extern crate termion;

use termion::event::Key;
use termion::input::TermRead;
use termion::raw::IntoRawMode;
use std::io::Write;
use std::io;
// use std::fs;
use std::collections::HashMap;

type Entry = f64;

const PROMPT_STR: &str = "> ";

const BEEP_STR: &str = "\x07";

fn min<T: Ord>(a: T, b: T) -> T {
	if b < a {b} else {a}
}

fn draw_entries(entries: &[Entry], up: isize) {
	assert!(up < 1<<16);
	if up < 0 {
		print!("{}", termion::cursor::Down((-up) as u16));
	} else if up > 0 {
		print!("{}", termion::cursor::Up(up as u16));
	}
	print!("\r");
	let mut first = true;
	for entry in entries {
		if first {first = false;}
		else {print!("\n\r");}
		print!("{}{}{}", " ".repeat(PROMPT_STR.len()), entry, termion::clear::UntilNewline);
	}
}

fn valid_input_char(c: char) -> bool {
	c.is_digit(10) || c == '.' || c == 'e'
}

type Callback = Box<(Fn(&mut Vec<Entry>) -> usize + 'static)>;

fn mk_callback<F>(f: F) -> Callback
		where F: Fn(&mut Vec<Entry>) -> usize + 'static {
	Box::new(f) as Callback
}

fn stk_binop<F>(f: F) -> Callback
		where F: Fn(Entry, Entry) -> Entry + 'static {
	mk_callback(move |stk| {
		let v2 = stk.pop().unwrap();
		let v1 = stk.pop().unwrap();
		stk.push(f(v1,v2));
		1
	})
}

struct State<'a> {
	stk: Vec<Entry>,
	entries_drawn: usize,
	term_height: usize,
	input_buffer: String,
	input_cursor: usize,
	command_map: &'a HashMap<String, (usize, Callback)>,
}

fn handle_key(key: Key, st: &mut State) -> Option<bool> {
	match key {
		// Quitting
		Key::Ctrl('c') | Key::Ctrl('d') => {
			if st.input_buffer.len() > 0 {
				print!("\n\r");
			} else {
				print!("\r{}", termion::clear::CurrentLine);
			}
			return Some(false);
		}

		// Moving around
		Key::Ctrl('a') => {
			print!("\r{}", termion::cursor::Right(PROMPT_STR.len() as u16));
			st.input_cursor = 0;
		}
		Key::Ctrl('e') => {
			print!("\r{}",
			       termion::cursor::Right((PROMPT_STR.len() + st.input_buffer.len()) as u16));
			st.input_cursor = st.input_buffer.len();
		}
		Key::Left => {
			if st.input_cursor > 0 {
				print!("{}", termion::cursor::Left(1));
				st.input_cursor -= 1;
			} else {
				return None;
			}
		}
		Key::Right => {
			if st.input_cursor < st.input_buffer.len() {
				print!("{}", termion::cursor::Right(1));
				st.input_cursor += 1;
			} else {
				return None;
			}
		}

		// Editing
		Key::Ctrl('u') => {
			st.input_buffer.clear();
			print!("\r{}{}", termion::clear::CurrentLine, PROMPT_STR);
			st.input_cursor = 0;
		}
		Key::Backspace => {
			if st.input_cursor == 0 {
				return None;
			}
			st.input_cursor -= 1;
			st.input_buffer.remove(st.input_cursor);
			let rest = &st.input_buffer[st.input_cursor..];
			print!("{}{}{}", termion::cursor::Left(1), rest,
			       termion::clear::UntilNewline);
			if rest.len() > 0 {
				print!("{}", termion::cursor::Left(rest.len() as u16));
			}
		}
		Key::Delete => {
			if st.input_buffer.len() == 0 {
				if st.stk.len() == 0 {
					return None;
				}
				if st.entries_drawn < st.stk.len() {
					draw_entries(&st.stk[(st.stk.len() - st.entries_drawn - 1)..(st.stk.len() - 1)],
					             st.entries_drawn as isize);
					st.input_buffer = match st.stk.last() {
						None => String::new(),
						Some(val) => val.to_string(),
					};
					print!("\n\r{}{}", PROMPT_STR, st.input_buffer);
					st.input_cursor = st.input_buffer.len();
				} else {
					st.entries_drawn -= 1;
					st.input_buffer = match st.stk.last() {
						None => String::new(),
						Some(val) => val.to_string(),
					};
					st.input_cursor = st.input_buffer.len();
					print!("{}{}\r{}{}", termion::clear::CurrentLine,
					       termion::cursor::Up(1),
					       PROMPT_STR,
					       termion::cursor::Right(st.input_cursor as u16))
				}
				st.stk.pop();
			} else if st.input_cursor == st.input_buffer.len() {
				return None;
			} else {
				st.input_buffer.remove(st.input_cursor);
				let rest = &st.input_buffer[st.input_cursor..];
				print!("{}{}", rest, termion::clear::UntilNewline);
				if rest.len() > 0 {
					print!("{}", termion::cursor::Left(rest.len() as u16));
				}
			}
		}

		// Inputting
		Key::Char(c) if valid_input_char(c) => {
			st.input_buffer.insert(st.input_cursor, c);
			let rest = &st.input_buffer[st.input_cursor..];
			print!("{}", rest);
			if rest.len() > 1 {
				print!("{}", termion::cursor::Left((rest.len() - 1) as u16));
			}
			st.input_cursor += 1;
		}

