Mail · Writing: the composer, recipients that suggest, a signature, send later

MailComposer writes a message: To, and Cc and Bcc once asked for, as
tag fields that suggest contacts and mark what is not an address; the
subject and the words; the files, each with a way off; the signature
under the words. Send wakes once there is someone to send to and every
address is one; it hands over the draft now or at a time, and Discard
lets it go. A new start from the owner begins the draft over.

forms::TagInput now suggests: the rows that hold the typed words float
under it through the list Combobox uses; Up, Down and Enter pick, and
Escape sets them aside. RecipientInput points to it. ScheduleSend
offers tomorrow morning, tomorrow afternoon, Monday morning, or a day
and hour picked in a dialog. SignatureEditor writes the lines and shows
how they sit under a message; it tells the owner's echo from a new
signature, so the caret stays.

src/mail/compose.rs

@@ -0,0 +1,387 @@
+use std::rc::Rc;
+
+use gpui::{
+    App, Context, ElementId, Entity, InteractiveElement, IntoElement, ParentElement, RenderOnce,
+    SharedString, Styled, Window, div, prelude::*,
+};
+use jiff::{Timestamp, tz::TimeZone};
+
+use super::{reader::Contact, send::ScheduleSend, signature::signature_block};
+use crate::{
+    buttons::{Button, ButtonVariant, IconButton},
+    chat::{Attachment, AttachmentChip},
+    forms::{Choice, Input, OnValue, Run, TagInput, TextInput, is_email},
+    primitives::IconName,
+    theme::{ActiveTheme, ControlSize, TextSize},
+};
+
+/// What a composer hands over: the addresses, the subject and the words.
+#[derive(Clone, Debug, PartialEq)]
+pub struct Draft {
+    pub to: Vec<SharedString>,
+    pub cc: Vec<SharedString>,
+    pub bcc: Vec<SharedString>,
+    pub subject: SharedString,
+    pub body: SharedString,
+}
+
+type OnDraft = Rc<dyn Fn(&Draft, &mut Window, &mut App)>;
+type OnDraftAt = Rc<dyn Fn(&Draft, Timestamp, &mut Window, &mut App)>;
+
+/// Whether a message can go: someone to send to, and every address an address.
+fn ready(to: &[SharedString], cc: &[SharedString], bcc: &[SharedString]) -> bool {
+    let mut all = to.iter().chain(cc).chain(bcc).peekable();
+    all.peek().is_some() && all.all(|address| is_email(address))
+}
+
+/// Which field of addresses.
+#[derive(Clone, Copy)]
+enum Field {
+    To,
+    Cc,
+    Bcc,
+}
+
+/// The message being written: the owner's start it came from, the addresses, whether Cc and Bcc show, and the subject and words.
+struct Composing {
+    seed: (Vec<SharedString>, SharedString),
+    to: Vec<SharedString>,
+    cc: Vec<SharedString>,
+    bcc: Vec<SharedString>,
+    copies: bool,
+    subject: Entity<TextInput>,
+    body: Entity<TextInput>,
+}
+
+impl Composing {
+    /// Starts over from the owner's addresses and subject, with no words.
+    fn fill(&mut self, (to, subject): (Vec<SharedString>, SharedString), cx: &mut Context<Self>) {
+        self.to = to;
+        self.cc.clear();
+        self.bcc.clear();
+        self.copies = false;
+        self.subject
+            .update(cx, |input, cx| input.set_text(subject.to_string(), cx));
+        self.body.update(cx, |input, cx| input.set_text("", cx));
+    }
+
+    fn draft(&self, cx: &App) -> Draft {
+        Draft {
+            to: self.to.clone(),
+            cc: self.cc.clone(),
+            bcc: self.bcc.clone(),
+            subject: self.subject.read(cx).text().trim().to_string().into(),
+            body: self.body.read(cx).text().to_string().into(),
+        }
+    }
+}
+
+/// A message to write: To, and Cc and Bcc once asked for, as fields that suggest contacts and mark what is not an address; the subject and the words; the files, each with a way off; and the signature under the words. Send goes once there is someone to send to, now or at a time; Discard lets it go. A new start from the owner begins it over.
+#[derive(IntoElement)]
+pub struct MailComposer {
+    id: ElementId,
+    contacts: Vec<Contact>,
+    to: Vec<SharedString>,
+    subject: SharedString,
+    signature: Option<SharedString>,
+    files: Vec<Attachment>,
+    zone: Option<TimeZone>,
+    on_send: Option<OnDraft>,
+    on_schedule: Option<OnDraftAt>,
+    on_discard: Option<Run>,
+    on_attach: Option<Run>,
+    on_remove: Option<OnValue>,
+}
+
+impl MailComposer {
+    pub fn new(id: impl Into<ElementId>) -> Self {
+        Self {
+            id: id.into(),
+            contacts: Vec::new(),
+            to: Vec::new(),
+            subject: SharedString::default(),
+            signature: None,
+            files: Vec::new(),
+            zone: None,
+            on_send: None,
+            on_schedule: None,
+            on_discard: None,
+            on_attach: None,
+            on_remove: None,
+        }
+    }
+
+    /// People to suggest as addresses are typed.
+    pub fn contacts(mut self, contacts: impl IntoIterator<Item = Contact>) -> Self {
+        self.contacts = contacts.into_iter().collect();
+        self
+    }
+
+    /// The addresses it starts with, as a reply has them.
+    pub fn to(mut self, addresses: impl IntoIterator<Item = impl Into<SharedString>>) -> Self {
