Class: Nanoc3::Filter Abstract

Inherits:
Context show all
Extended by:
PluginRegistry::PluginMethods
Defined in:
lib/nanoc3/base/compilation/filter.rb

Overview

This class is abstract.

Subclass and override #run to implement a custom filter.

Nanoc3::Filter is responsible for filtering items. It is the superclass for all textual filters.

A filter instance should only be used once. Filters should not be reused since they store state.

When creating a filter with a hash containing assigned variables, those variables will be made available in the ‘@assigns` instance variable and the #assigns method. The assigns itself will also be available as instance variables and instance methods.

Examples:

Accessing assigns in different ways


filter = SomeFilter.new({ :foo => 'bar' })
filter.instance_eval { @assigns[:foo] }
  # => 'bar'
filter.instance_eval { assigns[:foo] }
  # => 'bar'
filter.instance_eval { @foo }
  # => 'bar'
filter.instance_eval { foo }
  # => 'bar'

Constant Summary collapse

TMP_BINARY_ITEMS_DIR =

The path to the directory where temporary binary items are stored

'tmp/binary_items'

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from PluginRegistry::PluginMethods

identifier, identifiers, named, register

Methods inherited from Context

#get_binding

Constructor Details

#initialize(hash = {}) ⇒ Filter

Creates a new filter that has access to the given assigns.

Parameters:

  • hash (Hash) (defaults to: {}) —

    A hash containing variables that should be made available during filtering.



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# File 'lib/nanoc3/base/compilation/filter.rb', line 86

def initialize(hash={})
  @assigns = hash
  super
end

Instance Attribute Details

#assigns ⇒ Hash (readonly)

A hash containing variables that will be made available during filtering.

Returns:



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# File 'lib/nanoc3/base/compilation/filter.rb', line 38

def assigns
  @assigns
end

Class Method Details

.from_binary? ⇒ Boolean

Returns True if this filter can be applied to binary item representations, false otherwise.

Returns:

  • (Boolean) —

    True if this filter can be applied to binary item representations, false otherwise



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# File 'lib/nanoc3/base/compilation/filter.rb', line 70

def from_binary?
  (@from || :text) == :binary
end

.to_binary? ⇒ Boolean

Returns True if this filter results in a binary item representation, false otherwise.

Returns:

  • (Boolean) —

    True if this filter results in a binary item representation, false otherwise



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# File 'lib/nanoc3/base/compilation/filter.rb', line 76

def to_binary?
  (@to || :text) == :binary
end

.type(arg) ⇒ void

This method returns an undefined value.

Sets the new type for the filter. The type can be ‘:binary` (default) or `:text`. The given argument can either be a symbol indicating both “from” and “to” types, or a hash where the only key is the “from” type and the only value is the “to” type.

Examples:

Specifying a text-to-text filter


type :text

Specifying a text-to-binary filter


type :text => :binary

Parameters:

  • arg (Symbol, Hash) —

    The new type of this filter



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# File 'lib/nanoc3/base/compilation/filter.rb', line 60

def type(arg)
  if arg.is_a?(Hash)
    @from, @to = arg.keys[0], arg.values[0]
  else
    @from, @to = arg, arg
  end
end

Instance Method Details

#depend_on(items) ⇒ void

This method returns an undefined value.

Creates a dependency from the item that is currently being filtered onto the given collection of items. In other words, require the given items to be compiled first before this items is processed.

Parameters:



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# File 'lib/nanoc3/base/compilation/filter.rb', line 149

def depend_on(items)
  # Notify
  items.each do |item|
    Nanoc3::NotificationCenter.post(:visit_started, item)
    Nanoc3::NotificationCenter.post(:visit_ended,   item)
  end

  # Raise unmet dependency error if necessary
  items.each do |item|
    rep = item.reps.find { |r| !r.compiled? }
    raise Nanoc3::Errors::UnmetDependency.new(rep) if rep
  end
end

#filename ⇒ String

Returns the filename associated with the item that is being filtered.

It is in the format `item <identifier> (rep <name>)`.

Returns:



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# File 'lib/nanoc3/base/compilation/filter.rb', line 132

def filename
  if assigns[:layout]
    "layout #{assigns[:layout].identifier}"
  elsif assigns[:item]
    "item #{assigns[:item].identifier} (rep #{assigns[:item_rep].name})"
  else
    '?'
  end
end

#output_filename ⇒ String

Returns a filename that is used to write data to. This method is only

used on binary items. When running a binary filter on a file, the
resulting file must end up in the location returned by this method.

The returned filename will be absolute, so it is safe to change to

another directory inside the filter.

Returns:

  • (String) —

    The output filename



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# File 'lib/nanoc3/base/compilation/filter.rb', line 117

def output_filename
  @output_filename ||= begin
    FileUtils.mkdir_p(TMP_BINARY_ITEMS_DIR)
    tempfile = Tempfile.new(filename.gsub(/[^a-z]/, '-'), TMP_BINARY_ITEMS_DIR)
    new_filename = tempfile.path
    tempfile.close!

    File.expand_path(new_filename)
  end
end

#run(content_or_filename, params = {}) ⇒ String, void

This method is abstract.

Runs the filter on the given content or filename.

Parameters:

  • content_or_filename (String) —

    The unprocessed content that should be filtered (if the item is a textual item) or the path to the file that should be filtered (if the item is a binary item)

  • params (Hash) (defaults to: {}) —

    A hash containing parameters. Filter subclasses can use these parameters to allow modifying the filter’s behaviour.

Returns:

  • (String, void) —

    If the filter output binary content, the return value is undefined; if the filter outputs textual content, the return value will be the filtered content.

Raises:

  • (NotImplementedError) 


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# File 'lib/nanoc3/base/compilation/filter.rb', line 105

def run(content_or_filename, params={})
  raise NotImplementedError.new("Nanoc3::Filter subclasses must implement #run")
end