import { TelemetryConfig, ResolvedConfig, resolveConfig } from "./config.js";
import { EventQueue } from "./queue.js";
import { BatchSubmitter } from "./submitter.js";
import { PredictionCache } from "./prediction-cache.js";
import { EventBuilder } from "./event-builder.js";
import { TaskCompletionEvent } from "./types/events.js";
import { PredictionQuery, PredictionResponse } from "./types/predictions.js";
import { BatchPredictionResponse } from "./types/common.js";

/**
 * Main telemetry client. Queues task-completion events for background
 * batch submission and provides access to crowd-sourced predictions.
 */
export class TelemetryClient {
  private readonly config: ResolvedConfig;
  private readonly queue: EventQueue;
  private readonly submitter: BatchSubmitter;
  private readonly predictionCache: PredictionCache;
  private readonly _eventBuilder: EventBuilder;
  private intervalId: ReturnType<typeof setInterval> | null = null;
  private _isRunning = false;

  constructor(config: TelemetryConfig) {
    this.config = resolveConfig(config);
    this.queue = new EventQueue(this.config.maxQueueSize);
    this.submitter = new BatchSubmitter(this.config);
    this.predictionCache = new PredictionCache(
      this.config.predictionCacheTtlMs,
    );
    this._eventBuilder = new EventBuilder(this.config);
  }

  /** Get the event builder for constructing events. */
  get eventBuilder(): EventBuilder {
    return this._eventBuilder;
  }

  /** Start background submission via setInterval. Idempotent. */
  start(): void {
    if (this._isRunning) {
      return;
    }
    this._isRunning = true;
    this.intervalId = setInterval(() => {
      void this.flush();
    }, this.config.submitIntervalMs);
  }

  /** Stop background submission, flush remaining events. */
  async stop(): Promise<void> {
    if (!this._isRunning) {
      return;
    }
    this._isRunning = false;
    if (this.intervalId !== null) {
      clearInterval(this.intervalId);
      this.intervalId = null;
    }
    await this.flush();
  }

  /** Queue an event for batch submission. Never throws. */
  track(event: TaskCompletionEvent): void {
    try {
      if (!this.config.enabled) {
        return;
      }
      this.queue.enqueue(event);
    } catch (error) {
      this.handleError(error);
    }
  }

  /** Get a cached prediction. Returns null if not cached/expired. */
  getPrediction(query: PredictionQuery): PredictionResponse | null {
    return this.predictionCache.get(query);
  }

  /** Force-refresh predictions from server. */
  async refreshPredictions(queries: PredictionQuery[]): Promise<void> {
    try {
      const url = `${this.config.serverUrl}/v1/predictions/batch`;
      const controller = new AbortController();
      const timeout = setTimeout(
        () => controller.abort(),
        this.config.requestTimeoutMs,
      );

      try {
        const response = await fetch(url, {
          method: "POST",
          headers: {
            "Content-Type": "application/json",
          },
          body: JSON.stringify({ queries }),
          signal: controller.signal,
        });

        if (!response.ok) {
          throw new Error(`HTTP ${response.status}: ${response.statusText}`);
        }

        const body = (await response.json()) as BatchPredictionResponse;

        for (let i = 0; i < queries.length; i++) {
          if (body.results[i]) {
            this.predictionCache.set(queries[i], body.results[i]);
          }
        }
      } finally {
        clearTimeout(timeout);
      }
    } catch (error) {
      this.handleError(error);
    }
  }

  /** Number of events currently queued. */
  get queueSize(): number {
    return this.queue.size;
  }

  /** Whether the client is currently running. */
  get isRunning(): boolean {
    return this._isRunning;
  }

  /** Flush the queue by draining and submitting batches. */
  private async flush(): Promise<void> {
    while (!this.queue.isEmpty) {
      const batch = this.queue.drain(this.config.batchSize);
      if (batch.length === 0) break;

      try {
        const result = await this.submitter.submit(batch);
        if (!result.success) {
          // Re-enqueue events that failed to submit
          this.queue.prepend(batch);
          if (result.error) {
            this.handleError(result.error);
          }
          break; // Stop flushing on failure to avoid loops
        }
      } catch (error) {
        this.queue.prepend(batch);
        this.handleError(error);
        break;
      }
    }
  }

  private handleError(error: unknown): void {
    const err = error instanceof Error ? error : new Error(String(error));
    try {
      this.config.onError(err);
    } catch {
      // Prevent error handler from throwing
    }
  }
}