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use proc_macro::TokenStream;
use proc_macro2::{TokenStream as TStream2, TokenTree};
use quote::quote;
use syn::{
parse_macro_input, parse_quote, Attribute, Data, DeriveInput, Fields, GenericParam, Generics,
Path, Type,
};
fn krate() -> TStream2 {
quote!(::telegraf)
}
#[proc_macro_derive(Metric, attributes(measurement, telegraf))]
pub fn derive_metric(tokens: TokenStream) -> TokenStream {
expand_metric(tokens)
}
fn expand_metric(tokens: TokenStream) -> TokenStream {
let krate = krate();
let input = parse_macro_input!(tokens as DeriveInput);
let name = &input.ident;
let measurement = get_measurement_name(&input);
let generics = add_trait_bounds(input.generics);
let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
let pt = get_to_point(&input.data);
let expanded = quote! {
impl #impl_generics #krate::Metric for #name #ty_generics #where_clause {
fn to_point(&self) -> #krate::Point {
let mut pf: Vec<(String, Box<dyn #krate::IntoFieldData>)> = Vec::new();
let mut pt: Vec<(String, String)> = Vec::new();
let mut tsp: Option<u64> = None;
#pt
#krate::Point::new(#measurement, pt, pf, tsp)
}
}
};
TokenStream::from(expanded)
}
fn get_measurement_name(input: &DeriveInput) -> TStream2 {
let default = &input.ident;
let measurement = input
.attrs
.iter()
.find(|a| a.path.segments.len() == 1 && a.path.segments[0].ident == "measurement");
match measurement {
Some(attr) => {
let q = attr
.tokens
.clone()
.into_iter()
.nth(1)
.map(|t| match t {
TokenTree::Literal(l) => l,
_ => panic!("unexpected type"),
})
.unwrap();
quote!(#q.to_string())
}
None => quote!(stringify!(#default).to_string()),
}
}
fn add_trait_bounds(mut generics: Generics) -> Generics {
let krate = krate();
for param in &mut generics.params {
if let GenericParam::Type(ref mut type_param) = *param {
type_param.bounds.push(parse_quote!(#krate::Metric));
}
}
generics
}
fn has_attr(attr: &Attribute) -> bool {
attr.path
.segments
.iter()
.last()
.map(|seg| seg.ident.to_string())
.unwrap_or_default()
== "telegraf"
}
fn check_attr(t_tree: TokenTree, cmp: &str) -> bool {
match t_tree {
TokenTree::Group(group) => group
.stream()
.into_iter()
.next()
.map(|token_tree| match token_tree {
TokenTree::Ident(ident) => ident == cmp,
_ => false,
})
.unwrap(),
_ => false,
}
}
fn is_tag(attr: &Attribute) -> bool {
if !has_attr(attr) {
return false;
}
attr.tokens
.clone()
.into_iter()
.next()
.map(|t_tree| check_attr(t_tree, "tag"))
.unwrap()
}
fn is_timestamp(attr: &Attribute) -> bool {
if !has_attr(attr) {
return false;
}
attr.tokens
.clone()
.into_iter()
.next()
.map(|t_tree| check_attr(t_tree, "timestamp"))
.unwrap()
}
fn get_to_point(data: &Data) -> TStream2 {
fn path_is_option(path: &Path) -> bool {
path.leading_colon.is_none()
&& path.segments.len() == 1
&& path.segments.iter().next().unwrap().ident == "Option"
}
match *data {
Data::Struct(ref data) => {
match data.fields {
Fields::Named(ref fields) => {
fields.named
.iter()
.map(|f| {
match &f.ty {
Type::Path(typath) if typath.qself.is_none() && path_is_option(&typath.path) => {
let name = &f.ident;
if f.attrs.iter().any(is_tag) {
quote!(
if let Some(ref v) = self.#name {
pt.push((stringify!(#name).to_string(), format!("{}", v)));
}
)
} else if f.attrs.iter().any(is_timestamp) {
quote!(
if let Some(ref v) = self.#name {
tsp = tsp.or(Some(v.into()));
}
)
} else {
quote!(
if let Some(ref v) = self.#name {
pf.push((stringify!(#name).to_string(), Box::new(v.clone())));
}
)
}
},
_ => {
let name = &f.ident;
if f.attrs.iter().any(is_tag) {
quote!(pt.push((stringify!(#name).to_string(), format!("{}", self.#name)));)
} else if f.attrs.iter().any(is_timestamp) {
quote!(tsp = tsp.or(Some(self.#name.into()));)
} else {
quote!(pf.push((stringify!(#name).to_string(), Box::new(self.#name.clone())));)
}
}
}
})
.collect()
}
_ => panic!("only named fields supported")
}
}
_ => panic!("cannot derive for data type")
}
}