/*
 * Copyright (C) 2010 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.text.method;

import android.text.Layout;
import android.text.Spannable;
import android.view.InputDevice;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.widget.TextView;

Base classes for movement methods.
/**
 * Base classes for movement methods.
 */
public class BaseMovementMethod implements MovementMethod {
    @Override
    public boolean canSelectArbitrarily() {
        return false;
    }

    @Override
    public void initialize(TextView widget, Spannable text) {
    }

    @Override
    public boolean onKeyDown(TextView widget, Spannable text, int keyCode, KeyEvent event) {
        final int movementMetaState = getMovementMetaState(text, event);
        boolean handled = handleMovementKey(widget, text, keyCode, movementMetaState, event);
        if (handled) {
            MetaKeyKeyListener.adjustMetaAfterKeypress(text);
            MetaKeyKeyListener.resetLockedMeta(text);
        }
        return handled;
    }

    @Override
    public boolean onKeyOther(TextView widget, Spannable text, KeyEvent event) {
        final int movementMetaState = getMovementMetaState(text, event);
        final int keyCode = event.getKeyCode();
        if (keyCode != KeyEvent.KEYCODE_UNKNOWN
                && event.getAction() == KeyEvent.ACTION_MULTIPLE) {
            final int repeat = event.getRepeatCount();
            boolean handled = false;
            for (int i = 0; i < repeat; i++) {
                if (!handleMovementKey(widget, text, keyCode, movementMetaState, event)) {
                    break;
                }
                handled = true;
            }
            if (handled) {
                MetaKeyKeyListener.adjustMetaAfterKeypress(text);
                MetaKeyKeyListener.resetLockedMeta(text);
            }
            return handled;
        }
        return false;
    }

    @Override
    public boolean onKeyUp(TextView widget, Spannable text, int keyCode, KeyEvent event) {
        return false;
    }

    @Override
    public void onTakeFocus(TextView widget, Spannable text, int direction) {
    }

    @Override
    public boolean onTouchEvent(TextView widget, Spannable text, MotionEvent event) {
        return false;
    }

    @Override
    public boolean onTrackballEvent(TextView widget, Spannable text, MotionEvent event) {
        return false;
    }

    @Override
    public boolean onGenericMotionEvent(TextView widget, Spannable text, MotionEvent event) {
        if ((event.getSource() & InputDevice.SOURCE_CLASS_POINTER) != 0) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_SCROLL: {
                    final float vscroll;
                    final float hscroll;
                    if ((event.getMetaState() & KeyEvent.META_SHIFT_ON) != 0) {
                        vscroll = 0;
                        hscroll = event.getAxisValue(MotionEvent.AXIS_VSCROLL);
                    } else {
                        vscroll = -event.getAxisValue(MotionEvent.AXIS_VSCROLL);
                        hscroll = event.getAxisValue(MotionEvent.AXIS_HSCROLL);
                    }

                    boolean handled = false;
                    if (hscroll < 0) {
                        handled |= scrollLeft(widget, text, (int)Math.ceil(-hscroll));
                    } else if (hscroll > 0) {
                        handled |= scrollRight(widget, text, (int)Math.ceil(hscroll));
                    }
                    if (vscroll < 0) {
                        handled |= scrollUp(widget, text, (int)Math.ceil(-vscroll));
                    } else if (vscroll > 0) {
                        handled |= scrollDown(widget, text, (int)Math.ceil(vscroll));
                    }
                    return handled;
                }
            }
        }
        return false;
    }

    
Gets the meta state used for movement using the modifiers tracked by the text
buffer as well as those present in the key event.
The movement meta state excludes the state of locked modifiers or the SHIFT key
since they are not used by movement actions (but they may be used for selection).
Params:
buffer – The text buffer.
event – The key event.
Returns:
The keyboard meta states used for movement./**
     * Gets the meta state used for movement using the modifiers tracked by the text
     * buffer as well as those present in the key event.
     *
     * The movement meta state excludes the state of locked modifiers or the SHIFT key
     * since they are not used by movement actions (but they may be used for selection).
     *
     * @param buffer The text buffer.
     * @param event The key event.
     * @return The keyboard meta states used for movement.
     */
    protected int getMovementMetaState(Spannable buffer, KeyEvent event) {
        // We ignore locked modifiers and SHIFT.
        int metaState = MetaKeyKeyListener.getMetaState(buffer, event)
                & ~(MetaKeyKeyListener.META_ALT_LOCKED | MetaKeyKeyListener.META_SYM_LOCKED);
        return KeyEvent.normalizeMetaState(metaState) & ~KeyEvent.META_SHIFT_MASK;
    }

