maestro/crates/maestro-tui/src/input.rs

//! `InputKey` — canonical, hashable representation of one keyboard or mouse
//! event. Used as the key in the keymap table (so users can write
//! `"ctrl-w h"` or `"mouse:click(pane)"` in TOML and we match the same string
//! at runtime).
//!
//! Also home to [`ChordState`], the small state machine that holds keys when
//! they extend a known prefix (`g` waiting for `t` to make `g t`).

use std::collections::HashSet;
use std::time::{Duration, Instant};

use crossterm::event::{
    Event as CtEvent, KeyCode, KeyEvent, KeyModifiers, MouseButton, MouseEvent, MouseEventKind,
};

/// Canonical input event. `Char` carries modifier flags; specials get their
/// own variant. Mouse events carry a resolved `Region` so the keymap can bind
/// per-region (`mouse:click(pane)` vs `mouse:click(sidebar-row)`).
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum InputKey {
    Char {
        c: char,
        ctrl: bool,
        alt: bool,
        shift: bool,
    },
    Esc,
    Enter,
    Tab,
    /// Shift-Tab. crossterm reports it as its own key code, not a modified Tab.
    BackTab,
    Backspace,
    Up,
    Down,
    Left,
    Right,
    Home,
    End,
    PageUp,
    PageDown,
    Delete,
    /// Bracketed paste: crossterm delivers the whole payload as one event, so
    /// text fields can insert it as a single operation.
    Paste(String),
    Mouse {
        kind: MouseKind,
        region: Region,
        col: u16,
        row: u16,
    },
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum MouseKind {
    Click,
    DblClick,
    Drag,
    ScrollUp,
    ScrollDown,
}

/// Regions the renderer tags so the input router can bind mouse events to
/// specific UI surfaces. The render layer fills in the `RegionMap` (added in
/// NAP-280); for now only the enum is needed.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Region {
    SidebarRow,
    Pane,
    Modal,
    Unknown,
}

#[derive(Debug, thiserror::Error, PartialEq, Eq)]
pub enum InputParseError {
    #[error("malformed input key {0:?}")]
    Malformed(String),
    #[error("unknown mouse kind {0:?}")]
    UnknownMouseKind(String),
    #[error("unknown region {0:?}")]
    UnknownRegion(String),
}

impl InputKey {
    /// Construct a bare-character key (no modifiers).
    pub fn char(c: char) -> Self {
        Self::Char {
            c,
            ctrl: false,
            alt: false,
            shift: false,
        }
    }

    /// Construct a `ctrl-<c>` key.
    pub fn ctrl_char(c: char) -> Self {
        Self::Char {
            c,
            ctrl: true,
            alt: false,
            shift: false,
        }
    }

    /// Canonical-string form used by the keymap table. Round-trips with
    /// [`InputKey::parse`].
    pub fn canonical(&self) -> String {
        match self {
            InputKey::Char {
                c,
                ctrl,
                alt,
                shift,
            } => {
                let mut out = String::new();
                if *ctrl {
                    out.push_str("ctrl-");
                }
                if *alt {
                    out.push_str("alt-");
                }
                // Uppercase already implies shift; crossterm sets the flag
                // on every such char, so skip the redundant prefix (#70).
                if *shift && !c.is_uppercase() {
                    out.push_str("shift-");
                }
                out.push(*c);
                out
            }
            InputKey::Esc => "esc".into(),
            InputKey::Enter => "enter".into(),
            InputKey::Tab => "tab".into(),
            InputKey::BackTab => "backtab".into(),
            InputKey::Backspace => "backspace".into(),
            InputKey::Up => "up".into(),
            InputKey::Down => "down".into(),
            InputKey::Left => "left".into(),
            InputKey::Right => "right".into(),
            InputKey::Home => "home".into(),
            InputKey::End => "end".into(),
            InputKey::PageUp => "pageup".into(),
            InputKey::PageDown => "pagedown".into(),
            InputKey::Delete => "delete".into(),
            // Pastes are not bindable; the canonical form exists only to
            // satisfy exhaustiveness and never round-trips through `parse`.
            InputKey::Paste(_) => "paste".into(),
            InputKey::Mouse { kind, region, .. } => {
                let k = match kind {
                    MouseKind::Click => "click",
                    MouseKind::DblClick => "dblclick",
                    MouseKind::Drag => "drag",
                    MouseKind::ScrollUp => "scrollup",
                    MouseKind::ScrollDown => "scrolldown",
                };
                let r = match region {
                    Region::SidebarRow => "sidebar-row",
                    Region::Pane => "pane",
                    Region::Modal => "modal",
                    Region::Unknown => "unknown",
                };
                format!("mouse:{k}({r})")
            }
        }
    }

