badterm_core/

ansi.rs

//! ANSI-BBS / ANSI X3.64 terminal emulation.
//!
//! [`Terminal`] consumes the byte stream from the remote system, drives a
//! [`Screen`], and collects any replies (cursor position reports, etc.) that
//! must be sent back.

use serde::{Deserialize, Serialize};

use crate::cp437;
use crate::music::{self, Tone};
use crate::palette::{ANSI_TO_VGA, rgb};
use crate::screen::{Cell, Color, DEFAULT_BG, DEFAULT_FG, Look, Screen, flags};

/// How incoming bytes are interpreted: the character set, and the
/// emulations that go with it.
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "lowercase")]
pub enum Encoding {
    #[default]
    Cp437,
    Utf8,
    /// Commodore 64 (see [`crate::petscii`]).
    Petscii,
    /// Atari 8-bit (see [`crate::atascii`]).
    Atascii,
    /// CP437 with AVT/0+ codes as well as ANSI (see [`crate::avatar`]).
    Avatar,
    /// CP437 ANSI with RIPscrip graphics (see [`crate::rip`]).
    Rip,
}

impl Encoding {
    pub const ALL: [Encoding; 6] =
        [Encoding::Cp437, Encoding::Utf8, Encoding::Petscii, Encoding::Atascii, Encoding::Avatar, Encoding::Rip];

    pub fn name(self) -> &'static str {
        match self {
            Encoding::Cp437 => "CP437",
            Encoding::Utf8 => "UTF-8",
            Encoding::Petscii => "PETSCII",
            Encoding::Atascii => "ATASCII",
            Encoding::Avatar => "Avatar",
            Encoding::Rip => "RIPscrip",
        }
    }

    /// A C64 or Atari system, with its own screen size and font.
    pub fn is_retro(self) -> bool {
        matches!(self, Encoding::Petscii | Encoding::Atascii)
    }

    /// The screen such a system has, if it has its own.
    pub fn screen_size(self) -> Option<(usize, usize)> {
        match self {
            Encoding::Petscii => Some((crate::petscii::COLS, crate::petscii::ROWS)),
            Encoding::Atascii => Some((crate::atascii::COLS, crate::atascii::ROWS)),
            Encoding::Rip => Some((crate::rip::COLS, crate::rip::ROWS)),
            _ => None,
        }
    }

    /// Typed or pasted text as the remote expects it. A CR (Enter) becomes
    /// the system's own end of line.
    pub fn encode_text(self, text: &str) -> Vec<u8> {
        match self {
            Encoding::Cp437 | Encoding::Avatar | Encoding::Rip => cp437::encode(text),
            Encoding::Utf8 => text.as_bytes().to_vec(),
            Encoding::Petscii => text
                .chars()
                .filter_map(|c| if c == '\r' { Some(0x0D) } else { crate::petscii::encode_char(c) })
                .collect(),
            Encoding::Atascii => text
                .chars()
                .filter_map(|c| if c == '\r' { Some(0x9B) } else { crate::atascii::encode_char(c) })
                .collect(),
        }
    }
}

const MAX_PARAMS: usize = 32;
const MAX_STRING: usize = 4096;

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
enum State {
    Ground,
    Escape,
    /// ESC followed by an intermediate byte, e.g. `ESC ( B`; waiting for the final byte.
    EscIntermediate,
    Csi,
    /// OSC: collected for the window title.
    Osc,
    /// DCS, SOS, PM, APC: ignored until ST.
    IgnoreString,
    /// Saw ESC inside a string; `\` terminates it.
    StringEsc,
    /// An ANSI music string, up to Ctrl-N.
    Music,
}