    
Performs a movement key action. The default implementation decodes the key down and invokes movement actions such as down and up. onKeyDown(TextView, Spannable, int, KeyEvent) calls this method once to handle an KeyEvent.ACTION_DOWN. onKeyOther(TextView, Spannable, KeyEvent) calls this method repeatedly to handle each repetition of an KeyEvent.ACTION_MULTIPLE. 
Params:
widget – The text view.
buffer – The text buffer.
event – The key event.
keyCode – The key code.
movementMetaState – The keyboard meta states used for movement.
event – The key event.
Returns:
True if the event was handled./**
     * Performs a movement key action.
     * The default implementation decodes the key down and invokes movement actions
     * such as {@link #down} and {@link #up}.
     * {@link #onKeyDown(TextView, Spannable, int, KeyEvent)} calls this method once
     * to handle an {@link KeyEvent#ACTION_DOWN}.
     * {@link #onKeyOther(TextView, Spannable, KeyEvent)} calls this method repeatedly
     * to handle each repetition of an {@link KeyEvent#ACTION_MULTIPLE}.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @param event The key event.
     * @param keyCode The key code.
     * @param movementMetaState The keyboard meta states used for movement.
     * @param event The key event.
     * @return True if the event was handled.
     */
    protected boolean handleMovementKey(TextView widget, Spannable buffer,
            int keyCode, int movementMetaState, KeyEvent event) {
        switch (keyCode) {
            case KeyEvent.KEYCODE_DPAD_LEFT:
                if (KeyEvent.metaStateHasNoModifiers(movementMetaState)) {
                    return left(widget, buffer);
                } else if (KeyEvent.metaStateHasModifiers(movementMetaState,
                        KeyEvent.META_CTRL_ON)) {
                    return leftWord(widget, buffer);
                } else if (KeyEvent.metaStateHasModifiers(movementMetaState,
                        KeyEvent.META_ALT_ON)) {
                    return lineStart(widget, buffer);
                }
                break;

            case KeyEvent.KEYCODE_DPAD_RIGHT:
                if (KeyEvent.metaStateHasNoModifiers(movementMetaState)) {
                    return right(widget, buffer);
                } else if (KeyEvent.metaStateHasModifiers(movementMetaState,
                        KeyEvent.META_CTRL_ON)) {
                    return rightWord(widget, buffer);
                } else if (KeyEvent.metaStateHasModifiers(movementMetaState,
                        KeyEvent.META_ALT_ON)) {
                    return lineEnd(widget, buffer);
                }
                break;

            case KeyEvent.KEYCODE_DPAD_UP:
                if (KeyEvent.metaStateHasNoModifiers(movementMetaState)) {
                    return up(widget, buffer);
                } else if (KeyEvent.metaStateHasModifiers(movementMetaState,
                        KeyEvent.META_ALT_ON)) {
                    return top(widget, buffer);
                }
                break;

            case KeyEvent.KEYCODE_DPAD_DOWN:
                if (KeyEvent.metaStateHasNoModifiers(movementMetaState)) {
                    return down(widget, buffer);
                } else if (KeyEvent.metaStateHasModifiers(movementMetaState,
                        KeyEvent.META_ALT_ON)) {
                    return bottom(widget, buffer);
                }
                break;

            case KeyEvent.KEYCODE_PAGE_UP:
                if (KeyEvent.metaStateHasNoModifiers(movementMetaState)) {
                    return pageUp(widget, buffer);
                } else if (KeyEvent.metaStateHasModifiers(movementMetaState,
                        KeyEvent.META_ALT_ON)) {
                    return top(widget, buffer);
                }
                break;

            case KeyEvent.KEYCODE_PAGE_DOWN:
                if (KeyEvent.metaStateHasNoModifiers(movementMetaState)) {
                    return pageDown(widget, buffer);
                } else if (KeyEvent.metaStateHasModifiers(movementMetaState,
                        KeyEvent.META_ALT_ON)) {
                    return bottom(widget, buffer);
                }
                break;

            case KeyEvent.KEYCODE_MOVE_HOME:
                if (KeyEvent.metaStateHasNoModifiers(movementMetaState)) {
                    return home(widget, buffer);
                } else if (KeyEvent.metaStateHasModifiers(movementMetaState,
                        KeyEvent.META_CTRL_ON)) {
                    return top(widget, buffer);
                }
                break;

            case KeyEvent.KEYCODE_MOVE_END:
                if (KeyEvent.metaStateHasNoModifiers(movementMetaState)) {
                    return end(widget, buffer);
                } else if (KeyEvent.metaStateHasModifiers(movementMetaState,
                        KeyEvent.META_CTRL_ON)) {
                    return bottom(widget, buffer);
                }
                break;
        }
        return false;
    }

