import java.util.LinkedList;
import java.util.Queue;

import android.content.Context;
import android.database.DataSetObserver;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.GestureDetector;
import android.view.GestureDetector.OnGestureListener;
import android.view.MotionEvent;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListAdapter;
import android.widget.Scroller;

public class HorizontalListView extends AdapterView<ListAdapter> {

    public boolean mAlwaysOverrideTouch = true;
    protected ListAdapter mAdapter;
    private int mLeftViewIndex = -1; // 左边View的下标
    private int mRightViewIndex = 0; // 右边View的下标
    protected int mCurrentX; // 当前x坐标
    protected int mNextX; // 一次移动后x坐标
    private int mMaxX = Integer.MAX_VALUE; // x坐标最大值
    private int mDisplayOffset = 0; // 偏移量
    protected Scroller mScroller;
    private GestureDetector mGesture;
    private Queue<View> mRemovedViewQueue = new LinkedList<View>();
    private OnItemSelectedListener mOnItemSelected;
    private OnItemClickListener mOnItemClicked;
    private OnItemLongClickListener mOnItemLongClicked;
    private boolean mDataChanged = false;
    // 获取屏幕宽度
    private DisplayMetrics metrics = getResources().getDisplayMetrics();
    private int screenWidth = metrics.widthPixels;

    /**
     * minItemWidth：表示每个item的最小宽度
     * itemCount   ：一屏能显示的item数量
     * itemWidth   ：每个item的实际宽度
     */
    private final int minItemWidth = (int) (metrics.density * 70);
    private int itemCount = screenWidth / minItemWidth;
    private int itemWidth = (int) (screenWidth * 1.0 / itemCount);

    public HorizontalListView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    private synchronized void initView() {
        mLeftViewIndex = -1;
        mRightViewIndex = 0;
        mDisplayOffset = 0;
        mCurrentX = 0;
        mNextX = 0;
        mMaxX = Integer.MAX_VALUE;
        mScroller = new Scroller(getContext());
        mGesture = new GestureDetector(getContext(), mOnGesture);
    }

    @Override
    public void setOnItemSelectedListener(
            AdapterView.OnItemSelectedListener listener) {
        mOnItemSelected = listener;
    }

    @Override
    public void setOnItemClickListener(AdapterView.OnItemClickListener listener) {
        mOnItemClicked = listener;
    }

    @Override
    public void setOnItemLongClickListener(
            AdapterView.OnItemLongClickListener listener) {
        mOnItemLongClicked = listener;
    }

    private DataSetObserver mDataObserver = new DataSetObserver() {

        @Override
        public void onChanged() {
            synchronized (HorizontalListView.this) {
                mDataChanged = true;
            }
            invalidate();
            requestLayout();
        }

        @Override
        public void onInvalidated() {
            reset();
            invalidate();
            requestLayout();
        }

    };

    @Override
    public ListAdapter getAdapter() {
        return mAdapter;
    }

    @Override
    public View getSelectedView() {
        // TODO: implement
        return null;
    }

    @Override
    public void setAdapter(ListAdapter adapter) {
        if (mAdapter != null) {
            mAdapter.unregisterDataSetObserver(mDataObserver);
        }
        mAdapter = adapter;
        mAdapter.registerDataSetObserver(mDataObserver);
        reset();
    }

    private synchronized void reset() {
        initView();
        removeAllViewsInLayout();
        requestLayout();
    }

    @Override
    public void setSelection(int position) {
        // TODO: implement
    }

    private void addAndMeasureChild(final View child, int viewPos) {
        LayoutParams params = child.getLayoutParams();
        if (params == null) {
            params = new LayoutParams(LayoutParams.FILL_PARENT,
                    LayoutParams.FILL_PARENT);
        }

        addViewInLayout(child, viewPos, params, true);
        child.measure(
                MeasureSpec.makeMeasureSpec(getWidth(), MeasureSpec.AT_MOST),
                MeasureSpec.makeMeasureSpec(getHeight(), MeasureSpec.AT_MOST));
    }

    @Override
    protected synchronized void onLayout(boolean changed, int left, int top,
            int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);

        if (mAdapter == null) {
            return;
        }

        if (mDataChanged) {
            int oldCurrentX = mCurrentX;
            initView();
            removeAllViewsInLayout();
            mNextX = oldCurrentX;
//在这个if()语句中执行了initView()方法，表示如果adapter中数据变更则重新执行initView()；
            //initView()方法中重新初始化了mScroller，mScroller.getCurrX()的值将变为0；
            //但是这里我点击某个图标之后仅仅希望图标的背景改变，不希望listView回到起点，所以要执行下面语句
            mScroller.setFinalX(oldCurrentX);
            //

            mDataChanged = false;

        }

        // computeScrollOffset()方法，如果返回true表示（滚动）动画还没有完成
        // 当你想知道当前位置(location)时调用该方法。
        if (mScroller.computeScrollOffset()) {
            int scrollx = mScroller.getCurrX();
            mNextX = scrollx;
        }

