//! # User Facing Error
//! A library for conveniently displaying well-formatted, and good looking
//! errors to users of CLI applications. Useful for bubbling up unrecoverable
//! errors to inform the user what they can do to fix them. Error messages you'd
//! be proud to show your mom.
#![deny(
    missing_docs,
    missing_debug_implementations,
    missing_copy_implementations,
    trivial_casts,
    trivial_numeric_casts,
    unstable_features,
    unsafe_code,
    unused_import_braces,
    unused_qualifications
)]

// Standard Library Dependencies
use core::fmt::{self, Debug, Display};
use std::error::Error;

/*************
 * CONSTANTS *
 *************/

// 'Error:' with a red background and white, bold, text
const SUMMARY_PREFIX: &str = "\u{001b}[97;41;22mError:\u{001b}[91;49;1m ";
// ' - ' bullet point in yellow and text in bold white
const REASON_PREFIX: &str = "\u{001b}[93;49;1m - \u{001b}[97;49;1m";
// Muted white help text
const HELPTEXT_PREFIX: &str = "\u{001b}[37;49;2m";
// ASCII Reset formatting escape code
const RESET: &str = "\u{001b}[0m";

// Helper function to keep things DRY
// Takes a dyn Error.source() and returns a Vec of Strings representing all the
// .sources() in the error chain (if any)
fn error_sources(mut source: Option<&(dyn Error + 'static)>) -> Option<Vec<String>> {
    /* Check if we have any sources to derive reasons from */
    if source.is_some() {
        /* Add all the error sources to a list of reasons for the error */
        let mut reasons = Vec::new();
        while let Some(error) = source {
            reasons.push(error.to_string());
            source = error.source();
        }
        Some(reasons)
    } else {
        None
    }
}

/*********
 * TRAIT *
 *********/

// Helper Functions

/// Convenience function that converts the summary into pretty String.
fn pretty_summary(summary: &str) -> String {
    [SUMMARY_PREFIX, summary, RESET].concat()
}

/// Convenience function that converts the reasons into pretty String.
fn pretty_reasons(reasons: Reasons) -> Option<String> {
    /* Print list of Reasons (if any) */
    if let Some(reasons) = reasons {
        /* Vector to store the intermediate bullet point strings */
        let mut reason_strings = Vec::with_capacity(reasons.len());
        for reason in reasons {
            let bullet_point = [REASON_PREFIX, &reason].concat();
            reason_strings.push(bullet_point);
        }
        /* Join the buller points with a newline, append a RESET ASCII escape code to the end */
        Some([&reason_strings.join("\n"), RESET].concat())
    } else {
        None
    }
}

/// Convenience function that converts the help text into pretty String.
fn pretty_helptext(helptext: Helptext) -> Option<String> {
    if let Some(helptext) = helptext {
        Some([HELPTEXT_PREFIX, &helptext, RESET].concat())
    } else {
        None
    }
}

/// You can implement UFE on your error types pretty print them. The default
/// implementation will print Error: <your error .to_string()> followed by a list
/// of reasons that are any errors returned by .source(). You should only
/// override the summary, reasons and help text functions. The pretty print
/// versions of these are used by print(), print_and_exit() and contain the
/// formatting. If you wish to change the formatting you should update it with
/// the formatting functions.
pub trait UFE: Error {
    /**************
     * IMPLENT ME *
     **************/

    /// Returns a summary of the error. This will be printed in red, prefixed
    /// by "Error: ", at the top of the error message.
    fn summary(&self) -> String {
        self.to_string()
    }

    /// Returns a vector of Strings that will be listed as bullet points below
    /// the summary. By default, lists any errors returned by .source()
    /// recursively.
    fn reasons(&self) -> Option<Vec<String>> {
        /* Helper function to keep things DRY */
        error_sources(self.source())
    }

    /// Returns help text that is listed below the reasons in a muted fashion.
    /// Useful for additional details, or suggested next steps.
    fn helptext(&self) -> Option<String> {
        None
    }

