lunar_wave/src/loader.rs

use std::io::Read;

use crate::{
	instruction::Instruction as Inst,
	state::{
		Block,
		Chunk,
	}
};

pub (crate) fn compile_bytecode_from_file (path: &str) -> Vec <u8> {
	use std::{
		process::{
			Command,
			Stdio,
		},
	};
	
	let child = Command::new ("luac5.4")
	.arg ("-o") // Output to...
	.arg ("-")  // Standard output
	.arg (path) 
	.stdout (Stdio::piped ())
	.spawn ()
	.expect ("failed to execute `luac5.4`. Is Lua installed?");
	
	let output = child
	.wait_with_output ()
	.expect ("failed to wait on child");
	
	output.stdout.as_slice ().to_vec ()
}

/// Invoke `luac` as a subprocess
/// Luckily luac is single-pass, so we can just pipe in and out
/// 
/// `source` is a Vec because we move it to a worker thread

pub (crate) fn compile_bytecode_from_stdin (source: Vec <u8>) -> Vec <u8> {
	use std::{
		io::Write,
		process::{
			Command,
			Stdio,
		},
	};
	
	let mut child = Command::new ("luac5.4")
	.arg ("-o") // Output to...
	.arg ("-")  // Standard output
	.arg ("-")  // Input from standard input
	.stdin (Stdio::piped ())
	.stdout (Stdio::piped ())
	.spawn ()
	.expect ("failed to execute `luac5.4`. Is Lua installed?");
	
	let mut stdin = child.stdin.take ().expect ("failed to get stdin");
	std::thread::spawn (move || {
		stdin.write_all (&source).expect ("failed to write to stdin");
	});
	
	let output = child
	.wait_with_output ()
	.expect ("failed to wait on child");
	
	output.stdout.as_slice ().to_vec ()
}

fn i_sb (buf: [u8; 4]) -> Option <i8> {
	let b = buf [2];
	i8::try_from (i32::try_from (b).ok ()? - 127).ok ()
}

fn i_sc (buf: [u8; 4]) -> Option <i8> {
	let c = buf [3];
	i8::try_from (i32::try_from (c).ok ()? - 127).ok ()
}

pub fn parse_inst (buf: [u8; 4]) -> Option <Inst>
{
	let opcode = buf [0] & 0x7f;
	
	let a = (buf [0] >> 7) | ((buf [1] & 0x7f) << 1);
	let b = buf [2];
	let ax = a as u32 + ((b as u32) << 8);
	let c = buf [3];
	let s_c = c - 0x80;
	let bx = 
		(((buf [1] >> 7) as u32) << 0) | 
		((buf [2] as u32) << 1) |
		((buf [3] as u32) << 9);
	let sbx = i32::try_from (bx).ok ()? - 65535;
	let k = (buf [1] & 0x80) >> 7 == 1;
	let s_j = a as i32 + ((b as i32) << 8) + 1;
	
	Some (match opcode {
		0x00 => Inst::Move (a, b),
		0x01 => Inst::LoadI (a, sbx),
		0x02 => Inst::LoadF (a, sbx),
		0x03 => Inst::LoadK (a, bx),
		0x05 => Inst::LoadFalse (a),
		0x07 => Inst::LoadTrue (a),
		0x08 => Inst::LoadNil (a),
		0x09 => Inst::GetUpVal (a, b),
		0x0b => Inst::GetTabUp (a, b, c),
		0x0c => Inst::GetTable (a, b, c),
		0x0d => Inst::GetI (a, b, c),
		0x0e => Inst::GetField (a, b, c),
		0x0f => Inst::SetTabUp (a, b, c),
		0x11 => Inst::SetI (a, b, c, k),
		0x12 => Inst::SetField (a, b, c, k),
		0x13 => Inst::NewTable (a),
		0x15 => Inst::AddI (a, b, i_sc (buf)?),
		0x18 => Inst::MulK (a, b, c),
		0x19 => Inst::ModK (a, b, c),
		0x22 => Inst::Add (a, b, c),
		0x24 => Inst::Mul (a, b, c),
		0x2e => Inst::MmBin (a, b, c),
		0x30 => Inst::MmBinK (a, b, c, k),
		0x33 => Inst::Not (a, b),
		0x34 => Inst::Len (a, b),
		0x3c => Inst::EqK (a, b, k),
		0x3d => Inst::EqI (a, i_sb (buf)?, k),
		0x38 => Inst::Jmp (s_j),
		0x42 => Inst::Test (a, k),
		0x44 => Inst::Call (a, b, c),
		0x45 => Inst::TailCall (a, b, c, k),
		0x46 => Inst::Return (a, b, c, k),
		0x47 => Inst::Return0,
		0x48 => Inst::Return1 (a),
		0x49 => Inst::ForLoop (a, bx),
		0x4a => Inst::ForPrep (a, bx),
		0x4e => Inst::SetList (a, b, c, k),
		0x4f => Inst::Closure (a, bx),
		0x51 => Inst::VarArgPrep (a.into ()),
		0x52 => Inst::ExtraArg (ax),
		_ => return None,
	})
}

