create table sections (
    id uuid DEFAULT gen_random_uuid() PRIMARY KEY,

    -- Title of the section
    title varchar(255) UNIQUE NOT NULL,
    -- Name to use when routing (this just makes for prettier URLs)
    shortname varchar(32) UNIQUE NOT NULL,
    -- Optional description of the section
    description text,
    -- Wether to show the section in the default list on the homepage
    is_default boolean NOT NULL DEFAULT false,
    -- Wether the posts should contain titles or not
    has_titles boolean NOT NULL DEFAULT true,
    -- Wether posts in this section should be shown publicly
    is_private boolean NOT NULL DEFAULT false
);

create index sections_shortname_index on sections(shortname);

create table posts (
    id uuid DEFAULT gen_random_uuid() PRIMARY KEY,

    -- Posts shouldn't get deleted when we delete a section, as they're the
    -- most valuable part of a blog
    section_id uuid NOT NULL REFERENCES sections(id) ON DELETE SET NULL,

    -- Wether a post should be private
    is_private boolean NOT NULL DEFAULT false,
    -- Wether the post is archived
    is_archived boolean NOT NULL DEFAULT false
);

create table versions (
    id uuid DEFAULT gen_random_uuid() PRIMARY KEY,

    -- A version should be deleted when its referenced post is deleted
    post_id uuid NOT NULL REFERENCES posts(id) ON DELETE CASCADE,

    -- Title of the post. Wether this is NULL or not is enforced using the
    -- enforce_post_titles trigger.
    title varchar(255),
    -- Publish date
    publish_date date,
    -- Content of the post, in Markdown
    content text NOT NULL DEFAULT '',
    -- Wether the version is still a draft
    is_draft boolean NOT NULL default true,

    -- This check allows draft posts to be created without having to enter a
    -- publish date, but forces them to have one if they're not a draft.
    CONSTRAINT no_null_published_date CHECK (is_draft OR publish_date IS NOT NULL)
);

create table tags (
    post_id uuid NOT NULL REFERENCES posts(id) ON DELETE CASCADE,
    value varchar(64) NOT NULL,

    PRIMARY KEY (post_id, value)
);

create function enforce_version_titles() returns trigger as $$
    begin
        -- Draft versions shouldn't be evaluated.
        if new.is_draft then
            return new;
        end if;

        -- Check for a wrongfully null title
        if new.title is null and exists (
            select 1 from posts 
                inner join sections on posts.section_id = sections.id
                where posts.id = new.post_id and sections.has_titles
        ) then
            raise exception 'Expected a post title, but got null.';
        end if;

        if new.title is not null and exists (
            select 1 from posts 
                inner join sections on posts.section_id = sections.id
                where posts.id = new.post_id and not sections.has_titles
        ) then
            raise exception 'Expected an empty post title, but got a value.';
        end if;

        return new;
    end;
$$ language plpgsql;

create trigger insert_enforce_version_titles
    before insert on versions
    for each row
    execute function enforce_version_titles();

create trigger update_enforce_version_titles
    before update of title on versions
    for each row
    when (old.title is distinct from new.title)
    execute function enforce_version_titles();