``diagrams``
============

This tool generates library, directory, file, entity, and predicate
diagrams for source files and for libraries of source files using the
Logtalk reflection API to collect the relevant information and a graph
language for representing the diagrams. Limited support is also
available for generating diagrams for Prolog module applications. It's
also possible in general to generate predicate cross-referencing
diagrams for plain Prolog files.

Linking library diagrams to entity diagrams to predicate
cross-referencing diagrams and linking directory diagrams to file
diagrams is also supported when using SVG output. This feature allows
using diagrams for navigating complex code by zooming into details. SVG
output can also easily link to both source code repositories and API
documentation. This allows diagrams to be used for source code
navigation.

Diagrams can also be used to uncover code issues. For example, comparing
loading diagrams with dependency diagrams can reveal implicit
dependencies. Loading diagrams can reveal circular dependencies that may
warrant code refactoring. Entity diagrams can provide a good overview of
code coupling. Predicate cross-referencing diagrams can be used to
access entity code complexity.

All diagrams support a comprehensive set of options, discussed below, to
customize the final contents and appearance.

Diagram generation can be easily automated using the ``doclet`` tool and
the ``logtalk_doclet`` script. See the ``doclet`` tool examples and
documentation for details. See also the ``diagrams`` tool ``lgt2svg``
script.

API documentation
-----------------

To consult this tool API documentation, open in a web browser the link:

`docs/library_index.html#diagrams <https://logtalk.org/docs/library_index.html#diagrams>`__

For sample queries, please see the `SCRIPT.txt <SCRIPT.txt>`__ file in
the tool directory.

Loading
-------

This tool can be loaded using the query:

::

   | ?- logtalk_load(diagrams(loader)).

Supported diagrams
------------------

The following entity diagrams are supported:

-  entity diagrams showing entity public interfaces, entity inheritance
   relations, and entity predicate cross-reference relations
-  predicate cross-reference diagrams (between entities or within an
   entity)
-  inheritance diagrams showing entity inheritance relations
-  uses diagrams showing which entities use resources from other
   entities

The following file diagrams are supported:

-  file loading diagrams showing which files load or include other files
-  file dependency diagrams showing which files contain entities with
   references to entities defined in other files

File dependency diagrams are specially useful in revealing dependencies
that are not represented in file loading diagrams due to files being
loaded indirectly by files external to the libraries being documented.

The following directory diagrams are supported:

-  directory loading diagrams showing which directories contain files
   that load files in other directories
-  directory dependency diagrams showing which directories contain
   entities with references to entities defined in other directories

The following library diagrams are supported:

-  library loading diagrams showing which libraries load other libraries
-  library dependency diagrams showing which libraries contain entities
   with references to entities defined in other libraries

Comparing directory (or file) loading diagrams with directory (or file)
dependency diagrams allows comparing what is explicitly loaded with the
actual directory (or file) dependencies, which are inferred from the
source code.

Library and directory dependency diagrams are specially useful for large
applications where file diagrams would be too large and complex to be
useful, specially when combined with the *zoom* option to link to,
respectively, entity and file diagrams.

A utility object, ``diagrams``, is provided for generating all supported
diagrams in one step. This object provides an interface common to all
diagrams but note that some predicates that generate diagrams only make
sense for some types of diagrams. For best results and fine-grained
customization of each diagram, the individual diagram objects should be
used.

Graph elements
--------------

Limitations in both the graph language and UML forces the invention of a
modeling language that can represent all kinds of Logtalk entities and
entity relations. Currently we use the following DOT shapes (libraries,
entities, predicates, and files) and arrows (entity, predicate, and file
relations):

-  | libraries
   | ``tab`` (lightsalmon)

-  | library loading and dependency relations
   | ``normal`` (arrow ending with a black triangle)

-  | objects (classes, instances, and prototypes)
   | ``box`` (rectangle, yellow for instances/classes and beige for
     prototypes)

-  | protocols
   | ``note`` (aqua marine rectangle with folded right-upper corners)

