cranpose_ui/

text_input_session.rs

//! Platform text-input session: soft-keyboard visibility hooks.
//!
//! Platforms with an on-screen keyboard (Android, iOS, some Linux shells)
//! install a [`PlatformTextInputHandler`] so the framework can tell them when
//! editable text gains or loses focus. The text-field focus manager
//! ([`crate::text_field_focus`]) fires these notifications:
//!
//! - a text field acquired focus → `notify_text_input_focus_gained` →
//!   `show_keyboard`
//! - focus was explicitly cleared, or the focused field left the composition →
//!   `notify_text_input_focus_lost` → `hide_keyboard`
//!
//! `show_keyboard` fires on *every* focus request, including taps on an
//! already-focused field. This is intentional: the user may have dismissed the
//! keyboard (e.g. Android back gesture) without the framework knowing, and
//! tapping the field again must bring it back. Platform show/hide calls are
//! expected to be idempotent. `hide_keyboard` is only forwarded when the
//! framework previously requested the keyboard, so repeated stale-focus checks
//! do not spam the platform.
//!
//! The handler is stored per [`AppContext`](crate::render_state::AppContext),
//! like the focus state itself, so multiple app instances in one process do
//! not observe each other's keyboards.

use std::{
    cell::{Cell, RefCell},
    rc::Rc,
};

/// Callbacks a platform installs to control its on-screen keyboard.
///
/// Implementations must be idempotent: `show_keyboard` may be invoked while
/// the keyboard is already visible (every tap on a text field re-requests it)
/// and `hide_keyboard` may race a keyboard the user already dismissed.
pub trait PlatformTextInputHandler {
    /// A text field gained focus; the platform should show its soft keyboard.
    fn show_keyboard(&self);
    /// No text field is focused anymore; the platform should hide its soft
    /// keyboard.
    fn hide_keyboard(&self);
}

pub(crate) struct PlatformTextInputState {
    handler: RefCell<Option<Rc<dyn PlatformTextInputHandler>>>,
    keyboard_requested: Cell<bool>,
}

impl PlatformTextInputState {
    pub(crate) fn new() -> Self {
        Self {
            handler: RefCell::new(None),
            keyboard_requested: Cell::new(false),
        }
    }

    fn set_handler(&self, handler: Option<Rc<dyn PlatformTextInputHandler>>) {
        *self.handler.borrow_mut() = handler;
        self.keyboard_requested.set(false);
    }

    fn handler(&self) -> Option<Rc<dyn PlatformTextInputHandler>> {
        self.handler.borrow().clone()
    }
}

/// Installs the platform soft-keyboard handler for the current app context.
///
/// Replaces any previously installed handler. Must be called inside an app
/// context (platform runtimes go through
/// `AppShell::set_platform_text_input`).
pub fn set_platform_text_input_handler(handler: Rc<dyn PlatformTextInputHandler>) {
    crate::render_state::with_text_input_session(|state| state.set_handler(Some(handler)));
}

/// Removes the installed platform soft-keyboard handler, if any.
pub fn clear_platform_text_input_handler() {
    crate::render_state::with_text_input_session(|state| state.set_handler(None));
}

pub(crate) fn notify_text_input_focus_gained() {
    let handler = crate::render_state::with_text_input_session(|state| {
        let handler = state.handler();
        if handler.is_some() {
            state.keyboard_requested.set(true);
        }
        handler
    });
    if let Some(handler) = handler {
        handler.show_keyboard();
    }
}

pub(crate) fn notify_text_input_focus_lost() {
    let handler = crate::render_state::with_text_input_session(|state| {
        if !state.keyboard_requested.replace(false) {
            return None;
        }
        state.handler()
    });
    if let Some(handler) = handler {
        handler.hide_keyboard();
    }
}

/// Notifies the framework that the host app was paused (backgrounded — e.g.
/// Android `onPause`).
///
/// Any outstanding soft-keyboard request is withdrawn and the platform is told
/// to hide its keyboard, clearing the "keyboard shown" state so it cannot
/// survive into the next resume. Without this, a platform that remembers the
/// last editor view (Android's `InputMethodManager`) re-shows the keyboard when
/// the app returns to the foreground even though the framework no longer has a
/// focused field. Gated on an outstanding request, so it is a no-op when the
/// keyboard was not showing.
pub fn notify_app_paused() {
    notify_text_input_focus_lost();
}

/// Notifies the framework that the host app resumed (foregrounded — e.g.
/// Android `onResume`).
///
/// The soft keyboard is **never** auto-shown on resume, even when a text field
/// is still focused. A warm resume (return from HOME / task switch / back-exit
/// then relaunch) restores the process with the field's focus and caret intact,
/// but the framework must not resurrect the keyboard for it: the platform's
/// `InputMethodManager` remembers the last editor and would otherwise pop the
/// keyboard back open on its own. The user brings it back by tapping the field
/// (which re-requests it through `notify_text_input_focus_gained`).
///
/// Always returns `false` so the platform runtime force-hides the OS-restored
/// keyboard. Pruning stale focus here keeps the keyboard-request bookkeeping
/// consistent (a focused-but-detached field is dropped and its outstanding
/// request withdrawn) without ever calling `show`.
pub fn notify_app_resumed() -> bool {
    let _ = crate::text_field_focus::has_focused_field();
    false
}

#[cfg(test)]
mod tests {
    use std::cell::RefCell as StdRefCell;

    use super::*;