#[derive (Debug, PartialEq)]
struct Header {
	inst_count: u8,
}

/// loadUnsigned in PUC Lua
/// Decodes a varint format that has 7 bits per bytes and the 8th bit
/// is set to 1 on the last byte.

fn load_unsigned <R: Read> (rdr: &mut R, limit: usize) -> usize {
	// Shrink the limit so we can tell when we pass it
	let limit = limit >> 7;
	
	let mut x = 0;
	for _ in 0..32 {
		let b = parse_byte (rdr).unwrap ();
		if x >= limit {
			panic! ("integer overflow {x} >= {limit}");
		}
		x = (x << 7) | (b as usize & 0x7f);
		if (b & 0x80) != 0 {
			break;
		}
	}
	
	x
}

fn load_size <R: Read> (rdr: &mut R) -> usize {
	load_unsigned (rdr, usize::MAX)
}

// loadString in PUC Lua. Doesn't work with long strings yet.

fn parse_string <R: Read> (rdr: &mut R) -> Option <String> {
	let len = match load_size (rdr) {
		0 => return Some (String::new ()),
		x => x - 1,
	};
	
	let mut buf = vec! [0u8; len];
	rdr.read_exact (&mut buf).ok ()?;
	Some (String::from_utf8 (buf).ok ()?)
}

// loadByte in PUC Lua

fn parse_byte <R: Read> (rdr: &mut R) -> Option <u8>
{
	let mut buf = [0u8; 1];
	rdr.read_exact (&mut buf).ok ()?;
	Some (buf [0])
}

fn parse_float <R: Read> (rdr: &mut R) -> Option <f64> {
	let mut buf = [0u8; 8];
	rdr.read_exact (&mut buf).ok ()?;
	Some (f64::from_ne_bytes(buf))
}

fn parse_int <R: Read> (rdr: &mut R) -> Option <u32>
{
	Some ((parse_byte (rdr)? - 0x80) as u32)
}

fn parse_i64 <R: Read> (rdr: &mut R) -> Option <i64> {
	let mut buf = [0u8; 8];
	rdr.read_exact (&mut buf).ok ()?;
	Some (i64::from_ne_bytes(buf))
}

// I'm doing this recursively so it's easy to match with the PUC Lua
// code, but I don't like recursion in general, and I don't know
// why PUC wrote it that way.

pub fn parse_block <R: Read> (rdr: &mut R, blocks: &mut Vec <Block>) 
-> Option <()> 
{
	// Ignore things I haven't implemented yet
	
	use crate::value::Value;
	
	parse_string (rdr)?; // function name
	parse_int (rdr).unwrap ();    // start line in source code
	parse_int (rdr).unwrap ();    // last line in source code
	parse_byte (rdr).unwrap ();   // num params
	parse_byte (rdr).unwrap ();   // is_vararg
	parse_byte (rdr).unwrap ();   // maxstacksize, might be same as num slots?
	