    /// Parse a canonical string into an [`InputKey`]. Mouse events parse with
    /// `col = row = 0`; in practice mouse keys are only constructed from real
    /// events, but parsing is needed so [`Keymap::set`](crate::keymap::Keymap::set)
    /// can validate keymap entries written in TOML.
    pub fn parse(s: &str) -> Result<Self, InputParseError> {
        if let Some(rest) = s.strip_prefix("mouse:") {
            let (k, rest) = rest
                .split_once('(')
                .ok_or_else(|| InputParseError::Malformed(s.into()))?;
            let r = rest
                .strip_suffix(')')
                .ok_or_else(|| InputParseError::Malformed(s.into()))?;
            let kind = match k {
                "click" => MouseKind::Click,
                "dblclick" => MouseKind::DblClick,
                "drag" => MouseKind::Drag,
                "scrollup" => MouseKind::ScrollUp,
                "scrolldown" => MouseKind::ScrollDown,
                other => return Err(InputParseError::UnknownMouseKind(other.into())),
            };
            let region = match r {
                "sidebar-row" => Region::SidebarRow,
                "pane" => Region::Pane,
                "modal" => Region::Modal,
                "unknown" => Region::Unknown,
                other => return Err(InputParseError::UnknownRegion(other.into())),
            };
            return Ok(InputKey::Mouse {
                kind,
                region,
                col: 0,
                row: 0,
            });
        }
        match s {
            "esc" => return Ok(InputKey::Esc),
            "enter" => return Ok(InputKey::Enter),
            "tab" => return Ok(InputKey::Tab),
            "backtab" => return Ok(InputKey::BackTab),
            "backspace" => return Ok(InputKey::Backspace),
            "up" => return Ok(InputKey::Up),
            "down" => return Ok(InputKey::Down),
            "left" => return Ok(InputKey::Left),
            "right" => return Ok(InputKey::Right),
            "home" => return Ok(InputKey::Home),
            "end" => return Ok(InputKey::End),
            "pageup" => return Ok(InputKey::PageUp),
            "pagedown" => return Ok(InputKey::PageDown),
            "delete" => return Ok(InputKey::Delete),
            _ => {}
        }
        // Modifier chain: ctrl-, alt-, shift- prefixes, then a single char.
        let mut ctrl = false;
        let mut alt = false;
        let mut shift = false;
        let mut rest = s;
        loop {
            if let Some(r) = rest.strip_prefix("ctrl-") {
                ctrl = true;
                rest = r;
                continue;
            }
            if let Some(r) = rest.strip_prefix("alt-") {
                alt = true;
                rest = r;
                continue;
            }
            if let Some(r) = rest.strip_prefix("shift-") {
                shift = true;
                rest = r;
                continue;
            }
            break;
        }
        let mut chars = rest.chars();
        let c = chars
            .next()
            .ok_or_else(|| InputParseError::Malformed(s.into()))?;
        if chars.next().is_some() {
            return Err(InputParseError::Malformed(s.into()));
        }
        Ok(InputKey::Char {
            c,
            ctrl,
            alt,
            shift,
        })
    }
}

