//! Arithmetic operations: add, subtract, etc.

use crate::prelude::*;
use crate::tile::prelude::*;

use veccell::VecRef;

#[derive(Debug, Clone, Default, Serialize, Deserialize)]
pub struct Store {
    signal: Option<Signal>,
}

impl Store {
    pub fn signal(&self) -> Option<&Signal> {
        self.signal.as_ref()
    }
}

impl Tile for Store {
    fn update<'b>(&'b mut self, mut context: UpdateContext<'b>) {
        if let Some(signal) = context.take_signal() {
            let position = context.position();

            // NOTE: we *could* write the signal immediately,
            // but by delaying the write we can read from a `Store` without being order-dependent
            context.callback(move |pane| {
                if let Some(mut this) = pane.borrow_mut_as::<Self>(position) {
                    this.signal = Some(signal);
                }
            });
        }

        if context.state() != State::Idle {
            context.next_state();
        }
    }

    fn draw_simple(&self, ctx: DrawContext) -> TextChar {
        if self.signal.is_some() {
            TextChar::from_state('\u{25c9}', ctx.state) // FISHEYE
        } else {
            TextChar::from_state('\u{25cb}', ctx.state) // WHITE CIRCLE
        }
    }
}

/// When a signal is received, reads a signal from a [`Store`] (at the reader's tail),
/// then outputs that signal (at the reader's head).
///
/// # Example
///
/// The following circuit can receive a value in `B`, then store it indefinitely.
/// Sending a signal in `A` will output the stored signal from `B` in `OUT`.
///
/// ```text
/// o = Store
/// ▸ = Reader(Right)
///
/// (A) ---+
///        |
/// (B) --o▸-- (OUT)
/// ```
#[derive(Debug, Clone, Default, Serialize, Deserialize)]
pub struct Reader(Direction);

impl Tile for Reader {
    fn update<'b>(&'b mut self, mut context: UpdateContext<'b>) {
        if let Some(_signal) = context.take_signal() {
            let _: Option<()> = try {
                let store_position = context.offset(self.0.opposite().into_offset())?;
                let store = context.get(store_position).and_then(get_store)?;
                let signal = store.signal.clone()?;
                drop(store);

                let target_position = context.offset(self.0.into_offset())?;

                context.send(target_position, self.0, signal);
            };
        }

        if context.state() != State::Idle {
            context.next_state();
        }
    }

    fn draw_simple(&self, ctx: DrawContext) -> TextChar {
        match self.0 {
            Direction::Down => TextChar::from_state('\u{25bd}', ctx.state), // WHITE DOWN-POINTING TRIANGLE
            Direction::Left => TextChar::from_state('\u{25c1}', ctx.state), // WHITE LEFT-POINTING TRIANGLE
            Direction::Right => TextChar::from_state('\u{25b7}', ctx.state), // WHITE RIGHT-POINTING TRIANGLE
            Direction::Up => TextChar::from_state('\u{25b3}', ctx.state), // WHITE UP-POINTING TRIANGLE
        }
    }
}

/// Tries to convert a [`FullTile`] to a [`Store`]
fn get_store<'a>(full: VecRef<'a, FullTile>) -> Option<VecRef<'a, Store>> {
    VecRef::try_map(full, |tile| {
        let tile = tile.get().ok_or(())?;
        let store = tile.try_into().map_err(|_| ())?;
        Ok::<&Store, ()>(store)
    }).ok()
}