/// Things the front end may want to react to.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum TermEvent {
    Bell,
    Title(String),
    /// ANSI music to play.
    Music(Vec<Tone>),
}

pub struct Terminal {
    pub screen: Screen,
    pub encoding: Encoding,
    /// Treat `ESC [ M` with no parameter as the start of ANSI music, as
    /// many BBS doors expect, instead of "delete one line". `ESC [ N` and
    /// `ESC [ |` always start music.
    pub music_on_csi_m: bool,
    state: State,
    string_is_osc: bool,
    private: u8,
    intermediate: u8,
    params: Vec<u32>,
    param_present: bool,
    osc: Vec<u8>,
    utf8_buf: [u8; 4],
    utf8_len: usize,
    utf8_need: usize,
    replies: Vec<u8>,
    events: Vec<TermEvent>,
    petscii: crate::petscii::Petscii,
    atascii: crate::atascii::Atascii,
    avatar: crate::avatar::Avatar,
    /// The RIPscrip canvas, when the encoding is RIP.
    rip: Option<Box<crate::rip::Rip>>,
    /// Nothing has been printed on this line yet (where a RIP line can
    /// start).
    line_start: bool,
}

impl Terminal {
    pub fn new(cols: usize, rows: usize, scrollback: usize) -> Self {
        Terminal {
            screen: Screen::new(cols, rows, scrollback),
            encoding: Encoding::Cp437,
            music_on_csi_m: false,
            state: State::Ground,
            string_is_osc: false,
            private: 0,
            intermediate: 0,
            params: Vec::with_capacity(MAX_PARAMS),
            param_present: false,
            osc: Vec::new(),
            utf8_buf: [0; 4],
            utf8_len: 0,
            utf8_need: 0,
            replies: Vec::new(),
            events: Vec::new(),
            petscii: Default::default(),
            atascii: Default::default(),
            avatar: Default::default(),
            rip: None,
            line_start: true,
        }
    }

    /// Set up the screen for the encoding: a C64 or Atari system gets that
    /// machine's colors and font.
    pub fn start_emulation(&mut self) {
        match self.encoding {
            Encoding::Petscii => self.petscii.start(&mut self.screen),
            Encoding::Atascii => self.atascii.start(&mut self.screen),
            Encoding::Rip => self.rip = Some(Box::default()),
            _ => {}
        }
    }

    /// The RIPscrip canvas, for a RIP system.
    pub fn rip(&self) -> Option<&crate::rip::Rip> {
        self.rip.as_deref()
    }

    pub fn rip_mut(&mut self) -> Option<&mut crate::rip::Rip> {
        self.rip.as_deref_mut()
    }

    /// Bytes the terminal wants sent to the remote (e.g. CPR replies).
    pub fn take_replies(&mut self) -> Vec<u8> {
        std::mem::take(&mut self.replies)
    }

    pub fn take_events(&mut self) -> Vec<TermEvent> {
        std::mem::take(&mut self.events)
    }

    pub fn feed(&mut self, data: &[u8]) {
        match self.encoding {
            Encoding::Petscii => {
                for &b in data {
                    self.petscii.byte(&mut self.screen, b, &mut self.events);
                }
            }
            Encoding::Atascii => {
                for &b in data {
                    self.atascii.byte(&mut self.screen, b, &mut self.events);
                }
            }
            _ => {
                for &b in data {
                    self.byte(b);
                }
            }
        }
    }

