checksmix 0.2.23

//! MMIX Object (MMO) file format support
//!
//! This module handles generation and parsing of MMIX object files (.mmo format).
//! The MMO format consists of records (not instructions) that specify how to load
//! code and data into memory at arbitrary 64-bit addresses.
//!
//! ## Format Specification (from MMOTYPE)
//!
//! ### Record Structure
//! - All records begin with MM escape code (0x98)
//! - Format: `MM lopcode Y Z [data...]`
//! - YZ = (Y << 8) | Z (16-bit value)
//! - All multi-byte values are big-endian
//!
//! ### Normal Data Tetrabytes
//! Any tetrabyte NOT preceded by MM (0x98) is loaded as data at cur_loc,
//! then cur_loc += 4. This is the primary way to load instruction/data bytes.
//!
//! ### Lopcodes (verified against mmotype.pdf)
//! - 0x00 (lop_quote): Quote single tetrabyte (YZ must = 1)
//! - 0x01 (lop_loc): Set current location
//! - 0x02 (lop_skip): Skip YZ bytes forward
//! - 0x03 (lop_fixo): Absolute fixup
//! - 0x04 (lop_fixr): Relative fixup
//! - 0x05 (lop_fixrx): Extended relative fixup
//! - 0x06 (lop_file): File name
//! - 0x07 (lop_line): Source line number
//! - 0x08 (lop_spec): Special data
//! - 0x09 (lop_pre): Preamble (Y=version, typically 1)
//! - 0x0A (lop_post): Postamble (Y=0, Z>=32)
//! - 0x0B (lop_stab): Symbol table
//! - 0x0C (lop_end): End of file (YZ=symbol table length)
//!
//! Reference: MMIXWARE documentation by Donald Knuth, mmotype.pdf

use crate::mmixal::MMixInstruction;
use std::collections::HashMap;
use tracing::debug;

use crate::encode::encode_instruction_bytes;

/// MMO escape code - all MMO files must start with this
pub const MM: u8 = 0x98;

/// MMO record types (lopcodes) as defined in the MMIXAL specification
/// Reference: MMIXWARE documentation, Section on MMO Format
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[repr(u8)]
#[allow(clippy::enum_variant_names)]
pub enum MmoRecordType {
    /// lop_quote (0): Literal data to load at current address
    LopQuote = 0,
    /// lop_loc (1): Set loading address
    LopLoc = 1,
    /// lop_skip (2): Advance current address
    LopSkip = 2,
    /// lop_fixo (3): Octabyte-fix lopcode
    LopFixo = 3,
    /// lop_fixr (4): Relative-fix lopcode
    LopFixr = 4,
    /// lop_fixrx (5): Extended relative-fix lopcode
    LopFixrx = 5,
    /// lop_file (6): File name lopcode
    LopFile = 6,
    /// lop_line (7): File position lopcode
    LopLine = 7,
    /// lop_spec (8): Special hook lopcode
    LopSpec = 8,
    /// lop_pre (9): Preamble lopcode
    LopPre = 9,
    /// lop_post (10): Postamble lopcode
    LopPost = 10,
    /// lop_stab (11): Symbol table lopcode
    LopStab = 11,
    /// lop_end (12): End-it-all lopcode
    LopEnd = 12,
}

impl TryFrom<u8> for MmoRecordType {
    type Error = String;

    fn try_from(value: u8) -> Result<Self, Self::Error> {
        match value {
            0x0 => Ok(MmoRecordType::LopQuote),
            0x1 => Ok(MmoRecordType::LopLoc),
            0x2 => Ok(MmoRecordType::LopSkip),
            0x3 => Ok(MmoRecordType::LopFixo),
            0x4 => Ok(MmoRecordType::LopFixr),
            0x5 => Ok(MmoRecordType::LopFixrx),
            0x6 => Ok(MmoRecordType::LopFile),
            0x7 => Ok(MmoRecordType::LopLine),
            0x8 => Ok(MmoRecordType::LopSpec),
            0x9 => Ok(MmoRecordType::LopPre),
            0xa => Ok(MmoRecordType::LopPost),
            0xb => Ok(MmoRecordType::LopStab),
            0xc => Ok(MmoRecordType::LopEnd),
            _ => Err(format!("Unknown MMO lopcode: 0x{:02X}", value)),
        }
    }
}

