budibase/packages/string-templates/README.md

# String templating
This package provides a common system for string templating across the Budibase Builder, client and server.
The templating is provided through the use of [Handlebars](https://handlebarsjs.com/) an extension of Mustache
which is capable of carrying out logic. We have also extended the base Handlebars functionality through the use 
of a set of helpers provided through the [handlebars-helpers](https://github.com/helpers/handlebars-helpers) package.

We have not implemented all the helpers provided by the helpers package as some of them provide functionality
we felt would not be beneficial. The following collections of helpers have been implemented:
1. [Math](https://github.com/helpers/handlebars-helpers/tree/master#math) - a set of useful helpers for 
carrying out logic pertaining to numbers e.g. `avg`, `add`, `abs` and so on.
2. [Array](https://github.com/helpers/handlebars-helpers/tree/master#array) - some very specific helpers
for use with arrays, useful for example in automations. Helpers like `first`, `last`, `after` and `join` 
can be useful for getting particular portions of arrays or turning them into strings.
3. [Number](https://github.com/helpers/handlebars-helpers/tree/master#number) - unlike the math helpers these
are useful for converting numbers into useful formats for display, e.g. `bytes`, `addCommas` and `toPrecision`.
4. [URL](https://github.com/helpers/handlebars-helpers/tree/master#url) - very specific helpers for dealing with URLs,
such as `encodeURI`, `escape`, `stripQueryString` and `stripProtocol`. These are primarily useful
for building up particular URLs to hit as say part of an automation.
5. [String](https://github.com/helpers/handlebars-helpers/tree/master#string) - these helpers are useful for building 
strings and preparing them for display, e.g. `append`, `camelcase`, `capitalize` and `ellipsis`.
6. [Comparison](https://github.com/helpers/handlebars-helpers/tree/master#comparison) - these helpers are mainly for 
building strings when particular conditions are met, for example `and`, `or`, `gt`, `lt`, `not` and so on. This is a very
extensive set of helpers but is mostly as would be expected from a set of logical operators.

## Format
There are two main ways that the templating system can be used, the first is very similar to that which
would be produced by Mustache - a single statement:
```
Hello I'm building a {{uppercase adjective}} string with Handlebars!
```
In the statement above provided a context of `{adjective: "cool"}` will produce a string of `Hello I'm building a COOL string with Handlebars!`.
Here we can see an example of how string helpers can be used to make a string exactly as we need it. These statements are relatively
simple; we can also stack helpers as such: `{{ uppercase (remove string "bad") }}` with the use of parenthesis.

The other type of statement that can be made with the templating system is conditional ones, that appear as such:
```
Hello I'm building a {{ #gte score "50" }}Great{{ else }}Bad{{ /gte }} string with Handlebars!
``` 
In this string we can see that the string `Great` or `Bad` will be inserted depending on the state of the 
`score` context variable. The comparison, string and array helpers all provide some conditional operators which can be used
in this way. There will also be some operators which will be built with a very similar syntax but will produce an 
iterative operation, like a for each - an example of this would be the `forEach` array helper.

## Usage
Usage of this templating package is through one of the primary functions provided by the package - these functions are 
as follows:
1. `processString` - `async (string, object)` - given a template string and a context object this will build a string 
using our pre-processors, post-processors and handlebars.
2. `processObject` - `async (object, object)` - carries out the functionality provided by `processString` for any string 
inside the given object. This will recurse deeply into the provided object so for very large objects this could be slow.
3. `processStringSync` - `(string, object)` - a reduced functionality processing of strings which is synchronous, like 
functions provided by Node (e.g. `readdirSync`)
4. `processObjectSync` - `(object, object)` - as with the sync'd string, recurses an object to process it synchronously.
5. `makePropSafe` - `(string)` - some properties cannot be handled by Handlebars, for example `Table 1` is not valid due 
to spaces found in the property name. This will update the property name to `[Table 1]` wrapping it in literal
specifiers so that it is safe for use in Handlebars. Ideally this function should be called for every level of an object
being accessed, for example `[Table 1].[property name]` is the syntax that is required for Handlebars. 
6. `isValid` - `(string)` - checks the given string for any templates and provides a boolean stating whether it is a valid
template.

## Development
This library is built with [Rollup](https://rollupjs.org/guide/en/) as many of the packages built by Budibase are. We have
built the string templating package as a UMD so that it can be used by Node and Browser based applications. This package also 
builds Typescript stubs which when making use of the library will be used by your IDE to provide code completion. The following 
commands are provided for development purposes:
1. `yarn build` - will build the Typescript stubs and the bundle into the `dist` directory.
2. `yarn test` - runs the test suite which will check various helpers are still functioning as
expected and a few expected use cases.
3. `yarn dev:builder` - an internal command which is used by lerna to watch and build any changes
to the package as part of the main `yarn dev` of the repo.

It is also important to note this package is managed in the same manner as all other in the mono-repo,
through lerna.