Render every outgoing e-mail from an editable text template

The wording of the dunning and SEPA pre-notification mails was hard-coded in
Python, so adjusting a single sentence required a new release. Both texts now
live in plain text templates that ship as defaults, are copied into the store's
templates/mail/ directory on first start and can be edited there or under
Optionen -> E-Mail-Vorlagen; an existing file is never overwritten and a deleted
one is restored from the shipped default.

A template carries its subject in the first line and the body after a blank
line. Placeholders use the same {{ ... }} syntax as the document templates and
share their member/organization values, so a name means the same thing in a
letter and in the mail that carries it. Unknown placeholders are rejected while
editing instead of during a send run, a line holding nothing but placeholders
that render empty is dropped, and {{#claims}} ... {{/claims}} repeats per entry.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/ccma/ui/options_dialog.py

@@ -7,6 +7,12 @@ from tkinter import filedialog, messagebox, ttk
 
 from ccma.config import AppConfig
 from ccma.domain.contributions import decimal_value, money_text
+from ccma.domain.mail_templates import (
+    MAIL_TEMPLATES,
+    MailTemplateError,
+    default_mail_template,
+    template_spec,
+)
 from ccma.domain.models import HOUSEKEEPER_MEMBER_FIELD_LABELS
 from ccma.services.intervals import (
     IntervalValidationError,
@@ -67,6 +73,14 @@ class OptionsDialog(tk.Toplevel):
                 "website", "iban", "bic", "creditor_id",
             )
         }
+        # Mail templates are edited one at a time but saved together with the rest of
+        # the options, so the edits of every tab are kept in memory until "Speichern".
+        self.mail_template_key = MAIL_TEMPLATES[0].key
+        self.mail_template_edits: dict[str, tuple[str, str]] = {}
+        self.mail_template_original: dict[str, tuple[str, str]] = {}
+        self.mail_template_var = tk.StringVar(value=MAIL_TEMPLATES[0].label)
+        self.mail_template_subject_var = tk.StringVar()
+        self.mail_template_hint_var = tk.StringVar()
         self.title("Optionen")
         self.transient(master.winfo_toplevel())
         self.grab_set()
@@ -102,6 +116,7 @@ class OptionsDialog(tk.Toplevel):
         automation = ttk.Frame(notebook, padding=16)
         reminders = ttk.Frame(notebook, padding=16)
         email = ttk.Frame(notebook, padding=16)
+        mail_templates = ttk.Frame(notebook, padding=16)
         changelog = ChangelogView(notebook)
         notebook.add(paths, text="Pfade")
         notebook.add(appearance, text="Darstellung")
@@ -110,6 +125,7 @@ class OptionsDialog(tk.Toplevel):
         notebook.add(automation, text="Hausmeister")
         notebook.add(reminders, text="Mahnungen")
         notebook.add(email, text="E-Mail-Versand")
+        notebook.add(mail_templates, text="E-Mail-Vorlagen")
         notebook.add(changelog, text="Changelog")
         self._build_paths(paths)
         self._build_appearance(appearance)
@@ -118,6 +134,7 @@ class OptionsDialog(tk.Toplevel):
         self._build_automation(automation)
         self._build_reminders(reminders)
         self._build_email(email)
+        self._build_mail_templates(mail_templates)
 
         buttons = ttk.Frame(root)
         buttons.grid(row=1, column=0, sticky="e", pady=(12, 0))
@@ -907,6 +924,7 @@ class OptionsDialog(tk.Toplevel):
                 standard_fee_items=self.standard_items,
             )
             self.repository.save_email_settings(**email_settings)
+            self._save_mail_templates()
         except (OSError, RepositoryError) as exc:
             messagebox.showerror("Optionen konnten nicht gespeichert werden", str(exc), parent=self)
             return
@@ -914,6 +932,166 @@ class OptionsDialog(tk.Toplevel):
             self.on_saved(store_changed)
         self.destroy()
 
