start adding page validation

internal/id/page.go

@@ -0,0 +1,31 @@
+package id
+
+import (
+	"github.com/superseriousbusiness/gotosocial/internal/paging"
+)
+
+// ValidatePage ...
+func ValidatePage(page *paging.Page) {
+	if page == nil {
+		// unpaged
+		return
+	}
+
+	switch page.Order() {
+	// If the page order is ascending,
+	// ensure that a minimum value is set.
+	// This will be used as the cursor.
+	case paging.OrderAscending:
+		if page.Min.Value == "" {
+			page.Min.Value = Lowest
+		}
+
+	// If the page order is descending,
+	// ensure that a maximum value is set.
+	// This will be used as the cursor.
+	case paging.OrderDescending:
+		if page.Max.Value == "" {
+			page.Max.Value = Highest
+		}
+	}
+}