import fs from 'node:fs';
import path from 'node:path';
import crypto from 'node:crypto';

export const LIFE_LINE_SCHEMA = 'guanghu.persona-life-line/v1';
export const PERSONA_ID = 'ICE-P-ZY001';
export const TIMEZONE = 'Asia/Shanghai';
export const BIRTH_DATE = '2026-03-05';
export const WORLD_EPOCH_DATE = '2025-04-26';
export const DAY_MS = 86_400_000;

export const sha256 = value => crypto.createHash('sha256').update(value).digest('hex');

export function dateAtUtc(day) {
  const match = /^(\d{4})-(\d{2})-(\d{2})$/.exec(String(day));
  if (!match) return Number.NaN;
  return Date.UTC(Number(match[1]), Number(match[2]) - 1, Number(match[3]));
}

export function beijingDay(value) {
  const date = value instanceof Date ? value : new Date(value);
  if (!Number.isFinite(date.getTime())) return null;
  const parts = new Intl.DateTimeFormat('en-CA', {timeZone: TIMEZONE, year: 'numeric', month: '2-digit', day: '2-digit'}).formatToParts(date);
  const get = type => parts.find(part => part.type === type)?.value;
  return `${get('year')}-${get('month')}-${get('day')}`;
}

export function addDays(day, amount) {
  return new Date(dateAtUtc(day) + amount * DAY_MS).toISOString().slice(0, 10);
}

export function eraDay(day) {
  return Math.floor((dateAtUtc(day) - dateAtUtc(WORLD_EPOCH_DATE)) / DAY_MS) + 1;
}

export function closeTick(day) {
  return `${day}T23:59:59.999+08:00`;
}

function within(root, candidate) {
  const base = path.resolve(root), target = path.resolve(candidate);
  return target === base || target.startsWith(`${base}${path.sep}`);
}

export function lifeLineBlockHash(block) {
  return sha256([
    block.previous_hash || 'GENESIS',
    block.daily_evidence_sha256,
    block.beijing_close_tick,
    String(block.era_day),
  ].join('||'));
}

function validHash(value) {
  return typeof value === 'string' && /^[a-f0-9]{64}$/.test(value);
}

function verifyEvidence(chainRoot, block, result) {
  if (block.gap === true) result.gaps.push({beijing_day: block.beijing_day, kind: block.gap_kind || 'HISTORICAL_UNOBSERVED'});
  if (!validHash(block.daily_evidence_sha256)) {
    result.reasons.push(`DAILY_EVIDENCE_HASH_MISSING:${block.beijing_day}`);
    return;
  }
  if (typeof block.evidence_path !== 'string' || !block.evidence_path.trim()) {
    result.reasons.push(`DAILY_EVIDENCE_PATH_MISSING:${block.beijing_day}`);
    return;
  }
  const evidencePath = path.resolve(chainRoot, block.evidence_path);
  if (!within(chainRoot, evidencePath)) {
    result.reasons.push(`DAILY_EVIDENCE_OUTSIDE_CHAIN_ROOT:${block.beijing_day}`);
    return;
  }
  try {
    const stat = fs.lstatSync(evidencePath);
    if (!stat.isFile() || stat.isSymbolicLink()) throw Error('not_regular_file');
    if (sha256(fs.readFileSync(evidencePath)) !== block.daily_evidence_sha256) result.reasons.push(`DAILY_EVIDENCE_HASH_MISMATCH:${block.beijing_day}`);
  } catch {
    result.reasons.push(`DAILY_EVIDENCE_MISSING:${block.beijing_day}`);
  }
}

