app-path 1.1.2

use std::env::current_exe;
use std::path::PathBuf;

/// Error type for AppPath operations.
///
/// This enum represents the possible failures that can occur when working with
/// AppPath instances. These include both system-level failures and I/O errors.
///
/// # When These Errors Occur
///
/// - **`ExecutableNotFound`**: When [`std::env::current_exe()`] fails
///   - Very rare, but can happen in some embedded or heavily sandboxed environments
///   - May occur if the executable has been deleted while running
///   - Can happen in some containerized environments with unusual configurations
///
/// - **`InvalidExecutablePath`**: When the executable path is empty
///   - Extremely rare, indicates a corrupted or broken system
///   - May occur with custom or non-standard program loaders
///
/// - **`IoError`**: When I/O operations fail
///   - Directory creation fails due to insufficient permissions
///   - Disk space issues or filesystem errors
///   - Invalid path characters for the target filesystem
///   - Network filesystem problems
///
/// System-level errors are typically unrecoverable for portable applications,
/// while I/O errors may be recoverable depending on the specific cause.
///
/// # Examples
///
/// ```rust
/// use app_path::{AppPath, AppPathError};
///
/// // Handle errors explicitly
/// match AppPath::try_with("config.toml") {
///     Ok(config) => {
///         println!("Config path: {}", config.display());
///     }
///     Err(AppPathError::ExecutableNotFound(msg)) => {
///         eprintln!("Cannot find executable: {msg}");
///         // Fallback to alternative configuration
///     }
///     Err(AppPathError::InvalidExecutablePath(msg)) => {
///         eprintln!("Invalid executable path: {msg}");
///         // Fallback to alternative configuration
///     }
///     Err(AppPathError::IoError(io_err)) => {
///         eprintln!("I/O operation failed: {io_err}");
///         // Handle specific I/O error types
///         match io_err.kind() {
///             std::io::ErrorKind::PermissionDenied => {
///                 eprintln!("Permission denied - check file permissions");
///             }
///             std::io::ErrorKind::NotFound => {
///                 eprintln!("File or directory not found");
///             }
///             _ => eprintln!("Other I/O error: {io_err}"),
///         }
///     }
/// }
/// ```
#[derive(Debug)]
pub enum AppPathError {
    /// Failed to determine the current executable path.
    ///
    /// This error occurs when [`std::env::current_exe()`] fails, which is rare
    /// but can happen in some embedded or heavily sandboxed environments.
    ExecutableNotFound(String),

    /// Executable path is empty or invalid.
    ///
    /// This error occurs when the system returns an empty executable path,
    /// which is extremely rare and indicates a corrupted or broken system.
    InvalidExecutablePath(String),

    /// An I/O operation failed.
    ///
    /// This error occurs when filesystem operations fail, such as:
    /// - Creating directories fails due to permissions
    /// - Disk space is insufficient
    /// - Path contains invalid characters for the filesystem
    /// - Network filesystem issues
    ///
    /// The original `std::io::Error` is preserved, allowing users to:
    /// - Check specific error kinds (`error.kind()`)
    /// - Access OS error codes (`error.raw_os_error()`)
    /// - Handle different I/O errors appropriately
    IoError(std::io::Error),
}

impl std::fmt::Display for AppPathError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            AppPathError::ExecutableNotFound(msg) => {
                write!(f, "Failed to determine executable location: {msg}")
            }
            AppPathError::InvalidExecutablePath(msg) => {
                write!(f, "Invalid executable path: {msg}")
            }
            AppPathError::IoError(err) => {
                write!(f, "I/O operation failed: {err}")
            }
        }
    }
}

impl std::error::Error for AppPathError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match self {
            AppPathError::IoError(err) => Some(err),
            _ => None,
        }
    }
}

impl From<std::io::Error> for AppPathError {
    fn from(err: std::io::Error) -> Self {
        AppPathError::IoError(err)
    }
}

/// Creates an IoError with path context for better debugging.
///
/// This implementation adds the file path to I/O error messages, making it easier
/// to identify which path caused the failure in complex directory operations.
///
/// # Examples
///
/// ```rust
/// use app_path::AppPathError;
/// use std::path::PathBuf;
///
/// let io_error = std::io::Error::new(std::io::ErrorKind::PermissionDenied, "access denied");
/// let path = PathBuf::from("/some/restricted/path");
/// let app_error = AppPathError::from((io_error, &path));
///
/// // Error message includes both the original error and the path
/// assert!(app_error.to_string().contains("access denied"));
/// assert!(app_error.to_string().contains("/some/restricted/path"));
/// ```
impl From<(std::io::Error, &PathBuf)> for AppPathError {
    fn from((err, path): (std::io::Error, &PathBuf)) -> Self {
        // Create a new io::Error that includes path context in the message
        let kind = err.kind();
        let msg = format!("{err} (path: {})", path.display());
        AppPathError::IoError(std::io::Error::new(kind, msg))
    }
}

/// Try to determine the executable directory (fallible version).
///
/// This is the internal fallible initialization function that both the fallible
/// and infallible APIs use. It handles all the edge cases properly without
/// exposing them as errors to API users.
pub(crate) fn try_exe_dir_init() -> Result<PathBuf, AppPathError> {
    let exe = current_exe().map_err(|e| {
        AppPathError::ExecutableNotFound(format!(
            "std::env::current_exe() failed: {e} (environment: {})",
            std::env::var("OS").unwrap_or_else(|_| "unknown OS".to_string())
        ))
    })?;

    if exe.as_os_str().is_empty() {
        return Err(AppPathError::InvalidExecutablePath(format!(
            "Executable path is empty - unsupported environment (process id: {})",
            std::process::id()
        )));
    }

    // Handle edge case: executable at filesystem root (jailed environments, etc.)
    // This is NOT an error - it's a valid case that should be handled internally
    let dir = match exe.parent() {
        Some(parent) => parent.to_path_buf(),
        None => {
            // If exe has no parent (e.g., running as "/init" or "C:\myapp.exe"),
            // use the root directory itself
            exe.ancestors().last().unwrap_or(&exe).to_path_buf()
        }
    };

    Ok(dir)
}