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Provides additional IO support for CLIs such as colorization and text formatting

There is a newer version: 3.0.0

/**
 * Copyright (C) 2010-15 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 com.github.rvesse.airline.io;

import java.io.IOException;

/**
 * Class used to track the state of a control allowing it to be lazily written
 * to the output only if necessary and ensuring it can be appropriately reset
 * when necessary
 *
 * @param 
 *            Attribute source type
 */
public abstract class ControlTracker {

    protected final ControlCodeSource provider;
    private T current, previous;
    private boolean requireWrite = false;

    public ControlTracker(ControlCodeSource provider) {
        if (provider == null)
            throw new NullPointerException("provider cannot be null");
        this.provider = provider;
    }

    /**
     * Sets the value for the control
     * 
     * @param value
     *            Value
     */
    public final void set(T value) {
        this.current = value;
        this.requireWrite = this.current != null && !this.current.equals(this.previous);
    }

    /**
     * Resets the control to the default unintialized state, if necessary this
     * will will cause the
     * 
     * @throws IOException
     */
    public final void reset() throws IOException {
        if (this.previous != null) {
            this.resetInternal(this.previous);
            this.previous = null;
        }
    }

    /**
     * Method that derived classes must implement to add the actual logic for
     * resetting the control against the stream
     * 
     * @param value
     *            Value to be reset from
     * @throws IOException
     */
    protected abstract void resetInternal(T value) throws IOException;

    /**
     * Applies the control, if the current state of the control has not been
     * previously applied to the stream then it will be applied now
     * 
     * @throws IOException
     */
    public final void apply() throws IOException {
        if (this.requireWrite) {
            this.applyInternal(this.current);
            this.previous = this.current;
            this.requireWrite = false;
        }
    }

    /**
     * Method that derived classes must implement to add the actual logic for
     * applying the control to the stream
     * 
     * @param value
     *            Value to be applied
     * @throws IOException
     */
    protected abstract void applyInternal(T value) throws IOException;
}