/*
 *  Copyright 2018 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.
 */

package org.webrtc;

import android.opengl.GLES11Ext;
import android.opengl.GLES20;
import android.support.annotation.Nullable;
import java.nio.FloatBuffer;
import org.webrtc.GlShader;
import org.webrtc.GlUtil;
import org.webrtc.RendererCommon;

/**
 * Helper class to implement an instance of RendererCommon.GlDrawer that can accept multiple input
 * sources (OES, RGB, or YUV) using a generic fragment shader as input. The generic fragment shader
 * should sample pixel values from the function "sample" that will be provided by this class and
 * provides an abstraction for the input source type (OES, RGB, or YUV). The texture coordinate
 * variable name will be "tc" and the texture matrix in the vertex shader will be "tex_mat". The
 * simplest possible generic shader that just draws pixel from the frame unmodified looks like:
 * void main() {
 *   gl_FragColor = sample(tc);
 * }
 * This class covers the cases for most simple shaders and generates the necessary boiler plate.
 * Advanced shaders can always implement RendererCommon.GlDrawer directly.
 */
class GlGenericDrawer implements RendererCommon.GlDrawer {
  /**
   * The different shader types representing different input sources. YUV here represents three
   * separate Y, U, V textures.
   */
  public static enum ShaderType { OES, RGB, YUV }

  /**
   * The shader callbacks is used to customize behavior for a GlDrawer. It provides a hook to set
   * uniform variables in the shader before a frame is drawn.
   */
  public static interface ShaderCallbacks {
    /**
     * This callback is called when a new shader has been compiled and created. It will be called
     * for the first frame as well as when the shader type is changed. This callback can be used to
     * do custom initialization of the shader that only needs to happen once.
     */
    void onNewShader(GlShader shader);

    /**
     * This callback is called before rendering a frame. It can be used to do custom preparation of
     * the shader that needs to happen every frame.
     */
    void onPrepareShader(GlShader shader, float[] texMatrix, int frameWidth, int frameHeight,
        int viewportWidth, int viewportHeight);
  }

  private static final String INPUT_VERTEX_COORDINATE_NAME = "in_pos";
  private static final String INPUT_TEXTURE_COORDINATE_NAME = "in_tc";
  private static final String TEXTURE_MATRIX_NAME = "tex_mat";
  private static final String DEFAULT_VERTEX_SHADER_STRING = "varying vec2 tc;\n"
      + "attribute vec4 in_pos;\n"
      + "attribute vec4 in_tc;\n"
      + "uniform mat4 tex_mat;\n"
      + "void main() {\n"
      + "  gl_Position = in_pos;\n"
      + "  tc = (tex_mat * in_tc).xy;\n"
      + "}\n";

  // Vertex coordinates in Normalized Device Coordinates, i.e. (-1, -1) is bottom-left and (1, 1)
  // is top-right.
  private static final FloatBuffer FULL_RECTANGLE_BUFFER = GlUtil.createFloatBuffer(new float[] {
      -1.0f, -1.0f, // Bottom left.
      1.0f, -1.0f, // Bottom right.
      -1.0f, 1.0f, // Top left.
      1.0f, 1.0f, // Top right.
  });

  // Texture coordinates - (0, 0) is bottom-left and (1, 1) is top-right.
  private static final FloatBuffer FULL_RECTANGLE_TEXTURE_BUFFER =
      GlUtil.createFloatBuffer(new float[] {
          0.0f, 0.0f, // Bottom left.
          1.0f, 0.0f, // Bottom right.
          0.0f, 1.0f, // Top left.
          1.0f, 1.0f, // Top right.
      });

  static String createFragmentShaderString(String genericFragmentSource, ShaderType shaderType) {
    final StringBuilder stringBuilder = new StringBuilder();
    if (shaderType == ShaderType.OES) {
      stringBuilder.append("#extension GL_OES_EGL_image_external : require\n");
    }
    stringBuilder.append("precision mediump float;\n");
    stringBuilder.append("varying vec2 tc;\n");

    if (shaderType == ShaderType.YUV) {
      stringBuilder.append("uniform sampler2D y_tex;\n");
      stringBuilder.append("uniform sampler2D u_tex;\n");
      stringBuilder.append("uniform sampler2D v_tex;\n");

