# Contains logic belonging to the +CourseSection+ model.
class CourseSection < ApplicationRecord
  # Each +CourseSection+ belongs to a +Course+ and an +Instructor+.
  belongs_to :course
  belongs_to :instructor

  # Ensure all necessary fields are present.
  validates :name, presence: true
  validates :crn, presence: true
  validates :title, presence: true
  validates :course_id, presence: true

  def labs
    return nil unless section_type == "Lecture"

    lecture_number = name.split[name.split.length - 1]
    course.course_sections.select do |s|
      s.title.split[s.title.split.length - 1] == lecture_number
    end
  end

  # Select all course sections that have an instructor that matches the given name
  def self.with_instructor(name: "")
    joins(:instructor).where("instructors.name LIKE ?", "%#{name}%").select('course_sections.*, instructors.name as instructor_name')
  end

  def self.from_crn(base_query, crn)
    base_query.where("course_sections.crn = ?", crn)
  end

  def self.from_course_id(base_query, course_id)
    base_query.where("course_sections.course_id = ?", course_id)
  end

  # Select all revelevant course sections given the provided filters
  def self.fetch(filters)
    query = CourseSection.joins(:course).select("course_sections.*")

    filters.each do |filter, value|
      case filter
      when "crn"
        query = from_crn(query, value)
      when "course_id"
        query = from_course_id(query, value)
      when "course_number"
        query = Course.from_course_number(query, value)
      when "subject"
        query = Course.from_subject(query, value)
      when "title"
        query = Course.from_title(query, value)
      end
    end

    query
  end
end