.. default-domain:: js
.. highlight:: javascript
.. _posix-argv-parser:

=================
posix-argv-parser
=================

Version:
    0.1.0 (2012-06-13)

Module:
    ``require("posix-argv-parser");``

An command line interface (CLI) argument parser that is:

- `POSIX "Utility Argument Syntax"
  <http://pubs.opengroup.org/onlinepubs/9699919799/>`_ compliant
- **Unobtrusive** - Does not mandate flow control, does not print to STDOUT on
  your behalf, and does not magically manage ``--help``
- **Ambiguity aware** - lets you specify how to handle ambiguities such as
  ``-bar``, which can mean both ``-b -a -r`` and ``-b=ar``.

::

    var pap = require("posix-argv-parser");
    var args = pap.create();
    var v = pap.validators;

    args.createOption(["-p", "--port"], {
        // All options are optional

        // Implies hasValue: true, which allows parser to read -p2345 as -p=2345
        defaultValue: 8282,

        // Both built-in and custom validations supported,
        // synchronous as well as asynchronous (promise based)
        validators: [v.integer("Custom message. ${1} must be a number.")],

        // Transforms allow you to get more intelligent values
        // than raw strings back
        transform: function (value) { return parseInt(value, 10); }
    });

    args.createOption(["-v"], {
        validators: [function (opt) {
            // See also asynchronous validators
            if (opt.timesSet < 1) {
                throw new Error("Set " + opt.signature + " at least once!");
            }
        }]
    });

    // Operands are statements without options.
    // Example: the path in `mything --port=1234 path/to/stuff`
    args.createOperand("rootPath", {
        // Used in error msgs
        signature: "Presentation root directory",
        // Both will use default error messages
        validators: [v.file(), v.required()]
    });

    posixArgvParser.parse(process.argv.slice(2), function (errors, options) {
        if (errors) { return console.log(errors[0]); }

        // Various useful ways to get the values from the options.
        options["-v"].timesSet;
        options["--port"].isSet;
        // Will be a true number thanks to the transform
        options["--port"].value;
        options.rootPath.value;
    });


Methods
=======

.. function:: posixArgvParser.create()

    ::

        var args = require("posix-argv-parser").create();

    Creates a new instance of posix-argv-parser that holds a collection of
    options and operands.

.. function:: posixArgvParser.createOption(flags[, options])

    ::

        args.createOption(["-h", "--help"]);

    Creates a new ``option``. An option has all the properties of an
    ``argument``, as well as :attr:`option.hasValue` and
    :attr:`option.timesSet`. The ``options`` object is optional.

.. function:: posixArgvParser.addShorthand(opt, [argv1, ...])

    A shorthand is a convenience method for adding options to your CLI that
    simply set other options.

    ::

        args.createOption("--env", { hasValue: true });
        args.addShorthand("--dev", ["--env", "dev"]);
        args.addShorthand("--prod", ["--env", "prod"]);

    This makes passing ``--dev`` an equlvalent to passing
    ``--env dev``.

.. function:: posixArgvParser.createOperand([name][, options])

    ::

        args.createOperand();

    Creates a new operand. An operand has all the properties of an ``argument``,
    as well as ``greedy: true|false`` - i.e. whether or not it will eat many
    arguments or just one (defaults to `false`, just one).
    The name is optional, and should be a string. The name is used to access
    the value through the ``options`` object passed to the ``parse`` callback.
    If not provided, it defaults to "OPD" (beware when using more than one
    operand).

.. function:: posixArgvParser.parse(args, callback)

    Performs parsing and validation of argv. In Node.JS, make sure to discard
    the first two items of `process.argv
    <http://nodejs.org/api/process.html#process_process_argv>`_, as they
    contain unrelated arguments ("node" and the file name).

    The callback is called with two arguments, ``errors``, which is either
    undefined, or an array of errors and/or validation messages, and an
    ``options`` object, which is used to retrieve data from configured options.

    ::

        var args = require("posix-argv-parser").create();
        args.handle(process.argv.slice(2), function (errors, options) {
            if (errors) {
                // Print an error msg, i.e. console.log(errors[0])
                return;
            }
            // Continue with normal operation. I.e. options["-v"].hasValue,
            // options["-v"].timesSet, options["-p"].value, etc.
        });


Arguments (options and operands)
================================

:func:`Options <args.createOption>` and :func:`operands
<args.createOperand>` are the two types of arguments handled by
posix-argv-parser, and they share common functionality, listed below this
introduction.

An **option** is a flag, with or without a value. ``-p``, ``-p abc``,
``-pabc``, ``-p=abc``, ``--port abc`` and ``--port=abc`` are all supported by
posix-argv-parser.

