SLY / src / component.rs

use std::io;
use std::sync::mpsc;
use std::time::Duration;

use crate::block::Block;
use crate::input::{self, Key, RawMode};
use crate::terminal;
use crate::view::View;

/// A Component is a pure state machine combined with a renderer.
/// Uses closures (matching Gleam's record-of-functions pattern).
pub struct Component<S, R> {
    pub state: S,
    pub render: Box<dyn Fn(&S) -> Block>,
    pub update: Box<dyn Fn(&S, &Key) -> Update<S, R>>,
}

/// The result of processing a key event in a component.
pub enum Update<S, R> {
    /// Key handled, new state -- keep the event loop running
    Continue(S),
    /// Yield a value while continuing (for multi-step flows)
    Emit(S, R),
    /// Component is done -- return this final value
    Finish(R),
    /// User cancelled (Escape/CtrlC)
    Cancel,
    /// Key not handled by this component (for focus management)
    Ignore,
}

/// Errors that can occur when running a component.
#[derive(Debug)]
pub enum RunError {
    /// User pressed Escape or Ctrl+C
    Cancelled,
    /// Error reading from the terminal
    InputError(io::Error),
}

impl<S, R> Component<S, R> {
    pub fn new(
        state: S,
        render: impl Fn(&S) -> Block + 'static,
        update: impl Fn(&S, &Key) -> Update<S, R> + 'static,
    ) -> Self {
        Component {
            state,
            render: Box::new(render),
            update: Box::new(update),
        }
    }

    /// Run this component's interactive event loop.
    /// Installs a SIGWINCH handler so that terminal resizes cause an immediate
    /// redraw at the new width.
    pub fn run(self, mode: &RawMode) -> Result<R, RunError> {
        let width = terminal::get_size()
            .map(|(cols, _)| cols as usize)
            .unwrap_or(80);
        terminal::install_resize_handler();
        self.run_with_width(mode, width)
    }

    /// Run with an explicit rendering width.
    pub fn run_with_width(self, mode: &RawMode, width: usize) -> Result<R, RunError> {
        let Component {
            state,
            render,
            update,
        } = self;
        let initial_block = (render)(&state);
        let mut view = View::create(&initial_block, width);
        let result = event_loop(&render, &update, state, &mut view, mode);
        match &result {
            Ok(_) => view.finish(),
            Err(RunError::Cancelled) => view.erase(),
            Err(RunError::InputError(_)) => view.finish(),
        }
        result
    }

    /// Run with periodic tick updates (for animated components like spinners).
    pub fn run_animated(
        self,
        mode: &RawMode,
        tick_ms: u64,
        on_tick: impl Fn(S) -> S,
    ) -> Result<R, RunError> {
        let width = terminal::get_size()
            .map(|(cols, _)| cols as usize)
            .unwrap_or(80);
        let Component {
            state,
            render,
            update,
        } = self;
        let initial_block = (render)(&state);
        let mut view = View::create(&initial_block, width);
        let result = animated_loop(&render, &update, state, &mut view, mode, tick_ms, &on_tick);
        match &result {
            Ok(_) => view.finish(),
            Err(RunError::Cancelled) => view.erase(),
            Err(RunError::InputError(_)) => view.finish(),
        }
        result
    }

    /// Run with a message channel. The event loop multiplexes between stdin
    /// keypresses and messages from background threads.
    ///
    /// `on_msg` is called for each received message and produces an `Update`,
    /// just like the `update` function for keypresses.
    ///
    /// Uses a short `read_key_timeout` interval (10 ms) to poll the channel
    /// between key reads, keeping message latency low without busy-spinning.
    pub fn run_with_channel<Msg>(
        self,
        mode: &RawMode,
        rx: mpsc::Receiver<Msg>,
        on_msg: impl Fn(&S, Msg) -> Update<S, R> + 'static,
    ) -> Result<R, RunError> {
        let width = terminal::get_size()
            .map(|(cols, _)| cols as usize)
            .unwrap_or(80);
        terminal::install_resize_handler();
        let Component {
            state,
            render,
            update,
        } = self;
        let initial_block = (render)(&state);
        let mut view = View::create(&initial_block, width);
        let result = channel_loop(&render, &update, &on_msg, state, &mut view, mode, &rx);
        match &result {
            Ok(_) => view.finish(),
            Err(RunError::Cancelled) => view.erase(),
            Err(RunError::InputError(_)) => view.finish(),
        }
        result
    }

