/*
 * Copyright (C) 2014 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 com.android.systemui.statusbar.stack;

import android.content.Context;
import android.content.res.Resources;
import android.util.Log;
import android.view.View;
import android.view.ViewGroup;
import com.android.systemui.R;
import com.android.systemui.statusbar.DismissView;
import com.android.systemui.statusbar.EmptyShadeView;
import com.android.systemui.statusbar.ExpandableNotificationRow;
import com.android.systemui.statusbar.ExpandableView;
import com.android.systemui.statusbar.NotificationShelf;
import com.android.systemui.statusbar.notification.NotificationUtils;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

/**
 * The Algorithm of the {@link com.android.systemui.statusbar.stack
 * .NotificationStackScrollLayout} which can be queried for {@link com.android.systemui.statusbar
 * .stack.StackScrollState}
 */
public class StackScrollAlgorithm {

    private static final String LOG_TAG = "StackScrollAlgorithm";

    private int mPaddingBetweenElements;
    private int mIncreasedPaddingBetweenElements;
    private int mCollapsedSize;

    private StackScrollAlgorithmState mTempAlgorithmState = new StackScrollAlgorithmState();
    private boolean mIsExpanded;
    private boolean mClipNotificationScrollToTop;
    private int mStatusBarHeight;

    public StackScrollAlgorithm(Context context) {
        initView(context);
    }

    public void initView(Context context) {
        initConstants(context);
    }

    private void initConstants(Context context) {
        Resources res = context.getResources();
        mPaddingBetweenElements = res.getDimensionPixelSize(
                R.dimen.notification_divider_height);
        mIncreasedPaddingBetweenElements =
                res.getDimensionPixelSize(R.dimen.notification_divider_height_increased);
        mCollapsedSize = res.getDimensionPixelSize(R.dimen.notification_min_height);
        mStatusBarHeight = res.getDimensionPixelSize(R.dimen.status_bar_height);
        mClipNotificationScrollToTop = res.getBoolean(R.bool.config_clipNotificationScrollToTop);
    }

    public void getStackScrollState(AmbientState ambientState, StackScrollState resultState) {
        // The state of the local variables are saved in an algorithmState to easily subdivide it
        // into multiple phases.
        StackScrollAlgorithmState algorithmState = mTempAlgorithmState;

        // First we reset the view states to their default values.
        resultState.resetViewStates();

        initAlgorithmState(resultState, algorithmState, ambientState);

        updatePositionsForState(resultState, algorithmState, ambientState);

        updateZValuesForState(resultState, algorithmState, ambientState);

        updateHeadsUpStates(resultState, algorithmState, ambientState);

        handleDraggedViews(ambientState, resultState, algorithmState);
        updateDimmedActivatedHideSensitive(ambientState, resultState, algorithmState);
        updateClipping(resultState, algorithmState, ambientState);
        updateSpeedBumpState(resultState, algorithmState, ambientState);
        updateShelfState(resultState, ambientState);
        getNotificationChildrenStates(resultState, algorithmState);
    }

    private void getNotificationChildrenStates(StackScrollState resultState,
            StackScrollAlgorithmState algorithmState) {
        int childCount = algorithmState.visibleChildren.size();
        for (int i = 0; i < childCount; i++) {
            ExpandableView v = algorithmState.visibleChildren.get(i);
            if (v instanceof ExpandableNotificationRow) {
                ExpandableNotificationRow row = (ExpandableNotificationRow) v;
                row.getChildrenStates(resultState);
            }
        }
    }

    private void updateSpeedBumpState(StackScrollState resultState,
            StackScrollAlgorithmState algorithmState, AmbientState ambientState) {
        int childCount = algorithmState.visibleChildren.size();
        int belowSpeedBump = ambientState.getSpeedBumpIndex();
        for (int i = 0; i < childCount; i++) {
            View child = algorithmState.visibleChildren.get(i);
            ExpandableViewState childViewState = resultState.getViewStateForView(child);

            // The speed bump can also be gone, so equality needs to be taken when comparing
            // indices.
            childViewState.belowSpeedBump = i >= belowSpeedBump;
        }

