# argv.js

Simple argv parser


## Motivation

I needed a new argv parser for a quick and dirty project I was working 
on and evaluating and selecting the proper existing parser and then 
learning its API, quirks and adapting the architecture to it seemed 
to be more complicated, require more effort and far less fun than 
putting together a trivial parser myself in a couple of hours.  
This code is an evolution of that parser.


## Features

- Simple
- Supports both the _option_ (a-la `ls`) and _command_ (a-la `git`) paradigms
- Nestable  
  parsers can be nested as option/command handlers defining independent 
  nested contexts
- Option expansion  
  `-abc` expands to `-a -b -c` if `-abc` is not defined
- Option/command value passing  
  implicit `-a 123` (requires definition or manual handling) or explicit 
  `-a=123`
- Environment variable option/command value defaults
- Option/command value conversion
- Option/command value collection
- Multiple option prefix support
- Reasonable defaults:
  - `-help` – generate and print help
  - `-version` – print version
  - `-quiet` – suppress printing
  - `-` – stop argument processing
- Extensible:
  - Hooks for dynamic option/command handling
  - Customizable error and stop condition handling


## Planned Features

- Run `<command>-<sub-command>` scripts
- Option doc grouping (???)



<!-- XXX ### Alternatives -->

## Contents
- [argv.js](#argvjs)
	- [Motivation](#motivation)
	- [Features](#features)
	- [Planned Features](#planned-features)
	- [Contents](#contents)
	- [Installation](#installation)
	- [Basic usage](#basic-usage)
	- [Error reporting](#error-reporting)
	- [XXX add subsections by task](#xxx-add-subsections-by-task)
	- [Configuration](#configuration)
		- [Option/command configuration](#optioncommand-configuration)
			- [`<option>.handler(..)`](#optionhandler)
			- [`<option>.doc`](#optiondoc)
			- [`<option>.priority`](#optionpriority)
			- [`<option>.arg`](#optionarg)
			- [`<option>.type`](#optiontype)
			- [`<option>.collect`](#optioncollect)
			- [`<option>.env`](#optionenv)
			- [`<option>.default`](#optiondefault)
			- [`<option>.required`](#optionrequired)
			- [`<option>.valueRequired`](#optionvaluerequired)
		- [Built-in options](#built-in-options)
			- [`-` / `--`](#-----)
			- [`-*` / `@*`](#---)
			- [`-v` / `--version`](#-v----version)
			- [`-q` / `--quiet`](#-q----quiet)
			- [`-h` / `--help`](#-h----help)
				- [Value placeholders](#value-placeholders)
				- [Automatically defined values](#automatically-defined-values)
				- [`<parser>.doc`](#parserdoc)
				- [`<parser>.usage`](#parserusage)
				- [`<parser>.version`](#parserversion)
				- [`<parser>.license`](#parserlicense)
				- [`<parser>.examples`](#parserexamples)
				- [`<parser>.footer`](#parserfooter)
				- [More control over help...](#more-control-over-help)
		- [Nested parsers](#nested-parsers)
	- [Components and API](#components-and-api)
		- [`THEN` / `STOP`](#then--stop)
		- [`ParserError(..)`](#parsererror)
		- [`Parser(..)`](#parser)
			- [`<parser>.then(..)`](#parserthen)
			- [`<parser>.stop(..)`](#parserstop)
			- [`<parser>.error(..)`](#parsererror-1)
			- [`<parser>.off(..)`](#parseroff)
			- [`<parser>(..)`](#parser-1)
	- [Advanced parser API](#advanced-parser-api)
		- [`<parser>.print(..)` / `<parser>.printError(..)`](#parserprint--parserprinterror)
		- [`<parser>.handlerDefault(..)`](#parserhandlerdefault)
		- [`<parser>.handleArgumentValue(..)`](#parserhandleargumentvalue)
		- [`<parser>.handleErrorExit(..)`](#parserhandleerrorexit)
		- [`<parser>.handle(..)`](#parserhandle)
		- [`<parser>.setHandlerValue(..)`](#parsersethandlervalue)
		- [More...](#more)
	- [License](#license)


