/*
 * Copyright 2018 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 androidx.viewpager.widget;

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.text.method.SingleLineTransformationMethod;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.widget.TextView;

import androidx.annotation.ColorInt;
import androidx.annotation.FloatRange;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.core.view.ViewCompat;
import androidx.core.widget.TextViewCompat;

import java.lang.ref.WeakReference;
import java.util.Locale;

/**
 * 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.
 *
 * <p>For an interactive indicator, see {@link PagerTabStrip}.</p>
 */
@ViewPager.DecorView
public class PagerTitleStrip extends ViewGroup {
    ViewPager mPager;
    TextView mPrevText;
    TextView mCurrText;
    TextView mNextText;

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

    private boolean mUpdatingText;
    private boolean mUpdatingPositions;

    private final PageListener mPageListener = new PageListener();

    private WeakReference<PagerAdapter> mWatchingAdapter;

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

    private static final int[] TEXT_ATTRS = new int[] {
        0x0101038c // android.R.attr.textAllCaps
    };

    private static final float SIDE_ALPHA = 0.6f;
    private static final int TEXT_SPACING = 16; // dip

    private int mNonPrimaryAlpha;
    int mTextColor;

    private static class SingleLineAllCapsTransform extends SingleLineTransformationMethod {
        private Locale mLocale;

        @SuppressWarnings("deprecation")
        SingleLineAllCapsTransform(Context context) {
            mLocale = context.getResources().getConfiguration().locale;
        }

        @Override
        public CharSequence getTransformation(CharSequence source, View view) {
            source = super.getTransformation(source, view);
            return source != null ? source.toString().toUpperCase(mLocale) : null;
        }
    }

    private static void setSingleLineAllCaps(TextView text) {
        text.setTransformationMethod(new SingleLineAllCapsTransform(text.getContext()));
    }

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

    public PagerTitleStrip(@NonNull Context context, @Nullable 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);
        ViewCompat.saveAttributeDataForStyleable(this, context, ATTRS, attrs, a, 0, 0);
        final int textAppearance = a.getResourceId(0, 0);
        if (textAppearance != 0) {
            TextViewCompat.setTextAppearance(mPrevText, textAppearance);
            TextViewCompat.setTextAppearance(mCurrText, textAppearance);
            TextViewCompat.setTextAppearance(mNextText, textAppearance);
        }
        final int textSize = a.getDimensionPixelSize(1, 0);
        if (textSize != 0) {
            setTextSize(TypedValue.COMPLEX_UNIT_PX, textSize);
        }
        if (a.hasValue(2)) {
            final int textColor = a.getColor(2, 0);
            mPrevText.setTextColor(textColor);
            mCurrText.setTextColor(textColor);
            mNextText.setTextColor(textColor);
        }
        mGravity = a.getInteger(3, Gravity.BOTTOM);
        a.recycle();

        mTextColor = mCurrText.getTextColors().getDefaultColor();
        setNonPrimaryAlpha(SIDE_ALPHA);

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

        boolean allCaps = false;
        if (textAppearance != 0) {
            final TypedArray ta = context.obtainStyledAttributes(textAppearance, TEXT_ATTRS);
            allCaps = ta.getBoolean(0, false);
            ta.recycle();
        }

        if (allCaps) {
            setSingleLineAllCaps(mPrevText);
            setSingleLineAllCaps(mCurrText);
            setSingleLineAllCaps(mNextText);
        } else {
            mPrevText.setSingleLine();
            mCurrText.setSingleLine();
            mNextText.setSingleLine();
        }

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

    /**
     * Set the required spacing between title segments.
     *
     * @param spacingPixels Spacing between each title displayed in pixels
     */
    public void setTextSpacing(int spacingPixels) {
        mScaledTextSpacing = spacingPixels;
        requestLayout();
    }

    /**
     * @return The required spacing between title segments in pixels
     */
    public int getTextSpacing() {
        return mScaledTextSpacing;
    }

