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/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * 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 android.support.v4.view;

import android.content.Context;
import android.content.res.TypedArray;
import android.database.DataSetObserver;
import android.graphics.drawable.Drawable;
import android.text.TextUtils.TruncateAt;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.widget.TextView;

/**
 * PagerTitleStrip is a non-interactive indicator of the current, next,
 * and previous pages of a {@link ViewPager}. It is intended to be used as a
 * child view of a ViewPager widget in your XML layout.
 * Add it as a child of a ViewPager in your layout file and set its
 * android:layout_gravity to TOP or BOTTOM to pin it to the top or bottom
 * of the ViewPager. The title from each page is supplied by the method
 * {@link PagerAdapter#getPageTitle(int)} in the adapter supplied to
 * the ViewPager.
 */
public class PagerTitleStrip extends ViewGroup implements ViewPager.Decor {
    private static final String TAG = "PagerTitleStrip";

    ViewPager mPager;
    private TextView mPrevText;
    private TextView mCurrText;
    private TextView mNextText;

    private int mLastKnownCurrentPage = -1;
    private float mLastKnownPositionOffset = -1;
    private int mScaledTextSpacing;

    private boolean mUpdatingText;
    private boolean mUpdatingPositions;

    private final PageListener mPageListener = new PageListener();

    private static final int[] ATTRS = new int[] {
        android.R.attr.textAppearance,
        android.R.attr.textColor,
        android.R.attr.textSize
    };

    private static final int SIDE_ALPHA = 0x99; // single-byte alpha, 0 = invisible, FF = opaque
    private static final int TEXT_SPACING = 16; // dip

    public PagerTitleStrip(Context context) {
        this(context, null);
    }

    public PagerTitleStrip(Context context, AttributeSet attrs) {
        super(context, attrs);

        addView(mPrevText = new TextView(context));
        addView(mCurrText = new TextView(context));
        addView(mNextText = new TextView(context));

        final TypedArray a = context.obtainStyledAttributes(attrs, ATTRS);
        final int textAppearance = a.getResourceId(0, 0);
        if (textAppearance != 0) {
            mPrevText.setTextAppearance(context, textAppearance);
            mCurrText.setTextAppearance(context, textAppearance);
            mNextText.setTextAppearance(context, textAppearance);
        }
        if (a.hasValue(1)) {
            final int textColor = a.getColor(1, 0);
            mPrevText.setTextColor(textColor);
            mCurrText.setTextColor(textColor);
            mNextText.setTextColor(textColor);
        }
        final int textSize = a.getDimensionPixelSize(2, 0);
        if (textSize != 0) {
            mPrevText.setTextSize(TypedValue.COMPLEX_UNIT_PX, textSize);
            mCurrText.setTextSize(TypedValue.COMPLEX_UNIT_PX, textSize);
            mNextText.setTextSize(TypedValue.COMPLEX_UNIT_PX, textSize);
        }
        a.recycle();

        final int defaultColor = mPrevText.getTextColors().getDefaultColor();
        final int transparentColor = (SIDE_ALPHA << 24) | (defaultColor & 0xFFFFFF);
        mPrevText.setTextColor(transparentColor);
        mNextText.setTextColor(transparentColor);

        mPrevText.setEllipsize(TruncateAt.END);
        mCurrText.setEllipsize(TruncateAt.END);
        mNextText.setEllipsize(TruncateAt.END);
        mPrevText.setSingleLine();
        mCurrText.setSingleLine();
        mNextText.setSingleLine();

        final float density = context.getResources().getDisplayMetrics().density;
        mScaledTextSpacing = (int) (TEXT_SPACING * density);
    }

    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();

        final ViewParent parent = getParent();
        if (!(parent instanceof ViewPager)) {
            throw new IllegalStateException(
                    "PagerTitleStrip must be a direct child of a ViewPager.");
        }

        final ViewPager pager = (ViewPager) parent;
        final PagerAdapter adapter = pager.getAdapter();

        pager.setInternalPageChangeListener(mPageListener);
        pager.setOnAdapterChangeListener(mPageListener);
        mPager = pager;
        updateAdapter(null, adapter);
    }

    @Override
    protected void onDetachedFromWindow() {
        updateAdapter(mPager.getAdapter(), null);
        mPager.setInternalPageChangeListener(null);
        mPager.setOnAdapterChangeListener(null);
        mPager = null;
    }

    void updateText(int currentItem, PagerAdapter adapter) {
        final int itemCount = adapter != null ? adapter.getCount() : 0;
        mUpdatingText = true;

        CharSequence text = null;
        if (currentItem >= 1 && adapter != null) {
            text = adapter.getPageTitle(currentItem - 1);
        }
        mPrevText.setText(text);

        mCurrText.setText(adapter != null ? adapter.getPageTitle(currentItem) : null);

        text = null;
        if (currentItem + 1 < itemCount && adapter != null) {
            text = adapter.getPageTitle(currentItem + 1);
        }
        mNextText.setText(text);

