package main

import (
	"crypto/rand"
	"crypto/subtle"
	"encoding/hex"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"time"
)

// #40: admin endpoint with an install-time key. The key is read from
// PALETTE_ADMIN_KEY when set; otherwise a 32-char random hex key is generated
// and persisted to <db-dir>/admin-key (0600) so it survives restarts.

// Settings holds the runtime-tunable values the admin API exposes. The list
// is intentionally small and extensible: add a field + JSON tag, wire it into
// the consumer, and it round-trips through GET/POST /admin/api/settings.
type Settings struct {
	RateLimitBurst             float64 `json:"rate_limit_burst"`
	RateLimitPerMinute         float64 `json:"rate_limit_per_minute"`
	MaxContentBytes            int64   `json:"max_content_bytes"`
	DefaultExpiry              string  `json:"default_expiry"`
	CustomSlugReservationDays  int     `json:"custom_slug_reservation_days"`
	BurnViewerWindowMinutes    int     `json:"burn_viewer_window_minutes"`
}

func defaultSettings(cfg Config) Settings {
	return Settings{
		RateLimitBurst:             5,
		RateLimitPerMinute:         60, // 1 req/sec refill
		MaxContentBytes:            cfg.MaxTextBytes,
		DefaultExpiry:              "", // no default: pastes are permanent unless expires_in given
		CustomSlugReservationDays:  customSlugReservationDays,
		BurnViewerWindowMinutes:    readWindowMinutes,
	}
}

// settingsStore keeps the current settings in memory (mutex-guarded) and
// persists them as JSON to <db-dir>/settings.json.
type settingsStore struct {
	mu   sync.RWMutex
	cur  Settings
	path string
}

func loadSettingsStore(dbPath string, cfg Config) *settingsStore {
	p := filepath.Join(filepath.Dir(dbPath), "settings.json")
	ss := &settingsStore{cur: defaultSettings(cfg), path: p}
	if b, err := os.ReadFile(p); err == nil {
		var s Settings
		if json.Unmarshal(b, &s) == nil {
			// merge over defaults so newly added fields keep sane values
			def := defaultSettings(cfg)
			if s.RateLimitBurst > 0 {
				def.RateLimitBurst = s.RateLimitBurst
			}
			if s.RateLimitPerMinute > 0 {
				def.RateLimitPerMinute = s.RateLimitPerMinute
			}
			if s.MaxContentBytes > 0 {
				def.MaxContentBytes = s.MaxContentBytes
			}
			if s.DefaultExpiry != "" {
				def.DefaultExpiry = s.DefaultExpiry
			}
			if s.CustomSlugReservationDays > 0 {
				def.CustomSlugReservationDays = s.CustomSlugReservationDays
			}
			if s.BurnViewerWindowMinutes > 0 {
				def.BurnViewerWindowMinutes = s.BurnViewerWindowMinutes
			}
			ss.cur = def
		}
	}
	return ss
}

func (ss *settingsStore) get() Settings {
	ss.mu.RLock()
	defer ss.mu.RUnlock()
	return ss.cur
}

func (ss *settingsStore) set(s Settings) error {
	if s.RateLimitBurst <= 0 || s.RateLimitPerMinute <= 0 || s.MaxContentBytes <= 0 ||
		s.CustomSlugReservationDays <= 0 || s.BurnViewerWindowMinutes <= 0 {
		return fmt.Errorf("all numeric settings must be positive")
	}
	if s.DefaultExpiry != "" {
		d, err := time.ParseDuration(s.DefaultExpiry)
		if err != nil || !validExpiry(d) {
			return fmt.Errorf("default_expiry must be a duration between 1 minute and 1 year (or empty)")
		}
	}
	ss.mu.Lock()
	defer ss.mu.Unlock()
	b, _ := json.Marshal(s)
	if err := os.WriteFile(ss.path, b, 0600); err != nil {
		return err
	}
	ss.cur = s
	return nil
}

// resetAdminKeyFile deletes the persisted admin key file (if any) and returns
// the path so callers can regenerate. Used by --reset-admin-key (#40).
func resetAdminKeyFile(dbPath string) string {
	p := filepath.Join(filepath.Dir(dbPath), "admin-key")
	os.Remove(p)
	return p
}

// resolveAdminKey returns the admin key: env PALETTE_ADMIN_KEY wins; else the
// persisted key file is reused; else a new 32-char hex key is generated and
// persisted with 0600 perms.
func resolveAdminKey(dbPath string) (string, error) {
	if v := os.Getenv("PALETTE_ADMIN_KEY"); v != "" {
		return v, nil
	}
	p := filepath.Join(filepath.Dir(dbPath), "admin-key")
	if b, err := os.ReadFile(p); err == nil && len(strings.TrimSpace(string(b))) >= 16 {
		return strings.TrimSpace(string(b)), nil
	}
	b := make([]byte, 16)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	key := hex.EncodeToString(b)
	if err := os.WriteFile(p, []byte(key+"\n"), 0600); err != nil {
		return "", err
	}
	log.Printf("generated admin key, persisted to %s", p)
	return key, nil
}

// handleResetAdminKey implements the --reset-admin-key flag: delete the key
// file, generate a fresh key, print it.
func handleResetAdminKey(dbPath string) {
	p := resetAdminKeyFile(dbPath)
	key, err := resolveAdminKey(dbPath)
	if err != nil {
		log.Fatalf("reset admin key: %v", err)
	}
	fmt.Printf("admin key reset; new key written to %s:\n%s\n", p, key)
}

// adminKeyOK reports whether the request carries the correct admin key via
// X-Admin-Key header or ?key=. Constant-time compare; failures and successes
// are both logged (#40).
func (a *apiServer) adminKeyOK(r *http.Request, key string) bool {
	given := r.Header.Get("X-Admin-Key")
	if given == "" {
		given = r.URL.Query().Get("key")
	}
	return subtle.ConstantTimeCompare([]byte(given), []byte(key)) == 1
}

func (a *apiServer) adminAuth(next http.HandlerFunc, key string) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if !a.adminKeyOK(r, key) {
			log.Printf("admin auth FAILURE: %s %s from %s", r.Method, r.URL.Path, r.RemoteAddr)
			writeErr(w, 401, "unauthorized")
			return
		}
		log.Printf("admin auth OK: %s %s from %s", r.Method, r.URL.Path, r.RemoteAddr)
		next(w, r)
	}
}

func (a *apiServer) handleAdminPage(w http.ResponseWriter, r *http.Request) {
	renderPage(w, "admin.html", map[string]any{"Page": "admin"})
}

func (a *apiServer) handleAdminGetSettings(w http.ResponseWriter, r *http.Request) {
	writeJSON(w, 200, a.settings.get())
}

func (a *apiServer) handleAdminPostSettings(w http.ResponseWriter, r *http.Request) {
	var s Settings
	if err := json.NewDecoder(r.Body).Decode(&s); err != nil {
		writeErr(w, 400, "invalid json body")
		return
	}
	if err := a.settings.set(s); err != nil {
		writeErr(w, 400, err.Error())
		return
	}
	writeJSON(w, 200, a.settings.get())
}