# encoding: utf-8

require_relative "yzz/version"
require_relative "yzz/side"
require_relative "yzz/side_pair"

# Module Yzz is a mixin that provides qualities of a ZZ structure cell to its
# includers.
#
# A ZZ structure consists of ZZ objects, which exist in multiple dimensions. ZZ
# objects may be connected by directed edges -- connections. Connected objects
# are called neighbors. Each connection belongs to exactly one dimension. A ZZ
# object is considered as having two <em>sides</em> in each dimension:
# <em>posward</em> side and <em>negward</em> side. A connection always points
# away from the posward side, and towards the negward side of the neighbor. In
# each dimension, a ZZ object can have at most one posward and one negward
# neighbor. The relation is bijective: If B is the posward neighbor of A along
# dimension X, then A is a negward neighbor of B along X, and vice-versa. There
# is no limitation as to what objects can be connected. Circles are allowed. A ZZ
# object can even be connected to itself, forming a loop.
# 
# To this basic definition, Ted Nelson adds a bunch of additional terminology.
# A <em>rank</em> is a series of ZZ objects connected along the same dimension.
# A rank viewed horizontally is referred to as <em>row</em>. A rank viewed
# vertically is referred to as <em>column</em>. Ted Nelson's terms related not
# to the ZZ structure itself, but rather to the proposed user interface (such
# as <em>cursor</em>, <em>view</em>...) are not implemented in yzz, but rather
# in <em>y_nelson</em> gem.
# 
module Yzz
  # Adds initialization of the @zz_dimensions hash to #initialize.
  # 
  def initialize *args
    @zz_dimensions = Hash.new { |ꜧ, missing_dimension|
      ꜧ[ missing_dimension ] = Yzz::SidePair
        .new( zz: self, dimension: missing_dimension )
    } # initialize the @zz_dimensions hash
    super # and proceed as usual
  end

  # Returns a SidePair instance along the requested dimension.
  # 
  def along dimension
    @zz_dimensions[ dimension ]
  end

  # Returns all sides actually connected to a zz object.
  # 
  def connections
    @zz_dimensions.map { |_, pair| [ pair.negward, pair.posward ] }
      .reduce( [], :+ ).select { |side| side.neighbor.is_a_zz? }
  end
  alias connectivity connections

  # Returns all neighbors of a zz object.
  # 
  def neighbors
    connections.map &:neighbor
  end

  # Returns all sides facing another zz object supplied as argument. (Note that
  # this can be <em>more than 1</em> side: object A can be connected to B along
  # more than 1 dimension.
  # 
  def towards other
    connectivity.select { |side| side.neighbor == other }
  end

  # Prints the labels of the sides facing towards a given zz object.
  # 
  def tw other
    puts towards( other ).map &:label
  end

  # Short string describing the object.
  # 
  def to_s
    "#<Yzz, #{connections.size} conn.>"
  end

  # Inspect string of the object.
  # 
  def inspect
    to_s
  end
end

class Object
  def is_a_zz?
    is_a? ::Yzz
    # class_complies? ::YTed::Zz
  end
end