package function;

import java.util.ArrayList;

import function.builtin.EVAL;
import sexpression.*;
import table.*;

public class UserDefinedFunction extends LispFunction {

    private String name;
    private Cons body;
    private Cons lambdaExpression;
    private ExecutionContext executionContext;
    private SymbolTable functionScope;
    private ArrayList<String> formalParameters;
    private ArgumentValidator argumentValidator;

    public UserDefinedFunction(String name, Cons lambdaList, Cons body) {
        this.name = name;
        this.body = body;
        this.lambdaExpression = new Cons(new Symbol(name), new Cons(lambdaList, body));
        this.executionContext = ExecutionContext.getInstance();
        this.functionScope = executionContext.getScope();

        for (this.formalParameters = new ArrayList<>(); lambdaList.consp(); lambdaList = (Cons) lambdaList.getCdr())
            this.formalParameters.add(lambdaList.getCar().toString());

        this.argumentValidator = new ArgumentValidator(this.name);
        this.argumentValidator.setExactNumberOfArguments(this.formalParameters.size());
    }

    public SExpression call(Cons argumentList) {
        argumentValidator.validate(argumentList);

        bindParameterValues(argumentList);
        SymbolTable callingScope = executionContext.getScope();
        executionContext.setScope(functionScope);

        SExpression lastEvaluation = Nil.getInstance();

        for (Cons expression = body; expression.consp(); expression = (Cons) expression.getCdr())
            lastEvaluation = EVAL.eval(expression.getCar());

        executionContext.setScope(callingScope);
        releaseParameterValues();

        return lastEvaluation;
    }

    private void bindParameterValues(Cons argumentList) {
        functionScope = new SymbolTable(functionScope);

        for (String parameter : formalParameters) {
            SExpression currentArg = argumentList.getCar();
            functionScope.put(parameter, currentArg);
            argumentList = (Cons) argumentList.getCdr();
        }
    }

    private void releaseParameterValues() {
        functionScope = new SymbolTable(functionScope.getParent());
    }

    public Cons getLambdaExpression() {
        return lambdaExpression;
    }

}