package acl

import (
	"encoding/json"
	"errors"
	"net/http"

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

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

// Handler bedient den Freigabedialog. Die Zugriffsprüfung selbst passiert im
// files-Paket; hier geht es nur ums Erteilen, Ansehen und Widerrufen.
//
// Freigeben darf ausschließlich der Eigentümer. Wer selbst nur eine
// Schreibfreigabe hat, kann sie nicht weiterreichen – sonst verlöre der
// Eigentümer die Kontrolle darüber, wer seine Daten sieht.
type Handler struct {
	store   *Store
	auditor *audit.Logger
}

func NewHandler(store *Store, auditor *audit.Logger) *Handler {
	return &Handler{store: store, auditor: auditor}
}

// logShare hält fest, wer wem Zugriff auf was gegeben oder genommen hat. Bei
// Freigaben ist das die interessanteste Spur überhaupt: Sie erklärt, wie jemand
// an Daten kam, die ihm nicht gehören.
func (h *Handler) logShare(r *http.Request, action, resourceType, resourceID, detail string) {
	user := auth.UserFromContext(r.Context())
	e := audit.Event{
		Action:     action,
		TargetType: resourceType,
		TargetID:   resourceID,
		Detail:     detail,
		IP:         middleware.RealIP(r),
	}
	if user != nil {
		e.ActorID = &user.ID
		e.ActorName = user.Username
	}
	h.auditor.Log(r.Context(), e)
}

// ownedFolder / ownedFile liefern die Ressourcen-ID und den Anfragenden –
// aber nur, wenn ihm die Ressource auch gehört. Alles andere ist bereits
// beantwortet.
func (h *Handler) ownedFolder(w http.ResponseWriter, r *http.Request) (uuid.UUID, uuid.UUID, bool) {
	user := auth.UserFromContext(r.Context())
	id, err := uuid.Parse(chi.URLParam(r, "id"))
	if err != nil {
		response.Error(w, http.StatusBadRequest, "invalid folder id")
		return uuid.Nil, uuid.Nil, false
	}
	a, err := h.store.ResolveFolder(r.Context(), user.ID, id)
	if err != nil {
		response.Error(w, http.StatusNotFound, "folder not found")
		return uuid.Nil, uuid.Nil, false
	}
	if a.OwnerID != user.ID {
		response.Error(w, http.StatusForbidden, "only the owner can manage sharing")
		return uuid.Nil, uuid.Nil, false
	}
	return id, user.ID, true
}

func (h *Handler) ownedFile(w http.ResponseWriter, r *http.Request) (uuid.UUID, uuid.UUID, bool) {
	user := auth.UserFromContext(r.Context())
	id, err := uuid.Parse(chi.URLParam(r, "id"))
	if err != nil {
		response.Error(w, http.StatusBadRequest, "invalid file id")
		return uuid.Nil, uuid.Nil, false
	}
	a, err := h.store.ResolveFile(r.Context(), user.ID, id)
	if err != nil {
		response.Error(w, http.StatusNotFound, "file not found")
		return uuid.Nil, uuid.Nil, false
	}
	if a.OwnerID != user.ID {
		response.Error(w, http.StatusForbidden, "only the owner can manage sharing")
		return uuid.Nil, uuid.Nil, false
	}
	return id, user.ID, true
}

func userFrom(r *http.Request) uuid.UUID {
	if u := auth.UserFromContext(r.Context()); u != nil {
		return u.ID
	}
	return uuid.Nil
}

type grantRequest struct {
	SubjectID   string     `json:"subject_id"`
	SubjectType string     `json:"subject_type"` // "user" | "group"
	Permission  Permission `json:"permission"`
}

// GET /api/v1/folders/{id}/acl
func (h *Handler) ListFolderACL(w http.ResponseWriter, r *http.Request) {
	id, _, ok := h.ownedFolder(w, r)
	if !ok {
		return
	}
	entries, err := h.store.ListForFolder(r.Context(), id)
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "could not load shares")
		return
	}
	response.JSON(w, http.StatusOK, entries)
}

// POST /api/v1/folders/{id}/acl
func (h *Handler) GrantFolderACL(w http.ResponseWriter, r *http.Request) {
	id, owner, ok := h.ownedFolder(w, r)
	if !ok {
		return
	}
	req, ok := decodeGrant(w, r)
	if !ok {
		return
	}
	entry, err := h.store.GrantFolder(r.Context(), id, req.subjectID, req.isGroup, req.perm, owner)
	if err == nil {
		h.logShare(r, audit.ActionShareGrant, "folder", id.String(),
			string(req.perm)+" for "+req.subjectType()+" "+req.subjectID.String())
	}
	writeGrantResult(w, entry, err)
}

