Class: Stupidedi::Parser::ConstraintTable::ValueBased

Inherits:
Stupidedi::Parser::ConstraintTable show all
Defined in:
lib/stupidedi/parser/constraint_table.rb

Overview

Chooses the subset of Instruction values based on the distinguishing values allowed by each Schema::SegmentUse. For instance, there are often several loops that begin with NM1, which are distinguished by the qualifier in element NM101.

Instance Attribute Summary

Attributes inherited from Stupidedi::Parser::ConstraintTable

#instructions

Instance Method Summary collapse

Methods inherited from Stupidedi::Parser::ConstraintTable

build, #copy, #critique, #pretty_print

Constructor Details

#initialize(instructions) ⇒ ValueBased

Returns a new instance of ValueBased.


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# File 'lib/stupidedi/parser/constraint_table.rb', line 116

def initialize(instructions)
  @instructions = instructions
  @__basis      = {}
end

Instance Method Details

#basis(instructions, mode) ⇒ Array(Array<(Integer, Integer, Map)>, Array<(Integer, Integer, Map)>)

Returns:

  • (Array(Array<(Integer, Integer, Map)>, Array<(Integer, Integer, Map)>))

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# File 'lib/stupidedi/parser/constraint_table.rb', line 228

def basis(instructions, mode)
  @__basis[mode] ||= begin
    # When inserting segments, given a choice between two otherwise
    # equivalent instructions, prefer the one with smallest `pop_count`.
    # For example, when inserting an HL*20 in X221 835, the new 2000A
    # loop could potentially go in the current "Table 2 - Billing
    # Provider Detail" (smaller pop_count), or the parser could create
    # a whole new table (larger pop_count).
    #
    # When searching for segments in a parse tree (mode == :read), we
    # need to try both choices. That's because this "Table 2 - Billing
    # Provider Detail" could be followed by a different "Table 2 -
    # Subscriber Detail", which is then followed by another "Table 2 -
    # Billing Provider Detail". Then the next HL*20 would belong to the
    # uncle table, not the current table.
    if mode == :insert
      instructions = shallowest(instructions)
    end

    disjoint_elements = []
    distinct_elements = []

    # The first SegmentUse is used to represent the structure that must
    # be shared by the others: number of elements and type of elements
    element_uses = instructions.head.segment_use.definition.element_uses

    # Iterate over each element across all SegmentUses (think columns)
    #   NM1*[IL]*[  ]*..*..*..*..*..*[  ]*..*..*{..}*..
    #   NM1*[40]*[  ]*..*..*..*..*..*[  ]*..*..*{..}*..
    element_uses.length.times do |n|
      if element_uses.at(n).composite?
        ms = 0 .. element_uses.at(n).definition.component_uses.length - 1
      else
        ms = [nil]
      end

      # If this is a composite element, we iterate over each component.
      # Otherwise this loop iterates once with the index {m} set to nil.
      ms.each do |m|
        last  = nil        # the last subset we examined
        total = Sets.empty # the union of all examined subsets

        distinct = false
        disjoint = true

        instructions.each do |i|
          element_use = i.segment_use.definition.element_uses.at(n)

          unless m.nil?
            element_use = element_use.definition.component_uses.at(m)
          end

          allowed_vals = element_use.allowed_values

          # We want to know if every instruction's set of allowed values
          # is disjoint (with one another). Instead of comparing each set
          # with every other set, which takes (N-1)! comparisons, we can
          # do it in N steps.
          disjoint &&= allowed_vals.disjoint?(total)

          # We also want to know if one instruction's set of allowed vals
          # contains elements that aren't present in at least one other
          # set. The opposite condition is easy to test: all sets contain
          # the same elements (are equal). So we can similarly, check this
          # condition in N steps rather than (N-1)!
          distinct ||= allowed_vals != last unless last.nil?

