index.js

'use strict'
const arrify = require("arrify")

const types = {
	add: "added",
	change: "changed",
	unlink: "removed"
}

module.exports = function (fly) {
	fly.plugin('watch', {every: 0, files: 0}, function * (_, globs, tasks, opts) {
		globs = arrify(globs)
		tasks = arrify(tasks)
		opts = opts || {}
		// announce start
		this.emit("fly_watch")

		return require("chokidar")
			.watch(globs, {ignoreInitial: 1})
			.on("error", this.$.error)
			.on("all", (event, filepath) => {
				// store previous globs (`prevs`)
				// used within `target` for `trims`
				this._.prevs = globs
				// also update ALL chained `tasks` for their own `target`
				tasks.forEach(k => {
					fly.tasks[k].data.prevs = globs
				})
				// broadcast
				this.emit("fly_watch_event", {action: types[event], file: filepath})
				// pass single file to task params
				opts.src = filepath
				// re-run task chain
				return this.serial(tasks, opts)
			})
	})
}