/* -*- Mode: Java; c-basic-offset: 4; tab-width: 20; indent-tabs-mode: nil; -*-
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

package org.mozilla.gecko.gfx;

import org.mozilla.gecko.util.FloatUtils;

import android.graphics.Bitmap;
import android.graphics.Rect;
import android.graphics.RectF;
import android.opengl.GLES20;

import java.nio.FloatBuffer;

public class ScrollbarLayer extends TileLayer {
    public static final long FADE_DELAY = 500; // milliseconds before fade-out starts
    private static final float FADE_AMOUNT = 0.03f; // how much (as a percent) the scrollbar should fade per frame

    private final boolean mVertical;
    private float mOpacity;

    // To avoid excessive GC, declare some objects here that would otherwise
    // be created and destroyed frequently during draw().
    private final RectF mBarRectF;
    private final Rect mBarRect;
    private final float[] mCoords;
    private final RectF mCapRectF;

    private LayerRenderer mRenderer;
    private int mProgram;
    private int mPositionHandle;
    private int mTextureHandle;
    private int mSampleHandle;
    private int mTMatrixHandle;
    private int mOpacityHandle;

    // Fragment shader used to draw the scroll-bar with opacity
    private static final String FRAGMENT_SHADER =
        "precision mediump float;\n" +
        "varying vec2 vTexCoord;\n" +
        "uniform sampler2D sTexture;\n" +
        "uniform float uOpacity;\n" +
        "void main() {\n" +
        "    gl_FragColor = texture2D(sTexture, vTexCoord);\n" +
        "    gl_FragColor.a *= uOpacity;\n" +
        "}\n";

    // Dimensions of the texture bitmap (will always be power-of-two)
    private final int mTexWidth;
    private final int mTexHeight;
    // Some useful dimensions of the actual content in the bitmap
    private final int mBarWidth;
    private final int mCapLength;

    private final Rect mStartCapTexCoords;  // top/left endcap coordinates
    private final Rect mBodyTexCoords;      // 1-pixel slice of the texture to be stretched
    private final Rect mEndCapTexCoords;    // bottom/right endcap coordinates

    ScrollbarLayer(LayerRenderer renderer, Bitmap scrollbarImage, IntSize imageSize, boolean vertical) {
        super(new BufferedCairoImage(scrollbarImage), TileLayer.PaintMode.NORMAL);
        mRenderer = renderer;
        mVertical = vertical;

        mBarRectF = new RectF();
        mBarRect = new Rect();
        mCoords = new float[20];
        mCapRectF = new RectF();

        mTexHeight = scrollbarImage.getHeight();
        mTexWidth = scrollbarImage.getWidth();

        if (mVertical) {
            mBarWidth = imageSize.width;
            mCapLength = imageSize.height / 2;
            mStartCapTexCoords = new Rect(0, mTexHeight - mCapLength, imageSize.width, mTexHeight);
            mBodyTexCoords = new Rect(0, mTexHeight - (mCapLength + 1), imageSize.width, mTexHeight - mCapLength);
            mEndCapTexCoords = new Rect(0, mTexHeight - imageSize.height, imageSize.width, mTexHeight - (mCapLength + 1));
        } else {
            mBarWidth = imageSize.height;
            mCapLength = imageSize.width / 2;
            mStartCapTexCoords = new Rect(0, mTexHeight - imageSize.height, mCapLength, mTexHeight);
            mBodyTexCoords = new Rect(mCapLength, mTexHeight - imageSize.height, mCapLength + 1, mTexHeight);
            mEndCapTexCoords = new Rect(mCapLength + 1, mTexHeight - imageSize.height, imageSize.width, mTexHeight);
        }
    }

    private void createProgram() {
        int vertexShader = LayerRenderer.loadShader(GLES20.GL_VERTEX_SHADER,
                                                    LayerRenderer.DEFAULT_VERTEX_SHADER);
        int fragmentShader = LayerRenderer.loadShader(GLES20.GL_FRAGMENT_SHADER,
                                                      FRAGMENT_SHADER);

        mProgram = GLES20.glCreateProgram();
        GLES20.glAttachShader(mProgram, vertexShader);   // add the vertex shader to program
        GLES20.glAttachShader(mProgram, fragmentShader); // add the fragment shader to program
        GLES20.glLinkProgram(mProgram);                  // creates OpenGL program executables

