# Fat Free CRM
# Copyright (C) 2008-2011 by Michael Dvorkin
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#------------------------------------------------------------------------------

# == Schema Information
#
# Table name: fields
#
#  id             :integer         not null, primary key
#  type           :string(255)
#  field_group_id :integer
#  position       :integer
#  name           :string(64)
#  label          :string(128)
#  hint           :string(255)
#  placeholder    :string(255)
#  as             :string(32)
#  collection     :text
#  disabled       :boolean
#  required       :boolean
#  maxlength      :integer
#  created_at     :datetime
#  updated_at     :datetime
#

# Implementation Notes
#------------------------------------------------------------------------------
# Adding database columns dynamically is not usually recommended,
# and can be potentially unsafe. However, the only alternative would be static migrations,
# and we want to let users add custom fields without having to restart their server.
# We could not use the EAV model for performance reasons, since we need to retain the
# ability to filter and search across thousands of records with potentially hundreds
# of custom fields.
#
# We have solved all of the major issues:
#
# * Custom fields for view templates are dynamically generated based on normalized
#   database records in the 'fields' table, instead of ActiveRecord's cached attributes.
# * Concurrency issues are resolved by using 'method_missing' to refresh a model's column information
#   when fields are added by a separate server process.
# * The custom field can be renamed or deleted, but database columns are never renamed or destroyed.
#   A rake task can be run to purge any orphaned columns.
# * Custom field types can only be changed if the database can support the transition.
#   For example, you can change an 'email' field to a 'string', but not to a 'datetime',
#   since changing the type of the database column would cause data to be lost.
#

class CustomField < Field
  after_validation :update_column, :on => :update
  before_create    :add_column

  SAFE_DB_TRANSITIONS = {
    :any => [[:date, :time, :timestamp], [:integer, :float]],
    :one => {:string => :text}
  }

  def available_as
    Field.field_types.reject do |new_type, params|
      db_transition_safety(as, new_type) == :unsafe
    end
  end

protected

  # When changing a custom field's type, it may be necessary to
  # change the column type in the database. This method returns
  # the safety of a given transition.
  # Returns:
  #   :null   => no transition needed
  #   :safe   => transition is safe
  #   :unsafe => transition is unsafe
  def db_transition_safety(old_type, new_type = self.as)
    old_col, new_col = [old_type, new_type].map{|t| column_type(t) }
    return :null if old_col == new_col  # no transition needed
    return :safe if SAFE_DB_TRANSITIONS[:one].any? do |start, final|
      old_col == start && new_col == final  # one-to-one
    end
    return :safe if SAFE_DB_TRANSITIONS[:any].any? do |col_set|
      [old_col, new_col].all?{|c| col_set.include?(c)}  # any-to-any
    end
    :unsafe # Else, unsafe.
  end

  def table_name
    klass.table_name
  end

  def klass_column_names
    klass.columns.map(&:name)
  end

  def generate_column_name
    # Generate column name for custom field.
    # If column name is already taken, a numeric suffix is appended.
    # Example column sequence: cf_custom, cf_custom_2, cf_custom_3, ...
    suffix = nil
    field_name = 'cf_' + label.downcase.gsub(/[^a-z0-9]+/, '_')
    while (final_name = [field_name, suffix].compact.join('_')) &&
          klass_column_names.include?(final_name) do
      suffix = (suffix || 1) + 1
    end
    final_name
  end

  # Returns options for ActiveRecord operations
  def column_options
    Field.field_types[self.as][:options] || {}
  end

  def add_column
    self.name = generate_column_name if name.blank?
    connection.add_column(table_name, name, column_type, column_options)
    klass.reset_column_information
  end

  def update_column
    # Change database column type if appropriate
    # (NOTE: Columns will never be renamed or destroyed)
    if self.errors.empty? && db_transition_safety(as_was) == :safe
      connection.change_column(table_name, name, column_type, column_options)
      klass.reset_column_information
    end
  end
end