use proc_macro::TokenStream;
use quote::quote;
use syn::{
    buffer::Cursor,
    parse::{Parse, ParseStream, StepCursor},
    Error,
};
use syn::{parse, LitInt, Result};

struct IncludeData {
    year: String,
    day: String,
}

fn get_string<'a, 'b>(cursor: StepCursor<'a, 'b>) -> Result<(String, Cursor<'a>)> {
    let (lit, c) = cursor.literal().unwrap();
    Ok((lit.span().source_text().unwrap(), c))
}

impl Parse for IncludeData {
    fn parse(input: ParseStream) -> Result<Self> {
        let mut data = IncludeData {
            year: "".into(),
            day: "".into(),
        };
        let mut look = input.lookahead1();
        if !look.peek(LitInt) {
            let s = input.span();
            return Err(Error::new(s, format!("{} is not an valid Year", s.source_text().unwrap())));
        }
        data.year = input.step(get_string).expect("Wanted an string");
        look = input.lookahead1();
        if !look.peek(LitInt) {
            let s = input.span();
            return Err(Error::new(s, format!("{} is not an valid Day", s.source_text().unwrap())));
        }
        data.day = input.step(get_string).expect("Wanted an string");
        Ok(data)
    }
}

/// includes Data from Advent of code
/// ```ignore (cannot-doctest-external-file-dependency)
/// include_data!(2015 01)
/// 
/// fn main() {
///     print!("{DATA}");
/// }
/// ```
#[proc_macro]
pub fn include_data(data: TokenStream)->TokenStream {
    let gen = match parse::<IncludeData>(data) {
        Ok(data) => {
            let path = format!("../../../data/{}/{}.txt", data.year, data.day);
    quote! {
        static DATA: &str = include_str!(#path);
    }
        },
        Err(_) => {
            quote! {
                static DATA: &str = "";
            }
        },
    };
    gen.into()
}