package session

import (
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"sort"
	"sync"
)

// Registry is the daemon's set of live sessions.
type Registry struct {
	mu       sync.RWMutex
	sessions map[string]*Session
}

func NewRegistry() *Registry {
	return &Registry{sessions: make(map[string]*Session)}
}

// Create starts a new session and registers it under a fresh ID.
func (r *Registry) Create(opts Options) (*Session, error) {
	r.mu.Lock()
	defer r.mu.Unlock()
	var id string
	for {
		b := make([]byte, 3)
		if _, err := rand.Read(b); err != nil {
			return nil, fmt.Errorf("generating session id: %w", err)
		}
		id = hex.EncodeToString(b)
		if _, taken := r.sessions[id]; !taken {
			break
		}
	}
	s, err := New(id, opts)
	if err != nil {
		return nil, err
	}
	r.sessions[id] = s
	return s, nil
}

// Get returns the session or nil.
func (r *Registry) Get(id string) *Session {
	r.mu.RLock()
	defer r.mu.RUnlock()
	return r.sessions[id]
}

// List returns all sessions sorted by ID.
func (r *Registry) List() []*Session {
	r.mu.RLock()
	defer r.mu.RUnlock()
	out := make([]*Session, 0, len(r.sessions))
	for _, s := range r.sessions {
		out = append(out, s)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].ID < out[j].ID })
	return out
}

// Remove unregisters a session (the caller is responsible for Kill).
func (r *Registry) Remove(id string) {
	r.mu.Lock()
	defer r.mu.Unlock()
	delete(r.sessions, id)
}