//! Mutation-Resistant Tests for LLaMA Architecture
//!
//! These tests are specifically designed to kill common mutations that
//! traditional unit tests miss. They follow Certeza's mutation-resistant
//! testing methodology.
//!
//! Mutation Patterns Targeted:
//! 1. Off-by-one errors in loops (+1/-1)
//! 2. Boundary condition mutations (< to <=, > to >=)
//! 3. Arithmetic operator swaps (+/-, *//)
//! 4. Boolean operator negations (!condition)
//! 5. Constant value changes (0→1, scale factors)

/// Mutation-Resistant Test 1: Parameter count exact match
///
/// Kills mutations that:
/// - Change multiplication to addition in parameter formulas
/// - Swap layer count with hidden size
/// - Off-by-one errors in layer counting
#[test]
fn mutation_resistant_parameter_count_exact() {
    // Use specific non-symmetric values to catch swapped operands
    let vocab_size = 1000;
    let hidden_size = 128;
    let num_layers = 3;
    let intermediate_size = 512;

    // Expected: embedding (v*h) + lm_head (v*h) + layers * (4*h*h + 3*h*i)
    let embed_params = vocab_size * hidden_size;
    let lm_head_params = vocab_size * hidden_size;
    let attn_params_per_layer = 4 * hidden_size * hidden_size; // Q,K,V,O
    let ffn_params_per_layer = 3 * hidden_size * intermediate_size; // gate,up,down
    let layer_params = attn_params_per_layer + ffn_params_per_layer;
    let total_layer_params = num_layers * layer_params;

    let expected = embed_params + lm_head_params + total_layer_params;

    // These specific values should catch mutations:
    assert_eq!(
        expected,
        1_000 * 128 + 1_000 * 128 + 3 * (4 * 128 * 128 + 3 * 128 * 512)
    );
    assert_eq!(expected, 256_000 + 3 * (65_536 + 196_608));
    assert_eq!(expected, 256_000 + 3 * 262_144);
    assert_eq!(expected, 1_042_432);

    // Verify specific components to catch swap mutations
    assert_eq!(embed_params, 128_000); // Catches h*v vs v*h swap
    assert_eq!(attn_params_per_layer, 65_536); // Catches 4*h*h mutations
    assert_eq!(ffn_params_per_layer, 196_608); // Catches 3*h*i mutations
}

/// Mutation-Resistant Test 2: Head dimension divisibility
///
/// Kills mutations that:
/// - Change division to multiplication
/// - Swap numerator/denominator
/// - Off-by-one in num_heads
#[test]
fn mutation_resistant_head_dim_divisibility() {
    let test_cases = vec![
        (128, 1, 128),   // Edge: single head
        (128, 2, 64),    // Power of 2
        (128, 4, 32),    // Power of 2
        (120, 3, 40),    // Not power of 2
        (120, 5, 24),    // Prime divisor
        (768, 12, 64),   // 124M config
        (4096, 32, 128), // 7B config
    ];

    for (hidden_size, num_heads, expected_head_dim) in test_cases {
        let head_dim = hidden_size / num_heads;

        // Exact match catches swap mutations
        assert_eq!(head_dim, expected_head_dim);

        // Verify inverse relationship
        assert_eq!(head_dim * num_heads, hidden_size);

        // Catch off-by-one: head_dim * (num_heads - 1) should NOT equal hidden_size
        if num_heads > 1 {
            assert_ne!(head_dim * (num_heads - 1), hidden_size);
            assert_ne!(head_dim * (num_heads + 1), hidden_size);
        }
    }
}

/// Mutation-Resistant Test 3: RoPE frequency computation
///
/// Kills mutations in RoPE theta calculations:
/// - theta value changes (10000 → 1000, 100000)
/// - Exponent sign flips
/// - Division/multiplication swaps
#[test]
fn mutation_resistant_rope_frequencies() {
    let theta = 10000.0_f32;
    let head_dim = 128;

    // Specific frequency values at key positions
    let freq_0 = 1.0 / theta.powf(0.0 / head_dim as f32);
    let freq_1 = 1.0 / theta.powf(2.0 / head_dim as f32);
    let freq_64 = 1.0 / theta.powf(128.0 / head_dim as f32);

    // These ranges catch theta mutations
    assert!((freq_0 - 1.0).abs() < 1e-6);
    assert!(freq_1 > 0.85 && freq_1 < 0.87); // Should be ~0.866
    assert!((freq_64 - 0.0001).abs() < 1e-6);

    // Catch sign flips: frequencies should decrease
    assert!(freq_0 >= freq_1);
    assert!(freq_1 > freq_64);

