add paste functionality

Backend/paste/store.go

@@ -0,0 +1,95 @@
+package paste
+
+import (
+	"crypto/rand"
+	"errors"
+	"sync"
+	"time"
+)
+
+var ErrNotFound = errors.New("paste not found")
+
+type Paste struct {
+	ID        string     `json:"id"`
+	Title     string     `json:"title"`
+	Content   string     `json:"content"`
+	Language  string     `json:"language"`
+	CreatedAt time.Time  `json:"created_at"`
+	ExpiresAt *time.Time `json:"expires_at"`
+}
+
+type Store struct {
+	mu     sync.RWMutex
+	pastes map[string]*Paste
+}
+
+func NewStore() *Store {
+	return &Store{pastes: make(map[string]*Paste)}
+}
+
+func (s *Store) Create(p *Paste) error {
+	id, err := generateID()
+	if err != nil {
+		return err
+	}
+	p.ID = id
+	p.CreatedAt = time.Now().UTC()
+
+	s.mu.Lock()
+	s.pastes[id] = p
+	s.mu.Unlock()
+	return nil
+}
+
+func (s *Store) Get(id string) (*Paste, error) {
+	s.mu.RLock()
+	p, ok := s.pastes[id]
+	s.mu.RUnlock()
+	if !ok {
+		return nil, ErrNotFound
+	}
+	return p, nil
+}
+
+func (s *Store) Delete(id string) error {
+	s.mu.Lock()
+	delete(s.pastes, id)
+	s.mu.Unlock()
+	return nil
+}
+
+func (s *Store) ForEach(fn func(p *Paste) error) error {
+	s.mu.RLock()
+	ids := make([]string, 0, len(s.pastes))
+	for id := range s.pastes {
+		ids = append(ids, id)
+	}
+	s.mu.RUnlock()
+
+	for _, id := range ids {
+		s.mu.RLock()
+		p, ok := s.pastes[id]
+		s.mu.RUnlock()
+		if !ok {
+			continue
+		}
+		if err := fn(p); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+const base62Chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+
+func generateID() (string, error) {
+	b := make([]byte, 8)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	result := make([]byte, 8)
+	for i, v := range b {
+		result[i] = base62Chars[int(v)%62]
+	}
+	return string(result), nil
+}