    fn byte(&mut self, b: u8) {
        if self.state == State::Ground {
            let taken = match self.encoding {
                Encoding::Avatar => self.avatar_byte(b),
                Encoding::Rip => self.rip_byte(b),
                _ => false,
            };
            if taken {
                return;
            }
        }
        // CAN and SUB abort any sequence in progress (ECMA-48).
        if self.state != State::Ground && (b == 0x18 || b == 0x1A) {
            self.state = State::Ground;
            return;
        }
        match self.state {
            State::Ground => self.ground(b),
            State::Escape => self.escape(b),
            State::EscIntermediate => self.state = State::Ground,
            State::Csi => self.csi(b),
            State::Osc | State::IgnoreString => match b {
                0x07 if self.state == State::Osc => self.finish_string(),
                0x1B => self.state = State::StringEsc,
                _ if self.state == State::Osc && self.osc.len() < MAX_STRING => self.osc.push(b),
                _ => {}
            },
            State::Music => match b {
                0x0E => {
                    self.state = State::Ground;
                    let tones = music::parse(&self.osc);
                    if !tones.is_empty() {
                        self.events.push(TermEvent::Music(tones));
                    }
                }
                _ if self.osc.len() < MAX_STRING => self.osc.push(b),
                // Too long to be music: give up on it.
                _ => self.state = State::Ground,
            },
            State::StringEsc => {
                if b == b'\\' {
                    self.finish_string();
                } else {
                    // Not ST: abandon the string and treat this as a new escape.
                    self.state = State::Escape;
                    self.escape(b);
                }
            }
        }
    }

    /// AVATAR codes, in the text stream (see [`crate::avatar`]).
    fn avatar_byte(&mut self, b: u8) -> bool {
        use crate::avatar::Outcome;
        match self.avatar.byte(&mut self.screen, b) {
            Outcome::Pass => false,
            Outcome::Done => true,
            Outcome::Show(bytes) => {
                for b in bytes {
                    self.byte(b);
                }
                true
            }
        }
    }

    /// RIP lines, which start a line with `!|` (see [`crate::rip`]).
    fn rip_byte(&mut self, b: u8) -> bool {
        use crate::rip::Feed;
        let Some(rip) = self.rip.as_mut() else { return false };
        match rip.byte(&mut self.screen, b, self.line_start) {
            Feed::Pass => false,
            Feed::Done => true,
            Feed::Text(bytes) => {
                self.line_start = false;
                for b in bytes {
                    self.byte(b);
                }
                true
            }
        }
    }

    fn ground(&mut self, b: u8) {
        if self.encoding == Encoding::Utf8 && self.utf8_need > 0 {
            if b & 0xC0 == 0x80 {
                self.utf8_buf[self.utf8_len] = b;
                self.utf8_len += 1;
                if self.utf8_len == self.utf8_need {
                    let ch = std::str::from_utf8(&self.utf8_buf[..self.utf8_len]).ok().and_then(|s| s.chars().next());
                    self.utf8_need = 0;
                    self.screen.put(ch.and_then(cp437::from_unicode).unwrap_or(b'?'));
                }
                return;
            }
            // Truncated sequence: show a replacement and handle this byte normally.
            self.utf8_need = 0;
            self.screen.put(b'?');
        }
        match b {
            0x00 | 0x7F => {}
            0x07 => self.events.push(TermEvent::Bell),
            0x08 => self.screen.backspace(),
            0x09 => self.screen.tab(),
            0x0A => {
                self.screen.line_feed();
                self.line_start = true;
            }
            0x0C => self.screen.erase_display(2),
            0x0D => {
                self.screen.carriage_return();
                self.line_start = true;
            }
            0x1B => self.state = State::Escape,
            _ => match self.encoding {
                // Like ANSI.SYS, every other byte is a glyph, including the
                // "graphic" control characters (☺, ♥, ►, ...).
                Encoding::Cp437 | Encoding::Petscii | Encoding::Atascii | Encoding::Avatar | Encoding::Rip => {
                    if self.avatar.insert {
                        self.screen.insert_chars(1);
                    }
                    self.line_start = false;
                    self.screen.put(b)
                }
                Encoding::Utf8 => match b {
                    0x01..=0x1F => {}
                    0x20..=0x7E => self.screen.put(b),
                    0xC2..=0xDF => self.utf8_start(b, 2),
                    0xE0..=0xEF => self.utf8_start(b, 3),
                    0xF0..=0xF4 => self.utf8_start(b, 4),
                    _ => self.screen.put(b'?'),
                },
            },
        }
    }

    fn utf8_start(&mut self, b: u8, need: usize) {
        self.utf8_buf[0] = b;
        self.utf8_len = 1;
        self.utf8_need = need;
    }