    
Performs a left movement action.
Moves the cursor or scrolls left by one character.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled./**
     * Performs a left movement action.
     * Moves the cursor or scrolls left by one character.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     */
    protected boolean left(TextView widget, Spannable buffer) {
        return false;
    }

    
Performs a right movement action.
Moves the cursor or scrolls right by one character.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled./**
     * Performs a right movement action.
     * Moves the cursor or scrolls right by one character.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     */
    protected boolean right(TextView widget, Spannable buffer) {
        return false;
    }

    
Performs an up movement action.
Moves the cursor or scrolls up by one line.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled./**
     * Performs an up movement action.
     * Moves the cursor or scrolls up by one line.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     */
    protected boolean up(TextView widget, Spannable buffer) {
        return false;
    }

    
Performs a down movement action.
Moves the cursor or scrolls down by one line.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled./**
     * Performs a down movement action.
     * Moves the cursor or scrolls down by one line.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     */
    protected boolean down(TextView widget, Spannable buffer) {
        return false;
    }

    
Performs a page-up movement action.
Moves the cursor or scrolls up by one page.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled./**
     * Performs a page-up movement action.
     * Moves the cursor or scrolls up by one page.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     */
    protected boolean pageUp(TextView widget, Spannable buffer) {
        return false;
    }

    
Performs a page-down movement action.
Moves the cursor or scrolls down by one page.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled./**
     * Performs a page-down movement action.
     * Moves the cursor or scrolls down by one page.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     */
    protected boolean pageDown(TextView widget, Spannable buffer) {
        return false;
    }

    
Performs a top movement action.
Moves the cursor or scrolls to the top of the buffer.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled./**
     * Performs a top movement action.
     * Moves the cursor or scrolls to the top of the buffer.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     */
    protected boolean top(TextView widget, Spannable buffer) {
        return false;
    }

    
Performs a bottom movement action.
Moves the cursor or scrolls to the bottom of the buffer.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled./**
     * Performs a bottom movement action.
     * Moves the cursor or scrolls to the bottom of the buffer.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     */
    protected boolean bottom(TextView widget, Spannable buffer) {
        return false;
    }

    
Performs a line-start movement action.
Moves the cursor or scrolls to the start of the line.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled./**
     * Performs a line-start movement action.
     * Moves the cursor or scrolls to the start of the line.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     */
    protected boolean lineStart(TextView widget, Spannable buffer) {
        return false;
    }

    
Performs a line-end movement action.
Moves the cursor or scrolls to the end of the line.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled./**
     * Performs a line-end movement action.
     * Moves the cursor or scrolls to the end of the line.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     */
    protected boolean lineEnd(TextView widget, Spannable buffer) {
        return false;
    }

    
{@hide} /** {@hide} */
    protected boolean leftWord(TextView widget, Spannable buffer) {
        return false;
    }

    
{@hide} /** {@hide} */
    protected boolean rightWord(TextView widget, Spannable buffer) {
        return false;
    }

    
Performs a home movement action.
Moves the cursor or scrolls to the start of the line or to the top of the
document depending on whether the insertion point is being moved or
the document is being scrolled.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled./**
     * Performs a home movement action.
     * Moves the cursor or scrolls to the start of the line or to the top of the
     * document depending on whether the insertion point is being moved or
     * the document is being scrolled.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     */
    protected boolean home(TextView widget, Spannable buffer) {
        return false;
    }

    
Performs an end movement action.
Moves the cursor or scrolls to the start of the line or to the top of the
document depending on whether the insertion point is being moved or
the document is being scrolled.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled./**
     * Performs an end movement action.
     * Moves the cursor or scrolls to the start of the line or to the top of the
     * document depending on whether the insertion point is being moved or
     * the document is being scrolled.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     */
    protected boolean end(TextView widget, Spannable buffer) {
        return false;
    }

    private int getTopLine(TextView widget) {
        return widget.getLayout().getLineForVertical(widget.getScrollY());
    }

    private int getBottomLine(TextView widget) {
        return widget.getLayout().getLineForVertical(widget.getScrollY() + getInnerHeight(widget));
    }

    private int getInnerWidth(TextView widget) {
        return widget.getWidth() - widget.getTotalPaddingLeft() - widget.getTotalPaddingRight();
    }