+        self.to = addresses.into_iter().map(Into::into).collect();
+        self
+    }
+
+    /// The subject it starts with.
+    pub fn subject(mut self, subject: impl Into<SharedString>) -> Self {
+        self.subject = subject.into();
+        self
+    }
+
+    pub fn signature(mut self, text: impl Into<SharedString>) -> Self {
+        self.signature = Some(text.into());
+        self
+    }
+
+    /// Files the owner attached.
+    pub fn files(mut self, files: impl IntoIterator<Item = Attachment>) -> Self {
+        self.files = files.into_iter().collect();
+        self
+    }
+
+    /// The zone its times to send read in; the system's otherwise.
+    pub fn zone(mut self, zone: TimeZone) -> Self {
+        self.zone = Some(zone);
+        self
+    }
+
+    pub fn on_send(mut self, handler: impl Fn(&Draft, &mut Window, &mut App) + 'static) -> Self {
+        self.on_send = Some(Rc::new(handler));
+        self
+    }
+
+    /// Gets the draft and the moment to send it.
+    pub fn on_schedule(
+        mut self,
+        handler: impl Fn(&Draft, Timestamp, &mut Window, &mut App) + 'static,
+    ) -> Self {
+        self.on_schedule = Some(Rc::new(handler));
+        self
+    }
+
+    pub fn on_discard(mut self, handler: impl Fn(&mut Window, &mut App) + 'static) -> Self {
+        self.on_discard = Some(Rc::new(handler));
+        self
+    }
+
+    /// Asks the owner for files to attach.
+    pub fn on_attach(mut self, handler: impl Fn(&mut Window, &mut App) + 'static) -> Self {
+        self.on_attach = Some(Rc::new(handler));
+        self
+    }
+
+    /// Gets the key of the file to take off.
+    pub fn on_remove(
+        mut self,
+        handler: impl Fn(&SharedString, &mut Window, &mut App) + 'static,
+    ) -> Self {
+        self.on_remove = Some(Rc::new(handler));
+        self
+    }
+}
+
+impl RenderOnce for MailComposer {
+    fn render(self, window: &mut Window, cx: &mut App) -> impl IntoElement {
+        let seed = (self.to.clone(), self.subject.clone());
+        let state = window.use_keyed_state(
+            (self.id.clone(), "draft"),
+            cx,
+            |window, cx: &mut Context<Composing>| {
+                let subject = cx.new(|cx| TextInput::new(window, cx).placeholder("Subject"));
+                let body = cx.new(|cx| {
+                    TextInput::new(window, cx)
+                        .multi_line(6, 16)
+                        .placeholder("Write your message")
+                });
+                let mut composing = Composing {
+                    seed: seed.clone(),
+                    to: Vec::new(),
+                    cc: Vec::new(),
+                    bcc: Vec::new(),
+                    copies: false,
+                    subject,
+                    body,
+                };
+                composing.fill(seed.clone(), cx);
+                composing
+            },
+        );
+        if state.read(cx).seed != seed {
+            log::info!("mail composer {}: started over", self.id);
+            state.update(cx, |composing, cx| {
+                composing.seed = seed.clone();
+                composing.fill(seed, cx);
+            });
+        }
+        let now = state.read(cx);
+        let (to, cc, bcc, copies) = (now.to.clone(), now.cc.clone(), now.bcc.clone(), now.copies);
+        let (subject, body) = (now.subject.clone(), now.body.clone());
+        let can_send = ready(&to, &cc, &bcc);
+        let choices: Vec<Choice> = self
+            .contacts
+            .iter()
+            .map(|contact| Choice::new(contact.address.clone(), contact.name.clone()))
+            .collect();
+        let theme = cx.theme();
+        let colors = &theme.colors;
+        let row = |label: &'static str, field: Field, tags: Vec<SharedString>| {
+            let owner = state.clone();
+            div()
+                .debug_selector(move || format!("composer-{label}"))
+                .flex()
+                .items_center()
+                .gap_2()
+                .child(
+                    div()
+                        .flex_none()
+                        .w_10()
+                        .text_size(theme.text_size(TextSize::Sm))
+                        .text_color(colors.fg_muted)
+                        .child(label),
+                )
+                .child(
+                    div().flex_1().min_w_0().child(
+                        TagInput::new((self.id.clone(), label), tags)
+                            .placeholder("Add people")
+                            .check(is_email)
+                            .suggestions(choices.clone())
+                            .on_change(move |next, _, cx| {
+                                log::info!("mail composer: {label} holds {}", next.len());
+                                owner.update(cx, |composing, cx| {
+                                    match field {
+                                        Field::To => composing.to = next,
+                                        Field::Cc => composing.cc = next,
+                                        Field::Bcc => composing.bcc = next,