		// Submitting
		Key::Char('\n') | Key::Char('\r') => {
			match st.input_buffer.parse::<Entry>() {
				Ok(val) => {
					st.stk.push(val);
					print!("{}\r{}{}\n\r{}",
					       termion::clear::CurrentLine, " ".repeat(PROMPT_STR.len()),
					       val, PROMPT_STR);
					st.input_buffer.clear();
					st.input_cursor = 0;
					if st.entries_drawn < st.term_height - 1 {
						st.entries_drawn += 1;
					}
				}
				Err(_) => return None,
			}
		}

		// Command
		Key::Char(c) | Key::Alt(c) => {
			let mut delay_lf = 0;
			if st.input_buffer.len() != 0 {
				match st.input_buffer.parse::<Entry>() {
					Ok(val) => {
						st.stk.push(val);
						print!("{}\r{}{}",
						       termion::clear::CurrentLine, " ".repeat(PROMPT_STR.len()),
						       val);
						st.input_buffer.clear();
						st.input_cursor = 0;
						if st.entries_drawn < st.term_height - 1 {
							st.entries_drawn += 1;
						}
						delay_lf = 1;
					}
					Err(_) => return None,
				}
			}

			let name = String::from(c.to_string());
			if let Some(&(nargs, ref f)) = st.command_map.get(&name) {
				if st.stk.len() < nargs {
					return None;
				}
				let prevlen = st.stk.len();
				let npushed = f(&mut st.stk);
				let sizeincr = st.stk.len() as isize - prevlen as isize;
				assert!(sizeincr < 0 || npushed >= sizeincr as usize);
				let mut print_newline = true;
				if sizeincr >= 0 {
					// Stack grew
					let usizeincr = sizeincr as usize;
					draw_entries(&st.stk[(st.stk.len() - npushed)..],
					             npushed as isize - sizeincr - delay_lf);
					st.entries_drawn = min(st.entries_drawn + usizeincr,
					                       st.term_height - 1);
				} else if prevlen >= st.term_height && st.stk.len() < st.term_height {
					// Didn't fit before, but fits now
					draw_entries(&st.stk[..], st.stk.len() as isize);
					st.entries_drawn = st.stk.len();
				} else if prevlen < st.term_height {
					// Fit before, and still fits
					assert!(st.stk.len() < st.term_height);
					draw_entries(&st.stk[(st.stk.len() - npushed)..],
					             (-sizeincr) + npushed as isize - delay_lf);
					st.entries_drawn = st.stk.len();
					if npushed == 0 {print_newline = false;}
				} else {
					// Didn't fit before, and still doesn't fit
					assert!(prevlen >= st.term_height && st.stk.len() >= st.term_height);
					if sizeincr + delay_lf == 0 {
						let up = min(npushed, st.term_height - 1);
						draw_entries(&st.stk[(st.stk.len() - up)..], up as isize);
					} else {
						draw_entries(&st.stk[(st.stk.len() - st.term_height + 1)..],
						             st.term_height as isize - 1);
					}
					st.entries_drawn = st.term_height - 1;
				}
				if print_newline {print!("\n\r");}
				print!("{}{}", termion::clear::AfterCursor, PROMPT_STR);
			} else {
				return None;
			}
		}

		// Otherwise
		_ => return None,
	}

	Some(true)
}

fn main() {
	let command_map = {
		let mut h = HashMap::new();

		h.insert(String::from("+"), (2, stk_binop(|a,b| a+b)));
		h.insert(String::from("-"), (2, stk_binop(|a,b| a-b)));
		h.insert(String::from("*"), (2, stk_binop(|a,b| a*b)));
		h.insert(String::from("/"), (2, stk_binop(|a,b| a/b)));
		h.insert(String::from("m"), (1, mk_callback(|stk| {
			let v = stk.pop().unwrap();
			stk.push(-v);
			1
		})));
		h.insert(String::from("s"), (2, mk_callback(|stk| {
			let v = stk.pop().unwrap();
			let len = stk.len();
			stk.insert(len - 1, v);
			2
		})));
		h.insert(String::from("d"), (1, mk_callback(|stk| {
			let v = stk[stk.len() - 1];
			stk.push(v);
			2
		})));
		h.insert(String::from("D"), (1, mk_callback(|stk| {
			stk.pop();
			0
		})));

		h
	};

	let mut st = State {
		stk: Vec::<Entry>::new(),
		entries_drawn: 0,
		term_height: 0,
		input_buffer: String::new(),
		input_cursor: 0,
		command_map: &command_map,
	};

	let stdin = io::stdin();
	let mut stdout = io::stdout().into_raw_mode().unwrap();

	print!("{}", PROMPT_STR);
	stdout.flush().unwrap();

	for key in stdin.keys() {
		let new_term_height = termion::terminal_size().unwrap().1 as usize;
		if new_term_height < st.term_height {
			st.entries_drawn = min(new_term_height - 1, st.stk.len());
		} else if new_term_height > st.term_height {
			let extra_num = min(new_term_height - st.term_height, st.stk.len() - st.entries_drawn);
			if extra_num > 0 {
				let idx = st.stk.len() - st.entries_drawn - extra_num;
				draw_entries(&st.stk[idx..], (st.stk.len() - st.entries_drawn) as isize);
				st.entries_drawn += extra_num;
			}
		}
		st.term_height = new_term_height;

		match handle_key(key.unwrap(), &mut st) {
			None => print!("{}", BEEP_STR),
			Some(true) => {},
			Some(false) => break,
		}
		stdout.flush().unwrap();
	}
}