        // 如果滑动位置要超过边界值，则把当前位置设为边界值，并强制终止滑动
        if (mNextX <= 0) {
            mNextX = 0;
            mScroller.forceFinished(true);
        }
        if (mNextX >= mMaxX) {
            mNextX = mMaxX;
            mScroller.forceFinished(true);
        }

        //dx表示一次滑动的位移
        int dx = mCurrentX - mNextX;

        removeNonVisibleItems(dx);
        fillList(dx);
        positionItems(dx);

        mCurrentX = mNextX;

        if (!mScroller.isFinished()) {
            post(new Runnable() {
                @Override
                public void run() {
                    requestLayout();
                }
            });

        } else if (!isTouched) {
            isTouched = true;
            dx = mScroller.getCurrX() % itemWidth;
            // 从上面dx的计算方法可以看出，dx表示每次滑动结束之后与
            if (dx != 0) {
                if (dx > itemWidth / 2) {
                    dx = dx - itemWidth;
                }
                /**
                 * void android.widget.Scroller.startScroll(int startX, int startY, int dx, int dy)
                 * 该方法可以是Scroller从(startX,startY)滚动到(startX+dx,startY+dy)，滚动时间为默认的250ms
                 * startX:滚动起始x坐标 
                 * startY:滚动起始y坐标 
                 * dx：滚动x坐标偏移量，正直表示向左滚动
                 * dy：滚动y坐标偏移量，正直表示向上滚动
                 */
                mScroller.startScroll(mScroller.getCurrX(), mScroller.getCurrY(), -dx, 0);

                post(new Runnable() {

                    @Override
                    public void run() {
                        // TODO Auto-generated method stub
                        requestLayout();
                    }
                });
            }
        }
    }

    // 填充列表，fillList()传入一次移动的偏移量dx
    private void fillList(final int dx) {
        int edge = 0;
        View child = getChildAt(getChildCount() - 1);
        if (child != null) {
            edge = child.getRight();
        }
        fillListRight(edge, dx);

        edge = 0;
        child = getChildAt(0);
        if (child != null) {
            edge = child.getLeft();
        }
        fillListLeft(edge, dx);

    }

    private void fillListRight(int rightEdge, final int dx) {
        // rightEdge是为了计算mMaxX(最大长度的X坐标)
        while (rightEdge + dx < getWidth()
                && mRightViewIndex < mAdapter.getCount()) {
            // Queue的Object poll()方法：获取队列头部的元素，并删除该元素。如果此队列为空，则返回null。
            View child = mAdapter.getView(mRightViewIndex,
                    mRemovedViewQueue.poll(), this);
            addAndMeasureChild(child, -1);
            rightEdge += child.getMeasuredWidth();

            // 如果右边View的下标已经是适配器的总数，则计算出mMaxX
            if (mRightViewIndex == mAdapter.getCount() - 1) {
                mMaxX = mCurrentX + rightEdge - getWidth();
            }

            if (mMaxX < 0) {
                mMaxX = 0;
            }
            mRightViewIndex++;
        }

    }

    private void fillListLeft(int leftEdge, final int dx) {
        while (leftEdge + dx > 0 && mLeftViewIndex >= 0) {
            View child = mAdapter.getView(mLeftViewIndex,
                    mRemovedViewQueue.poll(), this);
            addAndMeasureChild(child, 0);
            leftEdge -= child.getMeasuredWidth();
            mLeftViewIndex--;
            mDisplayOffset -= child.getMeasuredWidth();
        }
    }

    // 该方法从list两端找到不在屏幕内显示的子View，并作相应处理
    private void removeNonVisibleItems(final int dx) {
        // 从第一个子View开始
        View child = getChildAt(0);
        // 如果子View的右边界+偏移量<0,即该子View没在屏幕显示范围内(屏幕左边界之外)
        while (child != null && child.getRight() + dx <= 0) {
            mDisplayOffset += child.getMeasuredWidth();
            // Queue接口中的boolean offer(Object e)方法：将指定元素加入此队列的尾部。
            // 当使用有容量限制的队列时，此方法通常比add(Object e)方法更好。
            // 下面的语句把当前View加入removed组件队列之中。
            mRemovedViewQueue.offer(child);
            // 将当前View从Layout中移除。
            removeViewInLayout(child);
            // 最左边View下标加一。
            mLeftViewIndex++;
            // child移动到下一个View
            child = getChildAt(0);
        }

