//! TUI frontend: terminal lifecycle, rendering, and input handling.
//!
//! All communication with the core orchestrator flows through channels:
//! - [`UserAction`] sent via `action_tx` when the user submits input or quits
//! - [`UIEvent`] received via `event_rx` to display streaming assistant responses
//!
//! The terminal lifecycle follows the standard crossterm pattern:
//! 1. Enable raw mode
//! 2. Enter alternate screen
//! 3. On exit (or panic), disable raw mode and leave the alternate screen

mod events;
mod input;
mod render;

use std::io::{self, Stdout};
use std::time::Duration;

use crossterm::event::{Event, EventStream, KeyEvent};
use crossterm::execute;
use crossterm::terminal::{
    EnterAlternateScreen, LeaveAlternateScreen, disable_raw_mode, enable_raw_mode,
};
use futures::StreamExt;
use ratatui::Terminal;
use ratatui::backend::CrosstermBackend;
use tokio::sync::mpsc;

use crate::core::types::{Role, UIEvent, UserAction};

/// Errors that can occur in the TUI layer.
#[derive(Debug, thiserror::Error)]
pub enum TuiError {
    /// An underlying terminal I/O error.
    #[error("terminal IO error: {0}")]
    Io(#[from] std::io::Error),
}

/// Vim-style editing mode for the TUI.
///
/// The TUI starts in Insert mode so first-time users can type immediately.
/// Mode transitions:
///   Insert --Esc--> Normal
///   Normal --i--> Insert
///   Normal --:--> Command
///   Command --Esc/Enter--> Normal
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum Mode {
    /// Navigation and command entry. Keys are interpreted as commands, not text.
    Normal,
    /// Text input. Printable keys append to the input buffer.
    Insert,
    /// Ex-style command entry. The command buffer lives in `AppState::command_buffer`.
    Command,
}

/// The UI-layer view of a conversation: rendered messages and the current input buffer.
pub struct AppState {
    /// All conversation turns rendered as (role, content) pairs.
    pub messages: Vec<(Role, String)>,
    /// The current contents of the input box.
    pub input: String,
    /// Vertical scroll offset for the output pane (lines from top).
    pub scroll: u16,
    /// Current vim-style editing mode.
    pub mode: Mode,
    /// Partial command text in Command mode (without the leading `:`).
    pub command_buffer: String,
    /// Buffered keystrokes for multi-key chord resolution in Normal mode (e.g. `gg`).
    pub pending_keys: Vec<char>,
    /// Last-known viewport height (output pane lines). Updated each frame by `update_scroll`.
    pub viewport_height: u16,
    /// Transient error message shown in the status bar, cleared on next keypress.
    pub status_error: Option<String>,
    /// A tool approval request waiting for user input (y/n).
    pub pending_approval: Option<events::PendingApproval>,
    /// Whether the sandbox is in yolo (unsandboxed) mode.
    pub sandbox_yolo: bool,
    /// Whether network access is currently allowed.
    pub network_allowed: bool,
}

impl AppState {
    fn new() -> Self {
        Self {
            messages: Vec::new(),
            input: String::new(),
            scroll: 0,
            mode: Mode::Insert,
            command_buffer: String::new(),
            pending_keys: Vec::new(),
            viewport_height: 0,
            status_error: None,
            pending_approval: None,
            sandbox_yolo: false,
            network_allowed: false,
        }
    }
}

/// Initialise the terminal: enable raw mode and switch to the alternate screen.
///
/// Callers must pair this with [`restore_terminal`] (and [`install_panic_hook`]) to
/// guarantee cleanup even on abnormal exit.
pub fn init_terminal() -> Result<Terminal<CrosstermBackend<Stdout>>, TuiError> {
    enable_raw_mode()?;
    let mut stdout = io::stdout();
    execute!(stdout, EnterAlternateScreen)?;
    let backend = CrosstermBackend::new(stdout);
    let terminal = Terminal::new(backend)?;
    Ok(terminal)
}

/// Restore the terminal to its pre-launch state: disable raw mode and leave the
/// alternate screen.
pub fn restore_terminal() -> io::Result<()> {
    disable_raw_mode()?;
    execute!(io::stdout(), LeaveAlternateScreen)?;
    Ok(())
}

/// Install a panic hook that restores the terminal before printing the panic message.
///
/// Without this, a panic leaves the terminal in raw mode with the alternate screen
/// active, making the shell unusable until the user runs `reset`.
pub fn install_panic_hook() {
    let original = std::panic::take_hook();
    std::panic::set_hook(Box::new(move |info| {
        // Best-effort restore; if it fails the original hook still runs.
        let _ = restore_terminal();
        original(info);
    }));
}

/// Run the TUI event loop.
///
/// This function owns the terminal for its entire lifetime. It initialises the
/// terminal, installs the panic hook, then spins in a ~60 fps loop:
///
/// ```text
/// loop:
///   1. drain UIEvents (non-blocking try_recv)
///   2. poll keyboard for up to 16 ms via EventStream (async, no blocking thread)
///   3. handle key event -> Option<LoopControl>
///   4. render frame (scroll updated inside draw closure)
///   5. act on LoopControl: send message or break
/// ```
///
/// On `Ctrl+C` / `Ctrl+D`: sends [`UserAction::Quit`], restores the terminal, and
/// returns `Ok(())`.
pub async fn run(
    action_tx: mpsc::Sender<UserAction>,
    mut event_rx: mpsc::Receiver<UIEvent>,
    sandbox_yolo: bool,
) -> Result<(), TuiError> {
    install_panic_hook();
    let mut terminal = init_terminal()?;
    let mut state = AppState::new();
    state.sandbox_yolo = sandbox_yolo;
    let mut event_stream = EventStream::new();

    loop {
        // 1. Drain pending UI events.
        events::drain_ui_events(&mut event_rx, &mut state);

        // 2. Poll keyboard for up to 16 ms.  EventStream integrates with the
        //    Tokio runtime via futures::Stream, so no blocking thread is needed.
        //    Timeout expiry, stream end, non-key events, and I/O errors all map
        //    to None -- the frame is rendered regardless.
        let key_event: Option<KeyEvent> =
            match tokio::time::timeout(Duration::from_millis(16), event_stream.next()).await {
                Ok(Some(Ok(Event::Key(k)))) => Some(k),
                _ => None,
            };

        // 3. Handle key.
        let control = input::handle_key(key_event, &mut state);

        // 4. Render (scroll updated inside draw closure to use current frame area).
        terminal.draw(|frame| {
            render::update_scroll(&mut state, frame.area());
            render::render(frame, &state);
        })?;

        // 5. Act on control signal after render so the user sees the submitted message.
        match control {
            Some(input::LoopControl::SendMessage(msg)) => {
                if action_tx.send(UserAction::SendMessage(msg)).await.is_err() {
                    break;
                }
            }
            Some(input::LoopControl::Quit) => {
                let _ = action_tx.send(UserAction::Quit).await;
                break;
            }
            Some(input::LoopControl::ClearHistory) => {
                let _ = action_tx.send(UserAction::ClearHistory).await;
            }
            Some(input::LoopControl::ToolApproval {
                tool_use_id,
                approved,
            }) => {
                let _ = action_tx
                    .send(UserAction::ToolApprovalResponse {
                        tool_use_id,
                        approved,
                    })
                    .await;
            }
            Some(input::LoopControl::SetNetworkPolicy(allowed)) => {
                let _ = action_tx.send(UserAction::SetNetworkPolicy(allowed)).await;
            }
            None => {}
        }
    }

    restore_terminal()?;
    Ok(())
}