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// Copyright 2021 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//    https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use crate::ParseResult;
use proc_macro2::Ident;
use quote::{quote, ToTokens, TokenStreamExt};
use syn::parse::{Parse, ParseStream};

/// A little like [`syn::Path`] but simpler - contains only identifiers,
/// no path arguments. Guaranteed to always have at least one identifier.
#[derive(Debug, Clone)]
pub struct RustPath(Vec<Ident>);

impl RustPath {
    pub fn new_from_ident(id: Ident) -> Self {
        Self(vec![id])
    }

    #[must_use]
    pub fn append(&self, id: Ident) -> Self {
        Self(self.0.iter().cloned().chain(std::iter::once(id)).collect())
    }

    pub fn get_final_ident(&self) -> &Ident {
        self.0.last().unwrap()
    }
}

impl ToTokens for RustPath {
    fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
        let mut it = self.0.iter();
        let mut id = it.next();
        while id.is_some() {
            id.unwrap().to_tokens(tokens);
            let next = it.next();
            if next.is_some() {
                tokens.append_all(quote! { :: });
            }
            id = next;
        }
    }
}

impl Parse for RustPath {
    fn parse(input: ParseStream) -> ParseResult<Self> {
        let id: Ident = input.parse()?;
        let mut p = RustPath::new_from_ident(id);
        while input.parse::<Option<syn::token::Colon2>>()?.is_some() {
            let id: Ident = input.parse()?;
            p = p.append(id);
        }
        Ok(p)
    }
}