Bot command processing

[Half-Shot]

This PR is largely a repurposing of https://github.com/Half-Shot/matrix-github/blob/master/src/BotCommands.ts. Notably, it's a class which you bind onto another class that offers command handlers. The idea being that it's then relatively trivial to add new commands, you just add metadata to a function and the rest works.

As an example: https://github.com/Half-Shot/matrix-github/blob/master/src/Connections/GithubRepo.ts#L208-L231

[Half-Shot]

N.B it would be nice if the help command supported categories ala the irc bridge.

[tadzik]

I'm porting Slack command handling to this to see how it fares in practice – will come back with proper review and feedback once I'm done with that – I don't want it to be a component that we ship and then don't use ;)

[jaller94]

What is this? Metadata or a BotCommand?
Please pick a better variable name.

[jaller94]

typo

Suggested change

	Object.getOwnPropertyNames(proto).forEach(propetyKey => {
	const b = Reflect.getMetadata(botCommandSymbol, instance, propetyKey) as BotCommandMetadata;
	if (!b) {
	// Not a bot command function.
	return;
	}
	const optionalArgs = b.optionalArgs?.map((arg: string) => `[${arg}]`) || [];
	const args = [...(b.requiredArgs || []), ...optionalArgs].join(" ");
	content += ` - \`${this.prefix || ""}${b.name}\`${args && " "}${args} - ${b.help}\n`;
	// We know that this is safe.
	const fn = instance[propetyKey];
	Object.getOwnPropertyNames(proto).forEach(propertyKey => {
	const b = Reflect.getMetadata(botCommandSymbol, instance, propertyKey) as BotCommandMetadata;
	if (!b) {
	// Not a bot command function.
	return;
	}
	const optionalArgs = b.optionalArgs?.map((arg: string) => `[${arg}]`) || [];
	const args = [...(b.requiredArgs || []), ...optionalArgs].join(" ");
	content += ` - \`${this.prefix || ""}${b.name}\`${args && " "}${args} - ${b.help}\n`;
	// We know that this is safe.
	const fn = instance[propertyKey];

[jaller94]

Suggested change

	* should **include** any whitspace E.g. `!irc `.
	* should **include** any whitespace E.g. `!irc `.

[tadzik]

Implemented this in Slack for test run here, and a few things stand out:

1. Commands are case-insensitive, which slack did for one admin room but not the other – is it configurable? Desirable?
2. There's no support for documenting command arguments, they only have their names shown
3. No support for named arguments, which Slack admin room took advantage of
4. No type checking for arguments (yargs used to provide that, perhaps we should at least provide a replacement?)
5. No support for detailed help (more verbose than the regular help)
6. doOauth seems to not work, even though it advertises itself as available (is the case insensitivity playing tricks?):

Slack is a bit of an extreme case due to being yargs-based, and its commands could definitely be simplified – but perhaps employing a readymade command line parser is not that bad of an idea? Yargs was not fun to work with, but I've had good experiences with commander recently, and it would cover most of the above bases – perhaps we could plug that in as a backend?