-  | categories
   | ``component`` (light cyan rectangle with two small rectangles
     intercepting the left side)

-  | modules
   | ``tab`` (plum rectangle with small tab at top)

-  | public predicates
   | ``box`` (springgreen)

-  | public, multifile, predicates
   | ``box`` (skyblue)

-  | protected predicates
   | ``box`` (yellow)

-  | private predicates
   | ``box`` (indianred)

-  | external predicates
   | ``box`` (beige)

-  | exported module predicates
   | ``box`` (springgreen)

-  | directories
   | ``tab`` (lightsalmon)

-  | directory loading and dependency relations
   | ``normal`` (arrow ending with a black triangle)

-  | files
   | ``box`` (pale turquoise rectangle)

-  | file loading and dependency relations
   | ``normal`` (arrow ending with a black triangle)

-  | specialization relation
   | ``onormal`` (arrow ending with a white triangle)

-  | instantiation relation
   | ``normal`` (arrow ending with a black triangle)

-  | extends relation
   | ``vee`` (arrow ending with a "v")

-  | implements relation
   | ``dot`` (arrow ending with a black circle)

-  | imports relation
   | ``box`` (arrow ending with a black square)

-  | complements relation
   | ``obox`` (arrow ending with a white square)

-  | uses and use module relations
   | ``rdiamond`` (arrow ending with a black half diamond)

-  | predicate calls
   | ``normal`` (arrow ending with a black triangle)

-  | dynamic predicate updates
   | ``diamond`` (arrow ending with a black diamond)

The library, directory, file, entity, and predicate nodes that are not
part of the predicates, entities, files, or libraries for which we are
generating a diagram use a dashed border, a darker color, and are
described as external.

Supported graph languages
-------------------------

Currently only the DOT graph language is supported (tested with Graphviz
version 2.40.1 on macOS; visit the
`http://www.graphviz.org/ <http://www.graphviz.org/>`__ website for more
information). Some recent versions have a nasty regression in the SVG
exporter where text overflows the boxes that should contain it. Also,
stable version 2.40.1 have a bug (fixed in the current git version) that
can result in very long edges.

The diagrams ``.dot`` files are created on the current directory by
default. These files can be easily converted into a printable format
such as SVG, PDF, or Postscript. For example, using the ``dot``
command-line executable we can simply type:

::

   dot -Tpdf diagram.dot > diagram.pdf

This usually works fine for entity and predicate call cross-referencing
diagrams. For directory and file diagrams, the ``fdp`` and ``circo``
command-line executables may produce better results. For example:

::

   fdp -Tsvg diagram.dot > diagram.pdf
   circo -Tsvg diagram.dot > diagram.pdf

It's also worth to experiment with different layouts to find the one
that produces the best results (see the ``layout/1`` option described
below).

Some output formats such as SVG support tooltips and URL links, which
can be used for showing e.g. entity types, relation types, file paths,
and for navigating to files and directories of files (libraries). See
the relevant diagram options below in order to take advantage of these
features.

Sample helper scripts are provided for converting ``.dot`` files to
``.svg`` files:

-  ``lgt2svg.sh`` for POSIX systems
-  ``lgt2svg.js`` and ``lgt2svg.bat`` for Windows systems

The scripts assume that the ``dot`` executable is available from the
system path. Due to the lack of a Graphviz installer for Windows,
limited test is performed in Windows operating-systems. Use if possible
the bash script in a POSIX system (macOS, Linux, BSD, ...).

When generating diagrams for multiple libraries or directories, it's
possible to split a diagram with several disconnected library or
directory graphs using the ``ccomps`` command-line executable. For
example:

::

   ccomps -x -o subdiagram.dot diagram.dot

For more information on the DOT language and related tools see:

::

   http://www.graphviz.org/

When using Windows, there are known issues with some Prolog compilers
due to the internal representation of paths. If you encounter problems
with a specific backend Prolog compiler, try to use another supported
backend Prolog compiler when generating diagrams.

