/*
 * Copyright 2017 Google LLC
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.ar.core.examples.java.common.rendering;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.opengl.GLES20;
import android.opengl.GLSurfaceView;
import android.opengl.GLUtils;
import android.opengl.Matrix;
import com.google.ar.core.Camera;
import com.google.ar.core.Plane;
import com.google.ar.core.Pose;
import com.google.ar.core.TrackingState;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;
import java.nio.ShortBuffer;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/** Renders the detected AR planes. */
public class PlaneRenderer {
  private static final String TAG = PlaneRenderer.class.getSimpleName();

  // Shader names.
  private static final String VERTEX_SHADER_NAME = "shaders/plane.vert";
  private static final String FRAGMENT_SHADER_NAME = "shaders/plane.frag";

  private static final int BYTES_PER_FLOAT = Float.SIZE / 8;
  private static final int BYTES_PER_SHORT = Short.SIZE / 8;
  private static final int COORDS_PER_VERTEX = 3; // x, z, alpha

  private static final int VERTS_PER_BOUNDARY_VERT = 2;
  private static final int INDICES_PER_BOUNDARY_VERT = 3;
  private static final int INITIAL_BUFFER_BOUNDARY_VERTS = 64;

  private static final int INITIAL_VERTEX_BUFFER_SIZE_BYTES =
      BYTES_PER_FLOAT * COORDS_PER_VERTEX * VERTS_PER_BOUNDARY_VERT * INITIAL_BUFFER_BOUNDARY_VERTS;

  private static final int INITIAL_INDEX_BUFFER_SIZE_BYTES =
      BYTES_PER_SHORT
          * INDICES_PER_BOUNDARY_VERT
          * INDICES_PER_BOUNDARY_VERT
          * INITIAL_BUFFER_BOUNDARY_VERTS;

  private static final float FADE_RADIUS_M = 0.25f;
  private static final float DOTS_PER_METER = 10.0f;
  private static final float EQUILATERAL_TRIANGLE_SCALE = (float) (1 / Math.sqrt(3));

  // Using the "signed distance field" approach to render sharp lines and circles.
  // {dotThreshold, lineThreshold, lineFadeSpeed, occlusionScale}
  // dotThreshold/lineThreshold: red/green intensity above which dots/lines are present
  // lineFadeShrink:  lines will fade in between alpha = 1-(1/lineFadeShrink) and 1.0
  // occlusionShrink: occluded planes will fade out between alpha = 0 and 1/occlusionShrink
  private static final float[] GRID_CONTROL = {0.2f, 0.4f, 2.0f, 1.5f};

  private int planeProgram;
  private final int[] textures = new int[1];

  private int planeXZPositionAlphaAttribute;

  private int planeModelUniform;
  private int planeNormalUniform;
  private int planeModelViewProjectionUniform;
  private int textureUniform;
  private int gridControlUniform;
  private int planeUvMatrixUniform;

  private FloatBuffer vertexBuffer =
      ByteBuffer.allocateDirect(INITIAL_VERTEX_BUFFER_SIZE_BYTES)
          .order(ByteOrder.nativeOrder())
          .asFloatBuffer();
  private ShortBuffer indexBuffer =
      ByteBuffer.allocateDirect(INITIAL_INDEX_BUFFER_SIZE_BYTES)
          .order(ByteOrder.nativeOrder())
          .asShortBuffer();

  // Temporary lists/matrices allocated here to reduce number of allocations for each frame.
  private final float[] modelMatrix = new float[16];
  private final float[] modelViewMatrix = new float[16];
  private final float[] modelViewProjectionMatrix = new float[16];
  private final float[] planeAngleUvMatrix =
      new float[4]; // 2x2 rotation matrix applied to uv coords.