    fn escape(&mut self, b: u8) {
        self.state = State::Ground;
        match b {
            b'[' => {
                self.state = State::Csi;
                self.private = 0;
                self.intermediate = 0;
                self.params.clear();
                self.param_present = false;
            }
            b']' => {
                self.state = State::Osc;
                self.string_is_osc = true;
                self.osc.clear();
            }
            b'P' | b'X' | b'^' | b'_' => {
                self.state = State::IgnoreString;
                self.string_is_osc = false;
            }
            0x20..=0x2F => self.state = State::EscIntermediate,
            b'7' => self.screen.save_cursor(),
            b'8' => self.screen.restore_cursor(),
            b'c' => self.screen.reset(),
            b'D' => self.screen.line_feed(),
            b'E' => {
                self.screen.carriage_return();
                self.screen.line_feed();
            }
            b'M' => self.screen.reverse_index(),
            0x1B => self.state = State::Escape,
            _ => log::debug!("unhandled ESC {:?}", b as char),
        }
    }

    fn finish_string(&mut self) {
        self.state = State::Ground;
        if !self.string_is_osc {
            return;
        }
        let s = String::from_utf8_lossy(&self.osc).into_owned();
        let (code, rest) = s.split_once(';').unwrap_or((s.as_str(), ""));
        match code {
            // Set the window title.
            "0" | "2" => self.events.push(TermEvent::Title(rest.to_string())),
            "4" => self.set_palette(rest),
            "104" => self.reset_palette(rest),
            _ => log::debug!("unhandled OSC {code}"),
        }
    }

    /// `OSC 4 ; index ; color [; index ; color ...]`, where a color is
    /// `rgb:R/G/B` (1-4 hex digits each), `#RRGGBB`, or `?` to ask for it.
    fn set_palette(&mut self, args: &str) {
        let mut parts = args.split(';');
        while let (Some(i), Some(spec)) = (parts.next(), parts.next()) {
            let Ok(i) = i.trim().parse::<u8>() else { continue };
            if spec == "?" {
                let c = self.screen.look.palette[i as usize];
                let reply = format!("\x1b]4;{i};rgb:{:02x}/{:02x}/{:02x}\x1b\\", c >> 16, (c >> 8) & 0xFF, c & 0xFF);
                self.replies.extend_from_slice(reply.as_bytes());
            } else if let Some(c) = parse_color(spec) {
                self.screen.look.palette[i as usize] = c;
            }
        }
    }

    /// `OSC 104` resets the whole palette; `OSC 104 ; index ...` just those.
    fn reset_palette(&mut self, args: &str) {
        let standard = &Look::standard().palette;
        if args.trim().is_empty() {
            self.screen.look.palette = *standard;
            return;
        }
        for i in args.split(';').filter_map(|i| i.trim().parse::<u8>().ok()) {
            self.screen.look.palette[i as usize] = standard[i as usize];
        }
    }

    fn csi(&mut self, b: u8) {
        match b {
            b'0'..=b'9' => {
                if self.params.is_empty() {
                    self.params.push(0);
                }
                let p = self.params.last_mut().unwrap();
                *p = p.saturating_mul(10).saturating_add((b - b'0') as u32);
                self.param_present = true;
            }
            b';' | b':' => {
                if self.params.is_empty() {
                    self.params.push(0);
                }
                if self.params.len() < MAX_PARAMS {
                    self.params.push(0);
                }
                self.param_present = true;
            }
            0x3C..=0x3F => {
                if !self.param_present && self.private == 0 {
                    self.private = b;
                }
            }
            // `ESC [ !` asks whether this is a RIPscrip terminal.
            b'!' if self.encoding == Encoding::Rip && self.params.is_empty() && self.private == 0 => {
                self.state = State::Ground;
                self.replies.extend_from_slice(crate::rip::VERSION_REPLY);
            }
            0x20..=0x2F => self.intermediate = b,
            0x40..=0x7E => {
                self.state = State::Ground;
                self.dispatch_csi(b);
            }
            // C0 controls are executed even in the middle of a sequence.
            0x00..=0x1F => {
                if b == 0x1B {
                    self.state = State::Escape;
                } else {
                    self.ground(b);
                }
            }
            _ => self.state = State::Ground,
        }
    }

