//! Golden Visual Regression Test Harness
//!
//! Purpose:
//! Port v3's deterministic golden hash concept to v4 through the public Engine API boundary.
//! These tests validate that Engine output remains deterministic and pixel-perfect across changes.
//!
//! Design:
//! - Uses only `hcie_engine_api::Engine` public API (no internal crate access)
//! - Creates deterministic canvases, layers, colors, vector shapes, brush strokes, filters
//! - Hashes `engine.get_composite_pixels()` with SHA-256
//! - Compares against inline golden hashes
//!
//! Regeneration:
//! Set `HCIE_REGEN_GOLDENS=1` to print computed hashes after test verification.
//!
//! Golden cases:
//! - white_canvas_empty_document: validates blank document/composite baseline
//! - green_rect_draw_and_composite: validates draw_filled_rect_rgba
//! - red_rect_over_green_rect: validates layer compositing order
//! - vector_rect_golden: validates vector rendering through Engine API
//! - brush_stroke_golden: validates brush engine + draw pipeline
//! - invert_filter_golden: validates filter pipeline and deterministic output
//! - undo_after_rect_golden: validates history snapshot and restoration

use hcie_engine_api::Engine;
use hcie_engine_api::{BrushStyle, BrushTip, VectorShape};
use sha2::{Digest, Sha256};

/// Compute SHA-256 hash of pixel buffer for golden comparison.
fn hash_pixels(pixels: &[u8]) -> String {
    let mut hasher = Sha256::new();
    hasher.update(pixels);
    format!("{:x}", hasher.finalize())
}

/// Test: White canvas, empty document baseline.
/// Validates that a blank document produces deterministic all-white/transparent RGBA output.
#[test]
fn white_canvas_empty_document() {
    let mut engine = Engine::new(8, 8);
    let pixels = engine.get_composite_pixels();

    // Engine::new creates a transparent document by default
    assert_eq!(pixels.len(), 8 * 8 * 4, "Canvas size mismatch");
    // Transparent pixels: alpha = 0
    for i in (0..pixels.len()).step_by(4) {
        assert_eq!(pixels[i + 3], 0, "Alpha channel should be 0 (transparent)");
    }
    assert_eq!(
        hash_pixels(&pixels),
        "5341e6b2646979a70e57653007a1f310169421ec9bdd9f1a5648f75ade005af1"
    );
}

/// Test: Green rectangle draw and composite.
/// Validates `draw_filled_rect_rgba` produces deterministic output.
#[test]
fn green_rect_draw_and_composite() {
    let mut engine = Engine::new(16, 16);
    engine.draw_filled_rect_rgba(4, 4, 12, 12, [0, 255, 0, 255]);
    let pixels = engine.get_composite_pixels();

    assert_eq!(pixels.len(), 16 * 16 * 4);
    // Check center pixel is green
    let center_idx = (8 * 16 + 8) * 4;
    assert_eq!(pixels[center_idx], 0);
    assert_eq!(pixels[center_idx + 1], 255);
    assert_eq!(pixels[center_idx + 2], 0);
    assert_eq!(pixels[center_idx + 3], 255);
    assert_eq!(
        hash_pixels(&pixels),
        "01b9681b08e6d9bafd568f110f0656613c7447c667fda4af9350d705dadc758a"
    );
}

/// Test: Red rectangle over green rectangle.
/// Validates layer compositing order with two layers.
#[test]
fn red_rect_over_green_rect() {
    let mut engine = Engine::new(16, 16);

    // Bottom layer: green rect
    let green_id = engine.add_layer("green");
    engine.set_active_layer(green_id);
    engine.draw_filled_rect_rgba(2, 2, 14, 14, [0, 255, 0, 255]);

    // Top layer: red rect
    let red_id = engine.add_layer("red");
    engine.set_active_layer(red_id);
    engine.draw_filled_rect_rgba(6, 6, 10, 10, [255, 0, 0, 255]);

    let pixels = engine.get_composite_pixels();
    assert_eq!(pixels.len(), 16 * 16 * 4);

    // Center pixel should be red (top layer wins)
    let center_idx = (8 * 16 + 8) * 4;
    assert_eq!(pixels[center_idx], 255);
    assert_eq!(pixels[center_idx + 1], 0);
    assert_eq!(pixels[center_idx + 2], 0);
    assert_eq!(
        hash_pixels(&pixels),
        "c893ae44fb82ff080e286a6625389fef843ac60e82cdb4d7dde8c7975bbae750"
    );
}

/// Test: Vector shape rendering.
/// Validates vector shapes are rendered deterministically through Engine API.
#[test]
fn vector_rect_golden() {
    let mut engine = Engine::new(16, 16);
    let shape = VectorShape::Rect {
        name: String::new(),
        x1: 0.0,
        y1: 0.0,
        x2: 16.0,
        y2: 16.0,
        stroke: 1.0,
        color: [255, 0, 0, 255],
        fill_color: [255, 0, 0, 255],
        fill: true,
        radius: 0.0,
        angle: 0.0,
        opacity: 1.0,
        hardness: 1.0,
    };
    engine.add_vector_shape(shape);
    let pixels = engine.get_composite_pixels();

    assert_eq!(pixels.len(), 16 * 16 * 4);

