use std::borrow::Cow;
use std::error::Error;
use std::fs::File;
use std::io::{self, BufReader, BufWriter, prelude::*};
use std::process::ExitCode;

#[derive(Default)]
struct Definitions {
	definitions: Vec<(Box<str>, Box<str>)>,
}

// replace sequences of 2+ spaces with a single space
fn compact_spaces(s: &str) -> String {
	let mut s: String = s.into();
	// quite inefficient, but it doesn't really matter for our purposes.
	while s.contains("  ") {
		s = s.replace("  ", " ").to_owned();
	}
	s
}

impl Definitions {
	fn add_definition(&mut self, word: &str, def: &str) {
		self.definitions
			.push((compact_spaces(word).into(), compact_spaces(def).into()))
	}
	fn sort(&mut self) {
		self.definitions.sort_by(|x, y| x.0.cmp(&y.0));
	}
	fn write_to(&mut self, mut w: impl Write) -> io::Result<()> {
		for (title, definition) in &self.definitions {
			writeln!(w, "{title}  {definition}")?;
		}
		Ok(())
	}
}

// remove HTML comments from string
#[must_use]
fn remove_comments(mut text: &str) -> Cow<str> {
	if !text.contains("<!--") {
		// (by far) most common case
		return Cow::Borrowed(text);
	}
	let mut new_str = String::new();
	while let Some(comment_start) = text.find("<!--") {
		new_str.push_str(&text[..comment_start]);
		text = &text[comment_start..];
		let comment_end = text.find("-->").map_or(text.len(), |i| i + 3);
		text = &text[comment_end..];
	}
	new_str.push_str(text);
	Cow::Owned(new_str)
}

fn parse_xml(reader: impl BufRead, output: &mut Definitions) -> Result<(), Box<dyn Error>> {
	let mut config = xml::reader::ParserConfig::default();
	config.cdata_to_characters = true;
	#[derive(Debug, Clone, Copy)]
	enum Tag {
		Other,
		Title,
		Text,
		Ns,
	}
	let mut tags = vec![];
	let mut title = String::new();
	let mut body = String::new();
	let mut ns = 1;
	let mut ns_str = String::new();
	for event in xml::reader::EventReader::new_with_config(reader, config) {
		let event = event?;
		use xml::reader::XmlEvent;
		match (&event, tags.last()) {
			(XmlEvent::StartElement { name, .. }, _) => {
				let name = name.local_name.as_str();
				match name {
					"title" => {
						tags.push(Tag::Title);
						title.clear();
					}
					"text" => tags.push(Tag::Text),
					"ns" => {
						tags.push(Tag::Ns);
						ns_str.clear();
					}
					_ => tags.push(Tag::Other),
				}
			}
			(XmlEvent::Characters(s), Some(Tag::Title)) => {
				title.push_str(s);
			}
			(XmlEvent::Characters(s), Some(Tag::Ns)) => {
				ns_str.push_str(s);
			}
			(XmlEvent::Characters(s), Some(Tag::Text)) => {
				body.push_str(s);
			}
			(XmlEvent::EndElement { name, .. }, _) => {
				tags.pop();
				if name.local_name == "page" {
					title.clear();
				} else if name.local_name == "text" {
					if ns == 0
						&& let Some(eng_start) = body.find("==English==\n")
					{
						let eng = &body[eng_start..];
						let eng_end = eng
							.as_bytes()
							.windows(4)
							.position(|w| w.starts_with(b"\n==") && w[3] != b'=')
							.unwrap_or(eng.len());
						let eng = &eng[..eng_end];
						for (i, w) in eng.as_bytes().windows(3).enumerate() {
							if w != b"\n# " {
								continue;
							}
							let definition =
								eng[i + 3..].split_once('\n').map_or(&eng[i + 3..], |x| x.0);
							let definition = remove_comments(definition);
							output.add_definition(&title[..], &definition);
						}
					}
					body.clear();
				} else if name.local_name == "ns" {
					ns = ns_str.parse().unwrap_or(1);
				}
			}
			_ => {}
		}
	}
	Ok(())
}