+                                    }
+                                    cx.notify();
+                                })
+                            }),
+                    ),
+                )
+        };
+        let showing = state.clone();
+        let copies_button = (!copies).then(|| {
+            Button::new((self.id.clone(), "copies"), "Cc Bcc")
+                .variant(ButtonVariant::Ghost)
+                .size(ControlSize::Sm)
+                .on_click(move |_, _, cx| {
+                    log::info!("mail composer: shows Cc and Bcc");
+                    showing.update(cx, |composing, cx| {
+                        composing.copies = true;
+                        cx.notify();
+                    })
+                })
+        });
+        let files = self.files.iter().map(|file| {
+            let chip = AttachmentChip::new(
+                (self.id.clone(), format!("file-{}", file.key)),
+                file.clone(),
+            );
+            match self.on_remove.clone() {
+                Some(remove) => {
+                    let key = file.key.clone();
+                    chip.on_remove(move |window, cx| {
+                        log::info!("mail composer: takes off {key}");
+                        remove(&key, window, cx)
+                    })
+                    .into_any_element()
+                }
+                None => chip.into_any_element(),
+            }
+        });
+        let sending = state.clone();
+        let send = ScheduleSend::new((self.id.clone(), "send"))
+            .disabled(!can_send)
+            .when_some(self.zone.clone(), |send, zone| send.zone(zone))
+            .when_some(self.on_send.clone(), |send, on_send| {
+                send.on_send(move |window, cx| {
+                    let draft = sending.read(cx).draft(cx);
+                    log::info!("mail composer: sends to {}", draft.to.len());
+                    on_send(&draft, window, cx)
+                })
+            });
+        let scheduling = state.clone();
+        let send = match self.on_schedule.clone() {
+            Some(on_schedule) => send.on_schedule(move |at, window, cx| {
+                let draft = scheduling.read(cx).draft(cx);
+                log::info!("mail composer: sends at {at}");
+                on_schedule(&draft, at, window, cx)
+            }),
+            None => send,
+        };
+        let attach = self.on_attach.map(|attach| {
+            IconButton::new((self.id.clone(), "attach"), IconName::Paperclip)
+                .variant(ButtonVariant::Ghost)
+                .tooltip("Attach files")
+                .on_click(move |_, window, cx| {
+                    log::info!("mail composer: attach");
+                    attach(window, cx)
+                })
+        });
+        let discard = self.on_discard.map(|discard| {
+            IconButton::new((self.id.clone(), "discard"), IconName::Trash2)
+                .variant(ButtonVariant::Ghost)
+                .tooltip("Discard")
+                .on_click(move |_, window, cx| {
+                    log::info!("mail composer: discard");
+                    discard(window, cx)
+                })
+        });
+        div()
+            .debug_selector(|| "mail-composer".into())
+            .w_full()
+            .flex()
+            .flex_col()
+            .gap_3()
+            .child(
+                row("To", Field::To, to)
+                    .children(copies_button.map(|button| div().flex_none().child(button))),
+            )
+            .when(copies, |form| {
+                form.child(row("Cc", Field::Cc, cc))
+                    .child(row("Bcc", Field::Bcc, bcc))
+            })
+            .child(Input::new(&subject))
+            .child(Input::new(&body))
+            .when(!self.files.is_empty(), |form| {
+                form.child(div().flex().flex_wrap().gap_2().children(files))
+            })
+            .children(self.signature.map(|text| signature_block(&text, cx)))
+            .child(
+                div()
+                    .flex()
+                    .flex_wrap()
+                    .items_center()
+                    .justify_between()
+                    .gap_2()
+                    .child(
+                        div()
+                            .flex()
+                            .items_center()
+                            .gap_1()
+                            .child(send)
+                            .children(attach),
+                    )
+                    .children(discard),
+            )
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn a_message_goes_once_someone_holds_an_address() {
+        let ben: SharedString = "ben@atrium.studio".into();
+        let bad: SharedString = "ben@".into();
+        assert!(!ready(&[], &[], &[]), "nobody to send to");
+        assert!(ready(std::slice::from_ref(&ben), &[], &[]));
+        assert!(
+            ready(&[], &[], std::slice::from_ref(&ben)),
+            "a blind copy alone"
+        );
+        assert!(!ready(&[ben], &[bad], &[]), "an address that is not one");
+    }
+}

