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//! [`ExpandedUseTree`], an extension to [`syn::UseTree`].
#[cfg(any(test, feature = "quote"))]
#[cfg_attr(test, macro_use)]
extern crate quote;

#[macro_use]
extern crate syn;

use syn::punctuated::Punctuated;
use syn::{Ident, UseGlob, UseName, UseRename, UseTree};

#[cfg(any(test, feature = "quote"))]
use quote::{ToTokens, Tokens};

/// A leaf node from a [`UseTree`].
#[cfg_attr(feature = "clone-impls", derive(Clone))]
#[cfg_attr(feature = "extra-traits", derive(Debug, PartialEq, Eq, Hash))]
pub enum UseItem {
    /// A simple item, e.g. `name`.
    Name(UseName),

    /// A renamed item, e.g. `name as renamed`.
    Rename(UseRename),

    /// A glob import, i.e. `*`.
    Glob(UseGlob),
}
impl From<UseName> for UseItem {
    #[inline]
    fn from(name: UseName) -> UseItem {
        UseItem::Name(name)
    }
}
impl From<UseRename> for UseItem {
    #[inline]
    fn from(rename: UseRename) -> UseItem {
        UseItem::Rename(rename)
    }
}
impl From<UseGlob> for UseItem {
    #[inline]
    fn from(glob: UseGlob) -> UseItem {
        UseItem::Glob(glob)
    }
}
#[cfg(any(test, feature = "quote"))]
impl ToTokens for UseItem {
    #[inline]
    fn to_tokens(&self, tokens: &mut Tokens) {
        match *self {
            UseItem::Name(ref name) => name.to_tokens(tokens),
            UseItem::Rename(ref rename) => rename.to_tokens(tokens),
            UseItem::Glob(ref glob) => glob.to_tokens(tokens),
        }
    }
}

/// An expanded item from a [`UseTree`].
#[cfg_attr(feature = "clone-impls", derive(Clone))]
#[cfg_attr(feature = "extra-traits", derive(Debug, PartialEq, Eq, Hash))]
pub struct ExpandedUseItem {
    /// The path to the item, which may be empty.
    pub prefix: Punctuated<Ident, Token![::]>,

    /// Item itself.
    pub item: UseItem,
}
#[cfg(any(test, feature = "quote"))]
impl ToTokens for ExpandedUseItem {
    #[inline]
    fn to_tokens(&self, tokens: &mut Tokens) {
        self.prefix.to_tokens(tokens);
        self.item.to_tokens(tokens);
    }
}

/// An expanded [`UseTree`].
#[cfg_attr(feature = "clone-impls", derive(Clone))]
#[cfg_attr(feature = "extra-traits", derive(Debug, PartialEq, Eq, Hash))]
pub struct ExpandedUseTree {
    /// The expanded items.
    pub items: Punctuated<ExpandedUseItem, Token![,]>,
}
impl ExpandedUseTree {
    /// Expands the given [`UseTree`].
    pub fn new(tree: UseTree) -> Self {
        fn expand(
            tree: UseTree,
            expanded: &mut Punctuated<ExpandedUseItem, Token![,]>,
            prefix: &mut Punctuated<Ident, Token![::]>,
        ) {
            match tree {
                UseTree::Name(name) => expanded.push_value(ExpandedUseItem {
                    item: name.into(),
                    prefix: prefix.clone(),
                }),
                UseTree::Rename(rename) => expanded.push_value(ExpandedUseItem {
                    item: rename.into(),
                    prefix: prefix.clone(),
                }),
                UseTree::Glob(glob) => expanded.push_value(ExpandedUseItem {
                    item: glob.into(),
                    prefix: prefix.clone(),
                }),
                UseTree::Path(path) => {
                    prefix.push_value(path.ident);
                    prefix.push_punct(path.colon2_token);
                    expand(*path.tree, expanded, prefix);
                    prefix.pop();
                }
                UseTree::Group(group) => {
                    for pair in group.items.into_pairs() {
                        let (tree, comma) = pair.into_tuple();
                        expand(tree, expanded, prefix);
                        if let Some(comma) = comma {
                            if !expanded.empty_or_trailing() {
                                expanded.push_punct(comma);
                            }
                        }
                    }
                }
            }
        }
        let mut expanded = Punctuated::new();
        let mut prefix = Punctuated::new();
        expand(tree, &mut expanded, &mut prefix);
        ExpandedUseTree { items: expanded }
    }
}
impl<T: Into<UseTree>> From<T> for ExpandedUseTree {
    #[inline]
    fn from(tree: T) -> Self {
        Self::new(tree.into())
    }
}
#[cfg(any(test, feature = "quote"))]
impl ToTokens for ExpandedUseTree {
    #[inline]
    fn to_tokens(&self, tokens: &mut Tokens) {
        self.items.to_tokens(tokens);
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    macro_rules! test_tokens {
        ($name:ident: ($($lhs:tt)*) => ($($rhs:tt)*)) => (
            #[test]
            fn $name() {
                let tree: UseTree = parse_quote! { $($lhs)* };
                let expand = ExpandedUseTree::new(tree);
                assert_eq!(expand.into_tokens(), quote! { $($rhs)* });
            }
        )
    }

    test_tokens!(nested_empty:
        ({{}, {{},}, {},}) => ()
    );
    test_tokens!(nested_single1:
        ({a, {b,}, c, d}) => (a, b, c, d)
    );
    test_tokens!(nested_single2:
        ({{a}, {{b}}, {c,}, {}}) => (a, b, c,)
    );
    test_tokens!(nested_multi:
        ({{a, b, c,}, {{d}, {e, f},}, {g,}, {h,}}) => (a, b, c, d, e, f, g, h,)
    );
    test_tokens!(paths1:
        (a::{b, c::{d, e}}) => (a::b, a::c::d, a::c::e)
    );
    test_tokens!(paths2:
        ({a::{b, c}, {d, e}, {f::g::*, h}}) => (a::b, a::c, d, e, f::g::*, h)
    );
}