  private final Map<Plane, Integer> planeIndexMap = new HashMap<>();

  public PlaneRenderer() {}

  /**
   * Allocates and initializes OpenGL resources needed by the plane renderer. Must be called on the
   * OpenGL thread, typically in {@link GLSurfaceView.Renderer#onSurfaceCreated(GL10, EGLConfig)}.
   *
   * @param context Needed to access shader source and texture PNG.
   * @param gridDistanceTextureName Name of the PNG file containing the grid texture.
   */
  public void createOnGlThread(Context context, String gridDistanceTextureName) throws IOException {
    int vertexShader =
        ShaderUtil.loadGLShader(TAG, context, GLES20.GL_VERTEX_SHADER, VERTEX_SHADER_NAME);
    int passthroughShader =
        ShaderUtil.loadGLShader(TAG, context, GLES20.GL_FRAGMENT_SHADER, FRAGMENT_SHADER_NAME);

    planeProgram = GLES20.glCreateProgram();
    GLES20.glAttachShader(planeProgram, vertexShader);
    GLES20.glAttachShader(planeProgram, passthroughShader);
    GLES20.glLinkProgram(planeProgram);
    GLES20.glUseProgram(planeProgram);

    ShaderUtil.checkGLError(TAG, "Program creation");

    // Read the texture.
    Bitmap textureBitmap =
        BitmapFactory.decodeStream(context.getAssets().open(gridDistanceTextureName));

    GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
    GLES20.glGenTextures(textures.length, textures, 0);
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textures[0]);

    GLES20.glTexParameteri(
        GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER, GLES20.GL_LINEAR_MIPMAP_LINEAR);
    GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MAG_FILTER, GLES20.GL_LINEAR);
    GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, textureBitmap, 0);
    GLES20.glGenerateMipmap(GLES20.GL_TEXTURE_2D);
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);

    ShaderUtil.checkGLError(TAG, "Texture loading");

    planeXZPositionAlphaAttribute = GLES20.glGetAttribLocation(planeProgram, "a_XZPositionAlpha");

    planeModelUniform = GLES20.glGetUniformLocation(planeProgram, "u_Model");
    planeNormalUniform = GLES20.glGetUniformLocation(planeProgram, "u_Normal");
    planeModelViewProjectionUniform =
        GLES20.glGetUniformLocation(planeProgram, "u_ModelViewProjection");
    textureUniform = GLES20.glGetUniformLocation(planeProgram, "u_Texture");
    gridControlUniform = GLES20.glGetUniformLocation(planeProgram, "u_gridControl");
    planeUvMatrixUniform = GLES20.glGetUniformLocation(planeProgram, "u_PlaneUvMatrix");

    ShaderUtil.checkGLError(TAG, "Program parameters");
  }

  /** Updates the plane model transform matrix and extents. */
  private void updatePlaneParameters(
      float[] planeMatrix, float extentX, float extentZ, FloatBuffer boundary) {
    System.arraycopy(planeMatrix, 0, modelMatrix, 0, 16);
    if (boundary == null) {
      vertexBuffer.limit(0);
      indexBuffer.limit(0);
      return;
    }

    // Generate a new set of vertices and a corresponding triangle strip index set so that
    // the plane boundary polygon has a fading edge. This is done by making a copy of the
    // boundary polygon vertices and scaling it down around center to push it inwards. Then
    // the index buffer is setup accordingly.
    boundary.rewind();
    int boundaryVertices = boundary.limit() / 2;
    int numVertices;
    int numIndices;

    numVertices = boundaryVertices * VERTS_PER_BOUNDARY_VERT;
    // drawn as GL_TRIANGLE_STRIP with 3n-2 triangles (n-2 for fill, 2n for perimeter).
    numIndices = boundaryVertices * INDICES_PER_BOUNDARY_VERT;

    if (vertexBuffer.capacity() < numVertices * COORDS_PER_VERTEX) {
      int size = vertexBuffer.capacity();
      while (size < numVertices * COORDS_PER_VERTEX) {
        size *= 2;
      }
      vertexBuffer =
          ByteBuffer.allocateDirect(BYTES_PER_FLOAT * size)
              .order(ByteOrder.nativeOrder())
              .asFloatBuffer();
    }
    vertexBuffer.rewind();
    vertexBuffer.limit(numVertices * COORDS_PER_VERTEX);

    if (indexBuffer.capacity() < numIndices) {
      int size = indexBuffer.capacity();
      while (size < numIndices) {
        size *= 2;
      }
      indexBuffer =
          ByteBuffer.allocateDirect(BYTES_PER_SHORT * size)
              .order(ByteOrder.nativeOrder())
              .asShortBuffer();
    }
    indexBuffer.rewind();
    indexBuffer.limit(numIndices);

