package web

import (
	"fmt"
	"math"
	"slices"
	"time"
)

// window remembers when recent conversions started, so it can tell whether
// another one would go over a limit of n conversions per period.
type window []time.Time

// prune drops entries older than period.
func (w *window) prune(now time.Time, period time.Duration) {
	cut := 0
	for cut < len(*w) && now.Sub((*w)[cut]) >= period {
		cut++
	}
	*w = (*w)[cut:]
}

// full reports whether n conversions already started within period, and if
// so when the oldest of them stops counting.
func (w window) full(now time.Time, n int, period time.Duration) (bool, time.Time) {
	if len(w) < n {
		return false, time.Time{}
	}
	return true, w[len(w)-n].Add(period)
}

// remove takes back one entry made at t.
func (w *window) remove(t time.Time) {
	if i := slices.Index(*w, t); i >= 0 {
		*w = slices.Delete(*w, i, i+1)
	}
}

// minutes describes d in whole minutes, rounded up.
func minutes(d time.Duration) string {
	m := max(1, int(math.Ceil(d.Minutes())))
	if m == 1 {
		return "1 minute"
	}
	return fmt.Sprintf("%d minutes", m)
}