    /**********
     * USE ME *
     **********/

    /// Prints the formatted error.
    /// # Example
    /// ```
    /// use user_error::{UserFacingError, UFE};
    /// UserFacingError::new("File failed to open")
    ///         .reason("File not found")
    ///         .help("Try: touch file.txt")
    ///         .print();
    /// ```
    fn print(&self) {
        /* Print Summary */
        eprintln!("{}", pretty_summary(&self.summary()));

        /* Print list of Reasons (if any) */
        if let Some(reasons) = pretty_reasons(self.reasons()) {
            eprintln!("{}", reasons);
        }

        /* Print help text (if any) */
        if let Some(helptext) = pretty_helptext(self.helptext()) {
            eprintln!("{}", helptext);
        }
    }

    /// Convenience function that pretty prints the error and exits the program.
    /// # Example
    /// ```should_panic
    /// use user_error::{UserFacingError, UFE};
    /// UserFacingError::new("File failed to open")
    ///         .reason("File not found")
    ///         .help("Try: touch file.txt")
    ///         .print_and_exit();
    /// ```
    fn print_and_exit(&self) {
        self.print();
        std::process::exit(1)
    }

    /// Consumes the UFE and returns a UserFacingError. Useful if you want
    /// access to additional functions to edit the error message before exiting
    /// the program.
    /// # Example
    /// ```
    /// use user_error::{UserFacingError, UFE};
    /// use std::fmt::{self, Display};
    /// use std::error::Error;
    ///
    /// #[derive(Debug)]
    /// struct MyError {}
    ///
    /// impl Display for MyError {
    ///     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
    ///         write!(f, "MyError")
    ///     }
    /// }
    ///
    /// impl Error for MyError {
    ///     fn source(&self) -> Option<&(dyn Error + 'static)> { None }
    /// }
    ///
    /// impl UFE for MyError {}
    ///
    /// fn main() {
    ///     let me = MyError {};
    ///     me.print();
    ///     me.into_ufe()
    ///         .help("Added help text")
    ///         .print();
    /// }
    /// ```
    fn into_ufe(&self) -> UserFacingError {
        UserFacingError {
            summary: self.summary(),
            reasons: self.reasons(),
            helptext: self.helptext(),
            source: None,
        }
    }
}

/**********
 * STRUCT *
 **********/
type Summary = String;
type Reasons = Option<Vec<String>>;
type Helptext = Option<String>;
type Source = Option<Box<(dyn Error)>>;

/// The eponymous struct. You can create a new one from using
/// user_error::UserFacingError::new() however I recommend you use your own
/// error types and have them implement UFE instead of using UserFacingError
/// directly. This is more of an example type, or a way to construct a pretty
/// messages without implementing your own error type.
#[derive(Debug)]
pub struct UserFacingError {
    summary: Summary,
    reasons: Reasons,
    helptext: Helptext,
    source: Source,
}

/******************
 * IMPLEMENTATION *
 ******************/

// Implement Display so our struct also implements std::error::Error
impl Display for UserFacingError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let summary = pretty_summary(&self.summary());
        let reasons = pretty_reasons(self.reasons());
        let helptext = pretty_helptext(self.helptext());

        // Love this - thanks Rust!
        match (summary, reasons, helptext) {
            (summary, None, None) => writeln!(f, "{}", summary),
            (summary, Some(reasons), None) => writeln!(f, "{}\n{}", summary, reasons),
            (summary, None, Some(helptext)) => writeln!(f, "{}\n{}", summary, helptext),
            (summary, Some(reasons), Some(helptext)) => {
                writeln!(f, "{}\n{}\n{}", summary, reasons, helptext)
            }
        }
    }
}

// Implement std::error::Error
impl Error for UserFacingError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        match self.source {
            Some(_) => self.source.as_deref(),
            None => None,
        }
    }
}

// Implement our own trait for our example struct
// Cloning is not super efficient but this should be the last thing a program
// does, and it will only do it once so... ¯\_(ツ)_/¯
impl UFE for UserFacingError {
    fn summary(&self) -> Summary {
        self.summary.clone()
    }
    fn reasons(&self) -> Reasons {
        self.reasons.clone()
    }
    fn helptext(&self) -> Helptext {
        self.helptext.clone()
    }
}