/// Convert a raw `crossterm` event into a canonical [`InputKey`]. `region_for`
/// is the renderer's hit-test closure (resolves a screen coordinate to one
/// tagged region).
pub fn canonicalise<F>(ev: &CtEvent, region_for: F) -> Option<InputKey>
where
    F: FnOnce(u16, u16) -> Region,
{
    match ev {
        CtEvent::Key(KeyEvent {
            code, modifiers, ..
        }) => {
            let ctrl = modifiers.contains(KeyModifiers::CONTROL);
            let alt = modifiers.contains(KeyModifiers::ALT);
            let shift = modifiers.contains(KeyModifiers::SHIFT);
            Some(match code {
                KeyCode::Char(c) => InputKey::Char {
                    c: *c,
                    ctrl,
                    alt,
                    shift,
                },
                KeyCode::Esc => InputKey::Esc,
                KeyCode::Enter => InputKey::Enter,
                KeyCode::Tab => InputKey::Tab,
                KeyCode::BackTab => InputKey::BackTab,
                KeyCode::Backspace => InputKey::Backspace,
                KeyCode::Up => InputKey::Up,
                KeyCode::Down => InputKey::Down,
                KeyCode::Left => InputKey::Left,
                KeyCode::Right => InputKey::Right,
                KeyCode::Home => InputKey::Home,
                KeyCode::End => InputKey::End,
                KeyCode::PageUp => InputKey::PageUp,
                KeyCode::PageDown => InputKey::PageDown,
                KeyCode::Delete => InputKey::Delete,
                _ => return None,
            })
        }
        CtEvent::Paste(text) => Some(InputKey::Paste(text.clone())),
        CtEvent::Mouse(MouseEvent {
            kind, column, row, ..
        }) => {
            let mk = match kind {
                MouseEventKind::Down(MouseButton::Left) => MouseKind::Click,
                MouseEventKind::Drag(MouseButton::Left) => MouseKind::Drag,
                MouseEventKind::ScrollUp => MouseKind::ScrollUp,
                MouseEventKind::ScrollDown => MouseKind::ScrollDown,
                _ => return None,
            };
            let region = region_for(*column, *row);
            Some(InputKey::Mouse {
                kind: mk,
                region,
                col: *column,
                row: *row,
            })
        }
        _ => None,
    }
}

/// How long after a click a second click at the same cell counts as a
/// double-click. Matches the common desktop default.
pub const DOUBLE_CLICK_WINDOW: Duration = Duration::from_millis(400);

/// Remembers the last click so a second one at the same cell can be promoted to
/// [`MouseKind::DblClick`].
///
/// Kept out of [`canonicalise`], which stays a pure function of one event.
#[derive(Debug, Default)]
pub struct ClickTracker {
    last: Option<(u16, u16, Instant)>,
}

impl ClickTracker {
    pub fn new() -> Self {
        Self::default()
    }

    /// Upgrade a `Click` to a `DblClick` when it *immediately* follows another
    /// click at the same cell inside [`DOUBLE_CLICK_WINDOW`].
    ///
    /// Anything else passes through and clears the pending click: two clicks
    /// with a drag or a keystroke between them are two clicks, however fast.
    ///
    /// A promoted click also resets the tracker, so three rapid clicks are a
    /// click then a double-click, not two double-clicks.
    pub fn promote(&mut self, key: InputKey, now: Instant) -> InputKey {
        let InputKey::Mouse {
            kind: MouseKind::Click,
            region,
            col,
            row,
        } = key
        else {
            self.last = None;
            return key;
        };

        let is_double = matches!(
            self.last,
            Some((c, r, at))
                if c == col && r == row && now.duration_since(at) <= DOUBLE_CLICK_WINDOW
        );
        if is_double {
            self.last = None;
            return InputKey::Mouse {
                kind: MouseKind::DblClick,
                region,
                col,
                row,
            };
        }
        self.last = Some((col, row, now));
        key
    }
}

/// Result of feeding one key into [`ChordState`]. `Pending` = held because the
/// current sequence is a strict prefix of some known binding; `Resolved` =
/// dispatch this canonical string against the keymap.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum ChordResult {
    Pending,
    Resolved(String),
}

/// Tracks the partial-chord state ("the user has pressed `g`, waiting up to
/// `timeout` for the next key"). Per-cycle: when a key comes in, decide
/// whether to hold or resolve.
#[derive(Debug)]
pub struct ChordState {
    held: Vec<String>,
    last_press: Option<Instant>,
    timeout: Duration,
    /// A key bumped out of an abandoned chord (see [`Self::feed`]), waiting
    /// to be replayed as a fresh keystroke by the caller.
    replay: Option<InputKey>,
}

impl ChordState {
    pub fn new(timeout: Duration) -> Self {
        Self {
            held: Vec::new(),
            last_press: None,
            timeout,
            replay: None,
        }
    }

    /// Feed one canonical key.
    ///
    /// * `Pending` — the held sequence is a strict prefix of at least one
    ///   binding; wait for the next key.
    /// * `Resolved(s)` — `s` is the canonical chord (or single key) to look
    ///   up in the keymap. The held buffer is cleared.
    ///
    /// A held prefix that is itself directly bound (e.g. a leader key bound
    /// alone as well as chorded, like `ctrl-a` and `ctrl-a ctrl-k`) resolves
    /// to that binding the moment the next key fails to extend it, rather
    /// than swallowing the held key and losing its meaning — the new key
    /// never belonged to the chord and is handed back via [`Self::take_replay`]
    /// so the caller can process it as its own keystroke.
    pub fn feed(&mut self, key: &InputKey, known_bindings: &HashSet<String>) -> ChordResult {
        if let Some(t) = self.last_press {
            if t.elapsed() > self.timeout {
                self.held.clear();
            }
        }
        let key_s = key.canonical();
        let candidate = if self.held.is_empty() {
            key_s.clone()
        } else {
            format!("{} {}", self.held.join(" "), key_s)
        };

