# SPDX-FileCopyrightText: 2024 Xavier Bordoy
#
# SPDX-License-Identifier: GPL-2.0-or-later

require 'erb'

# It tries to model the automatic exercise.
#
# For us, an automatic exercise is some kind of information, stored in a ruby Hash called `contents` which is evaluated with some substitutions.
#
# The exercise could have some conditions to be satisfied in order to evaluate the susbtitutions (also known as assignments). These substitutions provide different instances of the same kind of exercise. By this way, the same question or problem is posed but the concrete numbers and information within are different everytime.
#
# We use [ERB](ihttps://docs.ruby-lang.org/en/master/ERB.html) to make substitutions.
#
# ## Example
#
# If we want to create an exercise for students to simply asks "What is a + b?", where ``a`` and ``b`` are arbitrary positive integer numbers, then we could model as this:
#
# ```
# require_relative automathlib
# e = automathlib.AutomaticExercise.new({:text => "Sum <%=a%>+<%=b%>", :solution => "<%=a+b%>", :conditions => "<%=a%> > 0 and <%=b%> > 0"})
# puts e.satisfied_conditions({:a => 5, :b => 3})
# # returns true
# puts e.numeric_value({:a => 2, :b=>3})
# # returns 5
# ```
#
class AutomaticExercise
  
  attr_accessor :info

  def initialize(info)
    @info = info
  end

  def conditions
    if @info.has_key?(:conditions)
      return @info[:conditions]
    else
      return nil
    end
  end

  def satisfied_conditions(assignments)
    return eval(ERB.new(self.conditions).result_with_hash(assignments))
  end

  # Replace variables with assignments
  #
  # == Parameters:
  # assignments::
  #  A Hash declaring the assignments or susbtitutions to apply
  #
  # == Returns: 
  # A Hash or nil. The variables with assignments applied. It returns nil if substitutions are not possible to apply to
  def numeric_value(assignments)
    if self.conditions != nil
      if self.satisfied_conditions(assignments) != true
        return nil
      end
    end

    r = Hash.new

    @info.keys.each do |k|
      r[k] = ERB.new(@info[k]).result_with_hash(assignments)
    end

    return r

  end

end