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

/*
 *  Copyright 2021 QuantumBadger
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

use std::fmt::{Debug, Display, Formatter};
use std::rc::Rc;

use backtrace::Backtrace;

/// An error with an associated backtrace, and an optional cause.
#[derive(Clone)]
pub struct BacktraceError<E>
where
    E: Debug + Display + 'static
{
    value: Rc<BacktraceErrorImpl<E>>
}

struct BacktraceErrorImpl<E>
where
    E: Debug + Display
{
    error: E,
    backtrace: Backtrace,
    cause: Option<Box<dyn std::error::Error>>
}

impl<E: Debug + Display> std::error::Error for BacktraceError<E> {}

impl<E: Debug + Display> Display for BacktraceError<E>
{
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result
    {
        Display::fmt(self.error(), f)
    }
}

impl<E: Debug + Display> Debug for BacktraceError<E>
{
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result
    {
        f.debug_struct("BacktraceError")
            .field("error", self.error())
            .field("backtrace", self.get_backtrace())
            .field("cause", self.cause())
            .finish()
    }
}

impl<E: Debug + Display> BacktraceError<E>
{
    #[must_use]
    pub(crate) fn new_with_cause<Cause: std::error::Error + 'static>(
        error: E,
        cause: Cause
    ) -> Self
    {
        BacktraceError {
            value: Rc::new(BacktraceErrorImpl {
                backtrace: Backtrace::new(),
                error,
                cause: Some(Box::new(cause))
            })
        }
    }

    #[must_use]
    pub(crate) fn new(error: E) -> Self
    {
        BacktraceError {
            value: Rc::new(BacktraceErrorImpl {
                backtrace: Backtrace::new(),
                error,
                cause: None
            })
        }
    }

    /// Returns the backtrace for this error.
    #[must_use]
    pub fn get_backtrace(&self) -> &Backtrace
    {
        &self.value.backtrace
    }

    /// Returns the error.
    #[must_use]
    pub fn error(&self) -> &E
    {
        &self.value.error
    }

    /// Returns the original cause of the error, if one is present.
    #[must_use]
    pub fn cause(&self) -> &Option<Box<dyn std::error::Error>>
    {
        &self.value.cause
    }

    #[must_use]
    pub(crate) fn context<S: AsRef<str>>(
        self,
        description: S
    ) -> BacktraceError<ErrorMessage>
    {
        BacktraceError::new_with_cause(
            ErrorMessage {
                description: description.as_ref().to_string()
            },
            self
        )
    }
}

/// A human-readable error message.
#[derive(Clone, Debug)]
pub struct ErrorMessage
{
    description: String
}

impl ErrorMessage
{
    pub(crate) fn msg<S: AsRef<str>>(description: S) -> BacktraceError<Self>
    {
        BacktraceError::new(Self {
            description: description.as_ref().to_string()
        })
    }

    pub(crate) fn msg_with_cause<S, Cause>(
        description: S,
        cause: Cause
    ) -> BacktraceError<Self>
    where
        S: AsRef<str>,
        Cause: std::error::Error + 'static
    {
        BacktraceError::new_with_cause(
            Self {
                description: description.as_ref().to_string()
            },
            cause
        )
    }
}

impl Display for ErrorMessage
{
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result
    {
        Display::fmt(&self.description, f)
    }
}

pub(crate) trait Context<R>
{
    fn context<S: AsRef<str>>(
        self,
        description: S
    ) -> Result<R, BacktraceError<ErrorMessage>>;
}

impl<R, E: std::error::Error + 'static> Context<R> for Result<R, E>
{
    fn context<S: AsRef<str>>(
        self,
        description: S
    ) -> Result<R, BacktraceError<ErrorMessage>>
    {
        match self {
            Ok(result) => Ok(result),
            Err(err) => Err(BacktraceError::new_with_cause(
                ErrorMessage {
                    description: description.as_ref().to_string()
                },
                err
            ))
        }
    }
}