1 files changed, 39 insertions, 0 deletions

diff --git a/cli/internal/util/parse_concurrency.go b/cli/internal/util/parse_concurrency.go
new file mode 100644
index 0000000..6917600
--- /dev/null
+++ b/cli/internal/util/parse_concurrency.go
@@ -0,0 +1,39 @@
+package util
+
+import (
+	"fmt"
+	"math"
+	"runtime"
+	"strconv"
+	"strings"
+)
+
+var (
+	// alias so we can mock in tests
+	runtimeNumCPU = runtime.NumCPU
+	// positive values check for +Inf
+	_positiveInfinity = 1
+)
+
+// ParseConcurrency parses a concurrency value, which can be a number (e.g. 2) or a percentage (e.g. 50%).
+func ParseConcurrency(concurrencyRaw string) (int, error) {
+	if strings.HasSuffix(concurrencyRaw, "%") {
+		if percent, err := strconv.ParseFloat(concurrencyRaw[:len(concurrencyRaw)-1], 64); err != nil {
+			return 0, fmt.Errorf("invalid value for --concurrency CLI flag. This should be a number --concurrency=4 or percentage of CPU cores --concurrency=50%% : %w", err)
+		} else {
+			if percent > 0 && !math.IsInf(percent, _positiveInfinity) {
+				return int(math.Max(1, float64(runtimeNumCPU())*percent/100)), nil
+			} else {
+				return 0, fmt.Errorf("invalid percentage value for --concurrency CLI flag. This should be a percentage of CPU cores, between 1%% and 100%% : %w", err)
+			}
+		}
+	} else if i, err := strconv.Atoi(concurrencyRaw); err != nil {
+		return 0, fmt.Errorf("invalid value for --concurrency CLI flag. This should be a positive integer greater than or equal to 1: %w", err)
+	} else {
+		if i >= 1 {
+			return i, nil
+		} else {
+			return 0, fmt.Errorf("invalid value %v for --concurrency CLI flag. This should be a positive integer greater than or equal to 1", i)
+		}
+	}
+}