package main

import (
	"bytes"
	"encoding/xml"
	"fmt"
	"io"
	"net/http"
	"net/http/cookiejar"
	"strings"
	"text/template"
	"time"
)

type FolderId struct {
	Id        string `xml:",attr"`
	ChangeKey string `xml:",attr"`
}

type CalendarItem struct {
	Subject string
	UID     string
	Start   time.Time
	End     time.Time
}

type EWSCalendar struct {
	httpClient *http.Client
	url        string
	username   string
	password   string
}

func NewEWSCalendar(url, username, password string) *EWSCalendar {
	// Prepare a cookie jar, since EWS uses some.
	jar, err := cookiejar.New(nil)
	if err != nil {
		panic(err)
	}
	return &EWSCalendar{
		httpClient: &http.Client{
			Jar: jar,
		},
		url:      url,
		username: username,
		password: password,
	}
}

func (e *EWSCalendar) prepareRequest(body io.Reader) (req *http.Request, err error) {
	req, err = http.NewRequest(http.MethodPost, e.url, body)
	req.Header.Set("Content-Type", "text/xml")
	req.Header.Set("Accept", "text/xml")
	req.SetBasicAuth(e.username, e.password)
	return
}

func (e *EWSCalendar) getCalendarFolderID() (id *FolderId, err error) {
	req, err := e.prepareRequest(strings.NewReader(folderIdRequest))
	if err != nil {
		return
	}

	resp, err := e.httpClient.Do(req)
	if err != nil {
		return
	}

	if resp.StatusCode != http.StatusOK {
		err = fmt.Errorf("unexpected status when querying folderID: %d", resp.StatusCode)
		return
	}

	d := xml.NewDecoder(resp.Body)
	defer resp.Body.Close()

	for {
		var t xml.Token
		t, err = d.Token()
		if err == io.EOF {
			err = nil
			return
		} else if err != nil {
			return
		}

		switch t := t.(type) {
		case xml.StartElement:
			if t.Name.Local == "FolderId" {
				id = &FolderId{}
				err = d.DecodeElement(id, &t)
				// The first one is enough
				return
			}
		}
	}
}

func (e *EWSCalendar) getCalendarItems(folder *FolderId, start, end time.Time) (items []CalendarItem, err error) {
	b := &bytes.Buffer{}
	model := struct {
		FolderId  *FolderId
		StartDate string
		EndDate   string
	}{folder, start.Format(time.RFC3339), end.Format(time.RFC3339)}

	err = calendarQuery.Execute(b, &model)
	if err != nil {
		return
	}

	req, err := e.prepareRequest(b)
	if err != nil {
		return
	}

	resp, err := e.httpClient.Do(req)
	if err != nil {
		return
	}

	if resp.StatusCode != http.StatusOK {
		err = fmt.Errorf("unexpected status when querying calendar items: %d", resp.StatusCode)
		return
	}

	d := xml.NewDecoder(resp.Body)
	defer resp.Body.Close()

	for {
		var t xml.Token
		t, err = d.Token()
		if err == io.EOF {
			err = nil
			return
		} else if err != nil {
			return
		}

		switch t := t.(type) {
		case xml.StartElement:
			if t.Name.Local == "CalendarItem" {
				item := CalendarItem{}
				err = d.DecodeElement(&item, &t)
				items = append(items, item)
			}
		}
	}
	return
}

const folderIdRequest = `<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Header>
    <t:RequestServerVersion Version="Exchange2013_SP1" />
  </soap:Header>
  <soap:Body>
    <m:GetFolder>
      <m:FolderShape>
        <t:BaseShape>AllProperties</t:BaseShape>
      </m:FolderShape>
      <m:FolderIds>
        <t:DistinguishedFolderId Id="calendar" />
      </m:FolderIds>
    </m:GetFolder>
  </soap:Body>
</soap:Envelope>`

var calendarQuery = template.Must(template.New("calendarQuery").Parse(`<?xml version="1.0" encoding="utf-8"?>
<soap:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:m="http://schemas.microsoft.com/exchange/services/2006/messages" xmlns:t="http://schemas.microsoft.com/exchange/services/2006/types" xmlns:soap="http://schemas.xmlsoap.org/soap/envelope/">
  <soap:Header>
    <t:RequestServerVersion Version="Exchange2013_SP1" />
  </soap:Header>
  <soap:Body>
    <m:FindItem Traversal="Shallow">
      <m:ItemShape>
        <t:BaseShape>IdOnly</t:BaseShape>
        <t:AdditionalProperties>
          <t:FieldURI FieldURI="item:Subject" />
          <t:FieldURI FieldURI="item:Sensitivity" />
          <t:FieldURI FieldURI="calendar:Start" />
          <t:FieldURI FieldURI="calendar:End" />
          <t:FieldURI FieldURI="calendar:UID" />
          <t:FieldURI FieldURI="calendar:RecurrenceId" />
          <t:FieldURI FieldURI="calendar:IsCancelled" />
          <t:FieldURI FieldURI="calendar:CalendarItemType" />
          <t:FieldURI FieldURI="calendar:CalendarItemType" />
        </t:AdditionalProperties>
      </m:ItemShape>
      <m:CalendarView StartDate="{{ .StartDate }}" EndDate="{{ .EndDate }}" />
      <m:ParentFolderIds>
        <t:FolderId Id="{{ .FolderId.Id }}" ChangeKey="{{ .FolderId.ChangeKey }}" />
      </m:ParentFolderIds>
    </m:FindItem>
  </soap:Body>
</soap:Envelope>`))