        // 右边的操作与左边类似
        child = getChildAt(getChildCount() - 1);
        while (child != null && child.getLeft() + dx >= getWidth()) {
            mRemovedViewQueue.offer(child);
            removeViewInLayout(child);
            mRightViewIndex--;
            child = getChildAt(getChildCount() - 1);
        }
    }

    private void positionItems(final int dx) {
        if (getChildCount() > 0) {
            mDisplayOffset += dx;
            int left = mDisplayOffset;
            for (int i = 0; i < getChildCount(); i++) {
                View child = getChildAt(i);
                int childWidth = child.getMeasuredWidth();
                child.layout(left, 0, left + childWidth,
                        child.getMeasuredHeight());
                left += childWidth + child.getPaddingRight();
            }
        }
    }

    public synchronized void scrollTo(int x) {
        mScroller.startScroll(mNextX, 0, x - mNextX, 0);
        requestLayout();
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        boolean handled = super.dispatchTouchEvent(ev);
        handled |= mGesture.onTouchEvent(ev);return handled;
    }

    protected boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
            float velocityY) {
        synchronized (HorizontalListView.this) {
            mScroller.fling(mNextX, 0, (int) -velocityX, 0, 0, mMaxX, 0, 0);
        }
        requestLayout();

        return true;
    }

    // 无论是否在滚动，如果有手指按下事件则立即停止滚动
    protected boolean onDown(MotionEvent e) {
        mScroller.forceFinished(true);
        return true;
    }

    private OnGestureListener mOnGesture = new GestureDetector.SimpleOnGestureListener() {

        @Override
        public boolean onDown(MotionEvent e) {
            return HorizontalListView.this.onDown(e);
        }

        @Override
        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
                float velocityY) {
            isTouched = false;
            return HorizontalListView.this
                    .onFling(e1, e2, velocityX, velocityY);
        }

        @Override
        public boolean onScroll(MotionEvent e1, MotionEvent e2,
                float distanceX, float distanceY) {

            synchronized (HorizontalListView.this) {
                mNextX += (int) distanceX;
            }
            requestLayout();

            return true;
        }

        @Override
        public boolean onSingleTapConfirmed(MotionEvent e) {
            for (int i = 0; i < getChildCount(); i++) {
                View child = getChildAt(i);
                if (isEventWithinView(e, child)) {
                    if (mOnItemClicked != null) {
                        mOnItemClicked.onItemClick(HorizontalListView.this,
                                child, mLeftViewIndex + 1 + i,
                                mAdapter.getItemId(mLeftViewIndex + 1 + i));
                    }

                    if (mOnItemSelected != null) {
                        mOnItemSelected.onItemSelected(HorizontalListView.this,
                                child, mLeftViewIndex + 1 + i,
                                mAdapter.getItemId(mLeftViewIndex + 1 + i));
                    }
                    break;
                }

            }
            return true;
        }

        @Override
        public void onLongPress(MotionEvent e) {
            int childCount = getChildCount();
            for (int i = 0; i < childCount; i++) {
                View child = getChildAt(i);
                if (isEventWithinView(e, child)) {
                    if (mOnItemLongClicked != null) {
                        mOnItemLongClicked.onItemLongClick(
                                HorizontalListView.this, child, mLeftViewIndex
                                        + 1 + i,
                                mAdapter.getItemId(mLeftViewIndex + 1 + i));
                    }
                    break;
                }

            }
        }

        private boolean isEventWithinView(MotionEvent e, View child) {
            Rect viewRect = new Rect();
            int[] childPosition = new int[2];
            child.getLocationOnScreen(childPosition);
            int left = childPosition[0];
            int right = left + child.getWidth();
            int top = childPosition[1];
            int bottom = top + child.getHeight();
            viewRect.set(left, top, right, bottom);
            return viewRect.contains((int) e.getRawX(), (int) e.getRawY());
        }
    };
    private boolean isTouched = false;
    private int downX, upX;
    private boolean cannotClick = false;

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // TODO Auto-generated method stub

        int ea = event.getAction();
        switch (ea) {
        case MotionEvent.ACTION_DOWN:
            isTouched = true;
            downX = (int) event.getRawX();
            if (mScroller.getCurrX() % itemWidth != 0) {
                Log.v("ACTION_DOWN", "ACTION_DOWN");
                cannotClick  = true;
                return true;
            }
            break;
        case MotionEvent.ACTION_MOVE:
            break;
        case MotionEvent.ACTION_UP:
            Log.v("ACTION_UP", "ACTION_UP");
            isTouched = true;
            upX = (int) event.getRawX();
            int dx = (-(upX - downX) + mScroller.getCurrX()) % itemWidth;
            // dx为正则向右移动，否则向左移动
            if (dx != 0) {
                Log.v("修正", "修正");
                if (dx < itemWidth / 2) {
                    // Log.v("ACTION_UP", "dx:"+dx);
                } else {
                    dx = dx - itemWidth;
                    // Log.v("ACTION_UP", "dx:"+dx);
                }
                mScroller.startScroll(mScroller.getCurrX() - (upX - downX),
                        mScroller.getCurrY(), -dx, 0);
                post(new Runnable() {

                    @Override
                    public void run() {
                        // TODO Auto-generated method stub
                        requestLayout();
                    }
                });
                return true;
            }
            break;
        default:
            break;
        }
        return super.onTouchEvent(event);
    }

}