1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132

use proc_macro2::TokenStream;
use quote::{format_ident, quote};
use std::cmp::min;
use syn::{spanned::Spanned, Data, DeriveInput, Error, Field, Fields, Ident, Result, Type};

struct ParsedFields {
	fields: Vec<(Ident, Type)>,
	named: bool
}

impl ParsedFields {
	fn from_named<I>(fields: I) -> Self
	where
		I: Iterator<Item = Field>
	{
		let fields = fields
			.map(|field| (field.ident.unwrap(), field.ty))
			.collect();
		Self {
			fields,
			named: true
		}
	}

	fn from_unnamed<I>(fields: I) -> Self
	where
		I: Iterator<Item = Field>
	{
		let fields = fields
			.enumerate()
			.map(|(i, field)| (format_ident!("arg{i}"), field.ty))
			.collect();
		Self {
			fields,
			named: false
		}
	}

	fn from_unit() -> Self {
		Self {
			fields: Vec::new(),
			named: false
		}
	}
}

pub fn expand_from_body(input: DeriveInput) -> Result<TokenStream> {
	let ident = input.ident;
	let generics = input.generics;

	let strukt = match input.data {
		Data::Enum(inum) => Err(inum.enum_token.span()),
		Data::Struct(strukt) => Ok(strukt),
		Data::Union(uni) => Err(uni.union_token.span())
	}
	.map_err(|span| Error::new(span, "#[derive(FromBody)] only works for structs"))?;

	let fields = match strukt.fields {
		Fields::Named(named) => ParsedFields::from_named(named.named.into_iter()),
		Fields::Unnamed(unnamed) => ParsedFields::from_unnamed(unnamed.unnamed.into_iter()),
		Fields::Unit => ParsedFields::from_unit()
	};

	let mut where_clause = quote!();
	let mut block = quote!();
	let mut body_ident = format_ident!("_body");
	let mut type_ident = format_ident!("_type");

	if let Some(body_field) = fields.fields.get(0) {
		body_ident = body_field.0.clone();
		let body_ty = &body_field.1;
		where_clause = quote! {
			#where_clause
			#body_ty: for<'a> From<&'a [u8]>,
		};
		block = quote! {
			#block
			let #body_ident: &[u8] = &#body_ident;
			let #body_ident: #body_ty = #body_ident.into();
		};
	}

	if let Some(type_field) = fields.fields.get(1) {
		type_ident = type_field.0.clone();
		let type_ty = &type_field.1;
		where_clause = quote! {
			#where_clause
			#type_ty: From<::gotham_restful::gotham::mime::Mime>,
		};
		block = quote! {
			#block
			let #type_ident: #type_ty = #type_ident.into();
		};
	}

	for field in &fields.fields[min(2, fields.fields.len())..] {
		let field_ident = &field.0;
		let field_ty = &field.1;
		where_clause = quote! {
			#where_clause
			#field_ty: ::std::default::Default,
		};
		block = quote! {
			#block
			let #field_ident: #field_ty = Default::default();
		};
	}

	let field_names: Vec<&Ident> = fields.fields.iter().map(|field| &field.0).collect();
	let ctor = if fields.named {
		quote!(Self { #(#field_names),* })
	} else {
		quote!(Self ( #(#field_names),* ))
	};

	Ok(quote! {
		impl #generics ::gotham_restful::FromBody for #ident #generics
		where #where_clause
		{
			type Err = ::std::convert::Infallible;

			fn from_body(
				#body_ident: ::gotham_restful::gotham::hyper::body::Bytes,
				#type_ident: ::gotham_restful::gotham::mime::Mime
			) -> ::std::result::Result<Self, ::std::convert::Infallible>
			{
				#block
				::std::result::Result::Ok(#ctor)
			}
		}
	})
}