      // Add separate function for sampling texture.
      // yuv_to_rgb_mat is inverse of the matrix defined in YuvConverter.
      stringBuilder.append("vec4 sample(vec2 p) {\n");
      stringBuilder.append("  float y = texture2D(y_tex, p).r * 1.16438;\n");
      stringBuilder.append("  float u = texture2D(u_tex, p).r;\n");
      stringBuilder.append("  float v = texture2D(v_tex, p).r;\n");
      stringBuilder.append("  return vec4(y + 1.59603 * v - 0.874202,\n");
      stringBuilder.append("    y - 0.391762 * u - 0.812968 * v + 0.531668,\n");
      stringBuilder.append("    y + 2.01723 * u - 1.08563, 1);\n");
      stringBuilder.append("}\n");
      stringBuilder.append(genericFragmentSource);
    } else {
      final String samplerName = shaderType == ShaderType.OES ? "samplerExternalOES" : "sampler2D";
      stringBuilder.append("uniform ").append(samplerName).append(" tex;\n");

      // Update the sampling function in-place.
      stringBuilder.append(genericFragmentSource.replace("sample(", "texture2D(tex, "));
    }

    return stringBuilder.toString();
  }

  private final String genericFragmentSource;
  private final String vertexShader;
  private final ShaderCallbacks shaderCallbacks;
  @Nullable private ShaderType currentShaderType;
  @Nullable private GlShader currentShader;
  private int inPosLocation;
  private int inTcLocation;
  private int texMatrixLocation;

  public GlGenericDrawer(String genericFragmentSource, ShaderCallbacks shaderCallbacks) {
    this(DEFAULT_VERTEX_SHADER_STRING, genericFragmentSource, shaderCallbacks);
  }

  public GlGenericDrawer(
      String vertexShader, String genericFragmentSource, ShaderCallbacks shaderCallbacks) {
    this.vertexShader = vertexShader;
    this.genericFragmentSource = genericFragmentSource;
    this.shaderCallbacks = shaderCallbacks;
  }

  // Visible for testing.
  GlShader createShader(ShaderType shaderType) {
    return new GlShader(
        vertexShader, createFragmentShaderString(genericFragmentSource, shaderType));
  }

  /**
   * Draw an OES texture frame with specified texture transformation matrix. Required resources are
   * allocated at the first call to this function.
   */
  @Override
  public void drawOes(int oesTextureId, float[] texMatrix, int frameWidth, int frameHeight,
      int viewportX, int viewportY, int viewportWidth, int viewportHeight) {
    prepareShader(
        ShaderType.OES, texMatrix, frameWidth, frameHeight, viewportWidth, viewportHeight);
    // Bind the texture.
    GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
    GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, oesTextureId);
    // Draw the texture.
    GLES20.glViewport(viewportX, viewportY, viewportWidth, viewportHeight);
    GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
    // Unbind the texture as a precaution.
    GLES20.glBindTexture(GLES11Ext.GL_TEXTURE_EXTERNAL_OES, 0);
  }

  /**
   * Draw a RGB(A) texture frame with specified texture transformation matrix. Required resources
   * are allocated at the first call to this function.
   */
  @Override
  public void drawRgb(int textureId, float[] texMatrix, int frameWidth, int frameHeight,
      int viewportX, int viewportY, int viewportWidth, int viewportHeight) {
    prepareShader(
        ShaderType.RGB, texMatrix, frameWidth, frameHeight, viewportWidth, viewportHeight);
    // Bind the texture.
    GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textureId);
    // Draw the texture.
    GLES20.glViewport(viewportX, viewportY, viewportWidth, viewportHeight);
    GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
    // Unbind the texture as a precaution.
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);
  }

