Add some core objects impl

src/knowledge/core_object/email_object.py

@@ -0,0 +1,47 @@
+from .rich_text_object import RichTextObject, RichTextObjectBuilder
+from ..object import ObjectID, ObjectType, KnowledgeObject
+
+
+class EmailObject(KnowledgeObject):
+    def __init__(self, meta: dict, tags: dict, rich_text: RichTextObject):
+        desc = dict()
+        body = dict()
+        desc["meta"] = meta
+        desc["tags"] = tags
+
+        # FIXME rich text content store in desc or body? which one is better?
+        body["content"] = rich_text
+
+        super().__init__(ObjectType.Email, desc, body)
+
+    def get_meta(self):
+        return self.desc["meta"]
+
+    def get_tags(self):
+        return self.desc["tags"]
+
+    def get_rich_text(self):
+        return self.body["rich_text"]
+
+
+class EmailObjectBuilder:
+    def __init__(self, meta: dict, tags: dict, folder: str):
+        self.meta = meta
+        self.tags = tags
+        self.folder = folder
+
+    def set_meta(self, meta: dict):
+        self.meta = meta
+        return self
+
+    def set_tags(self, tags: dict):
+        self.tags = tags
+        return self
+
+    def set_folder(self, folder: str):
+        self.folder = folder
+        return self
+
+    def build(self) -> EmailObject:
+        content = RichTextObjectBuilder(self.folder).build()
+        return EmailObject(self.meta, self.tags, content)