package auth

import (
	"context"
	"crypto/rand"
	"crypto/sha256"
	"crypto/subtle"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"strings"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"

	"aether/internal/audit"
	"aether/pkg/middleware"
	"aether/pkg/response"
)

// App-Passwörter ersetzen das Hauptpasswort in WebDAV-Clients. Ein verlorenes
// Handy kostet dann ein Token, nicht das Konto – und der Widerruf trifft nur
// dieses eine Gerät.

const (
	appPasswordGroups   = 5
	appPasswordGroupLen = 5
	// Ohne 0/1/l/o/i – auf einem Handy-Keyboard abgetippt sind die zu leicht
	// zu verwechseln.
	appPasswordAlphabet = "abcdefghjkmnpqrstuvwxyz23456789"
	maxAppPasswords     = 20
	// Schreiblast bremsen: WebDAV authentifiziert jeden Request einzeln, ein
	// UPDATE pro Aufruf wäre reine Verschwendung.
	lastUsedResolution = 5 * time.Minute
)

var ErrTooManyAppPasswords = errors.New("too many app passwords")

type AppPassword struct {
	ID         uuid.UUID  `json:"id"`
	Name       string     `json:"name"`
	LastUsedAt *time.Time `json:"last_used_at"`
	CreatedAt  time.Time  `json:"created_at"`
}

// GenerateAppPassword liefert ein Token in Fünfergruppen (aaaaa-bbbbb-…),
// damit es sich am Handy noch abtippen lässt.
func GenerateAppPassword() (string, error) {
	buf := make([]byte, appPasswordGroups*appPasswordGroupLen)
	if _, err := rand.Read(buf); err != nil {
		return "", fmt.Errorf("read random: %w", err)
	}
	var sb strings.Builder
	for i, b := range buf {
		if i > 0 && i%appPasswordGroupLen == 0 {
			sb.WriteByte('-')
		}
		sb.WriteByte(appPasswordAlphabet[int(b)%len(appPasswordAlphabet)])
	}
	return sb.String(), nil
}

// HashAppPassword: SHA-256 genügt, weil das Token zufällig und hochentropisch
// ist. Argon2 wäre hier nur langsam, nicht sicherer – und liefe bei WebDAV bei
// jedem einzelnen Request.
func HashAppPassword(token string) string {
	sum := sha256.Sum256([]byte(strings.TrimSpace(token)))
	return hex.EncodeToString(sum[:])
}

// ── Store ────────────────────────────────────────────────────────────────────

func (s *Store) ListAppPasswords(ctx context.Context, userID uuid.UUID) ([]AppPassword, error) {
	rows, err := s.db.Query(ctx,
		`SELECT id, name, last_used_at, created_at
		   FROM app_passwords WHERE user_id = $1 ORDER BY created_at DESC`,
		userID)
	if err != nil {
		return nil, fmt.Errorf("query app passwords: %w", err)
	}
	defer rows.Close()

	out := []AppPassword{}
	for rows.Next() {
		var a AppPassword
		if err := rows.Scan(&a.ID, &a.Name, &a.LastUsedAt, &a.CreatedAt); err != nil {
			return nil, fmt.Errorf("scan app password: %w", err)
		}
		out = append(out, a)
	}
	return out, rows.Err()
}

func (s *Store) CreateAppPassword(ctx context.Context, userID uuid.UUID, name, token string) (*AppPassword, error) {
	var count int
	if err := s.db.QueryRow(ctx,
		`SELECT count(*) FROM app_passwords WHERE user_id = $1`, userID).Scan(&count); err != nil {
		return nil, fmt.Errorf("count app passwords: %w", err)
	}
	if count >= maxAppPasswords {
		return nil, ErrTooManyAppPasswords
	}

	var a AppPassword
	err := s.db.QueryRow(ctx,
		`INSERT INTO app_passwords (user_id, name, token_hash)
		 VALUES ($1, $2, $3)
		 RETURNING id, name, last_used_at, created_at`,
		userID, name, HashAppPassword(token),
	).Scan(&a.ID, &a.Name, &a.LastUsedAt, &a.CreatedAt)
	if err != nil {
		return nil, fmt.Errorf("insert app password: %w", err)
	}
	return &a, nil
}

func (s *Store) DeleteAppPassword(ctx context.Context, userID, id uuid.UUID) error {
	tag, err := s.db.Exec(ctx,
		`DELETE FROM app_passwords WHERE id = $1 AND user_id = $2`, id, userID)
	if err != nil {
		return fmt.Errorf("delete app password: %w", err)
	}
	if tag.RowsAffected() == 0 {
		return ErrNotFound
	}
	return nil
}

