use crate::*;
use std::{sync::Arc, collections::BTreeMap, path::PathBuf};
/// A collection of input bindings.
///
/// Each contained layer defines a mapping from input event to command invocation
/// over a given state. Furthermore, each layer may have an associated cond,
/// so that only certain layers are active at a given time depending on state.
///
/// When a key is pressed, the bindings for it are checked in sequence.
/// When the first non-conditional or true conditional binding is executed,
/// that .event()binding's value is returned.
#[derive(Debug)]
pub struct EventMap<E, C>(
    /// Map of each event (e.g. key combination) to
    /// all command expressions bound to it by
    /// all loaded input layers.
    pub BTreeMap<E, Vec<Binding<C>>>
);
/// An input binding.
#[derive(Debug, Clone)]
pub struct Binding<C> {
    pub commands:    Arc<[C]>,
    pub condition:   Option<Condition>,
    pub description: Option<Arc<str>>,
    pub source:      Option<Arc<PathBuf>>,
}
impl<C> Binding<C> {
    pub fn from_dsl (dsl: impl Dsl) -> Usually<Self> {
        let command:     Option<C>            = None;
        let condition:   Option<Condition>    = None;
        let description: Option<Arc<str>>     = None;
        let source:      Option<Arc<PathBuf>> = None;
        if let Some(command) = command {
            Ok(Self { commands: [command].into(), condition, description, source })
        } else {
            Err(format!("no command in {dsl:?}").into())
        }
    }
}
/// Input bindings are only returned if this evaluates to true
#[derive(Clone)]
pub struct Condition(Arc<Box<dyn Fn()->bool + Send + Sync>>);
impl_debug!(Condition |self, w| { write!(w, "*") });
/// Default is always empty map regardless if `E` and `C` implement [Default].
impl<E, C> Default for EventMap<E, C> {
    fn default () -> Self { Self(Default::default()) }
}
impl<E: Clone + Ord, C> EventMap<E, C> {
    /// Create a new event map
    pub fn new () -> Self {
        Default::default()
    }
    /// Add a binding to an owned event map.
    pub fn def (mut self, event: E, binding: Binding<C>) -> Self {
        self.add(event, binding);
        self
    }
    /// Add a binding to an event map.
    pub fn add (&mut self, event: E, binding: Binding<C>) -> &mut Self {
        if !self.0.contains_key(&event) {
            self.0.insert(event.clone(), Default::default());
        }
        self.0.get_mut(&event).unwrap().push(binding);
        self
    }
    /// Return the binding(s) that correspond to an event.
    pub fn query (&self, event: &E) -> Option<&[Binding<C>]> {
        self.0.get(event).map(|x|x.as_slice())
    }
    /// Return the first binding that corresponds to an event, considering conditions.
    pub fn dispatch (&self, event: &E) -> Option<&Binding<C>> {
        self.query(event)
            .map(|bb|bb.iter().filter(|b|b.condition.as_ref().map(|c|(c.0)()).unwrap_or(true)).next())
            .flatten()
    }
}