const percentile = (values, p) => {
  if (!values.length) return null;
  const sorted = [...values].sort((a, b) => a - b);
  return sorted[Math.min(sorted.length - 1, Math.max(0, Math.ceil(sorted.length * p) - 1))];
};

const finite = (value) => typeof value === 'number' && Number.isFinite(value);
const round = (value, digits = 2) => finite(value) ? Number(value.toFixed(digits)) : value;

export const summarizeTimings = (rows, metricNames) => Object.fromEntries(
  metricNames.map((metric) => {
    const values = rows.map((row) => row[metric]).filter(finite);
    return [metric, {
      median: percentile(values, 0.5),
      p95: percentile(values, 0.95),
      min: values.length ? Math.min(...values) : null,
      max: values.length ? Math.max(...values) : null,
    }];
  }),
);

export const summarizeLongTasks = (rows) => {
  const totals = [];
  const counts = [];
  const singles = [];
  for (const row of rows) {
    const windows = Object.values(row.longTasks ?? {});
    totals.push(windows.reduce((sum, item) => sum + (item?.totalMs ?? 0), 0));
    counts.push(windows.reduce((sum, item) => sum + (item?.count ?? 0), 0));
    singles.push(...windows.map((item) => item?.maxMs ?? 0));
  }
  return {
    maxSingleMs: round(singles.length ? Math.max(...singles) : 0),
    countP95: percentile(counts, 0.95) ?? 0,
    totalP95Ms: round(percentile(totals, 0.95) ?? 0),
  };
};

const sameJson = (a, b) => JSON.stringify(a) === JSON.stringify(b);
const exactGitSha = (value) => typeof value === 'string' && /^[0-9a-f]{40}$/i.test(value);
const isIsometricProfile = (profile) => profile === 'large-house-isometric-v1'
  || profile === 'isometric-stage3-dense-v1';

const requireReport = (report, budgets, label, expectedSha = null) => {
  if (!report || report.schema !== 2) throw new Error(`${label}: unsupported report schema`);
  if (report.profile !== budgets.profile) throw new Error(`${label}: unexpected benchmark profile`);
  if (!Array.isArray(report.rows) || report.rows.length < budgets.minimumSamples) {
    throw new Error(`${label}: expected at least ${budgets.minimumSamples} measured samples`);
  }
  if (!isIsometricProfile(report.profile)) return;
  if (!exactGitSha(report.sourceSha)) throw new Error(`${label}: missing exact sourceSha`);
  if (expectedSha != null && report.sourceSha !== expectedSha) {
    throw new Error(`${label}: sourceSha does not match requested checkout`);
  }
  if (!sameJson(report.effectiveProjection, ['iso'])
      || report.rows.some((row) => row.effectiveProjection !== 'iso')) {
    throw new Error(`${label}: effectiveProjection is not exclusively iso`);
  }
  if (label === 'candidate' && report.rows.some((row) =>
    row.isoStructuralBuilds?.supported !== true
      || row.isoStructuralBuilds?.haUpdateDelta !== 0)) {
    throw new Error(`${label}: Iso structural build count is missing or changed on HA-only update`);
  }
  if (label === 'candidate' && report.profile === 'isometric-stage3-dense-v1') {
    // The profile/schema name is intentionally stable for baseline continuity;
    // the candidate DOM revision tracks the current experimental Stage 4.
    if (report.stage3Required !== true) throw new Error(`${label}: Stage 4 was not required`);
    if (!sameJson(report.isoStageRevision, ['4'])
        || report.rows.some((row) => row.isoStageRevision !== '4')) {
      throw new Error(`${label}: Stage 4 revision metadata is incomplete`);
    }
  }
};

const relativeLimit = (baseline, ratio, allowance) => Math.max(
  baseline * (1 + ratio),
  baseline + allowance,
);

const makeCheck = (id, actual, limit, details = {}) => ({
  id,
  actual: round(actual),
  limit: round(limit),
  pass: finite(actual) && actual <= limit,
  ...details,
});

