// Copyright (c) 2026 Gordon Bolton. MIT License.
const cache = require('./cache');
const { getSonarrInstances, getRadarrInstances } = require('./config');
const arrRetrieverRegistry = require('./arrRetrievers');

// Cache TTL for recent-history data: 5 minutes.
// History changes slowly compared to active downloads.
const HISTORY_CACHE_TTL = 5 * 60 * 1000;

// Staged loading configuration
const INITIAL_PAGE_SIZE = 100;
const MAX_TOTAL_RECORDS = 1000;
const MAX_PAGES = 10; // 10 pages * 100 records = 1000 total

// Background fetch state to prevent concurrent fetches
const backgroundFetchState = {
  sonarr: { inProgress: false, lastFetchTime: 0 },
  radarr: { inProgress: false, lastFetchTime: 0 }
};

// Event subscribers for history updates
const historyUpdateSubscribers = new Set();

// Sonarr event types that represent a successful import
const SONARR_IMPORTED_EVENTS = new Set(['downloadFolderImported', 'downloadImported']);
// Sonarr event types that represent a failed import
const SONARR_FAILED_EVENTS = new Set(['downloadFailed', 'importFailed']);
// Radarr equivalents
const RADARR_IMPORTED_EVENTS = new Set(['downloadFolderImported', 'downloadImported']);
const RADARR_FAILED_EVENTS = new Set(['downloadFailed', 'importFailed']);

/**
 * Fetch recent history records from all Sonarr instances for the given date window.
 * Results are cached under 'history:sonarr' for HISTORY_CACHE_TTL.
 * Uses staged loading: fetches 100 records immediately, then background-fetches up to 1000.
 * @param {Date} since - Only include records on or after this date
 * @returns {Promise<Array>} Flat array of Sonarr history records (with _instanceUrl and _instanceName)
 */
async function fetchSonarrHistory(since) {
  const cacheKey = 'history:sonarr';
  const cached = cache.get(cacheKey);
  if (cached) {
    // Trigger background refresh if cache is stale or incomplete
    if (!backgroundFetchState.sonarr.inProgress) {
      triggerBackgroundSonarrFetch(since);
    }
    return cached;
  }

  // Ensure retrievers are initialized
  await arrRetrieverRegistry.initialize();

  const instances = getSonarrInstances();
  const sonarrRetrievers = arrRetrieverRegistry.getRetrieversByType('sonarr');

  // Stage 1: Fetch initial batch (100 records)
  const results = await Promise.all(sonarrRetrievers.map(async (retriever) => {
    const inst = instances.find(i => i.id === retriever.getInstanceId());
    if (!inst) return [];

    try {
      const response = await retriever.getHistory({
        pageSize: INITIAL_PAGE_SIZE,
        maxPages: 1,
        sortKey: 'date',
        sortDir: 'descending',
        includeSeries: true,
        includeEpisode: true,
        startDate: since.toISOString()
      });
      const records = (response && response.records) || [];
      return records.map(r => {
        if (r.series) r.series._instanceUrl = inst.url;
        if (r.series) r.series._instanceName = inst.name || inst.id;
        r._instanceUrl = inst.url;
        r._instanceName = inst.name || inst.id;
        return r;
      });
    } catch (err) {
      console.error(`[HistoryFetcher] Sonarr ${inst.id} error:`, err.message);
      return [];
    }
  }));

  const flat = results.flat();
  cache.set(cacheKey, flat, HISTORY_CACHE_TTL);

  // Stage 2: Trigger background fetch for remaining records
  triggerBackgroundSonarrFetch(since);

  return flat;
}

/**
 * Trigger background fetch for remaining Sonarr history records.
 * Uses the retriever's built-in pagination to fetch up to 1000 records.
 */
async function triggerBackgroundSonarrFetch(since) {
  if (backgroundFetchState.sonarr.inProgress) return;
  
  // Debounce: don't fetch if we fetched within the last minute
  const now = Date.now();
  if (now - backgroundFetchState.sonarr.lastFetchTime < 60000) return;
  
  backgroundFetchState.sonarr.inProgress = true;
  backgroundFetchState.sonarr.lastFetchTime = now;

  try {
    await arrRetrieverRegistry.initialize();
    const instances = getSonarrInstances();
    const sonarrRetrievers = arrRetrieverRegistry.getRetrieversByType('sonarr');

