package twitter

import (
	"net/http"
	"regexp"

	"github.com/foxdeveloper/namecheck"
	"github.com/foxdeveloper/namecheck/util"
)

const (
	EndpointAPI            string = "https://twitter.com/"
	AvailableHTTPCode      int    = http.StatusNotFound
	UsernameShort          int    = 1
	UsernameLong           int    = 15
	UsernameLegalPattern   string = "^[A-Za-z0-9_]+$"
	UsernameIllegalPattern string = "twitter"
)

var (
	legalRegexp   = regexp.MustCompile(UsernameLegalPattern)
	illegalRegexp = regexp.MustCompile(UsernameIllegalPattern)
)

type Twitter struct{}

func init() {
	namecheck.AddSn(&Twitter{})
}

func (t *Twitter) String() string {
	return "Twitter"
}

// IsValid check the validity of the username
func (t *Twitter) IsValid(username string) bool {
	return isLongEnough(username) &&
		isShortEnough(username) &&
		containsNoIllegalPattern(username) &&
		containsOnlyLegalChars(username)
}

// IsAvailable check username availability
func (t *Twitter) IsAvailable(username string) (bool, error) {
	res, err := http.Get(EndpointAPI + username)
	if err != nil {
		myErr := &namecheck.ErrUnknownAvailability{Username: username, Cause: err}
		return false, myErr
	}

	// Prevent memory leaks
	defer res.Body.Close()

	return res.StatusCode == AvailableHTTPCode, nil
}

func isLongEnough(username string) bool {
	return util.Counter(username) >= UsernameShort
}

func isShortEnough(username string) bool {
	return util.Counter(username) <= UsernameLong
}

func containsOnlyLegalChars(username string) bool {
	return legalRegexp.MatchString(util.ToLower(username))
}

func containsNoIllegalPattern(username string) bool {
	return len(illegalRegexp.FindStringIndex(util.ToLower(username))) == 0
}