+    def _build_mail_templates(self, parent: ttk.Frame) -> None:
+        parent.columnconfigure(0, weight=1)
+        parent.rowconfigure(4, weight=1)
+        ttk.Label(
+            parent,
+            text=(
+                "Die Texte aller vom Programm erzeugten E-Mails liegen als bearbeitbare "
+                "Vorlagen im Mitglieder-Store unter templates/mail/. Platzhalter in doppelten "
+                "geschweiften Klammern werden beim Versand mit den Daten des Mitglieds gefüllt."
+            ),
+            style="Muted.TLabel",
+            wraplength=820,
+        ).grid(row=0, column=0, columnspan=2, sticky="w", pady=(0, 12))
+
+        chooser = ttk.Frame(parent)
+        chooser.grid(row=1, column=0, columnspan=2, sticky="ew")
+        chooser.columnconfigure(1, weight=1)
+        ttk.Label(chooser, text="Vorlage").grid(row=0, column=0, sticky="w", padx=(0, 12))
+        selector = ttk.Combobox(
+            chooser,
+            textvariable=self.mail_template_var,
+            values=[spec.label for spec in MAIL_TEMPLATES],
+            state="readonly",
+            width=32,
+        )
+        selector.grid(row=0, column=1, sticky="w")
+        selector.bind("<<ComboboxSelected>>", lambda _event: self._select_mail_template())
+        ttk.Button(
+            chooser, text="Standardtext wiederherstellen", command=self._reset_mail_template
+        ).grid(row=0, column=2, sticky="e", padx=(12, 0))
+        ttk.Label(
+            parent, textvariable=self.mail_template_hint_var, style="Muted.TLabel", wraplength=820
+        ).grid(row=2, column=0, columnspan=2, sticky="w", pady=(6, 12))
+
+        subject = ttk.Frame(parent)
+        subject.grid(row=3, column=0, columnspan=2, sticky="ew", pady=(0, 8))
+        subject.columnconfigure(1, weight=1)
+        ttk.Label(subject, text="Betreff").grid(row=0, column=0, sticky="w", padx=(0, 12))
+        ttk.Entry(subject, textvariable=self.mail_template_subject_var).grid(
+            row=0, column=1, sticky="ew"
+        )
+
+        editor = ttk.Frame(parent)
+        editor.grid(row=4, column=0, sticky="nsew")
+        editor.columnconfigure(0, weight=1)
+        editor.rowconfigure(0, weight=1)
+        self.mail_template_body = tk.Text(editor, wrap="word", height=16, width=70, undo=True)
+        self.mail_template_body.grid(row=0, column=0, sticky="nsew")
+        body_scroll = ttk.Scrollbar(editor, orient="vertical", command=self.mail_template_body.yview)
+        body_scroll.grid(row=0, column=1, sticky="ns")
+        self.mail_template_body.configure(yscrollcommand=body_scroll.set)
+
+        placeholders = ttk.Frame(parent)
+        placeholders.grid(row=4, column=1, sticky="nsew", padx=(12, 0))
+        placeholders.columnconfigure(0, weight=1)
+        placeholders.rowconfigure(1, weight=1)
+        ttk.Label(placeholders, text="Platzhalter (Doppelklick fügt ein)").grid(
+            row=0, column=0, columnspan=2, sticky="w", pady=(0, 4)
+        )
+        self.mail_template_placeholders = ttk.Treeview(
+            placeholders, columns=("name", "help"), show="headings", selectmode="browse", height=14
+        )
+        for key, title, width in (("name", "Platzhalter", 210), ("help", "Bedeutung", 230)):
+            self.mail_template_placeholders.heading(key, text=title)
+            self.mail_template_placeholders.column(key, width=width, anchor="w", stretch=key == "help")
+        self.mail_template_placeholders.grid(row=1, column=0, sticky="nsew")
+        placeholder_scroll = ttk.Scrollbar(
+            placeholders, orient="vertical", command=self.mail_template_placeholders.yview
+        )
+        placeholder_scroll.grid(row=1, column=1, sticky="ns")
+        self.mail_template_placeholders.configure(yscrollcommand=placeholder_scroll.set)
+        self.mail_template_placeholders.bind(
+            "<Double-1>", lambda _event: self._insert_mail_placeholder()
+        )
+        self.mail_template_placeholders.bind(
