neiam /gitgud

defmodule GitGud.Repo.Migrations.CreateModerationBans do
  use Ecto.Migration

  # Stopping a local user from acting in one repo, or across every repo
  # an org owns.
  #
  # Nothing here suspends an account instance-wide — that stays an
  # instance-admin power. This is scoped so a repo or org admin can
  # protect their own ground without reaching further than it.
  def change do
    create table(:moderation_bans) do
      add :organization_id, references(:organizations, on_delete: :delete_all)
      add :repository_id, references(:repositories, on_delete: :delete_all)

      add :banned_user_id, references(:users, on_delete: :delete_all), null: false
      add :banned_by_id, references(:users, on_delete: :nilify_all)

      add :reason, :string
      # Null means it lasts until someone lifts it.
      add :expires_at, :utc_datetime
      add :lifted_at, :utc_datetime
      add :lifted_by_id, references(:users, on_delete: :nilify_all)

      timestamps(type: :utc_datetime)
    end

    # Exactly one scope, never both and never neither.
    create constraint(:moderation_bans, :moderation_bans_one_scope,
             check: "(organization_id IS NULL) <> (repository_id IS NULL)"
           )

    # One live ban per person per scope; lifted ones are kept as record.
    create unique_index(:moderation_bans, [:organization_id, :banned_user_id],
             where: "lifted_at IS NULL AND organization_id IS NOT NULL",
             name: :moderation_bans_active_org_index
           )

    create unique_index(:moderation_bans, [:repository_id, :banned_user_id],
             where: "lifted_at IS NULL AND repository_id IS NOT NULL",
             name: :moderation_bans_active_repo_index
           )

    # "Is this person banned here?" — checked on every write.
    create index(:moderation_bans, [:banned_user_id, :lifted_at])
  end
end