    private int getInnerHeight(TextView widget) {
        return widget.getHeight() - widget.getTotalPaddingTop() - widget.getTotalPaddingBottom();
    }

    private int getCharacterWidth(TextView widget) {
        return (int) Math.ceil(widget.getPaint().getFontSpacing());
    }

    private int getScrollBoundsLeft(TextView widget) {
        final Layout layout = widget.getLayout();
        final int topLine = getTopLine(widget);
        final int bottomLine = getBottomLine(widget);
        if (topLine > bottomLine) {
            return 0;
        }
        int left = Integer.MAX_VALUE;
        for (int line = topLine; line <= bottomLine; line++) {
            final int lineLeft = (int) Math.floor(layout.getLineLeft(line));
            if (lineLeft < left) {
                left = lineLeft;
            }
        }
        return left;
    }

    private int getScrollBoundsRight(TextView widget) {
        final Layout layout = widget.getLayout();
        final int topLine = getTopLine(widget);
        final int bottomLine = getBottomLine(widget);
        if (topLine > bottomLine) {
            return 0;
        }
        int right = Integer.MIN_VALUE;
        for (int line = topLine; line <= bottomLine; line++) {
            final int lineRight = (int) Math.ceil(layout.getLineRight(line));
            if (lineRight > right) {
                right = lineRight;
            }
        }
        return right;
    }

    
Performs a scroll left action.
Scrolls left by the specified number of characters.
Params:
widget – The text view.
buffer – The text buffer.
amount – The number of characters to scroll by.  Must be at least 1.
Returns:
True if the event was handled.
@hide
/**
     * Performs a scroll left action.
     * Scrolls left by the specified number of characters.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @param amount The number of characters to scroll by.  Must be at least 1.
     * @return True if the event was handled.
     * @hide
     */
    protected boolean scrollLeft(TextView widget, Spannable buffer, int amount) {
        final int minScrollX = getScrollBoundsLeft(widget);
        int scrollX = widget.getScrollX();
        if (scrollX > minScrollX) {
            scrollX = Math.max(scrollX - getCharacterWidth(widget) * amount, minScrollX);
            widget.scrollTo(scrollX, widget.getScrollY());
            return true;
        }
        return false;
    }

    
Performs a scroll right action.
Scrolls right by the specified number of characters.
Params:
widget – The text view.
buffer – The text buffer.
amount – The number of characters to scroll by.  Must be at least 1.
Returns:
True if the event was handled.
@hide
/**
     * Performs a scroll right action.
     * Scrolls right by the specified number of characters.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @param amount The number of characters to scroll by.  Must be at least 1.
     * @return True if the event was handled.
     * @hide
     */
    protected boolean scrollRight(TextView widget, Spannable buffer, int amount) {
        final int maxScrollX = getScrollBoundsRight(widget) - getInnerWidth(widget);
        int scrollX = widget.getScrollX();
        if (scrollX < maxScrollX) {
            scrollX = Math.min(scrollX + getCharacterWidth(widget) * amount, maxScrollX);
            widget.scrollTo(scrollX, widget.getScrollY());
            return true;
        }
        return false;
    }

    
Performs a scroll up action.
Scrolls up by the specified number of lines.
Params:
widget – The text view.
buffer – The text buffer.
amount – The number of lines to scroll by.  Must be at least 1.
Returns:
True if the event was handled.
@hide
/**
     * Performs a scroll up action.
     * Scrolls up by the specified number of lines.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @param amount The number of lines to scroll by.  Must be at least 1.
     * @return True if the event was handled.
     * @hide
     */
    protected boolean scrollUp(TextView widget, Spannable buffer, int amount) {
        final Layout layout = widget.getLayout();
        final int top = widget.getScrollY();
        int topLine = layout.getLineForVertical(top);
        if (layout.getLineTop(topLine) == top) {
            // If the top line is partially visible, bring it all the way
            // into view; otherwise, bring the previous line into view.
            topLine -= 1;
        }
        if (topLine >= 0) {
            topLine = Math.max(topLine - amount + 1, 0);
            Touch.scrollTo(widget, layout, widget.getScrollX(), layout.getLineTop(topLine));
            return true;
        }
        return false;
    }

