#include "guimesh.h"
#include "opengl.h"
#include "imgui/imgui.h"

void GuiMesh::initGL()
{
    const GLchar *vertex_shader =
        "#version 330\n"
        "uniform mat4 ProjMtx;\n"
        "layout(location = 0)in vec2 Position;\n"
        "layout(location = 1)in vec2 UV;\n"
        "layout(location = 2)in vec4 Color;\n"
        "out vec2 Frag_UV;\n"
        "out vec4 Frag_Color;\n"
        "void main()\n"
        "{\n"
        "	Frag_UV = UV;\n"
        "	Frag_Color = Color;\n"
        "	gl_Position = ProjMtx * vec4(Position.xy,0,1);\n"
        "}\n";

    const GLchar* fragment_shader =
        "#version 330\n"
        "uniform sampler2D Texture;\n"
        "in vec2 Frag_UV;\n"
        "in vec4 Frag_Color;\n"
        "out vec4 Out_Color;\n"
        "void main()\n"
        "{\n"
        "	Out_Color = Frag_Color * texture( Texture, Frag_UV.st);\n"
        "}\n";

    ShaderHandle = glCreateProgram();
    VertHandle = glCreateShader(GL_VERTEX_SHADER);
    FragHandle = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(VertHandle, 1, &vertex_shader, 0);
    glShaderSource(FragHandle, 1, &fragment_shader, 0);
    glCompileShader(VertHandle);
    glCompileShader(FragHandle);
    glAttachShader(ShaderHandle, VertHandle);
    glAttachShader(ShaderHandle, FragHandle);
    glLinkProgram(ShaderHandle);

    AttribLocationTex = glGetUniformLocation(ShaderHandle, "Texture");
    AttribLocationProjMtx = glGetUniformLocation(ShaderHandle, "ProjMtx");

    glGenBuffers(1, &VboHandle);
    glGenBuffers(1, &ElementsHandle);

    glGenVertexArrays(1, &VaoHandle);
    glBindVertexArray(VaoHandle);
    glBindBuffer(GL_ARRAY_BUFFER, VboHandle);


#define OFFSETOF(TYPE, ELEMENT) ((size_t)&(((TYPE *)0)->ELEMENT))
    glEnableVertexAttribArray(0);
    glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, pos));

    glEnableVertexAttribArray(1);
    glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, uv));

    glEnableVertexAttribArray(2);
    glVertexAttribPointer(2, 4, GL_UNSIGNED_BYTE, GL_TRUE, sizeof(ImDrawVert), (GLvoid*)OFFSETOF(ImDrawVert, col));
#undef OFFSETOF

    // Build texture atlas
    ImGuiIO& io = ImGui::GetIO();
    unsigned char* pixels;
    int width, height;
    io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height);   // Load as RGBA 32-bits (75% of the memory is wasted, but default font is so small) because it is more likely to be compatible with user's existing shaders. If your ImTextureId represent a higher-level concept than just a GL texture id, consider calling GetTexDataAsAlpha8() instead to save on GPU memory.

    // Upload texture to graphics system
    glGenTextures(1, &FontTexture);
    glBindTexture(GL_TEXTURE_2D, FontTexture);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, GL_UNSIGNED_BYTE, pixels);

    // Store our identifier
    io.Fonts->TexID = (void *)(intptr_t)FontTexture;
}

void GuiMesh::drawGL()
{
	ImGui::Render();
	
    ImDrawData* draw_data = ImGui::GetDrawData();

    ImGuiIO& io = ImGui::GetIO();
    int fb_width = (int)(io.DisplaySize.x * io.DisplayFramebufferScale.x);
    int fb_height = (int)(io.DisplaySize.y * io.DisplayFramebufferScale.y);
    if (fb_width == 0 || fb_height == 0)
        return;
    draw_data->ScaleClipRects(io.DisplayFramebufferScale);

    // Setup render state: scissor enabled
    glEnable(GL_SCISSOR_TEST);
    glActiveTexture(GL_TEXTURE0);