For printing large diagrams, you will need to either use a tool to slice
the diagram in page-sized pieces or, preferably, use software capable of
tiled printing (e.g. Adobe Reader). You can also hand-edit the generated
``.dot`` files and play with settings such as aspect ratio for
fine-tuning the diagrams layout.

Customization
-------------

A set of options are available to specify the details to include in the
generated diagrams. For entity diagrams the options are:

-  | ``layout(Layout)``
   | diagram layout (one of the atoms
     ``{top_to_bottom,bottom_to_top,left_to_right,right_to_left}``;
     default is ``bottom_to_top``)

-  | ``title(Title)``
   | diagram title (an atom; default is ``''``)

-  | ``date(Boolean)``
   | print/omit current date and time (``true`` or ``false``; default is
     ``true``)

-  | ``interface(Boolean)``
   | print/omit public predicates (``true`` or ``false``; default is
     ``true``)

-  | ``file_labels(Boolean)``
   | print/omit file labels (``true`` or ``false``; default is ``true``)

-  | ``file_extensions(Boolean)``
   | print/omit file name extensions (``true`` or ``false``; default is
     ``true``)

-  | ``relation_labels(Boolean)``
   | print/omit entity relation labels (``true`` or ``false``; default
     is ``true``)

-  | ``externals(Boolean)``
   | print/omit external nodes (``true`` or ``false``; default is
     ``true``)

-  | ``node_type_captions(Boolean)``
   | print/omit node type captions (``true`` or ``false``; default is
     ``true``)

-  | ``inheritance_relations(Boolean)``
   | print/omit inheritance relations (``true`` or ``false``; default is
     ``true`` for entity inheritance diagrams and ``false`` for other
     entity diagrams)

-  | ``provide_relations(Boolean)``
   | print/omit provide relations (``true`` or ``false``; default is
     ``false``)

-  | ``xref_relations(Boolean)``
   | print/omit predicate call cross-reference relations (``true`` or
     ``false``; default depends on the specific diagram)

-  | ``xref_calls(Boolean)``
   | print/omit predicate cross-reference calls (``true`` or ``false``;
     default depends on the specific diagram)

-  | ``output_directory(Directory)``
   | directory for the .dot files (an atom; default is ``'./'``)

-  | ``exclude_directories(Directories)``
   | list of directories to exclude (default is ``[]``)

-  | ``exclude_files(Files)``
   | list of source files to exclude (default is ``[]``)

-  | ``exclude_libraries(Libraries)``
   | list of libraries to exclude (default is
     ``[startup, scratch_directory]``)

-  | ``exclude_entities(Entities)``
   | list of entities to exclude (default is ``[]``)

-  | ``path_url_prefixes(PathPrefix, CodeURLPrefix, DocURLPrefix)``
   | code and documenting URL prefixes for a path prefix used when
     generating cluster, library, directory, file, and entity links
     (atoms; no default; can be specified multiple times)

-  | ``url_prefixes(CodeURLPrefix, DocURLPrefix)``
   | default URL code and documenting URL prefixes used when generating
     cluster, library, file, and entity links (atoms; no default)

-  | ``entity_url_suffix_target(Suffix, Target)``
   | extension for entity documenting URLs (an atom; default is
     ``'.html'``) and target separating symbols (an atom; default is
     ``'#'``)

-  | ``omit_path_prefixes(Prefixes)``
   | omit common path prefixes when printing directory paths (a list of
     atoms; default is an empty list)

-  | ``zoom(Boolean)``
   | generate sub-diagrams and add links and zoom icons to library and
     entity nodes (``true`` or ``false``; default is ``false``)

-  | ``zoom_url_suffix(Suffix)``
   | extension for linked diagrams (an atom; default is ``'.svg'``)

In the particular case of cross-referencing diagrams, there is also the
option:

-  ``url_line_references(Host)``
   syntax for the URL source file line part (an atom; possible values
   are ``{github,gitlab,bitbucket}``; default is ``github``); when using
   this option, the ``CodeURLPrefix`` should be a permanent link (i.e.
   it should include the commit SHA1)

For directory and file diagrams the options are:

