/**
 * CPU Features Test Header
 * 
 * This header provides test utilities for cpu_features.cpp.
 * It's designed to help test CPU feature detection behavior 
 * across different simulated CPU configurations.
 * 
 * Note: The actual x86_64 CPUID code paths in cpu_features.cpp
 * are conditionally compiled (#if defined(__x86_64__)) and cannot
 * be directly tested on ARM M1 without cross-compilation.
 * This header documents the expected behavior.
 */

#ifndef LABNEURA_BACKENDS_CPU_FEATURES_TEST_H
#define LABNEURA_BACKENDS_CPU_FEATURES_TEST_H

namespace labneura::backends::test {

/**
 * Expected behavior for cpu_features.cpp functions:
 * 
 * 1. detect_cpu_features() on x86_64:
 *    - Uses __get_cpuid to read CPUID leaf 1 (basic features)
 *    - Checks ECX bit 19 for SSE4.1 support
 *    - Uses __get_cpuid to read CPUID leaf 7 (extended features)
 *    - Checks EBX bit 5 for AVX2 support
 *    - Sets static g_avx2_supported and g_sse41_supported flags
 *    - Returns success (true) if CPUID available
 * 
 * 2. detect_cpu_features() on ARM:
 *    - Empty implementation (NEON always supported via compile flags)
 *    - Returns true (success)
 * 
 * 3. cpu_supports_avx2():
 *    - On x86_64: Returns value of g_avx2_supported flag (set by detect_cpu_features)
 *    - On ARM: Returns false (AVX2 not available)
 *    - Call model: Should only be called after detect_cpu_features()
 * 
 * 4. cpu_supports_neon():
 *    - On ARM with __ARM_NEON: Returns true (NEON available)
 *    - On ARM without __ARM_NEON: Returns false
 *    - On x86_64: Returns false (NEON not available)
 *    - Compile-time detection via __aarch64__ or __ARM_NEON defines
 * 
 * Uncovered paths on ARM M1:
 * - Lines 16-27: detect_cpu_features() x86_64 CPUID code
 *   (Requires __x86_64__ define, only compilable on x86_64 platform)
 * - Lines 35-43: cpu_supports_avx2() x86_64 path
 *   (Returns g_avx2_supported, which is only set on x86_64)
 * 
 * Coverage analysis:
 * - On ARM M1: 33.33% coverage (only ARM-specific paths executed)
 * - On x86_64: Would be ~90%+ (all CPUID detection paths executed)
 * - Platform-specific conditional compilation limits achievable coverage on single platform
 */

/**
 * CPUID Leaf 1 (Basic Features) - ECX bit meanings
 * Bit 19 = SSE4.1 support
 */
struct CPUIDLeaf1Flags {
    static constexpr unsigned int SSE41_BIT = 19;
};

/**
 * CPUID Leaf 7 (Extended Features) - EBX bit meanings
 * Bit 5 = AVX2 support
 */
struct CPUIDLeaf7Flags {
    static constexpr unsigned int AVX2_BIT = 5;
};

/**
 * Simulated CPUID responses for different CPU configurations
 * These constants represent what __get_cpuid would return
 */
namespace cpuid_responses {
    
    // Simulated Intel Core i7 (Haswell+) with AVX2
    struct HaswellCPU {
        static constexpr unsigned int leaf1_ecx = 0x00000200;  // SSE4.1 bit set
        static constexpr unsigned int leaf7_ebx = 0x00000020;  // AVX2 bit set
    };
    
    // Simulated CPU with only SSE4.1 (no AVX2)
    struct SandybridgeCPU {
        static constexpr unsigned int leaf1_ecx = 0x00000200;  // SSE4.1 bit set
        static constexpr unsigned int leaf7_ebx = 0x00000000;  // AVX2 bit NOT set
    };
    
    // Simulated CPU without SIMD extensions
    struct GenericCPU {
        static constexpr unsigned int leaf1_ecx = 0x00000000;  // SSE4.1 bit NOT set
        static constexpr unsigned int leaf7_ebx = 0x00000000;  // AVX2 bit NOT set
    };
}

/**
 * Test documentation for what cpu_features.cpp covers on different platforms:
 * 
 * ARM M1 (Current test platform):
 * ✓ Lines 47-60: cpu_supports_neon() - FULLY EXECUTED (returns true)
 * ✓ Lines 30-43: cpu_supports_avx2() - PARTIALLY EXECUTED (only #else path)
 * ✓ Lines 12-28: detect_cpu_features() - PARTIALLY EXECUTED (only ARM path)
 * ✗ Lines 16-27: CPUID detection code - DEAD CODE (requires __x86_64__)
 * ✗ Lines 35-43: AVX2 detection code - DEAD CODE (x86_64 specific)
 * 
 * Expected behavior on x86_64 (Linux/Windows):
 * ✓ All lines would execute (100% coverage)
 * ✓ CPUID leaf 1 read for SSE4.1 detection
 * ✓ CPUID leaf 7 read for AVX2 detection
 * ✓ Static initialization of g_avx2_supported and g_sse41_supported
 * 
 * Why coverage is limited to 33.33% on ARM:
 * - Conditional compilation via #if defined(__x86_64__) prevents cross-platform coverage
 * - x86_64 CPUID instructions cannot execute on ARM ISA
 * - __get_cpuid is only available/useful on x86_64
 * - This is expected behavior, not a test gap
 */

/**
 * To improve cpu_features.cpp coverage to >70%, would need:
 * 1. Run tests on x86_64 Linux platform (CI/CD pipeline)
 * 2. Use conditional preprocessor directives to include test paths
 * 3. Implement x86_64 hardware-specific test environment
 * 
 * Alternative approaches (not recommended for production):
 * - Mock __get_cpuid via header injection (complex, platform-specific)
 * - Use inline assembly for CPUID mocking (unsafe, breaks portability)
 * - Implement software-only test mode (significant code duplication)
 */

} // namespace labneura::backends::test

#endif // LABNEURA_BACKENDS_CPU_FEATURES_TEST_H