        // Measure everything
        final int width = getWidth() - getPaddingLeft() - getPaddingRight();
        final int childHeight = getHeight() - getPaddingTop() - getPaddingBottom();
        final int childWidthSpec = MeasureSpec.makeMeasureSpec((int) (width * 0.8f),
                MeasureSpec.AT_MOST);
        final int childHeightSpec = MeasureSpec.makeMeasureSpec(childHeight, MeasureSpec.EXACTLY);
        mPrevText.measure(childWidthSpec, childHeightSpec);
        mCurrText.measure(childWidthSpec, childHeightSpec);
        mNextText.measure(childWidthSpec, childHeightSpec);

        mLastKnownCurrentPage = currentItem;

        if (!mUpdatingPositions) {
            updateTextPositions(currentItem, mLastKnownPositionOffset);
        }

        mUpdatingText = false;
    }

    @Override
    public void requestLayout() {
        if (!mUpdatingText) {
            super.requestLayout();
        }
    }

    void updateAdapter(PagerAdapter oldAdapter, PagerAdapter newAdapter) {
        if (oldAdapter != null) {
            oldAdapter.unregisterDataSetObserver(mPageListener);
        }
        if (newAdapter != null) {
            newAdapter.registerDataSetObserver(mPageListener);
        }
        if (mPager != null) {
            mLastKnownCurrentPage = -1;
            mLastKnownPositionOffset = -1;
            updateText(mPager.getCurrentItem(), newAdapter);
            requestLayout();
        }
    }

    void updateTextPositions(int position, float positionOffset) {
        if (position != mLastKnownCurrentPage) {
            updateText(position, mPager.getAdapter());
        } else if (positionOffset == mLastKnownPositionOffset) {
            return;
        }

        mUpdatingPositions = true;

        final int prevWidth = mPrevText.getMeasuredWidth();
        final int currWidth = mCurrText.getMeasuredWidth();
        final int nextWidth = mNextText.getMeasuredWidth();
        final int halfCurrWidth = currWidth / 2;

        final int stripWidth = getWidth();
        final int paddingLeft = getPaddingLeft();
        final int paddingRight = getPaddingRight();
        final int paddingTop = getPaddingTop();
        final int textPaddedLeft = paddingLeft + halfCurrWidth;
        final int textPaddedRight = paddingRight + halfCurrWidth;
        final int contentWidth = stripWidth - textPaddedLeft - textPaddedRight;

        float currOffset = positionOffset + 0.5f;
        if (currOffset > 1.f) {
            currOffset -= 1.f;
        }
        final int currCenter = stripWidth - textPaddedRight - (int) (contentWidth * currOffset);
        final int currLeft = currCenter - currWidth / 2;
        final int currRight = currLeft + currWidth;

        mCurrText.layout(currLeft, paddingTop, currRight,
                paddingTop + mCurrText.getMeasuredHeight());

        final int prevLeft = Math.min(paddingLeft, currLeft - mScaledTextSpacing - prevWidth);
        mPrevText.layout(prevLeft, paddingTop, prevLeft + prevWidth,
                paddingTop + mPrevText.getMeasuredHeight());

        final int nextLeft = Math.max(stripWidth - paddingRight - nextWidth,
                currRight + mScaledTextSpacing);
        mNextText.layout(nextLeft, paddingTop, nextLeft + nextWidth,
                paddingTop + mNextText.getMeasuredHeight());

        mLastKnownPositionOffset = positionOffset;
        mUpdatingPositions = false;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        final int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        final int heightSize = MeasureSpec.getSize(heightMeasureSpec);

        if (widthMode != MeasureSpec.EXACTLY) {
            throw new IllegalStateException("Must measure with an exact width");
        }

        int childHeight = heightSize;
        int minHeight = 0;
        int padding = 0;
        final Drawable bg = getBackground();
        if (bg != null) {
            minHeight = bg.getIntrinsicHeight();
        }
        padding = getPaddingTop() + getPaddingBottom();
        childHeight -= padding;

        final int childWidthSpec = MeasureSpec.makeMeasureSpec((int) (widthSize * 0.8f),
                MeasureSpec.AT_MOST);
        final int childHeightSpec = MeasureSpec.makeMeasureSpec(childHeight, heightMode);

        mPrevText.measure(childWidthSpec, childHeightSpec);
        mCurrText.measure(childWidthSpec, childHeightSpec);
        mNextText.measure(childWidthSpec, childHeightSpec);

        if (heightMode == MeasureSpec.EXACTLY) {
            setMeasuredDimension(widthSize, heightSize);
        } else {
            int textHeight = mCurrText.getMeasuredHeight();
            setMeasuredDimension(widthSize, Math.max(minHeight, textHeight + padding));
        }
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        if (mPager != null) {
            updateTextPositions(mPager.getCurrentItem(), 0.f);
        }
    }

    private class PageListener extends DataSetObserver implements ViewPager.OnPageChangeListener,
            ViewPager.OnAdapterChangeListener {
        private int mScrollState;

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            if (positionOffset > 0.5f) {
                // Consider ourselves to be on the next page when we're 50% of the way there.
                position++;
            }
            updateTextPositions(position, positionOffset);
        }

        @Override
        public void onPageSelected(int position) {
            if (mScrollState == ViewPager.SCROLL_STATE_IDLE) {
                // Only update the text here if we're not dragging or settling.
                updateText(mPager.getCurrentItem(), mPager.getAdapter());
            }
        }

        @Override
        public void onPageScrollStateChanged(int state) {
            mScrollState = state;
        }

        @Override
        public void onAdapterChanged(PagerAdapter oldAdapter, PagerAdapter newAdapter) {
            updateAdapter(oldAdapter, newAdapter);
        }

        @Override
        public void onChanged() {
            updateText(mPager.getCurrentItem(), mPager.getAdapter());
        }
    }
}