package compiler

import (
	"go/ast"
	"go/types"
	"log"
)

// A structScope holds the positions for it's fields. Struct fields have different
// positions then local variables in any scope.
type structScope struct {
	// identifier of the initialized struct in the program.
	name string

	// a mapping of field identifier and its position.
	fields map[string]int
}

func newStructScope() *structScope {
	return &structScope{
		fields: map[string]int{},
	}
}

func (s *structScope) newField(name string) int {
	i := len(s.fields)
	s.fields[name] = i
	return i
}

func (s *structScope) loadField(name string) int {
	i, ok := s.fields[name]
	if !ok {
		log.Fatalf("could not resolve field name %s for struct %s", name, s.name)
	}
	return i
}

func (s *structScope) initializeFields(ident *ast.Ident, tInfo *types.Info) {
	def, ok := tInfo.Defs[ident]
	if !ok {
		log.Fatalf("could not initialize fields of %s: definitions not found in typeinfo", ident.Name)
	}
	t, ok := def.Type().Underlying().(*types.Struct)
	if !ok {
		log.Fatalf("%s is not of type struct", ident.Name)
	}
	for i := 0; i < t.NumFields(); i++ {
		s.newField(t.Field(i).Name())
	}
}