Record to be used like the ActiveRecord::Base class

record.rb

# You can use a global variable, DB, which
# is an instance of SQLite3::Database
# NO NEED TO CREATE IT, JUST USE IT.

require 'sqlite3'
require 'pry-byebug'

db_file_path = File.join(File.dirname(__FILE__), "../../spec/support/posts_spec.db")
DB = SQLite3::Database.new(db_file_path)
DB.results_as_hash = true

class Record
  def self.inherited(base)
    base_table_name = "#{base.name.downcase.split(/\s/).join('_')}s"
    base.class.class_eval { attr_accessor :table_name }
    base.table_name = base_table_name

    table_columns = DB.execute("PRAGMA table_info(#{base_table_name})")

    table_columns.each do |column|
      column_name = column[1].gsub(/\s/, '_')

      define_method(column_name) do
        instance_variable_get("@#{column_name}")
      end

      define_method("#{column_name}=") do |value|
        instance_variable_set("@#{column_name}", value)
      end
    end
  end

  def initialize(attributes = {})
    attributes.each { |key, value| send("#{key}=", value) }
  end

  def self.all
    DB.execute("SELECT * FROM #{table_name}").map { |row| new(row) }
  end

  def self.find(id)
    row = DB.execute("SELECT * FROM #{table_name} WHERE id = ? LIMIT 1", id).first

    return unless row

    new(row)
  end

  def save
    new? ? create : update
  end

  def destroy
    DB.execute("DELETE FROM #{table_name} WHERE id = ?", @id)
  end

  def new?
    @id.nil?
  end

  def table_name
    self.class.table_name
  end

  # Returns an array with all the field names except id
  def field_names
    names = instance_variables.map { |var| var.to_s.sub('@', '') }
    names.delete('id')
    names
  end

  def fields_string
    "(#{field_names.join(', ')})"
  end

  def values_string
    value_count = instance_variables.size

    placeholders = Array.new(3) { '?' }

    "VALUES (#{placeholders.join(', ')})"
  end

  def update_string
    string = field_names.map { |field| "#{field} = ?" }

    "#{string.join(', ')} WHERE id = ?"
  end

  def all_values
    field_names.map { |field| send(field) }
  end

  def create
    DB.execute("INSERT INTO #{table_name} #{fields_string} #{values_string}", *all_values)
    @id = DB.last_insert_row_id

    self
  end

  def update
    DB.execute("UPDATE #{table_name} SET #{update_string}", *all_values, id)

    self
  end
end