'use strict';
/**
 * jsonl-hmac.js — JSONL 完整性链 (P1-JSONL-HMAC-V1)
 *
 * 防 evolution-log.jsonl / route-feedback.jsonl 离线投毒。
 * 红队识别风险: 攻击者可写 ~/.claude/，无 HMAC 链导致投毒后下个进程消费时被引导。
 */

const fs = require('fs');
const path = require('path');
const crypto = require('crypto');

const ROOT = path.join(__dirname, '..', '..');
const HMAC_KEY_FILE = path.join(ROOT, '.hmac-key');

let _cachedKey = null;
function getKey() {
  if (_cachedKey) return _cachedKey;
  try {
    _cachedKey = fs.readFileSync(HMAC_KEY_FILE, 'utf8').trim();
    if (_cachedKey.length < 32) {
      throw new Error('.hmac-key too short (' + _cachedKey.length + ' chars)');
    }
  } catch (e) {
    return null;
  }
  return _cachedKey;
}

/**
 * 计算单行 HMAC（含前一行 HMAC 形成链）
 */
function hmacLine(prevHmac, line) {
  const key = getKey();
  if (!key) return null;
  return crypto.createHmac('sha256', key).update(prevHmac + '\n' + line).digest('hex');
}

/**
 * 扫描 jsonl 文件计算 HMAC 链
 * @returns { ok, lastHmac, lineCount, sig, error?, badLines? }
 */
function computeChain(jsonlPath) {
  if (!fs.existsSync(jsonlPath)) {
    return { ok: false, error: 'file not found', lineCount: 0 };
  }
  const key = getKey();
  if (!key) return { ok: false, error: 'hmac-key unavailable' };

  let prev = '';
  let lineCount = 0;
  const badLines = [];
  const lines = fs.readFileSync(jsonlPath, 'utf8').split('\n');
  for (let i = 0; i < lines.length; i++) {
    const line = lines[i];
    if (!line) continue;
    try {
      JSON.parse(line);
      prev = hmacLine(prev, line);
      lineCount++;
    } catch (_) {
      badLines.push(i + 1);
    }
  }
  // 整体签名 = 最后一行 HMAC (即末态)
  return {
    ok: badLines.length === 0,
    lastHmac: prev,
    lineCount: lineCount,
    sig: prev,
    badLines: badLines.length ? badLines : undefined,
  };
}

/**
 * 把当前 jsonl 文件的链状态写入 baseline 文件
 */
function writeBaseline(jsonlPath, baselinePath) {
  const result = computeChain(jsonlPath);
  if (!result.ok && result.error !== 'file not found') {
    return { ok: false, error: result.error || 'compute failed' };
  }
  const baseline = {
    schema: 'bookworm-jsonl-hmac-baseline-v1',
    target: path.relative(ROOT, jsonlPath),
    sig: result.sig,
    lineCount: result.lineCount,
    builtAt: new Date().toISOString(),
    hmacKeyFingerprint: hmacKeyFingerprint(),
  };
  const dir = path.dirname(baselinePath);
  if (!fs.existsSync(dir)) fs.mkdirSync(dir, { recursive: true });
  const tmp = baselinePath + '.tmp.' + process.pid;
  fs.writeFileSync(tmp, JSON.stringify(baseline, null, 2));
  fs.renameSync(tmp, baselinePath);
  return { ok: true, baseline: baseline };
}

/**
 * 校验当前 jsonl 与 baseline
 * @returns { ok, drift, expected, actual, baselineLineCount, currentLineCount }
 */
function verifyChain(jsonlPath, baselinePath) {
  if (!fs.existsSync(baselinePath)) {
    return { ok: false, drift: 'no-baseline', expected: null, actual: null };
  }
  let baseline;
  try {
    baseline = JSON.parse(fs.readFileSync(baselinePath, 'utf8'));
  } catch (e) {
    return { ok: false, drift: 'baseline-malformed', error: e.message };
  }

  const current = computeChain(jsonlPath);
  if (!current.ok && current.error) {
    return { ok: false, drift: 'compute-error', error: current.error };
  }

  // 仅当 currentLineCount >= baselineLineCount 才视为追加增长（合法）
  // 此时 baseline.sig 应该出现在 current 链的某一中间状态
  // 简化：如果 current.lineCount >= baseline.lineCount 且 baseline 末态可在 current 复现 → ok
  if (current.lineCount < baseline.lineCount) {
    return {
      ok: false,
      drift: 'truncated',
      baselineLineCount: baseline.lineCount,
      currentLineCount: current.lineCount,
    };
  }

  // 重算到 baseline.lineCount 的末态
  const partial = computeChainPartial(jsonlPath, baseline.lineCount);
  if (partial.lastHmac !== baseline.sig) {
    return {
      ok: false,
      drift: 'tampered',
      expected: baseline.sig,
      actual: partial.lastHmac,
      atLine: baseline.lineCount,
    };
  }

  return {
    ok: true,
    drift: null,
    baselineLineCount: baseline.lineCount,
    currentLineCount: current.lineCount,
    appended: current.lineCount - baseline.lineCount,
    currentSig: current.sig,
  };
}

function computeChainPartial(jsonlPath, maxLines) {
  let prev = '';
  let n = 0;
  const lines = fs.readFileSync(jsonlPath, 'utf8').split('\n');
  for (let i = 0; i < lines.length && n < maxLines; i++) {
    const line = lines[i];
    if (!line) continue;
    prev = hmacLine(prev, line);
    n++;
  }
  return { lastHmac: prev, lineCount: n };
}

/**
 * seq 单调性检查（如果 jsonl 有 seq 字段）
 */
function assertSeqMonotonic(jsonlPath, seqField) {
  if (!seqField) seqField = 'seq';
  const lines = fs.readFileSync(jsonlPath, 'utf8').split('\n');
  let lastSeq = -Infinity;
  const violations = [];
  for (let i = 0; i < lines.length; i++) {
    const line = lines[i];
    if (!line) continue;
    try {
      const obj = JSON.parse(line);
      if (typeof obj[seqField] === 'number') {
        if (obj[seqField] < lastSeq) {
          violations.push({ lineNo: i + 1, seq: obj[seqField], prevSeq: lastSeq });
        }
        lastSeq = obj[seqField];
      }
    } catch (_) {}
  }
  return { ok: violations.length === 0, violations: violations };
}

function hmacKeyFingerprint() {
  const key = getKey();
  if (!key) return null;
  return crypto.createHash('sha256').update(key).digest('hex').slice(0, 12);
}

module.exports = {
  computeChain,
  writeBaseline,
  verifyChain,
  assertSeqMonotonic,
  hmacKeyFingerprint,
  __sentinel: 'P1-JSONL-HMAC-V1',
};