# Methods added to this helper will be available to all templates in the application.
module ApplicationHelper
  # Display a start/end datetime span in human readable form. If 
  # both are given, ' to ' is placed in the middle of the string.
  # 
  # +start_datetime+ is a Datetime instance, 
  # +end_datetime+ is optional.
  def datetime_span(start_datetime, end_datetime=nil)
    str = start_datetime.strftime('%Y-%m-%d@%H:%M')
    if end_datetime
      str += ' to ' + end_datetime.strftime('%Y-%m-%d@%H:%M')
    end
    str
  end
  
  # Display a default message for empty fields.
  # +field_value+ is the value to process.
  def d(field_value=nil)
    if field_value.blank?
      return content_tag('em', 'not specified')
    else
      return field_value
    end
  end
  
  # Display date in human-readable format, e.g. "8th January 1968".
  #
  # Returns +nil+ if +date_to_format+ is blank.
  def human_date(date_to_format)
    if date_to_format.blank?
      out = nil
    else
      # Get the day part of the date with
      # the "ordinal suffix" (th, rd, nd) appended
      day = date_to_format.day.ordinalize

      # strftime accepts a formatting string, which specifies
      # which parts of the date to include in the output string
      out = date_to_format.strftime("#{day} %B %Y")
    end
    
    out
  end
  
  # Display +field_value+ followed by a <br> element,
  # but only if +field_value+ is set; otherwise returns nil.
  def field_with_break(field_value)
    unless field_value.blank?
      return field_value + tag('br')
    else
      return nil
    end
  end

  # ... other helpers ...

  # Format a label element for a form field.
  # 
  # +options+ can include:
  # 
  # [:required] If +true+, an asterisk is added to the label.
  # [:field_name] If true, the for attribute on the label 
  #               is set from +model+ + +field_name+; 
  #               otherwise, for attribute is set from 
  #               +model+ + lowercased and underscored +label_text+.
  # 
  # Example call:
  #   label(:person, 'Email')
  # 
  # Example output:
  #   <strong><label for="person_email">Email</label>:</strong>
  def label(model, label_text, options={})
    # Use the field_name option if supplied
    field_name = options[:field_name]
    field_name ||= label_text.gsub(' ', '_')
    
    # The value for the for attribute.
    label_for = (model.to_s + '_' + field_name).downcase
    # The <label> tag
    label_tag = content_tag('label', label_text, :for => label_for)
    # Add an asterisk if :required option specified.
    label_tag += '*' if options[:required]
    # Finish off the label.
    label_tag += ':'
    
    # Wrap the <label> tag in a <strong> tag.
    content_tag('strong', label_tag)
  end
end