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extern crate chrono;
pub use chrono::offset::Utc;
pub use chrono::DateTime;
use std::cmp;
const HALF_LIFE: i32 = 45_000;
pub fn rank(
upvotes: &i32,
downvotes: &i32,
timestamp: DateTime<Utc>,
epoch: DateTime<Utc>,
) -> i32 {
let duration = timestamp.signed_duration_since(epoch);
let seconds = duration.num_seconds() as i32;
let score = upvotes - downvotes;
let upper = cmp::max(score, 1) as f32;
let order = upper.log(10.0) as i32;
let sign = match score {
n if n > 0 => 1,
n if n < 0 => -1,
_ => 0,
};
sign * order + seconds / HALF_LIFE
}
#[cfg(test)]
mod tests {
use super::*;
use chrono::prelude::*;
#[test]
fn one_upvote_one_downvote() {
let upvotes: i32 = 1;
let downvotes: i32 = 1;
let epoch = Utc.ymd(2014, 1, 1).and_hms(21, 15, 33);
let timestamp = Utc.ymd(2014, 1, 1).and_hms(21, 15, 33);
let ranking = rank(&upvotes, &downvotes, timestamp, epoch);
assert!(ranking == 0);
}
#[test]
fn twenty_upvotes_zero_downvotes() {
let upvotes: i32 = 50;
let downvotes: i32 = 0;
let epoch = Utc.ymd(2014, 1, 1).and_hms(21, 15, 33);
let timestamp = Utc.ymd(2014, 1, 1).and_hms(21, 15, 33);
let ranking = rank(&upvotes, &downvotes, timestamp, epoch);
assert!(ranking > 0);
}
#[test]
fn one_upvote_twenty_downvotes() {
let upvotes: i32 = 1;
let downvotes: i32 = 1000;
let epoch = Utc.ymd(2014, 1, 1).and_hms(21, 15, 33);
let timestamp = Utc.ymd(2014, 1, 1).and_hms(21, 15, 33);
let ranking = rank(&upvotes, &downvotes, timestamp, epoch);
println!("{}", ranking);
assert!(ranking == 0);
}
}