    /// Parameter `i`, with 0 or missing replaced by `default`.
    fn p(&self, i: usize, default: u32) -> u32 {
        match self.params.get(i) {
            Some(&v) if v != 0 => v,
            _ => default,
        }
    }

    fn dispatch_csi(&mut self, b: u8) {
        if self.intermediate != 0 {
            // CTerm font selection: `CSI slot ; font SP D`.
            if self.intermediate == b' ' && b == b'D' && self.private == 0 {
                let slot = self.params.first().copied().unwrap_or(0) as usize;
                let font = self.params.get(1).copied().unwrap_or(0);
                if slot < 4 && font <= 255 {
                    self.screen.look.fonts[slot] = font as u8;
                }
                return;
            }
            log::debug!("unhandled CSI with intermediate {:?} {:?}", self.intermediate as char, b as char);
            return;
        }
        match self.private {
            0 => {}
            b'?' => return self.dec_mode(b),
            _ => {
                log::debug!("unhandled private CSI {:?}{:?} {:?}", self.private as char, b as char, self.params);
                return;
            }
        }
        let no_params = self.params.is_empty();
        if b == b'|' || no_params && (b == b'N' || b == b'M' && self.music_on_csi_m) {
            self.state = State::Music;
            self.osc.clear();
            return;
        }
        let n = self.p(0, 1) as usize;
        let s = &mut self.screen;
        match b {
            b'@' => s.insert_chars(n),
            b'A' => s.move_by(0, -(n as isize)),
            b'B' | b'e' => s.move_by(0, n as isize),
            b'C' | b'a' => s.move_by(n as isize, 0),
            b'D' => s.move_by(-(n as isize), 0),
            b'E' => {
                s.move_by(0, n as isize);
                s.carriage_return();
            }
            b'F' => {
                s.move_by(0, -(n as isize));
                s.carriage_return();
            }
            b'G' | b'`' => {
                let y = s.cursor().1;
                s.move_to(n - 1, y);
            }
            b'd' => {
                let x = s.cursor().0;
                s.move_to(x, n - 1);
            }
            b'H' | b'f' => {
                let (row, col) = (self.p(0, 1) as usize, self.p(1, 1) as usize);
                self.screen.move_to(col - 1, row - 1);
            }
            b'J' => s.erase_display(self.params.first().copied().unwrap_or(0)),
            b'K' => s.erase_line(self.params.first().copied().unwrap_or(0)),
            b'L' => s.insert_lines(n),
            b'M' => s.delete_lines(n),
            b'P' => s.delete_chars(n),
            b'S' => s.scroll_up(n),
            b'T' => s.scroll_down(n),
            b'X' => s.erase_chars(n),
            b'Z' => s.back_tab(n),
            // Device Attributes: answer as a plain VT100. Claiming CTerm would
            // invite font and palette sequences that are not supported yet.
            b'c' if self.params.first().is_none_or(|&v| v == 0) => self.replies.extend_from_slice(b"\x1b[?1;0c"),
            b'm' => self.sgr(),
            b'n' => match self.params.first().copied().unwrap_or(0) {
                5 => self.replies.extend_from_slice(b"\x1b[0n"),
                6 => {
                    let (x, y) = self.screen.cursor();
                    self.replies.extend_from_slice(format!("\x1b[{};{}R", y + 1, x + 1).as_bytes());
                }
                _ => {}
            },
            b'r' => {
                let rows = self.screen.rows() as u32;
                let (top, bottom) = (self.p(0, 1), self.p(1, rows));
                self.screen.set_scroll_region(top as usize - 1, bottom as usize - 1);
            }
            b's' => s.save_cursor(),
            b'u' => s.restore_cursor(),
            // CTerm/PabloDraw 24-bit color: CSI 0;r;g;b t (bg) / CSI 1;r;g;b t (fg).
            b't' if self.params.len() == 4 => {
                let c = Color::Rgb(rgb(self.params[1] as u8, self.params[2] as u8, self.params[3] as u8));
                match self.params[0] {
                    0 => self.screen.pen.bg = c,
                    1 => self.screen.pen.fg = c,
                    _ => {}
                }
            }
            b'h' | b'l' => {}
            _ => log::debug!("unhandled CSI {:?} {:?}", b as char, self.params),
        }
    }

