foxhunt/ml/tests/ring_buffer_test.rs

//! Ring Buffer Tests (Wave G15: Memory Optimization)
//!
//! Validates fixed-size ring buffer implementation with zero heap allocations.
//! Tests cover:
//! - Basic push/pop operations with circular overwriting
//! - Statistical calculations (mean, std_dev, min, max)
//! - Memory safety (no heap allocations)
//! - Edge cases (empty buffer, single element, full buffer)

use ml::features::normalization::RingBuffer;

//
// Basic Operations (5 tests)
//

#[test]
fn test_ring_buffer_new() {
    let buffer: RingBuffer<f64, 10> = RingBuffer::new();
    assert_eq!(buffer.len(), 0);
    assert!(buffer.is_empty());
}

#[test]
fn test_ring_buffer_push_single() {
    let mut buffer: RingBuffer<f64, 10> = RingBuffer::new();
    buffer.push(42.0);
    assert_eq!(buffer.len(), 1);
    assert!(!buffer.is_empty());
    assert_eq!(buffer.iter().next(), Some(42.0));
}

#[test]
fn test_ring_buffer_push_multiple() {
    let mut buffer: RingBuffer<f64, 5> = RingBuffer::new();
    for i in 1..=5 {
        buffer.push(i as f64);
    }
    assert_eq!(buffer.len(), 5);

    // Verify values in insertion order
    let values: Vec<f64> = buffer.iter().collect();
    assert_eq!(values, vec![1.0, 2.0, 3.0, 4.0, 5.0]);
}

#[test]
fn test_ring_buffer_circular_overwrite() {
    let mut buffer: RingBuffer<f64, 3> = RingBuffer::new();

    // Fill buffer: [1, 2, 3]
    buffer.push(1.0);
    buffer.push(2.0);
    buffer.push(3.0);
    assert_eq!(buffer.len(), 3);

    // Overwrite oldest: [4, 2, 3] -> [2, 3, 4]
    buffer.push(4.0);
    assert_eq!(buffer.len(), 3); // Still 3 (circular)

    let values: Vec<f64> = buffer.iter().collect();
    assert_eq!(
        values,
        vec![2.0, 3.0, 4.0],
        "Oldest value (1.0) should be overwritten"
    );

    // Overwrite oldest again: [5, 3, 4] -> [3, 4, 5]
    buffer.push(5.0);
    let values: Vec<f64> = buffer.iter().collect();
    assert_eq!(
        values,
        vec![3.0, 4.0, 5.0],
        "Oldest value (2.0) should be overwritten"
    );
}

#[test]
fn test_ring_buffer_clear() {
    let mut buffer: RingBuffer<f64, 10> = RingBuffer::new();
    for i in 1..=5 {
        buffer.push(i as f64);
    }

    buffer.clear();
    assert_eq!(buffer.len(), 0);
    assert!(buffer.is_empty());
    assert_eq!(buffer.iter().count(), 0);
}

//
// Statistical Calculations (5 tests)
//

#[test]
fn test_ring_buffer_mean_single_value() {
    let mut buffer: RingBuffer<f64, 10> = RingBuffer::new();
    buffer.push(42.0);
    assert_eq!(buffer.mean(), 42.0);
}

#[test]
fn test_ring_buffer_mean_multiple_values() {
    let mut buffer: RingBuffer<f64, 10> = RingBuffer::new();
    for i in 1..=5 {
        buffer.push(i as f64);
    }
    // Mean of [1, 2, 3, 4, 5] = 15 / 5 = 3.0
    assert_eq!(buffer.mean(), 3.0);
}

#[test]
fn test_ring_buffer_std_dev() {
    let mut buffer: RingBuffer<f64, 10> = RingBuffer::new();
    // Data: [10, 20, 30, 40, 50]
    // Mean: 30
    // Variance: ((20)^2 + (10)^2 + (0)^2 + (10)^2 + (20)^2) / 4 = 250
    // StdDev: sqrt(250) ≈ 15.81
    for val in [10.0, 20.0, 30.0, 40.0, 50.0] {
        buffer.push(val);
    }

    let std_dev = buffer.std_dev();
    assert!(
        (std_dev - 15.81).abs() < 0.01,
        "Expected std_dev ≈ 15.81, got {}",
        std_dev
    );
}

