refactor(tgbot): share numeric keypad transitions (#6211)

Co-authored-by: n0ctal <293235942+n0ctal@users.noreply.github.com>

internal/web/service/tgbot/numeric_input_test.go

@@ -0,0 +1,38 @@
+package tgbot
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestUpdateNumericInput(t *testing.T) {
+	tests := []struct {
+		name       string
+		value, key int
+		want       int
+	}{
+		{name: "append digit", value: 12, key: 3, want: 123},
+		{name: "append zero", value: 12, key: 0, want: 120},
+		{name: "backspace", value: 123, key: -1, want: 12},
+		{name: "backspace zero", value: 0, key: -1, want: 0},
+		{name: "clear", value: 123, key: -2, want: 0},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := updateNumericInput(tt.value, tt.key); got != tt.want {
+				t.Fatalf("updateNumericInput(%d, %d) = %d, want %d", tt.value, tt.key, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestNumericInputTransitionIsUsedByEveryKeypad(t *testing.T) {
+	source, err := os.ReadFile("tgbot_router.go")
+	if err != nil {
+		t.Fatalf("read tgbot_router.go: %v", err)
+	}
+	if got := strings.Count(string(source), "updateNumericInput("); got != 6 {
+		t.Fatalf("numeric keypad transition call sites = %d, want 6", got)
+	}
+}