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#![allow(unused_imports)]
extern crate proc_macro;
use quote::{format_ident, quote, ToTokens};
use std::any::Any;
use syn::parse::{Parse, ParseStream, Result};
use syn::token::Token;
use syn::{
    bracketed,
    fold::{fold_ident, Fold},
    visit_mut::{self, VisitMut},
    ExprLit, Lit,
};
use syn::{parse_macro_input, Expr, Ident, Local, Pat, Stmt, Token};

const CLONE_NAME: &str = "_clone__fate__";
const VALUE_NAME: &str = "_value__fate__";
struct CloneFold<'a> {
    pub(crate) fate_idents: &'a Vec<Ident>,
    pub(crate) clones: String,
    pub(crate) values: String,
    pub(crate) dependencies: String,
    pub(crate) has_dependencies: bool,
}
impl Fold for CloneFold<'_> {
    fn fold_ident(&mut self, i: Ident) -> Ident {
        if self.fate_idents.contains(&i) {
            let clone_ident = format_ident!("{}{}", i, CLONE_NAME);
            let value_ident = format_ident!("{}{}", i, VALUE_NAME);

            self.clones += &format!("let {} = {}.clone(); ", clone_ident, i);
            self.dependencies += &format!("Box::new({}.clone()), ", i);
            self.has_dependencies = true;
            let value_expr_str =
                &format!("let {} = {}.get();", value_ident, clone_ident);
            if !self.values.contains(value_expr_str) {
                self.values += value_expr_str;
            }
            value_ident
        } else {
            i
        }
    }
}
impl<'a> CloneFold<'a> {
    pub(crate) fn new(fate_idents: &'a Vec<Ident>) -> Self {
        CloneFold {
            fate_idents,
            clones: "".to_string(),
            values: "".to_string(),
            dependencies: "".to_string(),
            has_dependencies: false,
        }
    }
}

struct Fate {
    quotes: Vec<proc_macro2::TokenStream>,
}
impl Parse for Fate {
    fn parse(input: ParseStream) -> Result<Self> {
        let mut quotes: Vec<proc_macro2::TokenStream> = Vec::new();
        let mut fate_idents: Vec<Ident> = Vec::new();
        let content;
        if input.peek(syn::token::Bracket) {
            bracketed!(content in input);
            while !content.is_empty() {
                let fate_ident = content.parse::<Ident>()?;
                fate_idents.push(fate_ident);
                if content.peek(Token![,]) {
                    content.parse::<Token![,]>()?;
                }
            }
        }
        while !input.is_empty() {
            let is_new = if input.peek(Token![let]) {
                input.parse::<Token![let]>()?;
                true
            } else {
                false
            };
            let fate_ident: Ident = input.parse()?;
            input.parse::<Token![=]>()?;
            let expr = input.parse::<Expr>()?;
            input.parse::<Token![;]>()?;

            let mut clone_fold = CloneFold::new(&fate_idents);
            let fixed_expr = clone_fold.fold_expr(expr);

            let clones: proc_macro2::TokenStream = clone_fold.clones.parse().unwrap();
            let dependencies: proc_macro2::TokenStream =
                clone_fold.dependencies.parse().unwrap();
            let value_expr: proc_macro2::TokenStream =
                clone_fold.values.parse().unwrap();

            let quote = if clone_fold.has_dependencies {
                let binding_quote = if is_new {
                    quote! {
                        let #fate_ident = Fate::from_expression
                    }
                } else {
                    quote! {
                        #fate_ident.bind_expression
                    }
                };
                quote! {
                    #clones;
                    #binding_quote(
                        Box::new(move || {#value_expr #fixed_expr}), vec![#dependencies]);
                }
            } else {
                let binding_quote = if is_new {
                    quote! {
                        let #fate_ident = Fate::from_value
                    }
                } else {
                    quote! {
                        #fate_ident.bind_value
                    }
                };
                quote! {
                    #clones;
                    #binding_quote(#value_expr #fixed_expr);
                }
            };
            quotes.push(quote);
        }

        Ok(Fate { quotes })
    }
}

#[proc_macro]
pub fn fate(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let Fate { quotes } = parse_macro_input!(input as Fate);

    let expanded = quote! {
        #(#quotes)*
    };

    // eprintln!("{}", expanded);

    proc_macro::TokenStream::from(expanded)
}