support ntables in Lua.Scan

1 files changed, 139 insertions, 0 deletions

diff --git a/lua_common.go b/lua_common.go
new file mode 100644
index 0000000..4e58d69
--- /dev/null
+++ b/lua_common.go
@@ -0,0 +1,139 @@
+package main
+
+import (
+	"reflect"
+	"slices"
+	"fmt"
+	"runtime/cgo"
+)
+
+// Scan scans values from the Lua stack into vars according to their types.
+func (l *Lua) Scan(vars ...any) error {
+	slices.Reverse(vars)
+	for i, v := range vars {
+		t := reflect.TypeOf(v)
+		// unwrap pointers
+		for t.Kind() == reflect.Ptr {
+			t = t.Elem()
+		}
+		tk := t.Kind()
+		if t.Name() == "LuaRef" {
+			if l.IsFunction(-1) == false {
+				return fmt.Errorf(
+					"passed arg #%d must be function",
+					len(vars)-i,
+				)
+			}
+			*v.(*LuaRef) = l.PopToRef()
+		} else if t.String() == "cgo.Handle" {
+			if l.IsNumber(-1) == false {
+				return fmt.Errorf(
+					"passed arg #%d must be Go handler",
+					len(vars)-i,
+				)
+			}
+			*v.(*cgo.Handle) = cgo.Handle(uintptr(l.ToInt(-1)))
+			l.Pop(1)
+		} else if tk == reflect.String {
+			if l.IsString(-1) == false {
+				return fmt.Errorf(
+					"passed arg #%d must be string",
+					len(vars)-i,
+				)
+			}
+			*v.(*string) = l.ToString(-1)
+			l.Pop(1)
+		} else if tk == reflect.Int {
+			if l.IsNumber(-1) == false {
+				return fmt.Errorf(
+					"passed arg #%d must be number",
+					len(vars)-i,
+				)
+			}
+			*v.(*int) = l.ToInt(-1)
+			l.Pop(1)
+		} else if tk == reflect.Map && t.Key().Kind() == reflect.String {
+			// TODO: should be possible to use maps with any types
+			// of value, not only strings.
+			vm, _ := v.(*map[string]string)
+			l.PushNil()
+			for l.Next() {
+				if !l.IsString(-1) {
+					return fmt.Errorf(
+						"map arg #%d must only have string values",
+						len(vars)-i,
+					)
+				}
+				if !l.IsString(-2) {
+					return fmt.Errorf(
+						"map arg #%d must only have string keys",
+						len(vars)-i,
+					)
+				}
+				v := l.ToString(-1)
+				l.Pop(1)
+				// We must not pop the item key from the stack
+				// because otherwise C.lua_next won't work
+				// properly.
+				k := l.ToString(-1)
+				(*vm)[k] = v
+			}
+			l.Pop(1)
+		} else if tk == reflect.Slice && t.Elem().Kind() == reflect.Interface {
+			if !l.IsTable(-1) {
+				return fmt.Errorf(
+					"passed arg #%d must be a table",
+					len(vars)-i,
+				)
+			}
+			va, _ := v.(*[]any)
+
+			// Check if table contains element "n" with
+			// a count of elements. Useful when an array may
+			// contain nils.
+			l.GetTableItem("n")
+			n := 0
+			if l.IsNumber(-1) {
+				n = l.ToInt(-1)
+			}
+			l.Pop(1)
+
+			scanAndAppend := func () error {
+				var v any = nil
+				if l.IsString(-1) {
+					v = l.ToString(-1)
+				} else if l.IsNumber(-1) {
+					v = l.ToInt(-1)
+				} else if l.IsBoolean(-1) {
+					v = l.ToBoolean(-1)
+				} else if l.IsNil(-1) {
+					v = nil
+				} else {
+					return fmt.Errorf("unknown value in array")
+				}
+				l.Pop(1)
+				(*va) = append((*va), v)
+				return nil
+			}
+			if n > 0 {
+				for i := 0; i < n; i++ {
+					l.RawGetI(-1, i + 1)
+					if err := scanAndAppend(); err != nil {
+						return err
+					}
+				}
+			} else {
+				l.PushNil()
+				for l.Next() {
+					if err := scanAndAppend(); err != nil {
+						return err
+					}
+				}
+			}
+			l.Pop(1)
+		} else {
+			return fmt.Errorf("unknown var type: %s", t)
+		}
+	}
+	return nil
+}