create table users (
    id integer primary key not null,

    username text unique not null,
    password_hash text not null
);

create table sessions (
    id bigint primary key not null,

    user_id bigint not null
        references users (id)
        on delete cascade,

    last_seen bigint not null,

    unique (id, user_id)
);

create table devices (
    id integer primary key not null,

    device_id text not null,
    user_id bigint not null
        references users (id)
        on delete cascade,
    sync_group_id bigint
        references sync_groups (id)
        on delete set null,

    caption text not null,
    type text not null,

    unique (user_id, device_id)
);

create table sync_groups (
    id integer primary key not null
);

create table device_subscriptions (
    id integer primary key not null,

    device_id bigint not null
        references devices (id)
        on delete cascade,

    podcast_url text not null,

    time_changed bigint not null,
    deleted boolean not null default false,

    unique (device_id, podcast_url)
);

create table episode_actions (
    id integer primary key not null,

    user_id bigint not null
        references users (id)
        on delete cascade,
    -- Can be null, as the device is not always provided
    device_id bigint
        references devices (id)
        on delete set null,

    podcast_url text not null,
    episode_url text not null,

    time_changed bigint not null,

    timestamp bigint,
    action text not null,
    started integer,
    position integer,
    total integer,

    -- Position should be set if the action type is "Play" and null otherwise
    check ((action = "play") = (position is not null)),

    -- Started and position can only be set if the action type is "Play"
    check (action = "play" or (started is null and position is null)),

    -- Started and position should be provided together
    check ((started is null) = (total is null))
);