/*
 * xemu User Interface Rendering Helpers
 *
 * Copyright (C) 2020-2021 Matt Borgerson
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include <SDL.h>
#include <epoxy/gl.h>
#include <stdio.h>
#include <math.h>
#include "xemu-shaders.h"
#include "ui/shader/xemu-logo-frag.h"

#define STB_IMAGE_IMPLEMENTATION
#include "stb_image.h"

GLuint compile_shader(GLenum type, const char *src)
{
    GLint status;
    char err_buf[512];
    GLuint shader = glCreateShader(type);
    if (shader == 0) {
        fprintf(stderr, "ERROR: Failed to create shader\n");
        return 0;
    }
    glShaderSource(shader, 1, &src, NULL);
    glCompileShader(shader);
    glGetShaderiv(shader, GL_COMPILE_STATUS, &status);
    if (status != GL_TRUE) {
        glGetShaderInfoLog(shader, sizeof(err_buf), NULL, err_buf);
        fprintf(stderr, "ERROR: Shader compilation failed!\n\n");
        fprintf(stderr, "[Shader Info Log]\n");
        fprintf(stderr, "%s\n", err_buf);
        fprintf(stderr, "[Shader Source]\n");
        fprintf(stderr, "%s\n", src);
        return 0;
    }

    return shader;
}

struct decal_shader *create_decal_shader(enum SHADER_TYPE type)
{
    // Allocate shader wrapper object
    struct decal_shader *s = (struct decal_shader *)malloc(sizeof(struct decal_shader));
    assert(s != NULL);
    s->flip = 0;
    s->scale = 1.4;
    s->smoothing = 1.0;
    s->outline_dist = 1.0;
    s->time = 0;

    const char *vert_src =
        "#version 150 core\n"
        "uniform bool in_FlipY;\n"
        "uniform vec4 in_ScaleOffset;\n"
        "uniform vec4 in_TexScaleOffset;\n"
        "in vec2 in_Position;\n"
        "in vec2 in_Texcoord;\n"
        "out vec2 Texcoord;\n"
        "void main() {\n"
        "    vec2 t = in_Texcoord;\n"
        "    if (in_FlipY) t.y = 1-t.y;\n"
        "    Texcoord = t*in_TexScaleOffset.xy + in_TexScaleOffset.zw;\n"
        "    gl_Position = vec4(in_Position*in_ScaleOffset.xy+in_ScaleOffset.zw, 0.0, 1.0);\n"
        "}\n";
    GLuint vert = compile_shader(GL_VERTEX_SHADER, vert_src);
    assert(vert != 0);

    const char *image_frag_src =
        "#version 150 core\n"
        "uniform sampler2D tex;\n"
        "uniform vec4 in_ColorPrimary;\n"
        "uniform vec4 in_ColorSecondary;\n"
        "uniform vec4 in_ColorFill;\n"
        "in  vec2 Texcoord;\n"
        "out vec4 out_Color;\n"
        "void main() {\n"
        "    vec4 t = texture(tex, Texcoord);\n"
        "    out_Color.rgba = t;\n"
        "}\n";
    // Simple 2-color decal shader
    // - in_ColorFill is first pass
    // - Red channel of the texture is used as primary color, mixed with 1-Red for
    //   secondary color.
    // - Blue is a lazy alpha removal for now
    // - Alpha channel passed through
    const char *mask_frag_src =
        "#version 150 core\n"
        "uniform sampler2D tex;\n"
        "uniform vec4 in_ColorPrimary;\n"
        "uniform vec4 in_ColorSecondary;\n"
        "uniform vec4 in_ColorFill;\n"
        "in  vec2 Texcoord;\n"
        "out vec4 out_Color;\n"
        "void main() {\n"
        "    vec4 t = texture(tex, Texcoord);\n"
        "    out_Color.rgba = in_ColorFill.rgba;\n"
        "    out_Color.rgb += mix(in_ColorSecondary.rgb, in_ColorPrimary.rgb, t.r);\n"
        "    out_Color.a += t.a - t.b;\n"
        "}\n";

    const char *frag_src = NULL;
    if (type == SHADER_TYPE_MASK) {
        frag_src = mask_frag_src;
    } else if (type == SHADER_TYPE_BLIT) {
        frag_src = image_frag_src;
    } else if (type == SHADER_TYPE_LOGO) {
        frag_src = xemu_logo_frag_src;
    } else {
        assert(0);
    }
    GLuint frag = compile_shader(GL_FRAGMENT_SHADER, frag_src);
    assert(frag != 0);

