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module ActiveSupport
# \FileUpdateChecker specifies the API used by Rails to watch files
# and control reloading. The API depends on four methods:
#
# * +initialize+ which expects two parameters and one block as
# described below;
#
# * +updated?+ which returns a boolean if there were updates in
# the filesystem or not;
#
# * +execute+ which executes the given block on initialization
# and updates the latest watched files and timestamp;
#
# * +execute_if_updated+ which just executes the block if it was updated;
#
# After initialization, a call to +execute_if_updated+ must execute
# the block only if there was really a change in the filesystem.
#
# == Examples
#
# This class is used by Rails to reload the I18n framework whenever
# they are changed upon a new request.
#
# i18n_reloader = ActiveSupport::FileUpdateChecker.new(paths) do
# I18n.reload!
# end
#
# ActionDispatch::Reloader.to_prepare do
# i18n_reloader.execute_if_updated
# end
#
class FileUpdateChecker
# It accepts two parameters on initialization. The first is an array
# of files and the second is an optional hash of directories. The hash must
# have directories as keys and the value is an array of extensions to be
# watched under that directory.
#
# This method must also receive a block that will be called once a path changes.
#
# == Implementation details
#
# This particular implementation checks for added, updated, and removed
# files. Directories lookup are compiled to a glob for performance.
# Therefore, while someone can add new files to the +files+ array after
# initialization (and parts of Rails do depend on this feature), adding
# new directories after initialization is not supported.
#
# Notice that other objects that implement the FileUpdateChecker API may
# not even allow new files to be added after initialization. If this
# is the case, we recommend freezing the +files+ after initialization to
# avoid changes that won't make effect.
def initialize(files, dirs={}, &block)
@files = files
@glob = compile_glob(dirs)
@block = block
@last_watched = watched
@last_update_at = updated_at(@last_watched)
end
# Check if any of the entries were updated. If so, the watched and/or
# updated_at values are cached until the block is executed via +execute+
# or +execute_if_updated+
def updated?
current_watched = watched
if @last_watched.size != current_watched.size
@watched = current_watched
true
else
current_updated_at = updated_at(current_watched)
if @last_update_at < current_updated_at
@watched = current_watched
@updated_at = current_updated_at
true
else
false
end
end
end
# Executes the given block and updates the latest watched files and timestamp.
def execute
@last_watched = watched
@last_update_at = updated_at(@last_watched)
@block.call
ensure
@watched = nil
@updated_at = nil
end
# Execute the block given if updated.
def execute_if_updated
if updated?
execute
true
else
false
end
end
private
def watched
@watched || begin
all = @files.select { |f| File.exists?(f) }
all.concat(Dir[@glob]) if @glob
all
end
end
def updated_at(paths)
@updated_at || paths.map { |path| File.mtime(path) }.max || Time.at(0)
end
def compile_glob(hash)
hash.freeze # Freeze so changes aren't accidently pushed
return if hash.empty?
globs = hash.map do |key, value|
"#{escape(key)}/**/*#{compile_ext(value)}"
end
"{#{globs.join(",")}}"
end
def escape(key)
key.gsub(',','\,')
end
def compile_ext(array)
array = Array(array)
return if array.empty?
".{#{array.join(",")}}"
end
end
end
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