/*
 * Copyright 2015, The Querydsl Team (http://www.querydsl.com/team)
 *
 * 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.querydsl.core.types.dsl;

import java.util.ArrayList;
import java.util.List;

import com.querydsl.core.types.*;

/**
 * {@code Coalesce} defines a coalesce function invocation. The coalesce function
 * returns null if all arguments are null and the first non-null argument
 * otherwise
 *
 * <p>Coalesce doesn't provide the full interface for comparable expressions. To get an immutable
 * copy with the full expressiveness of Comparable expressions, call getValue().</p>
 *
 * @author tiwe
 *
 * @param <T> expression type
 */
@SuppressWarnings("unchecked")
public class Coalesce<T extends Comparable> extends MutableExpressionBase<T> {

    private static final long serialVersionUID = 445439522266250417L;

    private final List<Expression<? extends T>> exprs = new ArrayList<Expression<? extends T>>();

    private transient volatile ComparableExpression<T> value;

    public Coalesce(Class<? extends T> type, Expression<?>... exprs) {
        super(type);
        // NOTE : type parameters for the varargs, would result in compiler warnings
        for (Expression expr : exprs) {
            add(expr);
        }
    }

    public Coalesce(Expression... exprs) {
        // NOTE : type parameters for the varargs, would result in compiler warnings
        this((exprs.length > 0 ? exprs[0].getType() : Object.class), exprs);
    }

    @Override
    public <R,C> R accept(Visitor<R,C> v, C context) {
        return getValue().accept(v, context);
    }

    public ComparableExpression<T> getValue() {
        if (value == null) {
            value = Expressions.comparableOperation(getType(), Ops.COALESCE, getExpressionList());
        }
        return value;
    }

    /**
     * Create an alias for the expression
     *
     * @return this as alias
     */
    public DslExpression<T> as(Path<T> alias) {
        return Expressions.dslOperation(getType(),Ops.ALIAS, this, alias);
    }

    /**
     * Create an alias for the expression
     *
     * @return this as alias
     */
    public DslExpression<T> as(String alias) {
        return as(ExpressionUtils.path(getType(), alias));
    }

    public final Coalesce<T> add(Expression<T> expr) {
        value = null;
        this.exprs.add(expr);
        return this;
    }

    public OrderSpecifier<T> asc() {
        return getValue().asc();
    }

    public OrderSpecifier<T> desc() {
        return getValue().desc();
    }

    public final Coalesce<T> add(T constant) {
        return add(ConstantImpl.create(constant));
    }

    public BooleanExpression asBoolean() {
        return Expressions.booleanOperation(Ops.COALESCE, getExpressionList());
    }

    public DateExpression<T> asDate() {
        return Expressions.dateOperation(getType(), Ops.COALESCE, getExpressionList());
    }

    public DateTimeExpression<T> asDateTime() {
        return Expressions.dateTimeOperation(getType(), Ops.COALESCE, getExpressionList());
    }

    public EnumExpression<?> asEnum() {
        return Expressions.enumOperation((Class) getType(), Ops.COALESCE, getExpressionList());
    }

    public NumberExpression<?> asNumber() {
        return Expressions.numberOperation((Class) getType(), Ops.COALESCE, getExpressionList());
    }

    public StringExpression asString() {
        return Expressions.stringOperation(Ops.COALESCE, getExpressionList());
    }

    public TimeExpression<T> asTime() {
        return Expressions.timeOperation(getType(), Ops.COALESCE, getExpressionList());
    }

    private Expression<?> getExpressionList() {
        return ExpressionUtils.list(getType(), exprs);
    }

    @Override
    public boolean equals(Object o) {
        if (o == this) {
            return true;
        } else if (o instanceof Coalesce<?>) {
            Coalesce<?> c = (Coalesce<?>) o;
            return c.exprs.equals(exprs);
        } else {
            return false;
        }
    }


}