package hcl

import (
	"errors"
	"fmt"
	"reflect"
	"strings"
)

const (
	ElementTypeAttribute ElementType = "attr"
	ElementTypeBlock     ElementType = "block"
	ElementTypeLabel     ElementType = "label"
	ElementTypeRemain    ElementType = "remain"
)

var ErrNoHclTag = errors.New("no hcl tag")

type ElementType string

type FieldMeta struct {
	Name     string
	Type     ElementType
	Optional bool
	Ignore   bool
}

func ExtractFieldMeta(t reflect.StructField, readTagName, writeTagName string) (FieldMeta, error) {
	hclTag, present := t.Tag.Lookup(readTagName)
	if !present {
		return FieldMeta{}, ErrNoHclTag
	}

	cfg := FieldMeta{
		Name: t.Name,
		Type: ElementTypeAttribute,
	}

	if hclWriteTag, present := t.Tag.Lookup(writeTagName); present && hclWriteTag == "-" {
		cfg.Ignore = true

		return cfg, nil
	}

	split := strings.Split(hclTag, ",")

	if len(split) > 0 && split[0] != "" {
		cfg.Name = split[0]
	}

	if len(split) > 1 {
		switch split[1] {
		case "":
			fallthrough
		case "attr":
			cfg.Type = ElementTypeAttribute
		case "optional":
			cfg.Optional = true
		case "label":
			cfg.Type = ElementTypeLabel
		case "block":
			cfg.Type = ElementTypeBlock
		case "remain":
			cfg.Type = ElementTypeRemain
		default:
			return FieldMeta{}, fmt.Errorf("unknown element type %q", split[1])
		}
	}

	return cfg, nil
}