    /**
     * Set the alpha value used for non-primary page titles.
     *
     * @param alpha Opacity value in the range 0-1f
     */
    public void setNonPrimaryAlpha(@FloatRange(from = 0.0, to = 1.0) float alpha) {
        mNonPrimaryAlpha = (int) (alpha * 255) & 0xFF;
        final int transparentColor = (mNonPrimaryAlpha << 24) | (mTextColor & 0xFFFFFF);
        mPrevText.setTextColor(transparentColor);
        mNextText.setTextColor(transparentColor);
    }

    /**
     * Set the color value used as the base color for all displayed page titles.
     * Alpha will be ignored for non-primary page titles. See {@link #setNonPrimaryAlpha(float)}.
     *
     * @param color Color hex code in 0xAARRGGBB format
     */
    public void setTextColor(@ColorInt int color) {
        mTextColor = color;
        mCurrText.setTextColor(color);
        final int transparentColor = (mNonPrimaryAlpha << 24) | (mTextColor & 0xFFFFFF);
        mPrevText.setTextColor(transparentColor);
        mNextText.setTextColor(transparentColor);
    }

    /**
     * Set the default text size to a given unit and value.
     * See {@link TypedValue} for the possible dimension units.
     *
     * <p>Example: to set the text size to 14px, use
     * setTextSize(TypedValue.COMPLEX_UNIT_PX, 14);</p>
     *
     * @param unit The desired dimension unit
     * @param size The desired size in the given units
     */
    public void setTextSize(int unit, float size) {
        mPrevText.setTextSize(unit, size);
        mCurrText.setTextSize(unit, size);
        mNextText.setTextSize(unit, size);
    }

    /**
     * Set the {@link Gravity} used to position text within the title strip.
     * Only the vertical gravity component is used.
     *
     * @param gravity {@link Gravity} constant for positioning title text
     */
    public void setGravity(int gravity) {
        mGravity = gravity;
        requestLayout();
    }

    @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.addOnAdapterChangeListener(mPageListener);
        mPager = pager;
        updateAdapter(mWatchingAdapter != null ? mWatchingAdapter.get() : null, adapter);
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        if (mPager != null) {
            updateAdapter(mPager.getAdapter(), null);
            mPager.setInternalPageChangeListener(null);
            mPager.removeOnAdapterChangeListener(mPageListener);
            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 && currentItem < itemCount
                ? 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 maxWidth = Math.max(0, (int) (width * 0.8f));
        final int childWidthSpec = MeasureSpec.makeMeasureSpec(maxWidth, MeasureSpec.AT_MOST);
        final int childHeight = getHeight() - getPaddingTop() - getPaddingBottom();
        final int maxHeight = Math.max(0, childHeight);
        final int childHeightSpec = MeasureSpec.makeMeasureSpec(maxHeight, MeasureSpec.AT_MOST);
        mPrevText.measure(childWidthSpec, childHeightSpec);
        mCurrText.measure(childWidthSpec, childHeightSpec);
        mNextText.measure(childWidthSpec, childHeightSpec);

        mLastKnownCurrentPage = currentItem;

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

        mUpdatingText = false;
    }

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

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

    void updateTextPositions(int position, float positionOffset, boolean force) {
        if (position != mLastKnownCurrentPage) {
            updateText(position, mPager.getAdapter());
        } else if (!force && 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 stripHeight = getHeight();
        final int paddingLeft = getPaddingLeft();
        final int paddingRight = getPaddingRight();
        final int paddingTop = getPaddingTop();
        final int paddingBottom = getPaddingBottom();
        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;