        // Get handles to the shaders' vPosition, aTexCoord, sTexture, and uTMatrix members.
        mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");
        mTextureHandle = GLES20.glGetAttribLocation(mProgram, "aTexCoord");
        mSampleHandle = GLES20.glGetUniformLocation(mProgram, "sTexture");
        mTMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uTMatrix");
        mOpacityHandle = GLES20.glGetUniformLocation(mProgram, "uOpacity");
    }

    private void activateProgram() {
        // Add the program to the OpenGL environment
        GLES20.glUseProgram(mProgram);

        // Set the transformation matrix
        GLES20.glUniformMatrix4fv(mTMatrixHandle, 1, false,
                                  LayerRenderer.DEFAULT_TEXTURE_MATRIX, 0);

        // Enable the arrays from which we get the vertex and texture coordinates
        GLES20.glEnableVertexAttribArray(mPositionHandle);
        GLES20.glEnableVertexAttribArray(mTextureHandle);

        GLES20.glUniform1i(mSampleHandle, 0);
        GLES20.glUniform1f(mOpacityHandle, mOpacity);
    }

    private void deactivateProgram() {
        GLES20.glDisableVertexAttribArray(mTextureHandle);
        GLES20.glDisableVertexAttribArray(mPositionHandle);
        GLES20.glUseProgram(0);
    }

    /**
     * Decrease the opacity of the scrollbar by one frame's worth.
     * Return true if the opacity was decreased, or false if the scrollbars
     * are already fully faded out.
     */
    public boolean fade() {
        if (FloatUtils.fuzzyEquals(mOpacity, 0.0f)) {
            return false;
        }
        beginTransaction(); // called on compositor thread
        mOpacity = Math.max(mOpacity - FADE_AMOUNT, 0.0f);
        endTransaction();
        return true;
    }

    /**
     * Restore the opacity of the scrollbar to fully opaque.
     * Return true if the opacity was changed, or false if the scrollbars
     * are already fully opaque.
     */
    public boolean unfade() {
        if (FloatUtils.fuzzyEquals(mOpacity, 1.0f)) {
            return false;
        }
        beginTransaction(); // called on compositor thread
        mOpacity = 1.0f;
        endTransaction();
        return true;
    }

    @Override
    public void draw(RenderContext context) {
        if (!initialized())
            return;

        // Create the shader program, if necessary
        if (mProgram == 0) {
            createProgram();
        }

        // Enable the shader program
        mRenderer.deactivateDefaultProgram();
        activateProgram();

        GLES20.glEnable(GLES20.GL_BLEND);
        GLES20.glBlendFunc(GLES20.GL_SRC_ALPHA, GLES20.GL_ONE_MINUS_SRC_ALPHA);

        if (mVertical) {
            getVerticalRect(context, mBarRectF);
        } else {
            getHorizontalRect(context, mBarRectF);
        }
        RectUtils.round(mBarRectF, mBarRect);

        GLES20.glActiveTexture(GLES20.GL_TEXTURE0);
        GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, getTextureID());

        float viewWidth = context.viewport.width();
        float viewHeight = context.viewport.height();

        mBarRectF.set(mBarRect.left, viewHeight - mBarRect.top, mBarRect.right, viewHeight - mBarRect.bottom);

        // We take a 1-pixel slice from the center of the image and scale it to become the bar
        fillRectCoordBuffer(mCoords, mBarRectF, viewWidth, viewHeight, mBodyTexCoords, mTexWidth, mTexHeight);

        // Get the buffer and handles from the context
        FloatBuffer coordBuffer = context.coordBuffer;
        int positionHandle = mPositionHandle;
        int textureHandle = mTextureHandle;

        // Make sure we are at position zero in the buffer in case other draw methods did not
        // clean up after themselves
        coordBuffer.position(0);
        coordBuffer.put(mCoords);

        // Unbind any the current array buffer so we can use client side buffers
        GLES20.glBindBuffer(GLES20.GL_ARRAY_BUFFER, 0);

        // Vertex coordinates are x,y,z starting at position 0 into the buffer.
        coordBuffer.position(0);
        GLES20.glVertexAttribPointer(positionHandle, 3, GLES20.GL_FLOAT, false, 20, coordBuffer);

