use std::fs;

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

const DATA_DIR: &str = "data";
const EXAMPLE_DIR: &str = "examples";

#[derive(Debug, Clone)]
struct IncludeData {
    year: String,
    day: String,
}

fn get_string<'a, 'b>(cursor: StepCursor<'a, 'b>) -> Result<(String, Cursor<'a>)> {
    let (lit, c) = match cursor.literal() {
        Some(literal) => literal,
        None => return Err(Error::new(cursor.span(), "Failed to get literal")),
    };
    let span = lit.span();
    let text = match span.source_text() {
        Some(text) => text,
        None => {
            let start = span.start();
            let end = span.end();
            return Err(Error::new(
                span,
                format!(
                    "Failed to get sourcetext for {}:{}-{}:{}",
                    start.line, start.column, end.line, end.column,
                ),
            ));
        }
    };
    Ok((text, 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)
    }
}

fn canonicalize(dir: &str, input: Result<IncludeData>) -> Option<String> {
    let pathname = match input {
        Ok(id) => Some(format!("{}/{}/{}.txt", dir, id.year, id.day)),
        Err(_) => None,
    };
    if let Some(p) = pathname {
        match fs::canonicalize(p.clone()) {
            Ok(canon) => {
                if canon.is_file() {
                    Some(canon.to_str().unwrap().to_string())
                } else {
                    println!("ERROR: {:?} is not a file", canon);
                    None
                }
            }
            Err(err) => {
                println!("ERROR: {} does not exist: {}", p, err);
                None
            }
        }
    } else {
        None
    }
}

/// includes Data from Advent of code
/// ```ignore (cannot-doctest-external-file-dependency)
/// include_data!(2015 01)
///
/// fn main() {
///     print!("{DATA}");
/// }
/// ```
/// The Equivalent is
/// ```ignore (cannot-doctest-external-file-dependency)
/// static DATA: &str = include_str!("../../../data/2015/01.txt");
/// ```
#[proc_macro]
pub fn include_data(data: TokenStream) -> TokenStream {
    let input = parse::<IncludeData>(data);
    let mut path = canonicalize(DATA_DIR, input.clone());
    if path.is_none() {
        path = canonicalize(EXAMPLE_DIR, input)
    }
    match path {
        Some(p) => quote! {
            static DATA: &str = include_str!(#p);
        }
        .into(),
        None => quote! {
            static DATA: &str = "";
        }
        .into(),
    }
}

#[proc_macro]
pub fn include_example(data: TokenStream) -> TokenStream {
    match canonicalize(EXAMPLE_DIR, parse::<IncludeData>(data)) {
        Some(p) => quote! {
            static DATA: &str = include_str!(#p);
        }
        .into(),
        None => quote! {
            static DATA: &str = "";
        }
        .into(),
    }
}