Add support for a generic Query function

Signed-off-by: Hiram Chirino <[email protected]>

query.go

@@ -0,0 +1,52 @@
+package quickbooks
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+)
+
+// QueryPaged is like Query but adds the ability to specify a start position and page size ot the query.
+func QueryPaged[T any](c *Client, query string, startpos int, pagesize int) ([]T, error) {
+	selectStatement := fmt.Sprintf("%s STARTPOSITION %d MAXRESULTS %d", query, startpos, pagesize)
+	return Query[T](c, selectStatement)
+
+}
+
+// Query allows you to query any QuickBooks Online entity and have the result unmarshalled into
+// a slice of a type you specify.
+//
+// Example:
+//
+//	type JournalEntry struct {
+//		 Id     string
+//		 Amount float64
+//	}
+//	result, err := quickbooks.Query[JournalEntry](client, "SELECT * FROM JournalEntry ORDERBY Id")
+func Query[T any](c *Client, query string) ([]T, error) {
+
+	var resp struct {
+		QueryResponse map[string]json.RawMessage
+	}
+
+	if err := c.query(query, &resp); err != nil {
+		return nil, err
+	}
+
+	for key, value := range resp.QueryResponse {
+		switch key {
+		case "startPosition", "maxResults", "totalCount": // skip these...
+		default:
+			var data []T
+			decoder := json.NewDecoder(bytes.NewReader(value))
+			decoder.UseNumber()
+			err := decoder.Decode(&data)
+			if err != nil {
+				return nil, err
+			}
+			return data, nil
+		}
+	}
+
+	return []T{}, nil
+}