/*
 * Copyright 2024 ScopeDB, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import { Client } from "scopedb";

// Layer: integration template (type-checked, not directly runnable).
// Requires a Web-standard server runtime with a waitUntil() lifecycle hook.

export interface FetchExecutionContext {
  /** Keeps the invocation alive for background work after returning a response. */
  waitUntil(task: Promise<unknown>): void;
}

export interface ServerlessTelemetryConfig {
  endpoint: string | URL;
  apiKey: string;
  table: string;
  database?: string;
  schema?: string;
}

/**
 * Creates a handler for Fetch runtimes that provide `waitUntil()`.
 * Call this once at module scope with configuration from the host runtime.
 */
export function createServerlessTelemetryHandler(
  config: ServerlessTelemetryConfig,
): (request: Request, context: FetchExecutionContext) => Response {
  const client = new Client(config.endpoint, { apiKey: config.apiKey });
  // Module scope lets warm invocations reuse the stream. Do not call shutdown()
  // after each invocation because shutdown permanently closes it.
  const telemetry = client
    .table(config.table, {
      database: config.database ?? "scopedb",
      schema: config.schema ?? "public",
    })
    .appendStream({ failurePolicy: "continue" })
    .attemptTimeoutMs(500)
    .maxRetries(1)
    .circuitBreaker(false)
    .build();

  return (request, context) => {
    const response = new Response("ok", { status: 200 });
    const accepted = telemetry.trySend({
      event_id: crypto.randomUUID(),
      occurred_at: new Date().toISOString(),
      path: new URL(request.url).pathname,
      status: response.status,
    });

    if (accepted) {
      // This settlement-first recipe flushes after every invocation. It favors
      // lifecycle safety over large batches. For higher throughput in a process
      // with graceful shutdown, use ../patterns/telemetry.ts.
      context.waitUntil(settleTelemetry());
    } else {
      console.error("serverless telemetry dropped locally", telemetry.stats());
    }

    return response;
  };

  async function settleTelemetry(): Promise<void> {
    try {
      // Keep the real barrier promise alive. attemptTimeoutMs() bounds each HTTP
      // attempt, while the platform's waitUntil budget governs the shared barrier.
      const report = await telemetry.flush();
      // A module-level report can cover other concurrent invocations too.
      if (report.outcome !== "ok") {
        console.error("serverless telemetry loss", report);
      }
    } catch (error) {
      console.error("serverless telemetry flush failed", error);
    }
  }
}