//! Exponential backoff for use with QCS.
//!
//! This re-exports types from [`backoff`](::backoff) and provides a [`default_backoff`] function
//! to create a more useful default [`ExpontentialBackoff`].

use std::time::Duration;

use http::StatusCode;

pub use ::backoff::*;

/// Create a default [`ExponentialBackoff`] for use with QCS.
///
/// This backoff will retry for up to 5 minutes, with a maximum interval of 30 seconds and some
/// randomized jitter.
#[allow(clippy::module_name_repetitions)]
#[must_use]
pub fn default_backoff() -> ExponentialBackoff {
    ExponentialBackoffBuilder::new()
        .with_max_elapsed_time(Some(Duration::from_secs(300)))
        .with_max_interval(Duration::from_secs(30))
        .build()
}

/// Return `true` if the status code is one that could be retried.
#[must_use]
pub const fn status_code_is_retry(code: StatusCode) -> bool {
    matches!(
        code,
        StatusCode::SERVICE_UNAVAILABLE | StatusCode::TOO_MANY_REQUESTS
    )
}

/// Return `Some` if the response specifies a `Retry-After` header or the provided `backoff` has
/// another backoff to try.
#[must_use]
pub fn duration_from_response(
    status: StatusCode,
    headers: &http::HeaderMap,
    backoff: &mut ExponentialBackoff,
) -> Option<Duration> {
    use ::backoff::backoff::Backoff;
    use time::{format_description::well_known::Rfc2822, OffsetDateTime};

    if status_code_is_retry(status) {
        if let Some(value) = headers.get(http::header::RETRY_AFTER) {
            if let Ok(value) = value.to_str() {
                if let Ok(value) = value.parse::<u64>() {
                    return Some(Duration::from_secs(value));
                } else if let Ok(date) = OffsetDateTime::parse(value, &Rfc2822) {
                    let duration = date - OffsetDateTime::now_utc();
                    // This will fail if the number is too large or negative
                    let millis = duration.whole_milliseconds().try_into().ok()?;
                    return Some(Duration::from_millis(millis));
                }
            }
        }

        backoff.next_backoff()
    } else {
        None
    }
}