/// MMO file generator
pub struct MmoGenerator {
    /// Instructions to encode, sorted by address
    instructions: Vec<(u64, MMixInstruction)>,
    /// Symbol table (labels)
    labels: HashMap<String, u64>,
}

impl MmoGenerator {
    /// Create a new MMO generator
    pub fn new(instructions: Vec<(u64, MMixInstruction)>, labels: HashMap<String, u64>) -> Self {
        Self {
            instructions,
            labels,
        }
    }

    /// Generate MMIX object code in .mmo format
    /// The format uses records (lopcodes) preceded by the MM escape code (0x98).
    /// Each record has the format: MM YZ X Z where YZ is a 16-bit value
    /// - lop_pre (9): Preamble
    /// - lop_loc (1): Set loading address (followed by 2 tetras for 64-bit addr)
    /// - lop_quote (0): Literal data bytes to load at current address
    /// - lop_post (10): Postamble
    pub fn generate(&self) -> Vec<u8> {
        debug!("Generating MMIX object code (.mmo format)");
        let mut mmo = Vec::new();

        // Write preamble: lop_pre
        // Format: MM lop_pre YZ (version in YZ, typically 1)
        self.emit_simple_record(&mut mmo, MmoRecordType::LopPre, 1);

        // Group instructions by contiguous address ranges
        let mut sorted_instructions: Vec<_> = self.instructions.iter().collect();
        sorted_instructions.sort_by_key(|(addr, _)| *addr);

        let mut current_loc: Option<u64> = None;
        let mut pending_bytes = Vec::new();

        for (addr, instruction) in sorted_instructions {
            let addr = *addr;
            // Encode a single instruction to bytes
            let bytes = encode_instruction_bytes(instruction);

            // Check if we need to emit a new lop_loc directive
            let need_new_loc = match current_loc {
                None => true,
                Some(loc) => {
                    // Need new LOC if not contiguous or pending buffer would be too large
                    addr != loc || pending_bytes.len() + bytes.len() > 252
                }
            };

            if need_new_loc {
                // Flush any pending bytes first
                if !pending_bytes.is_empty() {
                    self.emit_lop_quote(&mut mmo, &pending_bytes);
                    pending_bytes.clear();
                }

                // Emit lop_loc to set new address
                self.emit_lop_loc(&mut mmo, addr);
            }

            // Add bytes to pending buffer
            pending_bytes.extend_from_slice(&bytes);
            current_loc = Some(addr + bytes.len() as u64);
        }

        // Flush any remaining bytes
        if !pending_bytes.is_empty() {
            self.emit_lop_quote(&mut mmo, &pending_bytes);
        }

        // Write postamble: lop_post with entry point
        // Find Main label or use first instruction address
        let entry_point = self
            .labels
            .get("Main")
            .or_else(|| {
                self.instructions
                    .iter()
                    .find(|(addr, _)| *addr < 0x2000000000000000)
                    .map(|(addr, _)| addr)
            })
            .copied()
            .unwrap_or(0x100);

        self.emit_lop_post(&mut mmo, entry_point);

        debug!("Generated {} bytes of .mmo object code", mmo.len());
        mmo
    }

    /// Emit a simple record with just YZ value (no additional data)
    /// Format: MM lopcode YZ (4 bytes total)
    fn emit_simple_record(&self, mmo: &mut Vec<u8>, lopcode: MmoRecordType, yz: u16) {
        mmo.push(MM); // MM escape code
        mmo.push(lopcode as u8); // lopcode
        mmo.push((yz >> 8) as u8); // Y
        mmo.push((yz & 0xFF) as u8); // Z
    }