``-pabc`` can mean  both ``-p -a -b -c`` and ``-p=abc``. posix-argv-parser uses
:attr:`opt.hasValue` to separate the two. With :attr:`opt.hasValue` set to
true, ``-pabc`` will be handled as ``-p=abc``. When false (default), it will be
handled as ``-p -a -b -c``. In that case you also need to have option handlers
for ``-a``, ``-b`` and ``-c``, or you'll get a validation error such as
``"unknown option -a"`` (depending on which option posix-argv-parser first
encountered that didn't exist).

An **operand** is an option-less value, i.e. ``foo`` (with no ``-b`` or
``--myopt`` prefixing it). It's commonly used for arguments that always have to
be passed. Examples are ``nano path/to/file.txt``, ``git checkout
master``, ``rmdir my_dir``, etc. The validators :func:`validators.file`,
:func:`validators.directory`, and :func:`validators.fileOrDirectory` are very
useful for operands.

Note that the parser can handle a mix and match of options and operands in any
order, i.e. ``mycommand --port 1234 my/directory`` and ``mycommand my/directory
--port 1234`` will both work.

Multiple operands will be applied in order of creation. I.e. ``mycommand
something`` with two operands will assign ``"something"`` to the first and
``undefined`` to the second, unless the first is greedy, in which case it
will receive all the operand values.

See example usage at the beginning of this document for more information.

When creating options and operands, the following properties can be passed in
with the "options" object.

.. attribute:: opt.validators

    An array of validators. A validator is a function that accepts the argument
    result object as input. See below for a description of argument result objects.
    To fail validation, the validator can either throw an error, or return a
    rejecting promise.

.. attribute:: opt.transform

    A function that transforms the raw string value provided before assigning it
    to the :attr:`opt.value` property of an argument result object. The
    function receives the string value as input, and should return any value
    back.

.. attribute:: opt.hasValue

    If the argument takes a value, set to ``true``. Defaults to ``false`` for
    options, is always ``true`` for operands (thus it can be omitted).

.. attribute:: opt.defaultValue

    The default value to use if the argument was not provided. When
    :attr:`opt.defaultValue` is provided, :attr:`opt.hasValue` is implied and
    can be omitted. The default value should be a string, and will be validated
    and transformed like actual values.

.. attribute:: opt.signature

    The signature is used to identify options and operands in validation errors.
    Options automatically gets a signature consisting of the option flags assigned
    to it::

        var opt = args.createOption(["-v", "--version"]);
        opt.signature; // "-v/--version"
        opt.signature = "-v"; // custom signature

    Specifying a signature is more useful for operands, since an operand doesn't
    have any data that it can use to auto generate a signature (their default signature
    is "OPD")::

        var rootDir = args.createOperand();
        rootDir.signature; // "OPD", as the default name
        rootDir.signature = "Root directory";


Options
=======

Options has additional properties that operands doesn't have.

.. attribute:: opt.requiresValue

    Only makes sense if :attr:`opt.hasValue` is ``true``. When this property is
    ``false``, an option can both be provided as a flag with no value or as an
    option with a value.

    A common example of options that work with and without values are help options,
    that may be provided alone to get general help, e.g. `mything --help`, and with
    values to get help for specific topics, e.g. `mything --help bisect`.


Argument result
===============

Argument result objects are produced when calling :func:`args.parse` to parse
``argv`` into the predefined options and operands. There is one result object
per original option/operand. These objects have the following properties:

.. attribute:: argumentResult.isSet

    ``true`` or ``false`` depending on whether or not the argument was present
    in ``argv``.

.. attribute:: argumentResult.value

    The value of the argument. Is normally a string, but may be any object
    if the argument had a transform function.

.. attribute:: argumentResult.timesSet

    The number of times an argument was set. Useful for options like ``-v``
    (verbose) which you might want to allow setting multiple times, giving the
    user more and more verbose output from your program::

        -v // 1
        -vv // 2
        -v -v -v -v // 4
        -v -vv -vv -vvv // 8


Validators
==========

Validators let you add requirements with associated error messages to options
and operands.

posix-argv-parser has a number of built-in validators, and creating custom ones
is dead simple, as a validator is just a function.


Built-in validators
-------------------

The built in validators provides a selection of generic validators. You can
customize the error messages by passing strings with tokens like ``"${1}"`` in
them. The number and value maps are documented for each validator.

Validators are functions, yet the built-in validators are used by calling them
directly with custom error messages. This works because the built-in validators
all return the actual validation function.

