RDONLY | constants.O_NOFOLLOW | constants.O_NONBLOCK);
  } catch (error) {
    if (error.code === "ENOENT") refuse(`${what} not found: ${file}`, 4);
    refuse(`${what} must be a regular, non-symbolic-link file: ${file}`, 4);
  }
  let text;
  try {
    const stat = fstatSync(fd);
    if (!stat.isFile()) refuse(`${what} must be a regular, non-symbolic-link file: ${file}`, 4);
    checkStat?.(stat);
    text = readFileSync(fd, "utf8");
  } finally {
    closeSync(fd);
  }
  try {
    return JSON.parse(text);
  } catch (error) {
    refuse(`${what} is not valid JSON (${file}): ${error.message}`);
  }
}

// JSON with object keys sorted at every level, for digests.
export function canonicalJson(value) {
  if (Array.isArray(value)) return `[${value.map(canonicalJson).join(",")}]`;
  if (isPlainObject(value)) {
    return `{${Object.keys(value).sort().map((k) => `${JSON.stringify(k)}:${canonicalJson(value[k])}`).join(",")}}`;
  }
  return JSON.stringify(value);
}

export function sha256(text) {
  return createHash("sha256").update(text).digest("hex");
}

export function deepFreeze(value) {
  if (typeof value === "object" && value !== null && !Object.isFrozen(value)) {
    Object.freeze(value);
    for (const v of Object.values(value)) deepFreeze(v);
  }
  return value;
}