package src.com;

import android.content.Context;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.view.Display;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.WindowManager;
import android.widget.Scroller;

public final class PanelPager extends ViewGroup {
	
	private static final int ANIMATION_SCREEN_SET_DURATION_MILLIS = 500;
	private static final int FRACTION_OF_SCREEN_WIDTH_FOR_SWIPE = 4;
	private static final int INVALID_SCREEN = -1;
	private static final int SNAP_VELOCITY_DIP_PER_SECOND = 600;
	private static final int VELOCITY_UNIT_PIXELS_PER_SECOND = 1000;

	private static final int TOUCH_STATE_REST = 0;
	private static final int TOUCH_STATE_HORIZONTAL_SCROLLING = 1;
	private static final int TOUCH_STATE_VERTICAL_SCROLLING = -1;
	private int mCurrentScreen;
	private int mDensityAdjustedSnapVelocity;
	private boolean mFirstLayout = true;
	private float mLastMotionX;
	private float mLastMotionY;
	private OnScreenSwitchListener mOnScreenSwitchListener;
	private int mMaximumVelocity;
	private int mNextScreen = INVALID_SCREEN;
	private Scroller mScroller;
	private int mTouchSlop;
	private int mTouchState = TOUCH_STATE_REST;
	private VelocityTracker mVelocityTracker;
	private int mLastSeenLayoutWidth = -1;

	/**
	 * Simple constructor to use when creating a view from code.
	 * 
	 * @param context
	 *            The Context the view is running in, through which it can
	 *            access the current theme, resources, etc.
	 */
	public PanelPager(final Context context) {
		super(context);
		init();
	}

	/**
	 * Constructor that is called when inflating a view from XML. This is called
	 * when a view is being constructed from an XML file, supplying attributes
	 * that were specified in the XML file. This version uses a default style of
	 * 0, so the only attribute values applied are those in the Context's Theme
	 * and the given AttributeSet.
	 * 
	 * <p>
	 * The method onFinishInflate() will be called after all children have been
	 * added.
	 * 
	 * @param context
	 *            The Context the view is running in, through which it can
	 *            access the current theme, resources, etc.
	 * @param attrs
	 *            The attributes of the XML tag that is inflating the view.
	 * @see #View(Context, AttributeSet, int)
	 */
	public PanelPager(final Context context, final AttributeSet attrs) {
		super(context, attrs);
		init();
	}

	/**
	 * Sets up the scroller and touch/fling sensitivity parameters for the
	 * pager.
	 */
	private void init() {
		mScroller = new Scroller(getContext());

		// Calculate the density-dependent snap velocity in pixels
		DisplayMetrics displayMetrics = new DisplayMetrics();
		((WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE))
				.getDefaultDisplay().getMetrics(displayMetrics);
		mDensityAdjustedSnapVelocity = (int) (displayMetrics.density * SNAP_VELOCITY_DIP_PER_SECOND);

		final ViewConfiguration configuration = ViewConfiguration
				.get(getContext());
		mTouchSlop = configuration.getScaledTouchSlop();
		mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
	}

	@Override
	protected void onMeasure(final int widthMeasureSpec,
			final int heightMeasureSpec) {
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);

		final int width = MeasureSpec.getSize(widthMeasureSpec);
		final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
		if (widthMode != MeasureSpec.EXACTLY) {
			throw new IllegalStateException(
					"ViewSwitcher can only be used in EXACTLY mode.");
		}

		final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
		if (heightMode != MeasureSpec.EXACTLY) {
			throw new IllegalStateException(
					"ViewSwitcher can only be used in EXACTLY mode.");
		}