    }
    private void updateShelfState(StackScrollState resultState, AmbientState ambientState) {
        NotificationShelf shelf = ambientState.getShelf();
        if (shelf != null) {
            shelf.updateState(resultState, ambientState);
        }
    }

    private void updateClipping(StackScrollState resultState,
            StackScrollAlgorithmState algorithmState, AmbientState ambientState) {
        float drawStart = !ambientState.isOnKeyguard() ? ambientState.getTopPadding()
                + ambientState.getStackTranslation() + ambientState.getExpandAnimationTopChange()
                : 0;
        float previousNotificationEnd = 0;
        float previousNotificationStart = 0;
        int childCount = algorithmState.visibleChildren.size();
        for (int i = 0; i < childCount; i++) {
            ExpandableView child = algorithmState.visibleChildren.get(i);
            ExpandableViewState state = resultState.getViewStateForView(child);
            if (!child.mustStayOnScreen() || state.headsUpIsVisible) {
                previousNotificationEnd = Math.max(drawStart, previousNotificationEnd);
                previousNotificationStart = Math.max(drawStart, previousNotificationStart);
            }
            float newYTranslation = state.yTranslation;
            float newHeight = state.height;
            float newNotificationEnd = newYTranslation + newHeight;
            boolean isHeadsUp = (child instanceof ExpandableNotificationRow)
                    && ((ExpandableNotificationRow) child).isPinned();
            if (mClipNotificationScrollToTop
                    && !state.inShelf && newYTranslation < previousNotificationEnd
                    && (!isHeadsUp || ambientState.isShadeExpanded())) {
                // The previous view is overlapping on top, clip!
                float overlapAmount = previousNotificationEnd - newYTranslation;
                state.clipTopAmount = (int) overlapAmount;
            } else {
                state.clipTopAmount = 0;
            }

            if (!child.isTransparent()) {
                // Only update the previous values if we are not transparent,
                // otherwise we would clip to a transparent view.
                previousNotificationEnd = newNotificationEnd;
                previousNotificationStart = newYTranslation;
            }
        }
    }

    public static boolean canChildBeDismissed(View v) {
        if (!(v instanceof ExpandableNotificationRow)) {
            return false;
        }
        ExpandableNotificationRow row = (ExpandableNotificationRow) v;
        if (row.areGutsExposed()) {
            return false;
        }
        return row.canViewBeDismissed();
    }

    /**
     * Updates the dimmed, activated and hiding sensitive states of the children.
     */
    private void updateDimmedActivatedHideSensitive(AmbientState ambientState,
            StackScrollState resultState, StackScrollAlgorithmState algorithmState) {
        boolean dimmed = ambientState.isDimmed();
        boolean dark = ambientState.isDark();
        boolean hideSensitive = ambientState.isHideSensitive();
        View activatedChild = ambientState.getActivatedChild();
        int childCount = algorithmState.visibleChildren.size();
        for (int i = 0; i < childCount; i++) {
            View child = algorithmState.visibleChildren.get(i);
            ExpandableViewState childViewState = resultState.getViewStateForView(child);
            childViewState.dimmed = dimmed;
            childViewState.dark = dark;
            childViewState.hideSensitive = hideSensitive;
            boolean isActivatedChild = activatedChild == child;
            if (dimmed && isActivatedChild) {
                childViewState.zTranslation += 2.0f * ambientState.getZDistanceBetweenElements();
            }
        }
    }

    /**
     * Handle the special state when views are being dragged
     */
    private void handleDraggedViews(AmbientState ambientState, StackScrollState resultState,
            StackScrollAlgorithmState algorithmState) {
        ArrayList<View> draggedViews = ambientState.getDraggedViews();
        for (View draggedView : draggedViews) {
            int childIndex = algorithmState.visibleChildren.indexOf(draggedView);
            if (childIndex >= 0 && childIndex < algorithmState.visibleChildren.size() - 1) {
                View nextChild = algorithmState.visibleChildren.get(childIndex + 1);
                if (!draggedViews.contains(nextChild)) {
                    // only if the view is not dragged itself we modify its state to be fully
                    // visible
                    ExpandableViewState viewState = resultState.getViewStateForView(
                            nextChild);
                    // The child below the dragged one must be fully visible
                    if (ambientState.isShadeExpanded()) {
                        viewState.shadowAlpha = 1;
                        viewState.hidden = false;
                    }
                }

