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 isTypeExpandableTo(from PrimitiveType, to PrimitiveType) bool {
	if from == to {
		return true
	}

	switch from {
	case Primitive_I8, Primitive_U8:
		if to == Primitive_I16 || to == Primitive_U16 {
			return true
		}

		fallthrough
	case Primitive_I16, Primitive_U16:
		if to == Primitive_I32 || to == Primitive_U32 {
			return true
		}

		fallthrough
	case Primitive_I32, Primitive_U32:
		if to == Primitive_I64 || to == Primitive_U64 {
			return true
		}

	case Primitive_F32:
		if to == Primitive_F64 {
			return true
		}
	}

	return false
}

func getArithmeticResultType(left PrimitiveType, right PrimitiveType, operation ArithmeticOperation) (PrimitiveType, error) {
	if left == Primitive_Bool || right == Primitive_Bool {
		return InvalidValue, createError("bool type cannot be used in arithmetic expressions")
	}

	if isTypeExpandableTo(left, right) {
		return right, nil
	}

	if isTypeExpandableTo(right, left) {
		return left, nil
	}

	// TODO: boolean expressions etc.

	return InvalidValue, createError("cannot use these types in an arithmetic expression without an explicit cast") // TODO: include type names in error
}

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
		expr.Value = assignment
	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
		expr.Value = reference
	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
		if arithmethic.Left.ValueType.Type != Type_Primitive || arithmethic.Right.ValueType.Type != Type_Primitive {
			errors = append(errors, createError("both sides of an arithmetic expression must be a primitive type"))
			return errors
		}

		leftType := arithmethic.Left.ValueType.Value.(PrimitiveType)
		rightType := arithmethic.Right.ValueType.Value.(PrimitiveType)
		result, err := getArithmeticResultType(leftType, rightType, arithmethic.Operation)
		if err != nil {
			errors = append(errors, err)
			return errors
		}

		expr.ValueType = Type{Type: Type_Primitive, Value: result}
		expr.Value = arithmethic
	case Expression_Tuple:
		tuple := expr.Value.(TupleExpression)

		var types []Type
		for i := range tuple.Members {
			member := &tuple.Members[i]

			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}}
		expr.Value = tuple
	}

	return errors
}

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

	// TODO: support references to variables in parent block

	switch stmt.Type {
	case Statement_Expression:
		expression := stmt.Value.(ExpressionStatement)
		errors = append(errors, validateExpression(&expression.Expression, block)...)
		*stmt = Statement{Type: Statement_Expression, Value: expression}
	case Statement_Block:
		block := stmt.Value.(BlockStatement)
		errors = append(errors, validateBlock(&block.Block, functionLocals)...)
		*stmt = Statement{Type: Statement_Block, Value: 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)...)
		}

		if _, ok := block.Locals[dlv.Variable]; ok {
			errors = append(errors, createError("redeclaration of variable '"+dlv.Variable+"'"))
		}

		local := Local{Name: dlv.Variable, Type: dlv.VariableType, IsParameter: false, Index: len(*functionLocals)}
		block.Locals[dlv.Variable] = local
		*functionLocals = append(*functionLocals, local)
	}

	return errors
}

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

	if block.Locals == nil {
		block.Locals = make(map[string]Local)
	}

	for i := range block.Statements {
		stmt := &block.Statements[i]
		errors = append(errors, validateStatement(stmt, block, functionLocals)...)
	}

	return errors
}

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

	var locals []Local

	body := &function.Body
	body.Locals = make(map[string]Local)
	for _, param := range function.Parameters {
		local := Local{Name: param.Name, Type: param.Type, IsParameter: true, Index: len(locals)}
		locals = append(locals, local)
		body.Locals[param.Name] = local
	}

	errors = append(errors, validateBlock(body, &locals)...)

	function.Locals = locals

	return errors
}

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

	for i := range file.Imports {
		errors = append(errors, validateImport(&file.Imports[i])...)
	}

	for i := range file.Functions {
		errors = append(errors, validateFunction(&file.Functions[i])...)
	}

	return errors
}