feat: add comments

migrations/0036_create_post_comments.down.sql

@@ -0,0 +1,3 @@
+DROP TABLE IF EXISTS comment_reports;
+DROP TABLE IF EXISTS comment_likes;
+DROP TABLE IF EXISTS post_comments;

migrations/0036_create_post_comments.up.sql

@@ -0,0 +1,62 @@
+-- Post comments — two-level threads, likes, pinning, reports.
+--
+-- Threading is deliberately ONE level deep: `parent_id` is NULL for a
+-- top-level comment and otherwise points at a TOP-LEVEL comment (the thread
+-- root). When a user replies to a reply, the service flattens the new comment
+-- onto the same root and records `reply_to_user_id` so the UI can render the
+-- "@handle" it was addressed to — so every reply lives under one thread.
+-- ON DELETE CASCADE on parent_id means deleting a root removes its whole thread.
+CREATE TABLE IF NOT EXISTS post_comments (
+    id               UUID         PRIMARY KEY DEFAULT gen_random_uuid(),
+    post_id          UUID         NOT NULL REFERENCES posts(id) ON DELETE CASCADE,
+    user_id          UUID         NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    parent_id        UUID         REFERENCES post_comments(id) ON DELETE CASCADE,
+    -- The user a reply is addressed to (for the "@handle" prefix). NULL on
+    -- top-level comments. SET NULL if that user is later deleted.
+    reply_to_user_id UUID         REFERENCES users(id) ON DELETE SET NULL,
+    body             TEXT         NOT NULL,
+    -- Denormalized like counter (the UI shows only the count; comment_likes
+    -- keeps the relations). Kept in sync on like/unlike in the same txn — comment
+    -- likes are far lower-volume than post likes, so no Redis batching here.
+    likes_count      INTEGER      NOT NULL DEFAULT 0,
+    pinned_at        TIMESTAMPTZ,                       -- non-null = pinned (top-level only)
+    created_at       TIMESTAMPTZ  NOT NULL DEFAULT now(),
+    updated_at       TIMESTAMPTZ  NOT NULL DEFAULT now()
+);
+
+-- Dedup: a user can't post the identical text twice in the same scope (post +
+-- thread). COALESCE folds top-level (NULL parent) onto a fixed sentinel so the
+-- index covers it; md5(body) keeps the key small for long comments.
+CREATE UNIQUE INDEX IF NOT EXISTS post_comments_dedup
+    ON post_comments (post_id, user_id, COALESCE(parent_id, '00000000-0000-0000-0000-000000000000'::uuid), md5(body));
+
+-- Listing a post's top-level comments, and a thread's replies (oldest first).
+CREATE INDEX IF NOT EXISTS post_comments_post_idx   ON post_comments (post_id, created_at);
+CREATE INDEX IF NOT EXISTS post_comments_parent_idx ON post_comments (parent_id, created_at);
+
+-- At most one pinned comment per post.
+CREATE UNIQUE INDEX IF NOT EXISTS post_comments_one_pin
+    ON post_comments (post_id) WHERE pinned_at IS NOT NULL;
+
+-- Comment likes — membership rows backing the displayed count. Idempotent via PK.
+CREATE TABLE IF NOT EXISTS comment_likes (
+    comment_id UUID         NOT NULL REFERENCES post_comments(id) ON DELETE CASCADE,
+    user_id    UUID         NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    created_at TIMESTAMPTZ  NOT NULL DEFAULT now(),
+    PRIMARY KEY (comment_id, user_id)
+);
+-- "Which comments has this viewer liked?" — viewer-state hydration across a thread.
+CREATE INDEX IF NOT EXISTS comment_likes_user_idx ON comment_likes (user_id);
+
+-- Comment reports — mirrors post_reports, keyed to a comment.
+CREATE TABLE IF NOT EXISTS comment_reports (
+    id          UUID         PRIMARY KEY DEFAULT gen_random_uuid(),
+    reporter_id UUID         NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    comment_id  UUID         NOT NULL REFERENCES post_comments(id) ON DELETE CASCADE,
+    category    VARCHAR(32)  NOT NULL,
+    reason      TEXT         NOT NULL DEFAULT '',
+    created_at  TIMESTAMPTZ  NOT NULL DEFAULT now(),
+    resolved_at TIMESTAMPTZ
+);
+CREATE INDEX IF NOT EXISTS comment_reports_unresolved_idx
+    ON comment_reports (created_at DESC) WHERE resolved_at IS NULL;