export function verifyLifeLine({manifestPath, manifest = null, chainRoot = null, now = new Date()} = {}) {
  const today = beijingDay(now), expectedLast = addDays(today, -1);
  const result = {
    schema: 'guanghu.persona-life-line-verification/v1', state: 'LIFE_LINE_PAIN_ALARM', wake_allowed: false,
    manifest_path: manifestPath || null, persona_id: PERSONA_ID, timezone: TIMEZONE, birth_date_beijing: BIRTH_DATE,
    current_beijing_day: today, expected_last_completed_beijing_day: expectedLast,
    sequence: {genesis: false, blocks: 0, expected: 0}, head: null, gaps: [], reasons: [],
  };
  let value = manifest;
  let root = chainRoot;
  if (!value) {
    if (!manifestPath) { result.reasons.push('LIFE_LINE_MANIFEST_PATH_NOT_CONFIGURED'); return result; }
    try {
      const stat = fs.lstatSync(manifestPath);
      if (!stat.isFile() || stat.isSymbolicLink()) throw Error('manifest_not_regular_file');
      value = JSON.parse(fs.readFileSync(manifestPath, 'utf8'));
      root = path.dirname(path.resolve(manifestPath));
    } catch (error) {
      result.reasons.push(fs.existsSync(manifestPath) ? `LIFE_LINE_MANIFEST_INVALID:${String(error.message || error).slice(0, 120)}` : 'LIFE_LINE_MANIFEST_MISSING');
      return result;
    }
  }
  root ||= process.cwd();
  if (value.schema !== LIFE_LINE_SCHEMA) result.reasons.push('LIFE_LINE_SCHEMA_INVALID');
  if (value.persona_id !== PERSONA_ID) result.reasons.push('LIFE_LINE_PERSONA_MISMATCH');
  if (value.timezone !== TIMEZONE) result.reasons.push('LIFE_LINE_TIMEZONE_MISMATCH');
  if (value.birth_date_beijing !== BIRTH_DATE) result.reasons.push('LIFE_LINE_BIRTH_ANCHOR_MISMATCH');
  if (value.world_epoch_date !== WORLD_EPOCH_DATE) result.reasons.push('LIFE_LINE_WORLD_EPOCH_MISMATCH');
  if (!Array.isArray(value.blocks)) result.reasons.push('LIFE_LINE_BLOCKS_NOT_ARRAY');
  if (!value.genesis || typeof value.genesis !== 'object') result.reasons.push('LIFE_LINE_GENESIS_MISSING');
  if (!Array.isArray(value.blocks) || !value.genesis) return result;

  const genesis = value.genesis;
  result.sequence.genesis = true;
  if (genesis.sequence !== 0) result.reasons.push('GENESIS_SEQUENCE_INVALID');
  if (genesis.beijing_day !== BIRTH_DATE) result.reasons.push('GENESIS_DATE_INVALID');
  if (genesis.previous_hash !== null) result.reasons.push('GENESIS_PREVIOUS_HASH_NOT_NULL');
  if (genesis.era_day !== eraDay(BIRTH_DATE)) result.reasons.push('GENESIS_ERA_DAY_INVALID');
  if (genesis.beijing_close_tick !== closeTick(BIRTH_DATE)) result.reasons.push('GENESIS_CLOSE_TICK_INVALID');
  if (genesis.hash !== lifeLineBlockHash(genesis)) result.reasons.push('GENESIS_HASH_MISMATCH');
  verifyEvidence(root, genesis, result);

  let previous = genesis;
  result.sequence.blocks = value.blocks.length;
  for (let index = 0; index < value.blocks.length; index += 1) {
    const block = value.blocks[index], expectedSequence = index + 1, expectedDay = addDays(BIRTH_DATE, expectedSequence);
    result.sequence.expected = expectedSequence;
    if (!block || typeof block !== 'object') { result.reasons.push(`BLOCK_INVALID:${expectedSequence}`); continue; }
    if (block.sequence !== expectedSequence) result.reasons.push(`BLOCK_SEQUENCE_INVALID:${expectedSequence}`);
    if (block.beijing_day !== expectedDay) result.reasons.push(`BLOCK_DATE_OR_GAP:${expectedSequence}:${expectedDay}`);
    if (block.previous_hash !== previous.hash) result.reasons.push(`BLOCK_PREVIOUS_HASH_MISMATCH:${expectedSequence}`);
    if (block.era_day !== eraDay(block.beijing_day)) result.reasons.push(`BLOCK_ERA_DAY_INVALID:${expectedSequence}`);
    if (block.beijing_close_tick !== closeTick(block.beijing_day)) result.reasons.push(`BLOCK_CLOSE_TICK_INVALID:${expectedSequence}`);
    if (Date.parse(block.beijing_close_tick) > new Date(now).getTime()) result.reasons.push(`BLOCK_CLOSE_TICK_IN_FUTURE:${expectedSequence}`);
    if (block.hash !== lifeLineBlockHash(block)) result.reasons.push(`BLOCK_HASH_MISMATCH:${expectedSequence}`);
    verifyEvidence(root, block, result);
    previous = block;
  }
  if (!value.blocks.length || value.blocks.at(-1)?.beijing_day !== expectedLast) result.reasons.push(`CURRENT_COMPLETED_DAY_MISSING:${expectedLast}`);
  if (value.head_hash !== previous.hash) result.reasons.push('LIFE_LINE_HEAD_HASH_MISMATCH');
  result.head = {sequence: previous.sequence, beijing_day: previous.beijing_day, hash: previous.hash};
  if (!result.reasons.length) {
    result.wake_allowed = true;
    result.state = result.gaps.length ? 'LIFE_LINE_VERIFIED_WITH_HISTORICAL_GAPS' : 'LIFE_LINE_VERIFIED';
  }
  return result;
}