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

use std::fmt::Display;

/// Unwrap the value contained within the given [Result] and return it, else print the contained
/// [std::io::Error] and exit the process.
///
/// See [std::process::exit(i32)].
pub fn unwrap_io<T>(msg: &str, res: std::io::Result<T>) -> T {
    let err = match res {
        Ok(v) => return v,
        Err(err) => err,
    };

    let code = err.raw_os_error().unwrap_or_else(|| {
        eprintln!("note: the error code could not be found for this variant; reverting to -1...");
        -1
    });
    err.into_user_err().print_all(msg).exit(code);
}

/// A human-readable error interface.
/// ```
/// use uerr::UserError;
///
/// UserError::from("could not open file")
///     .and_reason("The system cannot find the file specified.")
///     .and_help("Does this file exist?")
///     .print_all("uerr/error: ")
///     .exit(1);
/// ```
#[derive(Default)]
pub struct UserError {
    message: String,
    reasons: Vec<String>,
    help: Vec<String>,
}

impl UserError {
    fn enumerator<'a, I>(&self, i: I, first: &str, rest: &str)
    where
        I: IntoIterator<Item = &'a String>,
    {
        let mut it = i.into_iter();

        if let Some(f) = it.next() {
            eprintln!("{first}{f}");
        }

        for f in it {
            eprintln!("{rest}{f}");
        }
    }

    /// Exit the process.
    ///
    /// See [std::process::exit(i32)].
    #[inline]
    pub fn exit(&self, code: i32) -> ! {
        std::process::exit(code);
    }

    /// Print the given prefix followed by the contained error message.
    ///
    /// No padding is inserted between either elements.
    pub fn print_all<D>(&self, prefix: D) -> &Self
    where
        D: Display,
    {
        eprintln!("{prefix}{}", self.message);
        self.enumerator(&self.reasons, " - caused by: ", "     |        ");
        self.enumerator(&self.help, " + help: ", "     |   ");
        self
    }

    /// Add a help message to this UserError.
    #[inline]
    pub fn add_help(&mut self, help: impl Into<String>) {
        self.help.push(help.into());
    }

    /// Add a reason to this UserError.
    #[inline]
    pub fn add_reason(&mut self, reason: impl Into<String>) {
        self.reasons.push(reason.into());
    }

    /// Add a help tip to this UserError.
    ///
    /// Returns the current instance.
    #[inline]
    pub fn and_help(mut self, help: impl Into<String>) -> Self {
        self.help.push(help.into());
        self
    }

    /// Add a reason to this UserError.
    ///
    /// Returns the current instance.
    #[inline]
    pub fn and_reason(mut self, reason: impl Into<String>) -> Self {
        self.reasons.push(reason.into());
        self
    }

    /// Create a new UserError.
    #[inline]
    pub fn new(message: String) -> Self {
        Self {
            message,
            reasons: Vec::new(),
            help: Vec::new(),
        }
    }

    /// Create a new UserError.
    #[inline]
    pub fn from(message: &str) -> Self {
        Self::new(message.to_string())
    }

    #[inline]
    pub const fn message(&self) -> &String {
        &self.message
    }

    #[inline]
    pub const fn reasons(&self) -> &Vec<String> {
        &self.reasons
    }

    #[inline]
    pub fn reasons_mut(&mut self) -> &mut Vec<String> {
        &mut self.reasons
    }

    #[inline]
    pub const fn help(&self) -> &Vec<String> {
        &self.help
    }

    #[inline]
    pub fn help_mut(&mut self) -> &mut Vec<String> {
        &mut self.help
    }
}

/// A trait marking a type as able to be converted into an [UserError].
/// # Examples
/// ```
/// use std::fs;
/// use uerr::IntoUserError;
///
/// let contents = fs::read_to_string("names.txt")
///     .map_err(|err| {
///         err.into_user_err()
///            .print_all("myprogram.exe: ")
///            .exit(err.raw_os_error().unwrap_or(-1))
///     });
/// ```
pub trait IntoUserError {
    /// Convert this value into an [UserError].
    fn into_user_err(self) -> UserError;
}

impl<D> IntoUserError for D
where
    D: Display,
{
    fn into_user_err(self) -> UserError {
        UserError::new(self.to_string())
    }
}

#[cfg(test)]
mod tests {
    use crate::UserError;

    #[test]
    fn sample_error() {
        UserError::from("could not open file")
            .and_reason("The system cannot find the file specified.")
            .and_reason("Filler reason.")
            .and_help("Does this file exist?")
            .and_help("Filler help.")
            .print_all("program.exe: ");
    }
}