    fn dec_mode(&mut self, b: u8) {
        let on = match b {
            b'h' => true,
            b'l' => false,
            _ => return,
        };
        for &mode in &self.params {
            match mode {
                7 => self.screen.autowrap = on,
                25 => self.screen.cursor_visible = on,
                // CTerm: blink attribute selects bright background (iCE colors).
                // CTerm: bright and blink select fonts, and need not
                // brighten or blink.
                31 => self.screen.look.bright_font = on,
                32 => self.screen.look.bright_plain = on,
                33 => self.screen.ice_colors = on,
                34 => self.screen.look.blink_font = on,
                35 => self.screen.look.blink_steady = on,
                _ => log::debug!("unhandled DEC mode {mode} {on}"),
            }
        }
    }

    fn sgr(&mut self) {
        if self.params.is_empty() {
            self.params.push(0);
        }
        let pen = &mut self.screen.pen;
        let mut i = 0;
        while i < self.params.len() {
            let p = self.params[i];
            match p {
                0 => *pen = Cell { ch: b' ', ..Cell::default() },
                1 => pen.flags = (pen.flags | flags::BOLD) & !flags::FAINT,
                2 => pen.flags = (pen.flags | flags::FAINT) & !flags::BOLD,
                4 => pen.flags |= flags::UNDERLINE,
                5 | 6 => pen.flags |= flags::BLINK,
                7 => pen.flags |= flags::REVERSE,
                8 => pen.flags |= flags::CONCEAL,
                21 | 22 => pen.flags &= !(flags::BOLD | flags::FAINT),
                24 => pen.flags &= !flags::UNDERLINE,
                25 => pen.flags &= !flags::BLINK,
                27 => pen.flags &= !flags::REVERSE,
                28 => pen.flags &= !flags::CONCEAL,
                30..=37 => pen.fg = Color::Pc(ANSI_TO_VGA[(p - 30) as usize]),
                39 => pen.fg = DEFAULT_FG,
                40..=47 => pen.bg = Color::Pc(ANSI_TO_VGA[(p - 40) as usize]),
                49 => pen.bg = DEFAULT_BG,
                90..=97 => pen.fg = Color::Pc(ANSI_TO_VGA[(p - 90) as usize] + 8),
                100..=107 => pen.bg = Color::Pc(ANSI_TO_VGA[(p - 100) as usize] + 8),
                38 | 48 => {
                    let color = match self.params.get(i + 1) {
                        Some(5) => {
                            let c = self.params.get(i + 2).map(|&v| Color::Xterm(v as u8));
                            i += 2;
                            c
                        }
                        Some(2) => {
                            let c = (i + 4 < self.params.len()).then(|| {
                                let v = &self.params[i + 2..i + 5];
                                Color::Rgb(rgb(v[0] as u8, v[1] as u8, v[2] as u8))
                            });
                            i += 4;
                            c
                        }
                        _ => None,
                    };
                    if let Some(c) = color {
                        if p == 38 { pen.fg = c } else { pen.bg = c }
                    }
                }
                _ => log::debug!("unhandled SGR {p}"),
            }
            i += 1;
        }
    }
}

