Subsequence.java

/*
 * Copyright (C) 2010, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.diff;

/**
 * Wraps a {@link org.eclipse.jgit.diff.Sequence} to have a narrower range of
 * elements.
 * <p>
 * This sequence acts as a proxy for the real sequence, translating element
 * indexes on the fly by adding {@code begin} to them. Sequences of this type
 * must be used with a {@link org.eclipse.jgit.diff.SubsequenceComparator}.
 *
 * @param <S>
 *            the base sequence type.
 */
public final class Subsequence<S extends Sequence> extends Sequence {
    /**
     * Construct a subsequence around the A region/base sequence.
     *
     * @param a
     *            the A sequence.
     * @param region
     *            the region of {@code a} to create a subsequence around.
     * @return subsequence of {@code base} as described by A in {@code region}.
     */
    public static <S extends Sequence> Subsequence<S> a(S a, Edit region) {
        return new Subsequence<>(a, region.beginA, region.endA);
    }

    /**
     * Construct a subsequence around the B region/base sequence.
     *
     * @param b
     *            the B sequence.
     * @param region
     *            the region of {@code b} to create a subsequence around.
     * @return subsequence of {@code base} as described by B in {@code region}.
     */
    public static <S extends Sequence> Subsequence<S> b(S b, Edit region) {
        return new Subsequence<>(b, region.beginB, region.endB);
    }

    /**
     * Adjust the Edit to reflect positions in the base sequence.
     *
     * @param e
     *            edit to adjust in-place. Prior to invocation the indexes are
     *            in terms of the two subsequences; after invocation the indexes
     *            are in terms of the base sequences.
     * @param a
     *            the A sequence.
     * @param b
     *            the B sequence.
     */
    public static <S extends Sequence> void toBase(Edit e, Subsequence<S> a,
            Subsequence<S> b) {
        e.beginA += a.begin;
        e.endA += a.begin;

        e.beginB += b.begin;
        e.endB += b.begin;
    }

    /**
     * Adjust the Edits to reflect positions in the base sequence.
     *
     * @param edits
     *            edits to adjust in-place. Prior to invocation the indexes are
     *            in terms of the two subsequences; after invocation the indexes
     *            are in terms of the base sequences.
     * @param a
     *            the A sequence.
     * @param b
     *            the B sequence.
     * @return always {@code edits} (as the list was updated in-place).
     */
    public static <S extends Sequence> EditList toBase(EditList edits,
            Subsequence<S> a, Subsequence<S> b) {
        for (Edit e : edits)
            toBase(e, a, b);
        return edits;
    }

    final S base;

    final int begin;

    private final int size;

    /**
     * Construct a subset of another sequence.
     *
     * The size of the subsequence will be {@code end - begin}.
     *
     * @param base
     *            the real sequence.
     * @param begin
     *            First element index of {@code base} that will be part of this
     *            new subsequence. The element at {@code begin} will be this
     *            sequence's element 0.
     * @param end
     *            One past the last element index of {@code base} that will be
     *            part of this new subsequence.
     */
    public Subsequence(S base, int begin, int end) {
        this.base = base;
        this.begin = begin;
        this.size = end - begin;
    }

    /** {@inheritDoc} */
    @Override
    public int size() {
        return size;
    }
}