/*-
 * #%L
 * java-diff-utils
 * %%
 * Copyright (C) 2009 - 2017 java-diff-utils
 * %%
 * 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.
 * #L%
 */
package com.github.difflib.patch;

import java.util.*;

/**
 * Describes the delta between original and revised texts.
 *
 * @author <a href="dm.naumenko@gmail.com">Dmitry Naumenko</a>
 * @param T The type of the compared elements in the 'lines'.
 */
public abstract class Delta<T> {

    private final DeltaType deltaType;
    private final Chunk<T> original;
    private final Chunk<T> revised;

    /**
     * Construct the delta for original and revised chunks
     *
     * @param original Chunk describing the original text. Must not be {@code null}.
     * @param revised Chunk describing the revised text. Must not be {@code null}.
     */
    public Delta(DeltaType deltaType, Chunk<T> original, Chunk<T> revised) {
        Objects.requireNonNull(deltaType, "deltaType must not be null");
        Objects.requireNonNull(original, "original must not be null");
        Objects.requireNonNull(revised, "revised must not be null");
        
        this.deltaType = deltaType;
        this.original = original;
        this.revised = revised;
    }

    /**
     * Verifies that this delta can be used to patch the given text.
     *
     * @param target the text to patch.
     * @throws PatchFailedException if the patch cannot be applied.
     */
    public void verify(List<T> target) throws PatchFailedException {
        getOriginal().verify(target);
    }

    /**
     * Applies this delta as the patch for a given target
     *
     * @param target the given target
     * @throws PatchFailedException
     */
    public abstract void applyTo(List<T> target) throws PatchFailedException;

    /**
     * Cancel this delta for a given revised text. The action is opposite to patch.
     *
     * @param target the given revised text
     */
    public abstract void restore(List<T> target);

    public final DeltaType getType() {
        return deltaType;
    }

    /**
     * @return The Chunk describing the original text.
     */
    public Chunk<T> getOriginal() {
        return original;
    }

    /**
     * @return The Chunk describing the revised text.
     */
    public Chunk<T> getRevised() {
        return revised;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((original == null) ? 0 : original.hashCode());
        result = prime * result + ((revised == null) ? 0 : revised.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        Delta<T> other = (Delta) obj;
        if (original == null) {
            if (other.original != null) {
                return false;
            }
        } else if (!original.equals(other.original)) {
            return false;
        }
        if (revised == null) {
            if (other.revised != null) {
                return false;
            }
        } else if (!revised.equals(other.revised)) {
            return false;
        }
        return true;
    }

}