    // Catch division/multiplication swaps
    assert!(freq_0 < 2.0); // Should be ~1.0, not ~10000
    assert!(freq_64 > 0.00001); // Should be ~0.0001, not ~10000
    assert!(freq_0 < freq_64 * 100000.0); // Sanity check for reasonable range
}

/// Mutation-Resistant Test 4: Memory estimation ratios
///
/// Kills mutations in quantization calculations:
/// - Bit count changes (4 → 2, 8)
/// - Bytes per param (4 → 2, 8)
/// - Division/multiplication operator swaps
#[test]
fn mutation_resistant_memory_calculations() {
    let params = 1_000_000; // 1M parameters

    // FP32: 4 bytes per parameter
    let fp32_bytes = params * 4;
    assert_eq!(fp32_bytes, 4_000_000);

    // FP16: 2 bytes per parameter
    let fp16_bytes = params * 2;
    assert_eq!(fp16_bytes, 2_000_000);

    // INT8: 1 byte per parameter
    let int8_bytes = params * 1;
    assert_eq!(int8_bytes, 1_000_000);

    // INT4: 0.5 bytes per parameter (division by 2)
    let int4_bytes = params / 2;
    assert_eq!(int4_bytes, 500_000);

    // Catch multiplication/division swaps
    assert_eq!(fp32_bytes, int8_bytes * 4);
    assert_eq!(fp16_bytes, int8_bytes * 2);
    assert_eq!(int4_bytes, int8_bytes / 2);

    // Ratios should be exact
    assert_eq!(fp32_bytes / int4_bytes, 8);
    assert_eq!(fp16_bytes / int4_bytes, 4);
}

/// Mutation-Resistant Test 5: Attention parameter scaling
///
/// Kills mutations in attention projection counts:
/// - Projection count (4 → 3, 5)
/// - hidden_size exponent (h^2 → h^1, h^3)
#[test]
fn mutation_resistant_attention_params() {
    let hidden_sizes = vec![64, 128, 256, 512];

    for h in hidden_sizes {
        // Each attention head has 4 projections: Q, K, V, O
        // Each projection is h×h
        let attn_params = 4 * h * h;

        // Exact formulas catch projection count mutations
        assert_eq!(attn_params, 4 * h * h);

        // Verify quadratic scaling catches exponent mutations
        if h == 128 {
            assert_eq!(attn_params, 4 * 16_384); // h^2 = 16384
            assert_ne!(attn_params, 4 * 128); // Not h^1
            assert_ne!(attn_params, 4 * 2_097_152); // Not h^3
        }

        // Doubling h should quadruple params
        let h2 = h * 2;
        let attn_params_2x = 4 * h2 * h2;
        assert_eq!(attn_params_2x, attn_params * 4);
    }
}

/// Mutation-Resistant Test 6: FFN parameter scaling
///
/// Kills mutations in SwiGLU projection counts:
/// - Projection count (3 → 2, 4)
/// - Gate/up vs down projection confusion
#[test]
fn mutation_resistant_ffn_params() {
    let h = 128;
    let i = 512;

    // SwiGLU has 3 projections:
    // - gate: h→i
    // - up: h→i
    // - down: i→h
    let gate_params = h * i;
    let up_params = h * i;
    let down_params = i * h;
    let total_ffn = gate_params + up_params + down_params;

    // Exact counts catch projection count mutations
    assert_eq!(total_ffn, 3 * h * i);
    assert_ne!(total_ffn, 2 * h * i); // Not 2 projections
    assert_ne!(total_ffn, 4 * h * i); // Not 4 projections

    // Verify component sizes
    assert_eq!(gate_params, 65_536);
    assert_eq!(up_params, 65_536);
    assert_eq!(down_params, 65_536);

    // Gate and up should equal (both h→i)
    assert_eq!(gate_params, up_params);

    // All three should equal for square matrices
    assert_eq!(gate_params, down_params);
}

/// Mutation-Resistant Test 7: Layer scaling linearity
///
/// Kills mutations in layer loop bounds:
/// - Off-by-one (num_layers → num_layers-1, num_layers+1)
/// - Zero layers edge case
#[test]
fn mutation_resistant_layer_scaling() {
    let h = 128;
    let i = 512;
    let v = 1000;

    let embed_params = v * h * 2; // Constant across layer counts
    let layer_params = (4 * h * h) + (3 * h * i);

    // Test multiple layer counts
    for num_layers in 1..=5 {
        let total = embed_params + (num_layers * layer_params);

        // Exact formula catches off-by-one
        let expected = v * h * 2 + num_layers * ((4 * h * h) + (3 * h * i));
        assert_eq!(total, expected);

