package types

import (
	"encoding/json"
	"fmt"
	"regexp"
	"sort"
)

type (
	// FieldList is a parameter type to represent a list of fields in the database
	// to return. It can be used with query.FieldListToSelect to build a
	// select clause to return the data that was requested.
	FieldList struct {
		fields map[string]bool
	}
)

var (
	// fieldIdentifier filters field names to allow only sane values
	// and at the same time make them save for database queries.
	fieldIdentifier = regexp.MustCompile(`\A[a-zA-Z]+[a-zA-Z0-9_\-]`)
)

func NewFieldList(fields ...string) FieldList {
	fl := FieldList{
		fields: map[string]bool{},
	}
	for _, field := range fields {
		fl.fields[field] = true
	}
	return fl
}

func (fl *FieldList) UnmarshalJSON(raw []byte) error {
	fields := []string{}
	if err := json.Unmarshal(raw, &fields); err != nil {
		return err
	}
	fl.fields = map[string]bool{}
	for _, field := range fields {
		if !fieldIdentifier.Match([]byte(field)) {
			return fmt.Errorf("`%s` is not an allowed field name. Allowed is only alpha numerical", field)
		}
		fl.fields[field] = true
	}
	return nil
}

// Contains returns true, when the string is found in the list.
func (fl FieldList) Contains(in string) bool {
	_, found := fl.fields[in]
	return found
}

// Fields returns a sorted list of the requested fields.
func (fl FieldList) Fields() []string {
	res := []string{}
	for name, _ := range fl.fields {
		res = append(res, name)
	}
	sort.Strings(res)
	return res
}