## Installation

```shell
$ npm install ig-argv
```

## Basic usage

Create a script and make it runnable
```shell
$ touch script.js
$ chmod +x script.js
```

Now for the code
```javascript
#!/usr/bin/env node

// compatible with both node's and RequireJS' require(..)
var argv = require('ig-argv')

var parser = argv.Parser({
		// option definitions...
		// ...
	})
	.then(function(){
		// things to do after the options are handled...
		// ...
	})

// run the parser...
__filename == require.main
	&& parser(process.argv)
```

Now let us populate the option definitions:
```javascript
var parser = argv.Parser({
		// doc sections...
		varsion: '0.0.1',
		doc: 'Example script options',
		author: 'John Smith <j.smith@some-mail.com>',
		footer: 'Written by $AUTHOR ($VERSION / $LICENSE).',
		license: 'BSD-3-Clause',


		// Basic options
		//
		// These simply asign a value to an attribute on the parsed 
		// object...
		//
		// If no value is given true is asigned to indicate that the 
		// option/command was given.

		'-bool': {
			doc: 'if given set .bool to true' },


		// option with a value...
		'-value': {
			doc: 'set .x to X',

			// 'X' (VALUE) is used for -help while 'x' (key) is where the 
			// value will be written...
			arg: 'X | x',

			// the value is optional by default but we can make it required by...
			//valueRequired: true,
		},


		// setup an alias -r -> -required
		'-r': '-required',

		// a required option...
		'-required': {
			doc: 'set .required_option_given to true'

			// NOTE: we can omit the VALUE part to not require a value...
			// NOTE: of no attr is specified in arg option name is used.
			arg: '| required_option_given',

			required: true,
		},


		'-int': {
			doc: 'pass an integer value',

			// NOTE: if not key is given the VALUE name is used as a key, so the 
			// 		value here is assigned to .INT...
			arg: 'INT',

			// convert the input value to int...
			type: 'int',
		},
		

		'-default': {
			doc: 'option with default value',
			arg: 'VALUE | default',

			default: 'some value',
		},


		'-home': {
			doc: 'set home path',
			arg: 'HOME | home',

			// get the default value from the environment variable $HOME...
			env: 'HOME',
		},

		
		// collecting values...
		'-p': '-push',
		'-push': {
			doc: 'push elements to a .list',
			arg: 'ELEM | list',

			// this will add each argument to a -push option to a list...
			collect: 'list',
		},


		// Command...
		//
		// The only difference between an option and a command is
		// the prefix ('-' vs. '@') that determines how it is parsed,
		// otherwise they are identical and everything above applies here 
		// too...
		'@command': {
			// ...
		},

		// Since options and commands are identical aliases from one to the 
		// other to commands are also supported...
		'-c': '@command',


		// Active options/commnads 
		//
		// These define .handler's...

		// XXX .handler


		// Nested parsers...
		//
		'@nested': argv.Parser({
				// ...
			}).then(function(){
				// ...
			}),

		// ...
	})
```

This will create a parser that supports the following:
```shell
$ ./script.js --help 

$ ./script.js --value 321

$ ./script.js --value=321

$ ./script.js command

$ ./script.js nested -h

$ ./script.js -fb

```


## Error reporting

XXX


## XXX add subsections by task

XXX

XXX might be a good idea to split out the rest to a INDETAIL.md or similar...



## Configuration

```
Parser(<spec>)
	-> <parser>
```

The `<spec>` object is "merged" into the `<parser>` instance overriding 
or extending it's API/data.

The `<parser>` expects/handles the following data in the `<spec>` object:

- the configuration attributes and methods  
	Attributes and methods used to configure, modify, extend or overload 
	parser functionality.

	Note that these attributes are the same attributes inherited by `<parser>`
	and are simply merged into the new instance created by `Parser(..)`, thus 
	there are no restrictions on what attributes/methods can be overloaded 
	or extended in this way, but care must be taken when overloading elements 
	that were not designed to be overloaded.

