import { createMemoryV2PluginBackends } from './memory-v2-plugin-backends.mjs';

const TRUE_VALUES = new Set(['1', 'true', 'yes', 'on']);
const FALSE_VALUES = new Set(['0', 'false', 'no', 'off']);
const MAX_MEMORY_TEXT_LENGTH = 2000;
const MAX_CONTEXT_ITEMS = 50;

function normalizeText(value, maxLength = MAX_MEMORY_TEXT_LENGTH) {
  const text = String(value ?? '').trim();
  if (!text) return null;
  return text.length > maxLength ? text.slice(0, maxLength) : text;
}

function readFlag(env, key, fallback) {
  const raw = env?.[key];
  if (raw == null || raw === '') return fallback;
  const normalized = String(raw).trim().toLowerCase();
  if (TRUE_VALUES.has(normalized)) return true;
  if (FALSE_VALUES.has(normalized)) return false;
  return fallback;
}

function emptyResolveResult({
  enabled,
  skipped = false,
  reason = null,
  degraded = false,
  source = null,
} = {}) {
  return {
    ok: !degraded,
    enabled: Boolean(enabled),
    skipped,
    reason,
    degraded,
    source,
    profile: null,
    semanticMemories: [],
    behaviorSummary: null,
    activeGoals: [],
    contextGoals: [],
    memories: [],
  };
}

function skippedWriteResult(reason) {
  return {
    ok: true,
    enabled: false,
    skipped: true,
    reason,
    source: null,
    saved: 0,
    analyzed: 0,
    memories: 0,
  };
}

export function resolveMemoryV2Policy({ env = process.env, overrides = {} } = {}) {
  const legacyDefault = readFlag(env, 'USER_CONVERSATION_MEMORY_ENABLED', true);
  const enabled = readFlag(env, 'MEMORY_ENABLED', legacyDefault);
  return {
    enabled,
    profileEnabled: readFlag(env, 'MEMORY_PROFILE_ENABLED', enabled),
    eventLogEnabled: readFlag(env, 'MEMORY_EVENT_LOG_ENABLED', enabled),
    vectorEnabled: readFlag(env, 'MEMORY_VECTOR_ENABLED', false),
    backend: String(env?.MEMORY_BACKEND ?? 'legacy').trim() || 'legacy',
    failOpen: readFlag(env, 'MEMORY_FAIL_OPEN', true),
    ...overrides,
  };
}

export function createLegacyMemoryBackend(conversationMemoryService) {
  return {
    name: 'legacy-conversation-memory',

    isAvailable() {
      return Boolean(conversationMemoryService);
    },

    async resolve({ userId, limit = 40 } = {}) {
      if (!conversationMemoryService?.listMemories || !userId) {
        return { memories: [] };
      }
      const memories = await conversationMemoryService.listMemories(userId, { limit });
      return { memories };
    },

    async write({ userId, sessionId, messages = [] } = {}) {
      if (!conversationMemoryService?.saveAndAnalyze || !userId || !sessionId) {
        return { saved: 0, analyzed: 0, memories: 0 };
      }
      return conversationMemoryService.saveAndAnalyze(sessionId, userId, messages);
    },

    async compact({ userId } = {}) {
      if (!conversationMemoryService?.analyzeUser || !userId) {
        return { analyzed: 0, memories: 0 };
      }
      return conversationMemoryService.analyzeUser(userId);
    },
  };
}

function normalizeMemoryItem(item) {
  if (typeof item === 'string') {
    const text = normalizeText(item);
    return text ? { label: 'memory', text } : null;
  }
  if (!item || typeof item !== 'object') return null;
  const text = normalizeText(
    item.text ?? item.content ?? item.memoryText ?? item.memory_text ?? '',
  );
  if (!text) return null;
  const normalized = {
    label: normalizeText(item.label ?? item.type ?? 'memory', 80) ?? 'memory',
    text,
  };
  if (item.id != null) normalized.id = String(item.id);
  const hasCreatedAt = Object.prototype.hasOwnProperty.call(item, 'createdAt')
    || Object.prototype.hasOwnProperty.call(item, 'created_at');
  if (hasCreatedAt) normalized.createdAt = item.createdAt ?? item.created_at ?? null;
  const score = item.score ?? item.confidence;
  if (score != null && Number.isFinite(Number(score))) normalized.score = Number(score);
  return normalized;
}

function normalizeStringList(values) {
  if (!Array.isArray(values)) return [];
  return values
    .map((value) => (
      typeof value === 'string'
        ? normalizeText(value)
        : normalizeText(value?.text ?? value?.content ?? value?.summary ?? '')
    ))
    .filter(Boolean)
    .slice(0, MAX_CONTEXT_ITEMS);
}

function normalizeMemoryList(values) {
  if (!Array.isArray(values)) return [];
  return values
    .map((item) => normalizeMemoryItem(item))
    .filter(Boolean)
    .slice(0, MAX_CONTEXT_ITEMS);
}

function normalizeResolvePayload(payload, source, policy) {
  const memories = normalizeMemoryList(payload?.memories);
  const semanticMemories = Array.isArray(payload?.semanticMemories)
    ? normalizeStringList(payload.semanticMemories)
    : memories;
  const contextGoals = normalizeStringList(
    Array.isArray(payload?.contextGoals)
      ? payload.contextGoals
      : (Array.isArray(payload?.userLongTermGoals) ? payload.userLongTermGoals : payload?.activeGoals),
  );
  return {
    ok: true,
    enabled: true,
    skipped: false,
    reason: null,
    degraded: false,
    source,
    profile: policy.profileEnabled ? (payload?.profile ?? null) : null,
    semanticMemories,
    behaviorSummary: normalizeText(payload?.behaviorSummary, 4000),
    activeGoals: contextGoals,
    contextGoals,
    memories,
  };
}