                // Lets set the alpha to the one it currently has, as its currently being dragged
                ExpandableViewState viewState = resultState.getViewStateForView(draggedView);
                // The dragged child should keep the set alpha
                viewState.alpha = draggedView.getAlpha();
            }
        }
    }

    /**
     * Initialize the algorithm state like updating the visible children.
     */
    private void initAlgorithmState(StackScrollState resultState, StackScrollAlgorithmState state,
            AmbientState ambientState) {
        float bottomOverScroll = ambientState.getOverScrollAmount(false /* onTop */);

        int scrollY = ambientState.getScrollY();

        // Due to the overScroller, the stackscroller can have negative scroll state. This is
        // already accounted for by the top padding and doesn't need an additional adaption
        scrollY = Math.max(0, scrollY);
        state.scrollY = (int) (scrollY + bottomOverScroll);

        //now init the visible children and update paddings
        ViewGroup hostView = resultState.getHostView();
        int childCount = hostView.getChildCount();
        state.visibleChildren.clear();
        state.visibleChildren.ensureCapacity(childCount);
        state.paddingMap.clear();
        int notGoneIndex = 0;
        ExpandableView lastView = null;
        int firstHiddenIndex = ambientState.isDark()
                ? (ambientState.hasPulsingNotifications() ? 1 : 0)
                : childCount;

        // The goal here is to fill the padding map, by iterating over how much padding each child
        // needs. The map is thereby reused, by first filling it with the padding amount and when
        // iterating over it again, it's filled with the actual resolved value.

        for (int i = 0; i < childCount; i++) {
            ExpandableView v = (ExpandableView) hostView.getChildAt(i);
            if (v.getVisibility() != View.GONE) {
                if (v == ambientState.getShelf()) {
                    continue;
                }
                if (i >= firstHiddenIndex) {
                    // we need normal padding now, to be in sync with what the stack calculates
                    lastView = null;
                    ExpandableViewState viewState = resultState.getViewStateForView(v);
                    viewState.hidden = true;
                }
                notGoneIndex = updateNotGoneIndex(resultState, state, notGoneIndex, v);
                float increasedPadding = v.getIncreasedPaddingAmount();
                if (increasedPadding != 0.0f) {
                    state.paddingMap.put(v, increasedPadding);
                    if (lastView != null) {
                        Float prevValue = state.paddingMap.get(lastView);
                        float newValue = getPaddingForValue(increasedPadding);
                        if (prevValue != null) {
                            float prevPadding = getPaddingForValue(prevValue);
                            if (increasedPadding > 0) {
                                newValue = NotificationUtils.interpolate(
                                        prevPadding,
                                        newValue,
                                        increasedPadding);
                            } else if (prevValue > 0) {
                                newValue = NotificationUtils.interpolate(
                                        newValue,
                                        prevPadding,
                                        prevValue);
                            }
                        }
                        state.paddingMap.put(lastView, newValue);
                    }
                } else if (lastView != null) {

                    // Let's now resolve the value to an actual padding
                    float newValue = getPaddingForValue(state.paddingMap.get(lastView));
                    state.paddingMap.put(lastView, newValue);
                }
                if (v instanceof ExpandableNotificationRow) {
                    ExpandableNotificationRow row = (ExpandableNotificationRow) v;

                    // handle the notgoneIndex for the children as well
                    List<ExpandableNotificationRow> children =
                            row.getNotificationChildren();
                    if (row.isSummaryWithChildren() && children != null) {
                        for (ExpandableNotificationRow childRow : children) {
                            if (childRow.getVisibility() != View.GONE) {
                                ExpandableViewState childState
                                        = resultState.getViewStateForView(childRow);
                                childState.notGoneIndex = notGoneIndex;
                                notGoneIndex++;
                            }
                        }
                    }
                }
                lastView = v;
            }
        }
        ExpandableNotificationRow expandingNotification = ambientState.getExpandingNotification();
        state.indexOfExpandingNotification = expandingNotification != null
                ? state.visibleChildren.indexOf(expandingNotification)
                : -1;
    }

