Use custom type for big int in graphql

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/server/graphql/types/bigint/bigint.go

@@ -0,0 +1,60 @@
+// Copyright (c) 2025 Probo Inc <hello@getprobo.com>.
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice appear in all copies.
+//
+// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
+// REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
+// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+// LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+// OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+// PERFORMANCE OF THIS SOFTWARE.
+
+package bigint
+
+import (
+	"fmt"
+	"io"
+	"strconv"
+
+	"github.com/99designs/gqlgen/graphql"
+)
+
+type BigIntScalar = int64
+
+func MarshalBigIntScalar(i int64) graphql.Marshaler {
+	return graphql.WriterFunc(func(w io.Writer) {
+		w.Write([]byte(strconv.FormatInt(i, 10)))
+	})
+}
+
+func UnmarshalBigIntScalar(v any) (int64, error) {
+	switch val := v.(type) {
+	case string:
+		i, err := strconv.ParseInt(val, 10, 64)
+		if err != nil {
+			return 0, fmt.Errorf("invalid BigInt value: %v", err)
+		}
+		return i, nil
+	case int:
+		return int64(val), nil
+	case int32:
+		return int64(val), nil
+	case int64:
+		return val, nil
+	case float32:
+		if val != float32(int64(val)) {
+			return 0, fmt.Errorf("BigInt cannot represent non-integer value: %v", val)
+		}
+		return int64(val), nil
+	case float64:
+		if val != float64(int64(val)) {
+			return 0, fmt.Errorf("BigInt cannot represent non-integer value: %v", val)
+		}
+		return int64(val), nil
+	default:
+		return 0, fmt.Errorf("cannot unmarshal %T into BigInt", v)
+	}
+}