-  | ``layout(Layout)``
   | diagram layout (one of the atoms
     ``{top_to_bottom,bottom_to_top,left_to_right,right_to_left}``;
     default is ``top_to_bottom``)

-  | ``title(Title)``
   | diagram title (an atom; default is ``''``)

-  | ``date(Boolean)``
   | print/omit current date and time (``true`` or ``false``; default is
     ``true``)

-  | ``directory_paths(Boolean)``
   | print/omit file directory paths (``true`` or ``false``; default is
     ``false``)

-  | ``file_extensions(Boolean)``
   | print/omit file name extensions (``true`` or ``false``; default is
     ``true``)

-  | ``path_url_prefixes(PathPrefix, CodeURLPrefix, DocURLPrefix)``
   | code and documenting URL prefixes for a path prefix used when
     generating cluster, directory, file, and entity links (atoms; no
     default; can be specified multiple times)

-  | ``url_prefixes(CodeURLPrefix, DocURLPrefix)``
   | default URL code and documenting URL prefixes used when generating
     cluster, library, file, and entity links (atoms; no default)

-  | ``omit_path_prefixes(Prefixes)``
   | omit common path prefixes when printing directory paths (a list of
     atoms; default is an empty list)

-  | ``relation_labels(Boolean)``
   | print/omit entity relation labels (``true`` or ``false``; default
     is ``false``)

-  | ``externals(Boolean)``
   | print/omit external nodes (``true`` or ``false``; default is
     ``true``)

-  | ``node_type_captions(Boolean)``
   | print/omit node type captions (``true`` or ``false``; default is
     ``false``)

-  | ``output_directory(Directory)``
   | directory for the .dot files (an atom; default is ``'./'``)

-  | ``exclude_directories(Directories)``
   | list of directories to exclude (default is ``[]``)

-  | ``exclude_files(Files)``
   | list of source files to exclude (default is ``[]``)

-  | ``zoom(Boolean)``
   | generate sub-diagrams and add links and zoom icons to library and
     entity nodes (``true`` or ``false``; default is ``false``)

-  | ``zoom_url_suffix(Suffix)``
   | extension for linked diagrams (an atom; default is ``'.svg'``)

For library diagrams the options are:

-  | ``layout(Layout)``
   | diagram layout (one of the atoms
     ``{top_to_bottom,bottom_to_top,left_to_right,right_to_left}``;
     default is ``top_to_bottom``)

-  | ``title(Title)``
   | diagram title (an atom; default is ``''``)

-  | ``date(Boolean)``
   | print/omit current date and time (``true`` or ``false``; default is
     ``true``)

-  | ``directory_paths(Boolean)``
   | print/omit file directory paths (``true`` or ``false``; default is
     ``false``)

-  | ``path_url_prefixes(PathPrefix, CodeURLPrefix, DocURLPrefix)``
   | code and documenting URL prefixes for a path prefix used when
     generating cluster, library, file, and entity links (atoms; no
     default; can be specified multiple times)

-  | ``url_prefixes(CodeURLPrefix, DocURLPrefix)``
   | default URL code and documenting URL prefixes used when generating
     cluster, library, file, and entity links (atoms; no default)

-  | ``omit_path_prefixes(Prefixes)``
   | omit common path prefixes when printing directory paths (a list of
     atoms; default is an empty list)

-  | ``relation_labels(Boolean)``
   | print/omit entity relation labels (``true`` or ``false``; default
     is ``false``)

-  | ``externals(Boolean)``
   | print/omit external nodes (``true`` or ``false``; default is
     ``true``)

-  | ``node_type_captions(Boolean)``
   | print/omit node type captions (``true`` or ``false``; default is
     ``false``)

-  | ``output_directory(Directory)``
   | directory for the .dot files (an atom; default is ``'./'``)

-  | ``exclude_directories(Directories)``
   | list of directories to exclude (default is ``[]``)

-  | ``exclude_files(Files)``
   | list of source files to exclude (default is ``[]``)

-  | ``exclude_libraries(Libraries)``
   | list of libraries to exclude (default is
     ``[startup, scratch_directory]``)

-  | ``zoom(Boolean)``
   | generate sub-diagrams and add links and zoom icons to library and
     entity nodes (``true`` or ``false``; default is ``false``)

-  | ``zoom_url_suffix(Suffix)``
   | extension for linked diagrams (an atom; default is ``'.svg'``)

The option ``omit_path_prefixes(Prefixes)`` with a non-empty list of
prefixes should be used together with the option
``directory_paths(true)``, in particular when generating library,
directory, or file diagrams that reference external libraries,
directories, or files.