        // A "strict prefix" check: is there a known binding that starts with
        // `candidate + ' '`? If so, we should hold and wait for more.
        let prefix_marker = format!("{candidate} ");
        let is_prefix = known_bindings
            .iter()
            .any(|kb| kb.starts_with(&prefix_marker));

        self.last_press = Some(Instant::now());

        if is_prefix {
            self.held.push(key_s);
            return ChordResult::Pending;
        }

        if known_bindings.contains(&candidate) {
            self.held.clear();
            return ChordResult::Resolved(candidate);
        }

        if !self.held.is_empty() {
            let held_str = self.held.join(" ");
            self.held.clear();
            if known_bindings.contains(&held_str) {
                self.replay = Some(key.clone());
                return ChordResult::Resolved(held_str);
            }
        }

        ChordResult::Resolved(candidate)
    }

    /// Take the key bumped out of an abandoned chord by the last [`Self::feed`]
    /// call, if any. The caller feeds it through again as a brand new
    /// keystroke.
    pub fn take_replay(&mut self) -> Option<InputKey> {
        self.replay.take()
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn click(col: u16, row: u16) -> InputKey {
        InputKey::Mouse {
            kind: MouseKind::Click,
            region: Region::SidebarRow,
            col,
            row,
        }
    }

    /// The shipped default binds `mouse:dblclick(sidebar-row)`. Nothing could
    /// produce a DblClick, so that binding could never fire.
    #[test]
    fn a_second_click_at_the_same_cell_becomes_a_double_click() {
        let mut t = ClickTracker::new();
        let t0 = Instant::now();

        assert_eq!(t.promote(click(3, 4), t0), click(3, 4));
        assert_eq!(
            t.promote(click(3, 4), t0 + Duration::from_millis(100)),
            InputKey::Mouse {
                kind: MouseKind::DblClick,
                region: Region::SidebarRow,
                col: 3,
                row: 4,
            }
        );
    }

    #[test]
    fn a_slow_second_click_stays_a_click() {
        let mut t = ClickTracker::new();
        let t0 = Instant::now();
        t.promote(click(3, 4), t0);
        let late = t0 + DOUBLE_CLICK_WINDOW + Duration::from_millis(1);
        assert_eq!(t.promote(click(3, 4), late), click(3, 4));
    }

    #[test]
    fn a_second_click_elsewhere_stays_a_click() {
        let mut t = ClickTracker::new();
        let t0 = Instant::now();
        t.promote(click(3, 4), t0);
        assert_eq!(
            t.promote(click(9, 4), t0 + Duration::from_millis(10)),
            click(9, 4)
        );
    }

    /// Three fast clicks are click, double-click, click — not two doubles.
    #[test]
    fn a_promoted_click_resets_the_tracker() {
        let mut t = ClickTracker::new();
        let t0 = Instant::now();
        t.promote(click(1, 1), t0);
        let second = t.promote(click(1, 1), t0 + Duration::from_millis(50));
        assert!(matches!(
            second,
            InputKey::Mouse {
                kind: MouseKind::DblClick,
                ..
            }
        ));
        let third = t.promote(click(1, 1), t0 + Duration::from_millis(100));
        assert_eq!(third, click(1, 1));
    }

    #[test]
    fn non_click_events_pass_through_untouched() {
        let mut t = ClickTracker::new();
        assert_eq!(t.promote(InputKey::Enter, Instant::now()), InputKey::Enter);
    }

    /// A drag between two clicks means the user dragged, not double-clicked —
    /// even at the same cell and well inside the window.
    #[test]
    fn a_drag_between_two_clicks_breaks_the_double() {
        let mut t = ClickTracker::new();
        let t0 = Instant::now();
        t.promote(click(3, 4), t0);

        let drag = InputKey::Mouse {
            kind: MouseKind::Drag,
            region: Region::SidebarRow,
            col: 3,
            row: 4,
        };
        assert_eq!(
            t.promote(drag.clone(), t0 + Duration::from_millis(20)),
            drag
        );

        assert_eq!(
            t.promote(click(3, 4), t0 + Duration::from_millis(40)),
            click(3, 4),
            "a drag must clear the pending click"
        );
    }