// Helper function to keep things DRY
fn get_ufe_struct_members(error: &(dyn Error)) -> (Summary, Reasons) {
    /* Error Display format is the summary */
    let summary = error.to_string();
    /* Form the reasons from the error source chain */
    let reasons = error_sources(error.source());
    (summary, reasons)
}

/// Allows you to create UserFacingErrors From std::io::Error for convenience
/// You should really just implement UFE for your error type, but if you wanted
/// to convert before quitting so you could add help text of something you can
/// use this.
impl From<std::io::Error> for UserFacingError {
    fn from(error: std::io::Error) -> UserFacingError {
        let (summary, reasons) = get_ufe_struct_members(&error);

        UserFacingError {
            summary,
            reasons,
            helptext: None,
            source: Some(Box::new(error)),
        }
    }
}

/// Allows you to create UserFacingErrors From std Errors.
/// You should really just implement UFE for your error type, but if you wanted
/// to convert before quitting so you could add help text of something you can
/// use this.
impl From<Box<(dyn Error)>> for UserFacingError {
    fn from(error: Box<(dyn Error)>) -> UserFacingError {
        let (summary, reasons) = get_ufe_struct_members(error.as_ref());

        UserFacingError {
            summary,
            reasons,
            helptext: None,
            source: Some(error),
        }
    }
}

/// Allows you to create UserFacingErrors From std Errors.
/// You should really just implement UFE for your error type, but if you wanted
/// to convert before quitting so you could add help text of something you can
/// use this.
impl From<&(dyn Error)> for UserFacingError {
    fn from(error: &(dyn Error)) -> UserFacingError {
        let (summary, reasons) = get_ufe_struct_members(error);

        UserFacingError {
            summary,
            reasons,
            helptext: None,
            source: None,
        }
    }
}

/// Allows you to create UserFacingErrors From std Errors wrapped in a Result
/// You should really just implement UFE for your error type, but if you wanted
/// to convert before quitting so you could add help text of something you can
/// use this.
impl<T: Debug> From<Result<T, Box<dyn Error>>> for UserFacingError {
    fn from(error: Result<T, Box<dyn Error>>) -> UserFacingError {
        /* Panics if you try to convert an Ok() Result to a UserFacingError */
        let error = error.unwrap_err();
        let (summary, reasons) = get_ufe_struct_members(error.as_ref());

        UserFacingError {
            summary,
            reasons,
            helptext: None,
            source: Some(error),
        }
    }
}

impl UserFacingError {
    /// This is how users create a new User Facing Error. The value passed to
    /// new() will be used as an error summary. Error summaries are displayed
    /// first, prefixed by 'Error: '.
    /// # Example
    /// ```
    /// # use user_error::UserFacingError;
    /// let err = UserFacingError::new("File failed to open");
    /// ```
    pub fn new<S: Into<String>>(summary: S) -> UserFacingError {
        UserFacingError {
            summary: summary.into(),
            reasons: None,
            helptext: None,
            source: None,
        }
    }

    /// Replace the error summary.
    /// # Example
    /// ```
    /// # use user_error::UserFacingError;
    /// let mut err = UserFacingError::new("File failed to open");
    /// err.update("Failed Task");
    /// ```
    pub fn update<S: Into<String>>(&mut self, summary: S) {
        self.summary = summary.into();
    }

    /// Replace the error summary and add the previous error summary to the
    /// list of reasons
    /// # Example
    /// ```
    /// # use user_error::UserFacingError;
    /// let mut err = UserFacingError::new("File failed to open");
    /// err.push("Failed Task");
    /// ```
    pub fn push<S: Into<String>>(&mut self, new_summary: S) {
        // Add the old summary to the list of reasons
        let old_summary = self.summary();
        match self.reasons.as_mut() {
            Some(reasons) => reasons.insert(0, old_summary),
            None => self.reasons = Some(vec![old_summary]),
        }

        // Update the summary
        self.summary = new_summary.into();
    }

    /// Add a reason to the UserFacingError. Reasons are displayed in a
    /// bulleted list below the summary, in the reverse order they were added.
    /// # Example
    /// ```
    /// # use user_error::UserFacingError;
    /// let err = UserFacingError::new("File failed to open")
    ///                             .reason("File not found")
    ///                             .reason("Directory cannot be entered");
    /// ```
    pub fn reason<S: Into<String>>(mut self, reason: S) -> UserFacingError {
        self.reasons = match self.reasons {
            Some(mut reasons) => {
                reasons.push(reason.into());
                Some(reasons)
            }
            None => Some(vec![reason.into()]),
        };
        self
    }

    // Return ref to previous?

