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
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211

extern crate proc_macro;

use proc_macro::TokenStream;
use proc_macro2::{Ident, Span};
use proc_macro_error::{abort, proc_macro_error};
use quote::quote;
use syn::{Expr, Lit, Meta, MetaList, MetaNameValue, PathSegment};

#[proc_macro_derive(Patch, attributes(patch_derive, patch_name, patch_skip))]
#[proc_macro_error]
pub fn derive_patch(item: TokenStream) -> TokenStream {
    let input = syn::parse_macro_input!(item as syn::DeriveInput);
    let struct_name = &input.ident;
    let mut patch_struct_name = None;
    let mut patch_derive = None;
    let attrs = input.attrs;

    for attr in attrs {
        let mut attr_clone = attr.clone();
        let syn::Attribute { meta, .. } = attr;
        match meta {
            Meta::List(MetaList {
                path,
                tokens,
                delimiter,
            }) => {
                let mut path_clone = path.clone();
                let mut segments = path.segments.clone();
                match path
                    .segments
                    .first()
                    .map(|s| s.ident.to_string())
                    .as_deref()
                {
                    Some("patch_derive") => {
                        if let Some(seg) = segments.first_mut() {
                            *seg = PathSegment {
                                ident: Ident::new("derive", Span::call_site()),
                                arguments: seg.arguments.clone(),
                            };
                        }
                        path_clone.segments = segments;
                        attr_clone.meta = Meta::List(MetaList {
                            path: path_clone,
                            tokens,
                            delimiter,
                        });
                        patch_derive = Some(attr_clone);
                    }
                    _ => {}
                }
            }
            Meta::NameValue(MetaNameValue {
                path,
                value: Expr::Lit(lit, ..),
                ..
            }) => {
                match path
                    .segments
                    .first()
                    .map(|s| s.ident.to_string())
                    .as_deref()
                {
                    Some("patch_name") => {
                        if let Lit::Str(l) = lit.lit {
                            patch_struct_name = Some(Ident::new(
                                format!("{}", l.value()).trim_matches('"'),
                                Span::call_site(),
                            ));
                        }
                    }
                    _ => {}
                }
            }
            _ => (),
        }
    }

    let fields = if let syn::Data::Struct(syn::DataStruct { fields, .. }) = &input.data {
        fields
    } else {
        abort!(&input.ident, "Patch derive only use for struct")
    };
    let fields_with_type = match fields {
        syn::Fields::Named(f) => f
            .clone()
            .named
            .into_pairs()
            .map(|p| p.into_value())
            .map(|f| (f.ident.unwrap(), f.ty, f.attrs))
            .collect::<Vec<_>>(),

        syn::Fields::Unnamed(f) => f
            .clone()
            .unnamed
            .into_pairs()
            .map(|p| p.into_value())
            .enumerate()
            .map(|(i, f)| (Ident::new(&i.to_string(), Span::call_site()), f.ty, f.attrs))
            .collect::<Vec<_>>(),
        syn::Fields::Unit => Vec::new(),
    };

    let wrapped_fields = &mut fields_with_type
        .iter()
        .filter_map(|(f, t, attrs)| {
            if attrs.iter().any(|syn::Attribute { meta, .. }| {
                if let Meta::Path(path) = meta {
                    path.segments
                        .first()
                        .map(|s| s.ident.to_string())
                        .as_deref()
                        == Some("patch_skip")
                } else {
                    false
                }
            }) {
                None
            } else {
                Some((
                    f.clone(),
                    syn::parse::<syn::Path>(quote!(Option<#t>).to_string().parse().unwrap())
                        .unwrap(),
                ))
            }
        })
        .collect::<Vec<_>>();

    let field_names = wrapped_fields.iter().map(|(f, _)| f).collect::<Vec<_>>();

    let wrapped_types = wrapped_fields.iter().map(|(_, t)| t);

    let patch_struct_name = patch_struct_name
        .unwrap_or_else(|| Ident::new(&format!("{}Patch", struct_name), Span::call_site()));

    let patch_struct = if let Some(patch_derive) = patch_derive {
        quote!(
            #patch_derive
            pub struct #patch_struct_name {
                #(pub #field_names: #wrapped_types,)*
            }
        )
    } else {
        quote::quote!(
            pub struct #patch_struct_name {
                #(pub #field_names: #wrapped_types,)*
            }
        )
    };

    #[cfg(feature = "status")]
    let patch_status_impl = quote!(
        impl struct_patch::traits::PatchStatus for #patch_struct_name {
            fn is_empty(&self) -> bool {
                #(
                    if self.#field_names.is_some() {
                        return false
                    }
                )*
                true
            }
        }
    );
    #[cfg(not(feature = "status"))]
    let patch_status_impl = quote!();

    let patch_impl = quote! {
        impl struct_patch::traits::Patch< #patch_struct_name > for #struct_name {
            fn apply(&mut self, patch: #patch_struct_name) {
                #(
                    if let Some(v) = patch.#field_names {
                        self.#field_names = v;
                    }
                )*
            }

            fn into_patch(self) -> #patch_struct_name {
                let mut p = Self::new_empty_patch();
                #(
                    p.#field_names = Some(self.#field_names);
                )*
                p
            }

            fn into_patch_by_diff(self, previous_struct: Self) -> #patch_struct_name {
                let mut p = Self::new_empty_patch();
                #(
                    if self.#field_names != previous_struct.#field_names {
                        p.#field_names = Some(self.#field_names);
                    }
                )*
                p
            }

            fn new_empty_patch() -> #patch_struct_name {
                #patch_struct_name {
                    #(
                        #field_names: None,
                    )*
                }
            }
        }
    };

    let expanded = quote! {
        #patch_struct
        #patch_status_impl
        #patch_impl
    };
    TokenStream::from(expanded)
}