#[test]
fn test_ring_buffer_min_max() {
    let mut buffer: RingBuffer<f64, 10> = RingBuffer::new();
    for val in [5.0, 2.0, 9.0, 1.0, 7.0] {
        buffer.push(val);
    }

    assert_eq!(buffer.min(), 1.0);
    assert_eq!(buffer.max(), 9.0);
}

#[test]
fn test_ring_buffer_statistics_after_overwrite() {
    let mut buffer: RingBuffer<f64, 3> = RingBuffer::new();

    // Initial: [1, 2, 3] -> mean=2, min=1, max=3
    buffer.push(1.0);
    buffer.push(2.0);
    buffer.push(3.0);
    assert_eq!(buffer.mean(), 2.0);
    assert_eq!(buffer.min(), 1.0);
    assert_eq!(buffer.max(), 3.0);

    // After overwrite: [4, 2, 3] -> [2, 3, 4] -> mean=3, min=2, max=4
    buffer.push(4.0);
    assert_eq!(buffer.mean(), 3.0);
    assert_eq!(buffer.min(), 2.0);
    assert_eq!(buffer.max(), 4.0);
}

//
// Edge Cases (5 tests)
//

#[test]
fn test_ring_buffer_empty_statistics() {
    let buffer: RingBuffer<f64, 10> = RingBuffer::new();
    assert_eq!(buffer.mean(), 0.0);
    assert_eq!(buffer.std_dev(), 0.0);
    assert_eq!(buffer.min(), f64::MAX);
    assert_eq!(buffer.max(), f64::MIN);
}

#[test]
fn test_ring_buffer_single_value_std_dev() {
    let mut buffer: RingBuffer<f64, 10> = RingBuffer::new();
    buffer.push(42.0);
    // Std dev of single value is undefined, return 0.0
    assert_eq!(buffer.std_dev(), 0.0);
}

#[test]
fn test_ring_buffer_large_capacity() {
    let mut buffer: RingBuffer<f64, 100> = RingBuffer::new();
    for i in 1..=100 {
        buffer.push(i as f64);
    }
    assert_eq!(buffer.len(), 100);
    assert_eq!(buffer.mean(), 50.5); // Mean of 1..=100
}

#[test]
fn test_ring_buffer_identical_values() {
    let mut buffer: RingBuffer<f64, 10> = RingBuffer::new();
    for _ in 0..10 {
        buffer.push(5.0);
    }

    assert_eq!(buffer.mean(), 5.0);
    assert_eq!(buffer.std_dev(), 0.0); // No variance
    assert_eq!(buffer.min(), 5.0);
    assert_eq!(buffer.max(), 5.0);
}

#[test]
fn test_ring_buffer_negative_values() {
    let mut buffer: RingBuffer<f64, 5> = RingBuffer::new();
    for val in [-5.0, -3.0, -1.0, 1.0, 3.0] {
        buffer.push(val);
    }

    assert_eq!(buffer.mean(), -1.0); // Sum = -5, count = 5
    assert_eq!(buffer.min(), -5.0);
    assert_eq!(buffer.max(), 3.0);
}

//
// Memory Safety (3 tests)
//

#[test]
fn test_ring_buffer_stack_allocation() {
    // Verify that RingBuffer is stack-allocated (no heap)
    let buffer: RingBuffer<f64, 100> = RingBuffer::new();

    // RingBuffer should be stack-allocated (const generic N)
    // Size should be: N × sizeof(Option<f64>) + 2 × sizeof(usize)
    // = 100 × 16 + 16 = 1616 bytes (stack)
    assert_eq!(std::mem::size_of_val(&buffer), 100 * 16 + 16);
}

#[test]
fn test_ring_buffer_clone() {
    let mut buffer: RingBuffer<f64, 5> = RingBuffer::new();
    for i in 1..=5 {
        buffer.push(i as f64);
    }

    // Clone should copy data (no shared heap)
    let cloned = buffer.clone();
    assert_eq!(cloned.len(), 5);
    assert_eq!(cloned.mean(), 3.0);

    // Original and clone should be independent
    assert_eq!(buffer.len(), 5);
    assert_eq!(buffer.mean(), 3.0);
}

#[test]
fn test_ring_buffer_zero_capacity() {
    // Edge case: zero-capacity buffer (compiles but useless)
    let mut buffer: RingBuffer<f64, 0> = RingBuffer::new();
    buffer.push(42.0);
    assert_eq!(buffer.len(), 0); // Cannot store any values
    assert_eq!(buffer.mean(), 0.0);
}