class DocumentMembership < ApplicationRecord
  belongs_to :document
  belongs_to :user
  belongs_to :share_link, optional: true

  enum :role, { viewer: 0, editor: 1 }, validate: true
  enum :source, { invite: 0, link: 1 }, validate: true

  # Grant access. An invitation is explicit: it sets exactly the invited role
  # and survives revoking any link. A link never weakens existing access and
  # never turns an invitation back into link-based access.
  def self.grant!(document:, user:, role:, source:, share_link: nil)
    return if document.owner_id == user.id
    m = find_or_initialize_by(document:, user:)
    if source.to_s == "invite"
      m.assign_attributes(role:, source: :invite, share_link: nil)
    elsif m.new_record?
      m.assign_attributes(role:, source: :link, share_link:)
    elsif m.link? && roles[role.to_s] > roles[m.role]
      m.assign_attributes(role:, share_link:)
    end
    m.save!
    m
  end
end