# frozen_string_literal: true

require "diff/lcs/change"

module Diff::LCS
  # This callback object implements the default set of callback events,
  # which only returns the event itself. Note that #finished_a and
  # #finished_b are not implemented -- I haven't yet figured out where they
  # would be useful.
  #
  # Note that this is intended to be called as is, e.g.,
  #
  #     Diff::LCS.LCS(seq1, seq2, Diff::LCS::DefaultCallbacks)
  class DefaultCallbacks
    class << self
      # Called when two items match.
      def match(event)
        event
      end

      # Called when the old value is discarded in favour of the new value.
      def discard_a(event)
        event
      end

      # Called when the new value is discarded in favour of the old value.
      def discard_b(event)
        event
      end

      # Called when both the old and new values have changed.
      def change(event)
        event
      end

      private :new
    end
  end

  # An alias for DefaultCallbacks that is used in
  # Diff::LCS#traverse_sequences.
  #
  #     Diff::LCS.LCS(seq1, seq2, Diff::LCS::SequenceCallbacks)
  SequenceCallbacks = DefaultCallbacks

  # An alias for DefaultCallbacks that is used in
  # Diff::LCS#traverse_balanced.
  #
  #     Diff::LCS.LCS(seq1, seq2, Diff::LCS::BalancedCallbacks)
  BalancedCallbacks = DefaultCallbacks

  def self.callbacks_for(callbacks)
    callbacks.new rescue callbacks
  end
end

# This will produce a compound array of simple diff change objects. Each
# element in the #diffs array is a +hunk+ or +hunk+ array, where each
# element in each +hunk+ array is a single Change object representing the
# addition or removal of a single element from one of the two tested
# sequences. The +hunk+ provides the full context for the changes.
#
#     diffs = Diff::LCS.diff(seq1, seq2)
#       # This example shows a simplified array format.
#       # [ [ [ '-',  0, 'a' ] ],   # 1
#       #   [ [ '+',  2, 'd' ] ],   # 2
#       #   [ [ '-',  4, 'h' ],     # 3
#       #     [ '+',  4, 'f' ] ],
#       #   [ [ '+',  6, 'k' ] ],   # 4
#       #   [ [ '-',  8, 'n' ],     # 5
#       #     [ '-',  9, 'p' ],
#       #     [ '+',  9, 'r' ],
#       #     [ '+', 10, 's' ],
#       #     [ '+', 11, 't' ] ] ]
#
# There are five hunks here. The first hunk says that the +a+ at position 0
# of the first sequence should be deleted (<tt>'-'</tt>). The second hunk
# says that the +d+ at position 2 of the second sequence should be inserted
# (<tt>'+'</tt>). The third hunk says that the +h+ at position 4 of the
# first sequence should be removed and replaced with the +f+ from position 4
# of the second sequence. The other two hunks are described similarly.
#
# === Use
#
# This callback object must be initialised and is used by the Diff::LCS#diff
# method.
#
#     cbo = Diff::LCS::DiffCallbacks.new
#     Diff::LCS.LCS(seq1, seq2, cbo)
#     cbo.finish
#
# Note that the call to #finish is absolutely necessary, or the last set of
# changes will not be visible. Alternatively, can be used as:
#
#     cbo = Diff::LCS::DiffCallbacks.new { |tcbo| Diff::LCS.LCS(seq1, seq2, tcbo) }
#
# The necessary #finish call will be made.
#
# === Simplified Array Format
#
# The simplified array format used in the example above can be obtained
# with:
#
#     require 'pp'
#     pp diffs.map { |e| e.map { |f| f.to_a } }
class Diff::LCS::DiffCallbacks
  # Returns the difference set collected during the diff process.
  attr_reader :diffs

  def initialize # :yields: self
    @hunk = []
    @diffs = []

    return unless block_given?

