package main

import (
	"encoding/base64"
	"encoding/json"
	"net/http"
	"strings"
	"time"
)

// Maximum accepted snapshot size (encrypted). Generous for a personal library.
const maxSyncPayload = 16 << 20 // 16 MiB

type syncGetResponse struct {
	Revision  int64  `json:"revision"`
	UpdatedAt string `json:"updatedAt"`
	Payload   string `json:"payload"` // base64 ciphertext
}

type syncPutRequest struct {
	BaseRevision int64  `json:"baseRevision"`
	Payload      string `json:"payload"` // base64 ciphertext
}

type syncPutResponse struct {
	Revision int64 `json:"revision"`
}

type syncConflictResponse struct {
	Error    string `json:"error"`
	Revision int64  `json:"revision"`
}

// authSubject validates the Bearer token and returns the user's subject/email.
func (s *server) authSubject(r *http.Request) (sub, email string, ok bool) {
	bearer := strings.TrimSpace(strings.TrimPrefix(r.Header.Get("Authorization"), "Bearer"))
	claims, err := verifyToken(s.cfg.SessionKey, bearer)
	if err != nil {
		return "", "", false
	}
	return claims.Subject, claims.Email, true
}

// handleSyncLibrary dispatches GET/PUT for the encrypted library snapshot.
func (s *server) handleSyncLibrary(w http.ResponseWriter, r *http.Request) {
	if s.store == nil {
		http.Error(w, "sync is not configured on this server", http.StatusNotImplemented)
		return
	}
	sub, email, ok := s.authSubject(r)
	if !ok {
		http.Error(w, "unauthorized", http.StatusUnauthorized)
		return
	}

	switch r.Method {
	case http.MethodGet:
		s.handleSyncGet(w, r, sub)
	case http.MethodPut:
		s.handleSyncPut(w, r, sub, email)
	default:
		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
	}
}

func (s *server) handleSyncGet(w http.ResponseWriter, r *http.Request, sub string) {
	blob, err := s.store.getBlob(r.Context(), sub)
	if err != nil {
		http.Error(w, "storage error", http.StatusInternalServerError)
		return
	}
	if blob == nil {
		http.Error(w, "no snapshot yet", http.StatusNotFound)
		return
	}
	writeJSON(w, http.StatusOK, syncGetResponse{
		Revision:  blob.Revision,
		UpdatedAt: blob.UpdatedAt.UTC().Format(time.RFC3339),
		Payload:   base64.StdEncoding.EncodeToString(blob.Payload),
	})
}

func (s *server) handleSyncPut(w http.ResponseWriter, r *http.Request, sub, email string) {
	var req syncPutRequest
	body := http.MaxBytesReader(w, r.Body, maxSyncPayload+(1<<16))
	if err := json.NewDecoder(body).Decode(&req); err != nil {
		http.Error(w, "bad request body", http.StatusBadRequest)
		return
	}
	payload, err := base64.StdEncoding.DecodeString(req.Payload)
	if err != nil {
		http.Error(w, "payload is not valid base64", http.StatusBadRequest)
		return
	}
	if len(payload) == 0 {
		http.Error(w, "empty payload", http.StatusBadRequest)
		return
	}
	if len(payload) > maxSyncPayload {
		http.Error(w, "payload too large", http.StatusRequestEntityTooLarge)
		return
	}

	next, err := s.store.putBlob(r.Context(), sub, email, req.BaseRevision, payload)
	if err == errRevisionConflict {
		writeJSON(w, http.StatusConflict, syncConflictResponse{
			Error:    "revision conflict",
			Revision: next,
		})
		return
	}
	if err != nil {
		http.Error(w, "storage error", http.StatusInternalServerError)
		return
	}
	writeJSON(w, http.StatusOK, syncPutResponse{Revision: next})
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}