package sharing

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"strconv"
	"time"

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

	"aether/internal/audit"
	"aether/internal/auth"
	"aether/internal/files"
	"aether/internal/storage"
	"aether/pkg/bg"
	"aether/pkg/middleware"
	"aether/pkg/response"
)

// Ein öffentlicher Endpunkt mit Passwort braucht dieselbe Bremse wie /dav
// und /caldav: Ohne sie kann man Passwörter unbegrenzt durchprobieren – und
// weil jeder Versuch Argon2 rechnet, ist das zugleich ein billiger Weg, den
// Server zu beschäftigen.
const (
	shareMaxFailures = 10
	shareWindow      = 15 * time.Minute
	shareLockout     = 15 * time.Minute
)

type Handler struct {
	store     *Store
	fileStore *files.Store
	storage   storage.Storage
	auditor   *audit.Logger
	limiter   *middleware.FailureLimiter
}

func NewHandler(store *Store, fileStore *files.Store, st storage.Storage, auditor *audit.Logger) *Handler {
	return &Handler{
		store: store, fileStore: fileStore, storage: st, auditor: auditor,
		limiter: middleware.NewFailureLimiter(shareMaxFailures, shareWindow, shareLockout),
	}
}

// POST /api/v1/files/{id}/share
func (h *Handler) Create(w http.ResponseWriter, r *http.Request) {
	user := auth.UserFromContext(r.Context())
	fileID, err := uuid.Parse(chi.URLParam(r, "id"))
	if err != nil {
		response.Error(w, http.StatusBadRequest, "invalid file id")
		return
	}
	if _, err := h.fileStore.GetFile(r.Context(), fileID, user.ID); err != nil {
		response.Error(w, http.StatusNotFound, "file not found")
		return
	}

	var body struct {
		Password  string `json:"password"`
		ExpiresIn *int   `json:"expires_in_hours"`
	}
	_ = json.NewDecoder(r.Body).Decode(&body)

	var passwordHash string
	if body.Password != "" {
		passwordHash, err = auth.HashPassword(body.Password)
		if err != nil {
			response.Error(w, http.StatusInternalServerError, "hash error")
			return
		}
	}

	var expiresAt *time.Time
	if body.ExpiresIn != nil && *body.ExpiresIn > 0 {
		t := time.Now().Add(time.Duration(*body.ExpiresIn) * time.Hour)
		expiresAt = &t
	}

	link, err := h.store.Create(r.Context(), fileID, user.ID, passwordHash, expiresAt)
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "create share link failed")
		return
	}
	// Ein Freigabelink macht eine Datei öffentlich erreichbar – gehört ins
	// Protokoll. Der Token selbst nicht: er IST der Zugang.
	detail := "no password"
	if passwordHash != "" {
		detail = "password protected"
	}
	if expiresAt != nil {
		detail += ", expires " + expiresAt.Format(time.RFC3339)
	}
	h.auditor.Log(r.Context(), audit.Event{
		ActorID:    &user.ID,
		ActorName:  user.Username,
		Action:     audit.ActionShareCreate,
		TargetType: "file",
		TargetID:   fileID.String(),
		IP:         middleware.RealIP(r),
		Detail:     detail,
	})
	response.JSON(w, http.StatusCreated, link)
}

// GET /api/v1/shares – list all share links owned by user
func (h *Handler) List(w http.ResponseWriter, r *http.Request) {
	user := auth.UserFromContext(r.Context())
	links, err := h.store.ListByOwner(r.Context(), user.ID)
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "database error")
		return
	}
	if links == nil {
		links = []*ShareLink{}
	}
	response.JSON(w, http.StatusOK, links)
}

// DELETE /api/v1/shares/{id}
func (h *Handler) Delete(w http.ResponseWriter, r *http.Request) {
	user := auth.UserFromContext(r.Context())
	id, err := uuid.Parse(chi.URLParam(r, "id"))
	if err != nil {
		response.Error(w, http.StatusBadRequest, "invalid share id")
		return
	}
	if err := h.store.Delete(r.Context(), id, user.ID); errors.Is(err, ErrNotFound) {
		response.Error(w, http.StatusNotFound, "share link not found")
		return
	} else if err != nil {
		response.Error(w, http.StatusInternalServerError, "database error")
		return
	}
	h.auditor.Log(r.Context(), audit.Event{
		ActorID:    &user.ID,
		ActorName:  user.Username,
		Action:     audit.ActionShareDelete,
		TargetType: "share",
		TargetID:   id.String(),
		IP:         middleware.RealIP(r),
	})
	response.NoContent(w)
}