    begin
      yield self
    ensure
      finish
    end
  end

  # Finalizes the diff process. If an unprocessed hunk still exists, then it
  # is appended to the diff list.
  def finish
    finish_hunk
  end

  def match(_event)
    finish_hunk
  end

  def discard_a(event)
    @hunk << Diff::LCS::Change.new("-", event.old_position, event.old_element)
  end

  def discard_b(event)
    @hunk << Diff::LCS::Change.new("+", event.new_position, event.new_element)
  end

  def finish_hunk
    @diffs << @hunk unless @hunk.empty?
    @hunk = []
  end
  private :finish_hunk
end

# This will produce a compound array of contextual diff change objects. Each
# element in the #diffs array is a "hunk" array, where each element in each
# "hunk" array is a single change. Each change is a Diff::LCS::ContextChange
# that contains both the old index and new index values for the change. The
# "hunk" provides the full context for the changes. Both old and new objects
# will be presented for changed objects. +nil+ will be substituted for a
# discarded object.
#
#     seq1 = %w(a b c e h j l m n p)
#     seq2 = %w(b c d e f j k l m r s t)
#
#     diffs = Diff::LCS.diff(seq1, seq2, Diff::LCS::ContextDiffCallbacks)
#       # This example shows a simplified array format.
#       # [ [ [ '-', [  0, 'a' ], [  0, nil ] ] ],   # 1
#       #   [ [ '+', [  3, nil ], [  2, 'd' ] ] ],   # 2
#       #   [ [ '-', [  4, 'h' ], [  4, nil ] ],     # 3
#       #     [ '+', [  5, nil ], [  4, 'f' ] ] ],
#       #   [ [ '+', [  6, nil ], [  6, 'k' ] ] ],   # 4
#       #   [ [ '-', [  8, 'n' ], [  9, nil ] ],     # 5
#       #     [ '+', [  9, nil ], [  9, 'r' ] ],
#       #     [ '-', [  9, 'p' ], [ 10, nil ] ],
#       #     [ '+', [ 10, nil ], [ 10, 's' ] ],
#       #     [ '+', [ 10, nil ], [ 11, 't' ] ] ] ]
#
# The five hunks shown are comprised of individual changes; if there is a
# related set of changes, they are still shown individually.
#
# This callback can also be used with Diff::LCS#sdiff, which will produce
# results like:
#
#     diffs = Diff::LCS.sdiff(seq1, seq2, Diff::LCS::ContextCallbacks)
#       # This example shows a simplified array format.
#       # [ [ [ "-", [  0, "a" ], [  0, nil ] ] ],  # 1
#       #   [ [ "+", [  3, nil ], [  2, "d" ] ] ],  # 2
#       #   [ [ "!", [  4, "h" ], [  4, "f" ] ] ],  # 3
#       #   [ [ "+", [  6, nil ], [  6, "k" ] ] ],  # 4
#       #   [ [ "!", [  8, "n" ], [  9, "r" ] ],    # 5
#       #     [ "!", [  9, "p" ], [ 10, "s" ] ],
#       #     [ "+", [ 10, nil ], [ 11, "t" ] ] ] ]
#
# The five hunks are still present, but are significantly shorter in total
# presentation, because changed items are shown as changes ("!") instead of
# potentially "mismatched" pairs of additions and deletions.
#
# The result of this operation is similar to that of
# Diff::LCS::SDiffCallbacks. They may be compared as:
#
#     s = Diff::LCS.sdiff(seq1, seq2).reject { |e| e.action == "=" }
#     c = Diff::LCS.sdiff(seq1, seq2, Diff::LCS::ContextDiffCallbacks).flatten(1)
#
#     s == c # -> true
#
# === Use
#
# This callback object must be initialised and can be used by the
# Diff::LCS#diff or Diff::LCS#sdiff methods.
#
#     cbo = Diff::LCS::ContextDiffCallbacks.new
#     Diff::LCS.LCS(seq1, seq2, cbo)
#     cbo.finish
#
# Note that the call to #finish is absolutely necessary, or the last set of
# changes will not be visible. Alternatively, can be used as:
#
#     cbo = Diff::LCS::ContextDiffCallbacks.new { |tcbo| Diff::LCS.LCS(seq1, seq2, tcbo) }
#
# The necessary #finish call will be made.
#
# === Simplified Array Format
#
# The simplified array format used in the example above can be obtained
# with:
#
#     require 'pp'
#     pp diffs.map { |e| e.map { |f| f.to_a } }
class Diff::LCS::ContextDiffCallbacks < Diff::LCS::DiffCallbacks
  def discard_a(event)
    @hunk << Diff::LCS::ContextChange.simplify(event)
  end

  def discard_b(event)
    @hunk << Diff::LCS::ContextChange.simplify(event)
  end

  def change(event)
    @hunk << Diff::LCS::ContextChange.simplify(event)
  end
end

