[comment {-*- tcl -*- paths manpage}]
[vset VERSION 0.5]
[manpage_begin pluginmgr n [vset VERSION]]
[keywords {plugin management}]
[keywords {plugin search}]
[copyright {2005 Andreas Kupries <andreas_kupries@users.sourceforge.net>}]
[moddesc   {Plugin management}]
[titledesc {Manage a plugin}]
[category  {Programming tools}]
[require Tcl "8.5 9"]
[require pluginmgr [opt [vset VERSION]]]
[description]

This package provides commands and objects for the generic management
of plugins which can be loaded into an application.

[para]

To avoid the implementation of yet another system to locate Tcl code
the system provides by this package is built on top of the regular
package management system. Each plugin is considered as a package and
a simple invokation of [cmd {package require}] is enough to locate and
load it, if it exists. The only time we will need additional paths is
when a plugin manager is part of a wrapped application and has to be
able to search for plugins existing outside of that application. For
this situation the package provides a command to create a general set
of such paths based on names for the plugin manager and/or application
in question.

[para]

The main contribution of this package is a generic framework which
allows the easy declaration of

[list_begin enumerated]
[enum]
How to translate a plugin name to the name of the package implementing
it, and vice versa.

[enum]
The list of commands a plugin has to provide as API, and also of more
complex checks as code.

[enum]
The list of commands expected by the plugin from the environment.

[list_end]

This then allows the easy generation of plugin managers customized to
particular types of plugins for an application.

[para]

It should be noted that all plugin code is considered untrusted and
will always be executed within a safe interpreter. The interpreter is
enabled enough to allow plugins the loading of all additional packages
they may need.

[section {PUBLIC API}]
[subsection {PACKAGE COMMANDS}]

[list_begin definitions]

[call [cmd ::pluginmgr] [arg objectName] [opt [arg "option value"]...]]

This command creates a new plugin manager object with an associated
Tcl command whose name is [arg objectName]. This [term object] command
is explained in full detail in the sections [sectref {OBJECT COMMAND}]
and [sectref {OBJECT METHODS}]. The object command will be created
under the current namespace if the [arg objectName] is not fully
qualified, and in the specified namespace otherwise.

[para]

The options and their values coming after the name of the object are
used to set the initial configuration of the mamager object,
specifying the applicable plugins and their API.

[call [cmd ::pluginmgr::paths] [arg objectName] [arg name]...]

This utility command adds a set of paths to the specified object,
based on the given [arg name]s.

It will search for:

[list_begin enumerated]

[enum]

The environment variable [var [arg name]_PLUGINS]. Its contents will
be interpreted as a list of package paths. The entries have to be
separated by either [const :] (unix) or [const \;] (windows).

[para]

The name will be converted to upper-case letters.

[enum]

The registry entry "HKEY_LOCAL_MACHINE\SOFTWARE\[arg name]\PLUGINS".
Its contents will be interpreted as a list of package paths. The
entries have to be separated by [const \;]. This item is considered
only when on Windows (tm).

[para]

The casing of letters is not changed.

[enum]

The registry entry "HKEY_CURRENT_USER\SOFTWARE\[arg name]\PLUGINS".
Its contents will be interpreted as a list of package paths. The
entries have to be separated by [const \;]. This item is considered
only when on Windows (tm).

[para]

The casing of letters is not changed.

[enum]

The directory [file "~/.[arg name]/plugin"].

[enum]

The directory [file "~/.[arg name]/plugins"].

[para]

The casing of letters is not changed.

[list_end]
[para]

and add all the paths found that way to the list of package paths
maintained by the object.

[para]

If [arg name] is namespaced each item in the list will be repeated per
prefix of [arg name], with conversion of :-sequences into the proper
separator (underscore for environment variables, backslash for
registry entries, and / for directories).

[para]
Examples:
[para]

[example {
    ::pluginmgr::paths ::obj docidx

    => env  DOCIDX_PLUGINS
       reg  HKEY_LOCAL_MACHINE\SOFTWARE\docidx\PLUGINS
       reg  HKEY_CURRENT_USER\SOFTWARE\docidx\PLUGINS
       path ~/.docidx/plugins

    ::pluginmgr::paths ::obj doctools::idx

    => env  DOCTOOLS_PLUGINS
       env  DOCTOOLS_IDX_PLUGINS
       reg  HKEY_LOCAL_MACHINE\SOFTWARE\doctools\PLUGINS
       reg  HKEY_LOCAL_MACHINE\SOFTWARE\doctools\idx\PLUGINS
       reg  HKEY_CURRENT_USER\SOFTWARE\doctools\PLUGINS
       reg  HKEY_CURRENT_USER\SOFTWARE\doctools\idx\PLUGINS
       path ~/.doctools/plugin
       path ~/.doctools/idx/plugin
}]

[list_end]

[subsection {OBJECT COMMAND}]

All commands created by the command [cmd ::pluginmgr] (See section
[sectref {PACKAGE COMMANDS}]) have the following general form and may
be used to invoke various operations on their plugin manager object.

[list_begin definitions]

[call [cmd objectName] [method method] [opt [arg "arg arg ..."]]]

The method [method method] and its [arg arg]'uments determine the exact
behavior of the command. See section [sectref {OBJECT METHODS}] for
the detailed specifications.

[list_end]

[subsection {OBJECT METHODS}]

[list_begin definitions]

[call [arg objectName] [method clone]]

This method creates a new plugin management object and returns the
associated object command. The generated object is a clone of the
object the method was invoked on. I.e. the new object will have the
same configuration as the current object. With regard to state, if the
current object has a plugin loaded then this plugin and all associated
state is moved to the generated clone and the current object is reset
into the base state (no plugin loaded). In this manner a configured
plugin manager is also a factory for loaded plugins.

