1 files changed, 130 insertions, 0 deletions
diff --git a/internal/progress/meter.go b/internal/progress/meter.go
new file mode 100644
index 00000000..0e4138de
--- /dev/null
+++ b/internal/progress/meter.go
@@ -0,0 +1,130 @@
+package progress
+
+import (
+	"time"
+
+	"lindenii.org/go/lgo/intconv"
+	"lindenii.org/go/lgo/iowrap"
+)
+
+const (
+	updateInterval     = time.Second
+	throughputInterval = 500 * time.Millisecond
+)
+
+// Meter renders one in-place progress line.
+type Meter struct {
+	writer iowrap.WriteFlusher
+
+	title      string
+	total      uint64
+	delay      time.Duration
+	sparse     bool
+	throughput bool
+
+	startedAt      time.Time
+	nextUpdateAt   time.Time
+	nextThroughput time.Time
+
+	lastDone     uint64
+	lastBytes    uint64
+	lastPercent  int
+	lastCounterW int
+	sawValue     bool
+
+	throughputSuffix string
+}
+
+// New creates one progress meter.
+func New(opts Options) *Meter {
+	now := time.Now()
+
+	return &Meter{
+		writer:         opts.Writer,
+		title:          opts.Title,
+		total:          opts.Total,
+		delay:          max(opts.Delay, time.Duration(0)),
+		sparse:         opts.Sparse,
+		throughput:     opts.Throughput,
+		startedAt:      now,
+		nextUpdateAt:   now.Add(updateInterval),
+		nextThroughput: now.Add(throughputInterval),
+		lastPercent:    -1,
+	}
+}
+
+// Options configures one progress meter.
+type Options struct {
+	Writer iowrap.WriteFlusher
+
+	Title string
+	Total uint64
+
+	// Delay suppresses progress output until Delay has elapsed since Start.
+	Delay time.Duration
+	// Sparse forces one final 100% line at Stop when the caller sampled updates.
+	Sparse bool
+	// Throughput appends ", <total> | <rate>/s" and refreshes rate every 500ms.
+	Throughput bool
+}
+
+// Set records current progress
+// and renders when percent changed or the 1s tick elapsed.
+func (meter *Meter) Set(done uint64, bytes uint64) {
+	meter.lastDone = done
+	meter.lastBytes = bytes
+	meter.sawValue = true
+
+	if meter.writer == nil {
+		return
+	}
+
+	now := time.Now()
+	forced := meter.consumeUpdateTick(now)
+
+	percentChanged := false
+
+	if meter.total > 0 {
+		percent, err := intconv.Uint64ToInt(done * 100 / meter.total)
+		if err != nil {
+			return // TODO
+		}
+
+		percentChanged = percent != meter.lastPercent
+	}
+
+	if !percentChanged && !forced {
+		return
+	}
+
+	meter.render(now, "\r")
+}
+
+// Stop forces the final progress line and appends ", <msg>.".
+func (meter *Meter) Stop(msg string) {
+	if !meter.sawValue || meter.writer == nil {
+		return
+	}
+
+	if msg == "" {
+		msg = "done"
+	}
+
+	if meter.sparse && meter.total > 0 && meter.lastDone != meter.total {
+		meter.lastDone = meter.total
+	}
+
+	meter.render(time.Now(), ", "+msg+".\n")
+}
+
+func (meter *Meter) consumeUpdateTick(now time.Time) bool {
+	if now.Before(meter.nextUpdateAt) {
+		return false
+	}
+
+	for !now.Before(meter.nextUpdateAt) {
+		meter.nextUpdateAt = meter.nextUpdateAt.Add(updateInterval)
+	}
+
+	return true
+}