1 files changed, 63 insertions, 0 deletions
diff --git a/progress.go b/progress.go
new file mode 100644
index 0000000..7660605
--- /dev/null
+++ b/progress.go
@@ -0,0 +1,63 @@
+package progress
+
+import (
+	"fmt"
+	"os"
+	"strings"
+	"time"
+
+	"gitlab.com/rhogenson/vecdeque"
+	"golang.org/x/term"
+)
+
+const measurements = 20
+
+type measurement struct {
+	t time.Time
+	i int
+}
+
+type Bar struct {
+	max          int
+	measurements vecdeque.DQ[measurement]
+	cols         int
+}
+
+func New(max int) *Bar {
+	b := &Bar{max: max}
+	b.measurements.Grow(measurements)
+	return b
+}
+
+func (b *Bar) Set(i int) {
+	if b.measurements.Len() == measurements {
+		b.measurements.PopFront()
+	}
+	b.measurements.PushBack(measurement{time.Now(), i})
+}
+
+func (b *Bar) Print() {
+	first := b.measurements.Get(0)
+	last := b.measurements.Get(b.measurements.Len() - 1)
+	deltaT := last.t.Sub(first.t)
+	delta := last.i - first.i
+	eta := time.Duration(-1)
+	if delta != 0 {
+		eta = time.Duration(float64(b.max-last.i) / float64(delta) * float64(deltaT))
+	}
+
+	if b.cols == 0 {
+		var err error
+		if b.cols, _, err = term.GetSize(int(os.Stderr.Fd())); err != nil {
+			fmt.Fprintf(os.Stderr, "Warning: unable to determine terminal size: %s\n", err)
+		}
+	} else {
+		p := last.i * b.cols / b.max
+		fmt.Fprintf(os.Stderr, "\033[2F\033[J%s>\n", strings.Repeat("=", max(p-1, 0)))
+	}
+	if eta < 0 {
+		fmt.Fprintln(os.Stderr, "ETA: calculating...")
+	} else {
+		fmt.Fprintf(os.Stderr, "ETA: %s\n", eta.Round(time.Second))
+	}
+}