    /// Emit lop_quote: literal bytes to load at current address
    /// Format: MM lop_quote YZ X, followed by YZ tetras of data (padded to tetra boundary)
    /// where YZ is a 16-bit count of tetras (not bytes)
    fn emit_lop_quote(&self, mmo: &mut Vec<u8>, bytes: &[u8]) {
        // Split into chunks of max 255 tetras (1020 bytes)
        for chunk in bytes.chunks(1020) {
            let chunk_tetras = chunk.len().div_ceil(4);
            let yz = chunk_tetras as u16;

            mmo.push(MM); // MM escape code
            mmo.push(MmoRecordType::LopQuote as u8); // lop_quote
            mmo.push((yz >> 8) as u8); // Y
            mmo.push((yz & 0xFF) as u8); // Z

            // Write data, padding to tetra boundary
            mmo.extend_from_slice(chunk);
            let padding = (4 - (chunk.len() % 4)) % 4;
            for _ in 0..padding {
                mmo.push(0);
            }
        }
    }

    /// Emit lop_loc: set current loading address
    /// Format: MM lop_loc YZ X (4 bytes), followed by 2 tetras (8 bytes) for 64-bit address
    /// Total: 12 bytes
    fn emit_lop_loc(&self, mmo: &mut Vec<u8>, addr: u64) {
        // Record header: MM lop_loc with YZ=2 (two tetras of address data follow)
        mmo.push(MM); // MM escape code
        mmo.push(MmoRecordType::LopLoc as u8); // lop_loc
        mmo.push(0x00); // Y
        mmo.push(0x02); // Z = 2 (two tetras follow)

        // Tetra 1: high 32 bits
        let high = (addr >> 32) as u32;
        mmo.extend_from_slice(&high.to_be_bytes());

        // Tetra 2: low 32 bits
        let low = (addr & 0xFFFFFFFF) as u32;
        mmo.extend_from_slice(&low.to_be_bytes());
    }

    /// Emit lop_post: postamble, storing entry point in register 255
    fn emit_lop_post(&self, mmo: &mut Vec<u8>, entry_point: u64) {
        mmo.push(MM); // MM escape code
        mmo.push(MmoRecordType::LopPost as u8); // lop_post
        mmo.push(0x00); // Y must be 0
        mmo.push(0xFF); // Z = 255 (start writing from g[255])

        let high = (entry_point >> 32) as u32;
        let low = (entry_point & 0xFFFF_FFFF) as u32;
        mmo.extend_from_slice(&high.to_be_bytes());
        mmo.extend_from_slice(&low.to_be_bytes());
    }
}

/// MMO file decoder
pub struct MmoDecoder {
    data: Vec<u8>,
}

impl MmoDecoder {
    /// Create a new MMO decoder
    pub fn new(data: Vec<u8>) -> Self {
        Self { data }
    }

    /// Decode MMO format and load into memory
    /// Returns the entry point address and a callback is invoked for each byte to write
    /// MMO format: each record starts with MM (0x98) followed by lopcode and data
    pub fn decode<F>(&self, mut write_byte: F) -> u64
    where
        F: FnMut(u64, u8),
    {
        debug!("Decoding MMIX object code (.mmo format)");
        let mut entry_point = 0x100u64; // Default entry point
        let mut i = 0;
        let mut current_addr = 0u64;

        while i < self.data.len() {
            // Check for MM escape code
            if i >= self.data.len() {
                break;
            }

            if self.data[i] != MM {
                // All records should start with MM in our MMO files
                debug!(
                    "Unexpected byte (not MM escape) at offset 0x{:X}: 0x{:02X}",
                    i, self.data[i]
                );
                i += 1;
                continue;
            }

            // We have MM, now get the lopcode
            i += 1;
            if i >= self.data.len() {
                break;
            }

            let lopcode_byte = self.data[i];
            i += 1;

