#pragma once

#include <variant>
#include <string>
#include <vector>
#include <string_view>
#include <optional>

#include "file.hpp"

/// The shader stage that the shader is written in.
enum class ShaderStage {
    Vertex,
    Fragment,
    Compute
};

/// The shader language that the shader is written in.
enum class ShaderLanguage {
    GLSL,
    SPIRV,
    MSL,
    HLSL,
    WGSL // lol how do we even convert to this
};

/// Compilation options when compiling shaders.
class CompileOptions {
public:
    /// Adds a GLSL define.
    void add_definition(const std::string_view name) {
        definitions.emplace_back(name);
    }
    
    std::vector<std::string> definitions;
    
    /// When compiling MSL, the result may differ whether or not we're targetting non-Mac Metal platforms.
    bool is_apple_mobile = false;
};

/// Represents the source code of a shader either in plaintext (GLSL, MSL) or bytecode (SPIR-V).
class ShaderSource {
public:
    ShaderSource() : source(std::monostate()) {}
    ShaderSource(const ShaderSource& rhs) : source (rhs.source) {}
    explicit ShaderSource(const std::string& source_string) : source(source_string) {}
    explicit ShaderSource(const std::vector<uint32_t>& source_bytecode) : source(source_bytecode) {}
    explicit ShaderSource(const prism::path& shader_path) : source(shader_path) {}

    std::variant<std::monostate, prism::path, std::string, std::vector<uint32_t>> source;
    
    /// Returns a view of the shader source as a path.
    [[nodiscard]] prism::path as_path() const {
        return std::get<prism::path>(source);
    }
    
    /// Returns a view of the shader source as plaintext.
    [[nodiscard]] std::string_view as_string() const {
        return std::get<std::string>(source);
    }
    
    /// Returns a copy of the shader source as bytecode.
    [[nodiscard]] std::vector<uint32_t> as_bytecode() const {
        return std::get<std::vector<uint32_t>>(source);
    }

    [[nodiscard]] bool empty() const {
        return std::holds_alternative<std::monostate>(source);
    }
    
    [[nodiscard]] bool is_path() const {
        return std::holds_alternative<prism::path>(source);
    }
    
    [[nodiscard]] bool is_string() const {
        return std::holds_alternative<std::string>(source);
    }
};

/// Compiles GLSL shaders to a specified shader language offline or at runtime.
class ShaderCompiler {
public:
    ShaderCompiler();
    
    /// Sets the include directory used to search for files inside of #include directives.
    void set_include_path(std::string_view path);
    
    /**
     Compiles from one shader language to another shader language.
     @param from_language The language the shader passed by shader_source is written in.
     @param shader_stage The shader stage of the shader.
     @param shader_source The shader code.
     @param to_language The shader language to compile to.
     @param options Optional compilation parameters.
     @note Right now, only GLSL is supported as a source shader language.
     */
    std::optional<ShaderSource> compile(ShaderLanguage from_language, ShaderStage shader_stage, const ShaderSource& shader_source, ShaderLanguage to_language, const CompileOptions& options = CompileOptions());
};

static inline ShaderCompiler shader_compiler;