package org.zwobble.couscous.interpreter;

import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.stream.IntStream;

import org.zwobble.couscous.Project;
import org.zwobble.couscous.ast.Assignment;
import org.zwobble.couscous.ast.ExpressionNode;
import org.zwobble.couscous.ast.ExpressionStatementNode;
import org.zwobble.couscous.ast.LiteralNode;
import org.zwobble.couscous.ast.MethodNode;
import org.zwobble.couscous.ast.ReturnNode;
import org.zwobble.couscous.ast.VariableReferenceNode;
import org.zwobble.couscous.ast.visitors.ExpressionNodeVisitor;
import org.zwobble.couscous.ast.visitors.StatementNodeVisitor;
import org.zwobble.couscous.values.InterpreterValue;

import static com.google.common.collect.Iterables.find;
import static java.util.stream.Collectors.toMap;
import static org.zwobble.couscous.values.UnitValue.UNIT;

import lombok.val;

public class Interpreter {
    private Project project;

    public Interpreter(Project project) {
        this.project = project;
    }
    
    public InterpreterValue run(String className, String methodName, List<InterpreterValue> arguments) {
        val clazz = project.findClass(className);
        val method = find(clazz.getMethods(),
            method -> method.getName().equals(methodName));
        val stackFrame = buildStackFrame(method, arguments);
        
        for (val statement : method.getBody()) {
            val result = statement.accept(new Executor(new Evaluator(stackFrame)));
            if (result.isPresent()) {
                return result.get();
            }
        }
        return UNIT;
    }

    private Map<Integer, InterpreterValue> buildStackFrame(
        final MethodNode method,
        List<InterpreterValue> arguments) {
        
        if (method.getArguments().size() != arguments.size()) {
            throw new WrongNumberOfArguments(method.getArguments().size(), arguments.size());
        }
        
        return IntStream.range(0, method.getArguments().size())
            .boxed()
            .collect(toMap(
                index -> method.getArguments().get(index).getId(),
                index -> arguments.get(index)));
    }
    
    private class Executor implements StatementNodeVisitor<Optional<InterpreterValue>> {
        private Evaluator evaluator;

        public Executor(Evaluator evaluator) {
            this.evaluator = evaluator;
        }
        
        @Override
        public Optional<InterpreterValue> visit(ReturnNode returnNode) {
            return Optional.of(evaluator.eval(returnNode.getValue()));
        }

        @Override
        public Optional<InterpreterValue> visit(ExpressionStatementNode expressionStatement) {
            evaluator.eval(expressionStatement.getExpression());
            return Optional.empty();
        }
    }
    
    private class Evaluator implements ExpressionNodeVisitor<InterpreterValue> {
        private final Map<Integer, InterpreterValue> stackFrame;

        public Evaluator(Map<Integer, InterpreterValue> stackFrame) {
            this.stackFrame = stackFrame;
        }
        
        public InterpreterValue eval(ExpressionNode expression) {
            return expression.accept(this);
        }

        @Override
        public InterpreterValue visit(LiteralNode literal) {
            return literal.getValue();
        }

        @Override
        public InterpreterValue visit(VariableReferenceNode variableReference) {
            return stackFrame.get(variableReference.getReferentId());
        }

        @Override
        public InterpreterValue visit(Assignment assignment) {
            val value = eval(assignment.getValue());
            stackFrame.put(assignment.getTarget().getReferentId(), value);
            return value;
        }
    }
}