/// An X11-style color: `rgb:R/G/B` with 1-4 hex digits per channel, or
/// `#RRGGBB`.
fn parse_color(spec: &str) -> Option<crate::palette::Rgb> {
    let spec = spec.trim();
    if let Some(hex) = spec.strip_prefix('#') {
        return (hex.len() == 6).then(|| u32::from_str_radix(hex, 16).ok()).flatten();
    }
    let mut channels = spec.strip_prefix("rgb:")?.split('/').map(|c| {
        let v = u32::from_str_radix(c, 16).ok().filter(|_| (1..=4).contains(&c.len()))?;
        // Scale to 8 bits: "f" and "ffff" are both full.
        Some((v * 255 / ((1 << (4 * c.len())) - 1)) as u8)
    });
    let (r, g, b) = (channels.next()??, channels.next()??, channels.next()??);
    channels.next().is_none().then(|| rgb(r, g, b))
}

#[cfg(test)]
mod tests {
    use super::*;

    fn term() -> Terminal {
        Terminal::new(80, 25, 100)
    }

    fn line(t: &Terminal, y: usize) -> String {
        Screen::row_text(t.screen.row(y))
    }

    #[test]
    fn cursor_position_and_text() {
        let mut t = term();
        t.feed(b"\x1b[3;5HHi");
        assert_eq!(line(&t, 2), "    Hi");
        assert_eq!(t.screen.cursor(), (6, 2));
    }

    #[test]
    fn sgr_colors() {
        let mut t = term();
        t.feed(b"\x1b[1;31;44mX");
        let c = t.screen.row(0)[0];
        assert_eq!(c.fg, Color::Pc(4));
        assert_eq!(c.bg, Color::Pc(1));
        assert!(c.flags & flags::BOLD != 0);
        t.feed(b"\x1b[0;38;2;10;20;30mY");
        assert_eq!(t.screen.row(0)[1].fg, Color::Rgb(0x0A141E));
        t.feed(b"\x1b[38;5;196mZ");
        assert_eq!(t.screen.row(0)[2].fg, Color::Xterm(196));
    }

    #[test]
    fn cursor_position_report() {
        let mut t = term();
        t.feed(b"\x1b[10;20H\x1b[6n");
        assert_eq!(t.take_replies(), b"\x1b[10;20R");
    }

    #[test]
    fn device_attributes() {
        let mut t = term();
        t.feed(b"\x1b[c\x1b[0c");
        assert_eq!(t.take_replies(), b"\x1b[?1;0c\x1b[?1;0c");
        // Secondary DA (`CSI > c`) and `CSI 1 c` are not answered.
        t.feed(b"\x1b[>c\x1b[1c");
        assert!(t.take_replies().is_empty());
    }

    #[test]
    fn ice_mode_toggle() {
        let mut t = term();
        t.feed(b"\x1b[?33h");
        assert!(t.screen.ice_colors);
        t.feed(b"\x1b[?33l");
        assert!(!t.screen.ice_colors);
    }

    #[test]
    fn cp437_glyphs_and_utf8() {
        let mut t = term();
        t.feed(&[0xDB, 0x03]);
        assert_eq!(t.screen.row(0)[0].ch, 0xDB);
        assert_eq!(t.screen.row(0)[1].ch, 0x03);
        t.encoding = Encoding::Utf8;
        t.feed("ۂ".as_bytes());
        assert_eq!(t.screen.row(0)[2].ch, 0xDB);
        assert_eq!(t.screen.row(0)[3].ch, 0x82);
    }

    #[test]
    fn osc_title_and_strings_ignored() {
        let mut t = term();
        t.feed(b"\x1b]0;My BBS\x07\x1bPjunk\x1b\\ok");
        assert_eq!(t.take_events(), vec![TermEvent::Title("My BBS".into())]);
        assert_eq!(line(&t, 0), "ok");
    }

