// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// This example program is based on Simple_VertexShader.c from:
//
// Book:            OpenGL(R) ES 2.0 Programming Guide
// Authors:     Aaftab Munshi, Dan Ginsburg, Dave Shreiner
// ISBN-10:     0321502795
// ISBN-13:     9780321502797
// Publisher: Addison-Wesley Professional
// URLs:            http://safari.informit.com/9780321563835
//                        http://www.opengles-book.com
//

#include "spinning_cube.h"
#include <math.h>
#include <stdlib.h>
#include <string.h>
#include <algorithm>
#include "GLES2/gl2.h"

namespace {

const float kPi = 3.14159265359f;

int GenerateCube(GLuint *vbo_vertices, GLuint *vbo_indices) {
    const int num_indices = 36;
    const GLfloat cube_vertices[] = {
        -0.5f, -0.5f, -0.5f,
        -0.5f, -0.5f,  0.5f,
        0.5f, -0.5f,  0.5f,
        0.5f, -0.5f, -0.5f,
        -0.5f,  0.5f, -0.5f,
        -0.5f,  0.5f,  0.5f,
        0.5f,  0.5f,  0.5f,
        0.5f,  0.5f, -0.5f,
        -0.5f, -0.5f, -0.5f,
        -0.5f,  0.5f, -0.5f,
        0.5f,  0.5f, -0.5f,
        0.5f, -0.5f, -0.5f,
        -0.5f, -0.5f, 0.5f,
        -0.5f,  0.5f, 0.5f,
        0.5f,  0.5f, 0.5f,
        0.5f, -0.5f, 0.5f,
        -0.5f, -0.5f, -0.5f,
        -0.5f, -0.5f,  0.5f,
        -0.5f,  0.5f,  0.5f,
        -0.5f,  0.5f, -0.5f,
        0.5f, -0.5f, -0.5f,
        0.5f, -0.5f,  0.5f,
        0.5f,  0.5f,  0.5f,
        0.5f,  0.5f, -0.5f,
    };

    const GLushort cube_indices[] = {
         0,  2,  1,
         0,  3,  2,
         4,  5,  6,
         4,  6,  7,
         8,  9, 10,
         8, 10, 11,
        12, 15, 14,
        12, 14, 13,
        16, 17, 18,
        16, 18, 19,
        20, 23, 22,
        20, 22, 21
    };

    if (vbo_vertices) {
        glGenBuffers(1, vbo_vertices);
        glBindBuffer(GL_ARRAY_BUFFER, *vbo_vertices);
        glBufferData(GL_ARRAY_BUFFER,
                                 sizeof(cube_vertices),
                                 cube_vertices,
                                 GL_STATIC_DRAW);
        glBindBuffer(GL_ARRAY_BUFFER, 0);
    }

    if (vbo_indices) {
        glGenBuffers(1, vbo_indices);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, *vbo_indices);
        glBufferData(GL_ELEMENT_ARRAY_BUFFER,
                                 sizeof(cube_indices),
                                 cube_indices,
                                 GL_STATIC_DRAW);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    }

    return num_indices;
}

GLuint LoadShader(GLenum type, const char* shader_source) {
    GLuint shader = glCreateShader(type);
    glShaderSource(shader, 1, &shader_source, NULL);
    glCompileShader(shader);
    GLint compiled = 0;
    glGetShaderiv(shader, GL_COMPILE_STATUS, &compiled);
    if (!compiled) {
        glDeleteShader(shader);
        return 0;
    }
    return shader;
}

GLuint LoadProgram(const char* vertext_shader_source, const char* fragment_shader_source) {
    GLuint vertex_shader = LoadShader(GL_VERTEX_SHADER,
        vertext_shader_source);
    if (!vertex_shader)
        return 0;
    GLuint fragment_shader = LoadShader(GL_FRAGMENT_SHADER,
        fragment_shader_source);
    if (!fragment_shader) {
        glDeleteShader(vertex_shader);
        return 0;
    }
    GLuint program_object = glCreateProgram();
    glAttachShader(program_object, vertex_shader);
    glAttachShader(program_object, fragment_shader);
    glLinkProgram(program_object);
    glDeleteShader(vertex_shader);
    glDeleteShader(fragment_shader);
    GLint linked = 0;
    glGetProgramiv(program_object, GL_LINK_STATUS, &linked);
    if (!linked) {
        glDeleteProgram(program_object);
        return 0;
    }
    return program_object;
}

class ESMatrix {
public:
    GLfloat m[4][4];