    // Setup viewport, orthographic projection matrix
    glViewport(0, 0, (GLsizei)fb_width, (GLsizei)fb_height);
    const float ortho_projection[4][4] =
    {
        { 2.0f/io.DisplaySize.x, 0.0f,                   0.0f, 0.0f },
        { 0.0f,                  2.0f/-io.DisplaySize.y, 0.0f, 0.0f },
        { 0.0f,                  0.0f,                  -1.0f, 0.0f },
        {-1.0f,                  1.0f,                   0.0f, 1.0f },
    };
    glUseProgram(ShaderHandle);
    glUniform1i(AttribLocationTex, 0);
    glUniformMatrix4fv(AttribLocationProjMtx, 1, GL_FALSE, &ortho_projection[0][0]);
    glBindVertexArray(VaoHandle);

    for (int n = 0; n < draw_data->CmdListsCount; n++)
    {
        const ImDrawList* cmd_list = draw_data->CmdLists[n];
        const ImDrawIdx* idx_buffer_offset = 0;

        glBindBuffer(GL_ARRAY_BUFFER, VboHandle);
        glBufferData(GL_ARRAY_BUFFER, (GLsizeiptr)cmd_list->VtxBuffer.Size * sizeof(ImDrawVert), (const GLvoid*)cmd_list->VtxBuffer.Data, GL_STREAM_DRAW);

        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ElementsHandle);
        glBufferData(GL_ELEMENT_ARRAY_BUFFER, (GLsizeiptr)cmd_list->IdxBuffer.Size * sizeof(ImDrawIdx), (const GLvoid*)cmd_list->IdxBuffer.Data, GL_STREAM_DRAW);

        for (int cmd_i = 0; cmd_i < cmd_list->CmdBuffer.Size; cmd_i++)
        {
            const ImDrawCmd* pcmd = &cmd_list->CmdBuffer[cmd_i];
            if (pcmd->UserCallback)
            {
                pcmd->UserCallback(cmd_list, pcmd);
            }
            else
            {
                glBindTexture(GL_TEXTURE_2D, (GLuint)(intptr_t)pcmd->TextureId);
                glScissor((int)pcmd->ClipRect.x, (int)(fb_height - pcmd->ClipRect.w), (int)(pcmd->ClipRect.z - pcmd->ClipRect.x), (int)(pcmd->ClipRect.w - pcmd->ClipRect.y));
                glDrawElements(GL_TRIANGLES, (GLsizei)pcmd->ElemCount, sizeof(ImDrawIdx) == 2 ? GL_UNSIGNED_SHORT : GL_UNSIGNED_INT, idx_buffer_offset);
            }
            idx_buffer_offset += pcmd->ElemCount;
        }
    }

    glDisable(GL_SCISSOR_TEST);
}

void GuiMesh::resizeGL(int w, int h)
{
    ImGuiIO& io = ImGui::GetIO();
    width = w;
    height = h;
    io.DisplaySize = ImVec2(w, h);
}

void GuiMesh::destroyGL()
{
    if (VaoHandle) glDeleteVertexArrays(1, &VaoHandle);
    if (VboHandle) glDeleteBuffers(1, &VboHandle);
    if (ElementsHandle) glDeleteBuffers(1, &ElementsHandle);
    VaoHandle = VboHandle = ElementsHandle = 0;

    if (ShaderHandle && VertHandle) glDetachShader(ShaderHandle, VertHandle);
    if (VertHandle) glDeleteShader(VertHandle);
    VertHandle = 0;

    if (ShaderHandle && FragHandle) glDetachShader(ShaderHandle, FragHandle);
    if (FragHandle) glDeleteShader(FragHandle);
    FragHandle = 0;

    if (ShaderHandle) glDeleteProgram(ShaderHandle);
    ShaderHandle = 0;

    if (FontTexture)
    {
        glDeleteTextures(1, &FontTexture);
        ImGui::GetIO().Fonts->TexID = 0;
        FontTexture = 0;
    }
}