    /// Transform the result type of this component.
    pub fn map<R2: 'static>(self, f: impl Fn(R) -> R2 + 'static) -> Component<S, R2>
    where
        S: 'static,
        R: 'static,
    {
        let update = self.update;
        Component {
            state: self.state,
            render: self.render,
            update: Box::new(move |state, key| match (update)(state, key) {
                Update::Continue(s) => Update::Continue(s),
                Update::Emit(s, r) => Update::Emit(s, f(r)),
                Update::Finish(r) => Update::Finish(f(r)),
                Update::Cancel => Update::Cancel,
                Update::Ignore => Update::Ignore,
            }),
        }
    }

    /// Set the initial state.
    pub fn with_state(self, state: S) -> Self {
        Component { state, ..self }
    }
}

fn event_loop<S, R>(
    render: &dyn Fn(&S) -> Block,
    update: &dyn Fn(&S, &Key) -> Update<S, R>,
    mut state: S,
    view: &mut View,
    mode: &RawMode,
) -> Result<R, RunError> {
    loop {
        // Check for terminal resize before blocking on the next key
        if terminal::take_resize() {
            let new_width = terminal::get_size()
                .map(|(c, _)| c as usize)
                .unwrap_or(view.width());
            let block = (render)(&state);
            view.resize(&block, new_width);
        }
        let key = input::read_key(mode).map_err(RunError::InputError)?;
        match (update)(&state, &key) {
            Update::Continue(new_state) => {
                state = new_state;
                let block = (render)(&state);
                view.update(&block);
            }
            Update::Emit(_, result) => return Ok(result),
            Update::Finish(result) => return Ok(result),
            Update::Cancel => return Err(RunError::Cancelled),
            Update::Ignore => {}
        }
    }
}

fn channel_loop<S, R, Msg>(
    render: &dyn Fn(&S) -> Block,
    update: &dyn Fn(&S, &Key) -> Update<S, R>,
    on_msg: &dyn Fn(&S, Msg) -> Update<S, R>,
    mut state: S,
    view: &mut View,
    mode: &RawMode,
    rx: &mpsc::Receiver<Msg>,
) -> Result<R, RunError> {
    // Poll interval — short enough for responsive messages, not a busy spin.
    let poll_ms = Duration::from_millis(10);
    loop {
        // Handle terminal resize
        if terminal::take_resize() {
            let new_width = terminal::get_size()
                .map(|(c, _)| c as usize)
                .unwrap_or(view.width());
            let block = (render)(&state);
            view.resize(&block, new_width);
        }

        // Drain all pending channel messages
        loop {
            match rx.try_recv() {
                Ok(msg) => match on_msg(&state, msg) {
                    Update::Continue(new_state) => {
                        state = new_state;
                        let block = (render)(&state);
                        view.update(&block);
                    }
                    Update::Emit(_, result) => return Ok(result),
                    Update::Finish(result) => return Ok(result),
                    Update::Cancel => return Err(RunError::Cancelled),
                    Update::Ignore => {}
                },
                Err(mpsc::TryRecvError::Empty) => break,
                Err(mpsc::TryRecvError::Disconnected) => break,
            }
        }

        // Wait briefly for a keypress
        match input::read_key_timeout(mode, poll_ms).map_err(RunError::InputError)? {
            None => {} // timeout — loop again to check channel
            Some(key) => match (update)(&state, &key) {
                Update::Continue(new_state) => {
                    state = new_state;
                    let block = (render)(&state);
                    view.update(&block);
                }
                Update::Emit(_, result) => return Ok(result),
                Update::Finish(result) => return Ok(result),
                Update::Cancel => return Err(RunError::Cancelled),
                Update::Ignore => {}
            },
        }
    }
}

fn animated_loop<S, R>(
    render: &dyn Fn(&S) -> Block,
    update: &dyn Fn(&S, &Key) -> Update<S, R>,
    mut state: S,
    view: &mut View,
    mode: &RawMode,
    tick_ms: u64,
    on_tick: &dyn Fn(S) -> S,
) -> Result<R, RunError> {
    let timeout = Duration::from_millis(tick_ms);
    loop {
        // Handle terminal resize
        if terminal::take_resize() {
            let new_width = terminal::get_size()
                .map(|(c, _)| c as usize)
                .unwrap_or(view.width());
            let block = (render)(&state);
            view.resize(&block, new_width);
        }
        match input::read_key_timeout(mode, timeout).map_err(RunError::InputError)? {
            None => {
                state = on_tick(state);
                let block = (render)(&state);
                view.update(&block);
            }
            Some(key) => match (update)(&state, &key) {
                Update::Continue(new_state) => {
                    state = new_state;
                    let block = (render)(&state);
                    view.update(&block);
                }
                Update::Emit(_, result) => return Ok(result),
                Update::Finish(result) => return Ok(result),
                Update::Cancel => return Err(RunError::Cancelled),
                Update::Ignore => {}
            },
        }
    }
}