Miles with expiration

This contract archetype manages the expiration date of a mile. An expired mile cannot be consumed and may be cleared out by the administrator.
A mille owner is identified by an address and possesses some miles. A mile is identified by a string id and has an expiration date. Every mile is possessed by one and only one owner:
basic model
A mile can be added and consumed if its expiration date is in the future. 
A storage optimisation is added to the above model. A mile is augmented with a quantity value to gather several miles with the same expiration date. For example, 3 miles with the same expiration date are merged into one mile with the quantity value set to 3:
3 miles with same expiration date ...
... modeled as one mile with a quantity value
This optimisation comes with a cost of algorithmic complexity in the consume entry (line 74).
All entries are called by the admin role, which is ensured by security predicate g1 (line 120).
miles_with_expiration.arl
miles_with_expiration.arl
archetype miles_with_expiration
​
variable admin : role = @tz1Lc2qBKEWCBeDU8npG6zCeCqpmaegRi6Jg
​
(* id is a string because it is generated off-chain *)
asset mile identified by id {
   id         : string;
   amount     : int;
   expiration : date
} with {
  m1 : amount > 0;
}
​
(* a partition ensures there is no direct access to mile collection *)
asset owner identified by addr {
  addr  : role;
  miles : partition<mile> = [] (* injective (owner x mile) *)
}
​
entry add (ow : address, newmile_id : string, newmile_amount : int, newmile_expiration : date) {
   called by admin
​
   require {
     c1 : newmile_amount > 0;
   }
​
   failif {
     c2 : mile.contains(newmile_id);
   }
​
   effect {
     owner.addupdate (ow, { miles += [{id = newmile_id; amount = newmile_amount; expiration = newmile_expiration} ] })
   }
}
​
entry consume (a : address, quantity : int) {
​
  specification {
​
    assert p1 {
      remainder = 0
    }
​
    postcondition p2 {
      mile.sum(the.amount) = before.mile.sum(the.amount) - quantity
      invariant for loop {
        0 <= remainder <= toiterate.sum(the.amount);
        before.mile.sum(the.amount) = mile.sum(the.amount) + quantity - remainder
      }
    }
​
    postcondition p3 {
      forall m in removed.mile, m.expiration >= now
      invariant for loop {
        removed.mile.subsetof(by_expiration)
      }
    }
​
    postcondition p4 {
      added.mile.isempty()
      invariant for loop {
        added.mile.isempty()
      }
    }
  }
​
  called by admin
​
  require {
    r2 : quantity >= 0;
  }
​
  effect {
    var by_expiration = owner[a].miles.sort(expiration).select(the.expiration > now);
    dorequire (by_expiration.sum(the.amount) >= quantity);
    var remainder = quantity;
    for : loop m in by_expiration do
      if remainder > 0
      then (
        if mile[m].amount > remainder
        then (
          mile.update(m, { amount -= remainder });
          remainder := 0
        )
        else if mile[m].amount = remainder
        then (
          remainder := 0;
          owner[a].miles.remove(m)
        ) else (
          remainder -= mile[m].amount;
          owner[a].miles.remove(m)
        )
      )
    done;
    assert p1
  }
}
​
entry clear_expired () {
  specification {
    postcondition s3 {
      forall m in removed.mile, m.expiration < now
      invariant for loop2 {
        forall m in removed.mile, m.expiration < now
      }
    }
  }
​
  called by admin
​
  effect {
    for : loop2 o in owner do
      owner[o].miles.removeif(the.expiration < now)
    done
  }
}
​
security {
  (*  this ensures that any mile was added with the 'add' entry *)
  g1 : only_by_role (anyentry, admin);
  g2 : only_in_entry (remove (mile), [consume or clear_expired]);
  g3 : not_in_entry (add (mile), consume);
  g4 : no_storage_fail (add)
}
​
Miles
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Last updated 8 months ago