use crate::config::ConfigValueParseError;

use std::fmt;

/// Common error cases that can happen in many different APIs

#[derive(Debug, derive_more::From)]

pub enum HgError {

    IoError {

        error: std::io::Error,

        context: IoErrorContext,

    },

    /// A file under `.hg/` normally only written by Mercurial is not in the

    /// expected format. This indicates a bug in Mercurial, filesystem

    /// corruption, or hardware failure.

    ///

    /// The given string is a short explanation for users, not intended to be

    /// machine-readable.

    CorruptedRepository(String),

    /// The respository or requested operation involves a feature not

    /// supported by the Rust implementation. Falling back to the Python

    /// implementation may or may not work.

    ///

    /// The given string is a short explanation for users, not intended to be

    /// machine-readable.

    UnsupportedFeature(String),

    /// Operation cannot proceed for some other reason.

    ///

    /// The given string is a short explanation for users, not intended to be

    /// machine-readable.

    Abort(String),

    /// A configuration value is not in the expected syntax.

    ///

    /// These errors can happen in many places in the code because values are

    /// parsed lazily as the file-level parser does not know the expected type

    /// and syntax of each value.

    #[from]

    ConfigValueParseError(ConfigValueParseError),

}

/// Details about where an I/O error happened

#[derive(Debug)]

pub enum IoErrorContext {

    ReadingFile(std::path::PathBuf),

    WritingFile(std::path::PathBuf),

    RemovingFile(std::path::PathBuf),

    RenamingFile {

        from: std::path::PathBuf,

        to: std::path::PathBuf,

    },

    /// `std::env::current_dir`

    CurrentDir,

    /// `std::env::current_exe`

    CurrentExe,

}

impl HgError {

    pub fn corrupted(explanation: impl Into<String>) -> Self {

        // TODO: capture a backtrace here and keep it in the error value

        // to aid debugging?

        // https://doc.rust-lang.org/std/backtrace/struct.Backtrace.html

        HgError::CorruptedRepository(explanation.into())

    }

    pub fn unsupported(explanation: impl Into<String>) -> Self {

        HgError::UnsupportedFeature(explanation.into())

    }

    pub fn abort(explanation: impl Into<String>) -> Self {

        HgError::Abort(explanation.into())

    }

}

// TODO: use `DisplayBytes` instead to show non-Unicode filenames losslessly?

impl fmt::Display for HgError {

    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

        match self {

            HgError::Abort(explanation) => write!(f, "{}", explanation),

            HgError::IoError { error, context } => {

                write!(f, "abort: {}: {}", context, error)

            }

            HgError::CorruptedRepository(explanation) => {

                write!(f, "abort: {}", explanation)

            }

            HgError::UnsupportedFeature(explanation) => {

                write!(f, "unsupported feature: {}", explanation)

            }

            HgError::ConfigValueParseError(ConfigValueParseError {

                origin: _,

                line: _,

                section,

                item,

                value,

                expected_type,

            }) => {

                // TODO: add origin and line number information, here and in

                // corresponding python code

                write!(

                    f,

                    "config error: {}.{} is not a {} ('{}')",

                    String::from_utf8_lossy(section),

                    String::from_utf8_lossy(item),

                    expected_type,

                    String::from_utf8_lossy(value)

                )

            }

        }

    }

}

// TODO: use `DisplayBytes` instead to show non-Unicode filenames losslessly?

impl fmt::Display for IoErrorContext {

    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

        match self {

            IoErrorContext::ReadingFile(path) => {

                write!(f, "when reading {}", path.display())

            }

            IoErrorContext::WritingFile(path) => {

                write!(f, "when writing {}", path.display())

            }

            IoErrorContext::RemovingFile(path) => {

                write!(f, "when removing {}", path.display())

            }

            IoErrorContext::RenamingFile { from, to } => write!(

                f,

                "when renaming {} to {}",

                from.display(),

                to.display()

            ),

            IoErrorContext::CurrentDir => {

                write!(f, "error getting current working directory")

            }

            IoErrorContext::CurrentExe => {

                write!(f, "error getting current executable")

            }

        }

    }

}

pub trait IoResultExt<T> {

    /// Annotate a possible I/O error as related to a reading a file at the

    /// given path.

    ///

    /// This allows printing something like “File not found when reading

    /// example.txt” instead of just “File not found”.

    ///

    /// Converts a `Result` with `std::io::Error` into one with `HgError`.

    fn when_reading_file(self, path: &std::path::Path) -> Result<T, HgError>;

    fn with_context(

        self,

        context: impl FnOnce() -> IoErrorContext,

    ) -> Result<T, HgError>;

}

impl<T> IoResultExt<T> for std::io::Result<T> {

    fn when_reading_file(self, path: &std::path::Path) -> Result<T, HgError> {

        self.with_context(|| IoErrorContext::ReadingFile(path.to_owned()))

    }

    fn with_context(

        self,

        context: impl FnOnce() -> IoErrorContext,

    ) -> Result<T, HgError> {

        self.map_err(|error| HgError::IoError {

            error,

            context: context(),

        })

    }

}

pub trait HgResultExt<T> {

    /// Handle missing files separately from other I/O error cases.

    ///

    /// Wraps the `Ok` type in an `Option`:

    ///

    /// * `Ok(x)` becomes `Ok(Some(x))`

    /// * An I/O "not found" error becomes `Ok(None)`

    /// * Other errors are unchanged

    fn io_not_found_as_none(self) -> Result<Option<T>, HgError>;

}

impl<T> HgResultExt<T> for Result<T, HgError> {

    fn io_not_found_as_none(self) -> Result<Option<T>, HgError> {

        match self {

            Ok(x) => Ok(Some(x)),

            Err(HgError::IoError { error, .. })

                if error.kind() == std::io::ErrorKind::NotFound =>

            {

                Ok(None)

            }

            Err(other_error) => Err(other_error),

        }

    }

}