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
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
// Copyright 2024 New Vector Ltd.
// Copyright 2022-2024 The Matrix.org Foundation C.I.C.
//
// SPDX-License-Identifier: AGPL-3.0-only
// Please see LICENSE in the repository root for full details.

use std::{collections::HashMap, hash::Hash};

use serde::{Deserialize, Serialize};

/// A trait which should be used for form field enums
pub trait FormField: Copy + Hash + PartialEq + Eq + Serialize + for<'de> Deserialize<'de> {
    /// Return false for fields where values should not be kept (e.g. password
    /// fields)
    fn keep(&self) -> bool;
}

/// An error on a form field
#[derive(Debug, Serialize)]
#[serde(rename_all = "snake_case", tag = "kind")]
pub enum FieldError {
    /// A required field is missing
    Required,

    /// An unspecified error on the field
    Unspecified,

    /// Invalid value for this field
    Invalid,

    /// The password confirmation doesn't match the password
    PasswordMismatch,

    /// That value already exists
    Exists,

    /// Denied by the policy
    Policy {
        /// Message for this policy violation
        message: String,
    },
}

/// An error on the whole form
#[derive(Debug, Serialize)]
#[serde(rename_all = "snake_case", tag = "kind")]
pub enum FormError {
    /// The given credentials are not valid
    InvalidCredentials,

    /// Password fields don't match
    PasswordMismatch,

    /// There was an internal error
    Internal,

    /// Rate limit exceeded
    RateLimitExceeded,

    /// Denied by the policy
    Policy {
        /// Message for this policy violation
        message: String,
    },

    /// Failed to validate CAPTCHA
    Captcha,
}

#[derive(Debug, Default, Serialize)]
struct FieldState {
    value: Option<String>,
    errors: Vec<FieldError>,
}

/// The state of a form and its fields
#[derive(Debug, Serialize)]
pub struct FormState<K: Hash + Eq> {
    fields: HashMap<K, FieldState>,
    errors: Vec<FormError>,

    #[serde(skip)]
    has_errors: bool,
}

impl<K: Hash + Eq> Default for FormState<K> {
    fn default() -> Self {
        FormState {
            fields: HashMap::default(),
            errors: Vec::default(),
            has_errors: false,
        }
    }
}

#[derive(Deserialize, PartialEq, Eq, Hash)]
#[serde(untagged)]
enum KeyOrOther<K> {
    Key(K),
    Other(String),
}

impl<K> KeyOrOther<K> {
    fn key(self) -> Option<K> {
        match self {
            Self::Key(key) => Some(key),
            Self::Other(_) => None,
        }
    }
}

impl<K: FormField> FormState<K> {
    /// Generate a [`FormState`] out of a form
    ///
    /// # Panics
    ///
    /// If the form fails to serialize, or the form field keys fail to
    /// deserialize
    pub fn from_form<F: Serialize>(form: &F) -> Self {
        let form = serde_json::to_value(form).unwrap();
        let fields: HashMap<KeyOrOther<K>, Option<String>> = serde_json::from_value(form).unwrap();

        let fields = fields
            .into_iter()
            .filter_map(|(key, value)| {
                let key = key.key()?;
                let value = key.keep().then_some(value).flatten();
                let field = FieldState {
                    value,
                    errors: Vec::new(),
                };
                Some((key, field))
            })
            .collect();

        FormState {
            fields,
            errors: Vec::new(),
            has_errors: false,
        }
    }

    /// Add an error on a form field
    pub fn add_error_on_field(&mut self, field: K, error: FieldError) {
        self.fields.entry(field).or_default().errors.push(error);
        self.has_errors = true;
    }

    /// Add an error on a form field
    #[must_use]
    pub fn with_error_on_field(mut self, field: K, error: FieldError) -> Self {
        self.add_error_on_field(field, error);
        self
    }

    /// Add an error on the form
    pub fn add_error_on_form(&mut self, error: FormError) {
        self.errors.push(error);
        self.has_errors = true;
    }

    /// Add an error on the form
    #[must_use]
    pub fn with_error_on_form(mut self, error: FormError) -> Self {
        self.add_error_on_form(error);
        self
    }

    /// Returns `true` if the form has no error attached to it
    #[must_use]
    pub fn is_valid(&self) -> bool {
        !self.has_errors
    }
}

/// Utility trait to help creating [`FormState`] out of a form
pub trait ToFormState: Serialize {
    /// The enum used for field names
    type Field: FormField;

    /// Generate a [`FormState`] out of [`Self`]
    ///
    /// # Panics
    ///
    /// If the form fails to serialize or [`Self::Field`] fails to deserialize
    fn to_form_state(&self) -> FormState<Self::Field> {
        FormState::from_form(&self)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[derive(Serialize)]
    struct TestForm {
        foo: String,
        bar: String,
    }

    #[derive(Serialize, Deserialize, Debug, Clone, Copy, Hash, PartialEq, Eq)]
    #[serde(rename_all = "snake_case")]
    enum TestFormField {
        Foo,
        Bar,
    }

    impl FormField for TestFormField {
        fn keep(&self) -> bool {
            match self {
                Self::Foo => true,
                Self::Bar => false,
            }
        }
    }

    impl ToFormState for TestForm {
        type Field = TestFormField;
    }

    #[test]
    fn form_state_serialization() {
        let form = TestForm {
            foo: "john".to_owned(),
            bar: "hunter2".to_owned(),
        };

        let state = form.to_form_state();
        let state = serde_json::to_value(state).unwrap();
        assert_eq!(
            state,
            serde_json::json!({
                "errors": [],
                "fields": {
                    "foo": {
                        "errors": [],
                        "value": "john",
                    },
                    "bar": {
                        "errors": [],
                        "value": null
                    },
                }
            })
        );

        let form = TestForm {
            foo: String::new(),
            bar: String::new(),
        };
        let state = form
            .to_form_state()
            .with_error_on_field(TestFormField::Foo, FieldError::Required)
            .with_error_on_field(TestFormField::Bar, FieldError::Required)
            .with_error_on_form(FormError::InvalidCredentials);

        let state = serde_json::to_value(state).unwrap();
        assert_eq!(
            state,
            serde_json::json!({
                "errors": [{"kind": "invalid_credentials"}],
                "fields": {
                    "foo": {
                        "errors": [{"kind": "required"}],
                        "value": "",
                    },
                    "bar": {
                        "errors": [{"kind": "required"}],
                        "value": null
                    },
                }
            })
        );
    }
}