+            "<Return>", lambda _event: self._insert_mail_placeholder()
+        )
+        self._load_mail_template(self.mail_template_key)
+
+    def _load_mail_template(self, key: str) -> None:
+        if key not in self.mail_template_edits:
+            try:
+                template = self.repository.get_mail_template(key)
+            except (OSError, RepositoryError) as exc:
+                messagebox.showerror(
+                    "Vorlage konnte nicht geladen werden", str(exc), parent=self
+                )
+                return
+            self.mail_template_edits[key] = (template.subject, template.body)
+            self.mail_template_original[key] = (template.subject, template.body)
+        subject, body = self.mail_template_edits[key]
+        self.mail_template_key = key
+        spec = template_spec(key)
+        self.mail_template_var.set(spec.label)
+        self.mail_template_hint_var.set(f"{spec.description} (Datei: {spec.filename})")
+        self.mail_template_subject_var.set(subject)
+        self.mail_template_body.delete("1.0", "end")
+        self.mail_template_body.insert("1.0", body)
+        self.mail_template_placeholders.delete(*self.mail_template_placeholders.get_children())
+        for name, description in spec.placeholders:
+            self.mail_template_placeholders.insert(
+                "", "end", values=(f"{{{{{name}}}}}", description)
+            )
+        for name, description, items in spec.blocks:
+            self.mail_template_placeholders.insert(
+                "", "end", values=(f"{{{{#{name}}}}} … {{{{/{name}}}}}", description)
+            )
+            for item_name, item_description in items:
+                self.mail_template_placeholders.insert(
+                    "", "end", values=(f"    {{{{{item_name}}}}}", item_description)
+                )
+
+    def _capture_mail_template(self) -> None:
+        if not hasattr(self, "mail_template_body"):
+            return
+        self.mail_template_edits[self.mail_template_key] = (
+            self.mail_template_subject_var.get(),
+            self.mail_template_body.get("1.0", "end-1c"),
+        )
+
+    def _select_mail_template(self) -> None:
+        self._capture_mail_template()
+        label = self.mail_template_var.get()
+        key = next((spec.key for spec in MAIL_TEMPLATES if spec.label == label), None)
+        if key:
+            self._load_mail_template(key)
+
+    def _reset_mail_template(self) -> None:
+        key = self.mail_template_key
+        spec = template_spec(key)
+        if not messagebox.askyesno(
+            "Standardtext wiederherstellen",
+            f"Soll die Vorlage „{spec.label}“ auf den mitgelieferten Standardtext "
+            "zurückgesetzt werden? Deine Änderungen an dieser Vorlage gehen dabei verloren.",
+            parent=self,
+        ):
+            return
+        try:
+            template = default_mail_template(key)
+        except MailTemplateError as exc:
+            messagebox.showerror("Standardtext nicht verfügbar", str(exc), parent=self)
+            return
+        self.mail_template_edits[key] = (template.subject, template.body)
+        self._load_mail_template(key)
+
+    def _insert_mail_placeholder(self) -> None:
+        selected = self.mail_template_placeholders.selection()
+        if not selected:
+            return
+        value = str(self.mail_template_placeholders.item(selected[0], "values")[0]).strip()
+        self.mail_template_body.insert("insert", value)
+        self.mail_template_body.focus_set()
+
+    def _save_mail_templates(self) -> None:
+        self._capture_mail_template()
+        for key, (subject, body) in self.mail_template_edits.items():
+            if self.mail_template_original.get(key) == (subject, body):
+                continue
+            self.repository.save_mail_template(key, subject=subject, body=body)
+
     def _center_on_parent(self) -> None:
         self.update_idletasks()
         parent = self.master.winfo_toplevel()