rat_event/

lib.rs

#![doc = include_str!("../readme.md")]

use std::cmp::max;

pub mod crossterm;
pub mod util;

/// All the regular and expected event-handling a widget can do.
///
/// All the normal key-handling dependent on an internal focus-state
/// All the mouse-handling.
#[derive(Debug, Default, Clone, Copy)]
pub struct Regular;

/// Handle mouse-events only. Useful whenever you want to write new key-bindings,
/// but keep the mouse-events.
#[derive(Debug, Default, Clone, Copy)]
pub struct MouseOnly;

/// With the latest enhancement of `Focus` this is obsolete.
///
/// Focus collects all the areas of widgets and containers and can set a z-index
/// for each area. With this information it runs a hit-test for each mouse event
/// and sets and sets the `mouse-focus` flag for each widget and container.
/// This works well with popups and overlapping widgets. This makes the
/// differentiation between regular widgets and widgets that might show a popup
/// that overlaps other widgets obsolete.
///
/// If you don't use Focus you will still have to consider the information below.
///
/// __Obsoleted__
///
/// Popup/Overlays are a bit difficult to handle, as there is no z-order/area tree,
/// which would direct mouse interactions. We can simulate a z-order in the
/// event-handler by trying the things with a higher z-order first.
///
/// If a widget might show a popup, you have to call its event-handling
/// before any other widgets that might be (partially) hidden behind the
/// widget. This applies for e.g. Menubar, Choice and ComboBox.
/// To make this difference visible in the application code, these widgets
/// use `Popup` as marker for their event-handling instead of `Regular`.
///
/// If you implement a widget with a popup, you must make sure to consume __all__
/// mouse-events within the widget area to prevent any interaction with
/// a hidden widget.
#[derive(Debug, Default, Clone, Copy)]
pub struct Popup;

/// Event-handling for a dialog like widget.
///
/// Similar to [Popup] but with the extra that it consumes _all_ events when active.
/// No regular widget gets any event, and we have modal behaviour.
#[derive(Debug, Default, Clone, Copy)]
pub struct Dialog;

/// Event-handler for double-click on a widget.
///
/// Events for this handler must be processed *before* calling
/// any other event-handling routines for the same widget.
/// Otherwise, the regular event-handling might interfere with
/// recognition of double-clicks by consuming the first click.
///
/// This event-handler doesn't consume the first click, just
/// the second one.
#[derive(Debug, Default, Clone, Copy)]
pub struct DoubleClick;

///
/// A very broad trait for an event handler.
///
/// Ratatui widgets have two separate structs, one that implements
/// Widget/StatefulWidget and the associated State. As the StatefulWidget
/// has a lifetime and is not meant to be kept, HandleEvent should be
/// implemented for the state struct. It can then modify some state and
/// the tui can be rendered anew with that changed state.
///
/// HandleEvent is not limited to State structs of course, any Type
/// that wants to interact with events can implement it.
///
/// * Event - The actual event type.
/// * Qualifier - The qualifier allows creating more than one event-handler
///   for a widget.
///
///   This can be used as a variant of type-state, where the type given
///   selects the widget's behaviour, or to give some external context
///   to the widget, or to write your own key-bindings for a widget.
///
/// * R - Result of event-handling. This can give information to the
///   application what changed due to handling the event. This can
///   be very specific for each widget, but there is one general [Outcome]
///   that describes a minimal set of results.
///
///   There should be one value that indicates 'I don't know this event'.
///   This is expressed with the ConsumedEvent trait.
///
pub trait HandleEvent<Event, Qualifier, Return>
where
    Return: ConsumedEvent,
{
    /// Handle an event.
    ///
    /// * self - The widget state.
    /// * event - Event type.
    /// * qualifier - Event handling qualifier.
    ///   This library defines some standard values [Regular], [MouseOnly].
    ///   Further ideas:
    ///     * ReadOnly
    ///     * Special behaviour like DoubleClick, HotKey.
    /// * Returns some result, see [Outcome]
    fn handle(&mut self, event: &Event, qualifier: Qualifier) -> Return;
}

/// Catch all event-handler for the null state `()`.
impl<E, Q> HandleEvent<E, Q, Outcome> for () {
    fn handle(&mut self, _event: &E, _qualifier: Q) -> Outcome {
        Outcome::Continue
    }
}

/// When calling multiple event-handlers, the minimum information required
/// from the result is 'has consumed/didn't consume' the event.
///
/// The event-handler **may** also react to the event and not call it
/// 'consuming the event'. But this is tricky, non-obvious and frowned upon.
/// The caller **may** also just ignore the fact.
///
/// See also [flow] and [try_flow] and the extra [break_flow].
pub trait ConsumedEvent {
    /// Is this the 'consumed' result.
    fn is_consumed(&self) -> bool;

    /// Or-Else chaining with `is_consumed()` as the split.
    #[inline(always)]
    fn or_else<F>(self, f: F) -> Self
    where
        F: FnOnce() -> Self,
        Self: Sized,
    {
        if self.is_consumed() { self } else { f() }
    }