    ESMatrix() {
        LoadZero();
    }

    void LoadZero() {
        memset(this, 0x0, sizeof(ESMatrix));
    }

    void LoadIdentity() {
        LoadZero();
        m[0][0] = 1.0f;
        m[1][1] = 1.0f;
        m[2][2] = 1.0f;
        m[3][3] = 1.0f;
    }

    void Multiply(ESMatrix* a, ESMatrix* b) {
        ESMatrix result;
        for (int i = 0; i < 4; ++i) {
            result.m[i][0] = (a->m[i][0] * b->m[0][0]) +
                     (a->m[i][1] * b->m[1][0]) +
                     (a->m[i][2] * b->m[2][0]) +
                     (a->m[i][3] * b->m[3][0]);
            result.m[i][1] = (a->m[i][0] * b->m[0][1]) +
                     (a->m[i][1] * b->m[1][1]) +
                     (a->m[i][2] * b->m[2][1]) +
                     (a->m[i][3] * b->m[3][1]);
            result.m[i][2] = (a->m[i][0] * b->m[0][2]) +
                     (a->m[i][1] * b->m[1][2]) +
                     (a->m[i][2] * b->m[2][2]) +
                     (a->m[i][3] * b->m[3][2]);
            result.m[i][3] = (a->m[i][0] * b->m[0][3]) +
                     (a->m[i][1] * b->m[1][3]) +
                     (a->m[i][2] * b->m[2][3]) +
                     (a->m[i][3] * b->m[3][3]);
        }
        *this = result;
    }

    void Frustum(float left,
                 float right,
                 float bottom,
                 float top,
                 float near_z,
                 float far_z) {
        float delta_x = right - left;
        float delta_y = top - bottom;
        float delta_z = far_z - near_z;
        if ((near_z <= 0.0f) ||
                (far_z <= 0.0f) ||
                (delta_z <= 0.0f) ||
                (delta_y <= 0.0f) ||
                (delta_y <= 0.0f))
            return;

        ESMatrix frust;
        frust.m[0][0] = 2.0f * near_z / delta_x;
        frust.m[0][1] = frust.m[0][2] = frust.m[0][3] = 0.0f;
        frust.m[1][1] = 2.0f * near_z / delta_y;
        frust.m[1][0] = frust.m[1][2] = frust.m[1][3] = 0.0f;
        frust.m[2][0] = (right + left) / delta_x;
        frust.m[2][1] = (top + bottom) / delta_y;
        frust.m[2][2] = -(near_z + far_z) / delta_z;
        frust.m[2][3] = -1.0f;
        frust.m[3][2] = -2.0f * near_z * far_z / delta_z;
        frust.m[3][0] = frust.m[3][1] = frust.m[3][3] = 0.0f;
        Multiply(&frust, this);
    }

    void Perspective(float fov_y, float aspect, float near_z, float far_z) {
        GLfloat frustum_h = tanf(fov_y / 360.0f * kPi) * near_z;
        GLfloat frustum_w = frustum_h * aspect;
        Frustum(-frustum_w, frustum_w, -frustum_h, frustum_h, near_z, far_z);
    }

    void Translate(GLfloat tx, GLfloat ty, GLfloat tz) {
        m[3][0] += m[0][0] * tx + m[1][0] * ty + m[2][0] * tz;
        m[3][1] += m[0][1] * tx + m[1][1] * ty + m[2][1] * tz;
        m[3][2] += m[0][2] * tx + m[1][2] * ty + m[2][2] * tz;
        m[3][3] += m[0][3] * tx + m[1][3] * ty + m[2][3] * tz;
    }

    void Rotate(GLfloat angle, GLfloat x, GLfloat y, GLfloat z) {
        GLfloat mag = sqrtf(x * x + y * y + z * z);
        GLfloat sin_angle = sinf(angle * kPi / 180.0f);
        GLfloat cos_angle = cosf(angle * kPi / 180.0f);
        if (mag > 0.0f) {
            GLfloat xx, yy, zz, xy, yz, zx, xs, ys, zs;
            GLfloat one_minus_cos;
            ESMatrix rotation;
            x /= mag;
            y /= mag;
            z /= mag;
            xx = x * x;
            yy = y * y;
            zz = z * z;
            xy = x * y;
            yz = y * z;
            zx = z * x;
            xs = x * sin_angle;
            ys = y * sin_angle;
            zs = z * sin_angle;
            one_minus_cos = 1.0f - cos_angle;
            rotation.m[0][0] = (one_minus_cos * xx) + cos_angle;
            rotation.m[0][1] = (one_minus_cos * xy) - zs;
            rotation.m[0][2] = (one_minus_cos * zx) + ys;
            rotation.m[0][3] = 0.0F;
            rotation.m[1][0] = (one_minus_cos * xy) + zs;
            rotation.m[1][1] = (one_minus_cos * yy) + cos_angle;
            rotation.m[1][2] = (one_minus_cos * yz) - xs;
            rotation.m[1][3] = 0.0F;
            rotation.m[2][0] = (one_minus_cos * zx) - ys;
            rotation.m[2][1] = (one_minus_cos * yz) + xs;
            rotation.m[2][2] = (one_minus_cos * zz) + cos_angle;
            rotation.m[2][3] = 0.0F;
            rotation.m[3][0] = 0.0F;
            rotation.m[3][1] = 0.0F;
            rotation.m[3][2] = 0.0F;
            rotation.m[3][3] = 1.0F;
            Multiply(&rotation, this);
        }
    }
};

float RotationForTimeDelta(float delta_time) {
    return delta_time * 40.0f;
}

float RotationForDragDistance(float drag_distance) {
    return drag_distance / 5; // Arbitrary damping.
}

