import { createHash } from "node:crypto";
import type { JsonValue } from "../jsonValue.js";

/** How a recorded clock value is spelled: ISO-8601 with its separator, fraction digits and zone, or an epoch number. */
export type ClockFormat =
  | {
      readonly kind: "iso";
      readonly separator: "T" | " ";
      readonly fraction: number;
      readonly zone: string;
    }
  | { readonly kind: "epoch"; readonly unit: "s" | "ms" };

interface ClockReading {
  readonly ms: number;
  /** Nanoseconds after the floored millisecond, so distinct recorded instants stay distinct. */
  readonly subMillisecond: number;
  readonly format: ClockFormat;
}

/** Compare recorded instants without rounding away their submillisecond digits. */
export const compareClockInstants = (
  left: Pick<ClockReading, "ms" | "subMillisecond">,
  right: Pick<ClockReading, "ms" | "subMillisecond">,
): number => left.ms - right.ms || left.subMillisecond - right.subMillisecond;

const ISO_INSTANT =
  /^(\d{4})-(\d{2})-(\d{2})([T ])(\d{2}):(\d{2}):(\d{2})(?:\.(\d{1,9}))?(Z|[+-]\d{2}:?\d{2})?$/u;
const MINUTE_MS = 60_000;

/** Minutes east of UTC that a zone suffix names; none and `Z` are UTC. */
const zoneMinutes = (zone: string): number | undefined => {
  if (zone === "" || zone === "Z") return 0;
  if (!/^[+-]\d{2}:?\d{2}$/u.test(zone)) return undefined;
  const digits = zone.slice(1).replace(":", "");
  const hours = Number(digits.slice(0, 2));
  const remainder = Number(digits.slice(2, 4));
  if (hours > 23 || remainder > 59) return undefined;
  const minutes = hours * 60 + remainder;
  return zone.startsWith("-") ? -minutes : minutes;
};

/** Whether a stored ISO clock format has a supported RFC 3339 offset suffix. */
export const isClockZone = (zone: string): boolean =>
  zoneMinutes(zone) !== undefined;

const zoneMinutesForFormat = (zone: string): number => {
  const minutes = zoneMinutes(zone);
  if (minutes === undefined)
    throw new TypeError(`Invalid clock zone in a derived format: ${zone}`);
  return minutes;
};

/** The instant of an ISO-8601 date-time and how it is spelled, or undefined when it is not one. */
const readIsoClock = (value: string): ClockReading | undefined => {
  const match = ISO_INSTANT.exec(value);
  if (match === null) return undefined;
  const [year, month, day, separator, hour, minute, second] = match
    .slice(1, 8)
    .map((part) => (part === "T" || part === " " ? part : Number(part)));
  const fraction = match[8] ?? "";
  const zone = match[9] ?? "";
  const offsetMinutes = zoneMinutes(zone);
  if (offsetMinutes === undefined) return undefined;
  // setUTCFullYear avoids Date.UTC's special 1900 adjustment for years 0–99.
  const rolled = new Date(0);
  rolled.setUTCFullYear(year as number, (month as number) - 1, day as number);
  rolled.setUTCHours(
    hour as number,
    minute as number,
    second as number,
    Number(`${fraction}000`.slice(0, 3)),
  );
  const local = rolled.getTime();
  // Date setters roll invalid fields over; the round trip refuses them.
  if (
    rolled.getUTCFullYear() !== year ||
    rolled.getUTCMonth() !== (month as number) - 1 ||
    rolled.getUTCDate() !== day ||
    rolled.getUTCHours() !== hour ||
    rolled.getUTCMinutes() !== minute ||
    rolled.getUTCSeconds() !== second
  )
    return undefined;
  return {
    ms: local - offsetMinutes * MINUTE_MS,
    subMillisecond: Number(fraction.padEnd(9, "0").slice(3)),
    format: {
      kind: "iso",
      separator: separator as "T" | " ",
      fraction: fraction.length,
      zone,
    },
  };
};

/** The instant a clock value names and its format: an ISO-8601 date-time, or epoch seconds or milliseconds. */
export const readClock = (
  value: JsonValue | undefined,
): ClockReading | undefined => {
  if (typeof value === "string") return readIsoClock(value);
  if (typeof value !== "number" || !Number.isSafeInteger(value))
    return undefined;
  if (value >= 1e9 && value < 1e10)
    return {
      ms: value * 1000,
      subMillisecond: 0,
      format: { kind: "epoch", unit: "s" },
    };
  if (value >= 1e12 && value < 1e13)
    return {
      ms: value,
      subMillisecond: 0,
      format: { kind: "epoch", unit: "ms" },
    };
  return undefined;
};

const pad = (value: number, width: number): string =>
  String(value).padStart(width, "0");

/** An ISO-8601 date-time from the UTC fields of `at`, with fraction digits and a zone suffix. */
const isoText = (
  at: Date,
  separator: string,
  digits: string,
  zone: string,
): string =>
  `${pad(at.getUTCFullYear(), 4)}-${pad(at.getUTCMonth() + 1, 2)}-${pad(at.getUTCDate(), 2)}${separator}${pad(at.getUTCHours(), 2)}:${pad(at.getUTCMinutes(), 2)}:${pad(at.getUTCSeconds(), 2)}${digits === "" ? "" : `.${digits}`}${zone}`;