src/mail/mod.rs

@@ -1,14 +1,20 @@
 mod boxes;
+mod compose;
 mod list;
 mod quoted;
 mod reader;
+mod send;
+mod signature;
 mod thread;
 
 #[cfg(all(test, feature = "test-support"))]
 mod tests;
 
 pub use boxes::{Mailbox, MailboxList};
+pub use compose::{Draft, MailComposer};
 pub use list::{Mail, MailItem, MailList};
 pub use quoted::QuotedText;
 pub use reader::{Contact, MailReader, Message};
+pub use send::ScheduleSend;
+pub use signature::SignatureEditor;
 pub use thread::MailThreadView;

src/mail/send.rs

@@ -0,0 +1,248 @@
+use std::rc::Rc;
+
+use gpui::{App, ElementId, IntoElement, ParentElement, RenderOnce, Window, div, prelude::*};
+use jiff::{Timestamp, ToSpan, civil::DateTime, tz::TimeZone};
+
+use crate::{
+    buttons::{Button, ButtonVariant},
+    forms::{DateTimePicker, Run},
+    menus::{Menu, MenuItem, SplitButton},
+    overlays::Dialog,
+    primitives::IconName,
+    typography::format,
+};
+
+pub(super) type OnTime = Rc<dyn Fn(Timestamp, &mut Window, &mut App)>;
+
+/// Times to send later from `now` in `zone`: tomorrow at 8:00 and at 13:00, and the next Monday at 8:00, each named with its day and hour.
+fn presets(now: Timestamp, zone: &TimeZone) -> [(String, Timestamp); 3] {
+    let today = now.to_zoned(zone.clone()).date();
+    let tomorrow = today.tomorrow().expect("a day follows today");
+    let ahead = 7 - i64::from(today.weekday().to_monday_zero_offset());
+    let monday = today
+        .checked_add(ahead.days())
+        .expect("a Monday lies ahead");
+    let at = |day: jiff::civil::Date, hour: i8| {
+        day.at(hour, 0, 0, 0)
+            .to_zoned(zone.clone())
+            .expect("the zone holds the hour")
+            .timestamp()
+    };
+    let named = |name: &str, when: Timestamp| {
+        let hour = format::datetime(when, zone, "%a %H:%M").expect("a fixed pattern formats");
+        (format!("{name} · {hour}"), when)
+    };
+    [
+        named("Tomorrow morning", at(tomorrow, 8)),
+        named("Tomorrow afternoon", at(tomorrow, 13)),
+        named("Monday morning", at(monday, 8)),
+    ]
+}
+
+/// Whether the dialog for a time of one's own shows, and the time picked in it.
+#[derive(Default)]
+struct Picking {
+    open: bool,
+    chosen: Option<DateTime>,
+}
+
+/// Send, and beside it the times to send later: tomorrow morning, tomorrow afternoon and Monday morning in the zone given, or a time picked in a dialog. Each only with its handler; disabled, only Send shows, dimmed.
+#[derive(IntoElement)]
+pub struct ScheduleSend {
+    id: ElementId,
+    zone: Option<TimeZone>,
+    disabled: bool,
+    on_send: Option<Run>,
+    on_schedule: Option<OnTime>,
+}
+
+impl ScheduleSend {
+    pub fn new(id: impl Into<ElementId>) -> Self {
+        Self {
+            id: id.into(),
+            zone: None,
+            disabled: false,
+            on_send: None,
+            on_schedule: None,
+        }
+    }
+
+    /// The zone its times read in; the system's otherwise.
+    pub fn zone(mut self, zone: TimeZone) -> Self {
+        self.zone = Some(zone);
+        self
+    }
+
+    /// Nothing to send yet.
+    pub fn disabled(mut self, disabled: bool) -> Self {
+        self.disabled = disabled;
+        self
+    }
+
+    pub fn on_send(mut self, handler: impl Fn(&mut Window, &mut App) + 'static) -> Self {
+        self.on_send = Some(Rc::new(handler));
+        self
+    }
+
+    /// Gets the moment to send at.
+    pub fn on_schedule(
+        mut self,
+        handler: impl Fn(Timestamp, &mut Window, &mut App) + 'static,
+    ) -> Self {
+        self.on_schedule = Some(Rc::new(handler));
+        self
+    }
+}
+
+impl RenderOnce for ScheduleSend {
+    fn render(self, window: &mut Window, cx: &mut App) -> impl IntoElement {
+        let zone = self
+            .zone
+            .unwrap_or_else(|| format::system_zone("schedule send"));
+        let picking =
+            window.use_keyed_state((self.id.clone(), "picking"), cx, |_, _| Picking::default());
+        let menu = self
+            .on_schedule
+            .clone()
+            .filter(|_| !self.disabled)
+            .map(|schedule| {
+                let presets = presets(Timestamp::now(), &zone).into_iter().fold(
+                    Menu::new(),
+                    |menu, (name, at)| {
+                        let schedule = schedule.clone();
+                        menu.item(MenuItem::new(name).on_click(move |window, cx| {
+                            log::info!("schedule send: at {at}");
+                            schedule(at, window, cx)
+                        }))
+                    },
+                );
+                let opening = picking.clone();
+                presets.separator().item(
+                    MenuItem::new("Pick a time…")
+                        .icon(IconName::Calendar)
