package org.simantics.scl.compiler.types;

import gnu.trove.map.hash.THashMap;
import gnu.trove.set.hash.THashSet;

import java.util.ArrayList;

import org.simantics.scl.compiler.environment.Environment;
import org.simantics.scl.compiler.internal.types.TypeHashCodeContext;
import org.simantics.scl.compiler.internal.types.ast.TVarAst;
import org.simantics.scl.compiler.internal.types.ast.TypeAst;
import org.simantics.scl.compiler.types.exceptions.KindUnificationException;
import org.simantics.scl.compiler.types.exceptions.UnificationException;
import org.simantics.scl.compiler.types.kinds.KMetaVar;
import org.simantics.scl.compiler.types.kinds.Kind;
import org.simantics.scl.compiler.types.kinds.Kinds;
import org.simantics.scl.compiler.types.util.Polarity;
import org.simantics.scl.compiler.types.util.TypeUnparsingContext;



/**
 * A meta-variable, a type that is currently unknown. This class
 * should occur only during type inference. Method removeMetaVars
 * can be used to remove all instances of TMetaVar from the type.
 * 
 * @author Hannu Niemistö
 */
public class TMetaVar extends Type {
    public static final TMetaVar[] EMPTY_ARRAY = new TMetaVar[0];
    
    Type ref = null;
    Polarity polarity = Polarity.NO_POLARITY;
    private Kind kind;
    
    TMetaVar(Kind kind) {
        this.kind = kind;
    }
    
    TMetaVar(Kind kind, Polarity polarity) {
        this.kind = kind;
        this.polarity = polarity;
    }
    
    public Kind getKind() {
        if(kind instanceof KMetaVar)
            kind = Kinds.canonical(kind);
        return kind;        
    }
    
    @Override
    public Type replace(TVar var, Type replacement) {
        if(ref == null)
            return this;
        else {
            Type newRef = ref.replace(var, replacement);
            if(newRef != ref)
                return newRef;
            else
                // We could also return newRef here, but in this way
                // we don't have to copy so many parent types.
                return this;
        }
    }

    @Override
    public TypeAst toTypeAst(TypeUnparsingContext context) {
        if(ref == null)
            return new TVarAst(/*polarity.getSymbol() +*/ context.getName(this));
        else
            return ref.toTypeAst(context);
    }
    
    @Override
    public int hashCode() {
        if(ref == null)
            return System.identityHashCode(this);
        else
            return ref.hashCode();
    }
    
    @Override
    public void updateHashCode(TypeHashCodeContext context) {
        if(ref == null)
            context.append(System.identityHashCode(this));
        else
            ref.updateHashCode(context);
    }

    @Override
    public void collectFreeVars(ArrayList<TVar> vars) {
        if(ref != null)
            ref.collectFreeVars(vars);
    }
    
    @Override
    public void collectMetaVars(ArrayList<TMetaVar> vars) {
        if(ref == null)
            vars.add(this);
        else
            ref.collectMetaVars(vars);
    }
    
    @Override
    public void collectMetaVars(THashSet<TMetaVar> vars) {
        if(ref == null)
            vars.add(this);
        else
            ref.collectMetaVars(vars);
    }
    
    @Override
    public void collectEffectMetaVars(ArrayList<TMetaVar> vars) {
        if(ref != null)
            ref.collectEffectMetaVars(vars);
    }

    public void setRef(Type a) throws UnificationException {
        a = Types.weakCanonical(a);
        if(a.contains(this))
            throw new UnificationException(this, a);
        ref = a;
        if(polarity != Polarity.NO_POLARITY)
            a.addPolarity(polarity);
    }
    
    public Type getRef() {
        return ref;
    }
    
    @Override
    public boolean contains(TMetaVar other) {
        if(ref == null)
            return this == other;
        else
            return ref.contains(other);
    }
    
    @Override
    public Type convertMetaVarsToVars() {
        if(ref == null) {
            if(kind == Kinds.EFFECT && !polarity.isNegative())
                ref = Types.NO_EFFECTS;
            else
                ref = Types.var(getKind());
            return ref;
        }
        else
            return ref.convertMetaVarsToVars();
    }

    @Override
    public boolean isGround() {
        if(ref == null)
            return false;
        else
            return ref.isGround();
    }

	public Kind inferKind(Environment context) throws KindUnificationException {
	    return Kinds.metaVar();
    }

    @Override
    public boolean containsMetaVars() {
        if(ref == null)
            return true;
        else
            return ref.containsMetaVars();
    }

    @Override
    public void toName(TypeUnparsingContext context, StringBuilder b) {
        if(ref != null)
            ref.toName(context, b);
        else
            b.append(context.getName(this));
    }
    
    @Override
    public int getClassId() {
        return METAVAR_ID;
    }
 
    @Override
    public boolean isMaximal() {
        return ref != null && ref.isMaximal(); 
    }
    
    @Override
    public boolean isMinimal() {
        return ref != null && ref.isMinimal();
    }

    @Override
    public void addPolarity(Polarity polarity) {        
        if(ref != null)
            ref.addPolarity(polarity);
        else
            this.polarity = this.polarity.add(polarity);
    }

    public Polarity getPolarity() {
        return polarity;
    }
    
    @Override
    public void collectConcreteEffects(ArrayList<TCon> concreteEffects) {
        if(ref != null)
            ref.collectConcreteEffects(concreteEffects);
    }

    @Override
    public Type head() {
        if(ref != null)
            return ref.head();
        else
            return this;
    }

    @Override
    public Type copySkeleton(THashMap<TMetaVar, TMetaVar> metaVarMap) {
        if(ref != null)
            return ref.copySkeleton(metaVarMap);
        else {
            TMetaVar result = metaVarMap.get(this);
            if(result == null) {
                result = new TMetaVar(kind, polarity);
                metaVarMap.put(this, result);
            }
            return result;
        }
    }
}