	let inst_count = load_size (rdr);
	let mut instructions = Vec::with_capacity (inst_count as usize);
	
	for _ in 0..inst_count {
		let mut buf = [0u8; 4];
		rdr.read_exact (&mut buf).ok ().unwrap ();
		instructions.push (parse_inst (buf).expect (&format! ("{buf:?}")));
	}
	
	let constant_count = parse_int (rdr).unwrap ();
	
	let mut constants = Vec::with_capacity (constant_count as usize);
	
	for i in 0..constant_count {
		// LUA_TNIL and friends from `lua.h` in PUC Lua
		let const_type = parse_byte (rdr)?;
		
		let val = match const_type {
			 3 => parse_i64 (rdr).unwrap ().into (),
			 4 => parse_string (rdr).unwrap ().into (),
			 
			// For LUA_TNUMBER, PUC Lua uses a macro that adds 16 to signify a float
			19 => parse_float (rdr).unwrap ().into (),
			// 0x10 + 4 = long string
			20 => parse_string (rdr).unwrap ().into (),
			x => panic! ("Constant {} has type {}", i, x),
		};
		
		constants.push (val);
	}
	
	let upvalue_count = parse_int (rdr).unwrap () as usize;
	let mut upvalues = Vec::with_capacity (upvalue_count);
	for _ in 0..upvalue_count {
		let in_stack = parse_byte (rdr).unwrap () == 1;
		let idx = parse_byte (rdr).unwrap ();
		let kind = parse_byte (rdr).unwrap ();
		
		let upvalue = crate::state::Upvalue {
			in_stack,
			idx,
			kind,
		};
		
		upvalues.push (upvalue);
	}
	
	blocks.push (Block {
		constants,
		instructions,
		upvalues,
	});
	
	// Recursion
	
	// Subfunctions. PUC calls them protos.
	let protos_count = parse_int (rdr).unwrap ();
	for _ in 0..protos_count {
		parse_block (rdr, blocks).unwrap ();
	}
	
	// Skip over debug stuff
	
	// I think this is delta line numbers, e.g. most instructions
	// have 0, but when you go to a new source line it's 1+.
	
	let lineinfo_count = parse_int (rdr).unwrap ();
	for _ in 0..lineinfo_count {
		parse_byte (rdr).unwrap ();
	}
	
	// Absolute line info, didn't see that in my test files
	
	let abslineinfo_count = parse_int (rdr).unwrap ();
	assert_eq! (abslineinfo_count, 0);
	
	let local_count = parse_int (rdr).unwrap ();
	for _ in 0..local_count {
		parse_string(rdr).unwrap ();
		parse_int (rdr).unwrap ();
		parse_int (rdr).unwrap ();
	}
	
	let upvalue_count = parse_int (rdr).unwrap ();
	for _ in 0..upvalue_count {
		parse_string (rdr).unwrap ();
	}
	
	Some (())
}


pub fn parse_chunk <R: Read> (rdr: &mut R) -> Option <Chunk> {
	// Discard 32 bytes from the start of the file.
	// This is magic number, version number, etc.
	
	let mut hdr = [0u8; 32];
	rdr.read_exact (&mut hdr).ok ()?;
	
	assert_eq! (&hdr [0..8], &[0x1b, 0x4c, 0x75, 0x61, 0x54, 0x00, 0x19, 0x93], "This isn't a Lua 5.4 bytecode file");
	
	let mut blocks = vec![];
	
	parse_block (rdr, &mut blocks).unwrap ();
	
	Some (Chunk {
		blocks,
	})
}

pub fn parse_chunk_from_bytes (b: &[u8]) -> Option <Chunk> {
	let mut rdr = std::io::Cursor::new (b);
	parse_chunk (&mut rdr)
}

#[cfg (test)]
mod tests {
	#[test]
	fn load_size () {
		let f = |input: &[u8]| {
			let mut cursor = std::io::Cursor::new (input);
			super::load_size (&mut cursor)
		};
		
		assert_eq! (f (&[0x80]), 0);
		assert_eq! (f (&[0x81]), 1);
		assert_eq! (f (&[0x82]), 2);
		
		assert_eq! (f (&[0xff]), 127);
		
		assert_eq! (f (&[0x01, 0x80]), 128);
		assert_eq! (f (&[0x01, 0x81]), 129);
		assert_eq! (f (&[0x02, 0x80]), 256);
		
		assert_eq! (f (&[0x7f, 0xfe]), 16382);
		assert_eq! (f (&[0x7f, 0xff]), 16383);
		assert_eq! (f (&[0x01, 0x00, 0x80]), 16384);
	}
	
