commit 8da41f5fe424084b823e017f79b34315b6d44a75
Author: Chris Mounce <christophermounce@gmail.com>
Date:   Tue Jan 20 17:31:44 2026 -0800

    Adapt ZZT world/board parsing from Marzipan

diff --git a/src/zzt/encoding.rs b/src/zzt/encoding.rs
new file mode 100644
index 0000000..6060631
--- /dev/null
+++ b/src/zzt/encoding.rs
@@ -0,0 +1,110 @@
+use codepage_437::CP437_WINGDINGS;
+
+use super::error::ParseError;
+
+/// Serialize a multi-line code string for an object or a scroll.
+/// Uses ZZT's convention of CR-terminated lines.
+pub fn encode_multiline(input: &str) -> Result<Vec<u8>, ParseError> {
+    input
+        .chars()
+        .map(|c| {
+            if c == '\n' {
+                Ok(b'\r')
+            } else {
+                CP437_WINGDINGS
+                    .encode(c)
+                    .ok_or_else(|| ParseError::EncodingError(c))
+            }
+        })
+        .collect()
+}
+
+/// Deserialize a multi-line code string.
+pub fn decode_multiline(input: &[u8]) -> String {
+    input
+        .iter()
+        .map(|&x| {
+            if x == b'\r' {
+                '\n'
+            } else {
+                CP437_WINGDINGS.decode(x)
+            }
+        })
+        .collect()
+}
+
+/// Serialize a single-line string for a board title.
+/// Newlines cannot be encoded because ZZT interprets them as dingbats (♪).
+pub fn encode_oneline(input: &str) -> Result<Vec<u8>, ParseError> {
+    input
+        .chars()
+        .map(|c| {
+            CP437_WINGDINGS
+                .encode(c)
+                .ok_or_else(|| ParseError::EncodingError(c))
+        })
+        .collect()
+}
+
+/// Deserialize a board title.
+pub fn decode_oneline(input: &[u8]) -> String {
+    input.iter().map(|&x| CP437_WINGDINGS.decode(x)).collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use insta::assert_debug_snapshot;
+
+    fn serialize_code(input: &str) -> Vec<u8> {
+        encode_multiline(input).expect("Error in test")
+    }
+
+    fn serialize_title(input: &str) -> Vec<u8> {
+        encode_oneline(input).expect("Error in test")
+    }
+
+    #[test]
+    fn roundtrip_multiline() {
+        let bytes: Vec<u8> = (0..=255).collect();
+        assert_eq!(bytes, serialize_code(&decode_multiline(&bytes)))
+    }
+
+    #[test]
+    fn roundtrip_oneline() {
+        let bytes: Vec<u8> = (0..=255).collect();
+        assert_eq!(bytes, serialize_title(&decode_oneline(&bytes)))
+    }
+
+    #[test]
+    fn newlines_to_cr() {
+        assert_debug_snapshot!(serialize_code("ABC\nDEF"), @r###"
+        [
+            65,
+            66,
+            67,
+            13,
+            68,
+            69,
+            70,
+        ]
+        "###)
+    }
+
+    #[test]
+    fn byte_13_to_dingbat() {
+        // Code is allowed to have newlines
+        let bytes = serialize_code("ABC\nDEF");
+        assert!(bytes.contains(&13));
+
+        // But in a board title, that same byte is a dingbat
+        assert_debug_snapshot!(decode_oneline(&bytes), @r#""ABC♪DEF""#);
+    }
+
+    #[test]
+    fn wingdings() {
+        assert_debug_snapshot!(decode_multiline(&(0..32).collect::<Vec<_>>()), @r###""\0☺☻♥♦♣♠•◘○◙♂♀\n♫☼►◄↕‼¶§▬↨↑↓→←∟↔▲▼""###);
+        assert_debug_snapshot!(decode_multiline(&(112..144).collect::<Vec<_>>()), @r###""pqrstuvwxyz{|}~⌂ÇüéâäàåçêëèïîìÄÅ""###);
+        assert_debug_snapshot!(decode_multiline(&(224..=255).collect::<Vec<_>>()), @r###""αßΓπΣσµτΦΘΩδ∞φε∩≡±≥≤⌠⌡÷≈°∙·√ⁿ²■\u{a0}""###);
+    }
+}
diff --git a/src/zzt/error.rs b/src/zzt/error.rs