# This will produce a simple array of diff change objects. Each element in
# the #diffs array is a single ContextChange. In the set of #diffs provided
# by SDiffCallbacks, both old and new objects will be presented for both
# changed <strong>and unchanged</strong> objects. +nil+ will be substituted
# for a discarded object.
#
# The diffset produced by this callback, when provided to Diff::LCS#sdiff,
# will compute and display the necessary components to show two sequences
# and their minimized differences side by side, just like the Unix utility
# +sdiff+.
#
#     same             same
#     before     |     after
#     old        <     -
#     -          >     new
#
#     seq1 = %w(a b c e h j l m n p)
#     seq2 = %w(b c d e f j k l m r s t)
#
#     diffs = Diff::LCS.sdiff(seq1, seq2)
#       # This example shows a simplified array format.
#       # [ [ "-", [  0, "a"], [  0, nil ] ],
#       #   [ "=", [  1, "b"], [  0, "b" ] ],
#       #   [ "=", [  2, "c"], [  1, "c" ] ],
#       #   [ "+", [  3, nil], [  2, "d" ] ],
#       #   [ "=", [  3, "e"], [  3, "e" ] ],
#       #   [ "!", [  4, "h"], [  4, "f" ] ],
#       #   [ "=", [  5, "j"], [  5, "j" ] ],
#       #   [ "+", [  6, nil], [  6, "k" ] ],
#       #   [ "=", [  6, "l"], [  7, "l" ] ],
#       #   [ "=", [  7, "m"], [  8, "m" ] ],
#       #   [ "!", [  8, "n"], [  9, "r" ] ],
#       #   [ "!", [  9, "p"], [ 10, "s" ] ],
#       #   [ "+", [ 10, nil], [ 11, "t" ] ] ]
#
# The result of this operation is similar to that of
# Diff::LCS::ContextDiffCallbacks. They may be compared as:
#
#     s = Diff::LCS.sdiff(seq1, seq2).reject { |e| e.action == "=" }
#     c = Diff::LCS.sdiff(seq1, seq2, Diff::LCS::ContextDiffCallbacks).flatten(1)
#
#     s == c # -> true
#
# === Use
#
# This callback object must be initialised and is used by the Diff::LCS#sdiff
# method.
#
#     cbo = Diff::LCS::SDiffCallbacks.new
#     Diff::LCS.LCS(seq1, seq2, cbo)
#
# As with the other initialisable callback objects,
# Diff::LCS::SDiffCallbacks can be initialised with a block. As there is no
# "fininishing" to be done, this has no effect on the state of the object.
#
#     cbo = Diff::LCS::SDiffCallbacks.new { |tcbo| Diff::LCS.LCS(seq1, seq2, tcbo) }
#
# === Simplified Array Format
#
# The simplified array format used in the example above can be obtained
# with:
#
#     require 'pp'
#     pp diffs.map { |e| e.to_a }
class Diff::LCS::SDiffCallbacks
  # Returns the difference set collected during the diff process.
  attr_reader :diffs

  def initialize # :yields: self
    @diffs = []
    yield self if block_given?
  end

  def match(event)
    @diffs << Diff::LCS::ContextChange.simplify(event)
  end

  def discard_a(event)
    @diffs << Diff::LCS::ContextChange.simplify(event)
  end

  def discard_b(event)
    @diffs << Diff::LCS::ContextChange.simplify(event)
  end

  def change(event)
    @diffs << Diff::LCS::ContextChange.simplify(event)
  end
end