package calendar

import (
	"bytes"
	"encoding/json"
	"fmt"
	"net/http"
	"strings"

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

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

// APIHandler bedient die angemeldete Web-Oberfläche unter /api/v1/calendars
// (Session-Auth, wie jeder andere Bereich). Getrennt vom CalDAV-Handler
// (Handler in handler.go), der eigene Basic-Auth mit App-Passwörtern nutzt –
// unterschiedliche Auth-Modelle, unterschiedliche Handler, wie /dav vs. der
// Rest der API.
type APIHandler struct {
	store *Store
}

func NewAPIHandler(store *Store) *APIHandler {
	return &APIHandler{store: store}
}

// GET /api/v1/calendars
func (h *APIHandler) List(w http.ResponseWriter, r *http.Request) {
	user := auth.UserFromContext(r.Context())
	// Wie im CalDAV-Weg: Wer noch keinen Kalender hat, bekommt einen. Sonst
	// steht ein neues Konto vor einer leeren Ansicht und muss erst erraten,
	// dass es selbst einen anlegen soll – und ein CalDAV-Client, der sich
	// vorher verbunden hat, sähe bereits einen, den die Weboberfläche nicht
	// zeigt.
	if _, err := h.store.EnsureDefaultCalendar(r.Context(), user.ID); err != nil {
		response.Error(w, http.StatusInternalServerError, "list calendars failed")
		return
	}
	cals, err := h.store.ListCalendars(r.Context(), user.ID)
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "list calendars failed")
		return
	}
	response.JSON(w, http.StatusOK, cals)
}

// POST /api/v1/calendars
func (h *APIHandler) Create(w http.ResponseWriter, r *http.Request) {
	user := auth.UserFromContext(r.Context())
	var body struct {
		Name        string `json:"name"`
		Color       string `json:"color"`
		Description string `json:"description"`
	}
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil || strings.TrimSpace(body.Name) == "" {
		response.Error(w, http.StatusBadRequest, "name is required")
		return
	}
	cal, err := h.store.CreateCalendar(r.Context(), user.ID, body.Name, body.Color, body.Description)
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "create calendar failed")
		return
	}
	response.JSON(w, http.StatusCreated, cal)
}

// PATCH /api/v1/calendars/{id}
func (h *APIHandler) Update(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.StatusNotFound, "calendar not found")
		return
	}
	var body struct {
		Name        *string `json:"name"`
		Color       *string `json:"color"`
		Description *string `json:"description"`
		TimeZone    *string `json:"timezone"`
	}
	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
		response.Error(w, http.StatusBadRequest, "invalid body")
		return
	}
	cal, err := h.store.UpdateCalendar(r.Context(), user.ID, id, body.Name, body.Color, body.Description, body.TimeZone)
	if err == ErrNotFound {
		response.Error(w, http.StatusNotFound, "calendar not found")
		return
	}
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "update calendar failed")
		return
	}
	response.JSON(w, http.StatusOK, cal)
}

// DELETE /api/v1/calendars/{id}
func (h *APIHandler) 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.StatusNotFound, "calendar not found")
		return
	}
	if err := h.store.DeleteCalendar(r.Context(), user.ID, id); err == ErrNotFound {
		response.Error(w, http.StatusNotFound, "calendar not found")
		return
	} else if err != nil {
		response.Error(w, http.StatusInternalServerError, "delete calendar failed")
		return
	}
	response.NoContent(w)
}

// GET /api/v1/calendars/{id}/export – ein .ics mit allen Terminen/Aufgaben
// des Kalenders zusammen, zum Sichern oder Umziehen in einen anderen Dienst.
func (h *APIHandler) Export(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.StatusNotFound, "calendar not found")
		return
	}
	cal, err := h.store.GetCalendar(r.Context(), user.ID, id)
	if err == ErrNotFound {
		response.Error(w, http.StatusNotFound, "calendar not found")
		return
	}
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "load calendar failed")
		return
	}
	objs, err := h.store.ListObjects(r.Context(), cal.ID)
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "list objects failed")
		return
	}

	out := ical.NewCalendar()
	out.Props.SetText(ical.PropVersion, "2.0")
	out.Props.SetText(ical.PropProductID, "-//Aether//Kalender//DE")

