package main

import (
	"errors"
)

func createError(message string) error {
	// TODO: pass token and get actual token position
	return errors.New(message)
}

func validateImport(imp *Import) []error {
	// TODO
	return nil
}

func validateExpression(expr *Expression, block *Block) []error {
	var errors []error

	switch expr.Type {
	case Expression_Assignment:
		assignment := expr.Value.(AssignmentExpression)
		var local Local
		var ok bool
		if local, ok = block.Locals[assignment.Variable]; !ok {
			errors = append(errors, createError("Assignment to undeclared variable "+assignment.Variable))
			return errors
		}

		valueErrors := validateExpression(&assignment.Value, block)
		if len(valueErrors) != 0 {
			errors = append(errors, valueErrors...)
			return errors
		}

		// TODO: check if assignment is valid
		expr.ValueType = local.Type
	case Expression_Literal:
		literal := expr.Value.(LiteralExpression)

		switch literal.Literal.Type {
		case Literal_Boolean:
		case Literal_Number:
			expr.ValueType = Type{Type: Type_Primitive, Value: literal.Literal.Primitive}
		case Literal_String:
			expr.ValueType = STRING_TYPE
		}
	case Expression_VariableReference:
		reference := expr.Value.(VariableReferenceExpression)
		var local Local
		var ok bool
		if local, ok = block.Locals[reference.Variable]; !ok {
			errors = append(errors, createError("Reference to undeclared variable "+reference.Variable))
			return errors
		}

		expr.ValueType = local.Type
	case Expression_Arithmetic:
		arithmethic := expr.Value.(ArithmeticExpression)

		errors = append(errors, validateExpression(&arithmethic.Left, block)...)
		errors = append(errors, validateExpression(&arithmethic.Right, block)...)

		if len(errors) != 0 {
			return errors
		}

		// TODO: validate types compatible and determine result type
	case Expression_Tuple:
		tuple := expr.Value.(TupleExpression)

		var types []Type
		for _, member := range tuple.Members {
			memberErrors := validateExpression(&member, block)
			if len(memberErrors) != 0 {
				errors = append(errors, memberErrors...)
				continue
			}

			types = append(types, member.ValueType)
		}

		if len(errors) != 0 {
			return errors
		}

		expr.ValueType = Type{Type: Type_Tuple, Value: TupleType{Types: types}}
	}

	return errors
}

func validateStatement(stmt *Statement, block *Block) []error {
	var errors []error

	switch stmt.Type {
	case Statement_Expression:
		expression := stmt.Value.(ExpressionStatement)
		errors = append(errors, validateExpression(&expression.Expression, block)...)
	case Statement_Block:
		block := stmt.Value.(BlockStatement)
		errors = append(errors, validateBlock(&block.Block)...)
	case Statement_Return:
		ret := stmt.Value.(ReturnStatement)
		if ret.Value != nil {
			errors = append(errors, validateExpression(ret.Value, block)...)
		}
	case Statement_DeclareLocalVariable:
		dlv := stmt.Value.(DeclareLocalVariableStatement)
		if dlv.Initializer != nil {
			errors = append(errors, validateExpression(dlv.Initializer, block)...)
		}

		block.Locals[dlv.Variable] = Local{Name: dlv.Variable, Type: dlv.VariableType}
	}

	return errors
}

func validateBlock(block *Block) []error {
	var errors []error

	block.Locals = make(map[string]Local)

	for _, stmt := range block.Statements {
		errors = append(errors, validateStatement(&stmt, block)...)
	}

	return errors
}

func validateFunction(function *ParsedFunction) []error {
	var errors []error

	errors = append(errors, validateBlock(&function.Body)...)

	return errors
}

func validator(file *ParsedFile) []error {
	var errors []error

	for _, imp := range file.Imports {
		errors = append(errors, validateImport(&imp)...)
	}

	for _, function := range file.Functions {
		errors = append(errors, validateFunction(&function)...)
	}

	return errors
}