#pragma once

#include <mbgl/shaders/hillshade_layer_ubo.hpp>
#include <mbgl/shaders/shader_source.hpp>
#include <mbgl/shaders/mtl/shader_program.hpp>

namespace mbgl {
namespace shaders {

constexpr auto hillshadeShaderPrelude = R"(

enum {
    idHillshadeDrawableUBO = idDrawableReservedVertexOnlyUBO,
    idHillshadeTilePropsUBO = idDrawableReservedFragmentOnlyUBO,
    idHillshadeEvaluatedPropsUBO = drawableReservedUBOCount,
    hillshadeUBOCount
};

struct alignas(16) HillshadeDrawableUBO {
    /*  0 */ float4x4 matrix;
    /* 64 */
};
static_assert(sizeof(HillshadeDrawableUBO) == 4 * 16, "wrong size");

struct alignas(16) HillshadeTilePropsUBO {
    /*  0 */ float2 latrange;
    /*  8 */ float exaggeration;
    /* 12 */ int32_t method;
    /* 16 */ int32_t num_lights;
    /* 20 */ float pad0;
    /* 24 */ float pad1;
    /* 28 */ float pad2;
    /* 32 */
};
static_assert(sizeof(HillshadeTilePropsUBO) == 2 * 16, "wrong size");

/// Evaluated properties that do not depend on the tile
struct alignas(16) HillshadeEvaluatedPropsUBO {
    /*  0 */ float4 accent;
    /* 16 */ float4 altitudes;       // Up to 4 altitude values (in radians)
    /* 32 */ float4 azimuths;        // Up to 4 azimuth values (in radians)
    /* 48 */ float4 shadows[4];      // Shadow colors (up to 4 lights)
    /* 112 */ float4 highlights[4];  // Highlight colors (up to 4 lights)
    /* 176 */
};
static_assert(sizeof(HillshadeEvaluatedPropsUBO) == 11 * 16, "wrong size");

)";

template <>
struct ShaderSource<BuiltIn::HillshadeShader, gfx::Backend::Type::Metal> {
    static constexpr auto name = "HillshadeShader";
    static constexpr auto vertexMainFunction = "vertexMain";
    static constexpr auto fragmentMainFunction = "fragmentMain";

    static const std::array<AttributeInfo, 2> attributes;
    static constexpr std::array<AttributeInfo, 0> instanceAttributes{};
    static const std::array<TextureInfo, 1> textures;

    static constexpr auto prelude = hillshadeShaderPrelude;
    static constexpr auto source = R"(

#define PI 3.141592653589793
#define STANDARD 0
#define COMBINED 1
#define IGOR 2
#define MULTIDIRECTIONAL 3
#define BASIC 4

struct VertexStage {
    short2 pos [[attribute(hillshadeUBOCount + 0)]];
    short2 texture_pos [[attribute(hillshadeUBOCount + 1)]];
};

struct FragmentStage {
    float4 position [[position, invariant]];
    float2 pos;
};

FragmentStage vertex vertexMain(thread const VertexStage vertx [[stage_in]],
                                device const uint32_t& uboIndex [[buffer(idGlobalUBOIndex)]],
                                device const HillshadeDrawableUBO* drawableVector [[buffer(idHillshadeDrawableUBO)]]) {

    device const HillshadeDrawableUBO& drawable = drawableVector[uboIndex];

    const float4 position = drawable.matrix * float4(float2(vertx.pos), 0, 1);
    float2 pos = float2(vertx.texture_pos) / 8192.0;
    // Metal's texture coordinate origin differs from some renderers;
    // restore Y-flip to match prepare pass and historical behavior.
    pos.y = 1.0 - pos.y;

    return {
        .position    = position,
        .pos         = pos,
    };
}

// Helper function to calculate aspect (normalized direction of slope)
float get_aspect(float2 deriv) {
    return deriv.x != 0.0 ? atan2(deriv.y, -deriv.x) : PI / 2.0 * (deriv.y > 0.0 ? 1.0 : -1.0);
}

