restrict-cost-and-percentage-increase.sentinel

# This policy uses the Sentinel tfrun import to restrict the
# both the total monthly cost and the percentage increase in
# the monthly cost that would be incurred if the current plan
# were applied

##### Imports #####

import "tfrun"
import "decimal"

##### Functions #####

# Validate that the proposed cost is less than the given limit and
# that the percentage increase in the monthly cost
# is less than a given percentage
restrict_cost_and_percentage_increase = func(limit, max_percent) {

  validated = true

  # Determine cost data
  prior_cost = decimal.new(tfrun.cost_estimate.prior_monthly_cost)
  proposed_cost = decimal.new(tfrun.cost_estimate.proposed_monthly_cost)
  increase_in_cost = decimal.new(tfrun.cost_estimate.delta_monthly_cost)

  # Compare proposed monthly cost to the limit
  if proposed_cost.gt(limit) {
    print("Proposed monthly cost", proposed_cost.string,
          "is over the limit:", limit.string)
    validated = false
  }

  # If prior_cost is not 0.0, compare percentage increase in monthly cost
  # to max_percent
  if prior_cost.is_not(0.0) {
    #print("We had a prior cost.")
    percentage_change = increase_in_cost.divide(prior_cost).multiply(100)
    #print("Percentage Change:", percentage_change.float)
    if decimal.new(percentage_change).gt(max_percent) {
      print("Proposed percentage increase", percentage_change.float,
            "is over the max percentage change:", max_percent.float)
      validated = false
    } else {
      print("Proposed percentage increase", percentage_change.float,
            "is under the max percentage change:", max_percent.float)
    }
  }

  return validated

}

##### Parameters #####
limit = decimal.new(10)
max_percent = decimal.new(5.0)

##### Rules #####
cost_validated = restrict_cost_and_percentage_increase(limit, max_percent)
main = rule {
  cost_validated
}