    
Performs a scroll down action.
Scrolls down by the specified number of lines.
Params:
widget – The text view.
buffer – The text buffer.
amount – The number of lines to scroll by.  Must be at least 1.
Returns:
True if the event was handled.
@hide
/**
     * Performs a scroll down action.
     * Scrolls down by the specified number of lines.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @param amount The number of lines to scroll by.  Must be at least 1.
     * @return True if the event was handled.
     * @hide
     */
    protected boolean scrollDown(TextView widget, Spannable buffer, int amount) {
        final Layout layout = widget.getLayout();
        final int innerHeight = getInnerHeight(widget);
        final int bottom = widget.getScrollY() + innerHeight;
        int bottomLine = layout.getLineForVertical(bottom);
        if (layout.getLineTop(bottomLine + 1) < bottom + 1) {
            // Less than a pixel of this line is out of view,
            // so we must have tried to make it entirely in view
            // and now want the next line to be in view instead.
            bottomLine += 1;
        }
        final int limit = layout.getLineCount() - 1;
        if (bottomLine <= limit) {
            bottomLine = Math.min(bottomLine + amount - 1, limit);
            Touch.scrollTo(widget, layout, widget.getScrollX(),
                    layout.getLineTop(bottomLine + 1) - innerHeight);
            return true;
        }
        return false;
    }

    
Performs a scroll page up action.
Scrolls up by one page.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled.
@hide
/**
     * Performs a scroll page up action.
     * Scrolls up by one page.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     * @hide
     */
    protected boolean scrollPageUp(TextView widget, Spannable buffer) {
        final Layout layout = widget.getLayout();
        final int top = widget.getScrollY() - getInnerHeight(widget);
        int topLine = layout.getLineForVertical(top);
        if (topLine >= 0) {
            Touch.scrollTo(widget, layout, widget.getScrollX(), layout.getLineTop(topLine));
            return true;
        }
        return false;
    }

    
Performs a scroll page up action.
Scrolls down by one page.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled.
@hide
/**
     * Performs a scroll page up action.
     * Scrolls down by one page.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     * @hide
     */
    protected boolean scrollPageDown(TextView widget, Spannable buffer) {
        final Layout layout = widget.getLayout();
        final int innerHeight = getInnerHeight(widget);
        final int bottom = widget.getScrollY() + innerHeight + innerHeight;
        int bottomLine = layout.getLineForVertical(bottom);
        if (bottomLine <= layout.getLineCount() - 1) {
            Touch.scrollTo(widget, layout, widget.getScrollX(),
                    layout.getLineTop(bottomLine + 1) - innerHeight);
            return true;
        }
        return false;
    }

    
Performs a scroll to top action.
Scrolls to the top of the document.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled.
@hide
/**
     * Performs a scroll to top action.
     * Scrolls to the top of the document.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     * @hide
     */
    protected boolean scrollTop(TextView widget, Spannable buffer) {
        final Layout layout = widget.getLayout();
        if (getTopLine(widget) >= 0) {
            Touch.scrollTo(widget, layout, widget.getScrollX(), layout.getLineTop(0));
            return true;
        }
        return false;
    }

    
Performs a scroll to bottom action.
Scrolls to the bottom of the document.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled.
@hide
/**
     * Performs a scroll to bottom action.
     * Scrolls to the bottom of the document.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     * @hide
     */
    protected boolean scrollBottom(TextView widget, Spannable buffer) {
        final Layout layout = widget.getLayout();
        final int lineCount = layout.getLineCount();
        if (getBottomLine(widget) <= lineCount - 1) {
            Touch.scrollTo(widget, layout, widget.getScrollX(),
                    layout.getLineTop(lineCount) - getInnerHeight(widget));
            return true;
        }
        return false;
    }

    
Performs a scroll to line start action.
Scrolls to the start of the line.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled.
@hide
/**
     * Performs a scroll to line start action.
     * Scrolls to the start of the line.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     * @hide
     */
    protected boolean scrollLineStart(TextView widget, Spannable buffer) {
        final int minScrollX = getScrollBoundsLeft(widget);
        int scrollX = widget.getScrollX();
        if (scrollX > minScrollX) {
            widget.scrollTo(minScrollX, widget.getScrollY());
            return true;
        }
        return false;
    }

    
Performs a scroll to line end action.
Scrolls to the end of the line.
Params:
widget – The text view.
buffer – The text buffer.
Returns:
True if the event was handled.
@hide
/**
     * Performs a scroll to line end action.
     * Scrolls to the end of the line.
     *
     * @param widget The text view.
     * @param buffer The text buffer.
     * @return True if the event was handled.
     * @hide
     */
    protected boolean scrollLineEnd(TextView widget, Spannable buffer) {
        final int maxScrollX = getScrollBoundsRight(widget) - getInnerWidth(widget);
        int scrollX = widget.getScrollX();
        if (scrollX < maxScrollX) {
            widget.scrollTo(maxScrollX, widget.getScrollY());
            return true;
        }
        return false;
    }
}