# `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 understanding the architecture of applications by navigating complex code and 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

This tool API documentation is available at:

../../docs/library_index.html#diagrams

For sample queries, please see the `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 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

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

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 with the intended set of options.

## 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 Graphviz 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 2.43 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, old stable versions such as 2.40.1 have a bug (fixed in the recent versions) 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 current date and time (`true` or `false`; default is `true`)
- `interface(Boolean)`
  print public predicates (`true` or `false`; default is `true`)
- `file_labels(Boolean)`
  print file labels (`true` or `false`; default is `true`)
- `file_extensions(Boolean)`
  print file name extensions (`true` or `false`; default is `true`)
- `relation_labels(Boolean)`
  print entity relation labels (`true` or `false`; default is `true`)
- `externals(Boolean)`
  print external nodes (`true` or `false`; default is `true`)
- `node_type_captions(Boolean)`
  print node type captions (`true` or `false`; default is `true`)
- `inheritance_relations(Boolean)`
  print inheritance relations (`true` or `false`; default is `true` for entity inheritance diagrams and `false` for other entity diagrams)
- `provide_relations(Boolean)`
  print provide relations (`true` or `false`; default is `false`)
- `xref_relations(Boolean)`
  print predicate call cross-reference relations (`true` or `false`; default depends on the specific diagram)
- `xref_calls(Boolean)`
  print 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 and when constructing URLs (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 current date and time (`true` or `false`; default is `true`)
- `directory_paths(Boolean)`
  print file directory paths (`true` or `false`; default is `false`)
- `file_extensions(Boolean)`
  print 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 and when constructing URLs (a list of atoms; default is an empty list)
- `relation_labels(Boolean)`
  print entity relation labels (`true` or `false`; default is `false`)
- `externals(Boolean)`
  print external nodes (`true` or `false`; default is `true`)
- `node_type_captions(Boolean)`
  print 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 current date and time (`true` or `false`; default is `true`)
- `directory_paths(Boolean)`
  print 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 and when constructing URLs (a list of atoms; default is an empty list)
- `relation_labels(Boolean)`
  print entity relation labels (`true` or `false`; default is `false`)
- `externals(Boolean)`
  print external nodes (`true` or `false`; default is `true`)
- `node_type_captions(Boolean)`
  print 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 preferably be used together with the option `directory_paths(true)` when generating library or file diagrams that reference external libraries 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 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.

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. As an example, consider the Logtalk library. Its source code is available from a GitHub repository and its documentation is published in the Logtalk website. The relevant URLs are:

- https://github.com/LogtalkDotOrg/logtalk3/tree/ (source code)

- https://logtalk.org/library/ (API documentation)

Git source code URLs should include the commit SHA1 to ensure that entity and predicate file line information in the URLs remain valid if the code changes in later commits. Assuming a `GitHub` variable bound to the SHA1 commit URL we want to reference, an inheritance diagram can be generated using the goal:

    | ?- GitHub  = 'https://github.com/LogtalkDotOrg/logtalk3/tree/...',
         APIDocs = 'https://logtalk.org/library/',
         logtalk_load(diagrams(loader)),
         set_logtalk_flag(source_data, on),
         logtalk_load(library(all_loader)),
         inheritance_diagram::rlibrary(library, [
             title('Logtalk library'),
             node_type_captions(true),
             zoom(true),
             path_url_prefixes('$LOGTALKUSER/', GitHub, APIDocs),
             path_url_prefixes('$LOGTALKHOME/', GitHub, APIDocs),
             omit_path_prefixes(['$LOGTALKUSER/', '$LOGTALKHOME/', '$HOME/'])
         ]).

The two `path_url_prefixes/3` options take care of source code and API documentation for entities loaded either from the Logtalk installation directory (whose location is given by the `LOGTALKHOME` environment variable) or from the Logtalk user directory (whose location is given by the `LOGTALKUSER` environment variable). As we also don’t want any local operating-system paths to be exposed in the diagram, we use the `omit_path_prefixes/1` option to suppress those path prefixes, Note that all the paths and URLs must end with a slash for proper handling.

See the `SCRIPT.txt` file in the tool directory for additional 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).

An alternative is to use the `object_wrapper_hook` provided by the `hook_objects` library:

    | ?- logtalk_load(hook_objects(object_wrapper_hook)).
    ...

    | ?- logtalk_load(code, [hook(object_wrapper_hook)]),
         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 `lgt2svg` scripts take care of copying this file.

When generating diagrams in SVG format, a copy of the `diagrams.css` file must exist in any directory used for publishing diagrams using it. The `lgt2svg` scripts take care of copying this file.

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 indented using tabs (a common setting is a tab width equivalent to 4 spaces).