    private float getPaddingForValue(Float increasedPadding) {
        if (increasedPadding == null) {
            return mPaddingBetweenElements;
        } else if (increasedPadding >= 0.0f) {
            return NotificationUtils.interpolate(
                    mPaddingBetweenElements,
                    mIncreasedPaddingBetweenElements,
                    increasedPadding);
        } else {
            return NotificationUtils.interpolate(
                    0,
                    mPaddingBetweenElements,
                    1.0f + increasedPadding);
        }
    }

    private int updateNotGoneIndex(StackScrollState resultState,
            StackScrollAlgorithmState state, int notGoneIndex,
            ExpandableView v) {
        ExpandableViewState viewState = resultState.getViewStateForView(v);
        viewState.notGoneIndex = notGoneIndex;
        state.visibleChildren.add(v);
        notGoneIndex++;
        return notGoneIndex;
    }

    /**
     * Determine the positions for the views. This is the main part of the algorithm.
     *
     * @param resultState The result state to update if a change to the properties of a child occurs
     * @param algorithmState The state in which the current pass of the algorithm is currently in
     * @param ambientState The current ambient state
     */
    private void updatePositionsForState(StackScrollState resultState,
            StackScrollAlgorithmState algorithmState, AmbientState ambientState) {

        // The y coordinate of the current child.
        float currentYPosition = -algorithmState.scrollY;
        int childCount = algorithmState.visibleChildren.size();
        for (int i = 0; i < childCount; i++) {
            currentYPosition = updateChild(i, resultState, algorithmState, ambientState,
                    currentYPosition);
        }
    }

    protected float updateChild(int i, StackScrollState resultState,
            StackScrollAlgorithmState algorithmState, AmbientState ambientState,
            float currentYPosition) {
        ExpandableView child = algorithmState.visibleChildren.get(i);
        ExpandableViewState childViewState = resultState.getViewStateForView(child);
        childViewState.location = ExpandableViewState.LOCATION_UNKNOWN;
        int paddingAfterChild = getPaddingAfterChild(algorithmState, child);
        int childHeight = getMaxAllowedChildHeight(child);
        childViewState.yTranslation = currentYPosition;
        boolean isDismissView = child instanceof DismissView;
        boolean isEmptyShadeView = child instanceof EmptyShadeView;

        childViewState.location = ExpandableViewState.LOCATION_MAIN_AREA;
        float inset = ambientState.getTopPadding() + ambientState.getStackTranslation();
        if (i < algorithmState.getIndexOfExpandingNotification()) {
            inset += ambientState.getExpandAnimationTopChange();
        }
        if (child.mustStayOnScreen() && childViewState.yTranslation >= 0) {
            // Even if we're not scrolled away we're in view and we're also not in the
            // shelf. We can relax the constraints and let us scroll off the top!
            float end = childViewState.yTranslation + childViewState.height + inset;
            childViewState.headsUpIsVisible = end < ambientState.getMaxHeadsUpTranslation();
        }
        if (isDismissView) {
            childViewState.yTranslation = Math.min(childViewState.yTranslation,
                    ambientState.getInnerHeight() - childHeight);
        } else if (isEmptyShadeView) {
            childViewState.yTranslation = ambientState.getInnerHeight() - childHeight
                    + ambientState.getStackTranslation() * 0.25f;
        } else {
            clampPositionToShelf(child, childViewState, ambientState);
        }

        currentYPosition = childViewState.yTranslation + childHeight + paddingAfterChild;
        if (currentYPosition <= 0) {
            childViewState.location = ExpandableViewState.LOCATION_HIDDEN_TOP;
        }
        if (childViewState.location == ExpandableViewState.LOCATION_UNKNOWN) {
            Log.wtf(LOG_TAG, "Failed to assign location for child " + i);
        }

        childViewState.yTranslation += inset;
        return currentYPosition;
    }

    protected int getPaddingAfterChild(StackScrollAlgorithmState algorithmState,
            ExpandableView child) {
        return algorithmState.getPaddingAfterChild(child);
    }

