add backend supporting opengraph and comments

backend/migrations/0001-init.sql

@@ -0,0 +1,37 @@
+-- all ids will be TEXT
+-- make a table for storing webpages and related opengraph information in json format
+CREATE TABLE webpages (
+    id TEXT PRIMARY KEY,
+    url TEXT NOT NULL UNIQUE,
+    opengraph JSONB NOT NULL
+);
+
+-- add an index to the url column
+CREATE INDEX url_index ON webpages (url);
+
+-- make a table for storing comments on webpages and replies to comments
+CREATE TABLE comments (
+    id TEXT PRIMARY KEY,
+    webpage_id TEXT NOT NULL,
+    parent_id TEXT, -- NULL if top-level comment
+    commenter TEXT NOT NULL,
+    content TEXT NOT NULL,
+    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+-- make a table for storing votes on comments and webpages
+CREATE TABLE votes (
+    id TEXT PRIMARY KEY,
+    webpage_id TEXT NOT NULL,
+    comment_id TEXT, -- NULL if vote is on webpage
+    voter TEXT NOT NULL,
+    vote_type TEXT NOT NULL,
+    created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+-- make a table for storing users
+CREATE TABLE users (
+    id TEXT PRIMARY KEY,
+    username TEXT NOT NULL,
+    avatar TEXT NOT NULL
+);