Be sure to set the ``source_data`` flag ``on`` before compiling the
libraries or files for which you want to generated diagrams.

Support for displaying Prolog modules and Prolog module files in
diagrams of Logtalk applications:

-  | ECLiPSe
   | file diagrams don't display module files

-  | SICStus Prolog
   | file diagrams don't display module files

-  | SWI-Prolog
   | full support (uses the SWI-Prolog ``prolog_xref`` library)

-  | YAP
   | full support (uses the YAP ``prolog_xref`` library)

Linking diagrams
----------------

When using SVG output, it's possible to generate diagrams that link to
other diagrams and also diagrams that link to API documentation and
source code repositories.

For generating links between diagrams, use the ``zoom(true)`` option.
This option allows (1) linking library diagrams to entity diagrams to
predicate cross-referencing diagrams and (2) linking directory diagrams
to file diagrams. The sub-diagrams are automatically generated. E.g.
using the predicates that generate library diagrams will automatically
also generate the entity and predicate cross-referencing diagrams. This
feature allows using diagrams for navigating complex code by zooming
into details.

To generate links to API documentation and source code repositories, use
the options ``path_url_prefixes/3`` (or ``url_prefixes/2`` for simpler
cases) and ``omit_path_prefixes/1``. The idea is that the
``omit_path_prefixes/1`` option specifies local file prefixes that will
be cut and replaced by the URL prefixes (which can be path prefix
specific when addressing multiple code repositories). To generate local
file system URLs, define the empty atom, ``''``, as a prefix. See the
``SCRIPT.txt`` file in the tool directory for some usage examples.

Creating diagrams for Prolog module applications
------------------------------------------------

Currently limited to SWI-Prolog and YAP Prolog module applications due
to the lack of a comprehensive reflection API in other Prolog systems.

Simply load your Prolog module application and its dependencies and then
use diagram entity, directory, or file predicates. Library diagram
predicates are not supported. See the ``SCRIPT.txt`` file in the tool
directory for some usage examples. Note that support for diagrams with
links to API documentation is quite limited, however, due to the lack of
Prolog standards.

Creating diagrams for plain Prolog files
----------------------------------------

This tool can also be used to create predicate cross-referencing
diagrams for plain Prolog files. For example, if the Prolog file is
named ``code.pl``, simply define an object including its code:

::

   :- object(code).
       :- include('code.pl').
   :- end_object.

Save the object to an e.g. ``code.lgt`` file in the same directory as
the Prolog file and then load it and create the diagram:

::

   ?- logtalk_load(code), xref_diagram::entity(code).

Other notes
-----------

Generating complete diagrams requires that all referenced entities are
loaded. When that is not the case, notably when generating
cross-referencing diagrams, missing entities can result in incomplete
diagrams.

The zoom icons, ``zoom.png`` and ``zoom.svg`` have been designed by Xinh
Studio:

`https://www.iconfinder.com/xinhstudio <https://www.iconfinder.com/xinhstudio>`__

Currently, only the ``zoom.png`` file is used. A copy of this file must
exist in any directory used for publishing diagrams using it.

The Graphviz command-line utilities, e.g. ``dot``, are notorious for
random crashes (segmentation faults usually), often requiring re-doing
conversions from ``.dot`` files to other formats. A possible workaround
is to repeat the command until it completes without error. See for
example the ``lgt2svg.sh`` script.

All source files are formatted using tabs (the recommended setting is a
tab width equivalent to 4 spaces).
