# Installing third party libraries

# Abstract

The current `ng install` process is faulty; third parties have to add a `bundles/` directory
with metadata that we expect. This document explores ways to improve on the process.

# Requirements

The following use cases need to be supported by `ng install`:

1. Support for _any_ thirdparties, ultimately falling back to running `npm install` only and
doing nothing else, if necessary.
1. Not a new package manager.
1. Metadata storage by thirdparties in `package.json`. This must be accessible by plugins for
the build process or even when scaffolding.
1. Proper configuration of SystemJs in the browser.
1. SystemJS configuration managed by the user needs to be kept separated from the autogenerated
part.
1. The build process right now is faulty because the `tmp/` directory used by Broccoli is
inside the project. TypeScript when using `moduleResolution: "node"` can resolve the
`node_modules` directory (since it's in an ancestor folder), which means that TypeScript
compiles properly, but the build does not copy files used by TypeScript to `dist/`. We need
to proper map the imports and move them to `tmp` before compiling, then to `dist/` properly.
1. Potentially hook into scaffolding.
1. Potentially hook into the build.
1. Safe uninstall path.

# Usages

Here's a few stories that should work right off:

```sh
$ ng new my-app && cd my-app/
$ ng install jquery
```
^(this makes jQuery available in the index)

```sh
$ ng install angularfire2
> Please specify your Firebase database URL [my-app.firebaseio.com]: _
```
^(makes firebase available and provided to the App)

```sh
$ ng install angularfire2 --dbUrl=my-firebase-db.example.com
```
^(skip prompts for values passed on the command line)

```sh
$ ng install angularfire2 --quiet
```
^(using `--quiet` to skip all prompts and use default values)

```sh
$ ng install less
```
^(now compiles CSS files with less for the appropriate extensions)

# Proposed Solution

The `install` task will perform the following subtasks:

1. **Run `npm install ${libName}`.** On failure, fail the install process.
1. **Run `preinstall` scripts.** If any script fails, run `npm uninstall ${libName}` and fail
   the install process.
1. **Copy the `appData` to the `angular.json` file of the generated app, creating it if it
   doesn't exist, under the `"modules"` key.** This data will be sent to the App as is. See the
   [appData](#appData) section for more information.
1. **Read the `package["angular-cli"].appPrompt` and prompt the user configuration values,
   if any.** See the [appData](#appData) section for more information.
1. **Add the providers specified in `package["angular-cli"]["providers"]` to the angular.js
   `providers` list.** Rebuild the `providers.js` file. See the [Providers](#providers)
   section for more information.
1. **Run `package["angular-cli"].scripts["install"]` if it exists.** If the script fails,
   run `npm uninstall ${libName}` and fail the install process.
1. **Detect if a package named `angular/cli-wrapper-${libName}` exist in the angular
   organization.** If so, run the steps above as if ng install angular/angular-${libName}. If
   this install fails, ignore the failure.

   These packages can be used to wrap libraries that we want to support but can't update
   easily, like Jasmine or LESS.
1. **Install typings.** See the [Typings](#typings) section.
1. **Run `postinstall` scripts.**

# Proof of Concept
A proof of concept is being developed.

# Hooks
The third party library can implement hooks into the scaffolding, and the build system. The
CLI's tasks will look for the proper hooks prior to running and execute them.

The order of execution of these hooks is breadth first, going through all node packages and
checking for the `package['angular-cli']['hooks']['${hookName}']`. The hooks are then
`require()`'d as is, from within the app root folder. Within the same level of the dependency
tree, there is no guarantee for the order of execution.

## Install Hooks
The only tricky part here is install hooks. The installed package should recursively call
its `(pre|post|)install` hooks only on packages that are newly installed. It should call
`(pre|post|)reinstall` on those who were already installed. A map of the currently installed
packages should be kept before performing `npm install`.

# <a name="appData">appData</a>
The `angular-cli` key in the generated app should be used for Angular CLI specific data.
This includes the CLI configuration itself, as well as third-parties library configuration.

Third-parties can store data that will be passed to the app, and can use that data themselves.
That data can be anything. Any keys starting with either `$` or `_` will be ignored and not
passed to the client. It could be used for builds or scaffolding information.

During installation, there's a step to prompt the user for data. The schema contains a prompt
text and a default value. The default value type is used to convert the string entered by the
user. The key used in `appPrompt` is the key saved in appData.

Example:

```typescript
{ // ...
  "angular-cli": {
    "appPrompt": {
      "number": {
        "prompt": "Please enter a number:",
        "defaultValue": 0
      },
      "url": {
        "prompt": "URL of your website:",
        "defaultValue": "${homepage}"
      }
    }
  }
}
```

The default value is necessary as a `quiet` mode is enforced, using default values to fill
in the data without user interaction. The special strings `${...}` can be used to replace
with special values in the default string values. The values are taken from the `package.json`.

We use a declarative style to enforce sensible defaults and make sure developers think about
this. *In the case where developers want more complex interaction, they can use the
install/uninstall hooks to prompt users.* But 3rd party libraries developers need to be aware
that those hooks might not prompt users (no STDIN) and throw an error.

# <a name="providers">Providers</a>
Adding Angular providers to the app should be seamless. The install process will create a
`providers.js` from all the providers contained in all the dependencies. The User can disclude
providers it doesn't want.

The `providers.js` file will always be overwritten by the `install` / `uninstall` process. It
needs to exist for toolings to be able to understand dependencies. These providers are global
to the application.

In order to prevent providers from being global, the user can use the `--no-global-providers`
flag during installation, or can change the dependencies by using `ng providers`. As an example:

```bash
ng new my-todo-app
ng generate component database
ng install --no-global-providers angularfirebase2
ng providers database angularfirebase2
```

Or, alternatively, the user can add its own providers and dependencies to its components.

# Dependencies
Because dependencies are handled by `npm`, we don't have to handle it.

# <a name="typings">Typings</a>
Typings should be added, but failure to find typings should not be a failure of installation. The
user might still want to install custom typings himself in the worst case.

The `typings` package can be used to install/verify that typings exist. If the typings do not exist natively, we should tell the user to install the ambient version if he wants to.

# Index.html
We do not touch the `index.html` file during the installation task. The default page should
link to a SystemJS configuration file that is auto generated by the CLI and not user
configurable (see SystemJS below). If the user install a third party library, like jQuery, and
wants to use it, they have to import it using `import * as $ from 'vendor/jquery'`.

The `index.html` also includes a section to configure SystemJS that can be managed by the user.
This is separate from the generated code.

# SystemJS
It is important that SystemJS works without any modifications by the user. It is also important
to leave the liberty to the user to change the SystemJS configuration so that it fits their needs.

We will not use SystemJS bundles in development. This is for better debugging, future proofing
(when moving the build system) and better CDN support, as many of the loaded files will end up
being pulled from a CDN in production. During the `ng build` process for production, the
SystemJS configuration script will be rebuilt to fetch from the CDN.

# Upgrade Strategy
The upgrade process simply uses NPM. If new appData is added, it should be added manually using
a migration hook for `postinstall`.

# Remaining Problems

1. Installing dependencies of packages need to be further sketched out.
2. Need to add a fully fledged example with Firebase.
