use tracing::{debug, error};
use once_cell::sync::Lazy;

#[derive(Debug)]
pub struct Calculation {
	pub equation: String,
	pub result: String,
}

pub fn calculate(query: &str) -> Option<Calculation> {
	debug!("Got query {}", query);
	let mut parser = Parser::new(Lexer::new(query));
	// debug!("final token was: {:?}", lexer.next());
	// debug!("Tokens: {:?}", lexer.lex_all());
	None
}

// TODO: put into own crate with dependency astro-float = "0.9.2" so I can use more than f64
#[derive(Debug)]
enum Token {
	Add,
	Subtract,
	Multiply,
	Divide,
	Exponent,
	LParen,
	RParen,
	Number(f64),
	Func(Func),
}

#[derive(Debug)]
enum Func {
	Sine,
	Cosine,
	Tangent,
	// sin-1, cos-1, tan-1
	ArcSine,
	ArcCosine,
	ArcTangent,
	Log2,
	Log10,
	LogN,
	Square,
	SquareRoot,
}

#[derive(Debug)]
enum Fault {
	Eof,
	Invalid,
}

// this can probably be swapped out with a lexer generator like Logos if needed

struct Lexer<'a> {
	data: &'a str,
	data_ptr: &'a str,
	idx: usize,
}

// TODO: refactor with iterator that returns Option(Token) where one token option is Eof (or a enum of Token(Token) and Eof, or just Option(Option(Token)))
impl Lexer<'_> {

	fn new(data: &str) -> Lexer { Lexer {data, data_ptr: data, idx: 0} }
	
	fn next(&mut self) -> Result<Token, Fault> {
		match self.data.chars().nth(self.idx) {
			Some(val) => {
				debug!("lexing char '{}' at idx {}", val, self.idx);
				// debug!("current char '{}'", self.data.chars().nth(0).unwrap());
				self.idx += 1;
				// TODO: make more efficient
				self.data_ptr = &self.data[self.idx..];
				match val {
					'+' => Ok(Token::Add),
					'-' => Ok(Token::Subtract),
					'×' | '*' => Ok(Token::Multiply),
					'÷' | '/' => Ok(Token::Divide),
					'^' => Ok(Token::Exponent),
					'(' => Ok(Token::LParen),
					')' => Ok(Token::RParen),
					_ if val.is_whitespace() => self.next(),
					// TODO: parse - as part of number so I can do '1 + -1' and similar
					_ if val.is_digit(10) => {
						let start = self.idx - 1;

						self.data_ptr.chars().take_while(|c| c.is_digit(10)).for_each(|_| self.idx += 1);//.next().unwrap_or(' ').is_digit(10) {self.idx += 1;}

						match self.data[start..self.idx].parse() {
							Ok(val) => Ok(Token::Number(val)),
							Err(e) => Err(Fault::Invalid),
						}
					},
					_ => {
						debug!("got invalid char '{}'", val);
						Err(Fault::Invalid)
					}
				}
			}
			None => Err(Fault::Eof),
		}
	}

	// TODO: replace with iterator so I can do parser.parse(lexer.iter()) and parse does lex_iter.next() & such
	fn lex_all(&mut self) -> Option<Vec<Token>> {
		let mut tokens: Vec<Token> = vec![];
		loop {
			match self.next() {
				Err(Fault::Eof) => return Some(tokens),
				Err(Fault::Invalid) => return None,
				Ok(tok) => tokens.push(tok),
			}
			// debug!("tokens: {:?}", tokens);
		}
	}
}

struct Parser<'a> {
	lex: Lexer<'a>,
}

impl Parser<'_> {
	fn new(lex: Lexer) -> Parser { Parser {lex} }

	fn parse(&mut self) -> Option<TokenTree>
}

// TODO: look at that parser video again
enum TokenTree {
	Leaf(Token),
	Thingy(TokenTree, TokenTree)
}