        // Texture coordinates are texture_x, texture_y starting at position 3 into the buffer.
        coordBuffer.position(3);
        GLES20.glVertexAttribPointer(textureHandle, 2, GLES20.GL_FLOAT, false, 20, coordBuffer);

        GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);

        // Reset the position in the buffer for the next set of vertex and texture coordinates.
        coordBuffer.position(0);
        if (mVertical) {
            // top endcap
            mCapRectF.set(mBarRectF.left, mBarRectF.top + mCapLength, mBarRectF.right, mBarRectF.top);
        } else {
            // left endcap
            mCapRectF.set(mBarRectF.left - mCapLength, mBarRectF.bottom + mBarWidth, mBarRectF.left, mBarRectF.bottom);
        }

        fillRectCoordBuffer(mCoords, mCapRectF, viewWidth, viewHeight, mStartCapTexCoords, mTexWidth, mTexHeight);
        coordBuffer.put(mCoords);

        // Vertex coordinates are x,y,z starting at position 0 into the buffer.
        coordBuffer.position(0);
        GLES20.glVertexAttribPointer(positionHandle, 3, GLES20.GL_FLOAT, false, 20, coordBuffer);

        // Texture coordinates are texture_x, texture_y starting at position 3 into the buffer.
        coordBuffer.position(3);
        GLES20.glVertexAttribPointer(textureHandle, 2, GLES20.GL_FLOAT, false, 20, coordBuffer);

        GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);

        // Reset the position in the buffer for the next set of vertex and texture coordinates.
        coordBuffer.position(0);
        if (mVertical) {
            // bottom endcap
            mCapRectF.set(mBarRectF.left, mBarRectF.bottom, mBarRectF.right, mBarRectF.bottom - mCapLength);
        } else {
            // right endcap
            mCapRectF.set(mBarRectF.right, mBarRectF.bottom + mBarWidth, mBarRectF.right + mCapLength, mBarRectF.bottom);
        }
        fillRectCoordBuffer(mCoords, mCapRectF, viewWidth, viewHeight, mEndCapTexCoords, mTexWidth, mTexHeight);
        coordBuffer.put(mCoords);

        // Vertex coordinates are x,y,z starting at position 0 into the buffer.
        coordBuffer.position(0);
        GLES20.glVertexAttribPointer(positionHandle, 3, GLES20.GL_FLOAT, false, 20, coordBuffer);

        // Texture coordinates are texture_x, texture_y starting at position 3 into the buffer.
        coordBuffer.position(3);
        GLES20.glVertexAttribPointer(textureHandle, 2, GLES20.GL_FLOAT, false, 20, coordBuffer);

        GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4);

        // Reset the position in the buffer for the next set of vertex and texture coordinates.
        coordBuffer.position(0);

        // Enable the default shader program again
        deactivateProgram();
        mRenderer.activateDefaultProgram();
    }

    private void getVerticalRect(RenderContext context, RectF dest) {
        RectF viewport = context.viewport;
        RectF pageRect = context.pageRect;
        float barStart = ((viewport.top - pageRect.top) * (viewport.height() / pageRect.height())) + mCapLength;
        float barEnd = ((viewport.bottom - pageRect.top) * (viewport.height() / pageRect.height())) - mCapLength;
        if (barStart > barEnd) {
            float middle = (barStart + barEnd) / 2.0f;
            barStart = barEnd = middle;
        }
        dest.set(viewport.width() - mBarWidth, barStart, viewport.width(), barEnd);
    }

    private void getHorizontalRect(RenderContext context, RectF dest) {
        RectF viewport = context.viewport;
        RectF pageRect = context.pageRect;
        float barStart = ((viewport.left - pageRect.left) * (viewport.width() / pageRect.width())) + mCapLength;
        float barEnd = ((viewport.right - pageRect.left) * (viewport.width() / pageRect.width())) - mCapLength;
        if (barStart > barEnd) {
            float middle = (barStart + barEnd) / 2.0f;
            barStart = barEnd = middle;
        }
        dest.set(barStart, viewport.height() - mBarWidth, barEnd, viewport.height());
    }
}
