use proc_macro2::{Ident, Span, TokenStream};
use proc_macro_crate::{crate_name, FoundCrate};
use quote::quote;
use syn::{parse::ParseStream, Error};

pub fn __make_absolute_path(name: &str, input: TokenStream) -> TokenStream {
    match name {
        // core and std are special because they don't appear in Cargo.toml
        "core" => quote! { ::core #input },
        "std" => quote! { ::std #input },
        name => {
            let prefix = match crate_name(name) {
                Ok(found) => match found {
                    FoundCrate::Itself => quote! { crate },
                    FoundCrate::Name(name) => {
                        let name = Ident::new(&name, Span::call_site());
                        quote! { :: #name }
                    }
                },
                Err(e) => {
                    // proc_macro_crate failed to do its thing, so we try our best to
                    // not break other people's builds.  Assume we're being called
                    // from another crate and the crate's author didn't rename us.
                    eprintln!("uwui_dsl: proc_macro_crate failed to resolve crate {name}, expect macro bugs!");
                    eprintln!("uwui_dsl: proc_macro_crate has this to say: \"{e}\"");
                    let name = Ident::new(name, Span::call_site());
                    quote! { :: #name }
                }
            };
            quote! { #prefix #input }
        }
    }
}

macro_rules! absolute_path {
    ($crate_name:ident $(::$segment:ident)*) => {
        $crate::util::__make_absolute_path(
            stringify!($crate_name),
            ::quote::quote!($(::$segment)*)
        )
    };
}
pub(crate) use absolute_path;

macro_rules! use_absolute {
    ($($crate_name:ident $(::$path:ident)* as $name:ident),* $(,)?) => {
        $(
            #[allow(non_snake_case)]
            let $name = $crate::util::absolute_path!($crate_name $(::$path)*);
        )*
    }
}
pub(crate) use use_absolute;

const RESERVED_IDENT_PREFIX: &str = "__uwui_";

pub fn make_reserved(name: &str, span: impl Into<Option<Span>>) -> Ident {
    let span = span.into().unwrap_or_else(Span::call_site);
    if name.starts_with(RESERVED_IDENT_PREFIX) {
        Ident::new(name, span)
    } else {
        Ident::new(&format!("{RESERVED_IDENT_PREFIX}{name}"), span)
    }
}

macro_rules! define_ident {
    ($($name:ident),* $(,)?) => {
        $(
            #[allow(non_snake_case)]
            let $name = $crate::util::make_reserved(stringify!($name), None);
        )*
    }
}
pub(crate) use define_ident;

/// Recursively walk through a `ParseStream` and examine all identifiers.
/// Emit an error for any identifiers that start with [`RESERVED_IDENT_PREFIX`]
/// (`__uwui_`).
///
/// TODO: See if we can wrap ParseStream in a monad that does this check when
///       actually consuming the tokens
pub fn scan_for_reserved_idents(stream: ParseStream) -> syn::Result<ParseStream> {
    let fork = stream.fork();
    match scan_buf_for_ident_prefix(&fork, RESERVED_IDENT_PREFIX) {
        Some(error) => Err(error),
        None => Ok(stream),
    }
}

fn scan_buf_for_ident_prefix(stream: ParseStream, prefix: &str) -> Option<Error> {
    todo!()
}