fn do_write<W, E: Error>(path: &str, write_func: W) -> Result<(), Box<dyn Error>>
where
	W: FnOnce(BufWriter<File>) -> Result<(), E>,
{
	println!("Writing output to {path}...");
	let tmp_name = format!(".{path}.tmp");
	let file = File::create(&tmp_name).map_err(|e| format!("Error creating {tmp_name}: {e}"))?;
	let writer = BufWriter::new(file);
	write_func(writer).map_err(|e| format!("Error writing to {tmp_name}: {e}"))?;
	_ = std::fs::remove_file(path); // OK if this already exists
	std::fs::rename(&tmp_name, path)
		.map_err(|e| format!("Error renaming {tmp_name} => {path}: {e}"))?;
	Ok(())
}

fn definitions(args: Vec<String>) -> Result<(), Box<dyn Error>> {
	let mut output = Definitions::default();
	let mut files: Vec<String> = vec![];
	for arg in args {
		if arg == "-h" || arg == "--help" {
			println!("Usage: {} definitions [FILES]", env!("CARGO_PKG_NAME"));
			println!("    Extract English-language definitions from Wiktionary");
			println!("    data dump files, writing output to definitions.txt.");
			println!("    Each line of the output file is of the format: Word  Definition");
			println!(
				"    Note the two spaces—this avoids ambiguity when the word contains a space."
			);
			println!("    A single Word can have multiple Definitions.");
			println!("    If FILES is not specified, will use ./*wiktionary*.xml-p*");
			return Ok(());
		}
		files.push(arg.to_owned());
	}
	let files_from_pwd = || -> Result<Vec<String>, Box<dyn Error>> {
		let mut files = vec![];
		for file in std::fs::read_dir(".")? {
			let file = file?;
			let mut r#type = file.file_type()?;
			let name = file.file_name();
			if r#type.is_symlink() {
				// get type of thing symlink is pointing to
				r#type = std::fs::metadata(file.path())?.file_type();
			}
			if !r#type.is_file() {
				continue;
			}
			let Some(name) = name.to_str() else {
				continue;
			};
			if name.contains("wiktionary") && name.contains(".xml-p") {
				files.push(name.into());
			}
		}
		files.sort();
		Ok(files)
	};
	if files.is_empty() {
		files = files_from_pwd()
			.map_err(|e| format!("No files specified and couldn't list PWD ({e}). Aborting."))?;
		println!("No files specified on command line.");
		println!("These files were found in the PWD:");
		for file in &files {
			println!("  {file}");
		}
		print!("Proceed with these files [Y/n]? ");
		_ = std::io::stdout().flush();
		let mut line = String::new();
		let result = std::io::stdin().read_line(&mut line);
		let line = line.trim();
		if result.is_err()
			|| line
				.chars()
				.next()
				.is_some_and(|c| c.to_lowercase().to_string() != "y")
		{
			return Err("Aborted.".into());
		}
	}
	for input_filename in &files {
		let input = File::open(input_filename)
			.map_err(|e| format!("Couldn't open {input_filename}: {e}"))?;
		let reader = BufReader::new(input);
		println!("Parsing {input_filename}...");
		parse_xml(reader, &mut output)
			.map_err(|e| format!("Couldn't parse {input_filename}: {e}"))?;
	}
	println!("Sorting {} definitions...", output.definitions.len());
	output.sort();
	do_write("definitions.txt", |writer| output.write_to(writer))?;
	println!("Done!");
	Ok(())
}

fn try_main() -> Result<(), Box<dyn Error>> {
	let mut args = std::env::args_os().skip(1);
	let command = args.next();
	let no_command = "No command specified. Commands available:
- definitions";
	let Some(command) = command else {
		return Err(no_command.into());
	};
	if command == "-h" || command == "--help" {
		return Err(no_command.into());
	}
	let mut command_args = vec![];
	for arg in args {
		let Some(arg) = arg.to_str() else {
			return Err(format!(
				"Bad UTF-8 in argument: {}",
				arg.to_string_lossy().escape_debug()
			)
			.into());
		};
		command_args.push(arg.to_owned());
	}
	match &command.to_string_lossy()[..] {
		"definitions" => definitions(command_args),
		x => Err(format!("Unrecognized command: {x}").into()),
	}
}

fn main() -> ExitCode {
	use std::time::Instant;
	let start_time = Instant::now();
	if let Err(e) = try_main() {
		eprintln!("Error: {e}");
		return ExitCode::FAILURE;
	}
	println!(
		"Time taken: {:?}",
		Instant::now().duration_since(start_time)
	);
	ExitCode::SUCCESS
}