// Package dav implements a CalDAV (RFC 4791) + CardDAV (RFC 6352) HTTP
// server covering the core operations real clients need: PROPFIND (Depth 0/1
// discovery), REPORT (calendar-query/multiget, addressbook-query/multiget —
// query filtering returns all objects in the collection in this pass, full
// time-range/property filtering deferred), PUT (create/update), GET
// (fetch), DELETE, OPTIONS. No MKCALENDAR/MKCOL — every user's default
// addressbook and calendar are auto-created on first access instead, which
// covers the common case (one addressbook, one calendar per user) without
// needing collection-creation UI in an early phase.
//
// URL layout:
//
//	/dav/contacts/{ownerType}/{ownerID}/          addressbook collection
//	/dav/contacts/{ownerType}/{ownerID}/{uid}.vcf  a contact
//	/dav/calendars/{ownerType}/{ownerID}/          calendar collection
//	/dav/calendars/{ownerType}/{ownerID}/{uid}.ics a calendar event
package dav

import (
	"encoding/xml"
	"fmt"
	"io"
	"log/slog"
	"net/http"
	"strings"
	"time"

	"gomail/internal/auth"
	"gomail/internal/crypto"
	"gomail/internal/db"
	"gomail/internal/ical"
	"gomail/internal/vcard"
	"github.com/google/uuid"
)

type Handler struct {
	database *db.DB
	mk       *crypto.MasterKey
}

func NewHandler(database *db.DB, mk *crypto.MasterKey) *Handler {
	return &Handler{database: database, mk: mk}
}

func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	user, ok := h.authenticate(r)
	if !ok {
		w.Header().Set("WWW-Authenticate", `Basic realm="GoMail DAV"`)
		http.Error(w, "unauthorized", http.StatusUnauthorized)
		return
	}

	path := strings.TrimPrefix(r.URL.Path, "/dav")
	switch {
	case strings.HasPrefix(path, "/contacts/"):
		h.serveCardDAV(w, r, user, strings.TrimPrefix(path, "/contacts/"))
	case strings.HasPrefix(path, "/calendars/"):
		h.serveCalDAV(w, r, user, strings.TrimPrefix(path, "/calendars/"))
	default:
		http.NotFound(w, r)
	}
}

func (h *Handler) authenticate(r *http.Request) (*db.User, bool) {
	username, password, ok := r.BasicAuth()
	if !ok {
		return nil, false
	}
	return auth.Authenticate(h.database, username, password, auth.ScopeCardDAV)
}

// ── CardDAV ───────────────────────────────────────────────────────────────────

func (h *Handler) serveCardDAV(w http.ResponseWriter, r *http.Request, user *db.User, rest string) {
	ownerType, ownerID, uid, ok := parseCollectionPath(rest, user)
	if !ok {
		http.NotFound(w, r)
		return
	}

	book, err := h.database.GetOrCreateAddressbook(ownerType, ownerID, "Default")
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	switch r.Method {
	case "OPTIONS":
		w.Header().Set("DAV", "1, 2, addressbook")
		w.Header().Set("Allow", "OPTIONS, PROPFIND, REPORT, GET, PUT, DELETE")
		w.WriteHeader(http.StatusOK)

	case "PROPFIND":
		h.propfindContacts(w, r, book, uid)

	case "REPORT":
		h.reportContacts(w, r, book)

	case http.MethodGet:
		if uid == "" {
			http.Error(w, "GET on collection not supported, use PROPFIND", http.StatusMethodNotAllowed)
			return
		}
		contact, err := h.database.GetContact(book.ID, strings.TrimSuffix(uid, ".vcf"))
		if err != nil {
			http.NotFound(w, r)
			return
		}
		plain, err := crypto.Decrypt(h.mk, contact.ID, "contact", contact.VCardEnc)
		if err != nil {
			http.Error(w, "decrypt error", http.StatusInternalServerError)
			return
		}
		w.Header().Set("Content-Type", "text/vcard; charset=utf-8")
		w.Header().Set("ETag", contact.ETag)
		w.Write(plain)

