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use std::default::Default;
use std::error::Error as StdError;
use std::fmt;
#[derive(Debug, Copy, Clone)]
pub enum Error {
QualityAboveFiveError(u8),
}
impl fmt::Display for Error {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
Error::QualityAboveFiveError(q) => {
write!(f, "Quality cannot be greater than 5, {} was given.", q)
}
}
}
}
impl StdError for Error {}
#[derive(Debug, Copy, Clone)]
pub struct Item {
repetitions: usize,
efactor: f64,
}
impl Default for Item {
fn default() -> Self {
Self {
repetitions: 0,
efactor: 2.5,
}
}
}
impl Item {
pub fn new(repetitions: usize, efactor: f64) -> Self {
Self {
repetitions,
efactor,
}
}
pub fn repetitions(&self) -> usize {
self.repetitions
}
pub fn efactor(&self) -> f64 {
self.efactor
}
pub fn interval(&self) -> usize {
match self.repetitions {
0 => 0,
1 => 1,
2 => 6,
_ => (6.0 * self.efactor.powi(self.repetitions as i32 - 2)).ceil() as usize,
}
}
fn new_efactor(&self, quality: u8) -> Result<f64, Error> {
let ef = if self.efactor < 1.3 {
1.3
} else {
self.efactor
};
if quality > 5 {
Err(Error::QualityAboveFiveError(quality))
} else {
Ok(ef + (0.1 - (5.0 - quality as f64) * (0.08 + (5.0 - quality as f64) * 0.02)))
}
}
fn new_repetitions(&self, quality: u8) -> Result<usize, Error> {
match quality {
0 | 1 | 2 => Ok(1),
3 | 4 | 5 => Ok(self.repetitions + 1),
_ => Err(Error::QualityAboveFiveError(quality)),
}
}
pub fn review(&self, quality: u8) -> Result<Self, Error> {
Ok(Self {
repetitions: self.new_repetitions(quality)?,
efactor: self.new_efactor(quality)?,
})
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn correct_default_values() {
let item = Item::default();
assert_eq!(item.repetitions, 0);
assert_eq!(item.efactor, 2.5);
}
#[test]
#[should_panic]
fn quality_above_5_returns_error() {
let item = Item::default();
item.review(6).unwrap();
}
#[test]
fn review_gives_correct_repetitions_and_efactor() {
let item = Item::new(3, 2.4);
let new_item = item.review(5).unwrap();
assert_eq!(new_item.repetitions, 4);
assert_eq!(new_item.efactor, 2.5);
}
#[test]
fn calculate_interval() {
let item = Item::new(5, 3.9);
assert_eq!(item.interval(), 356);
}
}