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use crate::headers::{HeaderName, HeaderValue, Headers, ToHeaderValues, EXPIRES};
use crate::utils::{fmt_http_date, parse_http_date};

use std::fmt::Debug;
use std::option;
use std::time::{Duration, SystemTime};

/// HTTP `Expires` header

///

/// # Specifications

///

/// - [RFC 7234, section 5.3: Expires](https://tools.ietf.org/html/rfc7234#section-5.3)

///

/// # Examples

///

/// ```

/// # fn main() -> http_types::Result<()> {

/// #

/// use http_types::Response;

/// use http_types::cache::Expires;

/// use std::time::{SystemTime, Duration};

///

/// let time = SystemTime::now() + Duration::from_secs(5 * 60);

/// let expires = Expires::new_at(time);

///

/// let mut res = Response::new(200);

/// expires.apply(&mut res);

///

/// let expires = Expires::from_headers(res)?.unwrap();

///

/// // HTTP dates only have second-precision.

/// let elapsed = time.duration_since(expires.expiration())?;

/// assert_eq!(elapsed.as_secs(), 0);

/// #

/// # Ok(()) }

/// ```

#[derive(Debug, Ord, PartialOrd, Eq, PartialEq)]
pub struct Expires {
    instant: SystemTime,
}

impl Expires {
    /// Create a new instance of `Expires`.

    pub fn new(dur: Duration) -> Self {
        let instant = SystemTime::now() + dur;
        Self { instant }
    }

    /// Create a new instance of `Expires` from secs.

    pub fn new_at(instant: SystemTime) -> Self {
        Self { instant }
    }

    /// Get the expiration time.

    pub fn expiration(&self) -> SystemTime {
        self.instant
    }

    /// Create an instance of `Expires` from a `Headers` instance.

    pub fn from_headers(headers: impl AsRef<Headers>) -> crate::Result<Option<Self>> {
        let headers = match headers.as_ref().get(EXPIRES) {
            Some(headers) => headers,
            None => return Ok(None),
        };

        // If we successfully parsed the header then there's always at least one

        // entry. We want the last entry.

        let header = headers.iter().last().unwrap();

        let instant = parse_http_date(header.as_str())?;
        Ok(Some(Self { instant }))
    }

    /// Insert a `HeaderName` + `HeaderValue` pair into a `Headers` instance.

    pub fn apply(&self, mut headers: impl AsMut<Headers>) {
        headers.as_mut().insert(EXPIRES, self.value());
    }

    /// Get the `HeaderName`.

    pub fn name(&self) -> HeaderName {
        EXPIRES
    }

    /// Get the `HeaderValue`.

    pub fn value(&self) -> HeaderValue {
        let output = fmt_http_date(self.instant);

        // SAFETY: the internal string is validated to be ASCII.

        unsafe { HeaderValue::from_bytes_unchecked(output.into()) }
    }
}

impl ToHeaderValues for Expires {
    type Iter = option::IntoIter<HeaderValue>;
    fn to_header_values(&self) -> crate::Result<Self::Iter> {
        // A HeaderValue will always convert into itself.

        Ok(self.value().to_header_values().unwrap())
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::headers::Headers;

    #[test]
    fn smoke() -> crate::Result<()> {
        let time = SystemTime::now() + Duration::from_secs(5 * 60);
        let expires = Expires::new_at(time);

        let mut headers = Headers::new();
        expires.apply(&mut headers);

        let expires = Expires::from_headers(headers)?.unwrap();

        // HTTP dates only have second-precision

        let elapsed = time.duration_since(expires.expiration())?;
        assert_eq!(elapsed.as_secs(), 0);
        Ok(())
    }

    #[test]
    fn bad_request_on_parse_error() -> crate::Result<()> {
        let mut headers = Headers::new();
        headers.insert(EXPIRES, "<nori ate the tag. yum.>");
        let err = Expires::from_headers(headers).unwrap_err();
        assert_eq!(err.status(), 400);
        Ok(())
    }
}