2 files changed, 217 insertions, 0 deletions
diff --git a/lib/calendar/calendar.go b/lib/calendar/calendar.go
new file mode 100644
index 00000000..d53aec5b
--- /dev/null
+++ b/lib/calendar/calendar.go
@@ -0,0 +1,201 @@
+package calendar
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net/mail"
+	"regexp"
+	"strings"
+	"time"
+
+	ics "github.com/arran4/golang-ical"
+)
+
+type Reply struct {
+	MimeType     string
+	Params       map[string]string
+	CalendarText io.ReadWriter
+	PlainText    io.ReadWriter
+	Organizers   []string
+}
+
+func (cr *Reply) AddOrganizer(o string) {
+	cr.Organizers = append(cr.Organizers, o)
+}
+
+// CreateReply parses a ics request and return a ics reply (RFC 2446, Section 3.2.3)
+func CreateReply(reader io.Reader, from *mail.Address, partstat string) (*Reply, error) {
+
+	cr := Reply{
+		MimeType: "text/calendar",
+		Params: map[string]string{
+			"charset": "UTF-8",
+			"method":  "REPLY",
+		},
+		CalendarText: &bytes.Buffer{},
+		PlainText:    &bytes.Buffer{},
+	}
+
+	var (
+		status ics.ParticipationStatus
+		action string
+	)
+
+	switch partstat {
+	case "accept":
+		status = ics.ParticipationStatusAccepted
+		action = "accepted"
+	case "accept-tentative":
+		status = ics.ParticipationStatusTentative
+		action = "tentatively accepted"
+	case "decline":
+		status = ics.ParticipationStatusDeclined
+		action = "declined"
+	default:
+		return nil, fmt.Errorf("participation status %s is not implemented", partstat)
+	}
+
+	name := from.Name
+	if name == "" {
+		name = from.Address
+	}
+	fmt.Fprintf(cr.PlainText, "%s has %s this invitation.", name, action)
+
+	invite, err := parse(reader)
+	if err != nil {
+		return nil, err
+	}
+
+	if ok := invite.request(); !ok {
+		return nil, fmt.Errorf("no reply is requested")
+	}
+
+	// update invite as a reply
+	reply := invite
+	reply.SetMethod(ics.MethodReply)
+	reply.SetProductId("aerc")
+
+	// check all events
+	for _, vevent := range reply.Events() {
+		e := event{vevent}
+
+		// check if we should answer
+		if err := e.isReplyRequested(from.Address); err != nil {
+			return nil, err
+		}
+
+		// make sure we send our reply to the meeting organizer
+		if organizer := e.GetProperty(ics.ComponentPropertyOrganizer); organizer != nil {
+			cr.AddOrganizer(organizer.Value)
+		}
+
+		// update attendee participation status
+		e.updateAttendees(status, from.Address)
+
+		// update timestamp
+		e.SetDtStampTime(time.Now())
+
+		// remove any subcomponents of event
+		e.Components = nil
+	}
+
+	// keep only timezone and event components
+	reply.clean()
+
+	if len(reply.Events()) == 0 {
+		return nil, fmt.Errorf("no events to respond to")
+	}
+
+	if err := reply.SerializeTo(cr.CalendarText); err != nil {
+		return nil, err
+	}
+	return &cr, nil
+}
+
+type calendar struct {
+	*ics.Calendar
+}
+
+func parse(reader io.Reader) (*calendar, error) {
+	// fix capitalized mailto for parsing of ics file
+	var sb strings.Builder
+	io.Copy(&sb, reader)
+	re := regexp.MustCompile("MAILTO:(.+@)")
+	str := re.ReplaceAllString(sb.String(), "mailto:${1}")
+
+	// parse calendar
+	invite, err := ics.ParseCalendar(strings.NewReader(str))
+	if err != nil {
+		return nil, err
+	}
+	return &calendar{invite}, nil
+}
+
+func (cal *calendar) request() (ok bool) {
+	ok = false
+	for i := range cal.CalendarProperties {
+		if cal.CalendarProperties[i].IANAToken == string(ics.PropertyMethod) {
+			if cal.CalendarProperties[i].Value == string(ics.MethodRequest) {
+				ok = true
+				return
+			}
+		}
+	}
+	return
+}
+
+func (cal *calendar) clean() {
+	var clean []ics.Component
+	for _, comp := range cal.Components {
+		switch comp.(type) {
+		case *ics.VTimezone, *ics.VEvent:
+			clean = append(clean, comp)
+		default:
+			continue
+		}
+	}
+	cal.Components = clean
+}
+
+type event struct {
+	*ics.VEvent
+}
+
+func (e *event) isReplyRequested(from string) error {
+	var present bool = false
+	var rsvp bool = false
+	for _, a := range e.Attendees() {
+		if a.Email() == from {
+			present = true
+			if r, ok := a.ICalParameters[string(ics.ParameterRsvp)]; ok {
+				if len(r) > 0 && strings.ToLower(r[0]) == "true" {
+					rsvp = true
+				}
+			}
+		}
+	}
+	if !present {
+		return fmt.Errorf("we are not invited")
+	}
+	if !rsvp {
+		return fmt.Errorf("we don't have to rsvp")
+	}
+	return nil
+}
+
+func (e *event) updateAttendees(status ics.ParticipationStatus, from string) {
+	var clean []ics.IANAProperty
+	for _, prop := range e.Properties {
+		if prop.IANAToken == string(ics.ComponentPropertyAttendee) {
+			att := ics.Attendee{prop}
+			if att.Email() != from {
+				continue
+			}
+			prop.ICalParameters[string(ics.ParameterParticipationStatus)] = []string{string(status)}
+			delete(prop.ICalParameters, string(ics.ParameterRsvp))
+		}
+		clean = append(clean, prop)
+	}
+	e.Properties = clean
+}
diff --git a/lib/structure_helpers.go b/lib/structure_helpers.go
index 95719dd7..ac6950af 100644
--- a/lib/structure_helpers.go
+++ b/lib/structure_helpers.go
@@ -22,6 +22,22 @@ func FindPlaintext(bs *models.BodyStructure, path []int) []int {
 	return nil
 }
 
+func FindCalendartext(bs *models.BodyStructure, path []int) []int {
+	for i, part := range bs.Parts {
+		cur := append(path, i+1)
+		if strings.ToLower(part.MIMEType) == "text" &&
+			strings.ToLower(part.MIMESubType) == "calendar" {
+			return cur
+		}
+		if strings.ToLower(part.MIMEType) == "multipart" {
+			if path := FindCalendartext(part, cur); path != nil {
+				return path
+			}
+		}
+	}
+	return nil
+}
+
 func FindFirstNonMultipart(bs *models.BodyStructure, path []int) []int {
 	for i, part := range bs.Parts {
 		cur := append(path, i+1)