    #[test]
    fn a_keystroke_between_two_clicks_breaks_the_double() {
        let mut t = ClickTracker::new();
        let t0 = Instant::now();
        t.promote(click(3, 4), t0);
        t.promote(InputKey::Enter, t0 + Duration::from_millis(20));

        assert_eq!(
            t.promote(click(3, 4), t0 + Duration::from_millis(40)),
            click(3, 4)
        );
    }

    /// A scroll also counts as an intervening event.
    #[test]
    fn a_scroll_between_two_clicks_breaks_the_double() {
        let mut t = ClickTracker::new();
        let t0 = Instant::now();
        t.promote(click(3, 4), t0);
        let scroll = InputKey::Mouse {
            kind: MouseKind::ScrollUp,
            region: Region::SidebarRow,
            col: 3,
            row: 4,
        };
        t.promote(scroll, t0 + Duration::from_millis(20));

        assert_eq!(
            t.promote(click(3, 4), t0 + Duration::from_millis(40)),
            click(3, 4)
        );
    }

    #[test]
    fn back_tab_round_trips_through_the_canonical_form() {
        assert_eq!(InputKey::BackTab.canonical(), "backtab");
        assert_eq!(InputKey::parse("backtab").unwrap(), InputKey::BackTab);
    }

    /// The parser must not accept region names the renderer cannot produce.
    #[test]
    fn unproducible_region_names_are_rejected() {
        assert!(InputKey::parse("mouse:click(sidebar)").is_err());
        assert!(InputKey::parse("mouse:click(split-divider)").is_err());
        assert!(InputKey::parse("mouse:click(sidebar-row)").is_ok());
    }

    #[test]
    fn canonical_round_trips_simple_chars() {
        for s in ["a", "ctrl-a", "ctrl-w", "alt-x"] {
            let k = InputKey::parse(s).unwrap();
            assert_eq!(k.canonical(), s, "round-trip {s:?}");
        }
    }

    /// crossterm 0.28 attaches `KeyModifiers::SHIFT` to any uppercase char,
    /// so a real Shift+S delivers `Char { c: 'S', shift: true }`. Its
    /// canonical form must be the bare `"S"` a keymap binds, not `"shift-S"` —
    /// the uppercase letter already says "shifted"; a redundant prefix would
    /// make every uppercase binding (the default `N`) unreachable from the
    /// keyboard (#70).
    #[test]
    fn shift_flag_is_redundant_for_an_already_uppercase_char() {
        let k = InputKey::Char {
            c: 'S',
            ctrl: false,
            alt: false,
            shift: true,
        };
        assert_eq!(k.canonical(), "S");
    }

    #[test]
    fn canonical_round_trips_specials() {
        for s in [
            "esc",
            "enter",
            "tab",
            "backspace",
            "up",
            "down",
            "left",
            "right",
            "home",
            "end",
            "pageup",
            "pagedown",
            "delete",
        ] {
            let k = InputKey::parse(s).unwrap();
            assert_eq!(k.canonical(), s, "round-trip {s:?}");
        }
    }

    /// A bracketed paste must arrive as one key carrying the whole payload,
    /// not a burst of per-character keys.
    #[test]
    fn canonicalise_paste_event_carries_the_whole_payload() {
        use crossterm::event::Event as CtEvent;
        let ev = CtEvent::Paste("/srv/work/maestro".into());
        let k = canonicalise(&ev, |_, _| Region::Unknown).unwrap();
        assert_eq!(k, InputKey::Paste("/srv/work/maestro".into()));
    }

    #[test]
    fn canonical_round_trips_mouse() {
        let s = "mouse:click(pane)";
        let k = InputKey::parse(s).unwrap();
        assert_eq!(k.canonical(), s);
        let s = "mouse:dblclick(sidebar-row)";
        let k = InputKey::parse(s).unwrap();
        assert_eq!(k.canonical(), s);
    }

    #[test]
    fn parse_rejects_unknown_modifier() {
        assert_eq!(
            InputKey::parse("ctrl-glorb").unwrap_err(),
            InputParseError::Malformed("ctrl-glorb".into()),
        );
    }

    #[test]
    fn parse_rejects_unknown_mouse_kind() {
        assert_eq!(
            InputKey::parse("mouse:zoom(pane)").unwrap_err(),
            InputParseError::UnknownMouseKind("zoom".into()),
        );
    }

