use crate::*;
use std::marker::PhantomData;

/// A [Command] that can be constructed from a [Token].
pub trait DslCommand<'state, C>: TryFromDsl<'state, C> + Command<C> {}

impl<'state, C, T: TryFromDsl<'state, C> + Command<C>> DslCommand<'state, C> for T {}

/// [Input] state that can be matched against a [Value].
pub trait DslInput: Input {
    fn matches_dsl (&self, token: &str) -> bool;
}

/// A pre-configured mapping of input events to commands.
pub trait KeyMap<'state, S, C: DslCommand<'state, S>, I: DslInput> {
    /// Try to find a command that matches the current input event.
    fn command (&'state self, state: &'state S, input: &'state I) -> Option<C>;
}

/// A [SourceIter] can be a [KeyMap].
impl<'state, S, C: DslCommand<'state, S>, I: DslInput> KeyMap<'state, S, C, I> for SourceIter<'state> {
    fn command (&'state self, state: &'state S, input: &'state I) -> Option<C> {
        let mut iter = self.clone();
        while let Some((token, rest)) = iter.next() {
            iter = rest;
            match token {
                Token { value: Value::Exp(0, exp_iter), .. } => {
                    let mut exp_iter = exp_iter.clone();
                    match exp_iter.next() {
                        Some(Token { value: Value::Sym(binding), .. }) => {
                            if input.matches_dsl(binding) {
                                if let Some(command) = C::try_from_expr(state, exp_iter.clone()) {
                                    return Some(command)
                                }
                            }
                        },
                        _ => panic!("invalid config (expected symbol)")
                    }
                },
                _ => panic!("invalid config (expected expression)")
            }
        }
        None
    }
}

/// A [TokenIter] can be a [KeyMap].
impl<'state, S, C: DslCommand<'state, S>, I: DslInput> KeyMap<'state, S, C, I> for TokenIter<'state> {
    fn command (&'state self, state: &'state S, input: &'state I) -> Option<C> {
        let mut iter = self.clone();
        while let Some(next) = iter.next() {
            match next {
                Token { value: Value::Exp(0, exp_iter), .. } => {
                    let mut exp_iter = exp_iter.clone();
                    match exp_iter.next() {
                        Some(Token { value: Value::Sym(binding), .. }) => {
                            if input.matches_dsl(binding) {
                                if let Some(command) = C::try_from_expr(state, exp_iter.clone()) {
                                    return Some(command)
                                }
                            }
                        },
                        _ => panic!("invalid config (expected symbol)")
                    }
                },
                _ => panic!("invalid config (expected expression)")
            }
        }
        None
    }
}

pub type InputLayerCond<'state, S> = Box<dyn Fn(&S)->bool + Send + Sync + 'state>;

/// A collection of pre-configured mappings of input events to commands,
/// which may be made available subject to given conditions.
pub struct InputMap<'state, S, C, I, M>
where
    C: DslCommand<'state, S>,
    I: DslInput,
    M: KeyMap<'state, S, C, I> + Send + Sync
{
    __: &'state PhantomData<(S, C, I)>,
    pub layers: Vec<(InputLayerCond<'state, S>, M)>,
}

impl<'state, S, C, I, M> Default for InputMap<'state, S, C, I, M>
where
    C: DslCommand<'state, S>,
    I: DslInput,
    M: KeyMap<'state, S, C, I> + Send + Sync
{
    fn default () -> Self {
        Self {
            __: &PhantomData,
            layers: vec![]
        }
    }
}

impl<'state, S, C, I, M> InputMap<'state, S, C, I, M>
where
    C: DslCommand<'state, S>,
    I: DslInput,
    M: KeyMap<'state, S, C, I> + Send + Sync
{
    pub fn new (keymap: M) -> Self {
        Self::default().layer(keymap)
    }
    pub fn layer (mut self, keymap: M) -> Self {
        self.add_layer(keymap);
        self
    }
    pub fn add_layer (&mut self, keymap: M) -> &mut Self {
        self.add_layer_if(Box::new(|_|true), keymap);
        self
    }
    pub fn layer_if (mut self, condition: InputLayerCond<'state, S>, keymap: M) -> Self {
        self.add_layer_if(condition, keymap);
        self
    }
    pub fn add_layer_if (&mut self, condition: InputLayerCond<'state, S>, keymap: M) -> &mut Self {
        self.layers.push((Box::new(condition), keymap));
        self
    }
}

impl<'state, S, C, I, M> std::fmt::Debug for InputMap<'state, S, C, I, M>
where
    C: DslCommand<'state, S>,
    I: DslInput,
    M: KeyMap<'state, S, C, I> + Send + Sync
{
    fn fmt (&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
        write!(f, "[InputMap: {} layer(s)]", self.layers.len());
        Ok(())
    }
}

/// An [InputMap] can be a [KeyMap].
impl<'state, S, C, I, M> KeyMap<'state, S, C, I> for InputMap<'state, S, C, I, M>
where
    C: DslCommand<'state, S>,
    I: DslInput,
    M: KeyMap<'state, S, C, I> + Send + Sync
{
    fn command (&'state self, state: &'state S, input: &'state I) -> Option<C> {
        for (condition, keymap) in self.layers.iter() {
            if !condition(state) {
                continue
            }
            if let Some(command) = keymap.command(state, input) {
                return Some(command)
            }
        }
        None
    }
}