const REQUIRED_STATUS_KEYS = [
  'enabled',
  'backend',
  'selectedBackend',
  'profileEnabled',
  'eventLogEnabled',
  'vectorEnabled',
  'failOpen',
  'backends',
];

function pass(name, details = {}) {
  return { name, ok: true, ...details };
}

function fail(name, message, details = {}) {
  return { name, ok: false, message, ...details };
}

function findBackend(status, name) {
  return Array.isArray(status?.backends)
    ? status.backends.find((backend) => backend?.name === name)
    : null;
}

function missingStatusKeys(status) {
  return REQUIRED_STATUS_KEYS.filter((key) => !(key in Object(status)));
}

export function evaluateMemoryV2Health({
  status,
  writeResult = null,
  compactResult = null,
  expectedBackend = null,
  requireEnabled = false,
  requireFailOpen = true,
} = {}) {
  const checks = [];
  const missing = missingStatusKeys(status);

  checks.push(
    missing.length === 0
      ? pass('status_contract')
      : fail('status_contract', `Missing status keys: ${missing.join(', ')}`, { missing }),
  );

  if (requireEnabled) {
    checks.push(
      status?.enabled === true
        ? pass('memory_enabled')
        : fail('memory_enabled', 'MEMORY_ENABLED is not enabled', { enabled: status?.enabled }),
    );
  } else {
    checks.push(pass('memory_enabled_optional', { enabled: Boolean(status?.enabled) }));
  }

  if (requireFailOpen) {
    checks.push(
      status?.failOpen === true
        ? pass('fail_open')
        : fail('fail_open', 'MEMORY_FAIL_OPEN must remain enabled for release safety', {
            failOpen: status?.failOpen,
          }),
    );
  }

  if (expectedBackend) {
    checks.push(
      status?.backend === expectedBackend
        ? pass('expected_backend', { backend: status?.backend })
        : fail('expected_backend', `Expected MEMORY_BACKEND=${expectedBackend}`, {
            backend: status?.backend,
          }),
    );
  }

  const legacy = findBackend(status, 'legacy-conversation-memory');
  checks.push(
    legacy?.available === true
      ? pass('legacy_available')
      : fail('legacy_available', 'Legacy conversation-memory backend must be available', {
          legacy,
        }),
  );

  checks.push(
    legacy?.supports?.write === true && legacy?.supports?.compact === true
      ? pass('legacy_write_compact_supported')
      : fail('legacy_write_compact_supported', 'Legacy backend must support write and compact', {
          supports: legacy?.supports ?? null,
        }),
  );

  const selectedBackend = status?.selectedBackend ?? null;
  checks.push(
    selectedBackend
      ? pass('selected_backend_present', { selectedBackend })
      : fail('selected_backend_present', 'No selected Memory V2 backend for resolve'),
  );

  const selected = findBackend(status, selectedBackend);
  checks.push(
    !selected || selected.available === true
      ? pass('selected_backend_available', { selectedBackend })
      : fail('selected_backend_available', 'Selected backend is not available', { selected }),
  );

  const pgvector = findBackend(status, 'pgvector');
  if (status?.backend === 'pgvector') {
    checks.push(
      pgvector?.available === true
        ? pass('pgvector_canary_available')
        : pass('pgvector_canary_fallback', {
            reason: pgvector?.reason ?? 'unavailable',
            selectedBackend,
          }),
    );
  }

  if (writeResult) {
    checks.push(
      writeResult.source === 'legacy-conversation-memory'
        ? pass('write_uses_legacy', { source: writeResult.source })
        : fail('write_uses_legacy', 'Memory V2 write must use legacy backend during semantic canary', {
            source: writeResult.source ?? null,
          }),
    );
  }

  if (compactResult) {
    checks.push(
      compactResult.source === 'legacy-conversation-memory'
        ? pass('compact_uses_legacy', { source: compactResult.source })
        : fail('compact_uses_legacy', 'Memory V2 compact must use legacy backend during semantic canary', {
            source: compactResult.source ?? null,
          }),
    );
  }

  return {
    ok: checks.every((check) => check.ok),
    checkedAt: new Date().toISOString(),
    summary: {
      enabled: Boolean(status?.enabled),
      backend: status?.backend ?? null,
      selectedBackend,
      failOpen: Boolean(status?.failOpen),
      backendCount: Array.isArray(status?.backends) ? status.backends.length : 0,
    },
    checks,
  };
}