    // Fetch all records up to MAX_PAGES using built-in pagination
    const results = await Promise.all(sonarrRetrievers.map(async (retriever) => {
      const inst = instances.find(i => i.id === retriever.getInstanceId());
      if (!inst) return [];

      try {
        const response = await retriever.getHistory({
          pageSize: INITIAL_PAGE_SIZE,
          maxPages: MAX_PAGES,
          sortKey: 'date',
          sortDir: 'descending',
          includeSeries: true,
          includeEpisode: true,
          startDate: since.toISOString()
        });
        const records = (response && response.records) || [];
        return records.map(r => {
          if (r.series) r.series._instanceUrl = inst.url;
          if (r.series) r.series._instanceName = inst.name || inst.id;
          r._instanceUrl = inst.url;
          r._instanceName = inst.name || inst.id;
          return r;
        });
      } catch (err) {
        console.error(`[HistoryFetcher] Sonarr background fetch ${inst.id} error:`, err.message);
        return [];
      }
    }));

    const allRecords = results.flat();
    
    // Update cache with all records
    cache.set('history:sonarr', allRecords, HISTORY_CACHE_TTL);
    
    // Emit SSE event for history update
    emitHistoryUpdate('sonarr');
    
    console.log(`[HistoryFetcher] Background fetch complete: ${allRecords.length} Sonarr records`);
  } catch (err) {
    console.error('[HistoryFetcher] Background Sonarr fetch error:', err.message);
  } finally {
    backgroundFetchState.sonarr.inProgress = false;
  }
}

/**
 * Fetch recent history records from all Radarr instances for the given date window.
 * Results are cached under 'history:radarr' for HISTORY_CACHE_TTL.
 * Uses staged loading: fetches 100 records immediately, then background-fetches up to 1000.
 * @param {Date} since - Only include records on or after this date
 * @returns {Promise<Array>} Flat array of Radarr history records (with _instanceUrl and _instanceName)
 */
async function fetchRadarrHistory(since) {
  const cacheKey = 'history:radarr';
  const cached = cache.get(cacheKey);
  if (cached) {
    // Trigger background refresh if cache is stale or incomplete
    if (!backgroundFetchState.radarr.inProgress) {
      triggerBackgroundRadarrFetch(since);
    }
    return cached;
  }

  // Ensure retrievers are initialized
  await arrRetrieverRegistry.initialize();

  const instances = getRadarrInstances();
  const radarrRetrievers = arrRetrieverRegistry.getRetrieversByType('radarr');

  // Stage 1: Fetch initial batch (100 records)
  const results = await Promise.all(radarrRetrievers.map(async (retriever) => {
    const inst = instances.find(i => i.id === retriever.getInstanceId());
    if (!inst) return [];

    try {
      const response = await retriever.getHistory({
        pageSize: INITIAL_PAGE_SIZE,
        maxPages: 1,
        sortKey: 'date',
        sortDir: 'descending',
        includeMovie: true,
        startDate: since.toISOString()
      });
      const records = (response && response.records) || [];
      return records.map(r => {
        if (r.movie) r.movie._instanceUrl = inst.url;
        if (r.movie) r.movie._instanceName = inst.name || inst.id;
        r._instanceUrl = inst.url;
        r._instanceName = inst.name || inst.id;
        return r;
      });
    } catch (err) {
      console.error(`[HistoryFetcher] Radarr ${inst.id} error:`, err.message);
      return [];
    }
  }));

  const flat = results.flat();
  cache.set(cacheKey, flat, HISTORY_CACHE_TTL);

  // Stage 2: Trigger background fetch for remaining records
  triggerBackgroundRadarrFetch(since);

  return flat;
}

/**
 * Trigger background fetch for remaining Radarr history records.
 * Uses the retriever's built-in pagination to fetch up to 1000 records.
 */
async function triggerBackgroundRadarrFetch(since) {
  if (backgroundFetchState.radarr.inProgress) return;
  
