Add post video storage (#21)

post_images.kind is image or video. A post can keep one video alongside up to four images.

Reviewed-on: #21
Co-authored-by: codegirl-007 <s.raide@gmail.com>

schema.sql

@@ -48,13 +48,23 @@ CREATE TABLE IF NOT EXISTS post_images (
   object_key TEXT NOT NULL UNIQUE,
   public_url TEXT NOT NULL,
   description TEXT NOT NULL DEFAULT '' CHECK (char_length(description) <= 500),
-  position SMALLINT NOT NULL CHECK (position BETWEEN 0 AND 3),
-  width INTEGER NOT NULL CHECK (width > 0),
-  height INTEGER NOT NULL CHECK (height > 0),
+  kind TEXT NOT NULL DEFAULT 'image',
+  position SMALLINT NOT NULL,
+  width INTEGER NOT NULL,
+  height INTEGER NOT NULL,
   created_at TEXT NOT NULL,
+  CONSTRAINT post_images_kind_check CHECK (kind IN ('image', 'video')),
+  CONSTRAINT post_images_width_check CHECK (width >= 0),
+  CONSTRAINT post_images_height_check CHECK (height >= 0),
+  CONSTRAINT post_images_image_dims_check CHECK (kind <> 'image' OR (width > 0 AND height > 0)),
+  CONSTRAINT post_images_position_check CHECK (position BETWEEN 0 AND 4),
   UNIQUE (post_id, position)
 );
 
+CREATE UNIQUE INDEX IF NOT EXISTS post_images_one_video_uidx
+  ON post_images (post_id)
+  WHERE kind = 'video';
+
 CREATE TABLE IF NOT EXISTS post_votes (
   user_id TEXT NOT NULL REFERENCES users(id),
   post_id TEXT NOT NULL REFERENCES posts(id) ON DELETE CASCADE,