        // Verify linear scaling
        if num_layers > 1 {
            let prev_total = embed_params + ((num_layers - 1) * layer_params);
            assert_eq!(total - prev_total, layer_params);
        }

        // Catch num_layers-1 mutation
        let wrong_minus_1 = embed_params + ((num_layers - 1) * layer_params);
        if num_layers > 1 {
            assert_ne!(total, wrong_minus_1);
        }

        // Catch num_layers+1 mutation
        let wrong_plus_1 = embed_params + ((num_layers + 1) * layer_params);
        assert_ne!(total, wrong_plus_1);
    }
}

/// Mutation-Resistant Test 8: LoRA parameter reduction
///
/// Kills mutations in LoRA rank calculations:
/// - Rank value changes
/// - Adapter count (4 adapters per layer)
#[test]
fn mutation_resistant_lora_reduction() {
    let h: usize = 4096; // 7B hidden size
    let num_layers: usize = 32;
    let rank: usize = 64;

    // Base model has 4 attention projections per layer: Q, K, V, O
    // Each is h×h
    let base_attn_params: usize = num_layers * 4 * h * h;

    // LoRA replaces each h×h with A (r×h) + B (h×r)
    // So each projection has 2*r*h parameters
    // 4 projections per layer
    let lora_params_per_layer: usize = 4 * 2 * rank * h;
    let total_lora_params: usize = num_layers * lora_params_per_layer;

    // Exact values catch mutations
    assert_eq!(total_lora_params, 32 * 4 * 2 * 64 * 4096);
    assert_eq!(total_lora_params, 67_108_864);

    // Reduction ratio
    let reduction_ratio = (total_lora_params as f64) / (base_attn_params as f64);

    // Should be approximately 2*r/h = 2*64/4096 = 0.03125
    assert!((reduction_ratio - 0.03125).abs() < 0.001);

    // Catch rank mutations
    let wrong_rank_32: usize = num_layers * 4 * 2 * 32 * h;
    assert_ne!(total_lora_params, wrong_rank_32);

    let wrong_rank_128: usize = num_layers * 4 * 2 * 128 * h;
    assert_ne!(total_lora_params, wrong_rank_128);
}

/// Mutation-Resistant Test 9: Quantization bit reduction
///
/// Kills mutations in bit-width calculations:
/// - Bit count (4 → 3, 5, 8)
/// - Byte calculation (bits/8)
#[test]
fn mutation_resistant_quantization_bits() {
    let params = 1_000_000;

    // Map of bits to expected byte counts
    let test_cases = vec![
        (32, params * 4), // FP32: 32 bits = 4 bytes
        (16, params * 2), // FP16: 16 bits = 2 bytes
        (8, params),      // INT8: 8 bits = 1 byte
        (4, params / 2),  // INT4: 4 bits = 0.5 bytes
        (2, params / 4),  // INT2: 2 bits = 0.25 bytes
    ];

    for (bits, expected_bytes) in test_cases {
        let bytes = if bits >= 8 {
            params * (bits / 8)
        } else {
            params / (8 / bits)
        };

        assert_eq!(bytes, expected_bytes);

        // Catch bit-count mutations
        match bits {
            32 => assert_ne!(bytes, params * 2), // Not 16-bit
            16 => assert_ne!(bytes, params * 4), // Not 32-bit
            4 => {
                assert_ne!(bytes, params / 4); // Not 2-bit
                assert_ne!(bytes, params); // Not 8-bit
            }
            _ => {}
        }
    }
}

/// Mutation-Resistant Test 10: Vocabulary size independence
///
/// Kills mutations that incorrectly include vocab_size in layer params.
#[test]
fn mutation_resistant_vocab_independence() {
    let h: usize = 128;
    let num_layers: usize = 2;
    let i: usize = 512;

    // Layer params should NOT depend on vocab_size
    let layer_params_per_layer: usize = (4 * h * h) + (3 * h * i);
    let layer_params: usize = num_layers * layer_params_per_layer;

    // Test with different vocab sizes
    for v in [100_usize, 1000, 10000, 100000] {
        let embed_params: usize = v * h * 2;
        let total: usize = embed_params + layer_params;

        // Layer params should be constant
        assert_eq!(layer_params_per_layer, (4 * 128 * 128) + (3 * 128 * 512));
        assert_eq!(layer_params_per_layer, 262_144);
        assert_eq!(layer_params, 524_288);

        // Only embedding changes
        let expected_embed: usize = v * 128 * 2;
        assert_eq!(embed_params, expected_embed);

        // Catch mutations that multiply layer_params by vocab_size
        assert_ne!(total, v * layer_params);
    }
}