function supportsOperation(backend, operation) {
  if (!operation) return true;
  return typeof backend?.[operation] === 'function';
}

function isBackendAvailable(backend) {
  try {
    return backend?.isAvailable?.() !== false;
  } catch {
    return false;
  }
}

function selectBackend(backends, policy, operation = null) {
  if (!Array.isArray(backends) || backends.length === 0) return null;
  const preferred = policy.backend;
  if (preferred && preferred !== 'legacy') {
    const exact = backends.find((backend) => backend?.name === preferred);
    if (exact && isBackendAvailable(exact) && supportsOperation(exact, operation)) {
      return exact;
    }
  }
  return backends.find((backend) => (
    isBackendAvailable(backend) && supportsOperation(backend, operation)
  )) ?? null;
}

function backendStatus(backend) {
  const name = String(backend?.name ?? 'unknown');
  let available = true;
  try {
    available = backend?.isAvailable?.() !== false;
  } catch {
    available = false;
  }
  const status = {
    name,
    available,
    supports: {
      resolve: typeof backend?.resolve === 'function',
      write: typeof backend?.write === 'function',
      compact: typeof backend?.compact === 'function',
    },
  };
  if (backend?.category) status.category = String(backend.category);
  if (backend?.role) status.role = String(backend.role);
  if (backend?.flag) status.flag = String(backend.flag);
  const reason = typeof backend?.getUnavailableReason === 'function'
    ? backend.getUnavailableReason()
    : backend?.unavailableReason;
  if (!available && reason) status.reason = String(reason);
  return status;
}

export function createMemoryV2({
  legacyMemoryService = null,
  backends = null,
  policy = null,
  env = process.env,
  logger = console,
} = {}) {
  const resolvedPolicy = policy ?? resolveMemoryV2Policy({ env });
  const resolvedBackends = backends ?? [
    createLegacyMemoryBackend(legacyMemoryService),
    ...createMemoryV2PluginBackends(),
  ];

  async function failOpen(operation, err, fallback) {
    logger?.warn?.(
      `[memory-v2] ${operation} degraded: ${err instanceof Error ? err.message : err}`,
    );
    if (resolvedPolicy.failOpen) return fallback;
    throw err;
  }

  async function resolve(input = {}) {
    if (!resolvedPolicy.enabled) {
      return emptyResolveResult({ enabled: false, skipped: true, reason: 'disabled' });
    }
    const backend = selectBackend(resolvedBackends, resolvedPolicy, 'resolve');
    if (!backend?.resolve) {
      return emptyResolveResult({ enabled: true, skipped: true, reason: 'no_backend' });
    }
    try {
      const payload = await backend.resolve(input);
      return normalizeResolvePayload(payload, backend.name ?? 'unknown', resolvedPolicy);
    } catch (err) {
      return failOpen(
        'resolve',
        err,
        emptyResolveResult({
          enabled: true,
          degraded: true,
          reason: 'backend_failure',
          source: backend.name ?? 'unknown',
        }),
      );
    }
  }

  async function write(input = {}) {
    if (!resolvedPolicy.enabled) return skippedWriteResult('disabled');
    if (!resolvedPolicy.eventLogEnabled) return skippedWriteResult('event_log_disabled');
    const backend = selectBackend(resolvedBackends, resolvedPolicy, 'write');
    if (!backend?.write) return skippedWriteResult('no_backend');
    try {
      const result = await backend.write(input);
      return {
        ok: true,
        enabled: true,
        skipped: false,
        reason: null,
        source: backend.name ?? 'unknown',
        saved: Number(result?.saved ?? 0),
        analyzed: Number(result?.analyzed ?? 0),
        memories: Number(result?.memories ?? 0),
      };
    } catch (err) {
      return failOpen('write', err, {
        ok: false,
        enabled: true,
        skipped: true,
        reason: 'backend_failure',
        source: backend.name ?? 'unknown',
        saved: 0,
        analyzed: 0,
        memories: 0,
      });
    }
  }

  async function compact(input = {}) {
    if (!resolvedPolicy.enabled) {
      return { ok: true, enabled: false, skipped: true, reason: 'disabled' };
    }
    const backend = selectBackend(resolvedBackends, resolvedPolicy, 'compact');
    if (!backend?.compact) {
      return { ok: true, enabled: true, skipped: true, reason: 'no_backend' };
    }
    try {
      const result = await backend.compact(input);
      return {
        ok: true,
        enabled: true,
        skipped: false,
        reason: null,
        source: backend.name ?? 'unknown',
        analyzed: Number(result?.analyzed ?? 0),
        memories: Number(result?.memories ?? 0),
      };
    } catch (err) {
      return failOpen('compact', err, {
        ok: false,
        enabled: true,
        skipped: true,
        reason: 'backend_failure',
        source: backend.name ?? 'unknown',
        analyzed: 0,
        memories: 0,
      });
    }
  }

  function getStatus() {
    const backends = resolvedBackends.map((backend) => backendStatus(backend));
    const selected = selectBackend(resolvedBackends, resolvedPolicy, 'resolve');
    return {
      enabled: Boolean(resolvedPolicy.enabled),
      backend: resolvedPolicy.backend,
      selectedBackend: selected?.name ?? null,
      profileEnabled: Boolean(resolvedPolicy.profileEnabled),
      eventLogEnabled: Boolean(resolvedPolicy.eventLogEnabled),
      vectorEnabled: Boolean(resolvedPolicy.vectorEnabled),
      failOpen: Boolean(resolvedPolicy.failOpen),
      backends,
    };
  }

  return {
    policy: resolvedPolicy,
    getStatus,
    resolve,
    write,
    compact,
  };
}