// GET /api/v1/files/{id}/acl
func (h *Handler) ListFileACL(w http.ResponseWriter, r *http.Request) {
	id, _, ok := h.ownedFile(w, r)
	if !ok {
		return
	}
	entries, err := h.store.ListForFile(r.Context(), id)
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "could not load shares")
		return
	}
	response.JSON(w, http.StatusOK, entries)
}

// POST /api/v1/files/{id}/acl
func (h *Handler) GrantFileACL(w http.ResponseWriter, r *http.Request) {
	id, owner, ok := h.ownedFile(w, r)
	if !ok {
		return
	}
	req, ok := decodeGrant(w, r)
	if !ok {
		return
	}
	entry, err := h.store.GrantFile(r.Context(), id, req.subjectID, req.isGroup, req.perm, owner)
	if err == nil {
		h.logShare(r, audit.ActionShareGrant, "file", id.String(),
			string(req.perm)+" for "+req.subjectType()+" "+req.subjectID.String())
	}
	writeGrantResult(w, entry, err)
}

// DELETE /api/v1/acl/{id}
func (h *Handler) RevokeACL(w http.ResponseWriter, r *http.Request) {
	user := userFrom(r)
	if user == uuid.Nil {
		response.Error(w, http.StatusUnauthorized, "unauthorized")
		return
	}
	entryID, err := uuid.Parse(chi.URLParam(r, "id"))
	if err != nil {
		response.Error(w, http.StatusBadRequest, "invalid id")
		return
	}
	if err := h.store.Revoke(r.Context(), entryID, user); errors.Is(err, ErrNotFound) {
		response.Error(w, http.StatusNotFound, "share not found")
		return
	} else if err != nil {
		response.Error(w, http.StatusInternalServerError, "could not revoke share")
		return
	}
	h.logShare(r, audit.ActionShareRevoke, "acl", entryID.String(), "")
	w.WriteHeader(http.StatusNoContent)
}

// GET /api/v1/shared-with-me
func (h *Handler) SharedWithMe(w http.ResponseWriter, r *http.Request) {
	user := userFrom(r)
	if user == uuid.Nil {
		response.Error(w, http.StatusUnauthorized, "unauthorized")
		return
	}
	items, err := h.store.ListSharedWith(r.Context(), user)
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "could not load shared items")
		return
	}
	response.JSON(w, http.StatusOK, items)
}

// GET /api/v1/share-recipients
func (h *Handler) Recipients(w http.ResponseWriter, r *http.Request) {
	user := userFrom(r)
	if user == uuid.Nil {
		response.Error(w, http.StatusUnauthorized, "unauthorized")
		return
	}
	list, err := h.store.Recipients(r.Context(), user)
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "could not load recipients")
		return
	}
	response.JSON(w, http.StatusOK, list)
}

// ── Hilfen ───────────────────────────────────────────────────────────────────

type parsedGrant struct {
	subjectID uuid.UUID
	isGroup   bool
	perm      Permission
}

func (g parsedGrant) subjectType() string { return subjectTypeName(g.isGroup) }

func decodeGrant(w http.ResponseWriter, r *http.Request) (parsedGrant, bool) {
	var body grantRequest
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
		response.Error(w, http.StatusBadRequest, "invalid request body")
		return parsedGrant{}, false
	}
	id, err := uuid.Parse(body.SubjectID)
	if err != nil {
		response.Error(w, http.StatusBadRequest, "invalid subject_id")
		return parsedGrant{}, false
	}
	if body.SubjectType != "user" && body.SubjectType != "group" {
		response.Error(w, http.StatusBadRequest, `subject_type must be "user" or "group"`)
		return parsedGrant{}, false
	}
	if !body.Permission.valid() {
		response.Error(w, http.StatusBadRequest, `permission must be "read" or "write"`)
		return parsedGrant{}, false
	}
	return parsedGrant{subjectID: id, isGroup: body.SubjectType == "group", perm: body.Permission}, true
}

func writeGrantResult(w http.ResponseWriter, entry *Entry, err error) {
	switch {
	case errors.Is(err, ErrSelfShare):
		response.Error(w, http.StatusBadRequest, "you already have access to this")
	case err != nil:
		response.Error(w, http.StatusInternalServerError, "could not share")
	default:
		response.JSON(w, http.StatusCreated, entry)
	}
}