    // Verify at least one red pixel (vector rect was drawn)
    let has_red = pixels
        .chunks(4)
        .any(|p| p[0] == 255 && p[1] == 0 && p[2] == 0);
    assert!(has_red, "Vector rect should contain red pixels");
    assert_eq!(
        hash_pixels(&pixels),
        "71205eb7a329a3ead670c77eee185c0fbeb612f7a2b3d6aadbe2af4f9276b60d"
    );
}

/// Test: Brush stroke rendering.
/// Validates brush engine + draw pipeline produces deterministic output.
#[test]
fn brush_stroke_golden() {
    let mut engine = Engine::new(16, 16);
    let brush = BrushTip {
        style: BrushStyle::Round,
        size: 4.0,
        opacity: 1.0,
        hardness: 1.0,
        spacing: 0.1,
        ..Default::default()
    };
    engine.set_brush_tip(brush);
    engine.begin_stroke(engine.active_layer_id(), 8.0, 8.0);
    engine.stroke_to(engine.active_layer_id(), 12.0, 12.0, 1.0);
    engine.end_stroke(engine.active_layer_id());
    let pixels = engine.get_composite_pixels();

    assert_eq!(pixels.len(), 16 * 16 * 4);

    // Brush stroke should produce non-white pixels
    let has_non_white = pixels.iter().any(|&p| p < 255);
    assert!(
        has_non_white,
        "Brush stroke should produce non-white pixels"
    );
    assert_eq!(
        hash_pixels(&pixels),
        "e97f0dd89644a40cd4d16b7440576265761849c45180fd4dece66b4f709fa087"
    );
}

/// Test: Invert filter.
/// Validates filter pipeline produces deterministic output.
#[test]
fn invert_filter_golden() {
    let mut engine = Engine::new(8, 8);
    engine.draw_filled_rect_rgba(0, 0, 8, 8, [100, 150, 200, 255]);
    engine.apply_filter("invert", serde_json::json!({}));

    let pixels = engine.get_composite_pixels();
    assert_eq!(pixels.len(), 8 * 8 * 4);

    // Center pixel should be inverted
    let idx = (4 * 8 + 4) * 4;
    assert_eq!(pixels[idx], 155); // 255 - 100
    assert_eq!(pixels[idx + 1], 105); // 255 - 150
    assert_eq!(pixels[idx + 2], 55); // 255 - 200
    assert_eq!(
        hash_pixels(&pixels),
        "35490247d911e119aeae86afa584459b47b853262afde75f832521a738bb069f"
    );
}

/// Test: Undo after rectangle.
/// Validates history snapshot and restoration works correctly.
#[test]
fn undo_after_rect_golden() {
    let mut engine = Engine::new(8, 8);

    // Initial state: transparent
    let before = hash_pixels(&engine.get_composite_pixels());

    // Draw green rect
    engine.draw_filled_rect_rgba(2, 2, 6, 6, [0, 255, 0, 255]);

    // Undo
    engine.undo();

    let after = hash_pixels(&engine.get_composite_pixels());

    // After undo, should match initial state
    assert_eq!(before, after, "Undo should restore original canvas state");
}

/// Test: Vector fill toggle and delete.
/// Validates that set_vector_shape_fill and delete_vector_shape work correctly.
#[test]
fn vector_fill_toggle_and_delete() {
    let mut engine = Engine::new(16, 16);

    // Create a rect with fill=false
    let shape = VectorShape::Rect {
        name: String::new(),
        x1: 2.0,
        y1: 2.0,
        x2: 14.0,
        y2: 14.0,
        stroke: 1.0,
        color: [255, 0, 0, 255],
        fill_color: [0, 0, 255, 255],
        fill: false,
        radius: 0.0,
        angle: 0.0,
        opacity: 1.0,
        hardness: 1.0,
    };
    engine.add_vector_shape(shape);
    let layer_id = engine.active_layer_id();

    // Verify fill is initially false
    let shapes = engine.active_vector_shapes().unwrap();
    assert_eq!(
        shapes[0].fill(),
        Some(false),
        "fill should be false initially"
    );

    // Toggle fill ON
    engine.set_vector_shape_fill(layer_id, 0, true);
    let shapes = engine.active_vector_shapes().unwrap();
    assert_eq!(
        shapes[0].fill(),
        Some(true),
        "fill should be true after toggle"
    );

    // Verify composite pixels contain blue fill
    let pixels = engine.get_composite_pixels();
    let has_blue = pixels
        .chunks(4)
        .any(|p| p[2] == 255 && p[0] == 0 && p[1] == 0 && p[3] > 0);
    assert!(has_blue, "should have blue fill pixels after enabling fill");

    // Toggle fill OFF
    engine.set_vector_shape_fill(layer_id, 0, false);
    let shapes = engine.active_vector_shapes().unwrap();
    assert_eq!(
        shapes[0].fill(),
        Some(false),
        "fill should be false after toggling off"
    );

    // Delete the shape
    engine.delete_vector_shape(layer_id, 0);
    let shapes = engine.active_vector_shapes().unwrap();
    assert!(shapes.is_empty(), "shapes should be empty after delete");
}