	case http.MethodPut:
		if uid == "" {
			http.Error(w, "PUT requires a resource path", http.StatusBadRequest)
			return
		}
		body, err := io.ReadAll(r.Body)
		if err != nil {
			http.Error(w, "read error", http.StatusBadRequest)
			return
		}
		card, err := vcard.Parse(string(body))
		if err != nil {
			http.Error(w, "invalid vCard: "+err.Error(), http.StatusBadRequest)
			return
		}
		contactID := uuid.NewString()
		if existing, err := h.database.GetContact(book.ID, card.UID); err == nil {
			contactID = existing.ID
		}
		encrypted, err := crypto.Encrypt(h.mk, contactID, "contact", body)
		if err != nil {
			http.Error(w, "encrypt error", http.StatusInternalServerError)
			return
		}
		etag := fmt.Sprintf(`"%d"`, time.Now().UnixNano())
		if err := h.database.UpsertContact(&db.Contact{
			ID: contactID, AddressbookID: book.ID, UID: card.UID, VCardEnc: encrypted, ETag: etag,
		}); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		w.Header().Set("ETag", etag)
		w.WriteHeader(http.StatusCreated)

	case http.MethodDelete:
		if uid == "" {
			http.Error(w, "DELETE requires a resource path", http.StatusBadRequest)
			return
		}
		if err := h.database.DeleteContact(book.ID, strings.TrimSuffix(uid, ".vcf")); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		w.WriteHeader(http.StatusNoContent)

	default:
		w.WriteHeader(http.StatusMethodNotAllowed)
	}
}

func (h *Handler) propfindContacts(w http.ResponseWriter, r *http.Request, book *db.Addressbook, uid string) {
	depth := r.Header.Get("Depth")

	var responses []multistatusResponse
	responses = append(responses, multistatusResponse{
		Href: r.URL.Path,
		Props: propSet{
			DisplayName:  book.DisplayName,
			ResourceType: "<collection xmlns=\"DAV:\"/><addressbook xmlns=\"urn:ietf:params:xml:ns:carddav\"/>",
		},
	})

	if depth == "1" && uid == "" {
		contacts, err := h.database.ListContacts(book.ID)
		if err == nil {
			for _, c := range contacts {
				responses = append(responses, multistatusResponse{
					Href:  strings.TrimSuffix(r.URL.Path, "/") + "/" + c.UID + ".vcf",
					Props: propSet{ETag: c.ETag, ContentType: "text/vcard; charset=utf-8"},
				})
			}
		}
	}

	writeMultistatus(w, responses)
}

func (h *Handler) reportContacts(w http.ResponseWriter, r *http.Request, book *db.Addressbook) {
	// addressbook-query and addressbook-multiget both return every contact's
	// current vCard in this pass — full filter/prop-match parsing is
	// deferred; clients doing a multiget for hrefs they already have (the
	// common sync pattern) get correct data, just not a filtered subset.
	contacts, err := h.database.ListContacts(book.ID)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	var responses []multistatusResponse
	for _, c := range contacts {
		plain, err := crypto.Decrypt(h.mk, c.ID, "contact", c.VCardEnc)
		if err != nil {
			continue
		}
		responses = append(responses, multistatusResponse{
			Href:      strings.TrimSuffix(r.URL.Path, "/") + "/" + c.UID + ".vcf",
			Props:     propSet{ETag: c.ETag},
			AddressData: string(plain),
		})
	}
	writeMultistatus(w, responses)
}

// ── CalDAV ────────────────────────────────────────────────────────────────────

func (h *Handler) serveCalDAV(w http.ResponseWriter, r *http.Request, user *db.User, rest string) {
	ownerType, ownerID, uid, ok := parseCollectionPath(rest, user)
	if !ok {
		http.NotFound(w, r)
		return
	}

	cal, err := h.database.GetOrCreateCalendar(ownerType, ownerID, "Default")
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	switch r.Method {
	case "OPTIONS":
		w.Header().Set("DAV", "1, 2, calendar-access")
		w.Header().Set("Allow", "OPTIONS, PROPFIND, REPORT, GET, PUT, DELETE")
		w.WriteHeader(http.StatusOK)

	case "PROPFIND":
		h.propfindCalendar(w, r, cal, uid)

