//! Line discipline over the PS/2 keyboard — the kernel's tty layer.
//!
//! Two modes, like a real UNIX terminal:
//! - **canonical** (`read_line`): input is echoed, buffered until Enter,
//!   ^C cancels the line, ^D on an empty line is EOF.
//! - **raw** (`read_byte` / `try_read_byte`): keys are translated to the
//!   classic terminal byte protocol (arrows → `ESC [ A–D`, Backspace →
//!   `0x7f`, ^X → `0x18`, …) and delivered one byte at a time, with no echo.
//!   Multi-byte sequences are queued internally so `read_byte` returns them
//!   in order.
//!
//! `interrupt_pressed` is the cooperative-interrupt check used by streaming
//! commands (cat/hexdump): it drains the keyboard non-blockingly and reports
//! whether ^C was seen.

use crate::ps2::{self, KeyEvent};
use crate::strbuf;
use crate::{gop, serial};

/// Max characters a single typed line can hold.  Long enough that no
/// realistic command line gets silently cut — the terminal wraps the
/// echo at the screen edge, and the full line is what's submitted.
pub const LINE_BUF_SIZE: usize = 1024;

/// Result of one canonical line-input session.
#[allow(clippy::large_enum_variant)] // stack buffer by design (no heap churn)
pub enum LineInput {
    Line(strbuf::String<LINE_BUF_SIZE>),
    Interrupted, // ^C
    Eof,         // ^D on an empty line
}

// Raw-mode byte queue: holds the tail of a multi-byte key sequence.
static mut RAW_QUEUE: [u8; 8] = [0; 8];
static mut RAW_LEN: usize = 0;

// ---------------------------------------------------------------------------
// canonical mode
// ---------------------------------------------------------------------------

/// Read one line in canonical mode: echo every key, ^C cancels the line,
/// ^D on an empty line is EOF.  Echo goes to the terminal (GOP) and serial.
pub fn read_line() -> LineInput {
    // Interactive input: make sure deferred scrolls are pushed first so
    // the screen shows the current state (no-op when nothing is pending).
    crate::vt::sync_scroll();
    let mut buf = strbuf::String::<LINE_BUF_SIZE>::new();
    loop {
        match ps2::poll_key() {
            KeyEvent::Enter => {
                gop::put_char('\n');
                serial::write_str("\r\n");
                return LineInput::Line(buf);
            }
            KeyEvent::Ctrl('c') => {
                // Cancel the current line — like a real terminal, echo ^C.
                buf.clear();
                gop::put_char('^');
                gop::put_char('C');
                gop::put_char('\n');
                serial::write_str("^C\r\n");
                return LineInput::Interrupted;
            }
            KeyEvent::Ctrl('d') => {
                if buf.is_empty() {
                    // EOF on an empty line — the caller decides what to do.
                    gop::put_char('^');
                    gop::put_char('D');
                    gop::put_char('\n');
                    serial::write_str("^D\r\n");
                    return LineInput::Eof;
                }
                // ^D with text on the line: ignored (bash semantics).
            }
            KeyEvent::Char(c) if c.is_ascii_graphic() || c == ' ' => {
                if buf.push(c).is_ok() {
                    gop::put_char(c);
                    let mut s = [0u8; 4];
                    let s = c.encode_utf8(&mut s);
                    serial::write_str(s);
                }
            }
            KeyEvent::Backspace => {
                if buf.pop().is_some() {
                    gop::put_char('\x08');
                    // Serial backspace: BS SP BS (standard terminal protocol)
                    serial::write_str("\x08 \x08");
                }
            }
            KeyEvent::Tab => {
                for _ in 0..4 {
                    if buf.push(' ').is_ok() {
                        gop::put_char(' ');
                        serial::write_str(" ");
                    }
                }
            }
            _ => {}
        }
    }
}

