implemented functionality to guess a letter

internal/game/session.go

@@ -3,6 +3,8 @@ package game
 import (
 	"crypto/ed25519"
 	"encoding/base64"
+	"errors"
+	"strings"
 
 	petname "github.com/dustinkirkland/golang-petname"
 )
@@ -16,17 +18,28 @@ type Session struct {
 	Name  string
 	Users []User
 
-	Phrase       []string
-	HiddenPhrase []string
+	phrase           []string
+	AskedLetters     []string
+	DiscoveredPhrase []string
+	Mistakes         int
+
+	userIndex   int
+	CurrentUser *User
 }
 
 func NewSession(phrase string) Session {
 	sessionName := petname.Generate(3, "-")
 
 	s := Session{
-		id:    lastSessionId,
-		Name:  sessionName,
-		Users: []User{},
+		id:               lastSessionId,
+		Name:             sessionName,
+		Users:            []User{},
+		phrase:           []string{phrase},
+		AskedLetters:     []string{},
+		DiscoveredPhrase: make([]string, len(phrase)),
+		Mistakes:         0,
+		userIndex:        0,
+		CurrentUser:      nil,
 	}
 
 	sessionStorage = append(sessionStorage, s)
@@ -42,6 +55,10 @@ func GetSession(name string) *Session {
 
 func (s *Session) AddUser(user User) {
 	s.Users = append(s.Users, user)
+
+	if s.CurrentUser == nil {
+		s.CurrentUser = &s.Users[s.userIndex]
+	}
 }
 
 func (s Session) VerifySignature(signature string, message []byte) *User {
@@ -55,3 +72,33 @@ func (s Session) VerifySignature(signature string, message []byte) *User {
 
 	return nil
 }
+
+func (s *Session) GuessLetter(letter string) (*Session, error) {
+	letter = strings.ToLower(letter)
+	if len(letter) != 1 {
+		return s, errors.New("the letter needs to have a length of one")
+	}
+	for _, asked := range s.AskedLetters {
+		if letter == asked {
+			return s, errors.New("the letter " + letter + " was already asked")
+		}
+	}
+
+	s.AskedLetters = append(s.AskedLetters, letter)
+
+	found := false
+	for i, l := range s.phrase {
+		if l == letter {
+			found = true
+			s.DiscoveredPhrase[i] = s.phrase[i]
+		}
+	}
+
+	if !found {
+		s.Mistakes++
+	}
+
+	s.userIndex = (s.userIndex + 1) % len(s.Users)
+	s.CurrentUser = &s.Users[s.userIndex]
+	return s, nil
+}