    // Note: when either dimension of the bounding box is smaller than 2*FADE_RADIUS_M we
    // generate a bunch of 0-area triangles.  These don't get rendered though so it works
    // out ok.
    float xScale = Math.max((extentX - 2 * FADE_RADIUS_M) / extentX, 0.0f);
    float zScale = Math.max((extentZ - 2 * FADE_RADIUS_M) / extentZ, 0.0f);

    while (boundary.hasRemaining()) {
      float x = boundary.get();
      float z = boundary.get();
      vertexBuffer.put(x);
      vertexBuffer.put(z);
      vertexBuffer.put(0.0f);
      vertexBuffer.put(x * xScale);
      vertexBuffer.put(z * zScale);
      vertexBuffer.put(1.0f);
    }

    // step 1, perimeter
    indexBuffer.put((short) ((boundaryVertices - 1) * 2));
    for (int i = 0; i < boundaryVertices; ++i) {
      indexBuffer.put((short) (i * 2));
      indexBuffer.put((short) (i * 2 + 1));
    }
    indexBuffer.put((short) 1);
    // This leaves us on the interior edge of the perimeter between the inset vertices
    // for boundary verts n-1 and 0.

    // step 2, interior:
    for (int i = 1; i < boundaryVertices / 2; ++i) {
      indexBuffer.put((short) ((boundaryVertices - 1 - i) * 2 + 1));
      indexBuffer.put((short) (i * 2 + 1));
    }
    if (boundaryVertices % 2 != 0) {
      indexBuffer.put((short) ((boundaryVertices / 2) * 2 + 1));
    }
  }

  private void draw(float[] cameraView, float[] cameraPerspective, float[] planeNormal) {
    // Build the ModelView and ModelViewProjection matrices
    // for calculating cube position and light.
    Matrix.multiplyMM(modelViewMatrix, 0, cameraView, 0, modelMatrix, 0);
    Matrix.multiplyMM(modelViewProjectionMatrix, 0, cameraPerspective, 0, modelViewMatrix, 0);

    // Set the position of the plane
    vertexBuffer.rewind();
    GLES20.glVertexAttribPointer(
        planeXZPositionAlphaAttribute,
        COORDS_PER_VERTEX,
        GLES20.GL_FLOAT,
        false,
        BYTES_PER_FLOAT * COORDS_PER_VERTEX,
        vertexBuffer);

    // Set the Model and ModelViewProjection matrices in the shader.
    GLES20.glUniformMatrix4fv(planeModelUniform, 1, false, modelMatrix, 0);
    GLES20.glUniform3f(planeNormalUniform, planeNormal[0], planeNormal[1], planeNormal[2]);
    GLES20.glUniformMatrix4fv(
        planeModelViewProjectionUniform, 1, false, modelViewProjectionMatrix, 0);

    indexBuffer.rewind();
    GLES20.glDrawElements(
        GLES20.GL_TRIANGLE_STRIP, indexBuffer.limit(), GLES20.GL_UNSIGNED_SHORT, indexBuffer);
    ShaderUtil.checkGLError(TAG, "Drawing plane");
  }

  static class SortablePlane {
    final float distance;
    final Plane plane;

    SortablePlane(float distance, Plane plane) {
      this.distance = distance;
      this.plane = plane;
    }
  }

  /**
   * Draws the collection of tracked planes, with closer planes hiding more distant ones.
   *
   * @param allPlanes The collection of planes to draw.
   * @param cameraPose The pose of the camera, as returned by {@link Camera#getPose()}
   * @param cameraPerspective The projection matrix, as returned by {@link
   *     Camera#getProjectionMatrix(float[], int, float, float)}
   */
  public void drawPlanes(Collection<Plane> allPlanes, Pose cameraPose, float[] cameraPerspective) {
    // Planes must be sorted by distance from camera so that we draw closer planes first, and
    // they occlude the farther planes.
    List<SortablePlane> sortedPlanes = new ArrayList<>();

    for (Plane plane : allPlanes) {
      if (plane.getTrackingState() != TrackingState.TRACKING || plane.getSubsumedBy() != null) {
        continue;
      }

      float distance = calculateDistanceToPlane(plane.getCenterPose(), cameraPose);
      if (distance < 0) { // Plane is back-facing.
        continue;
      }
      sortedPlanes.add(new SortablePlane(distance, plane));
    }
    Collections.sort(
        sortedPlanes,
        new Comparator<SortablePlane>() {
          @Override
          public int compare(SortablePlane a, SortablePlane b) {
            return Float.compare(b.distance, a.distance);
          }
        });

    float[] cameraView = new float[16];
    cameraPose.inverse().toMatrix(cameraView, 0);

