reidond/kedra/m13-domain-error

"How should I handle payment failures?"
    ↑ Ask: What are the business rules for retries?
    ↑ Check: domain-fintech (transaction requirements)
    ↑ Check: SLA (availability requirements)

"Need typed errors"
    ↓ m06-error-handling: thiserror for library
    ↓ m04-zero-cost: Error enum design
 
"Need error context"
    ↓ m06-error-handling: anyhow::Context
    ↓ Logging: tracing with fields
 
"Need retry logic"
    ↓ m07-concurrency: async retry patterns
    ↓ Crates: tokio-retry, backoff

#[derive(thiserror::Error, Debug)]
pub enum AppError {
    // User-facing
    #[error("Invalid input: {0}")]
    Validation(String),
 
    // Transient (retryable)
    #[error("Service temporarily unavailable")]
    ServiceUnavailable(#[source] reqwest::Error),
 
    // Internal (log details, show generic)
    #[error("Internal error")]
    Internal(#[source] anyhow::Error),
}
 
impl AppError {
    pub fn is_retryable(&self) -> bool {
        matches!(self, Self::ServiceUnavailable(_))
    }
}

use tokio_retry::{Retry, strategy::ExponentialBackoff};
 
async fn with_retry<F, T, E>(f: F) -> Result<T, E>
where
    F: Fn() -> impl Future<Output = Result<T, E>>,
    E: std::fmt::Debug,
{
    let strategy = ExponentialBackoff::from_millis(100)
        .max_delay(Duration::from_secs(10))
        .take(5);
 
    Retry::spawn(strategy, || f()).await
}