JSON transform example

expect.txt

person1
  a1
    b1
      2021-11-01 - 2021-11-07 (2021-11-01 - 2021-11-03): c1
      2021-11-01 - 2021-11-07 (2021-11-02 - ): c2
person2
  a1
    b2
      2021-11-01 - 2021-11-07 ( - ): c2
    b3
      2021-11-01 - 2021-11-07 ( - ): c3

task_notifier.rb

require "json"

Task = Struct.new(:task1, :task2, :task3, :task4,
                  :assignee1, :assignee2, :assignee3,
                  :startDate, :endDate, :actStartDate, :actEndDate) do
          def self.new(hash)
            obj = self.allocate
            hash.each_with_object(obj) {|(k, v), o| o[k] = v}
            obj
          end
          def to_s
            "#{self.startDate} - #{self.endDate} (#{self.actStartDate} - #{self.actEndDate}): #{self.task3}"
          end
       end

class TaskNotifier
  def initialize(file)
    tasks_json = File.read(file)

    @tasks = JSON.load(tasks_json)["data"].map {|hash|
      Task.new hash
    }

    @root = _treeize([:assignee1, :task1, :task2], @tasks)
  end

  def _treeize(keys, tasks)
    k = keys.first
    o = tasks.group_by {|o| o[keys.first]}
    if keys.size > 1
      o.each {|k, v|
        o[k] = _treeize(keys.drop(1), v)
      }
    end
    return o
  end

  def walk(&block)
    _walk(@root, 0, &block)
  end

  def _walk(node, level = 0, &block)
    if Hash === node
      # Tree
      node.each {|k, v|
        block.call :node, level, k
        _walk(v, level + 1, &block)
      }
    else
      # Leaf
      node.each {|v|
        block.call :leaf, level, v
      }
    end
  end
end

def main(out = STDOUT)
  obj = TaskNotifier.new("tasks.json")

  obj.walk do |type, level, value|
    out.print "  " * level, value
    out.puts
  end
end

if __FILE__ == $0
  main
end

tasks.json

{
  "projectId": "12345",
  "data": [
    {"task1": "a1", "task2": "b1", "task3": "c1", "task4": "",
      "assignee1": "person1", "assignee2": "person2", "assignee3": "",
      "startDate": "2021-11-01", "endDate": "2021-11-07", "actStartDate": "2021-11-01", "actEndDate": "2021-11-03"},
    {"task1": "a1", "task2": "b1", "task3": "c2", "task4": "",
      "assignee1": "person1", "assignee2": "person2", "assignee3": "",
      "startDate": "2021-11-01", "endDate": "2021-11-07", "actStartDate": "2021-11-02", "actEndDate": ""},
    {"task1": "a1", "task2": "b2", "task3": "c2", "task4": "",
      "assignee1": "person2", "assignee2": "", "assignee3": "",
      "startDate": "2021-11-01", "endDate": "2021-11-07", "actStartDate": "", "actEndDate": ""},
    {"task1": "a1", "task2": "b3", "task3": "c3", "task4": "",
      "assignee1": "person2", "assignee2": "", "assignee3": "",
      "startDate": "2021-11-01", "endDate": "2021-11-07", "actStartDate": "", "actEndDate": ""}
  ]
}

test_task_notifier.rb

require "minitest/autorun"
require_relative 'task_notifier'

$expect = File.read('expect.txt')

class Test < MiniTest::Test
  def setup
    require "stringio"
    @out = StringIO.new
    main @out
    @out.rewind
  end
  def test_
    assert_equal $expect, @out.read
  end
end