require 'set'
require 'abstractivator/proc_ext'

module Enumerable

  # joins items from left with items from right based on their keys.
  # get_{left,right}_key are callables which, given an item, return the item's key.
  # the defaults are used to form a pair for items which have no match.
  # returns an array of 2-element arrays, each of which is a left/right pair.
  def self.outer_join(left, right, get_left_key, get_right_key, left_default, right_default)

    ls = left.hash_map(get_left_key)
    rs = right.hash_map(get_right_key)

    raise 'duplicate left keys' if ls.size < left.size
    raise 'duplicate right keys' if rs.size < right.size

    result = []

    ls.each_pair do |k, l|
      r = rs[k]
      if r
        rs.delete(k)
      else
        r = get_default(right_default, l)
      end
      result.push [l, r]
    end

    rs.each_pair do |_, r|
      result.push [get_default(left_default, r), r]
    end

    result
  end

  def self.inner_join(left, right, get_left_key, get_right_key)
    sentinel = Object.new
    result = self.outer_join(left, right, get_left_key, get_right_key, sentinel, sentinel)
    result.reject { |pair| pair.first == sentinel || pair.last == sentinel }
  end

  def self.get_default(default, other_side_value)
    default.callable? ? default.call(other_side_value) : default
  end

  def self.proc?(x)
    x.respond_to?(:call)
  end

  def hash_map(get_key=->x{x}, &get_value)
    Hash[self.map{|x| [Proc.loose_call(get_key, [x]), get_value ? get_value.call(x) : x]}]
  end

  def outer_join(right, get_left_key, get_right_key, default_value)
    Enumerable.outer_join(self, right, get_left_key, get_right_key, default_value, default_value)
  end

  def inner_join(right, get_left_key, get_right_key)
    Enumerable.inner_join(self, right, get_left_key, get_right_key)
  end

  def uniq?
    seen = Set.new
    each_with_index do |x, i|
      seen << (block_given? ? yield(x) : x)
      return false if seen.size < i + 1
    end
    true
  end

  orig_detect = instance_method(:detect)
  define_method :detect do |*args, &block|
    detect = orig_detect.bind(self)

    if args.size == 1 && !args.first.callable? && block
      value = args.first
      detect.call {|x| block.call(x) == value}
    elsif args.size == 2 && !block
      attr_name, value = args
      detect.call {|x| x.send(attr_name) == value}
    else
      detect.call(*args, &block)
    end
  end

  def inject_right(*args, &block)
    self.reverse_each.inject(*args, &block) # reverse_each to avoid duplicating the enumerable, when possible
  end

  def pad_right(n, value=nil, &block)
    block ||= proc { value }
    self + ([n-self.size, 0].max).times.map(&block)
  end

  def stable_sort(&compare)
    compare = compare || ->(a, b){a <=> b}
    xis = self.each_with_index.map{|x, i| [x, i]}
    sorted = xis.sort do |(a, ai), (b, bi)|
      primary = compare.call(a, b)
      primary != 0 ? primary : (ai <=> bi)
    end
    sorted.map(&:first)
  end
end