new file mode 100644
index 0000000..a491bbd
--- /dev/null
+++ b/src/zzt/error.rs
@@ -0,0 +1,45 @@
+use nom::error::{ErrorKind, ParseError as NomParseError};
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum ParseError {
+    #[error("invalid ZZT file magic")]
+    InvalidMagic,
+
+    #[error("invalid tile count: {0}")]
+    InvalidTileCount(usize),
+
+    #[error("negative stat count")]
+    NegativeStatCount,
+
+    #[error("string too long")]
+    StringTooLong { max: u8 },
+
+    #[error("cannot encode character: {0}")]
+    EncodingError(char),
+
+    #[error("board data too large")]
+    BoardTooLarge,
+
+    #[error("parse error: {0}")]
+    ParseError(String),
+}
+
+impl<I> NomParseError<I> for ParseError {
+    fn from_error_kind(_input: I, kind: ErrorKind) -> Self {
+        Self::ParseError(kind.description().to_string())
+    }
+
+    fn append(_input: I, kind: ErrorKind, other: Self) -> Self {
+        Self::ParseError(format!("{}: {:?}", other, kind))
+    }
+}
+
+impl From<nom::Err<ParseError>> for ParseError {
+    fn from(value: nom::Err<ParseError>) -> Self {
+        match value {
+            nom::Err::Error(e) | nom::Err::Failure(e) => e,
+            nom::Err::Incomplete(needed) => Self::ParseError(format!("incomplete: {:?}", needed)),
+        }
+    }
+}
diff --git a/src/zzt/mod.rs b/src/zzt/mod.rs
new file mode 100644
index 0000000..84952b2
--- /dev/null
+++ b/src/zzt/mod.rs
@@ -0,0 +1,7 @@
+mod encoding;
+mod error;
+mod parse;
+
+pub use encoding::{decode_multiline, decode_oneline, encode_multiline, encode_oneline};
+pub use error::ParseError;
+pub use parse::{Board, Program, Stat, Tile, World};
diff --git a/src/zzt/parse.rs b/src/zzt/parse.rs
new file mode 100644
index 0000000..8b8262b
--- /dev/null
+++ b/src/zzt/parse.rs
@@ -0,0 +1,418 @@
+use nom::{
+    IResult, Parser,
+    bytes::complete::{tag, take},
+    multi::count,
+    number::complete::{le_i16, le_u8, le_u16},
+};
+
+use super::encoding::{decode_multiline, decode_oneline, encode_multiline, encode_oneline};
+use super::error::ParseError;
+
+/// A single tile on a ZZT board.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct Tile {
+    pub element: u8,
+    pub color: u8,
+}
+
+/// A stat's ZZT-OOP program.
+///
+/// In ZZT, stats can either have their own code or bind to another stat's code.
+/// This enum prevents invalid states where both are set.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Program {
+    /// The stat owns its own code.
+    Own(String),
+    /// The stat is bound to another stat (index into the stats list).
+    Bound(u16),
+}
+
+impl Default for Program {
+    fn default() -> Self {
+        Program::Own(String::new())
+    }
+}
+
+/// A status element on a ZZT board.
+#[derive(Debug, Clone)]
+pub struct Stat {
+    pub x: u8,
+    pub y: u8,
+    pub x_step: i16,
+    pub y_step: i16,
+    pub cycle: i16,
+    pub p1: u8,
+    pub p2: u8,
+    pub p3: u8,
+    pub follower: i16,
+    pub leader: i16,
+    pub under: Tile,
+    pub instruction_pointer: i16,
+    pub program: Program,
+}
+
+/// A ZZT board.
+#[derive(Debug, Clone)]
+pub struct Board {
+    pub name: String,
+    pub tiles: Vec<Tile>,
+    pub max_shots: u8,
+    pub is_dark: bool,
+    pub exit_north: u8,
+    pub exit_south: u8,
+    pub exit_west: u8,
+    pub exit_east: u8,
+    pub restart_on_zap: bool,
+    pub message: String,
+    pub enter_x: u8,
+    pub enter_y: u8,
+    pub time_limit: i16,
+    pub stats: Vec<Stat>,
+}
+
+/// A ZZT world file.