- option/command definitions  
	The keys for these are prefixed either by `"-"` for options or by `"@"` 
	for commands and are either _objects_, _functions_ or _parser_ instances.

	The only difference between an _option_ and a _command_ is that the former 
	are passed to the _script_ with a `"-"` or `"--"` prefix (by default) and 
	the later are passed by name without prefixes. 

	In all other regards options and commands are the same.

- option/command aliases  
	An alias is an option/command key with a _string_ value.  
	That value _references_ a different option or command, i.e. is an 
	option/command name.

	Looping (referencing the original alias) or dead-end (referencing 
	non-existent options) aliases are ignored.


### Option/command configuration

#### `<option>.handler(..)`

Option handler.


```javascript
'-option': {
	handler: function(opts, key, value){
		// handle the option...
		// ...
	},
},
```
or a shorthand:
```javascript
'-option': function(opts, key, value){
	// handle the option...
	// ...
},
```

The handler gets called if the option is given or if it was not explicitly 
given but has a default value set.

`opts` contains the mutable list of arguments passed to the script
starting just after the currently handled option/command. If the handler
needs to handle it's own arguments it can modify this list in place and
the _parser_ will continue from the resulting state.

One use-case for this would be and option handler that needs to handle
it's arguments in a custom manner, for example for handling multiple 
arguments.

`key` is the actual normalized (`[<prefix-char>]<name-str>`)
option/command triggering the `.handler(..)`.

This can be useful to identify the actual option triggering the handler
when using aliases, if a single handler is used for multiple options, or
when it is needed to handle a specific prefix differently (a-la `find`'s 
syntax with `+option` and `-option` having different semantics).

`value` gets the value passed to the option. 

A _value_ can be passed either explicitly passed (via `=` syntax), 
implicitly parsed from the `argv` via the `<option>.arg` definition or 
is `undefined` otherwise.

A handler can return one of the `THEN`, `STOP` or `ParserError` instance 
to control further parsing and/or execution.
(See: [`THEN` / `STOP`](#then-stop) for more info.)


#### `<option>.doc`

Option/command documentation string used in `-help`.

If this is set to `false` the option will be hidden from `-help`.


#### `<option>.priority`

Option/command priority in the `-help`.

Can be a positive or negative number or `undefined`.

Ordering is as follows:
- options in descending positive `.priority`,
- options with undefined `.priority` in order of definition,
- options in descending negative `.priority`.

Note that options and commands are grouped separately.


#### `<option>.arg`

Option/command argument definition.

```
arg: '<arg-name>'
arg: '<arg-name> | <key>'
```

If defined and no explicit value is passed to the option command (via `=`)
then the _parser_ will consume the directly next non-option if present in
`argv` as a value, passing it to the `<option>.type` handler, if defined,
then the `<option>.handler(..)`, if defined, or setting it to `<key>`
otherwise.

Sets the option/command argument name given in `-help` for the option
and the key where the value will be written.

The `<key>` is not used if `<option>.handler(..)` is defined.


#### `<option>.type`

Option/command argument type definition. 

The given type handler will be used to convert the option value before
it is passed to the handler or set to the given `<key>`.

Supported types:
- `"string"` (default behavior)
- `"bool"`
- `"int"`
- `"float"`
- `"number"`
- `"date"` &ndash; expects a `new Date(..)` compatible date string
- `"list"` &ndash; expects a `","`-separated value, split and written as 
	an `Array` object

Type handlers are defined in `Parser.typeHandlers` or can be overwritten
by `<spec>.typeHandlers`.

If not set values are written as strings. 