          total = allowed_vals.union(total)
          last  = allowed_vals
        end

      # puts "#{n}.#{m}: disjoint(#{disjoint}) distinct(#{distinct})"

        if disjoint
          # Since each instruction's set of allowed values is disjoint, we
          # can build a function/hash that returns the single instruction,
          # given one of the values. When given a value outside the set of
          # all (combined) values, it returns nil.
          disjoint_elements << [[n, m], build_disjoint(total, n, m, instructions)]
        elsif distinct
          # Not all instructions have the same set of allowed values. So
          # we can build a function/hash that accepts one of the values
          # and returns the subset of the instructions where that value
          # can occur. This might be some, none, or all of the original
          # instructions, so clearly this provides less information than
          # if each allowed value set was disjoint.

          # Currently disabled (and untested) because it doesn't look like
          # any of the HIPAA schemas would use this -- so testing it would
          # be a pain.
          #
          distinct_elements << [[n, m], build_distinct(total, n, m, instructions)]
        end
      end
    end

    [disjoint_elements, distinct_elements]
  end
end

#build_disjoint(total, n, m, instructions) ⇒ Hash<String, Array<Instruction>>

Returns:


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# File 'lib/stupidedi/parser/constraint_table.rb', line 329

def build_disjoint(total, n, m, instructions)
  if total.finite?
    # The sum of all allowed value sets is finite, so we know that each
    # individual allowed value set is finite (we can iterate over it).
    map = Hash.new

    instructions.each do |i|
      element_use = i.segment_use.definition.element_uses.at(n)

      unless m.nil?
        element_use = element_use.definition.component_uses.at(m)
      end

      allowed_vals = element_use.allowed_values
      allowed_vals.each{|v| map[v] = i.cons }
    end

    map
  else
    # At least one of allowed value sets is infinite. This happens when
    # it is RelativeComplement, which declares the values that are *not*
    # allowed in the set.
    map = Hash.new{|h,k| h[k] = instructions }

    instructions.each do |i|
      element_use = i.segment_use.definition.element_uses.at(n)
      unless m.nil?
        element_use = element_use.definition.component_uses.at(m)
      end

      allowed_vals = element_use.allowed_values

      unless allowed_vals.finite?
        allowed_vals.complement.each{|v| map[v] -= i }
      end
    end

    # Clear the default_proc so accesses don't change the Hash
    map.default = instructions
    map
  end
end

#build_distinct(total, n, m, instructions) ⇒ Hash<String, Array<Instruction>>

Returns:


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# File 'lib/stupidedi/parser/constraint_table.rb', line 373

def build_distinct(total, n, m, instructions)
  if total.finite?
    # The sum of all allowed value sets is finite, so we know that each
    # individual allowed value set is finite (we can iterate over it).
    map = Hash.new{|h,k| h[k] = [] }

    instructions.each do |i|
      element_use  = i.segment_use.definition.element_uses.at(n)

      unless m.nil?
        element_use = element_use.definition.component_uses.at(m)
      end

      allowed_vals = element_use.allowed_values
      allowed_vals.each{|v| map[v] << i }
    end

    # Clear the default_proc so accesses don't change the Hash
    map.default = []
    map
  else
    # At least one of allowed value sets is infinite. This happens when
    # it is RelativeComplement, which declares the values that are *not*
    # allowed in the set.
    map = Hash.new{|h,k| h[k] = instructions }

    instructions.each do |i|
      element_use  = i.segment_use.definition.element_uses.at(n)

      unless m.nil?
        element_use = element_use.definition.component_uses.at(m)
      end

      allowed_vals = element_use.allowed_values

      unless allowed_vals.finite?
        allowed_vals.complement.each{|v| map[v] -= i }
      end
    end

    # Clear the default_proc so accesses don't change the Hash
    map.default = instructions
    map
  end
end

#deconstruct(element_toks, m, n) ⇒ String?

Return the value of the m-th elemnt, or if n is not nil, return the value of the n-th component from the n-th element. When the value is blank, the function returns nil.

