require_relative '../db_connection'
require_relative '../student'
require_relative '../student_short'
require_relative '../data_list_student_short'
require 'date'

class StudentsListDB
  def initialize
    @db = DatabaseConnection.instance
  end

  # Получить объект Student по ID.
  def get_student_by_id(id)
    result = @db.query("SELECT * FROM student WHERE id = #{id} LIMIT 1")
    row = result.first
    row ? row_to_student(row) : nil
  end

  # Получить список из k студентов (страница n) в виде объекта DataList.
  def get_k_n_student_short_list(k, n)
    offset = (n - 1) * k
    results = @db.query("SELECT * FROM student ORDER BY surname, name, patronymic LIMIT #{k} OFFSET #{offset}")
    student_shorts = results.map { |row| StudentShort.from_student(row_to_student(row)) }
    DataListStudentShort.new(student_shorts)
  end

  # Добавить объект Student в БД (ID формируется автоматически).
  def add_student(student)
    sql = <<~SQL
      INSERT INTO student (git, surname, name, patronymic, birth_date, phone, telegram, email)
      VALUES (
        '#{escape(student.git)}',
        '#{escape(student.surname)}',
        '#{escape(student.name)}',
        '#{escape(student.patronymic)}',
        '#{student.birth_date}',
        #{student.phone ? "'#{escape(student.phone)}'" : "NULL"},
        #{student.telegram ? "'#{escape(student.telegram)}'" : "NULL"},
        #{student.email ? "'#{escape(student.email)}'" : "NULL"}
      )
    SQL

    @db.query(sql)
    new_id = @db.query("SELECT LAST_INSERT_ID() as id").first['id']
    student.id = new_id.to_s
    student
  end

  # Обновить студента по ID.
  def update_student_by_id(id, new_student)
    sql = <<~SQL
      UPDATE student SET 
        git = '#{escape(new_student.git)}',
        surname = '#{escape(new_student.surname)}',
        name = '#{escape(new_student.name)}',
        patronymic = '#{escape(new_student.patronymic)}',
        birth_date = '#{new_student.birth_date}',
        phone = #{new_student.phone ? "'#{escape(new_student.phone)}'" : "NULL"},
        telegram = #{new_student.telegram ? "'#{escape(new_student.telegram)}'" : "NULL"},
        email = #{new_student.email ? "'#{escape(new_student.email)}'" : "NULL"}
      WHERE id = #{id}
    SQL

    @db.query(sql)
    @db.client.affected_rows > 0
  end

  # Удалить студента по ID.
  def delete_student_by_id(id)
    @db.query("DELETE FROM student WHERE id = #{id}")
    @db.client.affected_rows > 0
  end

  # Получить количество студентов.
  def get_student_short_count
    result = @db.query("SELECT COUNT(*) as count FROM student")
    result.first['count']
  end

  private

  # Преобразование строки результата в объект Student.
  def row_to_student(row)
    Student.new(
      id:         row['id'].to_s,
      git:        row['git'],
      surname:    row['surname'],
      name:       row['name'],
      patronymic: row['patronymic'],
      birth_date: Date.parse(row['birth_date'].to_s),
      phone:      row['phone'],
      telegram:   row['telegram'],
      email:      row['email']
    )
  end

  # Простой метод для экранирования строк (на практике лучше использовать подготовленные выражения).
  def escape(value)
    @db.client.escape(value.to_s)
  end
end