            // Try to parse as a known lopcode
            match MmoRecordType::try_from(lopcode_byte) {
                Ok(MmoRecordType::LopQuote) => {
                    // lop_quote: YZ tetras of literal data follow
                    if i + 2 > self.data.len() {
                        break;
                    }
                    let yz = ((self.data[i] as usize) << 8) | (self.data[i + 1] as usize);
                    i += 2; // Skip YZ

                    // Load yz tetras (4*yz bytes) at current_addr
                    let byte_count = yz * 4;
                    debug!(
                        "lop_quote: loading {} bytes at 0x{:X}",
                        byte_count, current_addr
                    );
                    for offset in 0..byte_count {
                        if i + offset < self.data.len() {
                            write_byte(current_addr + offset as u64, self.data[i + offset]);
                        }
                    }
                    current_addr += byte_count as u64;
                    i += byte_count;
                }
                Ok(MmoRecordType::LopLoc) => {
                    // lop_loc: Set loading address
                    // Format: MM lop_loc YZ (lopcode already read)
                    // Followed by 2 tetras (8 bytes) for address
                    if i + 2 > self.data.len() {
                        break;
                    }
                    let _yz = ((self.data[i] as u16) << 8) | (self.data[i + 1] as u16);
                    i += 2; // Skip YZ

                    if i + 8 > self.data.len() {
                        break;
                    }

                    let high = u32::from_be_bytes([
                        self.data[i],
                        self.data[i + 1],
                        self.data[i + 2],
                        self.data[i + 3],
                    ]);
                    let low = u32::from_be_bytes([
                        self.data[i + 4],
                        self.data[i + 5],
                        self.data[i + 6],
                        self.data[i + 7],
                    ]);
                    current_addr = ((high as u64) << 32) | (low as u64);
                    debug!("lop_loc: set address to 0x{:X}", current_addr);
                    i += 8;
                }
                Ok(MmoRecordType::LopPre) => {
                    // lop_pre: Preamble (just YZ, no data)
                    if i + 2 > self.data.len() {
                        break;
                    }
                    i += 2; // Skip YZ
                }
                Ok(MmoRecordType::LopPost) => {
                    if i + 2 > self.data.len() {
                        break;
                    }
                    let _y = self.data[i];
                    let start = self.data[i + 1] as usize;
                    i += 2;
                    let mut reg_index = start;
                    while reg_index <= 255 {
                        if i + 8 > self.data.len() {
                            i = self.data.len();
                            break;
                        }
                        let high = u32::from_be_bytes([
                            self.data[i],
                            self.data[i + 1],
                            self.data[i + 2],
                            self.data[i + 3],
                        ]);
                        let low = u32::from_be_bytes([
                            self.data[i + 4],
                            self.data[i + 5],
                            self.data[i + 6],
                            self.data[i + 7],
                        ]);
                        let value = ((high as u64) << 32) | (low as u64);
                        if reg_index == 255 {
                            entry_point = value;
                        }
                        i += 8;
                        reg_index += 1;
                    }
                }
                Ok(MmoRecordType::LopSkip) => {
                    // lop_skip: Advance current address by YZ tetras
                    if i + 2 > self.data.len() {
                        break;
                    }
                    let yz = ((self.data[i] as u64) << 8) | (self.data[i + 1] as u64);
                    current_addr += yz * 4; // Skip YZ tetras
                    i += 2;
                }
                Ok(MmoRecordType::LopEnd) => {
                    // lop_end: End of file
                    break;
                }
                Ok(_) => {
                    // Other lopcodes we don't handle yet - skip the YZ bytes
                    debug!(
                        "Unhandled lopcode: {:?}",
                        MmoRecordType::try_from(lopcode_byte)
                    );
                    if i + 2 <= self.data.len() {
                        i += 2;
                    } else {
                        break;
                    }
                }
                Err(e) => {
                    // Unknown lopcode
                    debug!("Error: {}", e);
                    // Try to skip - assume YZ follows
                    if i + 2 <= self.data.len() {
                        i += 2;
                    } else {
                        break;
                    }
                }
            }
        }

        debug!("Decoded .mmo file, entry point: 0x{:X}", entry_point);
        entry_point
    }
}