// VerifyAppPassword sucht das Token über seinen Hash und gibt den zugehörigen
// User zurück. Der Username muss passen, damit ein Token nicht für ein fremdes
// Konto gilt.
func (s *Store) VerifyAppPassword(ctx context.Context, username, token string) (*User, error) {
	hash := HashAppPassword(token)

	var u User
	var storedHash string
	var pwID uuid.UUID
	var lastUsed *time.Time
	err := s.db.QueryRow(ctx,
		`SELECT ap.id, ap.token_hash, ap.last_used_at,
		        u.id, u.username, u.display_name, u.is_admin, u.quota_bytes, u.created_at
		   FROM app_passwords ap
		   JOIN users u ON u.id = ap.user_id
		  WHERE ap.token_hash = $1 AND u.username = $2`,
		hash, username,
	).Scan(&pwID, &storedHash, &lastUsed,
		&u.ID, &u.Username, &u.DisplayName, &u.IsAdmin, &u.QuotaBytes, &u.CreatedAt)
	if errors.Is(err, pgx.ErrNoRows) {
		return nil, ErrNotFound
	}
	if err != nil {
		return nil, fmt.Errorf("query app password: %w", err)
	}
	// Gürtel und Hosenträger – der Vergleich lief schon in der Datenbank.
	if subtle.ConstantTimeCompare([]byte(storedHash), []byte(hash)) != 1 {
		return nil, ErrNotFound
	}

	if lastUsed == nil || time.Since(*lastUsed) > lastUsedResolution {
		if _, err := s.db.Exec(ctx,
			`UPDATE app_passwords SET last_used_at = now() WHERE id = $1`, pwID); err != nil {
			return nil, fmt.Errorf("touch app password: %w", err)
		}
	}
	return &u, nil
}

// ── Handlers ─────────────────────────────────────────────────────────────────

// GET /api/v1/app-passwords
func (h *Handler) ListAppPasswords(w http.ResponseWriter, r *http.Request) {
	user := UserFromContext(r.Context())
	list, err := h.store.ListAppPasswords(r.Context(), user.ID)
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "could not load app passwords")
		return
	}
	response.JSON(w, http.StatusOK, list)
}

// POST /api/v1/app-passwords
func (h *Handler) CreateAppPassword(w http.ResponseWriter, r *http.Request) {
	user := UserFromContext(r.Context())

	var body struct {
		Name string `json:"name"`
	}
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
		response.Error(w, http.StatusBadRequest, "invalid request body")
		return
	}
	name := strings.TrimSpace(body.Name)
	if name == "" {
		response.Error(w, http.StatusBadRequest, "name required")
		return
	}
	if len(name) > 60 {
		name = name[:60]
	}

	token, err := GenerateAppPassword()
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "could not generate app password")
		return
	}

	created, err := h.store.CreateAppPassword(r.Context(), user.ID, name, token)
	if errors.Is(err, ErrTooManyAppPasswords) {
		response.Error(w, http.StatusConflict, "app password limit reached")
		return
	}
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "could not create app password")
		return
	}

	h.auditor.Log(r.Context(), audit.Event{
		ActorID:    &user.ID,
		ActorName:  user.Username,
		Action:     audit.ActionAppPasswordCreate,
		TargetType: "app_password",
		TargetID:   created.ID.String(),
		TargetName: created.Name,
		IP:         middleware.RealIP(r),
	})

	// Einziger Moment, in dem das Klartext-Token existiert – danach steht nur
	// noch der Hash in der Datenbank.
	response.JSON(w, http.StatusCreated, struct {
		AppPassword
		Password string `json:"password"`
	}{AppPassword: *created, Password: token})
}

// DELETE /api/v1/app-passwords/{id}
func (h *Handler) DeleteAppPassword(w http.ResponseWriter, r *http.Request) {
	user := UserFromContext(r.Context())

	id, err := uuid.Parse(chi.URLParam(r, "id"))
	if err != nil {
		response.Error(w, http.StatusBadRequest, "invalid id")
		return
	}
	if err := h.store.DeleteAppPassword(r.Context(), user.ID, id); errors.Is(err, ErrNotFound) {
		response.Error(w, http.StatusNotFound, "app password not found")
		return
	} else if err != nil {
		response.Error(w, http.StatusInternalServerError, "could not revoke app password")
		return
	}
	h.auditor.Log(r.Context(), audit.Event{
		ActorID:    &user.ID,
		ActorName:  user.Username,
		Action:     audit.ActionAppPasswordRevoke,
		TargetType: "app_password",
		TargetID:   id.String(),
		IP:         middleware.RealIP(r),
	})
	w.WriteHeader(http.StatusNoContent)
}