From 7f3d0a5328812cb66fa58e6cc3742b97696b07c0 Mon Sep 17 00:00:00 2001
From: Neeraj Gupta <254676+ua741@users.noreply.github.com>
Date: Wed, 18 Dec 2024 13:19:32 +0530
Subject: [PATCH] Add comment

---
 server/ente/filedata/filedata.go                | 15 +++++++++++++++
 server/migrations/94_file_data_preview.down.sql |  3 ++-
 server/migrations/94_file_data_preview.up.sql   |  2 --
 3 files changed, 17 insertions(+), 3 deletions(-)

diff --git a/server/ente/filedata/filedata.go b/server/ente/filedata/filedata.go
index fb1f17ae1d..9012a8249b 100644
--- a/server/ente/filedata/filedata.go
+++ b/server/ente/filedata/filedata.go
@@ -6,6 +6,21 @@ import (
 	"github.com/ente-io/museum/ente"
 )
 
+/*
+We store three types of derived data from a file, whose information is stored in the file_data table.
+Each derived data can have multiple objects, and each object is stored in the S3 bucket.
+1) MLData: This is the derived data from the file that is used for machine learning purposes.There's only
+one object for S3FileMetadata type.
+2) PreviewVideo: This is the derived data from the file that is used for previewing the video. This contains two objects.
+2.1) One object of type S3FileMetadata that contains the encrypted HLS playlist.
+2.2) Second object contains the encrypted video. The objectKey for this object is derived via ObjectKey function. The OG size column in the file_data
+contains sum of S3Metadata object size and the video object size. The object size is stored in the ObjectSize column.
+
+3) PreviewImage: This is the derived data from the file that is used for previewing the image. This just contain one object.
+The objectKey for this object is derived via ObjectKey function. We also store the nonce of the object in the ObjectNonce column.
+ObjectNonce is not stored for PreviewVideo type as HLS playlist contains a random key, that's only used once to encrypt the video with default nonce.
+*/
+
 type Entity struct {
 	FileID           int64           `json:"fileID"`
 	Type             ente.ObjectType `json:"type"`
diff --git a/server/migrations/94_file_data_preview.down.sql b/server/migrations/94_file_data_preview.down.sql
index 98b1223b83..77330b6171 100644
--- a/server/migrations/94_file_data_preview.down.sql
+++ b/server/migrations/94_file_data_preview.down.sql
@@ -1,3 +1,4 @@
 ALTER TABLE file_data
     DROP COLUMN obj_id,
-    DROP COLUMN obj_nonce;
\ No newline at end of file
+    DROP COLUMN obj_nonce,
+    DROP COLUMN obj_size;
diff --git a/server/migrations/94_file_data_preview.up.sql b/server/migrations/94_file_data_preview.up.sql
index 170c2bb765..94977e97cb 100644
--- a/server/migrations/94_file_data_preview.up.sql
+++ b/server/migrations/94_file_data_preview.up.sql
@@ -4,5 +4,3 @@ ALTER TABLE file_data
     ADD COLUMN obj_id TEXT,
     ADD COLUMN obj_nonce TEXT,
     ADD COLUMN obj_size INTEGER;
-
-