/*
 * Copyright [2017] Wikimedia Foundation
 *
 * 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.o19s.es.ltr.feature.store;

import com.o19s.es.ltr.LtrQueryContext;
import com.o19s.es.ltr.feature.Feature;
import com.o19s.es.ltr.feature.FeatureSet;
import com.o19s.es.ltr.query.DerivedExpressionQuery;
import com.o19s.es.ltr.utils.Scripting;
import org.apache.lucene.expressions.Expression;
import org.apache.lucene.search.Query;
import org.apache.lucene.util.Accountable;
import org.apache.lucene.util.RamUsageEstimator;

import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.stream.Collectors;

import static org.apache.lucene.util.RamUsageEstimator.NUM_BYTES_ARRAY_HEADER;

public class PrecompiledExpressionFeature implements Feature, Accountable {

    public static final String TEMPLATE_LANGUAGE = "derived_expression";

    private static final long BASE_RAM_USED = RamUsageEstimator.shallowSizeOfInstance(PrecompiledExpressionFeature.class);

    private final String name;
    private final Expression expression;
    private final Set<String> expressionVariables;
    private final Collection<String> queryParams;

    private PrecompiledExpressionFeature(String name, Expression expression, Collection<String> queryParams) {
        this.name = name;
        this.expression = expression;
        this.queryParams = queryParams;
        this.expressionVariables = new HashSet<>(Arrays.asList(this.expression.variables));
    }

    public static PrecompiledExpressionFeature compile(StoredFeature feature) {
        assert TEMPLATE_LANGUAGE.equals(feature.templateLanguage());
        Expression expr = (Expression) Scripting.compile(feature.template());
        return new PrecompiledExpressionFeature(feature.name(), expr, feature.queryParams());
    }

    @Override
    public long ramBytesUsed() {
        return BASE_RAM_USED +
                (Character.BYTES * name.length()) + NUM_BYTES_ARRAY_HEADER +
                (((Character.BYTES * expression.sourceText.length()) + NUM_BYTES_ARRAY_HEADER) * 2);
    }

    @Override
    public String name() {
        return name;
    }

    @Override
    public Query doToQuery(LtrQueryContext context, FeatureSet set, Map<String, Object> params) {
        List<String> missingParams = queryParams.stream()
                .filter((x) -> params == null || !params.containsKey(x))
                .collect(Collectors.toList());
        if (!missingParams.isEmpty()) {
            String names = missingParams.stream().collect(Collectors.joining(","));
            throw new IllegalArgumentException("Missing required param(s): [" + names + "]");
        }

        Map<String, Double> queryParamValues = getQueryParamValues(params);
        return new DerivedExpressionQuery(set, expression, queryParamValues);
    }


    private Map<String, Double> getQueryParamValues() {
        return getQueryParamValues();
    }

    /**
     * If a param is an expression variable then we need to use it as {@link Expression#variables} in lucene expression exposed via Bindings
     *
     * @param params Map all query params across features.
     * @return Map of {@link Expression#variables} names to params values (values are doubles).
     */
    private Map<String, Double> getQueryParamValues(Map<String, Object> params) {
        Map<String, Double> queryParamValues = new HashMap<>();
        for (String param : queryParams) {
            if (expressionVariables.contains(param)) {
                try {
                    Number number = (Number) params.get(param);
                    queryParamValues.put(param, number.doubleValue());
                } catch (ClassCastException classCastException) {
                    throw new IllegalArgumentException("parameter: " + param + " expected to be of type Double");
                }
            }
        }
        return queryParamValues;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }

        PrecompiledExpressionFeature that = (PrecompiledExpressionFeature) o;

        return Objects.equals(name, that.name)
                && Objects.equals(expression, that.expression)
                && Objects.equals(queryParams, that.queryParams)
                && Objects.equals(expressionVariables, that.expressionVariables);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, expression, queryParams, expressionVariables);
    }

    @Override
    public void validate(FeatureSet set) {
        for (String var : expression.variables) {
            if (!set.hasFeature(var) && !queryParams.contains(var)) {
                throw new IllegalArgumentException("Derived feature [" + this.name + "] refers " +
                        "to unknown feature or parameter: [" + var + "]");
            }
            if(set.hasFeature(var) && queryParams.contains(var)){
                throw new IllegalArgumentException("Duplicate name " + var + " . " +
                        "Cannot be used as both feature name and query parameter name");
            }
        }
    }
}