// MapLibre's legacy hillshade algorithm (Method 0: STANDARD)
void standard_hillshade(float2 deriv, device const HillshadeTilePropsUBO& tileProps, device const HillshadeEvaluatedPropsUBO& props, thread half4& fragColor) {
    float azimuth = props.azimuths.x + PI;
    float slope = atan(0.625 * length(deriv));
    float aspect = get_aspect(deriv);

    float intensity = tileProps.exaggeration;

    // Scale the slope exponentially based on intensity
    float base = 1.875 - intensity * 1.75;
    float maxValue = 0.5 * PI;
    float scaledSlope = abs(intensity - 0.5) > 1e-6 ? ((pow(base, slope) - 1.0) / (pow(base, maxValue) - 1.0)) * maxValue : slope;

    float accent = cos(scaledSlope);
    float4 accent_color = (1.0 - accent) * props.accent * clamp(intensity * 2.0, 0.0, 1.0);

    float shade = abs(glMod((aspect + azimuth) / PI + 0.5, 2.0) - 1.0);
    float4 shade_color = mix(props.shadows[0], props.highlights[0], shade) * sin(scaledSlope) * clamp(intensity * 2.0, 0.0, 1.0);

    fragColor = half4(accent_color * (1.0 - shade_color.a) + shade_color);
}

// Basic directional hillshade (Method 4: BASIC)
void basic_hillshade(float2 deriv, device const HillshadeTilePropsUBO& tileProps, device const HillshadeEvaluatedPropsUBO& props, thread half4& fragColor) {
    deriv = deriv * tileProps.exaggeration * 2.0;
    float azimuth = props.azimuths.x + PI;
    float cos_az = cos(azimuth);
    float sin_az = sin(azimuth);
    float cos_alt = cos(props.altitudes.x);
    float sin_alt = sin(props.altitudes.x);

    // Calculate the cosine of the angle between the light vector and the surface normal
    float cang = (sin_alt - (deriv.y * cos_az * cos_alt - deriv.x * sin_az * cos_alt)) / sqrt(1.0 + dot(deriv, deriv));
    float shade = clamp(cang, 0.0, 1.0);

    // Blend shadow and highlight based on intensity
    if (shade > 0.5) {
        fragColor = half4(props.highlights[0] * (2.0 * shade - 1.0));
    } else {
        fragColor = half4(props.shadows[0] * (1.0 - 2.0 * shade));
    }
}

// Multidirectional hillshade (Method 3: MULTIDIRECTIONAL)
void multidirectional_hillshade(float2 deriv, device const HillshadeTilePropsUBO& tileProps, device const HillshadeEvaluatedPropsUBO& props, thread half4& fragColor) {
    deriv = deriv * tileProps.exaggeration * 2.0;
    float4 total_color = float4(0, 0, 0, 0);

    int num_lights = min(tileProps.num_lights, 4);

    // Iterate through all light sources
    for (int i = 0; i < num_lights; i++) {
        // Access altitude and azimuth from vec4 UBOs
        float altitude = (i == 0) ? props.altitudes.x : (i == 1) ? props.altitudes.y : (i == 2) ? props.altitudes.z : props.altitudes.w;
        float azimuth = (i == 0) ? props.azimuths.x : (i == 1) ? props.azimuths.y : (i == 2) ? props.azimuths.z : props.azimuths.w;

        float cos_alt = cos(altitude);
        float sin_alt = sin(altitude);
        // Negate cos/sin azimuth for correct light direction
        float cos_az = -cos(azimuth);
        float sin_az = -sin(azimuth);

        // Calculate the cosine of the angle between the light vector and the surface normal
        float cang = (sin_alt - (deriv.y * cos_az * cos_alt - deriv.x * sin_az * cos_alt)) / sqrt(1.0 + dot(deriv, deriv));
        float shade = clamp(cang, 0.0, 1.0);