    #[derive(Default)]
    struct RecordingHandler {
        calls: StdRefCell<Vec<&'static str>>,
    }

    impl PlatformTextInputHandler for RecordingHandler {
        fn show_keyboard(&self) {
            self.calls.borrow_mut().push("show");
        }

        fn hide_keyboard(&self) {
            self.calls.borrow_mut().push("hide");
        }
    }

    fn install_recording_handler() -> Rc<RecordingHandler> {
        let handler = Rc::new(RecordingHandler::default());
        set_platform_text_input_handler(handler.clone());
        handler
    }

    #[test]
    fn focus_gained_shows_keyboard() {
        let _app_context = crate::render_state::app_context_test_scope();
        let handler = install_recording_handler();

        notify_text_input_focus_gained();

        assert_eq!(*handler.calls.borrow(), vec!["show"]);
    }

    #[test]
    fn focus_lost_hides_keyboard_once() {
        let _app_context = crate::render_state::app_context_test_scope();
        let handler = install_recording_handler();

        notify_text_input_focus_gained();
        notify_text_input_focus_lost();
        notify_text_input_focus_lost();

        assert_eq!(*handler.calls.borrow(), vec!["show", "hide"]);
    }

    #[test]
    fn focus_lost_without_prior_show_is_not_forwarded() {
        let _app_context = crate::render_state::app_context_test_scope();
        let handler = install_recording_handler();

        notify_text_input_focus_lost();

        assert!(handler.calls.borrow().is_empty());
    }

    #[test]
    fn repeated_focus_gain_reshows_keyboard() {
        let _app_context = crate::render_state::app_context_test_scope();
        let handler = install_recording_handler();

        notify_text_input_focus_gained();
        notify_text_input_focus_gained();

        assert_eq!(*handler.calls.borrow(), vec!["show", "show"]);
    }

    #[test]
    fn notifications_without_handler_are_noops() {
        let _app_context = crate::render_state::app_context_test_scope();
        notify_text_input_focus_gained();
        notify_text_input_focus_lost();
    }

    #[test]
    fn clearing_handler_stops_notifications() {
        let _app_context = crate::render_state::app_context_test_scope();
        let handler = install_recording_handler();

        notify_text_input_focus_gained();
        clear_platform_text_input_handler();
        notify_text_input_focus_lost();

        assert_eq!(*handler.calls.borrow(), vec!["show"]);
    }

    struct NoopFocusHandler;
    impl crate::text_field_focus::FocusedTextFieldHandler for NoopFocusHandler {
        fn handle_key(&self, _: &crate::key_event::KeyEvent) -> bool {
            false
        }
        fn insert_text(&self, _: &str) {}
        fn delete_surrounding(&self, _: usize, _: usize) {}
        fn copy_selection(&self) -> Option<String> {
            None
        }
        fn cut_selection(&self) -> Option<String> {
            None
        }
        fn set_composition(&self, _: &str, _: Option<(usize, usize)>) {}
    }

    fn focus_a_field() -> Rc<std::cell::RefCell<bool>> {
        let focus = Rc::new(std::cell::RefCell::new(false));
        crate::text_field_focus::request_focus(Rc::clone(&focus), Rc::new(NoopFocusHandler), 0);
        focus
    }

    #[test]
    fn resume_without_a_focused_field_does_not_show_the_keyboard() {
        let _app_context = crate::render_state::app_context_test_scope();
        let handler = install_recording_handler();

        notify_text_input_focus_gained();
        notify_app_paused();
        assert_eq!(*handler.calls.borrow(), vec!["show", "hide"]);

        assert!(!notify_app_resumed());
        assert_eq!(
            *handler.calls.borrow(),
            vec!["show", "hide"],
            "resume with no focused field must not re-show the keyboard"
        );
    }

    #[test]
    fn resume_never_reshows_the_keyboard_even_for_a_focused_field() {
        let _app_context = crate::render_state::app_context_test_scope();
        let handler = install_recording_handler();

        let focus = focus_a_field();
        assert_eq!(*handler.calls.borrow(), vec!["show"]);

        notify_app_paused();
        assert_eq!(*handler.calls.borrow(), vec!["show", "hide"]);

        assert!(!notify_app_resumed());
        assert_eq!(
            *handler.calls.borrow(),
            vec!["show", "hide"],
            "resume must leave the keyboard hidden"
        );

        crate::text_field_focus::request_focus(Rc::clone(&focus), Rc::new(NoopFocusHandler), 0);
        assert_eq!(
            *handler.calls.borrow(),
            vec!["show", "hide", "show"],
            "tapping the field after resume re-shows the keyboard"
        );

        crate::text_field_focus::clear_focus();
    }

    #[test]
    fn cold_start_with_no_focus_does_not_show_the_keyboard() {
        let _app_context = crate::render_state::app_context_test_scope();
        let handler = install_recording_handler();

        assert!(
            !notify_app_resumed(),
            "a launch with no focused field must not re-open the keyboard"
        );
        assert!(
            handler.calls.borrow().is_empty(),
            "no platform show/hide should be requested for an unfocused cold start"
        );
    }

    #[test]
    fn pause_is_a_noop_when_the_keyboard_was_not_showing() {
        let _app_context = crate::render_state::app_context_test_scope();
        let handler = install_recording_handler();

        notify_app_paused();
        assert!(
            handler.calls.borrow().is_empty(),
            "pausing without a shown keyboard must not call the platform"
        );
    }
}