        final int prevBaseline = mPrevText.getBaseline();
        final int currBaseline = mCurrText.getBaseline();
        final int nextBaseline = mNextText.getBaseline();
        final int maxBaseline = Math.max(Math.max(prevBaseline, currBaseline), nextBaseline);
        final int prevTopOffset = maxBaseline - prevBaseline;
        final int currTopOffset = maxBaseline - currBaseline;
        final int nextTopOffset = maxBaseline - nextBaseline;
        final int alignedPrevHeight = prevTopOffset + mPrevText.getMeasuredHeight();
        final int alignedCurrHeight = currTopOffset + mCurrText.getMeasuredHeight();
        final int alignedNextHeight = nextTopOffset + mNextText.getMeasuredHeight();
        final int maxTextHeight = Math.max(Math.max(alignedPrevHeight, alignedCurrHeight),
                alignedNextHeight);

        final int vgrav = mGravity & Gravity.VERTICAL_GRAVITY_MASK;

        int prevTop;
        int currTop;
        int nextTop;
        switch (vgrav) {
            default:
            case Gravity.TOP:
                prevTop = paddingTop + prevTopOffset;
                currTop = paddingTop + currTopOffset;
                nextTop = paddingTop + nextTopOffset;
                break;
            case Gravity.CENTER_VERTICAL:
                final int paddedHeight = stripHeight - paddingTop - paddingBottom;
                final int centeredTop = (paddedHeight - maxTextHeight) / 2;
                prevTop = centeredTop + prevTopOffset;
                currTop = centeredTop + currTopOffset;
                nextTop = centeredTop + nextTopOffset;
                break;
            case Gravity.BOTTOM:
                final int bottomGravTop = stripHeight - paddingBottom - maxTextHeight;
                prevTop = bottomGravTop + prevTopOffset;
                currTop = bottomGravTop + currTopOffset;
                nextTop = bottomGravTop + nextTopOffset;
                break;
        }

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

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

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

        mLastKnownPositionOffset = positionOffset;
        mUpdatingPositions = false;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        if (widthMode != MeasureSpec.EXACTLY) {
            throw new IllegalStateException("Must measure with an exact width");
        }

        final int heightPadding = getPaddingTop() + getPaddingBottom();
        final int childHeightSpec = getChildMeasureSpec(heightMeasureSpec,
                heightPadding, LayoutParams.WRAP_CONTENT);

        final int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        final int widthPadding = (int) (widthSize * 0.2f);
        final int childWidthSpec = getChildMeasureSpec(widthMeasureSpec,
                widthPadding, LayoutParams.WRAP_CONTENT);

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

        final int height;
        final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        if (heightMode == MeasureSpec.EXACTLY) {
            height = MeasureSpec.getSize(heightMeasureSpec);
        } else {
            final int textHeight = mCurrText.getMeasuredHeight();
            final int minHeight = getMinHeight();
            height = Math.max(minHeight, textHeight + heightPadding);
        }

        final int childState = mCurrText.getMeasuredState();
        final int measuredHeight = View.resolveSizeAndState(height, heightMeasureSpec,
                childState << View.MEASURED_HEIGHT_STATE_SHIFT);
        setMeasuredDimension(widthSize, measuredHeight);
    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        if (mPager != null) {
            final float offset = mLastKnownPositionOffset >= 0 ? mLastKnownPositionOffset : 0;
            updateTextPositions(mLastKnownCurrentPage, offset, true);
        }
    }

    int getMinHeight() {
        int minHeight = 0;
        final Drawable bg = getBackground();
        if (bg != null) {
            minHeight = bg.getIntrinsicHeight();
        }
        return minHeight;
    }

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

        PageListener() {
        }

        @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, false);
        }

        @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());

                final float offset = mLastKnownPositionOffset >= 0 ? mLastKnownPositionOffset : 0;
                updateTextPositions(mPager.getCurrentItem(), offset, true);
            }
        }

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

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

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

            final float offset = mLastKnownPositionOffset >= 0 ? mLastKnownPositionOffset : 0;
            updateTextPositions(mPager.getCurrentItem(), offset, true);
        }
    }
}