+                        .on_click(move |_, cx| {
+                            log::info!("schedule send: pick a time");
+                            opening.update(cx, |picking, cx| {
+                                picking.open = true;
+                                cx.notify();
+                            })
+                        }),
+                )
+            });
+        let send = self.on_send.clone();
+        let button = match menu {
+            Some(menu) => SplitButton::new((self.id.clone(), "send"), "Send", menu)
+                .variant(ButtonVariant::Primary)
+                .on_click(move |_, window, cx| {
+                    log::info!("schedule send: send");
+                    if let Some(send) = &send {
+                        send(window, cx);
+                    }
+                })
+                .into_any_element(),
+            None => Button::new((self.id.clone(), "send"), "Send")
+                .variant(ButtonVariant::Primary)
+                .disabled(self.disabled)
+                .on_click(move |_, window, cx| {
+                    log::info!("schedule send: send");
+                    if let Some(send) = &send {
+                        send(window, cx);
+                    }
+                })
+                .into_any_element(),
+        };
+        let now = picking.read(cx);
+        let dialog = (now.open).then(|| {
+            let chosen = now.chosen;
+            let (closing, choosing, id) = (picking.clone(), picking.clone(), self.id.clone());
+            let schedule = self.on_schedule.clone();
+            Dialog::new(
+                (self.id.clone(), "dialog"),
+                "Schedule send",
+                move |_, cx| {
+                    closing.update(cx, |picking, cx| {
+                        *picking = Picking::default();
+                        cx.notify();
+                    })
+                },
+            )
+            .detail("Pick the day and the hour it goes.")
+            .child(
+                DateTimePicker::new((id.clone(), "when"), chosen).on_change(move |at, _, cx| {
+                    choosing.update(cx, |picking, cx| {
+                        picking.chosen = Some(at);
+                        cx.notify();
+                    })
+                }),
+            )
+            .action(move |close| {
+                Button::new((id.clone(), "cancel"), "Cancel")
+                    .variant(ButtonVariant::Ghost)
+                    .on_click(move |_, window, cx| close(window, cx))
+            })
+            .action({
+                let (id, zone) = (self.id.clone(), zone.clone());
+                move |close| {
+                    Button::new((id, "schedule"), "Schedule")
+                        .variant(ButtonVariant::Primary)
+                        .disabled(chosen.is_none())
+                        .on_click(move |_, window, cx| {
+                            let at = chosen
+                                .expect("Schedule waits for a time")
+                                .to_zoned(zone.clone())
+                                .expect("the zone holds the time")
+                                .timestamp();
+                            log::info!("schedule send: at {at}");
+                            close(window, cx);
+                            if let Some(schedule) = &schedule {
+                                schedule(at, window, cx);
+                            }
+                        })
+                }
+            })
+        });
+        div().flex_none().child(button).children(dialog)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use jiff::civil::date;
+
+    use super::*;
+
+    fn at(day: i8, hour: i8) -> Timestamp {
+        date(2026, 9, day)
+            .at(hour, 0, 0, 0)
+            .to_zoned(TimeZone::UTC)
+            .expect("a UTC time")
+            .timestamp()
+    }
+
+    #[test]
+    fn presets_fall_tomorrow_and_on_the_next_monday() {
+        let [(morning, a), (afternoon, b), (monday, c)] = presets(at(26, 12), &TimeZone::UTC);
+        assert_eq!(
+            (morning.as_str(), a),
+            ("Tomorrow morning · Sun 08:00", at(27, 8))
+        );
+        assert_eq!(
+            (afternoon.as_str(), b),
+            ("Tomorrow afternoon · Sun 13:00", at(27, 13))
+        );
+        assert_eq!(
+            (monday.as_str(), c),
+            ("Monday morning · Mon 08:00", at(28, 8))
+        );
+        let [_, _, (_, next)] = presets(at(28, 9), &TimeZone::UTC);
+        assert_eq!(
+            next,
+            date(2026, 10, 5)
+                .at(8, 0, 0, 0)
+                .to_zoned(TimeZone::UTC)
+                .expect("a UTC time")
+                .timestamp(),
+            "on a Monday, the next one"
+        );
+    }
+}