    /// Or-Else chaining with `is_consumed()` as the split.
    #[inline(always)]
    fn or_else_try<F, E>(self, f: F) -> Result<Self, E>
    where
        Self: Sized,
        F: FnOnce() -> Result<Self, E>,
    {
        if self.is_consumed() {
            Ok(self)
        } else {
            Ok(f()?)
        }
    }

    /// And_then-chaining based on is_consumed().
    /// Returns max(self, f()).
    #[inline(always)]
    fn and_then<F>(self, f: F) -> Self
    where
        Self: Sized + Ord,
        F: FnOnce() -> Self,
    {
        if self.is_consumed() {
            max(self, f())
        } else {
            self
        }
    }

    /// And_then-chaining based on is_consumed().
    /// Returns max(self, f()).
    #[inline(always)]
    fn and_then_try<F, E>(self, f: F) -> Result<Self, E>
    where
        Self: Sized + Ord,
        F: FnOnce() -> Result<Self, E>,
    {
        if self.is_consumed() {
            Ok(max(self, f()?))
        } else {
            Ok(self)
        }
    }

    /// Then-chaining. Returns max(self, f()).
    #[inline(always)]
    #[deprecated(since = "1.2.2", note = "use and_then()")]
    fn and<F>(self, f: F) -> Self
    where
        Self: Sized + Ord,
        F: FnOnce() -> Self,
    {
        if self.is_consumed() {
            max(self, f())
        } else {
            self
        }
    }

    /// Then-chaining. Returns max(self, f()).
    #[inline(always)]
    #[deprecated(since = "1.2.2", note = "use and_then_try()")]
    fn and_try<F, E>(self, f: F) -> Result<Self, E>
    where
        Self: Sized + Ord,
        F: FnOnce() -> Result<Self, E>,
    {
        if self.is_consumed() {
            Ok(max(self, f()?))
        } else {
            Ok(self)
        }
    }
}

impl<V, E> ConsumedEvent for Result<V, E>
where
    V: ConsumedEvent,
{
    fn is_consumed(&self) -> bool {
        match self {
            Ok(v) => v.is_consumed(),
            Err(_) => true,
        }
    }
}

/// The baseline outcome for an event-handler.
///
/// A widget can define its own type, if it has more things to report.
/// It would be nice if those types are convertible to/from `Outcome`
/// and implement `ConsumedEvent` as well.
#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum Outcome {
    /// The given event has not been used at all.
    #[default]
    Continue,
    /// The event has been recognized, but nothing noticeable has changed.
    /// Further processing for this event may stop.
    /// Rendering the ui is not necessary.
    Unchanged,
    /// The event has been recognized and there is some change due to it.
    /// Further processing for this event may stop.
    /// Rendering the ui is advised.
    Changed,
}

impl ConsumedEvent for Outcome {
    fn is_consumed(&self) -> bool {
        *self != Outcome::Continue
    }
}

/// Widgets often define functions that return bool to indicate a changed state.
/// This converts `true` / `false` to `Outcome::Changed` / `Outcome::Unchanged`.
impl From<bool> for Outcome {
    fn from(value: bool) -> Self {
        if value {
            Outcome::Changed
        } else {
            Outcome::Unchanged
        }
    }
}

/// __Experimental__
///
/// Convert to Outcome from bool.
///
/// The problem is that there are two possible combinations
/// * true/false -> Changed/Unchanged
/// * true/false -> Changed/Continue
///
/// Which one, depends on the use-case. Do you want the event
/// to be handled finally or do you want to give a parent widget
/// the chance to react to an event unless your widget really
/// does something worth-wile.
///
/// This occurs for navigation keys.
/// - Left navigates backwards in your widget.
///   - When the start is reached the widget is done.
///     - There may be a super widget that can do it's super navigation
///       if it knows that fact.
///       => return Outcome::Changed as long as you change your location
///          and Outcome::Continue otherwise.
///
/// For the Changed/Unchanged pair I don't have a good example, so
/// maybe that was the wrong default anyway. But I can't change the
/// `From<bool>` behavior as that would *really* break things.
///
/// Hence, this trait.  
///
pub trait FromBool {
    fn as_changed_unchanged(self) -> Outcome;
    fn as_changed_continue(self) -> Outcome;
}

impl FromBool for bool {
    fn as_changed_unchanged(self) -> Outcome {
        match self {
            true => Outcome::Changed,
            false => Outcome::Unchanged,
        }
    }

    fn as_changed_continue(self) -> Outcome {
        match self {
            true => Outcome::Changed,
            false => Outcome::Continue,
        }
    }
}