    #[test]
    fn ansi_art_line_of_exactly_80_columns() {
        let mut t = term();
        let mut data = vec![b'#'; 80];
        data.extend_from_slice(b"\r\nnext");
        t.feed(&data);
        assert_eq!(line(&t, 1), "next");
    }

    #[test]
    fn save_restore_cursor() {
        let mut t = term();
        t.feed(b"\x1b[5;5H\x1b[s\x1b[1;1H\x1b[uX");
        assert_eq!(t.screen.row(4)[4].ch, b'X');
    }

    #[test]
    fn ansi_music() {
        let mut t = term();
        t.feed(b"Hi\x1b[NMLO3A\x0e there\x1b[|MLO3A8\x0e");
        assert_eq!(line(&t, 0), "Hi there");
        let a = Tone { hz: 440, ms: 500 };
        assert_eq!(t.take_events(), [TermEvent::Music(vec![a]), TermEvent::Music(vec![Tone { ms: 250, ..a }])]);

        // ESC [ M is delete-line unless music is wanted there.
        t.feed(b"\x1b[2;1Hx\x1b[1;1H\x1b[M");
        assert_eq!(line(&t, 0), "x");
        t.music_on_csi_m = true;
        t.feed(b"\x1b[MMLO3A\x0e\x1b[1M");
        assert_eq!(t.take_events(), [TermEvent::Music(vec![a])]);
        assert_eq!(line(&t, 0), "");
    }

    #[test]
    fn cterm_palette_and_fonts() {
        let mut t = Terminal::new(80, 25, 0);
        // Red (ANSI 1, VGA 4) becomes orange; bright blue (ANSI 12) too.
        t.feed(b"\x1b]4;1;rgb:ff/80/00;12;#123456\x1b\\");
        assert_eq!(t.screen.look.palette[1], 0xFF8000);
        assert_eq!(t.screen.look.rgb(Color::Pc(4)), 0xFF8000);
        assert_eq!(t.screen.look.rgb(Color::Pc(9)), 0x123456);
        t.feed(b"\x1b[31mX");
        assert_eq!(t.screen.row(0)[0].resolve_with(false, &t.screen.look).0, 0xFF8000);
        // Queried, then reset.
        t.feed(b"\x1b]4;1;?\x07");
        assert_eq!(t.take_replies(), b"\x1b]4;1;rgb:ff/80/00\x1b\\");
        t.feed(b"\x1b]104;1\x07");
        assert_eq!(t.screen.look.palette[1], 0xAA0000);
        assert_eq!(t.screen.look.palette[12], 0x123456);
        t.feed(b"\x1b]104\x07");
        assert_eq!(t.screen.look, *Look::standard());

        // Font slots, and bright text in slot 1 without brightening.
        t.feed(b"\x1b[0;42 D\x1b[1;40 D\x1b[?31h\x1b[?32h\x1b[1;32mB");
        let cell = t.screen.row(0)[1];
        assert_eq!(t.screen.look.fonts, [42, 40, 0, 0]);
        assert_eq!(t.screen.look.font_for(&cell), 40);
        assert_eq!(cell.resolve_with(false, &t.screen.look).0, 0x00AA00);
        t.feed(b"\x1b[?31l\x1b[?32l");
        assert_eq!(t.screen.look.font_for(&cell), 42);
        assert_eq!(cell.resolve_with(false, &t.screen.look).0, 0x55FF55);
        assert_eq!(parse_color("rgb:f/0/8"), Some(0xFF0088));
        assert_eq!(parse_color("rgb:ffff/0000/8080"), Some(0xFF0080));
        assert_eq!(parse_color("rgb:1/2"), None);
    }

    #[test]
    fn reset_returns_to_the_entrys_ice_setting() {
        let mut t = Terminal::new(80, 25, 0);
        t.screen.base_ice = true;
        t.feed(b"\x1b[?33l");
        assert!(!t.screen.ice_colors);
        t.feed(b"\x1bc");
        assert!(t.screen.ice_colors);
    }
}