package ui

import (
	"encoding/base64"
	"encoding/json"
	"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() },
		"joinDot":     func(parts []string) string { return strings.Join(parts, " · ") },
		"absTime": func(t time.Time) string {
			if t.IsZero() {
				return "—"
			}
			return t.Format("2006-01-02 15:04:05")
		},
		// b64 encodes a json.RawMessage (or any []byte / string) as
		// base64 — used by audit.html to stash arbitrary JSON in a
		// data- attribute without fighting html/template's contextual
		// escaping. JS atob() decodes on click.
		"b64": func(v any) string {
			switch x := v.(type) {
			case json.RawMessage:
				return base64.StdEncoding.EncodeToString(x)
			case []byte:
				return base64.StdEncoding.EncodeToString(x)
			case string:
				return base64.StdEncoding.EncodeToString([]byte(x))
			default:
				return base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%v", x)))
			}
		},
		// sortDir computes the dir param for a sort-header link:
		// click the active column → toggle asc/desc; click any other
		// column → start at desc (newest-first / Z→A) since that's
		// the conventional default for date and frequency-style data.
		"sortDir": func(thisCol, currentCol, currentDir string) string {
			if thisCol != currentCol {
				return "desc"
			}
			if currentDir == "asc" {
				return "desc"
			}
			return "asc"
		},
		// sortGlyph returns the unicode arrow glyph for the sort
		// header — empty string for inactive columns so they don't
		// shout.
		"sortGlyph": func(thisCol, currentCol, currentDir string) string {
			if thisCol != currentCol {
				return ""
			}
			if currentDir == "asc" {
				return "↑"
			}
			return "↓"
		},
		"derefInt": func(p *int) int {
			if p == nil {
				return 0
			}
			return *p
		},
		"sub": func(a, b int) int { return a - b },
		// durationHuman formats the elapsed time between two *time.Time
		// values as a short human string: "350ms", "4.2s", "2m 15s",
		// "1h 4m". Returns "—" when either pointer is nil.
		"durationHuman": func(start, end *time.Time) string {
			if start == nil || end == nil {
				return "—"
			}
			d := end.Sub(*start)
			if d < 0 {
				d = -d
			}
			if d < time.Second {
				return fmt.Sprintf("%dms", d.Milliseconds())
			}
			if d < time.Minute {
				return fmt.Sprintf("%.1fs", d.Seconds())
			}
			if d < time.Hour {
				return fmt.Sprintf("%dm %ds", int(d.Minutes()), int(d.Seconds())%60)
			}
			return fmt.Sprintf("%dh %dm", int(d.Hours()), int(d.Minutes())%60)
		},
		// joinComma joins a slice with ", ". Used by the schedule list
		// to render retention summaries.
		"joinComma": func(parts []string) string { return strings.Join(parts, ", ") },
		// list packs strings into a slice — handy for inline ranges
		// in templates (e.g. quick-pick cron presets).
		"list": func(items ...string) []string { return items },
		// dict builds a map[string]any from alternating key-value pairs.
		// Useful for passing multiple named values to a sub-template:
		//   {{template "foo" (dict "A" $a "B" $b)}}
		"dict": func(pairs ...any) map[string]any {
			m := make(map[string]any, len(pairs)/2)
			for i := 0; i+1 < len(pairs); i += 2 {
				if k, ok := pairs[i].(string); ok {
					m[k] = pairs[i+1]
				}
			}
			return m
		},
		// mapGet retrieves a string value from a map[string]string by key.
		// Returns "" when the key is absent or the map is nil. Used by the
		// alert_row partial to resolve host_id → host name.
		"mapGet": func(m map[string]string, key *string) string {
			if m == nil || key == nil {
				return ""
			}
			return m[*key]
		},
		// alertStatus derives the display status of an alert from its DB
		// fields: "open", "acknowledged", or "resolved".
		// Accepts any value — returns "" for unrecognised input so templates
		// can still render safely.
		"alertStatus": func(resolvedAt, acknowledgedAt any) string {
			isSet := func(v any) bool {
				if v == nil {
					return false
				}
				switch t := v.(type) {
				case *time.Time:
					return t != nil
				}
				return false
			}
			if isSet(resolvedAt) {
				return "resolved"
			}
			if isSet(acknowledgedAt) {
				return "acknowledged"
			}
			return "open"
		},
		// stillHappening returns true when last_seen_at is within the last
		// 60 seconds — used to render the "still happening · Ns ago" pill
		// on alert rows where the signal is still firing.
		"stillHappening": func(v any) bool {
			var t time.Time
			switch x := v.(type) {
			case time.Time:
				t = x
			case *time.Time:
				if x == nil {
					return false
				}
				t = *x
			default:
				return false
			}
			return time.Since(t) < 60*time.Second
		},
	}
}

// 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 "—".
//
// The output is wrapped in a <time data-rel-ts="..."> element so a
// small client-side ticker (see base.html) can refresh the label
// without a full page reload — otherwise a long-open tab shows
// timestamps frozen at render time.
func formatRelTime(v any) template.HTML {
	var t time.Time
	switch x := v.(type) {
	case time.Time:
		t = x
	case *time.Time:
		if x == nil {
			return template.HTML("—")
		}
		t = *x
	default:
		return template.HTML("—")
	}
	if t.IsZero() {
		return template.HTML("—")
	}
	label := relTimeLabel(time.Since(t))
	return template.HTML(fmt.Sprintf(
		`<time data-rel-ts="%s" title="%s">%s</time>`,
		t.UTC().Format(time.RFC3339Nano),
		t.UTC().Format("2006-01-02 15:04:05 UTC"),
		label,
	))
}

// relTimeLabel turns a duration-since-now into the short human label
// used by formatRelTime (and mirrored verbatim by the JS ticker, so
// keep the two in sync if you change the buckets).
func relTimeLabel(d time.Duration) string {
	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.
// Accepts int / int64 / int32 — anything else returns "—".
func formatComma(v any) string {
	var n int64
	switch x := v.(type) {
	case int:
		n = int64(x)
	case int32:
		n = int64(x)
	case int64:
		n = x
	default:
		return "—"
	}
	s := strconv.FormatInt(n, 10)
	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
}
