package backend

import (
	"bytes"
	"fmt"
	"html"
	"net/http"
	"net/mail"
	"os"
	"path/filepath"
	"strconv"
	"strings"
)

// Der Viewer betrachtet die LOKALEN mbox-Dateien im Browser (Outlook-2013-
// Dreispalter): links Konto/Ordner-Baum, Mitte Nachrichtenliste, rechts
// Lesebereich. Optional Weiterleiten einzelner Mails per SMTP (09-smtp.go).

func viewerHandler(w http.ResponseWriter, r *http.Request) {
	account := r.URL.Query().Get("account")
	folder := r.URL.Query().Get("folder")
	if account != "" && folder != "" {
		renderMessageList(w, account, folder)
		return
	}
	if r.Header.Get("HX-Request") == "true" {
		renderViewerTree(w)
		return
	}
	renderShell(w, "", `<div class="ef-empty">Backup-Postfach links waehlen.</div>`)
}

func messageHandler(w http.ResponseWriter, r *http.Request) {
	account := r.URL.Query().Get("account")
	folder := r.URL.Query().Get("folder")
	index, err := strconv.Atoi(r.URL.Query().Get("index"))
	if err != nil {
		http.Error(w, "bad index", http.StatusBadRequest)
		return
	}
	path, err := mboxPath(account, folder)
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	raw, err := ReadMboxMessage(path, index)
	if err != nil {
		http.Error(w, err.Error(), http.StatusNotFound)
		return
	}
	msg, err := mail.ReadMessage(bytes.NewReader(raw))
	if err != nil {
		renderReadPane(w, "(unlesbar)", "", "", string(raw))
		return
	}
	renderReadPane(w,
		decodeHeader(msg.Header.Get("Subject")),
		decodeHeader(msg.Header.Get("From")),
		decodeHeader(msg.Header.Get("Date")),
		messageBody(raw),
	)
}

func forwardHandler(w http.ResponseWriter, r *http.Request) {
	// TODO Codex: GET = Weiterleiten-Formular (An/Betreff/Text), POST =
	// ForwardMessage() aufrufen. NUR hier kommt SMTP zum Einsatz -- der Umzug
	// selbst nutzt IMAP APPEND.
}

func renderViewerTree(w http.ResponseWriter) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	fmt.Fprint(w, `<div class="pane-head">Backups</div>`)
	entries, err := os.ReadDir(Cfg.MboxRoot)
	if err != nil {
		fmt.Fprintf(w, `<div class="ef-empty">%s</div>`, html.EscapeString(err.Error()))
		return
	}
	found := false
	for _, entry := range entries {
		if !entry.IsDir() {
			continue
		}
		account := entry.Name()
		mboxes, _ := filepath.Glob(filepath.Join(Cfg.MboxRoot, account, "*.mbox"))
		if len(mboxes) == 0 {
			continue
		}
		found = true
		fmt.Fprintf(w, `<div class="tree-node account">%s</div>`, html.EscapeString(account))
		for _, path := range mboxes {
			folder := strings.TrimSuffix(filepath.Base(path), ".mbox")
			fmt.Fprintf(w, `<a class="tree-node" href="/view?account=%s&amp;folder=%s" hx-get="/view?account=%s&amp;folder=%s" hx-target="#list" hx-swap="innerHTML">%s</a>`,
				urlEsc(account), urlEsc(folder), urlEsc(account), urlEsc(folder), html.EscapeString(folder))
		}
	}
	if !found {
		fmt.Fprint(w, `<div class="ef-empty">Noch keine mbox-Backups.</div>`)
	}
}

func renderMessageList(w http.ResponseWriter, account, folder string) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	path, err := mboxPath(account, folder)
	if err != nil {
		fmt.Fprintf(w, `<div class="pane-head">Nachrichten</div><div class="ef-empty">%s</div>`, html.EscapeString(err.Error()))
		return
	}
	entries, err := ReadMboxList(path)
	if err != nil {
		fmt.Fprintf(w, `<div class="pane-head">Nachrichten</div><div class="ef-empty">%s</div>`, html.EscapeString(err.Error()))
		return
	}
	fmt.Fprintf(w, `<div class="pane-head">%s / %s (%d)</div>`, html.EscapeString(account), html.EscapeString(folder), len(entries))
	for _, entry := range entries {
		subject := entry.Subject
		if subject == "" {
			subject = "(ohne Betreff)"
		}
		from := entry.From
		if from == "" {
			from = "(ohne Absender)"
		}
		fmt.Fprintf(w, `<a class="msg-row" href="/view/message?account=%s&amp;folder=%s&amp;index=%d" hx-get="/view/message?account=%s&amp;folder=%s&amp;index=%d" hx-target="#read" hx-swap="innerHTML"><span class="msg-from">%s</span><span class="msg-subject">%s</span><span class="msg-date">%s</span></a>`,
			urlEsc(account), urlEsc(folder), entry.Index, urlEsc(account), urlEsc(folder), entry.Index,
			html.EscapeString(from), html.EscapeString(subject), html.EscapeString(entry.Date))
	}
	if len(entries) == 0 {
		fmt.Fprint(w, `<div class="ef-empty">Keine Nachrichten in dieser mbox.</div>`)
	}
}

func renderReadPane(w http.ResponseWriter, subject, from, date, body string) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	if subject == "" {
		subject = "(ohne Betreff)"
	}
	fmt.Fprintf(w, `<div class="pane-head">Lesebereich</div><div class="read-body"><div class="read-head"><h1 class="read-subject">%s</h1><div class="read-meta">Von: %s<br>Datum: %s</div></div><pre class="read-pre">%s</pre></div>`,
		html.EscapeString(subject), html.EscapeString(from), html.EscapeString(date), html.EscapeString(body))
}

func mboxPath(account, folder string) (string, error) {
	if account == "" || folder == "" || strings.Contains(account, "..") || strings.Contains(folder, "..") {
		return "", fmt.Errorf("ungueltiges Postfach")
	}
	root, err := filepath.Abs(Cfg.MboxRoot)
	if err != nil {
		return "", err
	}
	path, err := filepath.Abs(filepath.Join(root, account, safeMboxName(folder)+".mbox"))
	if err != nil {
		return "", err
	}
	rel, err := filepath.Rel(root, path)
	if err != nil || strings.HasPrefix(rel, "..") {
		return "", fmt.Errorf("ungueltiger mbox-Pfad")
	}
	return path, nil
}

func urlEsc(s string) string {
	r := strings.NewReplacer("%", "%25", " ", "%20", "&", "%26", "?", "%3F", "#", "%23", "+", "%2B", "/", "%2F")
	return r.Replace(s)
}