        // Accumulate shadow/highlight contribution from each light
        if (shade > 0.5) {
            total_color += props.highlights[i] * (2.0 * shade - 1.0) / float(num_lights);
        } else {
            total_color += props.shadows[i] * (1.0 - 2.0 * shade) / float(num_lights);
        }
    }

    fragColor = half4(total_color);
}

// Combined shadow and highlight method (Method 1: COMBINED)
void combined_hillshade(float2 deriv, device const HillshadeTilePropsUBO& tileProps, device const HillshadeEvaluatedPropsUBO& props, thread half4& fragColor) {
    // Only supports one light source (index 0)
    deriv = deriv * tileProps.exaggeration * 2.0;
    float azimuth = props.azimuths.x + PI;
    float cos_az = cos(azimuth);
    float sin_az = sin(azimuth);
    float cos_alt = cos(props.altitudes.x);
    float sin_alt = sin(props.altitudes.x);

    // Calculate the angle between the light vector and the surface normal
    float cang = acos((sin_alt - (deriv.y * cos_az * cos_alt - deriv.x * sin_az * cos_alt)) / sqrt(1.0 + dot(deriv, deriv)));

    cang = clamp(cang, 0.0, PI / 2.0);

    // Calculate shade and highlight components from angle and slope magnitude
    float shade = cang * atan(length(deriv)) * 4.0 / PI / PI;
    float highlight = (PI / 2.0 - cang) * atan(length(deriv)) * 4.0 / PI / PI;

    fragColor = half4(props.shadows[0] * shade + props.highlights[0] * highlight);
}

// Igor's shadow/highlight method (Method 2: IGOR)
void igor_hillshade(float2 deriv, device const HillshadeTilePropsUBO& tileProps, device const HillshadeEvaluatedPropsUBO& props, thread half4& fragColor) {
    // Only supports one light source (index 0)
    deriv = deriv * tileProps.exaggeration * 2.0;
    float aspect = get_aspect(deriv);
    float azimuth = props.azimuths.x + PI;

    // Slope strength is magnitude of slope vector, normalized to [0, 1]
    float slope_strength = atan(length(deriv)) * 2.0 / PI;

    // Aspect strength is difference between aspect and light azimuth, normalized to [0, 1]
    float aspect_strength = 1.0 - abs(glMod((aspect + azimuth) / PI + 0.5, 2.0) - 1.0);

    float shadow_strength = slope_strength * aspect_strength;
    float highlight_strength = slope_strength * (1.0 - aspect_strength);

    fragColor = half4(props.shadows[0] * shadow_strength + props.highlights[0] * highlight_strength);
}

half4 fragment fragmentMain(FragmentStage in [[stage_in]],
                            device const uint32_t& uboIndex [[buffer(idGlobalUBOIndex)]],
                            device const HillshadeTilePropsUBO* tilePropsVector [[buffer(idHillshadeTilePropsUBO)]],
                            device const HillshadeEvaluatedPropsUBO& props [[buffer(idHillshadeEvaluatedPropsUBO)]],
                            texture2d<float, access::sample> image [[texture(0)]],
                            sampler image_sampler [[sampler(0)]]) {
#if defined(OVERDRAW_INSPECTOR)
    return half4(1.0);
#endif

    device const HillshadeTilePropsUBO& tileProps = tilePropsVector[uboIndex];
    thread half4 fragColor;

    float4 pixel = image.sample(image_sampler, in.pos);

    // Scale the derivative based on the mercator distortion at this latitude
    float latitude = (tileProps.latrange.x - tileProps.latrange.y) * in.pos.y + tileProps.latrange.y;
    float scaleFactor = cos(radians(latitude));

    // The derivative is scaled back from [0, 1] texture range to world-space slope
    // Texture range [0, 1] corresponds to slope range [-4, 4]
    float2 deriv = ((pixel.rg * 8.0) - 4.0) / scaleFactor;

    // Dispatch to the selected hillshade method
    if (tileProps.method == BASIC) {
        basic_hillshade(deriv, tileProps, props, fragColor);
    } else if (tileProps.method == COMBINED) {
        combined_hillshade(deriv, tileProps, props, fragColor);
    } else if (tileProps.method == IGOR) {
        igor_hillshade(deriv, tileProps, props, fragColor);
    } else if (tileProps.method == MULTIDIRECTIONAL) {
        multidirectional_hillshade(deriv, tileProps, props, fragColor);
    } else {
        // Default to STANDARD
        standard_hillshade(deriv, tileProps, props, fragColor);
    }

    return fragColor;
}
)";
};

} // namespace shaders
} // namespace mbgl