    /// Clears all reasons from a UserFacingError.
    /// # Example
    /// ```
    /// # use user_error::UserFacingError;
    /// let mut err = UserFacingError::new("File failed to open")
    ///                             .reason("File not found")
    ///                             .reason("Directory cannot be entered");
    /// err.clear_reasons();
    /// ```
    pub fn clear_reasons(&mut self) {
        self.reasons = None;
    }

    /// Add help text to the error. Help text is displayed last, in a muted
    /// fashion.
    /// # Example
    /// ```
    /// # use user_error::UserFacingError;
    /// let err = UserFacingError::new("File failed to open")
    ///                             .reason("File not found")
    ///                             .help("Check if the file exists.");
    /// ```
    pub fn help<S: Into<String>>(mut self, helptext: S) -> UserFacingError {
        self.helptext = Some(helptext.into());
        self
    }

    /// Clears all the help text from a UserFacingError.
    /// # Example
    /// ```
    /// # use user_error::UserFacingError;
    /// let mut err = UserFacingError::new("File failed to open")
    ///                             .reason("File not found")
    ///                             .reason("Directory cannot be entered")
    ///                             .help("Check if the file exists.");
    /// err.clear_helptext();
    /// ```
    pub fn clear_helptext(&mut self) {
        self.helptext = None;
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    // Statics to keep the testing DRY/cleaner
    static S: &'static str = "Test Error";
    static R: &'static str = "Reason 1";
    static H: &'static str = "Try Again";

    #[test]
    fn new_test() {
        eprintln!("{}", UserFacingError::new("Test Error"));
    }

    #[test]
    fn summary_test() {
        let e = UserFacingError::new(S);
        let expected = [SUMMARY_PREFIX, S, RESET, "\n"].concat();
        assert_eq!(e.to_string(), String::from(expected));
        eprintln!("{}", e);
    }

    #[test]
    fn helptext_test() {
        let e = UserFacingError::new(S).help(H);
        let expected = format!(
            "{}{}{}\n{}{}{}\n",
            SUMMARY_PREFIX, S, RESET, HELPTEXT_PREFIX, H, RESET
        );
        assert_eq!(e.to_string(), expected);
        eprintln!("{}", e);
    }

    #[test]
    fn reason_test() {
        let e = UserFacingError::new(S).reason(R).reason(R);

        /* Create Reasons String */
        let reasons = vec![String::from(R), String::from(R)];
        let mut reason_strings = Vec::with_capacity(reasons.len());
        for reason in reasons {
            let bullet_point = [REASON_PREFIX, &reason].concat();
            reason_strings.push(bullet_point);
        }
        // Join the bullet points with a newline, append a RESET ASCII escape
        // code to the end.
        let reasons = [&reason_strings.join("\n"), RESET].concat();

        let expected = format!("{}{}{}\n{}\n", SUMMARY_PREFIX, S, RESET, reasons);
        assert_eq!(e.to_string(), expected);
        eprintln!("{}", e);
    }

    #[test]
    fn push_test() {
        let mut e = UserFacingError::new(S).reason("R1");
        e.push("R2");

        /* Create Reasons String */
        let reasons = vec![String::from(S), String::from("R1")];
        let mut reason_strings = Vec::with_capacity(reasons.len());
        for reason in reasons {
            let bullet_point = [REASON_PREFIX, &reason].concat();
            reason_strings.push(bullet_point);
        }
        // Join the bullet points with a newline, append a RESET ASCII escape
        // code to the end
        let reasons = [&reason_strings.join("\n"), RESET].concat();

        let expected = format!("{}{}{}\n{}\n", SUMMARY_PREFIX, "R2", RESET, reasons);
        assert_eq!(e.to_string(), expected);
        eprintln!("{}", e);
    }