    #[test]
    fn parse_rejects_unknown_region() {
        assert_eq!(
            InputKey::parse("mouse:click(margin)").unwrap_err(),
            InputParseError::UnknownRegion("margin".into()),
        );
    }

    #[test]
    fn canonicalise_key_event() {
        use crossterm::event::{KeyCode, KeyEvent, KeyModifiers};
        let ev = CtEvent::Key(KeyEvent::new(KeyCode::Char('a'), KeyModifiers::CONTROL));
        let k = canonicalise(&ev, |_, _| Region::Unknown).unwrap();
        assert_eq!(k, InputKey::ctrl_char('a'));
    }

    #[test]
    fn canonicalise_mouse_event_uses_region_callback() {
        use crossterm::event::{KeyModifiers, MouseButton, MouseEvent, MouseEventKind};
        let ev = CtEvent::Mouse(MouseEvent {
            kind: MouseEventKind::Down(MouseButton::Left),
            column: 10,
            row: 5,
            modifiers: KeyModifiers::NONE,
        });
        let k = canonicalise(&ev, |c, r| {
            assert_eq!((c, r), (10, 5));
            Region::Pane
        })
        .unwrap();
        assert!(matches!(
            k,
            InputKey::Mouse {
                kind: MouseKind::Click,
                region: Region::Pane,
                col: 10,
                row: 5,
            }
        ));
    }

    #[test]
    fn chord_state_holds_known_prefix() {
        let mut chord = ChordState::new(Duration::from_secs(10));
        let known: HashSet<String> = ["g t".into()].into_iter().collect();

        let r = chord.feed(&InputKey::char('g'), &known);
        assert_eq!(r, ChordResult::Pending);

        let r = chord.feed(&InputKey::char('t'), &known);
        assert_eq!(r, ChordResult::Resolved("g t".into()));
    }

    #[test]
    fn chord_state_drops_unknown_continuation() {
        let mut chord = ChordState::new(Duration::from_secs(10));
        let known: HashSet<String> = ["g t".into()].into_iter().collect();

        chord.feed(&InputKey::char('g'), &known);
        let r = chord.feed(&InputKey::char('x'), &known);
        // 'g' was a prefix candidate, but 'g x' isn't a binding;
        // resolver drops 'g' and treats 'x' as a fresh single-key resolve.
        assert_eq!(r, ChordResult::Resolved("g x".into()));
    }

    /// A key bound both alone and as a chord prefix (the leader: `ctrl-a` and
    /// `ctrl-a ctrl-k`) must still fire its own binding when the next key
    /// doesn't complete the chord — the held key's meaning isn't lost, and
    /// the new key comes back via `take_replay` for the caller to process on
    /// its own (#156).
    #[test]
    fn a_bound_prefix_resolves_itself_and_replays_the_breaking_key() {
        let mut chord = ChordState::new(Duration::from_secs(10));
        let known: HashSet<String> = ["ctrl-a".into(), "ctrl-a ctrl-k".into()]
            .into_iter()
            .collect();

        let r = chord.feed(&InputKey::ctrl_char('a'), &known);
        assert_eq!(r, ChordResult::Pending);

        let r = chord.feed(&InputKey::char('j'), &known);
        assert_eq!(r, ChordResult::Resolved("ctrl-a".into()));
        assert_eq!(chord.take_replay(), Some(InputKey::char('j')));
    }

    /// The full chord still resolves normally when the next key completes
    /// it — no replay, no early fire of the shorter binding.
    #[test]
    fn a_completed_chord_off_a_bound_prefix_has_no_replay() {
        let mut chord = ChordState::new(Duration::from_secs(10));
        let known: HashSet<String> = ["ctrl-a".into(), "ctrl-a ctrl-k".into()]
            .into_iter()
            .collect();

        chord.feed(&InputKey::ctrl_char('a'), &known);
        let r = chord.feed(&InputKey::ctrl_char('k'), &known);
        assert_eq!(r, ChordResult::Resolved("ctrl-a ctrl-k".into()));
        assert_eq!(chord.take_replay(), None);
    }

    #[test]
    fn chord_state_lone_key_resolves_immediately() {
        let mut chord = ChordState::new(Duration::from_secs(10));
        let known: HashSet<String> = ["i".into(), "g t".into()].into_iter().collect();

        let r = chord.feed(&InputKey::char('i'), &known);
        // 'i' is a complete binding, not a strict prefix of anything → resolve.
        assert_eq!(r, ChordResult::Resolved("i".into()));
    }
}