use std::io::Read;

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

/// Invoke `luac` as a subprocess
/// Luckily luac is single-pass, so we can just pipe in and out

pub (crate) fn compile_bytecode (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 ()
}

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 bx = 
		(((buf [1] >> 7) as u32) << 0) | 
		((buf [2] as u32) << 1) |
		((buf [3] as u32) << 9);
	let bx = bx.try_into().ok ()?;
	let sbx = bx - 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),
		0x0d => Inst::GetI (a, b, c),
		0x0f => Inst::SetTabUp (a, b, c),
		0x13 => Inst::NewTable (a),
		0x22 => Inst::Add (a, b, c),
		0x24 => Inst::Mul (a, b, c),
		0x2e => Inst::MmBin (a, b, c),
		0x33 => Inst::Not (a, b),
		0x3c => Inst::EqK (a, b, c),
		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),
		0x4f => Inst::Closure (a, bx),
		0x51 => Inst::VarArgPrep (a.into ()),
		0x52 => Inst::ExtraArg (ax),
		_ => return None,
	})
}

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

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

fn parse_string <R: Read> (rdr: &mut R) -> Option <String> {
	let len = match parse_int (rdr)? {
		0 => 0,
		x => x - 1,
	};
	
	let mut buf = vec! [0u8; len as usize];
	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_int <R: Read> (rdr: &mut R) -> Option <u32>
{
	Some ((parse_byte (rdr)? - 0x80) as u32)
}

// 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
	
	parse_string (rdr)?; // function name
	parse_int (rdr)?;    // start line in source code
	parse_int (rdr)?;    // last line in source code
	parse_byte (rdr)?;   // num params
	parse_byte (rdr)?;   // is_vararg
	parse_byte (rdr)?;   // maxstacksize, might be same as num slots?
	
	let inst_count = parse_int (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 ()?;
		instructions.push (parse_inst (buf).expect (&format! ("{buf:?}")));
	}
	
	let constant_count = parse_int (rdr)?;
	
	let mut constants = Vec::with_capacity (constant_count as usize);
	
	for _ in 0..constant_count {
		let const_type = parse_byte (rdr)?;
		assert_eq! (const_type, 0x04);
		
		let s = parse_string (rdr)?;
		constants.push (s.into ());
	}
	
	let upvalue_count = parse_int (rdr)? as usize;
	
	for _ in 0..upvalue_count {
		// Just ignore these
		
		for _ in 0..3 {
			parse_byte (rdr)?;
		}
	}
	
	blocks.push (Block {
		constants,
		instructions,
		upvalue_count,
	});
	
	// Recursion
	
	// Subfunctions. PUC calls them protos.
	let protos_count = parse_int (rdr)?;
	for _ in 0..protos_count {
		parse_block (rdr, blocks)?;
	}
	
	// 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)?;
	for _ in 0..lineinfo_count {
		parse_byte (rdr)?;
	}
	
	// Absolute line info, didn't see that in my test files
	
	let abslineinfo_count = parse_int (rdr)?;
	assert_eq! (abslineinfo_count, 0);
	
	let local_count = parse_int (rdr)?;
	for _ in 0..local_count {
		parse_string(rdr)?;
		parse_int (rdr)?;
		parse_int (rdr)?;
	}
	
	let upvalue_count = parse_int (rdr)?;
	for _ in 0..upvalue_count {
		parse_string (rdr)?;
	}
	
	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 ()?;
	
	let mut blocks = vec![];
	
	while let Some (_) = parse_block (rdr, &mut blocks) {
		// 
	}
	
	Some (Chunk {
		blocks,
	})
}

#[cfg (test)]
mod tests {
	#[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, 0)),
			([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);
		}
	}
}