/** An instant spelled in a recorded clock format; fraction digits past milliseconds are zeros. */
export const formatClock = (ms: number, format: ClockFormat): JsonValue => {
  if (format.kind === "epoch")
    return format.unit === "s" ? Math.floor(ms / 1000) : ms;
  const at = new Date(ms + zoneMinutesForFormat(format.zone) * MINUTE_MS);
  const digits = `${pad(at.getUTCMilliseconds(), 3)}${"0".repeat(9)}`.slice(
    0,
    format.fraction,
  );
  return isoText(at, format.separator, digits, format.zone);
};

/**
 * A clock value spelled in another ISO format: its wall clock in the format's zone, under the format's separator, with
 * the value's own fraction digits padded to the format's width, so no digit is lost; an epoch format is computed from
 * the instant.
 */
export const respellClock = (
  value: JsonValue,
  format: ClockFormat,
): JsonValue => {
  const clock = readClock(value);
  if (clock === undefined) return value;
  if (format.kind === "epoch") return formatClock(clock.ms, format);
  const millis = ((clock.ms % 1000) + 1000) % 1000;
  // An epoch value's fraction is its milliseconds, without trailing zeros.
  const digits =
    clock.format.kind === "epoch"
      ? pad(millis, 3).replace(/0+$/u, "")
      : `${pad(millis, 3)}${pad(clock.subMillisecond, 6)}`.slice(
          0,
          clock.format.fraction,
        );
  const at = new Date(
    clock.ms - millis + zoneMinutesForFormat(format.zone) * MINUTE_MS,
  );
  return isoText(
    at,
    format.separator,
    digits.padEnd(format.fraction, "0"),
    format.zone,
  );
};

const UUID = /^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/iu;

export const isUuid = (value: JsonValue | undefined): value is string =>
  typeof value === "string" && UUID.test(value);

/** An integer value as a number, from a JSON number or a string of digits. */
export const integerOf = (value: JsonValue | undefined): number | undefined =>
  typeof value === "number" && Number.isSafeInteger(value)
    ? value
    : typeof value === "string" && /^\d{1,15}$/u.test(value)
      ? Number(value)
      : undefined;

/**
 * The next value of a sequence. With nothing taken yet, that is the next held integer, or 1 when
 * the scope holds none. Otherwise it is one past the later of that and the last value taken.
 * A missing side leaves a negative value negative.
 */
export const nextSequence = (
  held: number | undefined,
  taken: number | undefined,
): number =>
  taken === undefined ? (held ?? 1) : Math.max(held ?? taken + 1, taken + 1);

/** An integer spelled as the recorded value spells integers: a number, or a string of digits. */
export const spelledLike = (exemplar: JsonValue, value: number): JsonValue =>
  maskedCount(exemplar) !== undefined
    ? fillMask(exemplar as string, value)
    : typeof exemplar === "string"
      ? String(value)
      : value;

const MASKED_DIGITS = /^\d{2,}(?:-\d{2,})+$/u;

/** The count `-`-separated digit groups of one width spell, such as an asset number `000-005`; dates, versions and addresses are not counts. */
const maskedCount = (value: JsonValue | undefined): number | undefined => {
  if (typeof value !== "string" || !MASKED_DIGITS.test(value)) return undefined;
  const groups = value.split("-");
  if (groups.some((group) => group.length !== groups[0]!.length))
    return undefined;
  const digits = groups.join("");
  return digits.length <= 15 ? Number(digits) : undefined;
};

/** A count that outgrew the exemplar's mask, read only when it is spelled as serving spells it, so dates never match. */
const outgrownMask = (
  value: JsonValue | undefined,
  exemplar: JsonValue | undefined,
): number | undefined => {
  if (typeof value !== "string" || maskedCount(exemplar) === undefined)
    return undefined;
  const digits = value.replaceAll("-", "");
  if (!/^\d{1,15}$/u.test(digits)) return undefined;
  const count = Number(digits);
  return fillMask(exemplar as string, count) === value ? count : undefined;
};

/** A sequence's number: an integer, digit groups that count, or with the sequence's exemplar a count that outgrew its mask. */
export const sequenceNumber = (
  value: JsonValue | undefined,
  exemplar?: JsonValue,
): number | undefined =>
  integerOf(value) ?? maskedCount(value) ?? outgrownMask(value, exemplar);

/** A number written into a mask's digit positions, zero-padded; digits that outgrow the mask lead it. */
const fillMask = (mask: string, value: number): string => {
  const padded = String(value).padStart(mask.replace(/\D/gu, "").length, "0");
  let next = padded.length - 1;
  let out = "";
  for (let at = mask.length - 1; at >= 0; at -= 1) {
    const character = mask[at]!;
    if (/\d/u.test(character)) {
      out = padded[next]! + out;
      next -= 1;
    } else out = character + out;
  }
  return padded.slice(0, next + 1) + out;
};