Defining a new global type handler:
```javascript
// check if a value is email-compatible...
argv.Parser.typeHandlers.email = function(value, ...options){
	if(!/[a-zA-Z][a-zA-Z.-]*@[a-zA-Z.-]+/.test(value)){
		throw new TypeRrror('email: format error:', value) }
	return value }
```

Defining a local to parser instance type handler:
```javascript
var parser = new Parser({
	// Note that inheriting from the global type handlers is required 
	// only if one needs to use the global types, otherwise just setting
	// a bare object is enough...
	typeHandlers: Object.assign(Object.create(Parser.typeHandlers), {
		email: function(value, ...options){
			// ...
		},
		// ...
	}),

	// ...
})
```


#### `<option>.collect`

Option value collection mode.

The given handler will be used to _collect_ values passed to multiple 
occurrences of the option and write the result to `<key>`.

Supported collection modes:
- `"list"` &ndash; group values into an `Array` object
- `"set"` &ndash; group values into a `Set` object
- `"string"` &ndash; concatenate values into a string.  
  This also supports an optional separator, for example `"string|\t"` will 
  collect values into a string joining them with a tab (i.e. `"\t"`).  
  Default separator is: `" "`
- `"toggle"` &ndash; toggle option value (bool).  
  Note that the actual value assigned to an option is ignored here and can
  be omitted.

Type handlers are defined in `Parser.valueCollectors` or can be overwritten
by `<spec>.valueCollectors`.

`<option>.collect` can be used in conjunction with `<option>.type` to both 
convert and collect values.

If not set, each subsequent option will overwrite the previously set value.

Defining a global value collector:
```javascript
// '+' prefixed flags will add values to set while '-' prefixed flag will 
// remove value from set...
argv.Parser.valueCollectors.Set = function(value, current, key){ 
	current = current || new Set()
	return key[0] != '-' ?
		current.add(value) 
		: (cur.delete(value), current) }
```

Defining handlers local to a parser instance handler is the same as for 
[type handlers](#optiontype) above.


#### `<option>.env`

Determines the environment variable to be used as the default value for
option/command, if set.

If this is set, the corresponding environment variable is non-zero and
`<option>.handler(..)` is defined, the handler will be called regardless
of weather the option was given by the user or not.


#### `<option>.default`

Sets the default value for option/command's value.

If this is set to a value other than `undefined` and
`<option>.handler(..)` is defined, the handler will be called regardless
of weather the option was given by the user or not.


#### `<option>.required`

Sets weather the _parser_ should complain/err if option/command is
not given.


#### `<option>.valueRequired`

Sets weather the _parser_ should complain/err if option/value value is
not given.



### Built-in options

#### `-` / `--`

Stop processing further options.

This can be used to terminate nested parsers or to stop option processing
in the root parser to handle the rest of the options in `<parser>.then(..)`,
for example.


#### `-*` / `@*`

Handle options/commands for which no definition is found.

By default `-*` will print an "unhandled option/command" error and terminate.

By default `@*` is an alias to `-*`.


#### `-v` / `--version`

This will output the value of `.version` and exit.


#### `-q` / `--quiet`

This will turn quiet mode on.

In quiet mode [`<parser>.print(..)`](#parserprint--parserprinterror) will 
not print anything.

Passing [`--help`](#-h----help) or [`--version`](#-v----version) will 
disable quiet mode and print normally.

Note that this will only set `<parser>.quiet` to `true` and disable output
of [`<parser>.print(..)`](#parserprint--parserprinterror), any user code 
needs to either also use [`<parser>.print(..)`](#parserprint--parserprinterror) 
for output (not always practical) or respect `<parser>.quiet`.


#### `-h` / `--help`

By default `-help` will output in the following format:
```
<usage>

<doc>

Options:
	<option-spec> <option-val>		
				- <option-doc>
				  (<opt-required>, <opt-default>, <opt-env>)
	...

Dynamic options:
	...

Commands:
	...

Examples:
	...

<footer>
```
All sections are optional and will not be rendered if they contain no data.


##### Value placeholders

All documentation strings can contain special placeholders that 
will get replaced with appropriate values when rendering help.

- `$SCRIPTNAME` replaced with the value of `.scriptName`,
- `$VERSION` replaced with `.version`,
- `$LICENSE` replaced with `.license`.


