gradle-master/subprojects/logging/src/main/java/org/gradle/internal/logging/console/DefaultRedrawableLabel.java
/*
 * Copyright 2017 the original author or authors.
 *
 * 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 org.gradle.internal.logging.console;

import org.gradle.api.Action;
import org.gradle.internal.logging.events.StyledTextOutputEvent;

import java.util.Collections;
import java.util.List;

public class DefaultRedrawableLabel implements RedrawableLabel {
    private final Cursor writePos;  // Relative coordinate system
    private List<StyledTextOutputEvent.Span> spans = Collections.emptyList();
    private List<StyledTextOutputEvent.Span> writtenSpans = Collections.emptyList();
    private int absolutePositionRow;  // Absolute coordinate system
    private int previousWriteRow = absolutePositionRow;
    private boolean isVisible = true;
    private boolean previousVisibility = isVisible;

    DefaultRedrawableLabel(Cursor writePos) {
        this.writePos = writePos;
    }

    @Override
    public void setText(String text) {
        this.spans = Collections.singletonList(new StyledTextOutputEvent.Span(text));
    }

    @Override
    public void setText(StyledTextOutputEvent.Span span) {
        this.spans = Collections.singletonList(span);
    }

    @Override
    public void setText(List<StyledTextOutputEvent.Span> spans) {
        this.spans = spans;
    }

    public Cursor getWritePosition() {
        return writePos;
    }

    public void setVisible(boolean isVisible) {
        this.isVisible = isVisible;
    }

    public boolean isOverlappingWith(Cursor cursor) {
        return cursor.row == writePos.row && writePos.col > cursor.col;
    }

    @Override
    public void redraw(AnsiContext ansi) {
        if (writePos.row < 0) {
            // Does not need to be redrawn if component is out of bound
            return;
        }

        if (!isVisible && previousVisibility) {
            if (previousWriteRow == absolutePositionRow && writtenSpans.isEmpty()) {
                // Does not need to be redrawn
                return;
            }

            writePos.col = 0;
            ansi.cursorAt(writePos).eraseAll();

            writtenSpans = Collections.emptyList();
        }

        if (isVisible) {
            if (previousWriteRow == absolutePositionRow && writtenSpans.equals(spans)) {
                // Does not need to be redrawn
                return;
            }

            int writtenTextLength = writePos.col;
            writePos.col = 0;
            redrawText(ansi.writeAt(writePos), writtenTextLength);

            writtenSpans = spans;
            previousWriteRow = absolutePositionRow;
        }
    }

    private void redrawText(AnsiContext ansi, int writtenTextLength) {
        int textLength = 0;
        for (StyledTextOutputEvent.Span span : spans) {
            int length = span.getText().length();
            if (length > 0) {
                ansi.withStyle(span.getStyle(), writeText(span.getText()));
                textLength += length;
            }
        }

        if (previousWriteRow == absolutePositionRow && textLength < writtenTextLength) {
            ansi.eraseForward();
        }
        // Note: We can't conclude anything if the label scrolled so we leave the erasing to the parent widget.
    }

    private static Action<AnsiContext> writeText(final String text) {
        return new Action<AnsiContext>() {
            @Override
            public void execute(AnsiContext ansi) {
                ansi.a(text);
            }
        };
    }

    // Only for relative positioning
    public void newLineAdjustment() {
        writePos.row++;
    }

    // According to absolute positioning
    public void scrollBy(int rows) {
        writePos.row -= rows;
        absolutePositionRow += rows;
    }

    // According to absolute positioning
    public void scrollUpBy(int rows) {
        scrollBy(-rows);
    }

    // According to absolute positioning
    public void scrollDownBy(int rows) {
        scrollBy(rows);
    }
}