	case "REPORT":
		h.reportCalendar(w, r, cal)

	case http.MethodGet:
		if uid == "" {
			http.Error(w, "GET on collection not supported, use PROPFIND", http.StatusMethodNotAllowed)
			return
		}
		obj, err := h.database.GetCalendarObject(cal.ID, strings.TrimSuffix(uid, ".ics"))
		if err != nil {
			http.NotFound(w, r)
			return
		}
		plain, err := crypto.Decrypt(h.mk, obj.ID, "calendar", obj.ICalEnc)
		if err != nil {
			http.Error(w, "decrypt error", http.StatusInternalServerError)
			return
		}
		w.Header().Set("Content-Type", "text/calendar; charset=utf-8")
		w.Header().Set("ETag", obj.ETag)
		w.Write(plain)

	case http.MethodPut:
		if uid == "" {
			http.Error(w, "PUT requires a resource path", http.StatusBadRequest)
			return
		}
		body, err := io.ReadAll(r.Body)
		if err != nil {
			http.Error(w, "read error", http.StatusBadRequest)
			return
		}
		event, err := ical.Parse(string(body))
		if err != nil {
			http.Error(w, "invalid iCal: "+err.Error(), http.StatusBadRequest)
			return
		}
		objID := uuid.NewString()
		if existing, err := h.database.GetCalendarObject(cal.ID, event.UID); err == nil {
			objID = existing.ID
		}
		encrypted, err := crypto.Encrypt(h.mk, objID, "calendar", body)
		if err != nil {
			http.Error(w, "encrypt error", http.StatusInternalServerError)
			return
		}
		etag := fmt.Sprintf(`"%d"`, time.Now().UnixNano())
		obj := &db.CalendarObject{
			ID: objID, CalendarID: cal.ID, UID: event.UID, ICalEnc: encrypted,
			ComponentType: "VEVENT", Summary: event.Summary, ETag: etag,
		}
		if !event.DTStart.IsZero() {
			obj.DTStart = &event.DTStart
		}
		if !event.DTEnd.IsZero() {
			obj.DTEnd = &event.DTEnd
		}
		if err := h.database.UpsertCalendarObject(obj); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		w.Header().Set("ETag", etag)
		w.WriteHeader(http.StatusCreated)

	case http.MethodDelete:
		if uid == "" {
			http.Error(w, "DELETE requires a resource path", http.StatusBadRequest)
			return
		}
		if err := h.database.DeleteCalendarObject(cal.ID, strings.TrimSuffix(uid, ".ics")); err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		w.WriteHeader(http.StatusNoContent)

	default:
		w.WriteHeader(http.StatusMethodNotAllowed)
	}
}

func (h *Handler) propfindCalendar(w http.ResponseWriter, r *http.Request, cal *db.Calendar, uid string) {
	depth := r.Header.Get("Depth")

	var responses []multistatusResponse
	responses = append(responses, multistatusResponse{
		Href: r.URL.Path,
		Props: propSet{
			DisplayName:  cal.DisplayName,
			ResourceType: "<collection xmlns=\"DAV:\"/><calendar xmlns=\"urn:ietf:params:xml:ns:caldav\"/>",
		},
	})

	if depth == "1" && uid == "" {
		objs, err := h.database.ListCalendarObjects(cal.ID)
		if err == nil {
			for _, o := range objs {
				responses = append(responses, multistatusResponse{
					Href:  strings.TrimSuffix(r.URL.Path, "/") + "/" + o.UID + ".ics",
					Props: propSet{ETag: o.ETag, ContentType: "text/calendar; charset=utf-8"},
				})
			}
		}
	}

	writeMultistatus(w, responses)
}

func (h *Handler) reportCalendar(w http.ResponseWriter, r *http.Request, cal *db.Calendar) {
	// calendar-query and calendar-multiget both return every event in this
	// pass — time-range filtering (the most common real-world calendar-query
	// use, "give me events this week") is deferred; noted here rather than
	// silently ignored, since clients that rely on server-side time-range
	// filtering will over-fetch until that lands.
	objs, err := h.database.ListCalendarObjects(cal.ID)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	var responses []multistatusResponse
	for _, o := range objs {
		plain, err := crypto.Decrypt(h.mk, o.ID, "calendar", o.ICalEnc)
		if err != nil {
			continue
		}
		responses = append(responses, multistatusResponse{
			Href:         strings.TrimSuffix(r.URL.Path, "/") + "/" + o.UID + ".ics",
			Props:        propSet{ETag: o.ETag},
			CalendarData: string(plain),
		})
	}
	writeMultistatus(w, responses)
}

