use std::collections::HashMap;
use std::env;
use std::fs::File;
use std::io::{
	self,
	BufRead,
	BufReader,
	Write,
};

const MIN_SHIFT: usize = 1;
const MAX_SHIFT: usize = 22;

fn main() {
	let out_dir = env::var("OUT_DIR").unwrap();
	let root = env::var("CARGO_MANIFEST_DIR").unwrap();
	let data = format!("{root}/../data");

	println!("cargo:rerun-if-changed={data}/DerivedCoreProperties.txt");
	println!("cargo:rerun-if-changed={data}/PropList.txt");

	generate_from_file(
		&out_dir,
		&format!("{data}/DerivedCoreProperties.txt"),
		"XID_Start",
		"xid_start",
	);
	generate_from_file(
		&out_dir,
		&format!("{data}/DerivedCoreProperties.txt"),
		"XID_Continue",
		"xid_continue",
	);
	generate_from_file(
		&out_dir,
		&format!("{data}/PropList.txt"),
		"Pattern_White_Space",
		"pattern_white_space",
	);
	generate_from_codepoints(
		&out_dir,
		&[
			'\u{A}', '\u{B}', '\u{C}', '\u{D}', '\u{85}', '\u{2028}',
			'\u{2029}',
		],
		"line_terminator",
	);
}

fn generate_from_file(out_dir: &str, path: &str, prop: &str, name: &str) {
	let mut bitmap = vec![false; 0x110000];
	parse_file(path, prop, &mut bitmap)
		.unwrap_or_else(|e| panic!("failed to read {path}: {e}"));
	write_output(out_dir, name, &bitmap);
}

fn generate_from_codepoints(out_dir: &str, codepoints: &[char], name: &str) {
	let mut bitmap = vec![false; 0x110000];
	for &c in codepoints {
		bitmap[c as usize] = true;
	}
	write_output(out_dir, name, &bitmap);
}

fn write_output(out_dir: &str, name: &str, bitmap: &[bool]) {
	let (shift, lvl1, lvl2) = optimize_tables(bitmap);
	let mut f = File::create(format!("{out_dir}/{name}.rs")).unwrap();
	generate_code(&mut f, name, shift, &lvl1, &lvl2);
}

fn optimize_tables(bitmap: &[bool]) -> (usize, Vec<u16>, Vec<u64>) {
	let mut minsz = usize::MAX;
	let mut config = (0, Vec::new(), Vec::new());

	for i in MIN_SHIFT..=MAX_SHIFT {
		let (l1, l2) = build_tables(bitmap, i);
		let sz = l1.len() * 2 + l2.len() * 8;
		if sz < minsz {
			minsz = sz;
			config = (i, l1, l2);
		}
	}

	config
}

fn parse_file(path: &str, prop: &str, bitmap: &mut [bool]) -> io::Result<()> {
	let file = File::open(path)?;
	let reader = BufReader::new(file);

	for line in reader.lines() {
		let line = line?;
		let line = line.split('#').next().unwrap_or("").trim();
		if line.is_empty() {
			continue;
		}

		let parts: Vec<&str> = line.split(';').map(|s| s.trim()).collect();
		if parts.len() < 2 || parts[1] != prop {
			continue;
		}

		let (beg, end) = if parts[0].contains("..") {
			let mut range = parts[0].split("..");
			(
				u32::from_str_radix(range.next().unwrap(), 16).unwrap(),
				u32::from_str_radix(range.next().unwrap(), 16).unwrap(),
			)
		} else {
			let val = u32::from_str_radix(parts[0], 16).unwrap();
			(val, val)
		};

		for cp in beg..=end {
			if (cp as usize) < bitmap.len() {
				bitmap[cp as usize] = true;
			}
		}
	}

	Ok(())
}

fn build_tables(bitmap: &[bool], shift: usize) -> (Vec<u16>, Vec<u64>) {
	let blksz = 1 << shift;
	let u64s_per_block = (blksz + 63) / 64;

	let mut lvl2: Vec<u64> = Vec::new();
	let mut lvl1: Vec<u16> = Vec::new();
	let mut blkmap: HashMap<Vec<u64>, u16> = HashMap::new();

	for chunk in bitmap.chunks(blksz) {
		let mut blkdata = vec![0u64; u64s_per_block];

		for (i, &bit) in chunk.iter().enumerate() {
			if bit {
				let word_idx = i / 64;
				let bit_idx = i % 64;
				blkdata[word_idx] |= 1 << bit_idx;
			}
		}

		if let Some(&i) = blkmap.get(&blkdata) {
			lvl1.push(i);
		} else {
			let i = (lvl2.len() / u64s_per_block) as u16;
			lvl2.extend_from_slice(&blkdata);
			blkmap.insert(blkdata, i);
			lvl1.push(i);
		}
	}

	(lvl1, lvl2)
}

fn generate_code(
	f: &mut impl Write,
	prop_name: &str,
	shift: usize,
	level1: &[u16],
	level2: &[u64],
) {
	let upper_name = prop_name.to_uppercase();
	let lower_name = prop_name.to_lowercase();
	let block_size = 1 << shift;
	let mask = block_size - 1;
	let u64s_per_block = (block_size + 63) / 64;

	let pred_name = if lower_name.contains('_') {
		format!("{lower_name}_p")
	} else {
		format!("{lower_name}p")
	};

	writeln!(f, "/* Autogenerated – DO NOT EDIT */").unwrap();
	writeln!(f).unwrap();
	writeln!(f, "static {upper_name}_L1: [u16; {}] = {level1:?};", level1.len()).unwrap();
	writeln!(f, "static {upper_name}_L2: [u64; {}] = {level2:?};", level2.len()).unwrap();
	writeln!(f, "#[inline]").unwrap();
	writeln!(f, "pub fn {pred_name}(c: char) -> bool {{").unwrap();
	writeln!(f, "\tlet cp = c as usize;").unwrap();
	writeln!(f, "\tlet blki = unsafe {{ *{upper_name}_L1.get_unchecked(cp >> {shift}) }} as usize;").unwrap();
	writeln!(f, "\tlet in_blk_offset_p = cp & 0x{mask:X};").unwrap();
	if u64s_per_block == 1 {
		writeln!(f, "\tunsafe {{ return ({upper_name}_L2.get_unchecked(blki) & (1 << in_blk_offset_p)) != 0; }}").unwrap();
	} else {
		writeln!(f, "\tlet wordi = (blki * {u64s_per_block}) + (in_blk_offset_p >> 6);").unwrap();
		writeln!(f, "\tlet biti = in_blk_offset_p & 0x3F;").unwrap();
		writeln!(f, "\tunsafe {{ return (*{upper_name}_L2.get_unchecked(wordi) & (1 << biti)) != 0; }}").unwrap();
	}
	writeln!(f, "}}").unwrap();
}