src/mail/signature.rs

@@ -0,0 +1,140 @@
+use std::rc::Rc;
+
+use gpui::{
+    App, Context, Div, ElementId, Entity, IntoElement, ParentElement, RenderOnce, SharedString,
+    Styled, Subscription, Window, div, prelude::*,
+};
+
+use crate::{
+    forms::{Input, InputEvent, OnValue, TextInput},
+    theme::{ActiveTheme, TextSize},
+};
+
+/// A signature as it sits under a message: a short rule, then its lines in the muted tone.
+pub(super) fn signature_block(text: &str, cx: &App) -> Div {
+    let theme = cx.theme();
+    let colors = &theme.colors;
+    div()
+        .flex()
+        .flex_col()
+        .gap_1()
+        .text_size(theme.text_size(TextSize::Sm))
+        .text_color(colors.fg_muted)
+        .child(
+            div()
+                .w_6()
+                .mb_1()
+                .border_t_1()
+                .border_color(colors.border_strong),
+        )
+        .children(text.lines().map(|line| div().child(line.to_string())))
+}
+
+/// The field and what it last told the owner, so an echo is known from a new signature.
+struct Signed {
+    input: Entity<TextInput>,
+    seed: SharedString,
+    sent: Option<SharedString>,
+    on_change: Option<OnValue>,
+    _changes: Subscription,
+}
+
+/// Writes a signature: its lines in a field, and under it how it will sit below a message. The owner gets the words as they change; a new signature from the owner starts the field over.
+#[derive(IntoElement)]
+pub struct SignatureEditor {
+    id: ElementId,
+    text: SharedString,
+    on_change: Option<OnValue>,
+}
+
+impl SignatureEditor {
+    pub fn new(id: impl Into<ElementId>, text: impl Into<SharedString>) -> Self {
+        Self {
+            id: id.into(),
+            text: text.into(),
+            on_change: None,
+        }
+    }
+
+    /// Gets the words as they change.
+    pub fn on_change(
+        mut self,
+        handler: impl Fn(&SharedString, &mut Window, &mut App) + 'static,
+    ) -> Self {
+        self.on_change = Some(Rc::new(handler));
+        self
+    }
+}
+
+impl RenderOnce for SignatureEditor {
+    fn render(self, window: &mut Window, cx: &mut App) -> impl IntoElement {
+        let seed = self.text.clone();
+        let signed = window.use_keyed_state(
+            (self.id.clone(), "signed"),
+            cx,
+            |window, cx: &mut Context<Signed>| {
+                let input = cx.new(|cx| {
+                    let mut input = TextInput::new(window, cx)
+                        .multi_line(3, 6)
+                        .placeholder("Your name, your role, a way to reach you");
+                    input.set_text(seed.to_string(), cx);
+                    input
+                });
+                let changes =
+                    cx.subscribe_in(&input, window, |signed, input, event, window, cx| {
+                        if *event != InputEvent::Changed {
+                            return;
+                        }
+                        let words = SharedString::from(input.read(cx).text().to_string());
+                        if words == signed.seed {
+                            return;
+                        }
+                        log::info!("signature editor: {} characters", words.len());
+                        signed.sent = Some(words.clone());
+                        if let Some(on_change) = signed.on_change.clone() {
+                            on_change(&words, window, cx);
+                        }
+                        cx.notify();
+                    });
+                Signed {
+                    input,
+                    seed: seed.clone(),
+                    sent: None,
+                    on_change: None,
+                    _changes: changes,
+                }
+            },
+        );
+        let text = self.text.clone();
+        signed.update(cx, |signed, cx| {
+            signed.on_change = self.on_change.clone();
+            if signed.seed == text {
+                return;
+            }
+            signed.seed = text.clone();
+            if signed.sent.as_ref() == Some(&text) {
+                return;
+            }
+            log::info!("signature editor: started over");
+            signed
+                .input
+                .update(cx, |input, cx| input.set_text(text.to_string(), cx));
+        });
+        let input = signed.read(cx).input.clone();
+        let words = input.read(cx).text().to_string();
+        let theme = cx.theme();
+        div()
+            .w_full()
+            .flex()
+            .flex_col()
+            .gap_3()
+            .child(Input::new(&input))
+            .child(
+                div()
+                    .text_size(theme.text_size(TextSize::Xs))
+                    .text_color(theme.colors.fg_subtle)
+                    .child("Under each message"),
+            )
+            .child(signature_block(&words, cx))
+    }
+}

