use crate::locale::*;
use humantime::{self, DurationError};
use std::error::Error as StdError;
use std::fmt;
use std::time::Duration;

/// Error when loading locale
#[derive(Debug, PartialEq, Clone)]
pub enum Error {
    /// Invalid locate or locale currently not supported
    NotFoundLocale(String),
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Error::NotFoundLocale(input) => write!(f, "locale `{}` not found", input),
        }
    }
}

impl StdError for Error {}

#[derive(Debug, PartialEq)]
/// A wrapper type associated with `locale` and `to` info.
pub struct TimeDiff {
    // locale is the locale string used by time_diff function.
    locale: String,

    // before_current_ts is a boolean that judge whether to is a negative duration.
    before_current_ts: bool,

    // to is the duration to be formatted.
    to: String,
}

impl TimeDiff {
    /// Receive a duration string from input and initiate a `TimeDiff` struct.
    ///
    /// And the duration string should be a human-readable string like `3d` and etc.
    /// more human-readable duration detail -> [humantime]
    ///
    /// [humantime]: https://docs.rs/humantime/2.1.0/humantime/fn.parse_duration.html
    ///
    /// # Exmaple
    ///
    /// ```
    /// use timediff::*;
    /// assert_eq!(TimeDiff::to_diff(String::from("-10s")).parse(),Ok(String::from("a few seconds ago")))
    /// ```
    ///
    pub fn to_diff(to: String) -> Self {
        TimeDiff {
            locale: String::from("en-US"),
            before_current_ts: false,
            to,
        }
    }

    /// Receive a std duration and initiate a `TimeDiff` struct.
    ///
    /// # Exmaple
    ///
    /// ```
    /// use timediff::*;
    /// use std::time::Duration;
    /// assert_eq!(TimeDiff::to_diff_duration(Duration::new(30 * 60, 0)).parse(),Ok(String::from("in 30 minutes")))
    /// ```
    ///
    pub fn to_diff_duration(to: Duration) -> Self {
        TimeDiff {
            locale: String::from("en-US"),
            before_current_ts: false,
            to: humantime::format_duration(to).to_string(),
        }
    }

    /// Change the locale used for the diff operation on `TimeDiff`.
    /// Default locale is `en-US`, supports `zh-CN`, `tr-TR`, `ru-RU` and etc.
    /// if a custom locale is not supported currently, will return a not found error.
    ///
    /// # Exmaple
    ///
    /// ```
    /// use timediff::*;
    /// use timediff::TimeDiffError as Error;
    /// assert_eq!(
    ///     TimeDiff::to_diff(String::from("-10s"))
    ///         .locale(String::from("zh-CN"))
    ///         .unwrap()
    ///         .parse(),
    ///     Ok(String::from("几秒前"))
    /// );
    ///
    /// assert_eq!(
    ///     TimeDiff::to_diff(String::from("10day")).locale(String::from("unknown")),
    ///     Err(Error::NotFoundLocale(String::from("unknown")))
    /// );
    /// ```
    ///
    pub fn locale(&mut self, l: String) -> Result<&mut Self, Error> {
        match l.as_str() {
            "zh-CN" | "ru-RU" | "tr-TR" | "en-US" => self.locale = l,
            _ => return Err(Error::NotFoundLocale(l)),
        }

        Ok(self)
    }

    /// Parses and prints a human-readable string representing the difference between two timestamps (a period of a duration)
    ///
    /// # Exmaple
    ///
    /// ```
    /// use timediff::*;
    /// assert_eq!(TimeDiff::to_diff(String::from("-10s")).parse(),Ok(String::from("a few seconds ago")))
    /// ```
    pub fn parse(&mut self) -> Result<String, DurationError> {
        let c = self.to.find('-').unwrap_or(self.to.len());
        if c == 0 {
            self.before_current_ts = true;
            self.to = self.to[1..].to_string();
        }

        match self.locale.as_str() {
            "zh-CN" => zh_cn::format_duration(self.before_current_ts, &self.to),
            "tr-TR" => tr_tr::format_duration(self.before_current_ts, &self.to),
            "ru-RU" => ru_ru::format_duration(self.before_current_ts, &self.to),
            "en-US" => en_us::format_duration(self.before_current_ts, &self.to),

            _ => en_us::format_duration(self.before_current_ts, &self.to),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::Error;
    use super::TimeDiff;
    use std::time::Duration;

    #[test]
    fn it_works_default_locale() {
        assert_eq!(
            TimeDiff::to_diff(String::from("-10s")).parse(),
            Ok(String::from("a few seconds ago"))
        )
    }

    #[test]
    fn it_works_en_us() {
        assert_eq!(
            TimeDiff::to_diff(String::from("-10s"))
                .locale(String::from("en-US"))
                .unwrap()
                .parse(),
            Ok(String::from("a few seconds ago"))
        )
    }

    #[test]
    fn it_works_zh_cn() {
        assert_eq!(
            TimeDiff::to_diff(String::from("-10s"))
                .locale(String::from("zh-CN"))
                .unwrap()
                .parse(),
            Ok(String::from("几秒前"))
        );
    }

    #[test]
    fn it_works_ru_ru() {
        assert_eq!(
            TimeDiff::to_diff(String::from("-10s"))
                .locale(String::from("ru-RU"))
                .unwrap()
                .parse(),
            Ok(String::from("несколько секунд назад"))
        )
    }

    #[test]
    fn it_works_tr_tr() {
        assert_eq!(
            TimeDiff::to_diff(String::from("-10s"))
                .locale(String::from("tr-TR"))
                .unwrap()
                .parse(),
            Ok(String::from("birkaç saniye önce"))
        )
    }

    #[test]
    fn time_diff_invalid_locale() {
        assert_eq!(
            TimeDiff::to_diff(String::from("10day")).locale(String::from("unknown")),
            Err(Error::NotFoundLocale(String::from("unknown")))
        )
    }

    #[test]
    fn time_diff_with_duration() {
        assert_eq!(
            TimeDiff::to_diff_duration(Duration::new(30 * 60, 0)).parse(),
            Ok(String::from("in 30 minutes"))
        )
    }

    #[test]
    fn time_diff_with_invalid_duration_string() {
        assert_eq!(
            TimeDiff::to_diff(String::from("--sdf")).parse(),
            Err(humantime::DurationError::NumberExpected(0))
        )
    }
}