    private void updateHeadsUpStates(StackScrollState resultState,
            StackScrollAlgorithmState algorithmState, AmbientState ambientState) {
        int childCount = algorithmState.visibleChildren.size();
        ExpandableNotificationRow topHeadsUpEntry = null;
        for (int i = 0; i < childCount; i++) {
            View child = algorithmState.visibleChildren.get(i);
            if (!(child instanceof ExpandableNotificationRow)) {
                break;
            }
            ExpandableNotificationRow row = (ExpandableNotificationRow) child;
            if (!row.isHeadsUp()) {
                break;
            }
            ExpandableViewState childState = resultState.getViewStateForView(row);
            if (topHeadsUpEntry == null && row.mustStayOnScreen() && !childState.headsUpIsVisible) {
                topHeadsUpEntry = row;
                childState.location = ExpandableViewState.LOCATION_FIRST_HUN;
            }
            boolean isTopEntry = topHeadsUpEntry == row;
            float unmodifiedEndLocation = childState.yTranslation + childState.height;
            if (mIsExpanded) {
                if (row.mustStayOnScreen() && !childState.headsUpIsVisible) {
                    // Ensure that the heads up is always visible even when scrolled off
                    clampHunToTop(ambientState, row, childState);
                    if (i == 0 && ambientState.isAboveShelf(row)) {
                        // the first hun can't get off screen.
                        clampHunToMaxTranslation(ambientState, row, childState);
                        childState.hidden = false;
                    }
                }
            }
            if (row.isPinned()) {
                childState.yTranslation = Math.max(childState.yTranslation, 0);
                childState.height = Math.max(row.getIntrinsicHeight(), childState.height);
                childState.hidden = false;
                ExpandableViewState topState = resultState.getViewStateForView(topHeadsUpEntry);
                if (topState != null && !isTopEntry && (!mIsExpanded
                        || unmodifiedEndLocation < topState.yTranslation + topState.height)) {
                    // Ensure that a headsUp doesn't vertically extend further than the heads-up at
                    // the top most z-position
                    childState.height = row.getIntrinsicHeight();
                    childState.yTranslation = topState.yTranslation + topState.height
                            - childState.height;
                }
            }
            if (row.isHeadsUpAnimatingAway()) {
                childState.hidden = false;
            }
        }
    }

    private void clampHunToTop(AmbientState ambientState, ExpandableNotificationRow row,
            ExpandableViewState childState) {
        float newTranslation = Math.max(ambientState.getTopPadding()
                + ambientState.getStackTranslation(), childState.yTranslation);
        childState.height = (int) Math.max(childState.height - (newTranslation
                - childState.yTranslation), row.getCollapsedHeight());
        childState.yTranslation = newTranslation;
    }

    private void clampHunToMaxTranslation(AmbientState ambientState, ExpandableNotificationRow row,
            ExpandableViewState childState) {
        float newTranslation;
        float maxHeadsUpTranslation = ambientState.getMaxHeadsUpTranslation();
        float maxShelfPosition = ambientState.getInnerHeight() + ambientState.getTopPadding()
                + ambientState.getStackTranslation();
        maxHeadsUpTranslation = Math.min(maxHeadsUpTranslation, maxShelfPosition);
        float bottomPosition = maxHeadsUpTranslation - row.getCollapsedHeight();
        newTranslation = Math.min(childState.yTranslation, bottomPosition);
        childState.height = (int) Math.min(childState.height, maxHeadsUpTranslation
                - newTranslation);
        childState.yTranslation = newTranslation;
    }

    /**
     * Clamp the height of the child down such that its end is at most on the beginning of
     * the shelf.
     *
     * @param child
     * @param childViewState the view state of the child
     * @param ambientState the ambient state
     */
    private void clampPositionToShelf(ExpandableView child,
            ExpandableViewState childViewState,
            AmbientState ambientState) {
        if (ambientState.getShelf() == null) {
            return;
        }

        int shelfStart = ambientState.getInnerHeight()
                - ambientState.getShelf().getIntrinsicHeight();
        childViewState.yTranslation = Math.min(childViewState.yTranslation, shelfStart);
        if (childViewState.yTranslation >= shelfStart) {
            childViewState.hidden = !child.isExpandAnimationRunning();
            childViewState.inShelf = true;
            childViewState.headsUpIsVisible = false;
        }
        if (!ambientState.isShadeExpanded()) {
            childViewState.height = (int) (mStatusBarHeight - childViewState.yTranslation);
        }
    }

    protected int getMaxAllowedChildHeight(View child) {
        if (child instanceof ExpandableView) {
            ExpandableView expandableView = (ExpandableView) child;
            return expandableView.getIntrinsicHeight();
        }
        return child == null? mCollapsedSize : child.getHeight();
    }

