________________________________________________________________________

This file is part of Logtalk <https://logtalk.org/>  
Copyright 1998-2019 Paulo Moura <pmoura@logtalk.org>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
________________________________________________________________________


Overview
--------

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.


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/> 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 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 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

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).