/// Tries to unify the currently 3 flow! constructs.
///
/// * `flow!(expr) -> event_flow!(return expr)`
///   The non Result case stays gets a `return`. It's rather uncommon
///   to __not__ have a Result during event-handling, so this should be fine.
/// * `try_flow!(expr) -> event_flow!(expr)`
///   This becomes the main branch.
/// * `break_flow!('x: expr) -> event_flow!(break 'x expr)`
///   This now matches actual rust syntax, which is good for rustfmt.
///   The `break 'x` is stripped and reapplied after result-conversion.
///
/// __...___
///
/// I'll try this out... If it's fine I'll leave the other macros
/// with a discouraging remark and promote this variant.
///
/// note: of course the default is diametrical when you write
/// library code for a new widget. as usual :-|. stick with it
/// though as libraries should be used more often than written.
#[macro_export]
macro_rules! event_flow {
    (log $n:ident: return $x:expr) => {{
        use log::debug;
        use $crate::ConsumedEvent;
        let r = $x;
        if r.is_consumed() {
            debug!("{} {:#?}", stringify!($n), r);
            return r.into();
        } else {
            debug!("{} continue", stringify!($n));
        }
    }};
    (log $n:ident: break $l:lifetime $x:expr) => {{
        use log::debug;
        use $crate::ConsumedEvent;
        let r = $x;
        if r.is_consumed() {
            debug!("{} {:#?}", stringify!($n), r);
            break $l r.into();
        } else {
            debug!("{} continue", stringify!($n));
        }
    }};
    (log $n:ident: $x:expr) => {{
        use log::debug;
        use $crate::ConsumedEvent;
        let r = $x;
        if r.is_consumed() {
            debug!("{} {:#?}", stringify!($n), r);
            return Ok(r.into());
        } else {
            debug!("{} continue", stringify!($n));
        }
    }};
    (break $l:lifetime $x:expr) => {{
        use $crate::ConsumedEvent;
        let r = $x;
        if r.is_consumed() {
            break $l r.into();
        }
    }};
    (return $x:expr) => {{
        use $crate::ConsumedEvent;
        let r = $x;
        if r.is_consumed() {
            return r.into();
        }
    }};
    ($x:expr) => {{
        use $crate::ConsumedEvent;
        let r = $x;
        if r.is_consumed() {
            return Ok(r.into());
        }
    }};

}

/// Use `event_flow!` instead.
///
/// Returns from the current function if the block returns
/// a value for which `[ConsumedEvent::is_consumed] == true`.
///
/// This breaks the control-flow of the current function effectively.
///
/// As the return type of the current function can differ from
/// whatever function has been called, an `ìnto()` conversion
/// is thrown in too.  
///
/// *The difference to [try_flow] is that this on doesn't Ok-wrap the result.*
///
/// Extras: If you add a marker as in `flow!(log ident: {...});`
/// the result of the operation is written to the log.
#[macro_export]
macro_rules! flow {
    (log $n:ident: $x:expr) => {{
        use log::debug;
        use $crate::ConsumedEvent;
        let r = $x;
        if r.is_consumed() {
            debug!("{} {:#?}", stringify!($n), r);
            return r.into();
        } else {
            debug!("{} continue", stringify!($n));
        }
    }};
    ($x:expr) => {{
        use $crate::ConsumedEvent;
        let r = $x;
        if r.is_consumed() {
            return r.into();
        }
    }};
}

/// Use `event_flow!` instead.
///
/// Returns from the current function if the block returns
/// a value for which `[ConsumedEvent::is_consumed] == true`.
///
/// This breaks the control-flow of the current function effectively.
///
/// As the return type of the current function can differ from
/// whatever function has been called, an `ìnto()` conversion
/// is thrown in too.
///
/// *The difference to [flow] is that this one Ok-wraps the result.*
///
/// Extras: If you add a marker as in `try_flow!(log ident: {...});`
/// the result of the operation is written to the log.
#[macro_export]
macro_rules! try_flow {
    (log $n:ident: $x:expr) => {{
        use log::debug;
        use $crate::ConsumedEvent;
        let r = $x;
        if r.is_consumed() {
            debug!("{} {:#?}", stringify!($n), r);
            return Ok(r.into());
        } else {
            debug!("{} continue", stringify!($n));
        }
    }};
    ($x:expr) => {{
        use $crate::ConsumedEvent;
        let r = $x;
        if r.is_consumed() {
            return Ok(r.into());
        }
    }};
}

/// Use `event_flow!` instead.
///
/// This macro doesn't return from the current function, but
/// does a labeled break if the block returns a value for
/// which `[ConsumedEvent::is_consumed] == true`.
///
/// It also does and `into()` conversion and *breaks* with the
/// result to the enclosing block given as a `'l:{}` labeled block.
///
/// * The difference to [try_flow] is that this on doesn't Ok-wrap the result.*
/// * The difference to [flow] is that this breaks instead of return_ing.
///
/// Extras: If you add a marker as in `break_flow!(log 'f: ident: {...});`
/// the result of the operation is written to the log.
#[macro_export]
macro_rules! break_flow {
    (log $n:ident: $l:lifetime: $x:expr) => {{
        use log::debug;
        use $crate::ConsumedEvent;
        let r = $x;
        if r.is_consumed() {
            debug!("{} {:#?}", stringify!($n), r);
            break $l r.into();
        } else {
            debug!("{} continue", stringify!($n));
        }
    }};
    ($l:lifetime: $x:expr) => {{
        use $crate::ConsumedEvent;
        let r = $x;
        if r.is_consumed() {
            break $l r.into();
        }
    }};
}

mod _private {
    #[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
    pub struct NonExhaustive;
}