// shader_utils.cpp
#include "shader_utils.hpp"

#include <vector>

GLuint LoadShaders(const char * vertex_file_path, const char * fragment_file_path){
    // 创建着色器
    GLuint VertexShaderID = glCreateShader(GL_VERTEX_SHADER);
    GLuint FragmentShaderID = glCreateShader(GL_FRAGMENT_SHADER);

    // 从文件读取顶点着色器代码
    std::string VertexShaderCode;
    std::ifstream VertexShaderStream(vertex_file_path, std::ios::in);
    if(VertexShaderStream.is_open()){
        std::stringstream sstr;
        sstr << VertexShaderStream.rdbuf();
        VertexShaderCode = sstr.str();
        VertexShaderStream.close();
    } else {
        std::cerr << "无法打开 " << vertex_file_path << ". 你是否在正确的目录下运行程序?" << std::endl;
        getchar();
        return 0;
    }

    // 从文件读取片元着色器代码
    std::string FragmentShaderCode;
    std::ifstream FragmentShaderStream(fragment_file_path, std::ios::in);
    if(FragmentShaderStream.is_open()){
        std::stringstream sstr;
        sstr << FragmentShaderStream.rdbuf();
        FragmentShaderCode = sstr.str();
        FragmentShaderStream.close();
    } else {
        std::cerr << "无法打开 " << fragment_file_path << ". 你是否在正确的目录下运行程序?" << std::endl;
        getchar();
        return 0;
    }

    GLint Result = GL_FALSE;
    int InfoLogLength;

    // 编译顶点着色器
    std::cout << "编译着色器: " << vertex_file_path << std::endl;
    char const * VertexSourcePointer = VertexShaderCode.c_str();
    glShaderSource(VertexShaderID, 1, &VertexSourcePointer , NULL);
    glCompileShader(VertexShaderID);

    // 检查顶点着色器
    glGetShaderiv(VertexShaderID, GL_COMPILE_STATUS, &Result);
    glGetShaderiv(VertexShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength);
    if ( InfoLogLength > 0 ){
        std::vector<char> VertexShaderErrorMessage(InfoLogLength+1);
        glGetShaderInfoLog(VertexShaderID, InfoLogLength, NULL, &VertexShaderErrorMessage[0]);
        std::cerr << &VertexShaderErrorMessage[0] << std::endl;
    }

    // 编译片元着色器
    std::cout << "编译着色器: " << fragment_file_path << std::endl;
    char const * FragmentSourcePointer = FragmentShaderCode.c_str();
    glShaderSource(FragmentShaderID, 1, &FragmentSourcePointer , NULL);
    glCompileShader(FragmentShaderID);

    // 检查片元着色器
    glGetShaderiv(FragmentShaderID, GL_COMPILE_STATUS, &Result);
    glGetShaderiv(FragmentShaderID, GL_INFO_LOG_LENGTH, &InfoLogLength);
    if ( InfoLogLength > 0 ){
        std::vector<char> FragmentShaderErrorMessage(InfoLogLength+1);
        glGetShaderInfoLog(FragmentShaderID, InfoLogLength, NULL, &FragmentShaderErrorMessage[0]);
        std::cerr << &FragmentShaderErrorMessage[0] << std::endl;
    }

    // 链接程序
    std::cout << "链接程序" << std::endl;
    GLuint ProgramID = glCreateProgram();
    glAttachShader(ProgramID, VertexShaderID);
    glAttachShader(ProgramID, FragmentShaderID);
    glLinkProgram(ProgramID);

    // 检查程序
    glGetProgramiv(ProgramID, GL_LINK_STATUS, &Result);
    glGetProgramiv(ProgramID, GL_INFO_LOG_LENGTH, &InfoLogLength);
    if ( InfoLogLength > 0 ){
        std::vector<char> ProgramErrorMessage(InfoLogLength+1);
        glGetProgramInfoLog(ProgramID, InfoLogLength, NULL, &ProgramErrorMessage[0]);
        std::cerr << &ProgramErrorMessage[0] << std::endl;
    }

    glDetachShader(ProgramID, VertexShaderID);
    glDetachShader(ProgramID, FragmentShaderID);

    glDeleteShader(VertexShaderID);
    glDeleteShader(FragmentShaderID);

    return ProgramID;
}