use crate::*;
use std::{sync::Arc, collections::BTreeMap, path::{Path, PathBuf}, fs::{exists, read_to_string}};
/// Map of each event (e.g. key combination) to
/// all command expressions bound to it by
/// all loaded input layers.
type EventMapImpl<E, C> = BTreeMap<E, Vec<Binding<C>>>;
/// 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>(pub EventMapImpl<E, C>);
/// An input binding.
#[derive(Debug, Clone)]
pub struct Binding<C> {
    pub command:     C,
    pub condition:   Option<Condition>,
    pub description: Option<Arc<str>>,
    pub source:      Option<Arc<PathBuf>>,
}
/// 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()
    }
    /// Create event map from path to text file.
    pub fn load_from_path <'s> (
        &'s mut self, path: impl AsRef<Path>
    ) -> Usually<&mut Self> where Self: DslInto<C> + DslInto<E> {
        if exists(path.as_ref())? {
            let source = read_to_string(&path)?;
            let path: Arc<PathBuf> = Arc::new(path.as_ref().into());
            self.load_from_source(&source, &Some(&path))
        } else {
            return Err(format!("(e5) not found: {:?}", path.as_ref()).into())
        }
    }
    /// Create event map from DSL tokenizer.
    pub fn load_from_source (
        &mut self, dsl: impl Dsl, path: &Option<&Arc<PathBuf>>
    ) -> Usually<&mut Self> where Self: DslInto<C> + DslInto<E> {
        dsl.each(|dsl|self.load_from_source_one(&dsl, path).map(move|_|()))?;
        Ok(self)
    }
    /// Load one event binding into the event map.
    pub fn load_from_source_one <'s> (
        &'s mut self, dsl: impl Dsl, path: &Option<&Arc<PathBuf>>
    ) -> Usually<&mut Self> where Self: DslInto<C> + DslInto<E> {
        if let Some(exp)  = dsl.head()?.exp()?
        && let Some(sym)  = exp.head()?.sym()?
        && let Some(tail) = exp.tail()?
        {
            let event   = self.dsl_into_or_else(&sym, ||panic!())?;
            let command = self.dsl_into_or_else(&tail, ||panic!())?;
            Ok(self.add(event, Binding {
                command, condition: None, description: None, source: path.cloned()
            }))
        } else {
            Err(format!("unexpected: {:?}", dsl.head()?).into())
        }
    }
        //})Ok(if let Some(sym) = dsl.head()?.exp()?.head()?.sym()? {
            //if let Some(tail) = dsl.head()?.exp()?.tail()? {
                //let event: E = sym.into();
                //let binding: Binding<C> = Binding { command: tail.into(), condition: None, description: None, source: None };
                //if let Some(bindings) = map.0.get_mut(&event) {
                    //bindings.push(binding);
                //} else {
                    //map.0.insert(event, vec![binding]);
                //}
            //} else {
                //panic!("empty binding: {}", dsl.head()?.exp()?.unwrap_or_default())
            //}
        //} else if let Some(ref text) = dsl.text()? {
            //map.0.extend(Self::from_path(PathBuf::from(text))?.0);
        //} else {
            //return Err(format!("unexpected: {dsl:?}").into())
        //}));
        //Ok(map)
    //}
}
impl<C> Binding<C> {
    pub fn from_dsl (dsl: impl Dsl) -> Usually<Self> {
        let mut command:     Option<C>            = None;
        let mut condition:   Option<Condition>    = None;
        let mut description: Option<Arc<str>>     = None;
        let mut source:      Option<Arc<PathBuf>> = None;
        if let Some(command) = command {
            Ok(Self { command, condition, description, source })
        } else {
            Err(format!("no command in {dsl:?}").into())
        }
    }
}
fn unquote (x: &str) -> &str {
    let mut chars = x.chars();
    chars.next();
    //chars.next_back();
    chars.as_str()
}