package api

import (
	"encoding/json"
	"net/http"
	"strconv"
	"time"

	"github.com/go-chi/chi/v5"
	"github.com/sandrodach/mindsift/internal/auth"
	"github.com/sandrodach/mindsift/internal/collab"
	"github.com/sandrodach/mindsift/internal/storage"
)

const (
	syncMaxOps     = 500
	syncMaxLog     = 1000
	syncMaxBody    = 8 << 20
	longPollMax    = 25 * time.Second
	maxClientIDLen = 64
)

type syncLeases struct {
	Granted []string           `json:"granted"`
	Denied  []string           `json:"denied"`
	Others  []collab.LeaseInfo `json:"others"`
}

type syncResponse struct {
	Results  []collab.Result       `json:"results"`
	Ops      []storage.DocLogEntry `json:"ops"`
	HeadSeq  int64                 `json:"headSeq"`
	HasMore  bool                  `json:"hasMore"`
	Resync   bool                  `json:"resync,omitempty"` // client state is ahead of the server: reload the snapshot
	Role     string                `json:"role"`
	Shared   bool                  `json:"shared"`
	Sessions int                   `json:"sessions"`
	Presence []collab.Presence     `json:"presence"`
	Leases   syncLeases            `json:"leases"`
}

// docAccess resolves the caller's role; it writes 404 and returns "" without access.
func (s *Server) docAccess(w http.ResponseWriter, r *http.Request) (userID, docID, role string) {
	userID = auth.GetUserID(r.Context())
	docID = chi.URLParam(r, "id")
	role = s.store.DocRole(userID, docID)
	if role == "" {
		writeError(w, http.StatusNotFound, storage.ErrDocNotFound.Error())
	}
	return userID, docID, role
}

func (s *Server) handleDocSnapshot(w http.ResponseWriter, r *http.Request) {
	_, docID, role := s.docAccess(w, r)
	if role == "" {
		return
	}
	snap, err := s.store.GetDocSnapshot(docID)
	if err != nil {
		writeError(w, http.StatusNotFound, err.Error())
		return
	}
	writeJSON(w, http.StatusOK, map[string]interface{}{
		"docId":        snap.DocID,
		"title":        snap.Title,
		"titleVersion": snap.TitleVersion,
		"headSeq":      snap.HeadSeq,
		"blocks":       snap.Blocks,
		"role":         role,
		"shared":       s.store.IsDocShared(docID),
	})
}

// handleDocSync is the single round trip of the sync protocol: send own operations, hold or release
// block leases, and receive every log entry after lastSeq.
func (s *Server) handleDocSync(w http.ResponseWriter, r *http.Request) {
	userID, docID, role := s.docAccess(w, r)
	if role == "" {
		return
	}
	var req struct {
		ClientID string      `json:"clientId"`
		LastSeq  int64       `json:"lastSeq"`
		Ops      []collab.Op `json:"ops"`
		Leases   *struct {
			Hold    []string `json:"hold"`
			Release []string `json:"release"`
		} `json:"leases"`
	}
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, syncMaxBody)).Decode(&req); err != nil {
		writeError(w, http.StatusBadRequest, "Ungültiges JSON")
		return
	}
	if req.ClientID == "" || len(req.ClientID) > maxClientIDLen {
		writeError(w, http.StatusBadRequest, "clientId fehlt oder ist zu lang")
		return
	}
	if len(req.Ops) > syncMaxOps {
		writeError(w, http.StatusRequestEntityTooLarge, "Zu viele Änderungen in einer Anfrage")
		return
	}
	canEdit := storage.CanEditDoc(role)
	if len(req.Ops) > 0 && !canEdit {
		writeError(w, http.StatusForbidden, "Keine Schreibrechte für diese Notiz (nur Lesen)")
		return
	}

	actor := collab.Actor{UserID: userID, ClientID: req.ClientID}
	if u, err := s.store.GetUserByID(userID); err == nil {
		actor.Name = u.DisplayName
	}
	s.leases.Touch(docID, actor)

	resp := syncResponse{Results: []collab.Result{}, Role: role, Leases: syncLeases{Granted: []string{}, Denied: []string{}}}
	changed := false
	if req.Leases != nil && canEdit {
		s.leases.ReleaseAllExcept(docID, req.ClientID, req.Leases.Hold)
		s.leases.Release(docID, req.ClientID, req.Leases.Release)
		resp.Leases.Granted, resp.Leases.Denied = s.leases.Hold(docID, actor, req.Leases.Hold)
		changed = true
	}

