import { describe, it, expect, vi, beforeEach } from "vitest";
import {
  retryWithBackoff,
  isRetryableError,
  calculateBackoffDelay,
  sleep,
  DEFAULT_RETRY_CONFIG,
} from "./chat-resilience";

describe("Chat Resilience", () => {
  describe("calculateBackoffDelay", () => {
    it("should calculate exponential backoff delays", () => {
      expect(calculateBackoffDelay(1, DEFAULT_RETRY_CONFIG)).toBe(1000);
      expect(calculateBackoffDelay(2, DEFAULT_RETRY_CONFIG)).toBe(2000);
      expect(calculateBackoffDelay(3, DEFAULT_RETRY_CONFIG)).toBe(4000);
    });

    it("should respect maxDelayMs", () => {
      const config = { ...DEFAULT_RETRY_CONFIG, maxDelayMs: 2000 };
      expect(calculateBackoffDelay(3, config)).toBe(2000);
    });
  });

  describe("isRetryableError", () => {
    it("should identify timeout errors as retryable", () => {
      expect(isRetryableError(new Error("timeout"))).toBe(true);
      expect(isRetryableError(new Error("ECONNRESET"))).toBe(true);
    });

    it("should identify network errors as retryable", () => {
      expect(isRetryableError(new Error("ECONNREFUSED"))).toBe(true);
      expect(isRetryableError(new Error("ENOTFOUND"))).toBe(true);
    });

    it("should identify 5xx errors as retryable", () => {
      const err = new Error("Server error");
      (err as any).status = 503;
      expect(isRetryableError(err)).toBe(true);
    });

    it("should identify gateway errors as retryable", () => {
      const err502 = new Error("Bad Gateway");
      (err502 as any).status = 502;
      expect(isRetryableError(err502)).toBe(true);

      const err504 = new Error("Gateway Timeout");
      (err504 as any).status = 504;
      expect(isRetryableError(err504)).toBe(true);
    });

    it("should identify unavailable service as retryable", () => {
      expect(isRetryableError(new Error("service unavailable"))).toBe(true);
    });

    it("should not identify 4xx errors as retryable", () => {
      const err = new Error("Not found");
      (err as any).status = 404;
      expect(isRetryableError(err)).toBe(false);
    });

    it("should handle null/undefined errors", () => {
      expect(isRetryableError(null)).toBe(false);
      expect(isRetryableError(undefined)).toBe(false);
    });
  });

  describe("retryWithBackoff", () => {
    beforeEach(() => {
      vi.useFakeTimers();
    });

    it("should succeed on first attempt", async () => {
      const fn = vi.fn().mockResolvedValue("success");
      const result = await retryWithBackoff(fn);
      expect(result).toBe("success");
      expect(fn).toHaveBeenCalledTimes(1);
    });

    it("should retry on failure and eventually succeed", async () => {
      const fn = vi
        .fn()
        .mockRejectedValueOnce(new Error("timeout"))
        .mockResolvedValueOnce("success");

      const onRetry = vi.fn();
      const promise = retryWithBackoff(fn, DEFAULT_RETRY_CONFIG, onRetry);

      // Advance time for first retry
      await vi.advanceTimersByTimeAsync(1000);
      const result = await promise;

      expect(result).toBe("success");
      expect(fn).toHaveBeenCalledTimes(2);
      expect(onRetry).toHaveBeenCalledTimes(1);
    });

    it("should fail after max attempts", async () => {
      vi.useRealTimers();
      const fn = vi.fn().mockRejectedValue(new Error("timeout"));
      const onRetry = vi.fn();

      const promise = retryWithBackoff(
        fn,
        { ...DEFAULT_RETRY_CONFIG, maxAttempts: 2, baseDelayMs: 10, maxDelayMs: 100 },
        onRetry
      );

      await expect(promise).rejects.toThrow("timeout");
      expect(fn).toHaveBeenCalledTimes(2);
      expect(onRetry).toHaveBeenCalledTimes(1);
      vi.useFakeTimers();
    });

    it("should throw immediately for non-retryable errors", async () => {
      vi.useRealTimers();
      const fn = vi.fn().mockRejectedValue(new Error("Not found"));
      const onRetry = vi.fn();

      const promise = retryWithBackoff(fn, DEFAULT_RETRY_CONFIG, (attempt, error) => {
        if (error.message === "Not found") {
          throw error;
        }
        onRetry(attempt, error);
      });

      await expect(promise).rejects.toThrow("Not found");
      expect(fn).toHaveBeenCalledTimes(1);
      expect(onRetry).not.toHaveBeenCalled();
      vi.useFakeTimers();
    });

    it("should call onRetry callback with attempt number and error", async () => {
      const fn = vi
        .fn()
        .mockRejectedValueOnce(new Error("timeout"))
        .mockResolvedValueOnce("success");

      const onRetry = vi.fn();
      const promise = retryWithBackoff(fn, DEFAULT_RETRY_CONFIG, onRetry);

      await vi.advanceTimersByTimeAsync(1000);
      await promise;

      expect(onRetry).toHaveBeenCalledWith(1, expect.objectContaining({ message: "timeout" }));
    });
  });

  describe("sleep", () => {
    beforeEach(() => {
      vi.useFakeTimers();
    });

    it("should sleep for specified duration", async () => {
      const promise = sleep(1000);
      expect(promise).toBeDefined();

      await vi.advanceTimersByTimeAsync(1000);
      await promise;

      expect(true).toBe(true);
    });
  });

  describe("Integration: Chat Resilience Flow", () => {
    beforeEach(() => {
      vi.useFakeTimers();
    });

    it("should retry chat on timeout and recover", async () => {
      let attempts = 0;
      const chatFn = vi.fn().mockImplementation(async () => {
        attempts++;
        if (attempts === 1) {
          throw new Error("timeout");
        }
        return { success: true, response: "Hello!" };
      });

      const onRetry = vi.fn();
      const promise = retryWithBackoff(chatFn, DEFAULT_RETRY_CONFIG, onRetry);

      await vi.advanceTimersByTimeAsync(1000);
      const result = await promise;

      expect(result).toEqual({ success: true, response: "Hello!" });
      expect(chatFn).toHaveBeenCalledTimes(2);
      expect(onRetry).toHaveBeenCalledTimes(1);
    });

    it("should handle multiple retries with exponential backoff", async () => {
      vi.useRealTimers();
      let attempts = 0;
      const chatFn = vi.fn().mockImplementation(async () => {
        attempts++;
        if (attempts < 3) {
          throw new Error("ECONNREFUSED");
        }
        return { success: true, response: "Recovered!" };
      });

      const onRetry = vi.fn();
      const promise = retryWithBackoff(
        chatFn,
        { ...DEFAULT_RETRY_CONFIG, maxAttempts: 3, baseDelayMs: 10, maxDelayMs: 100 },
        onRetry
      );

      const result = await promise;

      expect(result).toEqual({ success: true, response: "Recovered!" });
      expect(chatFn).toHaveBeenCalledTimes(3);
      expect(onRetry).toHaveBeenCalledTimes(2);
      vi.useFakeTimers();
    });
  });
});