	// VTIMEZONE-Blöcke nur einmal je TZID mitnehmen – jedes einzeln
	// gespeicherte Objekt trägt seine eigenen mit, sonst stünde dieselbe
	// Definition mehrfach in der Ausgabedatei.
	seenTZ := map[string]bool{}
	for _, o := range objs {
		dec := ical.NewDecoder(strings.NewReader(o.Data))
		c, err := dec.Decode()
		if err != nil {
			continue // eine kaputte Einzeldatei darf den Export nicht abbrechen
		}
		for _, child := range c.Children {
			if child.Name == ical.CompTimezone {
				tzid, _ := child.Props.Text(ical.PropTimezoneID)
				if seenTZ[tzid] {
					continue
				}
				seenTZ[tzid] = true
			}
			out.Children = append(out.Children, child)
		}
	}

	var buf bytes.Buffer
	if err := ical.NewEncoder(&buf).Encode(out); err != nil {
		response.Error(w, http.StatusInternalServerError, "encode calendar failed")
		return
	}
	w.Header().Set("Content-Type", "text/calendar; charset=utf-8")
	w.Header().Set("Content-Disposition", fmt.Sprintf(`attachment; filename="%s.ics"`, sanitizeFilename(cal.Name)))
	w.WriteHeader(http.StatusOK)
	w.Write(buf.Bytes())
}

// POST /api/v1/calendars/{id}/import – eine hochgeladene .ics-Datei
// einlesen. Jede darin enthaltene VEVENT/VTODO-Komponente wird ein eigenes
// Objekt, wie beim einzelnen PUT über CalDAV – nur eben viele auf einmal.
func (h *APIHandler) Import(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.StatusNotFound, "calendar not found")
		return
	}
	cal, err := h.store.GetCalendar(r.Context(), user.ID, id)
	if err == ErrNotFound {
		response.Error(w, http.StatusNotFound, "calendar not found")
		return
	}
	if err != nil {
		response.Error(w, http.StatusInternalServerError, "load calendar failed")
		return
	}

	r.Body = http.MaxBytesReader(w, r.Body, 20<<20) // 20 MiB – reicht für sehr große Kalender
	src, err := ical.NewDecoder(r.Body).Decode()
	if err != nil {
		response.Error(w, http.StatusBadRequest, "invalid .ics file")
		return
	}

	var tzBlocks []*ical.Component
	for _, child := range src.Children {
		if child.Name == ical.CompTimezone {
			tzBlocks = append(tzBlocks, child)
		}
	}

	imported := 0
	for _, child := range src.Children {
		if child.Name != "VEVENT" && child.Name != "VTODO" {
			continue
		}
		uid, err := child.Props.Text("UID")
		if err != nil || uid == "" {
			continue // ohne UID kein gültiges CalDAV-Objekt – überspringen statt den ganzen Import abzubrechen
		}

		single := ical.NewCalendar()
		single.Props.SetText(ical.PropVersion, "2.0")
		single.Props.SetText(ical.PropProductID, "-//Aether//Kalender//DE")
		single.Children = append(single.Children, tzBlocks...)
		single.Children = append(single.Children, child)

		var buf bytes.Buffer
		if err := ical.NewEncoder(&buf).Encode(single); err != nil {
			continue
		}
		data := buf.String()
		start, end := timeRange(single)
		if _, err := h.store.PutObject(r.Context(), cal.ID, uid, child.Name, data, etagFor(data), start, end); err != nil {
			continue
		}
		imported++
	}

	response.JSON(w, http.StatusOK, map[string]int{"imported": imported})
}

func sanitizeFilename(name string) string {
	name = strings.Map(func(r rune) rune {
		switch r {
		case '/', '\\', ':', '"':
			return '_'
		}
		return r
	}, name)
	if name == "" {
		return "kalender"
	}
	return name
}