ioquatix/geospatial

# Copyright, 2015, by Samuel G. D. Williams. <http://www.codeotaku.com>
#
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# of this software and associated documentation files (the "Software"), to deal
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#
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require_relative '../dimensions'
require_relative '../index'

module Geospatial
    module Hilbert
        class Curve
            def initialize(dimensions, order = 30)
                raise ArgumentError("Order #{order} must be positive integer!") unless order >= 1
                
                # Order is the number of levels of the curve, which is equivalent to the number of bits per dimension.
                @order = order
                @scale = 2**@order
                
                @dimensions = dimensions * @scale
                @origin = dimensions.origin
                @size = dimensions.size
            end
            
            attr :order
            attr :scale
            attr :dimensions
            
            def origin
                @dimensions.origin
            end
            
            def size
                @dimensions.size
            end
            
            def to_s
                "\#<#{self.class} order=#{@order} dimensions=#{@dimensions}>"
            end
            
            # This is a helper entry point for traversing Hilbert space.
            def traverse(&block)
                return to_enum(:traverse) unless block_given?
                
                traverse_recurse(@order-1, 0, 0, self.origin, self.size, &block)
            end
            
            def bit_width
                @dimensions.count
            end
            
            # Traversal enumerates all regions of a curve, top-down.
            def traverse_recurse(order, mask, value, origin, size, &block)
                half_size = size.collect{|value| value * 0.5}.freeze
                prefix_mask = (1 << order) | mask
                
                (2**bit_width).times do |prefix|
                    # These both do the same thing, not sure which one is faster:
                    child_value = (value << @dimensions.count) | prefix
                    prefix = child_value << (order*bit_width)
                    
                    index = HilbertIndex.from_integral(prefix, bit_width, @order).to_ordinal
                    
                    index = index & prefix_mask
                    
                    child_origin = @dimensions.unmap(index.axes).freeze
                    
                    # puts "yield(#{child_origin}, #{half_size}, #{prefix}, #{order})"
                    # We avoid calling traverse_recurse simply to hit the callback on the leaf nodes:
                    result = yield child_origin, half_size, prefix, order
                    
                    if order > 0 and result != :skip
                        self.traverse_recurse(order - 1, prefix_mask, child_value, child_origin, half_size, &block)
                    end
                end
            end
            
            def map(coordinates)
                axes = @dimensions.map(coordinates).map(&:floor)
                
                index = OrdinalIndex.new(axes, @order)
                
                return index.to_hilbert.to_i
            end
            
            def unmap(value)
                index = HilbertIndex.from_integral(value, @dimensions.count, @order)
                
                return @dimensions.unmap(index.to_ordinal.axes)
            end
        end
    end
end