import { generateSecureId } from '@openpanel/common/server';
import { type ILogger, createLogger } from '@openpanel/logger';
import { getRedisCache, runEvery } from '@openpanel/redis';

export class BaseBuffer {
  name: string;
  logger: ILogger;
  lockKey: string;
  lockTimeout = 60;
  onFlush: () => void;
  enableParallelProcessing: boolean;

  protected bufferCounterKey: string;

  constructor(options: {
    name: string;
    onFlush: () => Promise<void>;
    enableParallelProcessing?: boolean;
  }) {
    this.logger = createLogger({ name: options.name });
    this.name = options.name;
    this.lockKey = `lock:${this.name}`;
    this.onFlush = options.onFlush;
    this.bufferCounterKey = `${this.name}:buffer:count`;
    this.enableParallelProcessing = options.enableParallelProcessing ?? false;
  }

  protected chunks<T>(items: T[], size: number) {
    const chunks = [];
    for (let i = 0; i < items.length; i += size) {
      chunks.push(items.slice(i, i + size));
    }
    return chunks;
  }

  /**
   * Utility method to safely get buffer size with counter fallback
   */
  protected async getBufferSizeWithCounter(
    fallbackFn: () => Promise<number>,
  ): Promise<number> {
    const key = this.bufferCounterKey;
    try {
      await runEvery({
        interval: 60 * 60,
        key: `${this.name}-buffer:resync`,
        fn: async () => {
          try {
            const actual = await fallbackFn();
            await getRedisCache().set(this.bufferCounterKey, actual.toString());
          } catch (error) {
            this.logger.warn('Failed to resync buffer counter', { error });
          }
        },
      }).catch(() => {});

      const counterValue = await getRedisCache().get(key);
      if (counterValue !== null) {
        const parsed = Number.parseInt(counterValue, 10);
        if (!Number.isNaN(parsed)) {
          return Math.max(0, parsed);
        }
        // Corrupted value → treat as missing
        this.logger.warn('Invalid buffer counter value, reinitializing', {
          key,
          counterValue,
        });
      }

      // Initialize counter with current size
      const count = await fallbackFn();
      await getRedisCache().set(key, count.toString());
      return count;
    } catch (error) {
      this.logger.warn(
        'Failed to get buffer size from counter, using fallback',
        { error },
      );
      return fallbackFn();
    }
  }

  private async releaseLock(lockId: string): Promise<void> {
    this.logger.debug('Releasing lock...');
    const script = `
      if redis.call("get", KEYS[1]) == ARGV[1] then
        return redis.call("del", KEYS[1])
      else
        return 0
      end
    `;
    await getRedisCache().eval(script, 1, this.lockKey, lockId);
  }

  async tryFlush() {
    const now = performance.now();

    // Parallel mode: No locking, multiple workers can process simultaneously
    if (this.enableParallelProcessing) {
      try {
        this.logger.debug('Processing buffer (parallel mode)...');
        await this.onFlush();
        this.logger.debug('Flush completed (parallel mode)', {
          elapsed: performance.now() - now,
        });
      } catch (error) {
        this.logger.error('Failed to process buffer (parallel mode)', {
          error,
        });
        // In parallel mode, we can't safely reset counter as other workers might be active
        // Counter will be resynced automatically by the periodic job
      }
      return;
    }

    // Sequential mode: Use lock to ensure only one worker processes at a time
    const lockId = generateSecureId('lock');
    const acquired = await getRedisCache().set(
      this.lockKey,
      lockId,
      'EX',
      this.lockTimeout,
      'NX',
    );
    if (acquired === 'OK') {
      try {
        this.logger.debug('Acquired lock. Processing buffer...', {
          lockId,
        });
        await this.onFlush();
      } catch (error) {
        this.logger.error('Failed to process buffer', {
          error,
          lockId,
        });
        // On error, we might want to reset counter to avoid drift
        if (this.bufferCounterKey) {
          this.logger.warn('Resetting buffer counter due to flush error');
          await getRedisCache().del(this.bufferCounterKey);
        }
      } finally {
        await this.releaseLock(lockId);
        this.logger.debug('Flush completed', {
          elapsed: performance.now() - now,
          lockId,
        });
      }
    }
  }
}