    // Link vertex and fragment shaders
    s->prog = glCreateProgram();
    glAttachShader(s->prog, vert);
    glAttachShader(s->prog, frag);
    glBindFragDataLocation(s->prog, 0, "out_Color");
    glLinkProgram(s->prog);
    glUseProgram(s->prog);

    // Flag shaders for deletion when program is deleted
    glDeleteShader(vert);
    glDeleteShader(frag);

    s->FlipY_loc          = glGetUniformLocation(s->prog, "in_FlipY");
    s->ScaleOffset_loc    = glGetUniformLocation(s->prog, "in_ScaleOffset");
    s->TexScaleOffset_loc = glGetUniformLocation(s->prog, "in_TexScaleOffset");
    s->tex_loc            = glGetUniformLocation(s->prog, "tex");
    s->ColorPrimary_loc   = glGetUniformLocation(s->prog, "in_ColorPrimary");
    s->ColorSecondary_loc = glGetUniformLocation(s->prog, "in_ColorSecondary");
    s->ColorFill_loc      = glGetUniformLocation(s->prog, "in_ColorFill");
    s->time_loc           = glGetUniformLocation(s->prog, "iTime");
    s->scale_loc          = glGetUniformLocation(s->prog, "scale");

    // Create a vertex array object
    glGenVertexArrays(1, &s->vao);
    glBindVertexArray(s->vao);

    // Populate vertex buffer
    glGenBuffers(1, &s->vbo);
    glBindBuffer(GL_ARRAY_BUFFER, s->vbo);
    const GLfloat verts[6][4] = {
        //  x      y      s      t
        { -1.0f, -1.0f,  0.0f,  0.0f }, // BL
        { -1.0f,  1.0f,  0.0f,  1.0f }, // TL
        {  1.0f,  1.0f,  1.0f,  1.0f }, // TR
        {  1.0f, -1.0f,  1.0f,  0.0f }, // BR
    };
    glBufferData(GL_ARRAY_BUFFER, sizeof(verts), verts,  GL_STATIC_COPY);

    // Populate element buffer
    glGenBuffers(1, &s->ebo);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, s->ebo);
    const GLint indicies[] = { 0, 1, 2, 3 };
    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indicies), indicies, GL_STATIC_DRAW);

    // Bind vertex position attribute
    GLint pos_attr_loc = glGetAttribLocation(s->prog, "in_Position");
    glVertexAttribPointer(pos_attr_loc, 2, GL_FLOAT, GL_FALSE, 4*sizeof(GLfloat), (void*)0);
    glEnableVertexAttribArray(pos_attr_loc);

    // Bind vertex texture coordinate attribute
    GLint tex_attr_loc = glGetAttribLocation(s->prog, "in_Texcoord");
    if (tex_attr_loc >= 0) {
        glVertexAttribPointer(tex_attr_loc, 2, GL_FLOAT, GL_FALSE, 4*sizeof(GLfloat), (void*)(2*sizeof(GLfloat)));
        glEnableVertexAttribArray(tex_attr_loc);
    }

    return s;
}

static GLuint load_texture(unsigned char *data, int width, int height, int channels)
{
    GLuint tex;
    glGenTextures(1, &tex);
    assert(tex != 0);
    glBindTexture(GL_TEXTURE_2D, tex);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL,  0);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,     GL_CLAMP_TO_BORDER);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,     GL_CLAMP_TO_BORDER);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_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, data);
    return tex;
}

GLuint load_texture_from_file(const char *name)
{
    // Flip vertically so textures are loaded according to GL convention.
    stbi_set_flip_vertically_on_load(1);

    // Read file into memory
    int width, height, channels = 0;
    unsigned char *data = stbi_load(name, &width, &height, &channels, 4);
    assert(data != NULL);

    GLuint tex = load_texture(data, width, height, channels);
    stbi_image_free(data);

    return tex;
}

GLuint load_texture_from_memory(const unsigned char *buf, unsigned int size)
{
    // Flip vertically so textures are loaded according to GL convention.
    stbi_set_flip_vertically_on_load(1);

    int width, height, channels = 0;
    unsigned char *data = stbi_load_from_memory(buf, size, &width, &height, &channels, 4);
    assert(data != NULL);