/**
 * Evaluate a candidate report against stable absolute ceilings. Full captures
 * additionally compare a base-SHA report from the same runner; fast smoke
 * captures deliberately enforce only the hard candidate limits.
 */
export const evaluatePerformanceBudget = ({
  candidate, baseline, budgets, absoluteOnly = false,
  candidateSha = null, baselineSha = null,
}) => {
  requireReport(candidate, budgets, 'candidate', candidateSha);
  if (!absoluteOnly) {
    requireReport(baseline, budgets, 'baseline', baselineSha);
    if (!sameJson(candidate.fixture, baseline.fixture)) throw new Error('fixture mismatch');
    for (const key of ['node', 'chromium', 'platform', 'arch']) {
      if (candidate.runtime?.[key] !== baseline.runtime?.[key]) {
        throw new Error(`runtime mismatch for ${key}`);
      }
    }
  }

  const checks = [];
  for (const [metric, budget] of Object.entries(budgets.timings)) {
    const stat = budget.stat ?? 'median';
    const actual = candidate.summary?.[metric]?.[stat];
    const base = absoluteOnly ? null : baseline.summary?.[metric]?.[stat];
    if (!finite(actual) || (!absoluteOnly && !finite(base))) throw new Error(`missing ${stat} for ${metric}`);
    const regressionLimit = absoluteOnly
      ? Number.POSITIVE_INFINITY
      : relativeLimit(base, budget.maxRegressionRatio, budget.noiseAllowanceMs);
    checks.push(makeCheck(
      `timing.${metric}.${stat}`,
      actual,
      Math.min(budget.hardMaxMs, regressionLimit),
      {
        ...(absoluteOnly ? {} : { baseline: round(base), regressionLimit: round(regressionLimit) }),
        hardLimit: budget.hardMaxMs,
      },
    ));
  }

  const candidateLong = candidate.longTasks ?? summarizeLongTasks(candidate.rows);
  const baselineLong = absoluteOnly ? null : (baseline.longTasks ?? summarizeLongTasks(baseline.rows));
  const longTasksAvailable = candidate.rows.every((row) => {
    const windows = Object.values(row.longTasks ?? {});
    return windows.length > 0 && windows.every((item) => item?.supported === true);
  });
  checks.push({ id: 'longTask.available', actual: longTasksAvailable ? 1 : 0, limit: 1, pass: longTasksAvailable });
  const singleRegressionLimit = absoluteOnly ? Number.POSITIVE_INFINITY : relativeLimit(
    baselineLong.maxSingleMs, budgets.longTasks.maxSingleRegressionRatio,
    budgets.longTasks.maxSingleNoiseAllowanceMs,
  );
  checks.push(makeCheck(
    'longTask.maxSingleMs',
    candidateLong.maxSingleMs,
    Math.min(budgets.longTasks.maxSingleMs, singleRegressionLimit),
    {
      ...(absoluteOnly ? {} : { baseline: baselineLong.maxSingleMs }),
      hardLimit: budgets.longTasks.maxSingleMs,
    },
  ));
  const countRegressionLimit = absoluteOnly ? Number.POSITIVE_INFINITY : relativeLimit(
    baselineLong.countP95, budgets.longTasks.maxCountRegressionRatio,
    budgets.longTasks.countNoiseAllowance,
  );
  checks.push(makeCheck(
    'longTask.countP95',
    candidateLong.countP95,
    Math.min(budgets.longTasks.maxCountP95, countRegressionLimit),
    {
      ...(absoluteOnly ? {} : { baseline: baselineLong.countP95 }),
      hardLimit: budgets.longTasks.maxCountP95,
    },
  ));
  const longRegressionLimit = absoluteOnly ? Number.POSITIVE_INFINITY : relativeLimit(
    baselineLong.totalP95Ms, budgets.longTasks.maxTotalRegressionRatio,
    budgets.longTasks.noiseAllowanceMs,
  );
  checks.push(makeCheck(
    'longTask.totalP95Ms',
    candidateLong.totalP95Ms,
    Math.min(budgets.longTasks.maxTotalP95Ms, longRegressionLimit),
    {
      ...(absoluteOnly ? {} : { baseline: baselineLong.totalP95Ms }),
      hardLimit: budgets.longTasks.maxTotalP95Ms,
    },
  ));

