feat: add friends!

migrations/2025-07-07-131320_add_friends/down.sql

@@ -0,0 +1,4 @@
+-- This file should undo anything in `up.sql`
+DROP TABLE friend_requests;
+DROP FUNCTION check_friend_request;
+DROP TABLE friends;

migrations/2025-07-07-131320_add_friends/up.sql

@@ -0,0 +1,35 @@
+-- Your SQL goes here
+CREATE TABLE friends (
+    uuid1 UUID REFERENCES users(uuid),
+    uuid2 UUID REFERENCES users(uuid),
+    accepted_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    PRIMARY KEY (uuid1, uuid2),
+    CHECK (uuid1 < uuid2)
+);
+
+CREATE TABLE friend_requests (
+    sender UUID REFERENCES users(uuid),
+    receiver UUID REFERENCES users(uuid),
+    requested_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
+    PRIMARY KEY (sender, receiver),
+    CHECK (sender <> receiver)
+);
+
+-- Create a function to check for existing friendships
+CREATE FUNCTION check_friend_request()
+RETURNS TRIGGER AS $$
+BEGIN
+    IF EXISTS (
+        SELECT 1 FROM friends 
+        WHERE (uuid1, uuid2) = (LEAST(NEW.sender, NEW.receiver), GREATEST(NEW.sender, NEW.receiver))
+    ) THEN
+        RAISE EXCEPTION 'Users are already friends';
+    END IF;
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+
+-- Create the trigger
+CREATE TRIGGER prevent_friend_request_conflict
+BEFORE INSERT OR UPDATE ON friend_requests
+FOR EACH ROW EXECUTE FUNCTION check_friend_request();