		// The children are given the same width and height as the workspace
		final int count = getChildCount();
		for (int i = 0; i < count; i++) {
			getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
		}

		if (mFirstLayout) {
			scrollTo(mCurrentScreen * width, 0);
			mFirstLayout = false;
		}

		else if (width != mLastSeenLayoutWidth) { // Width has changed
			/*
			 * Recalculate the width and scroll to the right position to be sure
			 * we're in the right place in the event that we had a rotation that
			 * didn't result in an activity restart (code by aveyD). Without
			 * this you can end up between two pages after a rotation.
			 */
			Display display = ((WindowManager) getContext().getSystemService(
					Context.WINDOW_SERVICE)).getDefaultDisplay();
			int displayWidth = display.getWidth();

			mNextScreen = Math.max(0,
					Math.min(getCurrentScreen(), getChildCount() - 1));
			final int newX = mNextScreen * displayWidth;
			final int delta = newX - getScrollX();

			mScroller.startScroll(getScrollX(), 0, delta, 0, 0);
		}

		mLastSeenLayoutWidth = width;
	}

	@Override
	protected void onLayout(final boolean changed, final int l, final int t,
			final int r, final int b) {
		int childLeft = 0;
		final int count = getChildCount();

		for (int i = 0; i < count; i++) {
			final View child = getChildAt(i);
			if (child.getVisibility() != View.GONE) {
				final int childWidth = child.getMeasuredWidth();
				child.layout(childLeft, 0, childLeft + childWidth,
						child.getMeasuredHeight());
				childLeft += childWidth;
			}
		}
	}

	@Override
	public boolean onInterceptTouchEvent(final MotionEvent ev) {
		/*
		 * By Yoni Samlan: Modified onInterceptTouchEvent based on standard
		 * ScrollView's onIntercept. The logic is designed to support a nested
		 * vertically scrolling view inside this one; once a scroll registers
		 * for X-wise scrolling, handle it in this view and don't let the
		 * children, but once a scroll registers for y-wise scrolling, let the
		 * children handle it exclusively.
		 */
		final int action = ev.getAction();
		boolean intercept = false;

		switch (action) {
		case MotionEvent.ACTION_MOVE:
			/*
			 * If we're in a horizontal scroll event, take it (intercept further
			 * events). But if we're mid-vertical-scroll, don't even try; let
			 * the children deal with it. If we haven't found a scroll event
			 * yet, check for one.
			 */
			if (mTouchState == TOUCH_STATE_HORIZONTAL_SCROLLING) {
				/*
				 * We've already started a horizontal scroll; set intercept to
				 * true so we can take the remainder of all touch events in
				 * onTouchEvent.
				 */
				intercept = true;
			} else if (mTouchState == TOUCH_STATE_VERTICAL_SCROLLING) {
				// Let children handle the events for the duration of the scroll
				// event.
				intercept = false;
			} else { // We haven't picked up a scroll event yet; check for one.

				/*
				 * If we detected a horizontal scroll event, start stealing
				 * touch events (mark as scrolling). Otherwise, see if we had a
				 * vertical scroll event -- if so, let the children handle it
				 * and don't look to intercept again until the motion is done.
				 */

				final float x = ev.getX();
				final int xDiff = (int) Math.abs(x - mLastMotionX);
				boolean xMoved = xDiff > mTouchSlop;

				if (xMoved) {
					// Scroll if the user moved far enough along the X axis
					mTouchState = TOUCH_STATE_HORIZONTAL_SCROLLING;
					mLastMotionX = x;
				}

				final float y = ev.getY();
				final int yDiff = (int) Math.abs(y - mLastMotionY);
				boolean yMoved = yDiff > mTouchSlop;

				if (yMoved) {
					mTouchState = TOUCH_STATE_VERTICAL_SCROLLING;
				}
			}

			break;
		case MotionEvent.ACTION_CANCEL:
		case MotionEvent.ACTION_UP:
			// Release the drag.
			mTouchState = TOUCH_STATE_REST;
			break;
		case MotionEvent.ACTION_DOWN:
			/*
			 * No motion yet, but register the coordinates so we can check for
			 * intercept at the next MOVE event.
			 */
			mLastMotionY = ev.getY();
			mLastMotionX = ev.getX();
			break;
		default:
			break;
		}