+#[derive(Debug, Default)]
+pub struct World {
+    pub ammo: i16,
+    pub gems: i16,
+    pub keys: [bool; 7],
+    pub health: i16,
+    pub starting_board: i16,
+    pub torches: i16,
+    pub torch_cycles: i16,
+    pub energizer_cycles: i16,
+    pub score: i16,
+    pub name: String,
+    pub flags: [String; 10],
+    pub time: i16,
+    pub time_ticks: i16,
+    pub locked: bool,
+    pub boards: Vec<Board>,
+}
+
+// Parsing helpers
+
+fn bool_u8(input: &[u8]) -> IResult<&[u8], bool, ParseError> {
+    let (input, byte) = le_u8(input)?;
+    Ok((input, byte != 0))
+}
+
+fn pstring(cap: u8) -> impl Fn(&[u8]) -> IResult<&[u8], String, ParseError> {
+    move |input: &[u8]| -> IResult<&[u8], String, ParseError> {
+        let (input, len) = le_u8(input)?;
+        let actual_len = len.min(cap);
+        let (input, data) = take(actual_len)(input)?;
+        let (input, _) = take(cap - actual_len)(input)?;
+        Ok((input, decode_oneline(data)))
+    }
+}
+
+fn board_slice(bytes: &[u8]) -> IResult<&[u8], &[u8], ParseError> {
+    let (_, size) = le_u16.parse(bytes)?;
+    take(size as usize + 2).parse(bytes)
+}
+
+// Serialization helpers
+
+trait SerializationHelpers {
+    fn push_bool(&mut self, value: bool);
+    fn push_i16(&mut self, value: i16);
+    fn push_string(&mut self, cap: u8, value: &str) -> Result<(), ParseError>;
+    fn push_padding(&mut self, size: usize);
+}
+
+impl SerializationHelpers for Vec<u8> {
+    fn push_bool(&mut self, value: bool) {
+        self.push(if value { 1 } else { 0 });
+    }
+
+    fn push_i16(&mut self, value: i16) {
+        self.extend(value.to_le_bytes());
+    }
+
+    fn push_string(&mut self, cap: u8, value: &str) -> Result<(), ParseError> {
+        let bytes = encode_oneline(value)?;
+        if bytes.len() > cap as usize {
+            return Err(ParseError::StringTooLong { max: cap });
+        }
+        self.push(bytes.len() as u8);
+        self.extend_from_slice(&bytes);
+        self.push_padding(cap as usize - bytes.len());
+        Ok(())
+    }
+
+    fn push_padding(&mut self, size: usize) {
+        self.resize(self.len() + size, 0);
+    }
+}
+
+impl World {
+    /// Parse a ZZT world from bytes.
+    pub fn from_bytes(bytes: &[u8]) -> Result<World, ParseError> {
+        let (input, _) = tag(&[0xff, 0xff][..])
+            .parse(bytes)
+            .map_err(|_: nom::Err<ParseError>| ParseError::InvalidMagic)?;
+        let (input, num_boards) = le_i16.parse(input)?;
+        let (input, (ammo, gems, keys)) = (le_i16, le_i16, count(bool_u8, 7)).parse(input)?;
+        let (input, (health, starting_board, torches, torch_cycles, energizer_cycles)) =
+            (le_i16, le_i16, le_i16, le_i16, le_i16).parse(input)?;
+        let (input, (_, score, name)) = (take(2usize), le_i16, pstring(20)).parse(input)?;
+        let (input, flags) = count(pstring(20), 10).parse(input)?;
+        let (_input, (time, time_ticks, locked)) = (le_i16, le_i16, bool_u8).parse(input)?;
+
+        // Rest of header is padding; fast-forward starting from original input
+        let (input, _) = take(512usize).parse(bytes)?;
+
+        // Load boards
+        let num_boards = num_boards as usize + 1;
+        let (_input, chunks) = count(board_slice, num_boards).parse(input)?;
+        let boards: Result<Vec<Board>, ParseError> = chunks
+            .iter()
+            .map(|bytes: &&[u8]| Board::from_bytes(bytes))
+            .collect();
+        let boards = boards?;
+
+        Ok(World {
+            ammo,
+            gems,
+            keys: keys.try_into().unwrap(),
+            health,
+            starting_board,
+            torches,
+            torch_cycles,
+            energizer_cycles,
+            score,
+            name,
+            flags: flags.try_into().unwrap(),
+            time,
+            time_ticks,
+            locked,
+            boards,
+        })
+    }
+
+    /// Serialize this world to bytes.