// GET /s/{token} – public share info (no auth required)
func (h *Handler) GetPublicInfo(w http.ResponseWriter, r *http.Request) {
	token := chi.URLParam(r, "token")
	link, _, err := h.store.GetByToken(r.Context(), token)
	if errors.Is(err, ErrNotFound) || errors.Is(err, ErrExpired) {
		response.Error(w, http.StatusNotFound, "share link not found or expired")
		return
	}
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "error")
		return
	}
	f, err := h.fileStore.GetFileByID(r.Context(), link.FileID)
	if err != nil {
		response.Error(w, http.StatusNotFound, "file not found")
		return
	}
	// Nur, was die öffentliche Seite wirklich braucht. Das ganze
	// Datenbankobjekt durchzureichen war bequem, gab aber owner_id und die
	// internen Kennungen an jeden heraus, der den Link hat: Zwei Links
	// desselben Besitzers ließen sich so einander zuordnen, ohne dass
	// irgendwer angemeldet ist.
	response.JSON(w, http.StatusOK, map[string]any{
		"has_password":   link.HasPassword,
		"expires_at":     link.ExpiresAt,
		"download_count": link.DownloadCount,
		"created_at":     link.CreatedAt,
		"file_name":      f.Name,
		"file_size":      f.Size,
		"mime_type":      f.MimeType,
	})
}

// POST /s/{token}/download – public download, optional password in body
func (h *Handler) Download(w http.ResponseWriter, r *http.Request) {
	token := chi.URLParam(r, "token")
	link, passwordHash, err := h.store.GetByToken(r.Context(), token)
	if errors.Is(err, ErrNotFound) || errors.Is(err, ErrExpired) {
		response.Error(w, http.StatusNotFound, "share link not found or expired")
		return
	}
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "error")
		return
	}

	if link.HasPassword {
		clientIP := middleware.RealIP(r)
		if erlaubt, retryAfter := h.limiter.Allowed(clientIP); !erlaubt {
			w.Header().Set("Retry-After", strconv.Itoa(int(retryAfter.Seconds())+1))
			response.Error(w, http.StatusTooManyRequests, "too many failed attempts")
			return
		}
		var body struct {
			Password string `json:"password"`
		}
		_ = json.NewDecoder(r.Body).Decode(&body)
		ok, _ := auth.VerifyPassword(body.Password, passwordHash)
		if !ok {
			h.limiter.Fail(clientIP)
			response.Error(w, http.StatusUnauthorized, "incorrect password")
			return
		}
		h.limiter.Reset(clientIP)
	}

	f, err := h.fileStore.GetFileByID(r.Context(), link.FileID)
	if err != nil {
		response.Error(w, http.StatusNotFound, "file not found")
		return
	}

	rc, err := h.storage.Get(r.Context(), f.StorageKey)
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "storage error")
		return
	}
	defer rc.Close()

	// context.WithoutCancel, nicht r.Context(): Der Request-Kontext wird
	// abgebrochen, sobald die Antwort draußen ist – die Zählung verlor das
	// Rennen fast immer und der Zähler blieb auf 0 stehen.
	zaehlCtx, abbrechen := context.WithTimeout(context.WithoutCancel(r.Context()), 5*time.Second)
	bg.Go("Freigabe-Zaehler", func() {
		defer abbrechen()
		h.store.IncrementDownloads(zaehlCtx, token)
	})

	w.Header().Set("Content-Type", f.MimeType)
	w.Header().Set("Content-Disposition", fmt.Sprintf(`attachment; filename=%q`, f.Name))
	w.Header().Set("Content-Length", fmt.Sprintf("%d", f.Size))
	_, _ = io.Copy(w, rc)
}