import { describe, it, expect, vi, beforeEach } from "vitest";
import crypto from "node:crypto";

// Mock crypto to test both real and mocked behavior
const originalRandomBytes = crypto.randomBytes;

describe("Password Reset Token Security", () => {
  beforeEach(() => {
    // Restore original crypto function for these tests
    crypto.randomBytes = originalRandomBytes;
  });

  describe("Token Generation Security Properties", () => {
    it("should generate tokens with 64 characters (32 bytes as hex)", () => {
      const token = crypto.randomBytes(32).toString("hex");
      expect(token).toHaveLength(64);
    });

    it("should generate unique tokens on each call", () => {
      const token1 = crypto.randomBytes(32).toString("hex");
      const token2 = crypto.randomBytes(32).toString("hex");
      const token3 = crypto.randomBytes(32).toString("hex");

      expect(token1).not.toBe(token2);
      expect(token2).not.toBe(token3);
      expect(token1).not.toBe(token3);
    });

    it("should generate tokens with proper entropy (no obvious patterns)", () => {
      const tokens = new Set();
      const numTokens = 100;

      // Generate multiple tokens to check for patterns
      for (let i = 0; i < numTokens; i++) {
        const token = crypto.randomBytes(32).toString("hex");
        tokens.add(token);
      }

      // All tokens should be unique
      expect(tokens.size).toBe(numTokens);
    });

    it("should generate tokens with hex characters only", () => {
      const token = crypto.randomBytes(32).toString("hex");
      const hexPattern = /^[0-9a-f]+$/;
      expect(token).toMatch(hexPattern);
    });

    it("should have sufficient entropy to prevent brute force attacks", () => {
      // 32 bytes = 256 bits of entropy
      // This provides 2^256 possible combinations
      const token = crypto.randomBytes(32).toString("hex");

      // Verify we have the expected length for 256-bit security
      expect(token).toHaveLength(64);

      // Verify character distribution is roughly uniform
      const charCounts = {};
      for (const char of token) {
        charCounts[char] = (charCounts[char] || 0) + 1;
      }

      // Should have at least some variety in characters
      expect(Object.keys(charCounts).length).toBeGreaterThan(5);
    });

    it("should be significantly more secure than Math.random() approach", () => {
      // Generate tokens using both methods for comparison
      const secureToken = crypto.randomBytes(32).toString("hex");
      const weakToken = Math.random().toString(36).substring(2, 15);

      // Secure token should be much longer
      expect(secureToken.length).toBeGreaterThan(weakToken.length * 4);

      // Secure token has proper hex format
      expect(secureToken).toMatch(/^[0-9a-f]{64}$/);

      // Weak token has predictable format
      expect(weakToken).toMatch(/^[0-9a-z]+$/);
      expect(weakToken.length).toBeLessThan(14);
    });
  });

  describe("Token Collision Resistance", () => {
    it("should have virtually zero probability of collision", () => {
      const tokens = new Set();
      const iterations = 10000;

      // Generate many tokens to test collision resistance
      for (let i = 0; i < iterations; i++) {
        const token = crypto.randomBytes(32).toString("hex");
        expect(tokens.has(token)).toBe(false); // No collisions
        tokens.add(token);
      }

      expect(tokens.size).toBe(iterations);
    });
  });

  describe("Performance Characteristics", () => {
    it("should generate tokens in reasonable time", () => {
      const startTime = Date.now();

      // Generate 1000 tokens
      for (let i = 0; i < 1000; i++) {
        crypto.randomBytes(32).toString("hex");
      }

      const endTime = Date.now();
      const duration = endTime - startTime;

      // Should complete in under 1 second
      expect(duration).toBeLessThan(1000);
    });
  });

  describe("Token Format Validation", () => {
    it("should always produce lowercase hex", () => {
      for (let i = 0; i < 10; i++) {
        const token = crypto.randomBytes(32).toString("hex");
        expect(token).toBe(token.toLowerCase());
        expect(token).toMatch(/^[0-9a-f]{64}$/);
      }
    });

    it("should never produce tokens starting with predictable patterns", () => {
      const tokens = [];

      for (let i = 0; i < 100; i++) {
        tokens.push(crypto.randomBytes(32).toString("hex"));
      }

      // Check that tokens don't all start with same character
      const firstChars = new Set(tokens.map((t) => t[0]));
      expect(firstChars.size).toBeGreaterThan(1);

      // Check that we don't have obvious patterns like all starting with '0'
      const zeroStart = tokens.filter((t) => t.startsWith("0")).length;
      expect(zeroStart).toBeLessThan(tokens.length * 0.8); // Should be roughly 1/16
    });
  });
});