+    pub fn to_bytes(&self) -> Result<Vec<u8>, ParseError> {
+        let mut result = Vec::with_capacity(512);
+        result.push_i16(-1); // file magic: ZZT world
+        result.push_i16(self.boards.len() as i16 - 1);
+        result.push_i16(self.ammo);
+        result.push_i16(self.gems);
+        for key in self.keys {
+            result.push_bool(key);
+        }
+        result.push_i16(self.health);
+        result.push_i16(self.starting_board);
+        result.push_i16(self.torches);
+        result.push_i16(self.torch_cycles);
+        result.push_i16(self.energizer_cycles);
+        result.push_padding(2);
+        result.push_i16(self.score);
+        result.push_string(20, &self.name)?;
+        for flag in &self.flags {
+            result.push_string(20, flag)?;
+        }
+        result.push_i16(self.time);
+        result.push_i16(self.time_ticks);
+        result.push_bool(self.locked);
+        result.push_padding(512 - result.len());
+
+        for board in &self.boards {
+            result.extend_from_slice(&board.to_bytes()?);
+        }
+        Ok(result)
+    }
+}
+
+impl Board {
+    /// Parse a board from bytes (including the 2-byte size header).
+    pub fn from_bytes(bytes: &[u8]) -> Result<Board, ParseError> {
+        // Ignore length bytes
+        let (input, _) = le_u16.parse(bytes)?;
+
+        // Read board name
+        let (input, name) = pstring(50)(input)?;
+
+        // Read terrain
+        const NUM_TILES: usize = 60 * 25;
+        let mut input = input;
+        let mut tiles = Vec::with_capacity(NUM_TILES);
+        while tiles.len() < NUM_TILES {
+            let (next_input, (count, element, color)) = (le_u8, le_u8, le_u8).parse(input)?;
+            input = next_input;
+            let count: usize = if count == 0 { 256 } else { count.into() };
+            for _ in 0..count {
+                tiles.push(Tile { element, color });
+                if tiles.len() > NUM_TILES {
+                    return Err(ParseError::InvalidTileCount(tiles.len()));
+                }
+            }
+        }
+
+        // Read board info
+        let (input, (max_shots, is_dark)) = (le_u8, bool_u8).parse(input)?;
+        let (input, (exit_north, exit_south, exit_west, exit_east)) =
+            (le_u8, le_u8, le_u8, le_u8).parse(input)?;
+        let (input, (restart_on_zap, message)) = (bool_u8, pstring(58)).parse(input)?;
+        let (input, (enter_x, enter_y, time_limit)) = (le_u8, le_u8, le_i16).parse(input)?;
+        let (input, _) = take(16usize)(input)?;
+
+        // Read stats
+        let (input, num_stats) = le_i16(input)?;
+        let num_stats = num_stats + 1;
+        if num_stats < 0 {
+            return Err(ParseError::NegativeStatCount);
+        }
+        let (_input, stats) = count(Stat::parse, num_stats as usize).parse(input)?;
+
+        Ok(Board {
+            name,
+            tiles,
+            max_shots,
+            is_dark,
+            exit_north,
+            exit_south,
+            exit_east,
+            exit_west,
+            restart_on_zap,
+            message,
+            enter_x,
+            enter_y,
+            time_limit,
+            stats,
+        })
+    }
+
+    /// Parse a standalone .brd file (same format, no world header).
+    pub fn from_brd_bytes(bytes: &[u8]) -> Result<Board, ParseError> {
+        Board::from_bytes(bytes)
+    }
+
+    /// Serialize this board to bytes.
