/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.jena.sparql.core;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.Objects;
import java.util.function.Function;

import org.apache.jena.graph.Node;
import org.apache.jena.graph.Node_Variable;
import org.apache.jena.sparql.ARQConstants;
import org.apache.jena.sparql.ARQInternalErrorException;
import org.apache.jena.sparql.engine.binding.Binding;
import org.apache.jena.sparql.expr.ExprVar;
import org.apache.jena.sys.JenaSystem;

/** A SPARQL variable */

public class Var extends Node_Variable
{
    // This class create Nodes (as Vars)
    static { JenaSystem.init(); }

    /* Variable used to indicate "don't bind"
     * Each use is unique.
     */

    // Legal SPARQL variable name but note it must be exactly this
    // object, not just the same name, to be anonymous.
    public static Var ANON = new Var("?_");

    public static Var alloc(String varName) {
        Objects.requireNonNull(varName);
//        if ( varName.equals("_") )
//            return ANON;
        return new Var(varName);
    }

    public static Var alloc(Node_Variable v) {
        if ( v instanceof Var )
            return (Var)v;
        return new Var(v);
    }

    public static Var alloc(Node v) {
        Objects.requireNonNull(v);
        if ( v instanceof Var )
            return (Var)v;
        if ( v instanceof Node_Variable )
            return new Var((Node_Variable)v);
        throw new NotAVariableException("Node: " + v);
    }

    public static Var alloc(Var v) {
        return Objects.requireNonNull(v);
    }

    public static Var alloc(ExprVar nv)         { return new Var(nv); }

    /** Return the value in the binding (if node is a Var) or the node itself. */
    public static Node lookup(Binding binding, Node node) {
        Objects.requireNonNull(binding);
        Objects.requireNonNull(node);
        if ( !Var.isVar(node) )
            return node;
        Var var = Var.alloc(node);
        return lookup(binding, var);
    }

    /** Return the value in the binding or the variable itself. */
    public static Node lookup(Binding binding, Var var) {
        Objects.requireNonNull(var);
        Node n = binding.get(var);
        if ( n != null )
            return n;
        return var;
    }

    /** Return the value of the access function or node itself. */
    public static Node lookup(Function<Var, Node> access, Node node) {
        if ( !Var.isVar(node) )
            return node;
        Var var = Var.alloc(node);
        return lookup(access, var);
    }

    /** Return the value of the access function or var itself. */
    public static Node lookup(Function<Var, Node> access, Var var) {
        Node n = access.apply(var);
        if ( n != null )
            return n;
        return var;
    }

    // Precalulated the hash code because hashCode() is used so heavily with Var's
    private final int hashCodeValue;

    private Var(String varName)      { super(varName); hashCodeValue = super.hashCode(); }

    private Var(Node_Variable v)     { this(v.getName()); }

    private Var(ExprVar v)           { this(v.getVarName()); }

    public String getVarName()       { return getName(); }

    static class NotAVariableException extends ARQInternalErrorException {
        NotAVariableException(String msg) { super(msg); }
    }

    @Override
    public final int hashCode() { return hashCodeValue; }

    @Override
    public final boolean equals(Object other) {
        if ( this == other ) return true;
        if ( ! ( other instanceof Var ) )
            return false;
        return super.equals(other);
    }

//    @Override
//    public String toString() { return node.toString(); }

    public boolean isNamedVar() { return isNamedVarName(getName()); }

    public boolean isBlankNodeVar() { return isBlankNodeVarName(getName()); }

    public boolean isAllocVar() { return isAllocVarName(getName()); }

    public boolean isAnonVar() { return isAnonVar(this); }

    // -------

    public static String canonical(String x) {
        if ( x.startsWith("?") )
            return x.substring(1);
        if ( x.startsWith("$") )
            return x.substring(1);
        return x;
    }

    public static boolean isVar(Node node) {
        if ( node instanceof Var )
            return true;
        if ( node != null && node.isVariable() )
            throw new NotAVariableException("Node_Variable (not a Var) found");
        return false;
    }

    public static boolean isRenamedVar(Node node)
    { return node.isVariable() && isRenamedVar(node.getName()); }

    public static boolean isRenamedVar(String x)
    { return x.startsWith(ARQConstants.allocVarScopeHiding); }

    public static boolean isNamedVar(Node node)
    { return node.isVariable() && isNamedVarName(node.getName()); }

    public static boolean isNamedVarName(String x)
    { return ! isBlankNodeVarName(x) && ! isAllocVarName(x); }

    public static boolean isBlankNodeVar(Node node)
    { return node.isVariable() && isBlankNodeVarName(node.getName()); }

    public static boolean isBlankNodeVarName(String x)
    { return x.startsWith(ARQConstants.allocVarAnonMarker); }

    public static boolean isAllocVar(Node node)
    { return node.isVariable() && isAllocVarName(node.getName()); }

    public static boolean isAllocVarName(String x)
    { return x.startsWith(ARQConstants.allocVarMarker); }

    /** Convert a collection of variable names to variables */
    public static List<Var> varList(Collection<String> varNames) {
        List<Var> x = new ArrayList<>();
        for ( String obj : varNames )
            x.add(Var.alloc(obj));
        return x;
    }

    public static boolean isAnonVar(Var var) {
        return var == ANON;
    }

    /** Return a list of String names from a collection of variables */
    public static List<String> varNames(Collection<Var> vars) {
        List<String> x = new ArrayList<>();
        for ( Var var : vars )
            x.add(var.getVarName());
        return x;
    }
}