    // Disable depth write.
    GLES20.glDepthMask(false);

    // Normal alpha blending with premultiplied alpha.
    GLES20.glEnable(GLES20.GL_BLEND);
    GLES20.glBlendFunc(GLES20.GL_ONE, GLES20.GL_ONE_MINUS_SRC_ALPHA);

    // Set up the shader.
    GLES20.glUseProgram(planeProgram);

    // Attach the texture.
    GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, textures[0]);
    GLES20.glUniform1i(textureUniform, 0);

    // Shared fragment uniforms.
    GLES20.glUniform4fv(gridControlUniform, 1, GRID_CONTROL, 0);

    // Enable vertex arrays
    GLES20.glEnableVertexAttribArray(planeXZPositionAlphaAttribute);

    ShaderUtil.checkGLError(TAG, "Setting up to draw planes");

    for (SortablePlane sortedPlane : sortedPlanes) {
      Plane plane = sortedPlane.plane;
      float[] planeMatrix = new float[16];
      plane.getCenterPose().toMatrix(planeMatrix, 0);

      float[] normal = new float[3];
      // Get transformed Y axis of plane's coordinate system.
      plane.getCenterPose().getTransformedAxis(1, 1.0f, normal, 0);

      updatePlaneParameters(
          planeMatrix, plane.getExtentX(), plane.getExtentZ(), plane.getPolygon());

      // Get plane index. Keep a map to assign same indices to same planes.
      Integer planeIndex = planeIndexMap.get(plane);
      if (planeIndex == null) {
        planeIndex = planeIndexMap.size();
        planeIndexMap.put(plane, planeIndex);
      }

      // Each plane will have its own angle offset from others, to make them easier to
      // distinguish. Compute a 2x2 rotation matrix from the angle.
      float angleRadians = planeIndex * 0.144f;
      float uScale = DOTS_PER_METER;
      float vScale = DOTS_PER_METER * EQUILATERAL_TRIANGLE_SCALE;
      planeAngleUvMatrix[0] = +(float) Math.cos(angleRadians) * uScale;
      planeAngleUvMatrix[1] = -(float) Math.sin(angleRadians) * vScale;
      planeAngleUvMatrix[2] = +(float) Math.sin(angleRadians) * uScale;
      planeAngleUvMatrix[3] = +(float) Math.cos(angleRadians) * vScale;
      GLES20.glUniformMatrix2fv(planeUvMatrixUniform, 1, false, planeAngleUvMatrix, 0);

      draw(cameraView, cameraPerspective, normal);
    }

    // Clean up the state we set
    GLES20.glDisableVertexAttribArray(planeXZPositionAlphaAttribute);
    GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, 0);
    GLES20.glDisable(GLES20.GL_BLEND);
    GLES20.glDepthMask(true);

    ShaderUtil.checkGLError(TAG, "Cleaning up after drawing planes");
  }

  // Calculate the normal distance to plane from cameraPose, the given planePose should have y axis
  // parallel to plane's normal, for example plane's center pose or hit test pose.
  public static float calculateDistanceToPlane(Pose planePose, Pose cameraPose) {
    float[] normal = new float[3];
    float cameraX = cameraPose.tx();
    float cameraY = cameraPose.ty();
    float cameraZ = cameraPose.tz();
    // Get transformed Y axis of plane's coordinate system.
    planePose.getTransformedAxis(1, 1.0f, normal, 0);
    // Compute dot product of plane's normal with vector from camera to plane center.
    return (cameraX - planePose.tx()) * normal[0]
        + (cameraY - planePose.ty()) * normal[1]
        + (cameraZ - planePose.tz()) * normal[2];
  }
}