// ── Path parsing ──────────────────────────────────────────────────────────────

// parseCollectionPath extracts (ownerType, ownerID, resourceUID) from a
// request path like "user/{userID}/{uid}.vcf" or "tenant/{tenantID}/". Only
// allows a user to address their own personal collection or their own
// tenant's shared one — cross-user access is rejected.
func parseCollectionPath(rest string, requestingUser *db.User) (db.OwnerType, string, string, bool) {
	parts := strings.SplitN(strings.TrimPrefix(rest, "/"), "/", 3)
	if len(parts) < 2 {
		return "", "", "", false
	}
	ownerType := db.OwnerType(parts[0])
	ownerID := parts[1]
	uid := ""
	if len(parts) == 3 {
		uid = parts[2]
	}

	switch ownerType {
	case db.OwnerUser:
		if ownerID != requestingUser.ID {
			return "", "", "", false // no cross-user access
		}
	case db.OwnerTenant:
		if ownerID != requestingUser.TenantID {
			return "", "", "", false // no cross-tenant access
		}
	default:
		return "", "", "", false
	}
	return ownerType, ownerID, uid, true
}

// ── Multistatus XML ───────────────────────────────────────────────────────────

type propSet struct {
	DisplayName  string
	ResourceType string // raw XML fragment, since it varies by collection type
	ETag         string
	ContentType  string
}

type multistatusResponse struct {
	Href         string
	Props        propSet
	AddressData  string // set only for CardDAV REPORT responses
	CalendarData string // set only for CalDAV REPORT responses
}

func writeMultistatus(w http.ResponseWriter, responses []multistatusResponse) {
	var b strings.Builder
	b.WriteString(xml.Header)
	b.WriteString(`<D:multistatus xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:carddav" xmlns:CAL="urn:ietf:params:xml:ns:caldav">` + "\n")

	for _, r := range responses {
		b.WriteString("  <D:response>\n")
		b.WriteString("    <D:href>" + xmlEscape(r.Href) + "</D:href>\n")
		b.WriteString("    <D:propstat>\n      <D:prop>\n")
		if r.Props.DisplayName != "" {
			b.WriteString("        <D:displayname>" + xmlEscape(r.Props.DisplayName) + "</D:displayname>\n")
		}
		if r.Props.ResourceType != "" {
			b.WriteString("        <D:resourcetype>" + r.Props.ResourceType + "</D:resourcetype>\n")
		}
		if r.Props.ETag != "" {
			b.WriteString("        <D:getetag>" + xmlEscape(r.Props.ETag) + "</D:getetag>\n")
		}
		if r.Props.ContentType != "" {
			b.WriteString("        <D:getcontenttype>" + xmlEscape(r.Props.ContentType) + "</D:getcontenttype>\n")
		}
		if r.AddressData != "" {
			b.WriteString("        <C:address-data>" + xmlEscape(r.AddressData) + "</C:address-data>\n")
		}
		if r.CalendarData != "" {
			b.WriteString("        <CAL:calendar-data>" + xmlEscape(r.CalendarData) + "</CAL:calendar-data>\n")
		}
		b.WriteString("      </D:prop>\n      <D:status>HTTP/1.1 200 OK</D:status>\n    </D:propstat>\n")
		b.WriteString("  </D:response>\n")
	}
	b.WriteString("</D:multistatus>\n")

	w.Header().Set("Content-Type", "application/xml; charset=utf-8")
	w.WriteHeader(207) // Multi-Status
	if _, err := w.Write([]byte(b.String())); err != nil {
		slog.Debug("dav: write error", "err", err)
	}
}

func xmlEscape(s string) string {
	var b strings.Builder
	xml.EscapeText(&b, []byte(s))
	return b.String()
}