	#[test]
	fn parse_inst () {
		use super::Inst;
		
		for (input, expected) in [
			([0x51, 0x00, 0x00, 0x00], Inst::VarArgPrep (0)),
			([0x4f, 0x00, 0x00, 0x00], Inst::Closure (0, 0)),
			([0xcf, 0x00, 0x00, 0x00], Inst::Closure (1, 0)),
			([0x8b, 0x00, 0x00, 0x00], Inst::GetTabUp (1, 0, 0)),
			([0x03, 0x81, 0x00, 0x00], Inst::LoadK (2, 1)),
			([0xc4, 0x00, 0x02, 0x01], Inst::Call (1, 2, 1)),
			([0x80, 0x00, 0x00, 0x00], Inst::Move (1, 0)),
			([0xc4, 0x00, 0x01, 0x02], Inst::Call (1, 1, 2)),
			([0x0b, 0x01, 0x00, 0x00], Inst::GetTabUp (2, 0, 0)),
			([0x83, 0x01, 0x01, 0x00], Inst::LoadK (3, 2)),
			([0x44, 0x01, 0x02, 0x01], Inst::Call (2, 2, 1)),
			([0x0b, 0x01, 0x00, 0x00], Inst::GetTabUp (2, 0, 0)),
			([0x80, 0x01, 0x01, 0x00], Inst::Move (3, 1)),
			([0xc4, 0x01, 0x01, 0x00], Inst::Call (3, 1, 0)),
			([0x44, 0x01, 0x00, 0x01], Inst::Call (2, 0, 1)),
			([0x0b, 0x01, 0x00, 0x00], Inst::GetTabUp (2, 0, 0)),
			([0x83, 0x81, 0x01, 0x00], Inst::LoadK (3, 3)),
			([0x44, 0x01, 0x02, 0x01], Inst::Call (2, 2, 1)),
			([0x46, 0x01, 0x01, 0x01], Inst::Return (2, 1, 1, false)),
			
			([0x01, 0x00, 0x02, 0x80], Inst::LoadI (0, 5)),
			([0xc6, 0x80, 0x02, 0x00], Inst::Return (1, 2, 0, true)),
			
			([0x09, 0x00, 0x01, 0x00], Inst::GetUpVal (0, 1)),
			([0x48, 0x00, 0x02, 0x00], Inst::Return1 (0)),
			([0x47, 0x00, 0x01, 0x00], Inst::Return0),
			([0x8d, 0x00, 0x01, 0x01], Inst::GetI (1, 1, 1)),
			([0xbc, 0x00, 0x01, 0x00], Inst::EqK (1, 1, false)),
			([0xb8, 0x02, 0x00, 0x80], Inst::Jmp (6)),
			([0x38, 0x02, 0x00, 0x80], Inst::Jmp (5)),
			([0x52, 0x00, 0x00, 0x00], Inst::ExtraArg (0)),
		] {
			let actual = super::parse_inst (input).unwrap ();
			assert_eq!(actual, expected);
		}
	}
	
	#[test]
	fn parse_nested_functions () {
		use std::io::Read;
		
		let bytecode = include_bytes! ("../test_vectors/functions.luac");
		
		{
			let mut rdr = std::io::Cursor::new (bytecode.clone ());
			
			let mut buf = [0u8; 32];
			rdr.read_exact (&mut buf).unwrap ();
			
			let mut blocks = vec! [];
			
			super::parse_block (&mut rdr, &mut blocks).unwrap ();
			
			assert_eq! (blocks [0].instructions.len (), 15);
			assert_eq! (blocks [1].instructions.len (),  6);
			assert_eq! (blocks [2].instructions.len (),  4);
			assert_eq! (blocks [3].instructions.len (),  4);
			assert_eq! (blocks [4].instructions.len (),  4);
		}
		
		if false {
			let mut rdr = std::io::Cursor::new (bytecode.clone ());
			let file = crate::loader::parse_chunk (&mut rdr).unwrap ();
			
			assert_eq! (file.blocks.len (), 5);
		}
	}
}