/// Non-blocking drain of the keyboard: true if a ^C is pending.  Used by
/// streaming commands (cat/hexdump) so a long dump can be interrupted.
pub fn interrupt_pressed() -> bool {
    let mut pressed = false;
    while let Some(ev) = ps2::try_poll_key() {
        if matches!(ev, KeyEvent::Ctrl('c')) {
            pressed = true;
        }
    }
    pressed
}

// ---------------------------------------------------------------------------
// raw mode
// ---------------------------------------------------------------------------

/// Blocking read of the next raw-mode byte.  Keys arrive translated to the
/// terminal byte protocol; multi-byte sequences are delivered in order.
pub fn read_byte() -> u8 {
    // Interactive (raw) input: push deferred scrolls so the full-screen
    // app draws over a current framebuffer.
    crate::vt::sync_scroll();
    loop {
        if let Some(b) = pop_raw() {
            return b;
        }
        let ev = ps2::poll_key();
        enqueue_key(ev);
    }
}

/// Non-blocking raw read: Some(byte) if one is available, else None.
pub fn try_read_byte() -> Option<u8> {
    if let Some(b) = pop_raw() {
        return Some(b);
    }
    match ps2::try_poll_key() {
        Some(ev) => {
            enqueue_key(ev);
            pop_raw()
        }
        None => None,
    }
}

fn pop_raw() -> Option<u8> {
    unsafe {
        if RAW_LEN == 0 {
            return None;
        }
        let b = RAW_QUEUE[0];
        for i in 1..RAW_LEN {
            RAW_QUEUE[i - 1] = RAW_QUEUE[i];
        }
        RAW_LEN -= 1;
        Some(b)
    }
}

fn enqueue_key(ev: KeyEvent) {
    let mut q = [0u8; 8];
    let n: usize = match ev {
        KeyEvent::Char(c) if c.is_ascii() => {
            q[0] = c as u8;
            1
        }
        KeyEvent::Enter => {
            q[0] = 0x0d;
            1
        }
        KeyEvent::Backspace => {
            q[0] = 0x7f;
            1
        }
        KeyEvent::Tab => {
            q[0] = 0x09;
            1
        }
        KeyEvent::Escape => {
            q[0] = 0x1b;
            1
        }
        KeyEvent::Ctrl(c) => {
            q[0] = (c as u8) & 0x1f;
            1
        }
        KeyEvent::ArrowUp => {
            q[..3].copy_from_slice(b"\x1b[A");
            3
        }
        KeyEvent::ArrowDown => {
            q[..3].copy_from_slice(b"\x1b[B");
            3
        }
        KeyEvent::ArrowRight => {
            q[..3].copy_from_slice(b"\x1b[C");
            3
        }
        KeyEvent::ArrowLeft => {
            q[..3].copy_from_slice(b"\x1b[D");
            3
        }
        KeyEvent::CtrlArrow(0) => {
            q[..6].copy_from_slice(b"\x1b[1;5A");
            6
        }
        KeyEvent::CtrlArrow(1) => {
            q[..6].copy_from_slice(b"\x1b[1;5B");
            6
        }
        KeyEvent::CtrlArrow(2) => {
            q[..6].copy_from_slice(b"\x1b[1;5D");
            6
        }
        KeyEvent::CtrlArrow(3) => {
            q[..6].copy_from_slice(b"\x1b[1;5C");
            6
        }
        KeyEvent::Home => {
            q[..3].copy_from_slice(b"\x1b[H");
            3
        }
        KeyEvent::End => {
            q[..3].copy_from_slice(b"\x1b[F");
            3
        }
        KeyEvent::PageUp => {
            q[..4].copy_from_slice(b"\x1b[5~");
            4
        }
        KeyEvent::PageDown => {
            q[..4].copy_from_slice(b"\x1b[6~");
            4
        }
        KeyEvent::Delete => {
            q[..4].copy_from_slice(b"\x1b[3~");
            4
        }
        _ => return,
    };
    unsafe {
        for (i, b) in q.iter().take(n).enumerate() {
            RAW_QUEUE[i] = *b;
        }
        RAW_LEN = n;
    }
}