	if len(req.Ops) > 0 {
		results, _, err := s.store.ApplyDocOps(docID, actor, req.Ops, s.leases.View(docID))
		if err != nil {
			writeError(w, http.StatusInternalServerError, err.Error())
			return
		}
		resp.Results = results
		// New blocks (and conflict copies) belong to their author right away
		var own []string
		for i, res := range results {
			if res.Status == collab.StatusApplied && req.Ops[i].Kind == collab.OpInsert {
				own = append(own, req.Ops[i].BlockID)
			}
			if res.ConflictBlockID != "" {
				own = append(own, res.ConflictBlockID)
			}
			if res.Seq > 0 {
				changed = true
			}
		}
		if len(own) > 0 {
			granted, _ := s.leases.Hold(docID, actor, own)
			resp.Leases.Granted = append(resp.Leases.Granted, granted...)
		}
	}

	entries, head, err := s.store.GetDocOpsSince(docID, req.LastSeq, syncMaxLog)
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}
	if req.LastSeq > head {
		resp.Resync = true
		entries = []storage.DocLogEntry{}
	}
	resp.Ops = entries
	resp.HeadSeq = head
	resp.HasMore = len(entries) == syncMaxLog && entries[len(entries)-1].Seq < head
	resp.Shared = s.store.IsDocShared(docID)
	resp.Sessions, resp.Presence = s.leases.Sessions(docID)
	resp.Leases.Others = s.leases.Others(docID, req.ClientID)

	if changed {
		s.notifyDocChanged(docID, head)
	}
	writeJSON(w, http.StatusOK, resp)
}

// notifyDocChanged wakes long-poll requests and pokes WebSocket/SSE clients in the note's room.
func (s *Server) notifyDocChanged(docID string, head int64) {
	s.notifier.Notify(docID)
	s.wsHub.BroadcastDocEvent(docID, "DOC_SEQ", map[string]interface{}{"docId": docID, "headSeq": head})
}

// handleDocChanges is the long-poll fallback: it returns as soon as the note changes (or leases/presence
// change), at the latest after `wait` seconds. Clients then call /sync to fetch the data.
func (s *Server) handleDocChanges(w http.ResponseWriter, r *http.Request) {
	_, docID, role := s.docAccess(w, r)
	if role == "" {
		return
	}
	since, _ := strconv.ParseInt(r.URL.Query().Get("since"), 10, 64)
	wait := longPollMax
	if sec, err := strconv.Atoi(r.URL.Query().Get("wait")); err == nil && sec >= 0 && time.Duration(sec)*time.Second < wait {
		wait = time.Duration(sec) * time.Second
	}
	_ = http.NewResponseController(w).SetWriteDeadline(time.Now().Add(wait + 10*time.Second))

	woken := s.notifier.Changed(docID) // subscribe before reading, so no change can slip through
	_, head, err := s.store.GetDocOpsSince(docID, since, 0)
	if err != nil {
		writeError(w, http.StatusInternalServerError, err.Error())
		return
	}
	changed := head > since
	if !changed {
		select {
		case <-woken:
			changed = true
		case <-time.After(wait):
		case <-r.Context().Done():
			return
		}
		_, head, _ = s.store.GetDocOpsSince(docID, since, 0)
	}
	writeJSON(w, http.StatusOK, map[string]interface{}{"headSeq": head, "changed": changed})
}

// handleDocLeave ends a client's session on a note and frees its leases (tab closed, app in background).
func (s *Server) handleDocLeave(w http.ResponseWriter, r *http.Request) {
	_, docID, role := s.docAccess(w, r)
	if role == "" {
		return
	}
	var req struct {
		ClientID string `json:"clientId"`
	}
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 4096)).Decode(&req); err != nil || req.ClientID == "" {
		writeError(w, http.StatusBadRequest, "clientId fehlt")
		return
	}
	s.leases.Leave(docID, req.ClientID)
	_, head, _ := s.store.GetDocOpsSince(docID, 0, 0)
	s.notifyDocChanged(docID, head)
	writeJSON(w, http.StatusOK, map[string]bool{"success": true})
}