Parameters:

Returns:

  • (String, nil)

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# File 'lib/stupidedi/parser/constraint_table.rb', line 428

def deconstruct(element_toks, m, n)
  element_tok = element_toks.at(m)
  element_tok = element_tok.element_toks.at(0) if element_tok.try(:repeated?)

  if element_tok.blank?
    nil
  elsif n.nil?
    element_tok.value
  else
    element_tok = element_tok.component_toks.at(n)

    if element_tok.blank?
      nil
    else
      element_tok.value
    end
  end
end

#matches(segment_tok, strict, mode) ⇒ Array<Instruction>

Returns:


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# File 'lib/stupidedi/parser/constraint_table.rb', line 122

def matches(segment_tok, strict, mode)
  invalid = true  # Were all present possibly distinguishing elements invalid?
  present = false # Were any possibly distinguishing elements present?

  disjoint, distinct = basis(@instructions, mode)

  # First check single elements that can narrow the search space to
  # a single matching Instruction.
  disjoint.each do |(n, m), map|
    value = deconstruct(segment_tok.element_toks, n, m)

    case value
    when nil, :not_used, :default
      # value wasn't present in segment_tok, can't use it to decide
    else
      singleton = map.at(value)
      present   = true

      unless singleton.nil?
        # Success, search is terminated
        return singleton
      else
        if strict
          designator = "#{segment_tok.id}#{"%02d" % (n + 1)}"
          designator = designator + "-%02d" % (m + 1) unless m.nil?

          raise ArgumentError,
            "value #{value.to_s} is not allowed in element #{designator}"
        end
      end
    end
  end

  # If we reach this line, none of the present elements could, on its
  # own, narrow the search space to a single Instruction. We now test
  # the combination of elements to iteratively narrow the search space
  space = @instructions

  # @todo: These filters could be ordered by probable effectiveness,
  # so we narrow the search space by the largest amount in the fewest
  # number of steps.
  distinct.each do |(n, m), map|
    value = deconstruct(segment_tok.element_toks, n, m)

    unless value.nil?
      # Lookup which instructions are compatible with this input
      subset  = map.at(value)
      present = true

      unless subset.blank?
        invalid = false
        space  &= subset

        if space.length <= 1
          # Success, search is terminated
          return space
        end
      else
        # This value isn't compatible with any instruction
        if strict
          designator = "#{segment_tok.id}#{"%02d" % (n + 1)}"
          designator = designator + "-%02d" % (m + 1) unless m.nil?

          raise ArgumentError,
            "value #{value.to_s} is not allowed in element #{designator}"
        end
      end
    end
  end

  if invalid and present
    # Some elements were present, but all contained invalid values, and
    # even ignoring those we could not narrow the matches to a single
    # instruction.
    #
    # We could return the remaining search space, but it is safest to
    # mark this as an invalid segment and avoid the non-determinism
    []
  else
    # Some elements were present and none were invalid, but it was not
    # possible to narrow the set of matches to a single instruction.
    #
    # It seems wrong to mark the segment invalid. The worst thing you
    # could say about the input is that it may have been missing a
    # required element that could have resolved the ambiguity; but it's
    # also possible all required elements were present and the grammar
    # is the problem (not the input). So here we return the remaining
    # search space, which will cause non-determinism in the parser.
    space
  end
end

#shallowest(instructions) ⇒ Array<Instruction>

Resolve conflicts between instructions that have identical SegmentUse values. For each SegmentUse, this chooses the Instruction that pops the fewest number of states.

Returns:


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# File 'lib/stupidedi/parser/constraint_table.rb', line 219

def shallowest(instructions)
  grouped = instructions.group_by{|i| i.segment_use.object_id }
  grouped.flat_map do |k, is|
    shallowest = is.map(&:pop_count).min
    is.select{|i| i.pop_count == shallowest }
  end
end