# This module encapsulates functionality related to the
# generation of Fibonacci sequences.
#--
# Copyright (c) 2004 Dave Thomas, The Pragmatic Programmers, LLC.
# Licensed under the same terms as Ruby. No warranty is provided.
module Fibonacci
    # Calculate the first _count_ Fibonacci numbers, starting with 1,1.
    #
    # :call-seq:
    # Fibonacci.sequence(count)              -> array
    # Fibonacci.sequence(count) {|val| ... } -> nil
    #
    # If a block is given, supply successive values to the block and
    # return +nil+, otherwise return all values as an array.
    def Fibonacci.sequence(count, &block)
        result, block = setup_optional_block(block)
        generate do |val|
            break if count <= 0
            count -= 1
            block[val]
        end
        result
    end
    # Calculate the Fibonacci numbers up to and including _max_.
    #
    # :call-seq:
    # Fibonacci.upto(count)               ->  array
    # Fibonacci.upto(count) {|val ... }   ->   nil
    #
    # If a block is given, supply successive values to the
    # block and return +nil+, otherwise return all values as an array.
    def Fibonacci.upto(max, &block)
        result, block = setup_optional_block(block)
        generate do |val|
            break if val > max
            block[val]
        end
        result
    end

private
    # Yield a sequence of Fibonacci numbers to a block.
    def Fibonacci.generate
        f1, f2 = 1, 1
        loop do
            yield f1
            f1, f2 = f2, f1+f2
        end
    end
    # If a block parameer is given, use it, otherwise accumulate into an
    # array. Return the result value and the block to use.
    def Fibonacci.setup_optional_block(block)
        if block.nil?
            [ result = [], lambda {|val| result << val } ]
        else
            [ nil, block ]
        end
    end
end