  /**
   * Draw a YUV frame with specified texture transformation matrix. Required resources are allocated
   * at the first call to this function.
   */
  @Override
  public void drawYuv(int[] yuvTextures, float[] texMatrix, int frameWidth, int frameHeight,
      int viewportX, int viewportY, int viewportWidth, int viewportHeight) {
    prepareShader(
        ShaderType.YUV, texMatrix, frameWidth, frameHeight, viewportWidth, viewportHeight);
    // Bind the textures.
    for (int i = 0; i < 3; ++i) {
      GLES20.glActiveTexture(GLES20.GL_TEXTURE0 + i);
      GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, yuvTextures[i]);
    }
    // Draw the textures.
    GLES20.glViewport(viewportX, viewportY, viewportWidth, viewportHeight);
    GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);
    // Unbind the textures as a precaution.
    for (int i = 0; i < 3; ++i) {
      GLES20.glActiveTexture(GLES20.GL_TEXTURE0 + i);
      GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);
    }
  }

  private void prepareShader(ShaderType shaderType, float[] texMatrix, int frameWidth,
      int frameHeight, int viewportWidth, int viewportHeight) {
    final GlShader shader;
    if (shaderType.equals(currentShaderType)) {
      // Same shader type as before, reuse exising shader.
      shader = currentShader;
    } else {
      // Allocate new shader.
      currentShaderType = shaderType;
      if (currentShader != null) {
        currentShader.release();
      }
      shader = createShader(shaderType);
      currentShader = shader;

      shader.useProgram();
      // Set input texture units.
      if (shaderType == ShaderType.YUV) {
        GLES20.glUniform1i(shader.getUniformLocation("y_tex"), 0);
        GLES20.glUniform1i(shader.getUniformLocation("u_tex"), 1);
        GLES20.glUniform1i(shader.getUniformLocation("v_tex"), 2);
      } else {
        GLES20.glUniform1i(shader.getUniformLocation("tex"), 0);
      }

      GlUtil.checkNoGLES2Error("Create shader");
      shaderCallbacks.onNewShader(shader);
      texMatrixLocation = shader.getUniformLocation(TEXTURE_MATRIX_NAME);
      inPosLocation = shader.getAttribLocation(INPUT_VERTEX_COORDINATE_NAME);
      inTcLocation = shader.getAttribLocation(INPUT_TEXTURE_COORDINATE_NAME);
    }

    shader.useProgram();

    // Upload the vertex coordinates.
    GLES20.glEnableVertexAttribArray(inPosLocation);
    GLES20.glVertexAttribPointer(inPosLocation, /* size= */ 2,
        /* type= */ GLES20.GL_FLOAT, /* normalized= */ false, /* stride= */ 0,
        FULL_RECTANGLE_BUFFER);

    // Upload the texture coordinates.
    GLES20.glEnableVertexAttribArray(inTcLocation);
    GLES20.glVertexAttribPointer(inTcLocation, /* size= */ 2,
        /* type= */ GLES20.GL_FLOAT, /* normalized= */ false, /* stride= */ 0,
        FULL_RECTANGLE_TEXTURE_BUFFER);

    // Upload the texture transformation matrix.
    GLES20.glUniformMatrix4fv(
        texMatrixLocation, 1 /* count= */, false /* transpose= */, texMatrix, 0 /* offset= */);

    // Do custom per-frame shader preparation.
    shaderCallbacks.onPrepareShader(
        shader, texMatrix, frameWidth, frameHeight, viewportWidth, viewportHeight);
    GlUtil.checkNoGLES2Error("Prepare shader");
  }

  /**
   * Release all GLES resources. This needs to be done manually, otherwise the resources are leaked.
   */
  @Override
  public void release() {
    if (currentShader != null) {
      currentShader.release();
      currentShader = null;
      currentShaderType = null;
    }
  }
}