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

    #[test]
    fn test_record_type_enum() {
        // Test conversion from u8 to MmoRecordType
        assert_eq!(MmoRecordType::try_from(0).unwrap(), MmoRecordType::LopQuote);
        assert_eq!(MmoRecordType::try_from(1).unwrap(), MmoRecordType::LopLoc);
        assert_eq!(MmoRecordType::try_from(2).unwrap(), MmoRecordType::LopSkip);
        assert_eq!(MmoRecordType::try_from(9).unwrap(), MmoRecordType::LopPre);
        assert_eq!(MmoRecordType::try_from(10).unwrap(), MmoRecordType::LopPost);
        assert_eq!(MmoRecordType::try_from(12).unwrap(), MmoRecordType::LopEnd);

        // Test invalid record type
        assert!(MmoRecordType::try_from(13).is_err());
        assert!(MmoRecordType::try_from(255).is_err());
    }

    #[test]
    fn test_mm_escape_code() {
        // Verify MM constant is correct
        assert_eq!(MM, 0x98);
    }

    #[test]
    fn test_mmo_format_debug() {
        // Debug test to see the actual bytes generated
        let instructions = vec![(0x100, MMixInstruction::SET(1, 42))];
        let labels = HashMap::new();

        let generator = MmoGenerator::new(instructions, labels);
        let mmo_data = generator.generate();

        // Print the raw bytes
        println!("Generated MMO bytes ({} total):", mmo_data.len());
        for (i, &byte) in mmo_data.iter().enumerate() {
            print!("{:02X} ", byte);
            if (i + 1) % 16 == 0 {
                println!();
            }
        }
        println!();

        // Decode and print what we got
        let decoder = MmoDecoder::new(mmo_data);
        let mut memory = HashMap::new();
        let entry_point = decoder.decode(|addr, byte| {
            println!("Loaded byte 0x{:02X} at address 0x{:X}", byte, addr);
            memory.insert(addr, byte);
        });

        println!("Entry point: 0x{:X}", entry_point);
        println!("Memory size: {}", memory.len());
    }

    #[test]
    fn test_mmo_encode_decode_simple() {
        // Create a simple program with one instruction
        // Note: SET expands to 4 instructions (SETH, SETMH, SETML, SETL) = 16 bytes
        let instructions = vec![(0x100, MMixInstruction::SETL(1, 42))];
        let labels = HashMap::new();

        let generator = MmoGenerator::new(instructions, labels);
        let mmo_data = generator.generate();

        // Verify the MMO data starts with MM escape code and preamble
        assert_eq!(mmo_data[0], MM);
        assert_eq!(mmo_data[1], MmoRecordType::LopPre as u8);

        // Decode and verify
        let decoder = MmoDecoder::new(mmo_data);
        let mut memory = HashMap::new();
        let entry_point = decoder.decode(|addr, byte| {
            memory.insert(addr, byte);
        });

        // Verify entry point
        assert_eq!(entry_point, 0x100);

        // Verify instruction was loaded at 0x100
        // SETL $1, 42 = E3 01 00 2A
        assert_eq!(memory.get(&0x100), Some(&0xE3));
        assert_eq!(memory.get(&0x101), Some(&0x01));
        assert_eq!(memory.get(&0x102), Some(&0x00));
        assert_eq!(memory.get(&0x103), Some(&0x2A));
    }

    #[test]
    fn test_mmo_encode_decode_multiple_instructions() {
        // Create a program with multiple contiguous instructions
        let instructions = vec![
            (0x100, MMixInstruction::SETL(1, 10)),
            (0x104, MMixInstruction::SETL(2, 20)),
            (0x108, MMixInstruction::ADD(3, 1, 2)),
        ];
        let labels = HashMap::new();

        let generator = MmoGenerator::new(instructions, labels);
        let mmo_data = generator.generate();