    /**
     * Calculate the Z positions for all children based on the number of items in both stacks and
     * save it in the resultState
     *  @param resultState The result state to update the zTranslation values
     * @param algorithmState The state in which the current pass of the algorithm is currently in
     * @param ambientState The ambient state of the algorithm
     */
    private void updateZValuesForState(StackScrollState resultState,
            StackScrollAlgorithmState algorithmState, AmbientState ambientState) {
        int childCount = algorithmState.visibleChildren.size();
        float childrenOnTop = 0.0f;
        for (int i = childCount - 1; i >= 0; i--) {
            childrenOnTop = updateChildZValue(i, childrenOnTop,
                    resultState, algorithmState, ambientState);
        }
    }

    protected float updateChildZValue(int i, float childrenOnTop,
            StackScrollState resultState, StackScrollAlgorithmState algorithmState,
            AmbientState ambientState) {
        ExpandableView child = algorithmState.visibleChildren.get(i);
        ExpandableViewState childViewState = resultState.getViewStateForView(child);
        int zDistanceBetweenElements = ambientState.getZDistanceBetweenElements();
        float baseZ = ambientState.getBaseZHeight();
        if (child.mustStayOnScreen() && !childViewState.headsUpIsVisible
                && !ambientState.isDozingAndNotPulsing(child)
                && childViewState.yTranslation < ambientState.getTopPadding()
                + ambientState.getStackTranslation()) {
            if (childrenOnTop != 0.0f) {
                childrenOnTop++;
            } else {
                float overlap = ambientState.getTopPadding()
                        + ambientState.getStackTranslation() - childViewState.yTranslation;
                childrenOnTop += Math.min(1.0f, overlap / childViewState.height);
            }
            childViewState.zTranslation = baseZ
                    + childrenOnTop * zDistanceBetweenElements;
        } else if (i == 0 && ambientState.isAboveShelf(child)) {
            // In case this is a new view that has never been measured before, we don't want to
            // elevate if we are currently expanded more then the notification
            int shelfHeight = ambientState.getShelf() == null ? 0 :
                    ambientState.getShelf().getIntrinsicHeight();
            float shelfStart = ambientState.getInnerHeight()
                    - shelfHeight + ambientState.getTopPadding()
                    + ambientState.getStackTranslation();
            float notificationEnd = childViewState.yTranslation + child.getPinnedHeadsUpHeight()
                    + mPaddingBetweenElements;
            if (shelfStart > notificationEnd) {
                childViewState.zTranslation = baseZ;
            } else {
                float factor = (notificationEnd - shelfStart) / shelfHeight;
                factor = Math.min(factor, 1.0f);
                childViewState.zTranslation = baseZ + factor * zDistanceBetweenElements;
            }
        } else {
            childViewState.zTranslation = baseZ;
        }
        return childrenOnTop;
    }

    public void setIsExpanded(boolean isExpanded) {
        this.mIsExpanded = isExpanded;
    }

    public class StackScrollAlgorithmState {

        /**
         * The scroll position of the algorithm
         */
        public int scrollY;

        /**
         * The children from the host view which are not gone.
         */
        public final ArrayList<ExpandableView> visibleChildren = new ArrayList<ExpandableView>();

        /**
         * The padding after each child measured in pixels.
         */
        public final HashMap<ExpandableView, Float> paddingMap = new HashMap<>();
        private int indexOfExpandingNotification;

        public int getPaddingAfterChild(ExpandableView child) {
            Float padding = paddingMap.get(child);
            if (padding == null) {
                // Should only happen for the last view
                return mPaddingBetweenElements;
            }
            return (int) padding.floatValue();
        }

        public int getIndexOfExpandingNotification() {
            return indexOfExpandingNotification;
        }
    }

}