require "grit"

module Graph
  class JsonBuilder
    attr_accessor :days, :commits, :ref_cache, :repo

    def self.max_count
      @max_count ||= 650
    end

    def initialize project, ref, commit
      @project = project
      @ref = ref
      @commit = commit
      @repo = project.repo
      @ref_cache = {}

      @commits = collect_commits
      @days = index_commits
    end

    def to_json(*args)
      {
        days: @days.compact.map { |d| [d.day, d.strftime("%b")] },
        commits: @commits.map(&:to_graph_hash)
      }.to_json(*args)
    end

  protected

    # Get commits from repository
    #
    def collect_commits

      @commits = Grit::Commit.find_all(repo, nil, {date_order: true, max_count: self.class.max_count, skip: to_commit}).dup

      # Decorate with app/models/commit.rb
      @commits.map! { |commit| Commit.new(commit) }

      # Decorate with lib/gitlab/graph/commit.rb
      @commits.map! { |commit| Graph::Commit.new(commit) }

      # add refs to each commit
      @commits.each { |commit| commit.add_refs(ref_cache, repo) }

      @commits
    end

    # Method is adding time and space on the
    # list of commits. As well as returns date list
    # corelated with time set on commits.
    #
    # @param [Array<Graph::Commit>] commits to index
    #
    # @return [Array<TimeDate>] list of commit dates corelated with time on commits
    def index_commits
      days, times = [], []
      map = {}

      commits.reverse.each_with_index do |c,i|
        c.time = i
        days[i] = c.committed_date
        map[c.id] = c
        times[i] = c
      end

      @_reserved = {}
      days.each_index do |i|
        @_reserved[i] = []
      end

      commits_sort_by_ref.each do |commit|
        if map.include? commit.id then
          place_chain(map[commit.id], map)
        end
      end

      # find parent spaces for not overlap lines
      times.each do |c|
        c.parent_spaces.concat(find_free_parent_spaces(c, map, times))
      end

      days
    end

    # Skip count that the target commit is displayed in center.
    def to_commit
      commits = Grit::Commit.find_all(repo, nil, {date_order: true})
      commit_index = commits.index do |c|
        c.id == @commit.id
      end

      if commit_index && (self.class.max_count / 2 < commit_index) then
        # get max index that commit is displayed in the center.
        commit_index - self.class.max_count / 2
      else
        0
      end
    end

    def commits_sort_by_ref
      commits.sort do |a,b|
        if include_ref?(a)
          -1
        elsif include_ref?(b)
          1
        else
          b.committed_date <=> a.committed_date
        end
      end
    end

    def include_ref?(commit)
      heads = commit.refs.select do |ref|
        ref.is_a?(Grit::Head) or ref.is_a?(Grit::Remote) or ref.is_a?(Grit::Tag)
      end

      heads.map! do |head|
        head.name
      end

      heads.include?(@ref)
    end

    def find_free_parent_spaces(commit, map, times)
      spaces = []

      commit.parents.each do |p|
        if map.include?(p.id) then
          parent = map[p.id]

          range = if commit.time < parent.time then
                    commit.time..parent.time
                  else
                    parent.time..commit.time
                  end

          space = if commit.space >= parent.space then
                    find_free_parent_space(range, parent.space, -1, commit.space, times)
                  else
                    find_free_parent_space(range, commit.space, -1, parent.space, times)
                  end

          mark_reserved(range, space)
          spaces << space
        end
      end

      spaces
    end

    def find_free_parent_space(range, space_base, space_step, space_default, times)
      if is_overlap?(range, times, space_default) then
        find_free_space(range, space_base, space_step, space_default)
      else
        space_default
      end
    end

    def is_overlap?(range, times, overlap_space)
      range.each do |i|
        if i != range.first &&
          i != range.last &&
          times[i].space == overlap_space then

          return true;
        end
      end

      false
    end

    # Add space mark on commit and its parents
    #
    # @param [Graph::Commit] the commit object.
    # @param [Hash<String,Graph::Commit>] map of commits
    def place_chain(commit, map, parent_time = nil)
      leaves = take_left_leaves(commit, map)
      if leaves.empty?
        return
      end
      # and mark it as reserved
      min_time = leaves.last.time
      max_space = 1
      parents = leaves.last.parents.collect
      parents.each do |p|
        if map.include? p.id
          parent = map[p.id]
          if parent.time < min_time
            min_time = parent.time
          end
          if max_space < parent.space then
            max_space = parent.space
          end
        end
      end
      if parent_time.nil?
        max_time = leaves.first.time
      else
        max_time = parent_time - 1
      end

      time_range = leaves.last.time..leaves.first.time
      space = find_free_space(time_range, max_space, 2)
      leaves.each{|l| l.space = space}

      mark_reserved(min_time..max_time, space)

      # Visit branching chains
      leaves.each do |l|
        parents = l.parents.collect.select{|p| map.include? p.id and map[p.id].space.zero?}
        for p in parents
          place_chain(map[p.id], map, l.time)
        end
      end
    end

    def mark_reserved(time_range, space)
      for day in time_range
        @_reserved[day].push(space)
      end
    end

    def find_free_space(time_range, space_base, space_step, space_default = 1)
      reserved = []
      for day in time_range
        reserved += @_reserved[day]
      end
      reserved.uniq!

      space = space_default
      while reserved.include?(space) do
        space += space_step
        if space < space_base then
          space_step *= -1
          space = space_base + space_step
        end
      end

      space
    end

    # Takes most left subtree branch of commits
    # which don't have space mark yet.
    #
    # @param [Graph::Commit] the commit object.
    # @param [Hash<String,Graph::Commit>] map of commits
    #
    # @return [Array<Graph::Commit>] list of branch commits
    def take_left_leaves(commit, map)
      leaves = []
      leaves.push(commit) if commit.space.zero?

      while true
        return leaves if commit.parents.count.zero?
        return leaves unless map.include? commit.parents.first.id

        commit = map[commit.parents.first.id]

        return leaves unless commit.space.zero?

        leaves.push(commit)
      end
    end
  end
end