abstract-state-router/lib/state-comparison.js

const stateStringParser = require('./state-string-parser')
const extend = require('./extend.js')

const combine = require('combine-arrays')
const pathToRegexp = require('path-to-regexp-with-reversible-keys')

module.exports = function StateComparison(stateState) {
	const getPathParameters = pathParameters()

	const parametersChanged = args => parametersThatMatterWereChanged(extend(args, { stateState, getPathParameters }))

	return args => stateComparison(extend(args, { parametersChanged }))
}

function pathParameters() {
	const parameters = {}

	return path => {
		if (!path) {
			return []
		}

		if (!parameters[path]) {
			parameters[path] = pathToRegexp(path).keys.map(function(key) {
				return key.name
			})
		}

		return parameters[path]
	}
}

function parametersThatMatterWereChanged({ stateState, getPathParameters, stateName, fromParameters, toParameters }) {
	const state = stateState.get(stateName)
	const querystringParameters = state.querystringParameters || []
	const parameters = getPathParameters(state.route).concat(querystringParameters)

	return Array.isArray(parameters) && parameters.some(
		key => fromParameters[key] !== toParameters[key]
	)
}

function stateComparison({ parametersChanged, original, destination }) {
	const states = combine({
		start: stateStringParser(original.name),
		end: stateStringParser(destination.name),
	})

	return states.map(({ start, end }) => ({
		nameBefore: start,
		nameAfter: end,
		stateNameChanged: start !== end,
		stateParametersChanged: start === end && parametersChanged({
			stateName: start,
			fromParameters: original.parameters,
			toParameters: destination.parameters,
		}),
	}))
}