    #[test]
    fn push_test_empty() {
        let mut e = UserFacingError::new(S);
        e.push("S2");

        // Create Reasons String
        let reasons = vec![String::from(S)];
        let mut reason_strings = Vec::with_capacity(reasons.len());
        for reason in reasons {
            let bullet_point = [REASON_PREFIX, &reason].concat();
            reason_strings.push(bullet_point);
        }
        // Join the bullet points with a newline, append a RESET ASCII escape
        // code to the end
        let reasons = [&reason_strings.join("\n"), RESET].concat();

        let expected = format!("{}{}{}\n{}\n", SUMMARY_PREFIX, "S2", RESET, reasons);
        assert_eq!(e.to_string(), expected);
        eprintln!("{}", e);
    }

    #[test]
    fn reason_and_helptext_test() {
        let e = UserFacingError::new(S).reason(R).reason(R).help(H);

        // Create Reasons String
        let reasons = vec![String::from(R), String::from(R)];
        let mut reason_strings = Vec::with_capacity(reasons.len());
        for reason in reasons {
            let bullet_point = [REASON_PREFIX, &reason].concat();
            reason_strings.push(bullet_point);
        }

        // Join the bullet points with a newline, append a RESET ASCII escape
        // code to the end
        let reasons = [&reason_strings.join("\n"), RESET].concat();

        let expected = format!(
            "{}{}{}\n{}\n{}{}{}\n",
            SUMMARY_PREFIX, S, RESET, reasons, HELPTEXT_PREFIX, H, RESET
        );
        assert_eq!(e.to_string(), expected);
        eprintln!("{}", e);
    }

    #[test]
    fn from_error_test() {
        let error_text = "Error";
        let ioe = std::io::Error::new(std::io::ErrorKind::Other, error_text);

        // Lose the type
        fn de(ioe: std::io::Error) -> Box<dyn Error> {
            Box::new(ioe)
        }
        // Convert to UFE
        let ufe: UserFacingError = de(ioe).into();

        let expected = [SUMMARY_PREFIX, error_text, RESET, "\n"].concat();
        assert_eq!(ufe.to_string(), expected);
    }

    #[test]
    fn from_error_source_test() {
        let ufe: UserFacingError = get_super_error().into();
        let expected = [
            SUMMARY_PREFIX,
            "SuperError",
            RESET,
            "\n",
            REASON_PREFIX,
            "Sidekick",
            RESET,
            "\n",
        ]
        .concat();

        assert_eq!(ufe.to_string(), expected);
    }

    // Used for to test that source is working correctly
    #[derive(Debug)]
    struct SuperError {
        side: SuperErrorSideKick,
    }

    impl Display for SuperError {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            write!(f, "SuperError")
        }
    }

    impl Error for SuperError {
        fn source(&self) -> Option<&(dyn Error + 'static)> {
            Some(&self.side)
        }
    }

    #[derive(Debug)]
    struct SuperErrorSideKick;

    impl Display for SuperErrorSideKick {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            write!(f, "Sidekick")
        }
    }

    impl Error for SuperErrorSideKick {
        fn source(&self) -> Option<&(dyn Error + 'static)> {
            None
        }
    }

    fn get_super_error() -> Result<(), Box<dyn Error>> {
        Err(Box::new(SuperError {
            side: SuperErrorSideKick,
        }))
    }

    // Custom Error Type
    #[derive(Debug)]
    struct MyError {
        mssg: String,
        src: Option<Box<dyn Error>>,
    }

    impl Display for MyError {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            write!(f, "{}", self.mssg.to_string())
        }
    }

    impl Error for MyError {
        fn source(&self) -> Option<&(dyn Error + 'static)> {
            self.src.as_deref()
        }
    }

    impl UFE for MyError {}

    #[test]
    fn custom_error_implements_ufe() {
        let me = MyError {
            mssg: "Program Failed".into(),
            src: Some(Box::new(MyError {
                mssg: "Reason 1".into(),
                src: Some(Box::new(MyError {
                    mssg: "Reason 2".into(),
                    src: None,
                })),
            })),
        };
        me.print();
        me.into_ufe().help("Helptext Added").print();
    }
}