		return intercept;
	}

	@Override
	public boolean onTouchEvent(final MotionEvent ev) {

		if (mVelocityTracker == null) {
			mVelocityTracker = VelocityTracker.obtain();
		}
		mVelocityTracker.addMovement(ev);

		final int action = ev.getAction();
		final float x = ev.getX();

		switch (action) {
		case MotionEvent.ACTION_DOWN:
			/*
			 * If being flinged and user touches, stop the fling. isFinished
			 * will be false if being flinged.
			 */
			if (!mScroller.isFinished()) {
				mScroller.abortAnimation();
			}

			// Remember where the motion event started
			mLastMotionX = x;

			if (mScroller.isFinished()) {
				mTouchState = TOUCH_STATE_REST;
			} else {
				mTouchState = TOUCH_STATE_HORIZONTAL_SCROLLING;
			}

			break;
		case MotionEvent.ACTION_MOVE:
			final int xDiff = (int) Math.abs(x - mLastMotionX);
			boolean xMoved = xDiff > mTouchSlop;

			if (xMoved) {
				// Scroll if the user moved far enough along the X axis
				mTouchState = TOUCH_STATE_HORIZONTAL_SCROLLING;
			}

			if (mTouchState == TOUCH_STATE_HORIZONTAL_SCROLLING) {
				// Scroll to follow the motion event
				final int deltaX = (int) (mLastMotionX - x);
				mLastMotionX = x;
				final int scrollX = getScrollX();

				if (deltaX < 0) {
					if (scrollX > 0) {
						scrollBy(Math.max(-scrollX, deltaX), 0);
					}
				} else if (deltaX > 0) {
					final int availableToScroll = getChildAt(
							getChildCount() - 1).getRight()
							- scrollX - getWidth();

					if (availableToScroll > 0) {
						scrollBy(Math.min(availableToScroll, deltaX), 0);
					}
				}
			}

			break;

		case MotionEvent.ACTION_UP:
			if (mTouchState == TOUCH_STATE_HORIZONTAL_SCROLLING) {
				final VelocityTracker velocityTracker = mVelocityTracker;
				velocityTracker.computeCurrentVelocity(
						VELOCITY_UNIT_PIXELS_PER_SECOND, mMaximumVelocity);
				int velocityX = (int) velocityTracker.getXVelocity();

				if (velocityX > mDensityAdjustedSnapVelocity
						&& mCurrentScreen > 0) {
					// Fling hard enough to move left
					snapToScreen(mCurrentScreen - 1);
				} else if (velocityX < -mDensityAdjustedSnapVelocity
						&& mCurrentScreen < getChildCount() - 1) {
					// Fling hard enough to move right
					snapToScreen(mCurrentScreen + 1);
				} else {
					snapToDestination();
				}

				if (mVelocityTracker != null) {
					mVelocityTracker.recycle();
					mVelocityTracker = null;
				}
			}

			mTouchState = TOUCH_STATE_REST;

			break;
		case MotionEvent.ACTION_CANCEL:
			mTouchState = TOUCH_STATE_REST;
			break;
		default:
			break;
		}

		return true;
	}

	@Override
	public void computeScroll() {
		if (mScroller.computeScrollOffset()) {
			scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
			postInvalidate();
		} else if (mNextScreen != INVALID_SCREEN) {
			mCurrentScreen = Math.max(0,
					Math.min(mNextScreen, getChildCount() - 1));

			// Notify observer about screen change
			if (mOnScreenSwitchListener != null) {
				mOnScreenSwitchListener.onScreenSwitched(mCurrentScreen);
			}

			mNextScreen = INVALID_SCREEN;
		}
	}

	/**
	 * Returns the index of the currently displayed screen.
	 * 
	 * @return The index of the currently displayed screen.
	 */
	public int getCurrentScreen() {
		return mCurrentScreen;
	}

