Except so far as a seller may have assumed a greater obligation and subject to the preceding section on substituted performance,
(1) delay in delivery or nondelivery in whole or in part by a seller who complies with (2) and (3) of this section is not a breach of the seller's duty under a contract for sale if performance as agreed has been made impracticable by the occurrence of a contingency, the nonoccurrence of which was a basic assumption on which the contract was made or by compliance in good faith with an applicable foreign or domestic governmental regulation or order whether or not it later proves to be invalid;
(2) if the causes mentioned in (1) of this section affect only a part of the seller's capacity to perform, the seller must allocate production and deliveries among the seller's customers, but may at the seller's option include regular customers not then under contract as well as the seller's own requirements for further manufacture; the seller may so allocate in a manner that is fair and reasonable;
(3) the seller must notify the buyer seasonably that there will be delay or nondelivery and, when allocation is required under (2) of this section, of the estimated quota thus made available for the buyer.