  // Debounce: don't fetch if we fetched within the last minute
  const now = Date.now();
  if (now - backgroundFetchState.radarr.lastFetchTime < 60000) return;
  
  backgroundFetchState.radarr.inProgress = true;
  backgroundFetchState.radarr.lastFetchTime = now;

  try {
    await arrRetrieverRegistry.initialize();
    const instances = getRadarrInstances();
    const radarrRetrievers = arrRetrieverRegistry.getRetrieversByType('radarr');

    // Fetch all records up to MAX_PAGES using built-in pagination
    const results = await Promise.all(radarrRetrievers.map(async (retriever) => {
      const inst = instances.find(i => i.id === retriever.getInstanceId());
      if (!inst) return [];

      try {
        const response = await retriever.getHistory({
          pageSize: INITIAL_PAGE_SIZE,
          maxPages: MAX_PAGES,
          sortKey: 'date',
          sortDir: 'descending',
          includeMovie: true,
          startDate: since.toISOString()
        });
        const records = (response && response.records) || [];
        return records.map(r => {
          if (r.movie) r.movie._instanceUrl = inst.url;
          if (r.movie) r.movie._instanceName = inst.name || inst.id;
          r._instanceUrl = inst.url;
          r._instanceName = inst.name || inst.id;
          return r;
        });
      } catch (err) {
        console.error(`[HistoryFetcher] Radarr background fetch ${inst.id} error:`, err.message);
        return [];
      }
    }));

    const allRecords = results.flat();
    
    // Update cache with all records
    cache.set('history:radarr', allRecords, HISTORY_CACHE_TTL);
    
    // Emit SSE event for history update
    emitHistoryUpdate('radarr');
    
    console.log(`[HistoryFetcher] Background fetch complete: ${allRecords.length} Radarr records`);
  } catch (err) {
    console.error('[HistoryFetcher] Background Radarr fetch error:', err.message);
  } finally {
    backgroundFetchState.radarr.inProgress = false;
  }
}

/**
 * Subscribe to history update events.
 * @param {Function} callback - Function to call when history is updated
 */
function onHistoryUpdate(callback) {
  historyUpdateSubscribers.add(callback);
}

/**
 * Unsubscribe from history update events.
 * @param {Function} callback - Function to remove from subscribers
 */
function offHistoryUpdate(callback) {
  historyUpdateSubscribers.delete(callback);
}

/**
 * Emit SSE event for history update.
 * Notifies all subscribers when history cache is updated.
 */
function emitHistoryUpdate(type) {
  console.log(`[HistoryFetcher] History updated for ${type}, notifying ${historyUpdateSubscribers.size} subscribers`);
  historyUpdateSubscribers.forEach(callback => {
    try {
      callback(type);
    } catch (err) {
      console.error('[HistoryFetcher] Error in history update subscriber:', err.message);
    }
  });
}

/**
 * Classify a Sonarr history record's event type.
 * @param {string} eventType
 * @returns {'imported'|'failed'|'other'}
 */
function classifySonarrEvent(eventType) {
  if (SONARR_IMPORTED_EVENTS.has(eventType)) return 'imported';
  if (SONARR_FAILED_EVENTS.has(eventType)) return 'failed';
  return 'other';
}

/**
 * Classify a Radarr history record's event type.
 * @param {string} eventType
 * @returns {'imported'|'failed'|'other'}
 */
function classifyRadarrEvent(eventType) {
  if (RADARR_IMPORTED_EVENTS.has(eventType)) return 'imported';
  if (RADARR_FAILED_EVENTS.has(eventType)) return 'failed';
  return 'other';
}

/**
 * Invalidate cached history so the next request fetches fresh data.
 * Called externally if needed (e.g. after a forced refresh).
 */
function invalidateHistoryCache() {
  cache.invalidate('history:sonarr');
  cache.invalidate('history:radarr');
}

module.exports = {
  fetchSonarrHistory,
  fetchRadarrHistory,
  classifySonarrEvent,
  classifyRadarrEvent,
  invalidateHistoryCache,
  onHistoryUpdate,
  offHistoryUpdate,
  HISTORY_CACHE_TTL
};