Add unified post storage (#3)

Adds one post creation path for roots and replies, recursive thread loading, body-only updates, root listings, and root-only voting across PostgreSQL and the in-memory store.

Co-authored-by: codegirl-007 <s.raide@gmail.com>

db/queries/posts.sql

@@ -0,0 +1,125 @@
+-- name: CreatePost :exec
+INSERT INTO posts (
+  id, parent_id, author_id, title, body, city, post_date, post_state, created_at, updated_at
+)
+VALUES (
+  sqlc.arg(id),
+  sqlc.arg(parent_id),
+  sqlc.arg(author_id),
+  sqlc.arg(title),
+  sqlc.arg(body),
+  sqlc.arg(city),
+  sqlc.arg(post_date),
+  sqlc.arg(post_state),
+  sqlc.arg(created_at),
+  sqlc.arg(updated_at)
+);
+
+-- name: GetPost :one
+SELECT
+  p.id, p.parent_id, p.author_id, u.name AS author_name, u.role AS author_role,
+  p.title, p.body, p.city, p.post_date, p.post_state, p.created_at, p.updated_at
+FROM posts p
+JOIN users u ON u.id = p.author_id
+WHERE p.id = sqlc.arg(id);
+
+-- name: ListPostThread :many
+WITH RECURSIVE thread AS (
+  SELECT p.*
+  FROM posts p
+  WHERE p.id = sqlc.arg(root_id) AND p.parent_id IS NULL
+
+  UNION ALL
+
+  SELECT child.*
+  FROM posts child
+  JOIN thread parent ON child.parent_id = parent.id
+)
+SELECT
+  thread.id, thread.parent_id, thread.author_id,
+  u.name AS author_name, u.role AS author_role,
+  thread.title, thread.body, thread.city, thread.post_date,
+  thread.post_state, thread.created_at, thread.updated_at
+FROM thread
+JOIN users u ON u.id = thread.author_id
+ORDER BY thread.created_at, thread.id;
+
+-- name: UpdatePost :execrows
+UPDATE posts
+SET
+  body = sqlc.arg(body),
+  updated_at = sqlc.arg(updated_at)
+WHERE id = sqlc.arg(id);
+
+-- name: ListRootPosts :many
+WITH RECURSIVE roots AS (
+  SELECT p.*
+  FROM posts p
+  WHERE p.parent_id IS NULL
+    AND p.post_date = sqlc.arg(post_date)
+    AND p.post_state <> sqlc.arg(hidden_state)
+),
+thread AS (
+  SELECT roots.id AS root_id, child.id AS post_id, child.author_id
+  FROM roots
+  JOIN posts child ON child.parent_id = roots.id
+
+  UNION ALL
+
+  SELECT thread.root_id, child.id, child.author_id
+  FROM thread
+  JOIN posts child ON child.parent_id = thread.post_id
+),
+answered AS (
+  SELECT DISTINCT thread.root_id
+  FROM thread
+  JOIN users u ON u.id = thread.author_id
+  WHERE u.role = 'admin'
+),
+scores AS (
+  SELECT votes.post_id, SUM(votes.value)::bigint AS score
+  FROM roots
+  JOIN post_votes votes ON votes.post_id = roots.id
+  GROUP BY votes.post_id
+)
+SELECT
+  roots.id, roots.parent_id, roots.author_id,
+  u.name AS author_name, u.role AS author_role,
+  roots.title, roots.body, roots.city, roots.post_date,
+  roots.post_state, roots.created_at, roots.updated_at,
+  COALESCE(scores.score, 0)::bigint AS score,
+  (answered.root_id IS NOT NULL)::bool AS answered,
+  COALESCE(viewer_vote.value, 0)::bigint AS user_vote
+FROM roots
+JOIN users u ON u.id = roots.author_id
+LEFT JOIN scores ON scores.post_id = roots.id
+LEFT JOIN answered ON answered.root_id = roots.id
+LEFT JOIN post_votes viewer_vote
+  ON viewer_vote.user_id = sqlc.arg(viewer_id)
+  AND viewer_vote.post_id = roots.id
+ORDER BY score DESC, roots.created_at, roots.id
+LIMIT sqlc.arg(row_limit);
+
+-- name: PostIsVisibleRoot :one
+SELECT EXISTS(
+  SELECT 1
+  FROM posts
+  WHERE id = sqlc.arg(id)
+    AND parent_id IS NULL
+    AND post_state <> sqlc.arg(hidden_state)
+)::bool;
+
+-- name: DeletePostVote :exec
+DELETE FROM post_votes
+WHERE user_id = sqlc.arg(user_id)
+  AND post_id = sqlc.arg(post_id);
+
+-- name: UpsertPostVoteOnVisibleRoot :execrows
+INSERT INTO post_votes (user_id, post_id, value)
+SELECT sqlc.arg(user_id), sqlc.arg(post_id), sqlc.arg(value)
+FROM posts p
+WHERE p.id = sqlc.arg(post_id)
+  AND p.parent_id IS NULL
+  AND p.post_state <> sqlc.arg(hidden_state)
+ON CONFLICT (user_id, post_id) DO UPDATE
+SET value = excluded.value;