Artifacto/internal/server/metrics.go

package server

import (
	"fmt"
	"html/template"
	"net/http"
	"strings"

	"github.com/go-chi/chi/v5"

	"git.hubris.network/dtoro/artifacto/internal/store"
)

type detailData struct {
	BaseURL   string
	Artifact  *store.Artifact
	Series    []store.DayPoint
	Referrers []store.ReferrerCount
	ChartSVG  template.HTML
}

func (s *Server) getArtifactDetail(w http.ResponseWriter, r *http.Request) {
	slug := chi.URLParam(r, "slug")
	art, err := s.store.GetArtifact(slug)
	if err != nil {
		http.NotFound(w, r)
		return
	}
	series, err := s.store.SeriesFor(slug, 30)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	refs, err := s.store.TopReferrers(slug, 10)
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	s.render(w, "detail", detailData{
		BaseURL:   s.cfg.BaseURL,
		Artifact:  art,
		Series:    series,
		Referrers: refs,
		ChartSVG:  template.HTML(renderChart(series)),
	})
}

// renderChart produces a tiny SVG line+area chart with day labels.
func renderChart(series []store.DayPoint) string {
	const w = 720
	const h = 160
	const padLeft = 30
	const padBottom = 20
	const padTop = 10
	const padRight = 10

	innerW := w - padLeft - padRight
	innerH := h - padTop - padBottom

	var max int64
	for _, p := range series {
		if p.Views > max {
			max = p.Views
		}
	}
	if max < 1 {
		max = 1
	}

	var b strings.Builder
	fmt.Fprintf(&b, `<svg viewBox="0 0 %d %d" class="w-full h-40 text-slate-400" xmlns="http://www.w3.org/2000/svg">`, w, h)
	// axes
	fmt.Fprintf(&b, `<line x1="%d" y1="%d" x2="%d" y2="%d" stroke="currentColor" stroke-width="1"/>`,
		padLeft, padTop, padLeft, padTop+innerH)
	fmt.Fprintf(&b, `<line x1="%d" y1="%d" x2="%d" y2="%d" stroke="currentColor" stroke-width="1"/>`,
		padLeft, padTop+innerH, padLeft+innerW, padTop+innerH)
	// horizontal gridline at max
	fmt.Fprintf(&b, `<text x="%d" y="%d" font-size="10" fill="currentColor" text-anchor="end">%d</text>`,
		padLeft-4, padTop+6, max)
	fmt.Fprintf(&b, `<text x="%d" y="%d" font-size="10" fill="currentColor" text-anchor="end">0</text>`,
		padLeft-4, padTop+innerH)

	n := len(series)
	if n == 0 {
		b.WriteString(`</svg>`)
		return b.String()
	}

	step := float64(innerW) / float64(maxInt(n-1, 1))

	// build polyline path
	var pts strings.Builder
	for i, p := range series {
		x := float64(padLeft) + float64(i)*step
		y := float64(padTop+innerH) - float64(p.Views)/float64(max)*float64(innerH)
		if i > 0 {
			pts.WriteByte(' ')
		}
		fmt.Fprintf(&pts, "%.1f,%.1f", x, y)
	}

	// area under curve
	var area strings.Builder
	fmt.Fprintf(&area, "M%d,%d ", padLeft, padTop+innerH)
	for i, p := range series {
		x := float64(padLeft) + float64(i)*step
		y := float64(padTop+innerH) - float64(p.Views)/float64(max)*float64(innerH)
		fmt.Fprintf(&area, "L%.1f,%.1f ", x, y)
	}
	fmt.Fprintf(&area, "L%.1f,%d Z", float64(padLeft)+float64(n-1)*step, padTop+innerH)

	fmt.Fprintf(&b, `<path d="%s" fill="rgb(99 102 241 / 0.15)" stroke="none"/>`, area.String())
	fmt.Fprintf(&b, `<polyline fill="none" stroke="rgb(99 102 241)" stroke-width="2" points="%s"/>`, pts.String())

	// x-axis tick labels: first, middle, last day
	labelIdx := []int{0, n / 2, n - 1}
	for _, i := range labelIdx {
		if i < 0 || i >= n {
			continue
		}
		x := float64(padLeft) + float64(i)*step
		fmt.Fprintf(&b, `<text x="%.1f" y="%d" font-size="10" fill="currentColor" text-anchor="middle">%s</text>`,
			x, padTop+innerH+14, shortDay(series[i].Day))
	}

	b.WriteString(`</svg>`)
	return b.String()
}

func shortDay(iso string) string {
	// yyyy-mm-dd → mm-dd
	if len(iso) >= 10 {
		return iso[5:10]
	}
	return iso
}