	/**
	 * Sets the current screen.
	 * 
	 * @param currentScreen
	 *            The new screen.
	 * @param animate
	 *            True to smoothly scroll to the screen, false to snap instantly
	 */
	public void setCurrentScreen(final int currentScreen, final boolean animate) {
		mCurrentScreen = Math.max(0,
				Math.min(currentScreen, getChildCount() - 1));
		if (animate) {
			snapToScreen(currentScreen, ANIMATION_SCREEN_SET_DURATION_MILLIS);
		} else {
			scrollTo(mCurrentScreen * getWidth(), 0);
		}
		invalidate();
	}

	/**
	 * Sets the {@link OnScreenSwitchListener}.
	 * 
	 * @param onScreenSwitchListener
	 *            The listener for switch events.
	 */
	public void setOnScreenSwitchListener(
			final OnScreenSwitchListener onScreenSwitchListener) {
		mOnScreenSwitchListener = onScreenSwitchListener;
	}

	/**
	 * Snaps to the screen we think the user wants (the current screen for very
	 * small movements; the next/prev screen for bigger movements).
	 */
	private void snapToDestination() {
		final int screenWidth = getWidth();
		int scrollX = getScrollX();
		int whichScreen = mCurrentScreen;
		int deltaX = scrollX - (screenWidth * mCurrentScreen);

		// Check if they want to go to the prev. screen
		if ((deltaX < 0)
				&& mCurrentScreen != 0
				&& ((screenWidth / FRACTION_OF_SCREEN_WIDTH_FOR_SWIPE) < -deltaX)) {
			whichScreen--;
			// Check if they want to go to the next screen
		} else if ((deltaX > 0)
				&& (mCurrentScreen + 1 != getChildCount())
				&& ((screenWidth / FRACTION_OF_SCREEN_WIDTH_FOR_SWIPE) < deltaX)) {
			whichScreen++;
		}

		snapToScreen(whichScreen);
	}

	/**
	 * Snap to a specific screen, animating automatically for a duration
	 * proportional to the distance left to scroll.
	 * 
	 * @param whichScreen
	 *            Screen to snap to
	 */
	private void snapToScreen(final int whichScreen) {
		snapToScreen(whichScreen, -1);
	}

	/**
	 * Snaps to a specific screen, animating for a specific amount of time to
	 * get there.
	 * 
	 * @param whichScreen
	 *            Screen to snap to
	 * @param duration
	 *            -1 to automatically time it based on scroll distance; a
	 *            positive number to make the scroll take an exact duration.
	 */
	private void snapToScreen(final int whichScreen, final int duration) {
		/*
		 * Modified by Yoni Samlan: Allow new snapping even during an ongoing
		 * scroll animation. This is intended to make HorizontalPager work as
		 * expected when used in conjunction with a RadioGroup used as "tabbed"
		 * controls. Also, make the animation take a percentage of our normal
		 * animation time, depending how far they've already scrolled.
		 */
		mNextScreen = Math.max(0, Math.min(whichScreen, getChildCount() - 1));
		final int newX = mNextScreen * getWidth();
		final int delta = newX - getScrollX();

		if (duration < 0) {
			// E.g. if they've scrolled 80% of the way, only animation for 20%
			// of the duration
			mScroller
					.startScroll(
							getScrollX(),
							0,
							delta,
							0,
							(int) (Math.abs(delta) / (float) getWidth() * ANIMATION_SCREEN_SET_DURATION_MILLIS));
		} else {
			mScroller.startScroll(getScrollX(), 0, delta, 0, duration);
		}

		invalidate();
	}

	/**
	 * Listener for the event that the HorizontalPager switches to a new view.
	 */
	public static interface OnScreenSwitchListener {
		/**
		 * Notifies listeners about the new screen. Runs after the animation
		 * completed.
		 * 
		 * @param screen
		 *            The new screen index.
		 */
		void onScreenSwitched(int screen);
	}
}