        // Decode
        let decoder = MmoDecoder::new(mmo_data);
        let mut memory = HashMap::new();
        decoder.decode(|addr, byte| {
            memory.insert(addr, byte);
        });

        // Verify all three instructions are loaded
        assert_eq!(memory.len(), 12); // 3 instructions * 4 bytes each
        assert!(memory.contains_key(&0x100));
        assert!(memory.contains_key(&0x104));
        assert!(memory.contains_key(&0x108));
    }

    #[test]
    fn test_mmo_encode_decode_non_contiguous() {
        // Create a program with non-contiguous instructions (should emit multiple LOC records)
        let instructions = vec![
            (0x100, MMixInstruction::SET(1, 1)),
            (0x200, MMixInstruction::SET(2, 2)),
            (0x300, MMixInstruction::SET(3, 3)),
        ];
        let labels = HashMap::new();

        let generator = MmoGenerator::new(instructions, labels);
        let mmo_data = generator.generate();

        // Count LOC records - each should be preceded by MM
        let loc_count = mmo_data
            .windows(2)
            .filter(|w| w[0] == MM && w[1] == MmoRecordType::LopLoc as u8)
            .count();
        assert_eq!(loc_count, 3); // Should have 3 LOC records for 3 non-contiguous addresses

        // Decode and verify
        let decoder = MmoDecoder::new(mmo_data);
        let mut memory = HashMap::new();
        decoder.decode(|addr, byte| {
            memory.insert(addr, byte);
        });

        // Verify all instructions are at correct addresses
        assert!(memory.contains_key(&0x100));
        assert!(memory.contains_key(&0x200));
        assert!(memory.contains_key(&0x300));
    }

    #[test]
    fn test_mmo_encode_decode_with_main_label() {
        // Create a program with Main label
        let instructions = vec![(0x1000, MMixInstruction::SET(1, 99))];
        let mut labels = HashMap::new();
        labels.insert("Main".to_string(), 0x1000);

        let generator = MmoGenerator::new(instructions, labels);
        let mmo_data = generator.generate();

        let decoder = MmoDecoder::new(mmo_data);
        let mut memory = HashMap::new();
        let entry_point = decoder.decode(|addr, byte| {
            memory.insert(addr, byte);
        });

        // Entry point should be Main label address
        assert_eq!(entry_point, 0x1000);
    }

    #[test]
    fn test_mmo_encode_decode_64bit_addresses() {
        // Test with high addresses (data segment)
        let instructions = vec![
            (0x100, MMixInstruction::SET(1, 1)),
            (0x2000000000000000, MMixInstruction::BYTE(65)), // 'A' in data segment
        ];
        let labels = HashMap::new();

        let generator = MmoGenerator::new(instructions, labels);
        let mmo_data = generator.generate();

        let decoder = MmoDecoder::new(mmo_data);
        let mut memory = HashMap::new();
        decoder.decode(|addr, byte| {
            memory.insert(addr, byte);
        });

        // Verify both low and high addresses are loaded
        assert!(memory.contains_key(&0x100));
        assert!(memory.contains_key(&0x2000000000000000));
        assert_eq!(memory.get(&0x2000000000000000), Some(&65));
    }

    #[test]
    fn test_mmo_lop_loc_format() {
        // Verify LOC record format is correct (12 bytes total: MM + lopcode + YZ + 8 bytes address)
        let instructions = vec![(0x123456789ABCDEF0, MMixInstruction::SET(1, 1))];
        let labels = HashMap::new();

        let generator = MmoGenerator::new(instructions, labels);
        let mmo_data = generator.generate();

