/*
 *  Copyright 2016 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#import "RTCShader.h"

#include <algorithm>
#include <array>
#include <memory>

#import "RTCShader+Private.h"

#include "webrtc/base/checks.h"
#include "webrtc/base/logging.h"

// Vertex shader doesn't do anything except pass coordinates through.
const char kRTCVertexShaderSource[] =
  SHADER_VERSION
  VERTEX_SHADER_IN " vec2 position;\n"
  VERTEX_SHADER_IN " vec2 texcoord;\n"
  VERTEX_SHADER_OUT " vec2 v_texcoord;\n"
  "void main() {\n"
  "    gl_Position = vec4(position.x, position.y, 0.0, 1.0);\n"
  "    v_texcoord = texcoord;\n"
  "}\n";

// Compiles a shader of the given |type| with GLSL source |source| and returns
// the shader handle or 0 on error.
GLuint RTCCreateShader(GLenum type, const GLchar *source) {
  GLuint shader = glCreateShader(type);
  if (!shader) {
    return 0;
  }
  glShaderSource(shader, 1, &source, NULL);
  glCompileShader(shader);
  GLint compileStatus = GL_FALSE;
  glGetShaderiv(shader, GL_COMPILE_STATUS, &compileStatus);
  if (compileStatus == GL_FALSE) {
    GLint logLength = 0;
    // The null termination character is included in the returned log length.
    glGetShaderiv(shader, GL_INFO_LOG_LENGTH, &logLength);
    if (logLength > 0) {
      std::unique_ptr<char[]> compileLog(new char[logLength]);
      // The returned string is null terminated.
      glGetShaderInfoLog(shader, logLength, NULL, compileLog.get());
      LOG(LS_ERROR) << "Shader compile error: " << compileLog.get();
    }
    glDeleteShader(shader);
    shader = 0;
  }
  return shader;
}

// Links a shader program with the given vertex and fragment shaders and
// returns the program handle or 0 on error.
GLuint RTCCreateProgram(GLuint vertexShader, GLuint fragmentShader) {
  if (vertexShader == 0 || fragmentShader == 0) {
    return 0;
  }
  GLuint program = glCreateProgram();
  if (!program) {
    return 0;
  }
  glAttachShader(program, vertexShader);
  glAttachShader(program, fragmentShader);
  glLinkProgram(program);
  GLint linkStatus = GL_FALSE;
  glGetProgramiv(program, GL_LINK_STATUS, &linkStatus);
  if (linkStatus == GL_FALSE) {
    glDeleteProgram(program);
    program = 0;
  }
  return program;
}

// Creates and links a shader program with the given fragment shader source and
// a plain vertex shader. Returns the program handle or 0 on error.
GLuint RTCCreateProgramFromFragmentSource(const char fragmentShaderSource[]) {
  GLuint vertexShader = RTCCreateShader(GL_VERTEX_SHADER, kRTCVertexShaderSource);
  RTC_CHECK(vertexShader) << "failed to create vertex shader";
  GLuint fragmentShader =
      RTCCreateShader(GL_FRAGMENT_SHADER, fragmentShaderSource);
  RTC_CHECK(fragmentShader) << "failed to create fragment shader";
  GLuint program = RTCCreateProgram(vertexShader, fragmentShader);
  // Shaders are created only to generate program.
  if (vertexShader) {
    glDeleteShader(vertexShader);
  }
  if (fragmentShader) {
    glDeleteShader(fragmentShader);
  }
  return program;
}

// Set vertex shader variables 'position' and 'texcoord' in |program| to use
// |vertexBuffer| and |vertexArray| to store the vertex data.
BOOL RTCSetupVerticesForProgram(GLuint program, GLuint* vertexBuffer, GLuint* vertexArray) {
  GLint position = glGetAttribLocation(program, "position");
  GLint texcoord = glGetAttribLocation(program, "texcoord");
  if (position < 0 || texcoord < 0) {
    return NO;
  }
#if !TARGET_OS_IPHONE
  glGenVertexArrays(1, vertexArray);
  if (*vertexArray == 0) {
    return NO;
  }
  glBindVertexArray(*vertexArray);
#endif
  glGenBuffers(1, vertexBuffer);
  if (*vertexBuffer == 0) {
    return NO;
  }
  glBindBuffer(GL_ARRAY_BUFFER, *vertexBuffer);
  glBufferData(GL_ARRAY_BUFFER, 4 * 4 * sizeof(GLfloat), NULL, GL_DYNAMIC_DRAW);

  // Read position attribute with size of 2 and stride of 4 beginning at the
  // start of the array. The last argument indicates offset of data within the
  // vertex buffer.
  glVertexAttribPointer(position, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat),
                        (void *)0);
  glEnableVertexAttribArray(position);

  // Read texcoord attribute from |gVertices| with size of 2 and stride of 4
  // beginning at the first texcoord in the array. The last argument indicates
  // offset of data within |gVertices| as supplied to the vertex buffer.
  glVertexAttribPointer(texcoord, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat),
                        (void *)(2 * sizeof(GLfloat)));
  glEnableVertexAttribArray(texcoord);

  return YES;
}

// Set vertex data to the currently bound vertex buffer.
void RTCSetVertexData(webrtc::VideoRotation rotation) {
  // When modelview and projection matrices are identity (default) the world is
  // contained in the square around origin with unit size 2. Drawing to these
  // coordinates is equivalent to drawing to the entire screen. The texture is
  // stretched over that square using texture coordinates (u, v) that range
  // from (0, 0) to (1, 1) inclusive. Texture coordinates are flipped vertically
  // here because the incoming frame has origin in upper left hand corner but
  // OpenGL expects origin in bottom left corner.
  std::array<std::array<GLfloat, 2>, 4> UVCoords = {{
      {{0, 1}},  // Lower left.
      {{1, 1}},  // Lower right.
      {{1, 0}},  // Upper right.
      {{0, 0}},  // Upper left.
  }};

  // Rotate the UV coordinates.
  int rotation_offset;
  switch (rotation) {
    case webrtc::kVideoRotation_0:
      rotation_offset = 0;
      break;
    case webrtc::kVideoRotation_90:
      rotation_offset = 1;
      break;
    case webrtc::kVideoRotation_180:
      rotation_offset = 2;
      break;
    case webrtc::kVideoRotation_270:
      rotation_offset = 3;
      break;
  }
  std::rotate(UVCoords.begin(), UVCoords.begin() + rotation_offset,
              UVCoords.end());

  const GLfloat gVertices[] = {
      // X, Y, U, V.
      -1, -1, UVCoords[0][0], UVCoords[0][1],
       1, -1, UVCoords[1][0], UVCoords[1][1],
       1,  1, UVCoords[2][0], UVCoords[2][1],
      -1,  1, UVCoords[3][0], UVCoords[3][1],
  };

  glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(gVertices), gVertices);
}