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use std::error::Error;
use std::fmt::{Display,Formatter};
use std::fmt::Error as FmtError;
use std::thread::sleep_ms;
#[derive(Debug)]
pub struct Retry<'a, F: FnMut() -> R + 'a, G: FnMut(&R) -> bool + 'a, R> {
condition_fn: &'a mut G,
tries: Option<u32>,
value_fn: &'a mut F,
wait: u32,
}
impl<'a, F: FnMut() -> R, G: FnMut(&R) -> bool, R> Retry<'a, F, G, R> {
pub fn new(
value_fn: &'a mut F,
condition_fn: &'a mut G
) -> Retry<'a, F, G, R> where F: FnMut() -> R, G: FnMut(&R) -> bool {
Retry {
condition_fn: condition_fn,
tries: None,
value_fn: value_fn,
wait: 0,
}
}
pub fn execute(self) -> Result<R, RetryError> {
if self.tries.is_some() && self.tries.unwrap() == 0 {
return Err(RetryError { message: "tries must be non-zero" });
}
let mut try = 0;
loop {
if self.tries.is_some() && self.tries.unwrap() == try {
return Err(RetryError { message: "reached last try without condition match" })
}
let value = (self.value_fn)();
if (self.condition_fn)(&value) {
return Ok(value);
}
if self.wait != 0 {
sleep_ms(self.wait);
}
try += 1;
}
}
pub fn try(mut self, tries: u32) -> Retry<'a, F, G, R> {
self.tries = Some(tries);
self
}
pub fn wait(mut self, wait: u32) -> Retry<'a, F, G, R> {
self.wait = wait;
self
}
}
pub fn retry<F, G, R>(
tries: u32,
wait: u32,
mut value_fn: F,
mut condition_fn: G
) -> Result<R, RetryError> where F: FnMut() -> R, G: FnMut(&R) -> bool {
Retry::new(&mut value_fn, &mut condition_fn).try(tries).wait(wait).execute()
}
#[derive(Debug)]
pub struct RetryError {
message: &'static str
}
impl Display for RetryError {
fn fmt(&self, formatter: &mut Formatter) -> Result<(), FmtError> {
write!(formatter, "{}", self.message)
}
}
impl Error for RetryError {
fn description(&self) -> &str {
self.message
}
}
#[cfg(test)]
mod tests {
use super::{Retry, retry};
#[test]
fn succeeds_without_try_count() {
let mut collection = vec![1, 2, 3, 4, 5].into_iter();
let value = Retry::new(
&mut || collection.next().unwrap(),
&mut |value| *value == 5
).execute().unwrap();
assert_eq!(value, 5);
}
#[test]
fn succeeds_on_first_try() {
let value = Retry::new(&mut || 1, &mut |value| *value == 1).try(1).execute().ok().unwrap();
assert_eq!(value, 1);
}
#[test]
fn requires_non_zero_tries() {
let error = Retry::new(&mut || 1, &mut |value| *value == 1).try(0).execute().err().unwrap();
assert_eq!(error.message, "tries must be non-zero");
}
#[test]
fn succeeds_on_subsequent_try() {
let mut collection = vec![1, 2].into_iter();
let value = Retry::new(
&mut || collection.next().unwrap(),
&mut |value| *value == 2
).try(2).execute().ok().unwrap();
assert_eq!(value, 2);
}
#[test]
fn fails_after_last_try() {
let mut collection = vec![1].into_iter();
let error = Retry::new(
&mut || collection.next().unwrap(),
&mut |value| *value == 2
).try(1).execute().err().unwrap();
assert_eq!(error.message, "reached last try without condition match");
}
#[test]
fn sets_custom_wait_time() {
let mut collection = vec![1, 2].into_iter();
let value = Retry::new(
&mut || collection.next().unwrap(),
&mut |value| *value == 2
).wait(1).execute().ok().unwrap();
assert_eq!(value, 2);
}
#[test]
fn retry_function() {
let mut collection = vec![1, 2].into_iter();
let value = retry(2, 0, || collection.next().unwrap(), |value| *value == 2).ok().unwrap();
assert_eq!(value, 2);
}
}