##### Automatically defined values

These values are set by the parser just before parsing starts:
- `.script` - full script path, usually this is the value of `argv[0]`,
- `.scriptName` - base name of the script,
- `.scriptPath` - path of the script.

These will be overwritten when the parser is called.


##### `<parser>.doc`
Script documentation.

    <spec>.doc = <string> | <function>

Default value: `undefined`


##### `<parser>.usage`
Basic usage hint.

    <spec>.usage = <string> | <function> | undefined

Default value: `"$SCRIPTNAME [OPTIONS]"`


##### `<parser>.version`
Version number.

    <spec>.usage = <string> | <function> | undefined

If this is not defined `-version` will print `"0.0.0"`.

Default value: `undefined`


##### `<parser>.license`
Short license information.

    <spec>.usage = <string> | <function> | undefined

Default value: `undefined`


##### `<parser>.examples`

    <spec>.usage = <string> | <list> | <function> | undefined

Example list format:

	[
		[<example-code>, <example-doc>, ...],
		...
	]

Default value: `undefined`


##### `<parser>.footer`

Additional information.

    <spec>.footer = <string> | <function> | undefined

Default value: `undefined`


##### More control over help...

For more info on help formatting see `<parser>.help*` attributes in the [source](./argv.js).


### Nested parsers

An option/command handler can be a _parser instance_.

From the point of view of the _nested parser_ nothing is different &ndash; 
it gets passed the remaining list of arguments and handles it on it's own.

The _containing parser_ treats the nested parser just like any normal 
handler with it's attributes and API.

Note that if the _nested parser_ consumes the rest of the arguments,
the _containing parser_ is left with an empty list and it will stop 
parsing and return normally.

A way to explicitly stop the _nested parser_ processing at a specific 
point in the argument list is to pass it a `-` argument at that point.

For example:
```shell
$ script -a nested -b -c - -x -y -z
```

Here `script` will handle `-a` then delegate to `nested` which in turn
will consume `-b`, `-c` and on `-` return, rest of the arguments are 
again handled by `script`.

This is similar to the way programming languages handle passing arguments 
to functions, for example in [Lisp](https://en.wikipedia.org/wiki/Common_Lisp) 
this is similar to:
```lisp
(script a (nested b c) x y z)
```

And in _C-like-call-syntax_ languages like 
[C](https://en.wikipedia.org/wiki/C_(programming_language))/[Python](https://python.org)/JavaScript/... 
this would (a bit less cleanly) be:
```javascript
script(a, nested(b, c), x, y, z)
```

The difference here is that `nested` has control over what it handles, and
depending on its definition, can either override the default `-` option as 
well as stop handling arguments at any point it chooses (similar to _words_ 
in stack languages like [Fort](https://en.wikipedia.org/wiki/Forth_(programming_language)) 
or [Factor](https://factorcode.org/)).

<!-- 
XXX split ./lang.js from ./test.js...

See [lang.js](./lang.js) for more fun with argv and programming languages ;)
-->



## Components and API

### `THEN` / `STOP`

Values that if returned by option/command handlers can control the parse flow.

- `THEN` &ndash; Stop parsing and call `<parser>.then(..)` callbacks.
- `STOP` &ndash; Stop parsing and call `<parser>.stop(..)` callbacks, 
  skipping `<parser>.then(..)`.


`THEN` is useful when we want to stop option processing and trigger the 
post-parse stage (i.e. calling `<parser>.then(..)`) for example to pass 
the rest of the options to some other command.

`STOP` is used for options like `-help` when no post-parsing is needed.


### `ParserError(..)` 

A base error constructor. 

If an instance of `ParseError` is thrown or returned by the handler parsing
is stopped, `<parsing>.error(..)` is called and then the parser will exit 
with an error (see: [`<parser>.handleErrorExit(..)`](#parserhandleerrorexit)).

The following error constructors are also defined:
- `ParserTypeError(..)`
- `ParserValueError(..)`

Note that `ParserError` instances can be both returned or thrown.


### `Parser(..)` 

Construct a parser instance
```
Parser(<spec>)
	-> <parser>
```

See [`<parser>(..)`](#parser-1) for more info.


