import { createHash } from 'node:crypto';
import { deterministicId, type AtmEvent } from '@atm/shared';

const MONTHS: Record<string, number> = {
  Jan: 0, Feb: 1, Mar: 2, Apr: 3, May: 4, Jun: 5, Jul: 6, Aug: 7, Sep: 8, Oct: 9, Nov: 10, Dec: 11,
};

function tzOffsetMs(utcMs: number, timeZone: string): number {
  const parts = new Intl.DateTimeFormat('en-US', {
    timeZone,
    hourCycle: 'h23',
    year: 'numeric',
    month: '2-digit',
    day: '2-digit',
    hour: '2-digit',
    minute: '2-digit',
    second: '2-digit',
  }).formatToParts(new Date(utcMs));
  const get = (t: string) => Number(parts.find((p) => p.type === t)!.value);
  const asUtc = Date.UTC(get('year'), get('month') - 1, get('day'), get('hour'), get('minute'), get('second'));
  return asUtc - Math.floor(utcMs / 1000) * 1000;
}

/** "12Oct2026 09:03:03.006" in the server's local time zone → epoch ms. */
export function parseLogTimestamp(s: string, timeZone: string): number {
  const m = /^(\d{2})([A-Z][a-z]{2})(\d{4}) (\d{2}):(\d{2}):(\d{2})\.(\d{3})$/.exec(s);
  if (!m || MONTHS[m[2]!] === undefined) return Number.NaN;
  const local = Date.UTC(+m[3]!, MONTHS[m[2]!]!, +m[1]!, +m[4]!, +m[5]!, +m[6]!, +m[7]!);
  let utc = local - tzOffsetMs(local, timeZone);
  utc = local - tzOffsetMs(utc, timeZone); // second pass settles DST boundaries
  return utc;
}

const LINE = /^\[([^\]]+)\] \[[^\]]+\] \[([^\]]+)\]: (.*)$/;
const NAME = '([A-Za-z0-9_]{1,16})';
const UUID_OF = new RegExp(`^UUID of player ${NAME} is ([0-9a-f-]{36})$`);
const JOINED = new RegExp(`^${NAME} joined the game$`);
const LEFT = new RegExp(`^${NAME} left the game$`);
const ADVANCEMENT = new RegExp(`^${NAME} has (?:made the advancement|reached the goal|completed the challenge) \\[(.+)\\]$`);
const SYSTEM_LOGGER = 'net.minecraft.server.MinecraftServer/';

/**
 * Parses complete lines of `logs/latest.log`. Only bytes up to the last newline are consumed, so a line that is
 * still being written is read again next time. `names` maps player name → uuid and is updated from
 * "UUID of player" lines; lines for players without known uuid are skipped.
 * Event IDs derive from the absolute byte offset and line content, so re-reading yields the same IDs.
 */
export function parseLogChunk(
  chunk: Buffer,
  baseOffset: number,
  names: Map<string, string>,
  timeZone: string,
): { events: AtmEvent[]; consumed: number } {
  const end = chunk.lastIndexOf(0x0a);
  if (end < 0) return { events: [], consumed: 0 };
  const events: AtmEvent[] = [];
  let offset = 0;
  while (offset <= end) {
    const nl = chunk.indexOf(0x0a, offset);
    const line = chunk.toString('utf8', offset, nl).replace(/\r$/, '');
    const lineOffset = baseOffset + offset;
    offset = nl + 1;

    const m = LINE.exec(line);
    if (!m) continue;
    const [, time, logger, msg] = m as unknown as [string, string, string, string];

    const uuidOf = UUID_OF.exec(msg);
    if (uuidOf) {
      names.set(uuidOf[1]!, uuidOf[2]!);
      continue;
    }
    if (logger !== SYSTEM_LOGGER) continue;

    const id = () => deterministicId(`log:${lineOffset}:${createHash('sha256').update(line).digest('hex')}`);
    const ts = parseLogTimestamp(time, timeZone);
    if (!Number.isFinite(ts)) continue;

    let hit: RegExpExecArray | null;
    if ((hit = JOINED.exec(msg)) || (hit = LEFT.exec(msg))) {
      const name = hit[1]!;
      const uuid = names.get(name);
      if (!uuid) continue;
      events.push({ id: id(), type: JOINED.test(msg) ? 'player_join' : 'player_leave', ts, uuid, name });
    } else if ((hit = ADVANCEMENT.exec(msg))) {
      const name = hit[1]!;
      const uuid = names.get(name);
      if (!uuid) continue;
      events.push({ id: id(), type: 'advancement', ts, uuid, name, advancementId: `log:${hit[2]}`, title: hit[2]! });
    }
  }
  return { events, consumed: end + 1 };
}