CopyOnWriteTextStore.java

/*******************************************************************************
 * Copyright (c) 2012-2015 Codenvy, S.A.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *   Codenvy, S.A. - initial API and implementation
 *******************************************************************************/
package org.eclipse.che.ide.ext.java.jdt.text;

import org.eclipse.che.ide.runtime.Assert;

/**
 * Copy-on-write <code>ITextStore</code> wrapper.
 * <p>
 * This implementation uses an unmodifiable text store for the initial content. Upon first modification attempt, the unmodifiable
 * store is replaced with a modifiable instance which must be supplied in the constructor.
 * </p>
 * <p>
 * This class is not intended to be subclassed.
 * </p>
 *
 * @noextend This class is not intended to be subclassed by clients.
 */
public class CopyOnWriteTextStore implements TextStore {

    /**
     * An unmodifiable String based text store. It is not possible to modify the initial content. Trying to {@link #replace} a text
     * range or {@link #set} new content will throw an <code>UnsupportedOperationException</code>.
     */
    private static class StringTextStore implements TextStore {

        /** Minimum text limit whether to enable String copying */
        private static final int SMALL_TEXT_LIMIT = 1024 * 1024;

        /** Represents the content of this text store. */
        private final String fText;

        /** Minimum length limit below which {@link #get(int, int)} will return a String copy */
        private final int fCopyLimit;

        /** Create an empty text store. */
        private StringTextStore() {
            this(""); //$NON-NLS-1$
        }

        /**
         * Create a text store with initial content.
         *
         * @param text
         *         the initial content
         */
        private StringTextStore(String text) {
            super();
            fText = text != null ? text : ""; //$NON-NLS-1$
            fCopyLimit = fText.length() > SMALL_TEXT_LIMIT ? fText.length() / 2 : 0;
        }

        /* @see org.eclipse.jface.text.ITextStore#get(int) */
        public char get(int offset) {
            return fText.charAt(offset);
        }

        /* @see org.eclipse.jface.text.ITextStore#get(int, int) */
        public String get(int offset, int length) {
            if (length < fCopyLimit) {
                // create a copy to avoid sharing of contained char[] - bug 292664
                return new String(fText.substring(offset, offset + length).toCharArray());
            }
            return fText.substring(offset, offset + length);
        }

        /* @see org.eclipse.jface.text.ITextStore#getLength() */
        public int getLength() {
            return fText.length();
        }

        /*
         * @see org.eclipse.jface.text.ITextStore#replace(int, int, java.lang.String)
         */
        public void replace(int offset, int length, String text) {
            // modification not supported
            throw new UnsupportedOperationException();
        }

        /* @see org.eclipse.jface.text.ITextStore#set(java.lang.String) */
        public void set(String text) {
            // modification not supported
            throw new UnsupportedOperationException();
        }

    }

    /** The underlying "real" text store */
    protected TextStore fTextStore = new StringTextStore();

    /** A modifiable <code>ITextStore</code> instance */
    private final TextStore fModifiableTextStore;

    /**
     * Creates an empty text store. The given text store will be used upon first modification attempt.
     *
     * @param modifiableTextStore
     *         a modifiable <code>ITextStore</code> instance, may not be <code>null</code>
     */
    public CopyOnWriteTextStore(TextStore modifiableTextStore) {
        Assert.isNotNull(modifiableTextStore);
        fTextStore = new StringTextStore();
        fModifiableTextStore = modifiableTextStore;
    }

    /* @see org.eclipse.jface.text.ITextStore#get(int) */
    public char get(int offset) {
        return fTextStore.get(offset);
    }

    /* @see org.eclipse.jface.text.ITextStore#get(int, int) */
    public String get(int offset, int length) {
        return fTextStore.get(offset, length);
    }

    /* @see org.eclipse.jface.text.ITextStore#getLength() */
    public int getLength() {
        return fTextStore.getLength();
    }

    /* @see org.eclipse.jface.text.ITextStore#replace(int, int, java.lang.String) */
    public void replace(int offset, int length, String text) {
        if (fTextStore != fModifiableTextStore) {
            String content = fTextStore.get(0, fTextStore.getLength());
            fTextStore = fModifiableTextStore;
            fTextStore.set(content);
        }
        fTextStore.replace(offset, length, text);
    }

    /* @see org.eclipse.jface.text.ITextStore#set(java.lang.String) */
    public void set(String text) {
        fTextStore = new StringTextStore(text);
        fModifiableTextStore.set(""); //$NON-NLS-1$
    }

}