budibase/packages/string-templates/src/index.js

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const handlebars = require("handlebars")
const { registerAll } = require("./helpers/index")
const HBS_CLEANING_REGEX = /{{[^}}]*}}/g
const hbsInstance = handlebars.create()
registerAll(hbsInstance)
function attemptToCorrectError(string) {
return string
}
/**
* When running handlebars statements to execute on the context of the automation it possible user's may input handlebars
* in a few different forms, some of which are invalid but are logically valid. An example of this would be the handlebars
* statement "{{steps[0].revision}}" here it is obvious the user is attempting to access an array or object using array
* like operators. These are not supported by handlebars and therefore the statement will fail. This function will clean up
* the handlebars statement so it instead reads as "{{steps.0.revision}}" which is valid and will work. It may also be expanded
* to include any other handlebars statement cleanup that has been deemed necessary for the system.
*
* @param {string} string The string which *may* contain handlebars statements, it is OK if it does not contain any.
* @returns {string} The string that was input with cleaned up handlebars statements as required.
*/
function cleanHandlebars(string) {
let charToReplace = {
"[": ".",
"]": "",
}
let regex = new RegExp(HBS_CLEANING_REGEX)
let matches = string.match(regex)
if (matches == null) {
return string
}
for (let match of matches) {
let baseIdx = string.indexOf(match)
for (let key of Object.keys(charToReplace)) {
let idxChar = match.indexOf(key)
if (idxChar !== -1) {
string =
string.slice(baseIdx, baseIdx + idxChar) +
charToReplace[key] +
string.slice(baseIdx + idxChar + 1)
}
}
}
return string
}
/**
* Given an input object this will recurse through all props to try and update
* any handlebars statements within.
* @param {object|array} object The input structure which is to be recursed, it is important to note that
* if the structure contains any cycles then this will fail.
* @param {object} context The context that handlebars should fill data from.
* @returns {object|array} The structure input, as fully updated as possible.
*/
module.exports.processObject = (object, context) => {
// JSON stringify will fail if there are any cycles, stops infinite recursion
try {
JSON.stringify(object)
} catch (err) {
throw "Unable to process inputs to JSON, cannot recurse"
}
for (let key of Object.keys(object)) {
let val = object[key]
if (typeof val === "string") {
object[key] = module.exports.processString(object[key], context)
}
// this covers objects and arrays
else if (typeof val === "object") {
object[key] = module.exports.processObject(object[key], context)
}
}
return object
}
/**
* This will process a single handlebars containing string. If the string passed in has no valid handlebars statements
* then nothing will occur.
* @param {string} string The template string which is the filled from the context object.
* @param {object} context An object of information which will be used to enrich the string.
* @returns {string} The enriched string, all templates should have been replaced if they can be.
*/
module.exports.processString = (string, context) => {
if (typeof string !== "string") {
throw "Cannot process non-string types."
}
let template
try {
string = cleanHandlebars(string)
template = hbsInstance.compile(string)
} catch (err) {
string = attemptToCorrectError(string)
template = hbsInstance.compile(string)
}
return template(context)
}
/**
* Errors can occur if a user of this library attempts to use a helper that has not been added to the system, these errors
* can be captured to alert the user of the mistake.
* @param {function} handler a function which will be called every time an error occurs when processing a handlebars
* statement.
*/
module.exports.errorEvents = handler => {
hbsInstance.registerHelper("helperMissing", handler)
}