#### `<parser>.then(..)`

Add callback to `then` "event".
```
<parser>.then(<callback>)
	-> <parser>
```

```
callback(<unhandled>, <root-value>, <rest>)
	-> <obj>
```

`then` is triggered when parsing is done or stopped from an option
handler by returning `THEN`.


#### `<parser>.stop(..)`

Add callback to `stop` "event".
```
<parser>.stop(<callback>)
	-> <parser>
```

```
callback(<arg>, <rest>)
	-> <obj>
```

`stop` is triggered when a handler returns `STOP`.


#### `<parser>.error(..)`

Add callback to `error` "event".
```
<parser>.error(<callback>)
	-> <parser>
```

```
callback(<reason>, <arg>, <rest>)
	-> <obj>
```

`error` is triggered when a handler returns `ERROR`.


#### `<parser>.off(..)`

Remove callback from "event".
```
	<parser>.off(<event>, <callback>)
		-> <parser>
```


#### `<parser>(..)`

Execute the `parser` instance.

Run the parser on `process.argv`
```
<parser>()
	-> <result>
```

Explicitly pass a list of arguments where `<argv>[0]` is treated as 
the script path.
```
<parser>(<argv>)
	-> <result>
```

Explicitly pass both a list of arguments and script path.
```
<parser>(<argv>, <main>)
	-> <result>
```

If `<main>` is present in `<argv>` all the arguments before it will 
be ignored, otherwise the whole list is processed as if `<main>` was 
its head.



## Advanced parser API

### `<parser>.print(..)` / `<parser>.printError(..)`

Handle how `<parser>` prints things.

`<parser>.print(..)` and `<parser>.printError(..)` are very similar but handle different 
cases, similar to `console.log(..)` and `console.error(..)`
```
<parser>.print(...)
	-> <parser>

<parser>.printError(...)
	-> <parser>
<parser>.printError(<error>, ...)
	-> <error>
```

Both support callback binding:
```
<parser>.print(<func>)
	-> <parser>

<parser>.printError(<func>)
	-> <parser>
```

Both `<parser>.print(..)` and `<parser>.printError(..)` can safely be 
overloaded if the callback feature is not going to be used by the user 
&ndash; the print callbacks are not used internally.  

For full callback API see: `extra.afterCallback(..)` in [argv.js](./argv.js).


### `<parser>.handlerDefault(..)`

Called when `<option>.handler(..)` is not defined.

By default this sets option values on the _parsed_ object.


### `<parser>.handleArgumentValue(..)`

Handle argument value conversion.

By default this handles the `<option>.type` mechanics.

If this is set to `false` values will be set as-is.


### `<parser>.handleErrorExit(..)`

Handle exit on error.

By default this will call process.exit(1) for the _root parser_ and does 
nothing for _nested parsers_.

If set to `false` the _parser_ will simply return like any normal function.


### `<parser>.handle(..)`

Manually trigger `<arg>` handling.
```
<parser>.handle(<arg>, <rest>, <key>, <value>)
	-> <res>
```

This is intended to be used for delegating handling from one handler to 
another. Note that this does not handle errors or other protocols handled
by `<parser>(..)`, this only calls the `<arg>` handler (or if it was not 
defined the _default handler_) so it is not recommended for this to be 
called from outside an option handler method/function.

This is not intended for overloading.


### `<parser>.setHandlerValue(..)`

Set handler value manually, this uses `<handler>.arg` and if not set `<key>` to 
write `<value>` on the _parsed_ object.
```
<parser>.setHandlerValue(<handler>, <key>, <value>)
	-> <parser>
```

This is useful when extending `argv.js`, for client code values can be set 
directly.

This is not intended for overloading.


### More...

For more info see the [source](./argv.js).


## License

[BSD 3-Clause License](./LICENSE)

Copyright (c) 2016-2020, Alex A. Naanou,  
All rights reserved.


<!-- vim:set ts=4 sw=4 spell : -->