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#![cfg_attr(feature = "nightly", feature(proc_macro_diagnostic))]

extern crate proc_macro;

use proc_macro2::{Literal, TokenStream};
use quote::quote;
use std::collections::{hash_map::Entry, HashMap};
use syn::parse::{self, Parse, ParseStream};
use syn::{braced, parse_macro_input, token, Ident, LitStr, Token};

struct FileTree(Vec<FileNode>);

struct FileNode {
    name: Ident,
    path: String,
    children: Option<FileTree>,
}

impl Parse for FileNode {
    fn parse(input: ParseStream) -> parse::Result<FileNode> {
        let name = input.parse()?;
        input.parse::<Token![:]>()?;
        let path = input.parse::<LitStr>()?.value();
        let children = if input.peek(token::Brace) {
            let tree;
            braced!(tree in input);
            Some(tree.parse()?)
        } else {
            None
        };

        Ok(FileNode {
            name,
            path,
            children,
        })
    }
}

impl Parse for FileTree {
    fn parse(input: ParseStream) -> parse::Result<FileTree> {
        let nodes = input.parse_terminated::<_, Token![,]>(FileNode::parse)?;
        Ok(FileTree(nodes.into_iter().collect()))
    }
}

impl FileTree {
    /// Checks for duplicates at each layer of the tree.
    fn validate(&self) {
        // Build up a map of names to spans for each node
        let mut names: HashMap<String, proc_macro::Span> = HashMap::new();
        for node in &self.0 {
            let span = node.name.span().unwrap();
            let name = node.name.to_string();

            match names.entry(name) {
                Entry::Occupied(entry) => {
                    // If a collision is found, report it
                    #[cfg(feature = "nightly")]
                    {
                        span.error(format!(
                            "Node named `{}` is a duplicate of a previous node",
                            node.name
                        ))
                        .span_note(
                            entry.get().clone(),
                            format!("Duplicate found here"),
                        )
                        .emit();
                    }
                    #[cfg(not(feature = "nightly"))]
                    {
                        panic!(
                            "Node named `{}` at {:?} is a duplicate of a \
                             previous node",
                            node.name,
                            entry.get(),
                        );
                    }
                },
                Entry::Vacant(entry) => {
                    entry.insert(span);
                },
            };
        }

        // Recursively validate all children
        for node in &self.0 {
            if let Some(ref children) = node.children {
                children.validate();
            }
        }
    }
}

impl FileNode {
    fn expand(self, parent: Option<String>) -> TokenStream {
        let FileNode {
            name,
            path,
            children,
        } = self;

        let fn_name = Ident::new(&name.to_string(), name.span());

        let path = match parent {
            Some(mut parent) => {
                // Construct the next segment of the path
                // Using '/' is okay here since it's supported on all platforms
                parent.push('/');
                parent.push_str(&path);
                parent
            },
            // This is the first segment, so just use path unaltered
            None => path,
        };
        let fs_name = Literal::string(&path);

        let mut expanded = quote! {
            pub fn #fn_name() -> &'static std::path::Path {
                std::path::Path::new(#fs_name)
            }
        };

        if let Some(children) = children {
            let children = children
                .0
                .into_iter()
                .map(|child| child.expand(Some(path.to_string())));
            expanded.extend(quote! {
                pub mod #name {
                    #(#children)*
                }
            })
        }

        expanded
    }
}

#[proc_macro]
pub fn directree(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let tree = parse_macro_input!(input as FileTree);
    tree.validate();

    let mut expanded = TokenStream::new();
    for node in tree.0 {
        expanded.extend(node.expand(None));
    }
    expanded.into()
}