take2.ts

interface Account {
  plan: AccountPlan
  // ...
}

interface AccountPlan {
  customer: AccountDID

  request(): Plan
  list(): Plan[]

  // Verifies that plan.customer === this.customer
  add(terms: Terms): Plan
  remove(plan: Plan): {}
}

type Plan = Variant<{
  active:       ActivePlan
  pending:      PendingPlan   
}>
  
interface PendingPlan {
   // URL user can navigate to complete setup
   url: URL
   customer: AccountDID
}
  
interface ActivePlan extends UCAN<{ with: ServiceDID: can: "plan/*", nb: { customer: AccountDID } }> {
   terms: Terms // terms of service
   customer: AccountDID  // Account that has a subscription
  
   subscription: PlanSubscription
  
   // ensures that terms.customer === this.customer
   update({ terms: Terms }): void
}
  
 interface Terms extends UCAN<{ with: ProviderDID, nb: { customer: AccountDID } }> {
    price: Price
    provider: ProviderDID
    customer: AccountDID
    protocol: Record<Ability, Schema>
 }
  
 interface Price extends Record<string, number> {}

  
interface PlanSubscription {
  list(): Subscription[]
  add(subscripton: Subscription): {}
  remove(subscription: Subscription): {}
}

  
interface Subscription {
  consumer: SpaceDID
  limit: Limit
}
 
interface Limit extends Record<PropertyKey, never> {
}