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// This Source Code Form is subject to the terms of the Mozilla Public License,
// v. 2.0. If a copy of the MPL was not distributed with this file, You can
// obtain one at https://mozilla.org/MPL/2.0/.

//! Error and Result module.

use std::error::Error as StdError;
use std::fmt;
use std::io;
use std::result::Result as StdResult;

/// Represents errors that can occur while generating the build details.
#[derive(Debug)]
pub enum Error {
    /// A formatting error.
    Fmt(fmt::Error),

    /// An IO error.
    Io(io::Error),

    /// Something was missing, but there's no information as to what it was.
    Missing,

    /// There was a required detail that could not be provided.
    MissingDetail(String),

    /// An environment variable required for code generation wasn't set.
    MissingEnv(&'static str),

    #[doc(hidden)]
    __Nonexhaustive,
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Error::Fmt(e) => write!(f, "Unable to format: {}", e),
            Error::Io(e) => write!(f, "Input/output error: {}", e),
            Error::Missing => write!(f, "Missing value"),
            Error::MissingDetail(x) => write!(f, "Missing value: {}", x),
            Error::MissingEnv(x) => write!(f, "A required environment variable is missing: {}", x),
            Error::__Nonexhaustive => unreachable!(),
        }
    }
}

impl StdError for Error {
    fn description(&self) -> &'static str {
        match self {
            Error::Fmt(_) => "formatting error",
            Error::Io(_) => "input/output error",
            Error::Missing => "missing detail",
            Error::MissingDetail(_) => "missing detail",
            Error::MissingEnv(_) => "missing environment variable",
            Error::__Nonexhaustive => unreachable!(),
        }
    }

    fn cause(&self) -> Option<&StdError> {
        match self {
            Error::Fmt(ref e) => Some(e),
            Error::Io(ref e) => Some(e),
            Error::Missing => None,
            Error::MissingDetail(_) => None,
            Error::MissingEnv(_) => None,
            Error::__Nonexhaustive => unreachable!(),
        }
    }
}

impl From<io::Error> for Error {
    fn from(o: io::Error) -> Error {
        Error::Io(o)
    }
}

impl From<fmt::Error> for Error {
    fn from(o: fmt::Error) -> Error {
        Error::Fmt(o)
    }
}

/// Wrapper of [`::std::result::Result<T, E>`].
pub type Result<T> = StdResult<T, Error>;