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extern crate proc_macro;
extern crate proc_macro2;
#[macro_use]
extern crate quote;
#[macro_use]
extern crate syn;

mod operator;

use crate::operator::Operator;
use proc_macro::TokenStream;
use syn::{parse_macro_input, DeriveInput};

#[proc_macro_derive(Prune, attributes(prune))]
pub fn prune(input: TokenStream) -> TokenStream {
    let ast = parse_macro_input!(input as DeriveInput);
    impl_prune(&ast).into()
}

fn impl_prune(ast: &syn::DeriveInput) -> proc_macro2::TokenStream {
    // Ensure the macro is on a struct with named fields
    let fields = match ast.data {
        syn::Data::Struct(syn::DataStruct { ref fields, .. }) => {
            if fields.iter().any(|field| field.ident.is_none()) {
                panic!("struct has unnamed fields");
            }
            fields.iter().cloned().collect::<Vec<syn::Field>>()
        }
        _ => panic!("#[derive(Prune)] can only be used with structs"),
    };

    let mut validations = vec![];

    for field in &fields {
        let field_operations = find_field_operations(field);
        for operator in field_operations {
            quote_field_operators(&field, operator, &mut validations);
        }
    }

    let ident = &ast.ident;
    let (impl_generics, type_generics, where_clause) = ast.generics.split_for_impl();
    let expanded = quote! {
        impl #impl_generics Prune for #ident #type_generics #where_clause {
            fn prune(mut self) -> Self {
                #(#validations)*

                self
            }
        }
    };

    expanded
}

fn find_field_operations(field: &syn::Field) -> Vec<Operator> {
    let field_ident = field.ident.clone().unwrap().to_string();
    let mut operators = vec![];

    for attr in &field.attrs {
        if attr.path != parse_quote!(prune) {
            continue;
        }
        match attr.interpret_meta() {
            Some(syn::Meta::List(syn::MetaList { ref nested, .. })) => {
                for meta in nested.iter() {
                    match *meta {
                        syn::NestedMeta::Meta(ref item) => match *item {
                            syn::Meta::Word(ref name) => match name.to_string().as_ref() {
                                "trim" => operators.push(Operator::Trim),
                                "trim_start" => operators.push(Operator::TrimStart),
                                "trim_end" => operators.push(Operator::TrimEnd),
                                "no_whitespace" => operators.push(Operator::NoWhitespace),
                                _ => panic!("Unexpected operation: {}", name),
                            },
                            _ => unreachable!("Found a non Meta while looking for operations"),
                        },
                        _ => unreachable!("Found a non Meta while looking for operations"),
                    }
                }
            }
            _ => unreachable!(
                "Got something other than a list of attributes while checking field `{}`",
                field_ident
            ),
        }
    }

    operators
}

fn quote_field_operators(
    field: &syn::Field,
    operator: Operator,
    operations: &mut Vec<proc_macro2::TokenStream>,
) {
    let name = &field.ident;

    match operator {
        Operator::Trim => operations.push(quote! {
            self.#name = self.#name.trim().into();
        }),
        Operator::TrimStart => operations.push(quote! {
            self.#name = self.#name.trim_start().into();
        }),
        Operator::TrimEnd => operations.push(quote! {
            self.#name = self.#name.trim_end().into();
        }),
        Operator::NoWhitespace => operations.push(quote! {
            self.#name = self.#name.split_whitespace().collect::<Vec<&str>>().join("").into();
        }),
    }
}