::

    // Uses built-in error message
    posixArgvParser.validators.required();

    // Specify your own error message
    posixArgvParser.validators.required("${1} has to be set");

.. function:: validators.required(errorMessage)

    Fails if the option is not set.

    Custom error message:

    ``${1}``:
        The option :attr:`opt.signature`

.. function:: validators.integer(errorMessage)

    Will fail validation if the option was not an integer, i.e. ``"foo"`` and
    ``42.5``.

    Custom error message:

    ``${1}``:
        The specified number

    ``${2}``:
       The option :attr:`opt.signature`

.. function:: validators.number(errorMessage)

    Will fail validation if the option was not a number, i.e. ``"foo"`` and
    ``?``.

    Custom error message:

    ``${1}``:
        The specified number

    ``${2}``:
        The option :attr:`opt.signature`

.. function:: validators.file(errorMessage)

    Will fail validation if the option was not a path pointing to an existing
    file in the file system.

    Custom error message:

    ``${1}``:
        The specified file

    ``${2}``:
        The option :attr:`opt.signature`

.. function:: validators.directory(errorMessage)

    Will fail validation if the option was not a path pointing to an existing
    directory in the file system.

    Custom error message:

    ``${1}``:
        The specified directory

    ``${2}``:
        The option :attr:`opt.signature`

.. function:: validators.fileOrDirectory(errorMessage)

    Will fail validation if the option was not a path pointing to an existing
    file or directory in the file system. Will fail for block devices, sockets,
    et c.

    Custom error message:

    ``${1}``:
        The specified file or directory

    ``${2}``:
        The option :attr:`opt.signature`


Custom validators
-----------------

A validator is a function that throws an error or returns a promise. If it does
not do any of those things, it is immediately considered passed. The function is
passed an argument result object.

::

    args.createOption("-v", {
        validators: [function (opt) {
            if (opt.value == "can not be this value") {
                throw new Error("This is the error message.");
            }
        }]
    });

Promises are used to facilitate asynchronous validators. Here's an example of a
validator that checks if a file is larger than 1MB::

    var when = require("when");
    args.createOption(["-f"], {
        validators: [function (opt) {
            var deferred = when.defer();
            fs.stat(opt.value, function (err, stat) {
                if (err) { deferred.reject("Unknown error: " + err); }

                if (stat.size > 1024) {
                    deferred.reject(opt.value +
                        " (" + opt.signature + ") was larger than 1MB");
                } else {
                    deferred.resolve();
                }
            });
            return deferred.promise;
        }]
    });

Given ``--myopt /path/to/file`` and the file is larger than 1MB, you'll get the
error message ``"/path/to/file (--myopt) was larger than 1MB"``.

Rejecting the promise counts as an error. The first argument should be a
string, and is the error message. (TODO: This will likely change to an
error object with a ``message`` property).


Transforms
==========

Transforms can mutate the values of options. A transform is a simple function
that receives the raw string value as input, and can return whatever it likes.::

    args.createOption(["-p"], {
        transform: function (value) { return parseInt(value, 10); }
    });


Types
=====

Types are predefined "options" objects that you can pass when creating options
and/or operands. For instance, the "number" type includes the number validator,
sets :attr:`opt.hasValue` to ``true``, and includes a transform that converts
the raw string to an actual number (by way of ``parseFloat``)::

    args.createOption(["-n"], args.types.number());

Note that the type is a function call - it returns the options object. You can
pass in additional options. The following example piggy-backs the number type
to create an option that only takes positive numbers::

    args.createOption(["-n"], args.types.number({
        validators: [function (opt) {
            if (parseFloat(opt.value) < 0) {
                throw new Error("Oh noes, negative number!");
            }
        }]
    }));


Providing ``--help``
====================

It's not in the nature of posix-argv-parser to automatically handle ``--help``
for you. It is however very easy to add such an option to your program. To help
you keep all CLI option data in one place, options and operands are allowed to
have a :attr:`opt.description` property that posix-argv-parser does not care
about::

    var args = require("posix-argv-parser").create();

    args.createOption(["--port"], {
        defaultValue: 1234
        description: "The port to start the server on."
    });

    args.createOption(["-v"], {
        description: "Level of detail in output. " +
            "Pass multiple times (i.e. -vvv) for more output."
    });

    args.createOption(["--help", "-h"], { description: "Show this text" });
    help.helpText = "Show this text";

    args.parse(process.argv.slice(2), function (errors, options) {
        if (errors) { return console.log(errors[0]); }

        if (options["-h"].isSet) {
            args.options.forEach(function (opt) {
                console.log(opt.signature + ": " + opt.description);
            });
        } else {
            // Proceed with normal program operation
        }
    });