Time buckets

// Category: pure
// Permissions: none
// Time without a clock: every instant comes from the data. Bucketing
// trade times into 15-minute bars, counting per bar, and durations as
// exact seconds.

lang ">=0.1.1, <0.2.0";
import std.time;
import std.list;

fn main() {
    let day = timestamp("2024-03-01T00:00:00Z");
    let offsets = [3min, 9min, 14min + 59s, 15min, 31min, 44min, 46min];
    let mut buckets: List<Timestamp> = [];
    let mut counts: List<Int> = [];
    for offset in offsets {
        let bar = time.floor(day + offset, 15min);
        match buckets.last() {
            Some(last) => {
                if last == bar {
                    let n = counts.len() - 1;
                    let current = counts.get(n).expect("one count per bucket");
                    counts = list.concat(list.take(counts, n), [current + 1]);
                } else {
                    buckets.push(bar);
                    counts.push(1);
                }
            }
            None => {
                buckets.push(bar);
                counts.push(1);
            }
        }
    }
    let mut i = 0;
    while i < buckets.len() {
        print(to_string(buckets[i]) + " " + to_string(counts[i]) + " trade(s)");
        i = i + 1;
    }
    let span = (day + 46min) - (day + 3min);
    print("first to last: " + to_string(time.seconds(span)) + " s");
    print("as unix ms: " + to_string(time.unix_ms(day)));
    print(time.from_seconds(0.25));
}
// expect-output: 2024-03-01T00:00:00Z 3 trade(s)
// expect-output: 2024-03-01T00:15:00Z 1 trade(s)
// expect-output: 2024-03-01T00:30:00Z 2 trade(s)
// expect-output: 2024-03-01T00:45:00Z 1 trade(s)
// expect-output: first to last: 2580 s
// expect-output: as unix ms: 1709251200000
// expect-output: 250ms