src/mail/tests/mod.rs

@@ -11,6 +11,7 @@ use crate::{
 };
 
 mod read;
+mod write;
 
 fn setup(cx: &mut TestAppContext) {
     cx.update(|cx| {

src/mail/tests/write.rs

@@ -0,0 +1,232 @@
+use gpui::{
+    Context, Entity, IntoElement, Render, SharedString, TestAppContext, VisualTestContext, Window,
+};
+use jiff::{Timestamp, tz::TimeZone};
+
+use super::{Mailing, heard, mailing, note, press, settle, tab_to};
+use crate::{
+    forms,
+    mail::{Contact, MailComposer, ScheduleSend, SignatureEditor},
+};
+
+fn contacts() -> [Contact; 2] {
+    [
+        Contact::new("Ana Lima", "ana@atrium.studio"),
+        Contact::new("Ben Ito", "ben@atrium.studio"),
+    ]
+}
+
+fn composer(owner: Entity<Mailing>) -> gpui::AnyElement {
+    let (send, discard) = (owner.clone(), owner);
+    MailComposer::new("composer")
+        .contacts(contacts())
+        .on_send(move |draft, _, cx| {
+            note(
+                &send,
+                format!(
+                    "send {} | {} | {}",
+                    draft.to.join(","),
+                    draft.subject,
+                    draft.body
+                ),
+                cx,
+            )
+        })
+        .on_discard(move |_, cx| note(&discard, "discard".into(), cx))
+        .into_any_element()
+}
+
+fn writing(
+    part: fn(Entity<Mailing>) -> gpui::AnyElement,
+    cx: &mut TestAppContext,
+) -> (Entity<Mailing>, &mut VisualTestContext) {
+    let (host, cx) = mailing(part, cx);
+    cx.update(|_, cx| forms::bind_keys(cx));
+    (host, cx)
+}
+
+fn next(cx: &mut VisualTestContext) {
+    cx.update(|window, _| window.focus_next());
+    settle(cx);
+}
+
+#[gpui::test]
+fn a_suggested_person_a_subject_and_words_go_out_as_one_draft(cx: &mut TestAppContext) {
+    let (host, cx) = writing(composer, cx);
+    tab_to(1, cx);
+    cx.simulate_input("be");
+    settle(cx);
+    press("enter", cx);
+    next(cx);
+    next(cx);
+    cx.simulate_input("Samples");
+    next(cx);
+    cx.simulate_input("They are dry.");
+    next(cx);
+    press("space", cx);
+    assert_eq!(
+        heard(&host, cx),
+        ["send ben@atrium.studio | Samples | They are dry."]
+    );
+}
+
+#[gpui::test]
+fn cc_and_bcc_show_once_asked(cx: &mut TestAppContext) {
+    let (_, cx) = writing(composer, cx);
+    assert!(cx.debug_bounds("composer-Cc").is_none());
+    tab_to(2, cx);
+    press("space", cx);
+    assert!(cx.debug_bounds("composer-Cc").is_some());
+    assert!(cx.debug_bounds("composer-Bcc").is_some());
+}
+
+#[gpui::test]
+fn with_nobody_to_send_to_send_steps_aside_for_discard(cx: &mut TestAppContext) {
+    let (host, cx) = writing(composer, cx);
+    tab_to(5, cx);
+    press("space", cx);
+    assert_eq!(
+        heard(&host, cx),
+        ["discard"],
+        "Send is off, so the stop after the words is Discard"
+    );
+}
+
+fn scheduling(owner: Entity<Mailing>) -> gpui::AnyElement {
+    let (send, later) = (owner.clone(), owner);
+    ScheduleSend::new("send")
+        .zone(TimeZone::UTC)
+        .on_send(move |_, cx| note(&send, "send".into(), cx))
+        .on_schedule(move |at, _, cx| note(&later, format!("at {at}"), cx))
+        .into_any_element()
+}
+
+#[gpui::test]
+fn the_first_time_to_send_later_is_tomorrow_morning(cx: &mut TestAppContext) {
+    let (host, cx) = writing(scheduling, cx);
+    tab_to(2, cx);
+    press("enter", cx);
+    press("enter", cx);
+    let morning = Timestamp::now()
+        .to_zoned(TimeZone::UTC)
+        .date()
