130 lines
2.9 KiB
Ruby
130 lines
2.9 KiB
Ruby
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# Avoid coupling the sender of a request to its receiver by giving more than one
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# object a chance to handle the request. Chain the receiving objects and pass
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# the request along the chain until an object handles it.
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# Implements the chain of responsibility pattern. Does not know anything
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# about the approval process, merely whether the current handler can approve
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# the request, or must pass it to a successor.
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class PurchaseApprover
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attr_reader :successor
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def initialize(successor)
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@successor = successor
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end
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def process_request(request)
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if approve_request request
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return
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elsif successor
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successor.process_request request
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else
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deny_request request
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end
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end
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# This may be overridden by a handler if it wants to provide a custom action
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# when it is the last member of the chain
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def deny_request request
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# Implementation
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end
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end
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# Parts of approving chain
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# Base class for approvers who only consider whether the request amount is allowable
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class AmountApprover < PurchaseApprover
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BASE = 500
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def approve_request(request)
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if request.amount < self.class::ALLOWABLE
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print_approval request
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return true
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else
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return false
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end
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end
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end
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class Manager < AmountApprover
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ALLOWABLE = 10 * BASE
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def print_approval(request)
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puts "Manager will approve $#{request.amount}"
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end
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end
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class Director < AmountApprover
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ALLOWABLE = 20 * BASE
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def print_approval(request)
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puts "Director will approve $#{request.amount}"
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end
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end
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class VicePresident < AmountApprover
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ALLOWABLE = 40 * BASE
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def print_approval request
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puts "VicePresident will approve $#{request.amount}"
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end
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end
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class President < AmountApprover
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ALLOWABLE = 60 * BASE
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def print_approval(request)
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puts "President will approve $#{request.amount}"
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end
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end
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class ChiefFinancialOperations < PurchaseApprover
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# An example of a handler that does not inherit from AmountApprover
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def approve_request(request)
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if within_annual_budget? request
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puts "CFO will approve $#{request.amount}"
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return true
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else
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return false
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end
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end
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def within_annual_budget?(request)
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# Implementation
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end
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end
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class PurchaseRequest
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attr_reader :amount, :amount, :purpose
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def initialize(number, amount, purpose)
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@number = number
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@amount = amount
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@purpose = purpose
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end
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end
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# Realization of pattern class
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class CLP
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def initialize(*approvers)
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@authority = build_approvers(approvers).first
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end
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def process_request(request)
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@authority.process_request request
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end
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private
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def build_approvers(approver_classes)
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[].tap do |approvers|
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approver_classes.reverse.inject(nil) do |successor, approver|
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approver.new(successor).tap {|approver| approvers.unshift approver }
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end
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end
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end
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end
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# Usage
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approvers = CLP.new(Manager, Director, VicePresident, President)
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approvers.process_request PurchaseRequest.new(0, amount, 'General')
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