#!/usr/bin/perl
# Copyright 2015 Jeffrey Kegler
# This file is part of Marpa::R2.  Marpa::R2 is free software: you can
# redistribute it and/or modify it under the terms of the GNU Lesser
# General Public License as published by the Free Software Foundation,
# either version 3 of the License, or (at your option) any later version.
#
# Marpa::R2 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
# Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser
# General Public License along with Marpa::R2.  If not, see
# http://www.gnu.org/licenses/.

=head1 Name

C<html_score> - Show complexity metric and other stats for web page

=head1 Synopsis

=for Marpa::R2::Display
ignore: 1

    html_score [--html] [uri|file]

=for Marpa::R2::Display::End

=head1 Examples

=for Marpa::R2::Display
ignore: 1

    html_score http://perl.org

    html_score --html http://perl6.org

=for Marpa::R2::Display::End

=head1 Description

Given a URI or a file name,
treats its referent as HTML
and prints a complexity metric,
the maximum element depth, and per-element statistics.
The per-element statistics appear in rows, one per tag name.
For each tag name, its row contains:

=over 4

=item *
The maximum nesting depth of elements with
that tag name.
This is per-tag-name nesting depth,
and does not take
into account nesting within other elements with
other tag names.

=item *
A count of the elements with that tag name in the document.

=item *
The total number of characters in elements with that tag name.
Characters in nested elements are counted multiple times.
For example, if a page contains a table within a table,
characters in the inner table will be counted twice.

=item *
The average size of elements with this tag name, in characters.

=back

The argument to L<html_score> can be either a URI or a file
name.  If it starts with alphanumerics followed by a colon, it is treated
as a URI.  Otherwise it is treated as file name.
If the C<--html> option is specified, the output is written
as an HTML table.

The complexity metric is the average depth (or nesting level), in elements, of a character,
divided by the logarithm of the length of the HTML.
Whitespace and comments are ignored in calculating the complexity metric.
The division by the logarithm of the HTML length is based on the idea that,
all else being equal,
it is reasonable for the nesting to increase logarithmically as
a web page grows in length.

=head1 Sample output

Here is the first part of the output for C<http://perl.org>.

=for Marpa::R2::Display
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    http://perl.org
    Complexity Score = 0.873
    Maximum Depth = 12
                  Maximum   Number of  Size in      Average
       Element    Nesting   Elements  Characters     Size  
    a                    1         56       3533         63
    body                 1          1       7615       7615
    div                  5         30      24695        823
    em                   1          1         13         13
    h1                   1          1         37         37
    h4                   1         11        559         50

=for Marpa::R2::Display::End

=head1 Interpreting the complexity metric

With caution,
the complexity metric can be used as a self-assessment
of website quality.
Well designed websites often have low numbers,
particularly if fast loading is an important goal.
But high values of the complexity metric do not necessarily mean low quality.
Everything depends on what the mission is, and how well
complexity is being used to serve the site's mission.

=head1 Purpose

This program is a demo of a demo.
It purpose is to show how easy it is to write applications which look
at the structure of web pages using L<Marpa::R2::HTML>.
And the purpose of L<Marpa::R2::HTML>
is to demonstrate the power of its parse engine,
L<Marpa::R2>.
L<Marpa::R2::HTML> was written in a few days,
and its logic 
is a straightforward,
natural expression of the structure of HTML.

=head1 Acknowledgements

The starting template for this code was
L<HTML::TokeParser>, by Gisle Aas.

=head1 Copyright and License

=for Marpa::R2::Display
ignore: 1

  Copyright 2015 Jeffrey Kegler
  This file is part of Marpa::R2.  Marpa::R2 is free software: you can
  redistribute it and/or modify it under the terms of the GNU Lesser
  General Public License as published by the Free Software Foundation,
  either version 3 of the License, or (at your option) any later version.

  Marpa::R2 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
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser
  General Public License along with Marpa::R2.  If not, see
  http://www.gnu.org/licenses/.

=for Marpa::R2::Display::End

=cut