package ui

import (
	"fmt"
	"html/template"
	"strconv"
	"strings"
	"time"
)

// funcMap returns the template functions every page can call.
// Kept small on purpose: anything fancier belongs in the handler,
// which can pre-compute and pass primitives into the view.
func funcMap() template.FuncMap {
	return template.FuncMap{
		"bytes":   formatBytes,
		"relTime": formatRelTime,
		"comma":   formatComma,
		"deref":   derefStr,
		"timeNotZero": func(t *time.Time) bool { return t != nil && !t.IsZero() },
	}
}

// formatBytes renders a byte count as a short human string —
// "412 GB", "3.7 TB", "8.4 GB". Single decimal place for sub-1000
// values, none above. Returns "—" for zero so the dashboard's
// "never run" rows read clean.
func formatBytes(n int64) template.HTML {
	if n == 0 {
		return template.HTML(`<span class="text-ink-fade">—</span>`)
	}
	const (
		kb = 1000
		mb = 1000 * kb
		gb = 1000 * mb
		tb = 1000 * gb
	)
	var (
		val  float64
		unit string
	)
	switch {
	case n >= tb:
		val, unit = float64(n)/float64(tb), "TB"
	case n >= gb:
		val, unit = float64(n)/float64(gb), "GB"
	case n >= mb:
		val, unit = float64(n)/float64(mb), "MB"
	case n >= kb:
		val, unit = float64(n)/float64(kb), "kB"
	default:
		return template.HTML(fmt.Sprintf(`%d <span class="text-ink-mute text-[11px]">B</span>`, n))
	}
	num := strconv.FormatFloat(val, 'f', -1, 64)
	if val < 100 && !strings.Contains(num, ".") {
		num += ".0"
	} else if val < 100 && strings.Contains(num, ".") {
		// One decimal max, e.g. "3.7" not "3.74".
		idx := strings.Index(num, ".")
		if len(num) > idx+2 {
			num = num[:idx+2]
		}
	} else {
		// Above 100, no decimals — "412" not "412.4".
		if idx := strings.Index(num, "."); idx > 0 {
			num = num[:idx]
		}
	}
	return template.HTML(fmt.Sprintf(`%s <span class="text-ink-mute text-[11px]">%s</span>`, num, unit))
}

// formatRelTime renders a time as a short relative string like
// "3m ago" / "2d ago" / "5w ago". Future times render as
// "in 5m"-style. Accepts *time.Time or time.Time so templates can
// pass either without fighting Go's lack of an address-of operator.
// Anything else returns "—".
func formatRelTime(v any) string {
	var t time.Time
	switch x := v.(type) {
	case time.Time:
		t = x
	case *time.Time:
		if x == nil {
			return "—"
		}
		t = *x
	default:
		return "—"
	}
	if t.IsZero() {
		return "—"
	}
	d := time.Since(t)
	suffix := "ago"
	if d < 0 {
		d = -d
		suffix = "from now"
	}
	switch {
	case d < time.Minute:
		return fmt.Sprintf("%ds %s", int(d.Seconds()), suffix)
	case d < time.Hour:
		return fmt.Sprintf("%dm %s", int(d.Minutes()), suffix)
	case d < 24*time.Hour:
		return fmt.Sprintf("%dh %s", int(d.Hours()), suffix)
	case d < 7*24*time.Hour:
		return fmt.Sprintf("%dd %s", int(d.Hours()/24), suffix)
	default:
		return fmt.Sprintf("%dw %s", int(d.Hours()/(24*7)), suffix)
	}
}

// formatComma renders 1847 as "1,847". Used for snapshot counts and
// any other count that benefits from grouping at this scale.
func formatComma(n int) string {
	s := strconv.Itoa(n)
	if n < 1000 && n > -1000 {
		return s
	}
	// Hand-rolled grouping; Go has no builtin and we don't want a
	// dep for this. Negative numbers handled by stripping the sign,
	// grouping, then putting it back.
	neg := false
	if s[0] == '-' {
		neg = true
		s = s[1:]
	}
	var b strings.Builder
	for i, c := range s {
		if i > 0 && (len(s)-i)%3 == 0 {
			b.WriteByte(',')
		}
		b.WriteRune(c)
	}
	if neg {
		return "-" + b.String()
	}
	return b.String()
}

// derefStr returns the string a pointer points to, or "" if nil.
// Avoids "<nil>" appearing in templates that hit a missing FK.
func derefStr(p *string) string {
	if p == nil {
		return ""
	}
	return *p
}