/** Lower case, with every run of other characters joined by one `-` and none at either end. */
export const slugOf = (text: string): string =>
  text
    .normalize("NFKD")
    .replace(/[̀-ͯ]/gu, "")
    .toLowerCase()
    .replace(/[^a-z0-9]+/gu, "-")
    .replace(/^-+|-+$/gu, "");

const isAlphanumeric = (character: string | undefined): boolean =>
  character !== undefined && /[\p{L}\p{N}]/u.test(character);

/** Source offsets stay UTF-16, while delimiter classification reads complete code points. */
const previousCharacter = (text: string, at: number): string | undefined => {
  if (at === 0) return undefined;
  const last = text.charCodeAt(at - 1);
  return last >= 0xdc00 && last <= 0xdfff && at > 1
    ? text.slice(at - 2, at)
    : text[at - 1];
};

const nextCharacter = (text: string, at: number): string | undefined => {
  const point = text.codePointAt(at);
  return point === undefined ? undefined : String.fromCodePoint(point);
};

/** Start offsets of `token` in `text` where neither neighbour is a letter or digit. */
export const delimitedOffsets = (text: string, token: string): number[] => {
  const offsets: number[] = [];
  if (token.length === 0) return offsets;
  let at = text.indexOf(token);
  while (at >= 0) {
    const delimited =
      !isAlphanumeric(previousCharacter(text, at)) &&
      !isAlphanumeric(nextCharacter(text, at + token.length));
    if (delimited) offsets.push(at);
    // A rejected match may overlap a delimited one, so the search moves on by one character.
    at = text.indexOf(token, at + (delimited ? token.length : 1));
  }
  return offsets;
};

/** `text` with every delimited occurrence of `token` replaced. */
export const replaceDelimited = (
  text: string,
  token: string,
  replacement: string,
): string => {
  let result = "";
  let from = 0;
  for (const at of delimitedOffsets(text, token)) {
    result += text.slice(from, at) + replacement;
    from = at + token.length;
  }
  return result + text.slice(from);
};

/** Whether any string inside a value holds `token` delimited. */
export const containsDelimited = (value: JsonValue, token: string): boolean => {
  const pending: JsonValue[] = [value];
  for (let next = pending.pop(); next !== undefined; next = pending.pop()) {
    if (typeof next === "string") {
      if (delimitedOffsets(next, token).length > 0) return true;
    } else if (typeof next === "object" && next !== null)
      // One at a time: spreading a wide array into push overflows the call stack.
      for (const child of Array.isArray(next) ? next : Object.values(next))
        pending.push(child);
  }
  return false;
};

/** SHA-256 bytes of a seed, extended by counter blocks to the requested length. */
const seededBytes = (seed: string, length: number): Uint8Array => {
  const bytes = new Uint8Array(length);
  for (let block = 0; block * 32 < length; block += 1) {
    const digest = createHash("sha256")
      .update(`${seed}#${String(block)}`)
      .digest();
    bytes.set(
      digest.subarray(0, Math.min(32, length - block * 32)),
      block * 32,
    );
  }
  return bytes;
};

/** A version 4 UUID derived from a seed, in the recorded value's letter case. */
export const seededUuid = (seed: string, exemplar: string): string => {
  const bytes = seededBytes(seed, 16);
  bytes[6] = (bytes[6]! & 0x0f) | 0x40;
  bytes[8] = (bytes[8]! & 0x3f) | 0x80;
  const hex = Buffer.from(bytes).toString("hex");
  const uuid = `${hex.slice(0, 8)}-${hex.slice(8, 12)}-${hex.slice(12, 16)}-${hex.slice(16, 20)}-${hex.slice(20)}`;
  return exemplar === exemplar.toUpperCase() && /[A-F]/u.test(exemplar)
    ? uuid.toUpperCase()
    : uuid;
};

const DIGITS = "0123456789";
const LOWER = "abcdefghijklmnopqrstuvwxyz";
const UPPER = LOWER.toUpperCase();

/** The characters a token of this spelling draws from: hexadecimal, or the digit and letter cases it uses. */
const tokenAlphabet = (exemplar: string): string => {
  if (/^[0-9a-f]+$/u.test(exemplar) && /[0-9]/u.test(exemplar))
    return `${DIGITS}abcdef`;
  if (/^[0-9A-F]+$/u.test(exemplar) && /[0-9]/u.test(exemplar))
    return `${DIGITS}ABCDEF`;
  const alphabet =
    (/[0-9]/u.test(exemplar) ? DIGITS : "") +
    (/[a-z]/u.test(exemplar) ? LOWER : "") +
    (/[A-Z]/u.test(exemplar) ? UPPER : "");
  return alphabet === "" ? LOWER : alphabet;
};

/** A token as long as the recorded one, from its alphabet, keeping its other characters in place. */
export const seededToken = (seed: string, exemplar: string): string => {
  const alphabet = tokenAlphabet(exemplar);
  const bytes = seededBytes(seed, exemplar.length);
  return [...exemplar]
    .map((character, index) =>
      /[0-9A-Za-z]/u.test(character)
        ? alphabet[bytes[index]! % alphabet.length]!
        : character,
    )
    .join("");
};