  for (const [windowName, budget] of Object.entries(budgets.longTaskWindows ?? {})) {
    const windows = candidate.rows.map((row) => row.longTasks?.[windowName]);
    const available = windows.every((window) => window?.supported === true);
    checks.push({
      id: `longTask.${windowName}.available`, actual: available ? 1 : 0, limit: 1, pass: available,
    });
    const maxSingle = available ? Math.max(...windows.map((window) => window.maxMs)) : NaN;
    const countP95 = available ? percentile(windows.map((window) => window.count), 0.95) : NaN;
    const totalP95 = available ? percentile(windows.map((window) => window.totalMs), 0.95) : NaN;
    checks.push(makeCheck(`longTask.${windowName}.maxSingleMs`, maxSingle, budget.maxSingleMs));
    checks.push(makeCheck(`longTask.${windowName}.countP95`, countP95, budget.maxCountP95));
    checks.push(makeCheck(`longTask.${windowName}.totalP95Ms`, totalP95, budget.maxTotalP95Ms));
  }

  const candidateHeap = candidate.rows
    .map((row) => row.heapGrowthBytes)
    .filter(finite)
    .map((value) => Math.max(0, value));
  const baselineHeap = absoluteOnly ? [] : baseline.rows
    .map((row) => row.heapGrowthBytes)
    .filter(finite)
    .map((value) => Math.max(0, value));
  const preciseGc = candidate.rows.every((row) => row.preciseGc === true);
  checks.push({
    id: 'heap.preciseGc', actual: preciseGc ? 1 : 0, limit: budgets.heap.required ? 1 : 0,
    pass: !budgets.heap.required || preciseGc,
  });
  if (budgets.heap.required && (!candidateHeap.length || (!absoluteOnly && !baselineHeap.length))) {
    checks.push({ id: 'heap.available', actual: candidateHeap.length, limit: 1, pass: false });
  } else if (candidateHeap.length && (absoluteOnly || baselineHeap.length)) {
    const actual = percentile(candidateHeap, 0.95);
    const base = absoluteOnly ? null : percentile(baselineHeap, 0.95);
    const regressionLimit = absoluteOnly ? Number.POSITIVE_INFINITY : relativeLimit(
      base, budgets.heap.maxRegressionRatio, budgets.heap.noiseAllowanceBytes,
    );
    checks.push(makeCheck(
      'heap.growthP95Bytes',
      actual,
      Math.min(budgets.heap.hardMaxGrowthBytes, regressionLimit),
      {
        ...(absoluteOnly ? {} : { baseline: base }),
        hardLimit: budgets.heap.hardMaxGrowthBytes,
      },
    ));
  }

  for (const [cache, limit] of Object.entries(budgets.cacheEntries)) {
    const actual = Math.max(...candidate.rows.map((row) => row.cacheEntries?.[cache] ?? Number.POSITIVE_INFINITY));
    checks.push(makeCheck(`cache.entries.${cache}`, actual, limit));
  }
  for (const [cache, limit] of Object.entries(budgets.cacheGrowth)) {
    const actual = Math.max(...candidate.rows.map((row) => row.cacheGrowth?.[cache] ?? Number.POSITIVE_INFINITY));
    checks.push(makeCheck(`cache.growth.${cache}`, actual, limit));
  }

  const renderedDevices = Math.min(...candidate.rows.map((row) => row.renderedDevices ?? -1));
  checks.push({
    id: 'renderedDevices',
    actual: renderedDevices,
    limit: budgets.renderedDevices,
    pass: renderedDevices === budgets.renderedDevices,
  });

  const failures = checks.filter((check) => !check.pass);
  return {
    schema: 1,
    profile: budgets.profile,
    pass: failures.length === 0,
    mode: absoluteOnly ? 'absolute' : 'relative',
    candidateFingerprint: candidate.buildFingerprint,
    baselineFingerprint: baseline?.buildFingerprint ?? null,
    candidateSha: candidate.sourceSha ?? null,
    baselineSha: baseline?.sourceSha ?? null,
    checks,
    failures,
  };
};

export const performanceSummaryMarkdown = (evaluation) => {
  const icon = evaluation.pass ? '✅' : '❌';
  const lines = [
    `### ${icon} House Plan large-house performance`,
    '',
    '| Check | Candidate | Limit | Base |',
    '|---|---:|---:|---:|',
  ];
  for (const check of evaluation.checks) {
    lines.push(`| ${check.pass ? '✅' : '❌'} ${check.id} | ${check.actual} | ${check.limit} | ${check.baseline ?? '—'} |`);
  }
  return `${lines.join('\n')}\n`;
};