+        .tomorrow()
+        .expect("a day follows")
+        .at(8, 0, 0, 0)
+        .to_zoned(TimeZone::UTC)
+        .expect("a UTC time")
+        .timestamp();
+    assert_eq!(heard(&host, cx), [format!("at {morning}")]);
+}
+
+/// A signature the host keeps, and every change it heard.
+struct Signing {
+    words: SharedString,
+    heard: Vec<String>,
+}
+
+impl Render for Signing {
+    fn render(&mut self, _: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
+        let owner = cx.entity();
+        SignatureEditor::new("signature", self.words.clone()).on_change(move |words, _, cx| {
+            owner.update(cx, |host, cx| {
+                host.heard.push(words.to_string());
+                host.words = words.clone();
+                cx.notify();
+            })
+        })
+    }
+}
+
+fn signing<'a>(
+    words: &str,
+    cx: &'a mut TestAppContext,
+) -> (Entity<Signing>, &'a mut VisualTestContext) {
+    super::setup(cx);
+    cx.update(forms::bind_keys);
+    let (host, cx) = cx.add_window_view(|_, _| Signing {
+        words: SharedString::from(words.to_string()),
+        heard: Vec::new(),
+    });
+    cx.update(|window, _| window.activate_window());
+    settle(cx);
+    (host, cx)
+}
+
+#[gpui::test]
+fn an_echo_keeps_the_caret_where_it_is(cx: &mut TestAppContext) {
+    let (host, cx) = signing("", cx);
+    tab_to(1, cx);
+    cx.simulate_input("ab");
+    settle(cx);
+    press("left", cx);
+    cx.simulate_input("X");
+    settle(cx);
+    cx.simulate_input("Y");
+    settle(cx);
+    let heard = host.read_with(cx, |host, _| host.heard.clone());
+    assert_eq!(
+        heard.last().map(String::as_str),
+        Some("aXYb"),
+        "the caret stayed after X"
+    );
+}
+
+#[gpui::test]
+fn a_new_signature_from_the_owner_starts_the_field_over(cx: &mut TestAppContext) {
+    let (host, cx) = signing("Ana", cx);
+    host.update(cx, |host, cx| {
+        host.words = "Ben Ito".into();
+        cx.notify();
+    });
+    settle(cx);
+    tab_to(1, cx);
+    cx.simulate_input("!");
+    settle(cx);
+    let heard = host.read_with(cx, |host, _| host.heard.clone());
+    assert_eq!(heard, ["Ben Ito!"]);
+}
+
+/// A composer the host starts from an address, and what it sent.
+struct Replying {
+    to: SharedString,
+    sent: Vec<String>,
+}
+
+impl Render for Replying {
+    fn render(&mut self, _: &mut Window, cx: &mut Context<Self>) -> impl IntoElement {
+        let owner = cx.entity();
+        MailComposer::new("composer")
+            .to([self.to.clone()])
+            .subject("Re: Samples")
+            .on_send(move |draft, _, cx| {
+                owner.update(cx, |host, _| {
+                    host.sent
+                        .push(format!("{} | {}", draft.to.join(","), draft.subject))
+                })
+            })
+    }
+}
+
+#[gpui::test]
+fn a_new_start_from_the_owner_begins_the_draft_over(cx: &mut TestAppContext) {
+    super::setup(cx);
+    cx.update(forms::bind_keys);
+    let (host, cx) = cx.add_window_view(|_, _| Replying {
+        to: "ana@atrium.studio".into(),
+        sent: Vec::new(),
+    });
+    cx.update(|window, _| window.activate_window());
+    settle(cx);
+    host.update(cx, |host, cx| {
+        host.to = "ben@atrium.studio".into();
+        cx.notify();
+    });
+    settle(cx);
+    tab_to(5, cx);
+    press("space", cx);
+    assert_eq!(
+        host.read_with(cx, |host, _| host.sent.clone()),
+        ["ben@atrium.studio | Re: Samples"]
+    );
+}