        // Find the LOC record (MM followed by lop_loc)
        let loc_pos = mmo_data
            .windows(2)
            .position(|w| w[0] == MM && w[1] == MmoRecordType::LopLoc as u8)
            .expect("Should have LOC record");

        // Verify LOC record structure (12 bytes):
        // Byte 0: MM (0x98)
        // Byte 1: lop_loc (1)
        // Bytes 2-3: YZ (should be 2 for two tetras)
        // Bytes 4-7: high 32 bits
        // Bytes 8-11: low 32 bits
        assert_eq!(mmo_data[loc_pos], MM);
        assert_eq!(mmo_data[loc_pos + 1], MmoRecordType::LopLoc as u8);
        assert_eq!(mmo_data[loc_pos + 2], 0x00); // Y
        assert_eq!(mmo_data[loc_pos + 3], 0x02); // Z = 2 (two tetras follow)

        // Verify the address is stored correctly (big-endian)
        let high = u32::from_be_bytes([
            mmo_data[loc_pos + 4],
            mmo_data[loc_pos + 5],
            mmo_data[loc_pos + 6],
            mmo_data[loc_pos + 7],
        ]);
        let low = u32::from_be_bytes([
            mmo_data[loc_pos + 8],
            mmo_data[loc_pos + 9],
            mmo_data[loc_pos + 10],
            mmo_data[loc_pos + 11],
        ]);
        let reconstructed_addr = ((high as u64) << 32) | (low as u64);
        assert_eq!(reconstructed_addr, 0x123456789ABCDEF0);
    }

    #[test]
    fn test_mmo_lop_quote_format() {
        // Test that lop_quote pads data to tetra boundary
        let instructions = vec![
            (0x100, MMixInstruction::BYTE(1)),
            (0x101, MMixInstruction::BYTE(2)),
            (0x102, MMixInstruction::BYTE(3)),
            // 3 bytes should be padded to 4
        ];
        let labels = HashMap::new();

        let generator = MmoGenerator::new(instructions, labels);
        let mmo_data = generator.generate();

        // Find lop_quote record (MM followed by lop_quote)
        let quote_pos = mmo_data
            .windows(2)
            .position(|w| w[0] == MM && w[1] == MmoRecordType::LopQuote as u8)
            .expect("Should have QUOTE record");

        // Byte 0: MM (0x98)
        // Byte 1: lop_quote (0)
        // Bytes 2-3: YZ (tetra count)
        // Bytes 4+: data (padded to tetra boundary)
        assert_eq!(mmo_data[quote_pos], MM);
        assert_eq!(mmo_data[quote_pos + 1], MmoRecordType::LopQuote as u8);

        // YZ should be 1 (1 tetra = 4 bytes, even though we only have 3 bytes of data)
        let yz = ((mmo_data[quote_pos + 2] as u16) << 8) | (mmo_data[quote_pos + 3] as u16);
        assert_eq!(yz, 1);
    }

    #[test]
    fn test_mmo_roundtrip() {
        // Test that encode -> decode produces the same memory layout
        let instructions = vec![
            (0x100, MMixInstruction::SETL(1, 42)),
            (0x104, MMixInstruction::ADD(2, 1, 1)),
            (0x108, MMixInstruction::TRAP(0, 0, 0)),
        ];
        let labels = HashMap::new();

        // Encode
        let generator = MmoGenerator::new(instructions.clone(), labels);
        let mmo_data = generator.generate();

        // Decode
        let decoder = MmoDecoder::new(mmo_data);
        let mut memory = HashMap::new();
        decoder.decode(|addr, byte| {
            memory.insert(addr, byte);
        });

        // Verify each instruction
        for (addr, inst) in &instructions {
            let bytes = encode_instruction_bytes(inst);
            for (offset, &expected_byte) in bytes.iter().enumerate() {
                assert_eq!(
                    memory.get(&(addr + offset as u64)),
                    Some(&expected_byte),
                    "Mismatch at address 0x{:X} offset {}",
                    addr,
                    offset
                );
            }
        }
    }
}