    GLuint tex = load_texture(data, width, height, channels);
    stbi_image_free(data);

    return tex;
}

void render_decal(
    struct decal_shader *s,
    float x,     float y,     float w,     float h,
    float tex_x, float tex_y, float tex_w, float tex_h,
    uint32_t primary, uint32_t secondary, uint32_t fill
    )
{
    GLint vp[4];
    glGetIntegerv(GL_VIEWPORT, vp);
    float ww = vp[2], wh = vp[3];

    x = (int)x;
    y = (int)y;
    w = (int)w;
    h = (int)h;
    tex_x = (int)tex_x;
    tex_y = (int)tex_y;
    tex_w = (int)tex_w;
    tex_h = (int)tex_h;

    int tw_i, th_i;
    glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_WIDTH,  &tw_i);
    glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_HEIGHT, &th_i);
    float tw = tw_i, th = th_i;

    #define COL(color, c) (float)(((color)>>((c)*8)) & 0xff)/255.0
    glUniform1i(s->FlipY_loc, s->flip);
    glUniform4f(s->ScaleOffset_loc,    w/ww,     h/wh,     -1+((2*x+w)/ww), -1+((2*y+h)/wh));
    glUniform4f(s->TexScaleOffset_loc, tex_w/tw, tex_h/th, tex_x/tw,        tex_y/th);
    glUniform1i(s->tex_loc, 0);
    glUniform4f(s->ColorPrimary_loc,   COL(primary,   3), COL(primary,   2), COL(primary,   1), COL(primary,   0));
    glUniform4f(s->ColorSecondary_loc, COL(secondary, 3), COL(secondary, 2), COL(secondary, 1), COL(secondary, 0));
    glUniform4f(s->ColorFill_loc,      COL(fill,      3), COL(fill,      2), COL(fill,      1), COL(fill,      0));
    if (s->time_loc >= 0) glUniform1f(s->time_loc, s->time/1000.0f);
    if (s->scale_loc >= 0) glUniform1f(s->scale_loc, s->scale);
    #undef COL
    glDrawElements(GL_TRIANGLE_FAN, 4, GL_UNSIGNED_INT, NULL);
}

void render_decal_image(
    struct decal_shader *s,
    float x,     float y,     float w,     float h,
    float tex_x, float tex_y, float tex_w, float tex_h
    )
{
    GLint vp[4];
    glGetIntegerv(GL_VIEWPORT, vp);
    float ww = vp[2], wh = vp[3];

    int tw_i, th_i;
    glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_WIDTH,  &tw_i);
    glGetTexLevelParameteriv(GL_TEXTURE_2D, 0, GL_TEXTURE_HEIGHT, &th_i);
    float tw = tw_i, th = th_i;

    glUniform1i(s->FlipY_loc, s->flip);
    glUniform4f(s->ScaleOffset_loc,    w/ww,     h/wh,     -1+((2*x+w)/ww), -1+((2*y+h)/wh));
    glUniform4f(s->TexScaleOffset_loc, tex_w/tw, tex_h/th, tex_x/tw,        tex_y/th);
    glUniform1i(s->tex_loc, 0);
    glDrawElements(GL_TRIANGLE_FAN, 4, GL_UNSIGNED_INT, NULL);
}

struct fbo *create_fbo(int width, int height)
{
    struct fbo *fbo = (struct fbo *)malloc(sizeof(struct fbo));
    assert(fbo != NULL);

    fbo->w = width;
    fbo->h = height;

    // Allocate the texture
    glGenTextures(1, &fbo->tex);
    glBindTexture(GL_TEXTURE_2D, fbo->tex);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAX_LEVEL,  0);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S,     GL_CLAMP_TO_BORDER);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T,     GL_CLAMP_TO_BORDER);
    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, fbo->w, fbo->h, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);

    // Allocate the framebuffer object
    glGenFramebuffers(1, &fbo->fbo);
    glBindFramebuffer(GL_FRAMEBUFFER, fbo->fbo);
    glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, fbo->tex, 0);
    GLenum DrawBuffers[1] = {GL_COLOR_ATTACHMENT0};
    glDrawBuffers(1, DrawBuffers);

    return fbo;
}

static GLboolean m_blend;

void render_to_default_fb(void)
{
    if (!m_blend) {
        glDisable(GL_BLEND);
    }

    // Restore default framebuffer, viewport, blending funciton
    glBindFramebuffer(GL_FRAMEBUFFER, main_fb);
    glViewport(vp[0], vp[1], vp[2], vp[3]);
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
}

GLuint render_to_fbo(struct fbo *fbo)
{
    m_blend = glIsEnabled(GL_BLEND);
    if (!m_blend) {
        glEnable(GL_BLEND);
    }
    glBindFramebuffer(GL_FRAMEBUFFER, fbo->fbo);
    glViewport(0, 0, fbo->w, fbo->h);
    glClearColor(0, 0, 0, 0);
    glClear(GL_COLOR_BUFFER_BIT);
    return fbo->tex;
}