}    // namespace

class SpinningCube::GLState {
public:
    GLState();
    void OnGLContextLost();
    GLfloat angle_;    // Survives losing the GL context.
    GLuint program_object_;
    GLint position_location_;
    GLint mvp_location_;
    GLuint vbo_vertices_;
    GLuint vbo_indices_;
    int num_indices_;
    ESMatrix mvp_matrix_;
};

SpinningCube::GLState::GLState()
        : angle_(0) {
    OnGLContextLost();
}

void SpinningCube::GLState::OnGLContextLost() {
    program_object_ = 0;
    position_location_ = 0;
    mvp_location_ = 0;
    vbo_vertices_ = 0;
    vbo_indices_ = 0;
    num_indices_ = 0;
}

SpinningCube::SpinningCube()
      : initialized_(false),
        width_(0),
        height_(0),
        state_(new GLState()),
        fling_multiplier_(1.0f),
        direction_(1) {
    state_->angle_ = 45.0f;
}

SpinningCube::~SpinningCube() {
    if (!initialized_)
        return;
    if (state_->vbo_vertices_)
        glDeleteBuffers(1, &state_->vbo_vertices_);
    if (state_->vbo_indices_)
        glDeleteBuffers(1, &state_->vbo_indices_);
    if (state_->program_object_)
        glDeleteProgram(state_->program_object_);
    delete state_;
}

void SpinningCube::Init(uint32_t width, uint32_t height) {
    width_ = width;
    height_ = height;
    if (!initialized_) {
        initialized_ = true;
        const char vertext_shader_source[] =
                "uniform mat4 u_mvpMatrix;\n"
                "attribute vec4 a_position;\n"
                "void main()\n"
                "{\n"
                "     gl_Position = u_mvpMatrix * a_position;\n"
                "}\n";
        const char fragment_shader_source[] =
                "precision mediump float;\n"
                "void main()\n"
                "{\n"
                "    gl_FragColor = vec4( 0.0, 0.0, 1.0, 1.0 );\n"
                "}\n";
        state_->program_object_ = LoadProgram(
                vertext_shader_source, fragment_shader_source);
        state_->position_location_ = glGetAttribLocation(
                state_->program_object_, "a_position");
        state_->mvp_location_ = glGetUniformLocation(
                state_->program_object_, "u_mvpMatrix");
        state_->num_indices_ = GenerateCube(
                &state_->vbo_vertices_, &state_->vbo_indices_);
        glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    }
}

void SpinningCube::OnGLContextLost() {
    // TODO(yzshen): Is it correct that in this case we don't need to do cleanup
    // for program and buffers?
    initialized_ = false;
    height_ = 0;
    width_ = 0;
    state_->OnGLContextLost();
}

void SpinningCube::SetFlingMultiplier(float drag_distance, float drag_time) {
    fling_multiplier_ = RotationForDragDistance(drag_distance) / RotationForTimeDelta(drag_time);
}

void SpinningCube::UpdateForTimeDelta(float delta_time) {
    state_->angle_ += RotationForTimeDelta(delta_time) * fling_multiplier_;
    if (state_->angle_ >= 360.0f)
        state_->angle_ -= 360.0f;
    // Arbitrary 50-step linear reduction in spin speed.
    if (fling_multiplier_ > 1.0f) {
        fling_multiplier_ = std::max(1.0f, fling_multiplier_ - (fling_multiplier_ - 1.0f) / 50);
    }
    Update();
}

void SpinningCube::UpdateForDragDistance(float distance) {
    state_->angle_ += RotationForDragDistance(distance);
    if (state_->angle_ >= 360.0f )
        state_->angle_ -= 360.0f;
    Update();
}

void SpinningCube::Draw() {
    glViewport(0, 0, width_, height_);
    glClear(GL_COLOR_BUFFER_BIT);
    glUseProgram(state_->program_object_);
    glBindBuffer(GL_ARRAY_BUFFER, state_->vbo_vertices_);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, state_->vbo_indices_);
    glVertexAttribPointer(state_->position_location_, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), 0);
    glEnableVertexAttribArray(state_->position_location_);
    glUniformMatrix4fv(state_->mvp_location_, 1, GL_FALSE, (GLfloat*) &state_->mvp_matrix_.m[0][0]);
    glDrawElements(GL_TRIANGLES, state_->num_indices_, GL_UNSIGNED_SHORT, 0);
}

void SpinningCube::Update() {
    float aspect = static_cast<GLfloat>(width_) / static_cast<GLfloat>(height_);
    ESMatrix perspective;
    perspective.LoadIdentity();
    perspective.Perspective(60.0f, aspect, 1.0f, 20.0f );
    ESMatrix modelview;
    modelview.LoadIdentity();
    modelview.Translate(0.0, 0.0, -2.0);
    modelview.Rotate(state_->angle_ * direction_, 1.0, 0.0, 1.0);
    state_->mvp_matrix_.Multiply(&modelview, &perspective);
}