+    pub fn to_bytes(&self) -> Result<Vec<u8>, ParseError> {
+        let mut result = vec![];
+        result.push_padding(2); // reserve space for board size
+        result.push_string(50, &self.name)?;
+
+        // Encode terrain
+        if self.tiles.len() != 1500 {
+            return Err(ParseError::InvalidTileCount(self.tiles.len()));
+        }
+        let mut iter = self.tiles.iter().peekable();
+        while let Some(tile) = iter.next() {
+            let mut count: u8 = 1;
+            while count < 255 && iter.peek().map_or(false, |&next_tile| next_tile == tile) {
+                count += 1;
+                iter.next();
+            }
+            result.push(count);
+            result.push(tile.element);
+            result.push(tile.color);
+        }
+
+        // Board info
+        result.push(self.max_shots);
+        result.push_bool(self.is_dark);
+        result.push(self.exit_north);
+        result.push(self.exit_south);
+        result.push(self.exit_west);
+        result.push(self.exit_east);
+        result.push_bool(self.restart_on_zap);
+        result.push_string(58, &self.message)?;
+        result.push(self.enter_x);
+        result.push(self.enter_y);
+        result.push_i16(self.time_limit);
+        result.push_padding(16);
+
+        // Stats
+        let num_stats: i16 = (self.stats.len() as i16) - 1;
+        result.push_i16(num_stats);
+        for stat in &self.stats {
+            result.extend_from_slice(&stat.to_bytes()?);
+        }
+
+        // Fix up board size
+        let size: u16 = (result.len() - 2)
+            .try_into()
+            .map_err(|_| ParseError::BoardTooLarge)?;
+        result.splice(0..2, size.to_le_bytes());
+
+        Ok(result)
+    }
+}
+
+impl Stat {
+    fn parse(input: &[u8]) -> IResult<&[u8], Self, ParseError> {
+        let (input, (x, y, x_step, y_step)) = (le_u8, le_u8, le_i16, le_i16).parse(input)?;
+        let (input, (cycle, p1, p2, p3)) = (le_i16, le_u8, le_u8, le_u8).parse(input)?;
+        let (input, (follower, leader)) = (le_i16, le_i16).parse(input)?;
+        let (input, (under_element, under_color)) = (le_u8, le_u8).parse(input)?;
+        let (input, _) = take(4usize)(input)?; // unused pointer
+        let (input, (instruction_pointer, length)) = (le_i16, le_i16).parse(input)?;
+        let (input, _) = take(8usize)(input)?; // padding
+
+        let (input, program) = if length < 0 {
+            // Negative length means bound to another stat
+            (input, Program::Bound((-length) as u16))
+        } else {
+            // Positive length means own code
+            let (input, code_bytes) = take(length as usize)(input)?;
+            (input, Program::Own(decode_multiline(code_bytes)))
+        };
+
+        Ok((
+            input,
+            Stat {
+                x,
+                y,
+                x_step,
+                y_step,
+                follower,
+                leader,
+                cycle,
+                p1,
+                p2,
+                p3,
+                under: Tile {
+                    element: under_element,
+                    color: under_color,
+                },
+                instruction_pointer,
+                program,
+            },
+        ))
+    }
+
+    fn to_bytes(&self) -> Result<Vec<u8>, ParseError> {
+        let mut result = vec![];
+        result.push(self.x);
+        result.push(self.y);
+        result.push_i16(self.x_step);
+        result.push_i16(self.y_step);
+        result.push_i16(self.cycle);
+        result.push(self.p1);
+        result.push(self.p2);
+        result.push(self.p3);
+        result.push_i16(self.follower);
+        result.push_i16(self.leader);
+        result.push(self.under.element);
+        result.push(self.under.color);
+        result.push_padding(4); // unused pointer
+        result.push_i16(self.instruction_pointer);
+
+        match &self.program {
+            Program::Bound(index) => {
+                result.push_i16(-(*index as i16));
+                result.push_padding(8);
+            }
+            Program::Own(code) => {
+                let code_bytes = encode_multiline(code)?;
+                result.push_i16(code_bytes.len() as i16);
+                result.push_padding(8);
+                result.extend_from_slice(&code_bytes);
+            }
+        }
+
+        Ok(result)
+    }
+}