// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.searchdefinition;

import com.yahoo.searchlib.rankingexpression.evaluation.TensorValue;
import com.yahoo.searchlib.rankingexpression.evaluation.Value;
import com.yahoo.searchlib.rankingexpression.rule.CompositeNode;
import com.yahoo.searchlib.rankingexpression.rule.ExpressionNode;
import com.yahoo.searchlib.rankingexpression.rule.NameNode;
import com.yahoo.searchlib.rankingexpression.rule.ReferenceNode;
import com.yahoo.searchlib.rankingexpression.transform.ExpressionTransformer;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;

/**
 * Transforms named references to constant tensors with the rank feature 'constant'.
 *
 * @author geirst
 */
class ConstantTensorTransformer extends ExpressionTransformer {

    private final Map<String, Value> constants;
    private final Map<String, String> rankPropertiesOutput;

    public ConstantTensorTransformer(Map<String, Value> constants,
                                     Map<String, String> rankPropertiesOutput) {
        this.constants = constants;
        this.rankPropertiesOutput = rankPropertiesOutput;
    }

    @Override
    public ExpressionNode transform(ExpressionNode node) {
        if (node instanceof ReferenceNode) {
            return transformFeature((ReferenceNode) node);
        } else if (node instanceof CompositeNode) {
            return transformChildren((CompositeNode) node);
        } else {
            return node;
        }
    }

    private ExpressionNode transformFeature(ReferenceNode node) {
        if (!node.getArguments().isEmpty()) {
            return transformArguments(node);
        } else {
            return transformConstantReference(node);
        }
    }

    private ExpressionNode transformArguments(ReferenceNode node) {
        List<ExpressionNode> arguments = node.getArguments().expressions();
        List<ExpressionNode> transformedArguments = new ArrayList<>(arguments.size());
        for (ExpressionNode argument : arguments) {
            transformedArguments.add(transform(argument));
        }
        return node.setArguments(transformedArguments);
    }

    private ExpressionNode transformConstantReference(ReferenceNode node) {
        Value value = constants.get(node.getName());
        if (value == null || !(value instanceof TensorValue)) {
            return node;
        }
        TensorValue tensorValue = (TensorValue)value;
        String featureName = "constant(" + node.getName() + ")";
        String tensorType = tensorValue.asTensor().type().toString();
        rankPropertiesOutput.put(featureName + ".value", tensorValue.toString());
        rankPropertiesOutput.put(featureName + ".type", tensorType);
        return new ReferenceNode("constant", Arrays.asList(new NameNode(node.getName())), null);
    }

}