[call [arg objectName] [method configure]]

The method returns a list of all known options and their current
values when called without any arguments.

[call [arg objectName] [method configure] [arg option]]

The method behaves like the method [method cget] when called with a
single argument and returns the value of the option specified by said
argument.

[call [arg objectName] [method configure] [option -option] [arg value]...]

The method reconfigures the specified [option option]s of the object,
setting them to the associated [arg value]s, when called with an even
number of arguments, at least two.

[para]

The legal options are described in the section
[sectref {OBJECT CONFIGURATION}].

[call [arg objectName] [method cget] [option -option]]

This method expects a legal configuration option as argument and will
return the current value of that option for the object the method was
invoked for.

[para]

The legal configuration options are described in section
[sectref {OBJECT CONFIGURATION}].

[call [arg objectName] [method destroy]]

This method destroys the object it is invoked for.

[call [arg objectName] [method do] [arg arg]...]

This method interprets its list of arguments as the words of a command
and invokes this command in the execution context of the plugin.

The result of the invoked command is made the result of the method.

The call will fail with an error if no valid plugin has been loaded
into the manager object.

[call [arg objectName] [method interpreter]]

This method returns the handle of the safe interpreter the current
plugin is loaded into. An empty string as return value signals that
the manager currently has no valid plugin loaded.

[call [arg objectName] [method plugin]]

This method returns the name of the plugin currently loaded. An empty
string as return value signals that the manager currently has no valid
plugin loaded.

[call [arg objectName] [method load] [arg string]]

This method loads, validates, and initializes a named plugin into the
manager object.

[para]
The algorithm to locate and load the plugin employed is:

[list_begin enumerated]
[enum]

If the [arg string] contains the path to an existing file then this
file is taken as the implementation of the plugin.

[enum]
Otherwise the plugin name is translated into a package name via the value
of the option [option -pattern] and then loaded through the
regular package management.

[enum]
The load fails.

[list_end]
[para]

The algorithm to validate and initialize the loaded code is:

[list_begin enumerated]
[enum]
If the option [option -api] is non-empty introspection commands are
used to ascertain that the plugin provides the listed commands.

[enum]
If the option [option -check] is non-empty the specified command
prefix is called.

[enum]
If either of the above fails the candidate plugin is unloaded again

[enum]
Otherwise all the commands specified via the option
[option -cmds] are installed in the plugin.

[list_end]
[para]

A previously loaded plugin is discarded, but only if the new plugin
was found and sucessfully validated and initialized. Note that there
will be no intereference between old and new plugin as both will be
put into separate safe interpreters.

[call [arg objectName] [method unload]]

This method unloads the currently loaded plugin. It returns the empty
string. The call will be silently ignored if no plugin is loaded at
all.

[call [arg objectName] [method list]]

This method uses the contents of the option [option -pattern] to find
all packages which can be plugins under the purview of this manager
object. It translates their names into plugin names and returns a list
containing them.

[call [arg objectName] [method path] [arg path]]

This methods adds the specified [arg path] to the list of additional
package paths to look at when searching for a plugin. It returns the
empty string. Duplicate paths are ignored, i.e. each path is added
only once. Paths are made absolute, but are not normalized.

[call [arg objectName] [method paths]]

This method returns a list containing all additional paths which have
been added to the plugin manager object since its creation.

[list_end]

[subsection {OBJECT CONFIGURATION}]

All plugin manager objects understand the following configuration options:

[list_begin options]

[opt_def -pattern [arg string]]

The value of this option is a glob pattern which has to contain
exactly one '*'-operator. All packages whose names match this pattern
are the plugins recognized by the manager object. And vice versa, the
replacement of the '*'-operator with a plugin name will yield the name
of the package implementing that plugin.

[para]

This option has no default, except if option [option -name] was set.
It has to be set before attempting to load a plugin, either directly,
or through option [option -name].

[opt_def -api [arg list]]

The value of this option is a list of command names, and any plugin
loaded has to provide these commands. Names which are not fully
qualified are considered to be rooted in the global namespace.

If empty no expectations are made on the plugin. The default value is
the empty list.

[opt_def -check [arg cmdprefix]]

The value of this option is interpreted as a command prefix.

Its purpose is to perform complex checks on a loaded plugin package to
validate it, which go beyond a simple list of provided commands.

[para]

It is called with the manager object command as the only argument and
has to return a boolean value. A value of [const true] will be
interpreted to mean that the candidate plugin passed the test.

The call will happen if and only if the candidate plugin already
passed the basic API check specified through the option [option -api].

[para]

The default value is the empty list, which causes the manager object
to suppress the call and to assume the candidate plugin passes.

[opt_def -cmds [arg dict]]

The value of this option is a dictionary.  It specifies the commands
which will be made available to the plugin (as keys), and the trusted
commands in the environment which implement them (as values).

The trusted commands will be executed in the interpreter specified by
the option [option -cmdip].

The default value is the empty dictionary.

[opt_def -cmdip [arg ipspec]]

The value of this option is the path of the interpreter where the
trusted commands given to the plugin will be executed in.

The default is the empty string, referring to the current interpreter.

[opt_def -setup [arg cmdprefix]]

The value of this option is interpreted as a command prefix.

[para]

It is called whenever a new safe interpreter for a plugin has been
created, but before a plugin is loaded. It is provided with the
manager object command and the interpreter handle as its only
arguments. Any return value will be ignored.

[para]

Its purpose is give a user of the plugin management the ability to
define commands, packages, etc. a chosen plugin may need while being
loaded.

[list_end]

[vset CATEGORY pluginmgr]
[include ../common-text/feedback.inc]
[manpage_end]
