/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * 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.android.ide.eclipse.gltrace.state.transforms;

import com.android.ide.eclipse.gltrace.state.IGLProperty;

/**
 * A PropertyChangeTransform object provides the ability to alter the value of a
 * single GL State variable. An optional predicate provides the ability to perform
 * the change only if the predicate succeeds.
 */
public class PropertyChangeTransform implements IStateTransform {
    private final IGLPropertyAccessor mAccessor;
    private final Object mNewValue;
    private final IPredicate mPredicate;
    private Object mOldValue;

    /**
     * Construct a state transform that will extract the property using the accessor,
     * and modify its value to the provided value.
     */
    PropertyChangeTransform(IGLPropertyAccessor accessor, Object newValue) {
        this(accessor, newValue, null);
    }

    /**
     * Construct a state transform that will extract the property using the accessor,
     * check if the predicate function accepts the current value, and if so modify its
     * value to the provided value.
     */
    public PropertyChangeTransform(IGLPropertyAccessor accessor, Object newValue,
            IPredicate predicate) {
        mAccessor = accessor;
        mNewValue = newValue;
        mPredicate = predicate;
        mOldValue = null;
    }

    /** Apply the state transformation on the given OpenGL state. */
    @Override
    public void apply(IGLProperty state) {
        IGLProperty property = mAccessor.getProperty(state);

        assert mOldValue == null : "Transform cannot be applied multiple times";
        if (mPredicate != null) {
            // if predicate is not null, then first check if the current value
            // passes the predicate function.
            if (!mPredicate.apply(property.getValue())) {
                return;
            }
        }

        if (property != null) {
            mOldValue = property.getValue();
            property.setValue(mNewValue);
        } else {
            throw new RuntimeException("No such property: " + mAccessor.getPath());
        }
    }

    /**
     * Reverses the effect of this state transform. It restores the property's value to the same
     * state as it was before this transformation was applied. If this transform was never
     * {@link #apply(IGLProperty)}'ed, then performing a revert has no effect.
     */
    @Override
    public void revert(IGLProperty state) {
        if (mOldValue != null) {
            IGLProperty property = mAccessor.getProperty(state);
            property.setValue(mOldValue);
            mOldValue = null;
        }
    }

    /** Gets the property that will be affected by applying this transformation. */
    @Override
    public IGLProperty getChangedProperty(IGLProperty state) {
        if (mPredicate != null) {
            Object value = mOldValue == null ? mNewValue : mOldValue;
            if (!mPredicate.apply(value)) {
                // if the value doesn't match the predicate, then this property
                // is not altered.
                return null;
            }
        }

        return mAccessor.getProperty(state);
    }
}