[WIP] Add conventions documentation

guides/conventions.md

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+# Conventions
+
+1. [Application Namespaces](conventions/namespaces.md)
+2. [Rails Conventions](conventions/rails.md)
+3. [File Structure](conventions/file-structure.md)

guides/conventions/file-structure.md

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+[Conventions](/guides/conventions.md) /
+
+# File Structure
+
+- [assets](file-structure/assets.md)
+- [components](file-structure/components.md)
+- [controllers](file-structure/controllers.md)

guides/conventions/file-structure/assets.md

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+[Conventions](/guides/conventions.md) / [File Structure](/guides/conventions/file-structure.md) /
+
+# Assets
+
+Images, videos, and stylesheets are stored in the `assets` directory.
+
+```
+.
+└ app
+  └─ assets
+      ├─ images
+      └─ stylesheets
+          ├─ [namespace]
+          │   └─ application.scss
+          └─ application.scss
+```
+
+The top-level `application.scss` is the shared stylesheet for all namespaces.
+
+The `find/application.scss` stylesheet should be included into the `layouts/find/application.html.erb` layout alongside the top-level `application.scss` stylesheet.

guides/conventions/file-structure/components.md

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+[Conventions](/guides/conventions.md) / [File Structure](/guides/conventions/file-structure.md) /
+
+# View Components
+
+We use [View Components](https://viewcomponent.org/) to create reusable components in our Rails applications.
+
+```
+.
+└ app
+  └─ components
+      ├─ [namespace] (Namespace-specific components)
+      │   ├─ [component_name].rb
+      │   └─ [component_name].html.erb
+      ├─ [model_name] (Model-specific components)
+      │   ├─ [component_name].rb
+      │   └─ [component_name].html.erb
+      ├─ [component_name].rb
+      └─ [component_name].html.erb
+```

guides/conventions/file-structure/controllers.md

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+[Conventions](/guides/conventions.md) / [File Structure](/guides/conventions/file-structure.md) /
+
+# Controllers
+
+We organise our controllers within our namespaces.
+
+We should follow resourceful controller conventions.
+
+```
+.
+└ app
+  └─ controllers
+      ├─ [namespace] (Namespace-specific controllers)
+      │   ├─ [controller_name]_controller.rb
+      │   └─ application_controller.rb
+      └─ application_controller.rb
+```
+
+Each namespace has its own `ApplicationController` as a base for all controllers within that namespace.
+
+```ruby
+# Top-level application controller.
+# Shared functionality across all namespaces.
+class ApplicationController < ActionController::Base
+  include Pundit::Authorization
+end
+
+# Find application controller.
+# Base controller for all Find controllers.
+class Find::ApplicationController < ApplicationController
+end
+
+# The API application controller inherits from ActionController::API.
+# Base controller for all API controllers.
+class API::ApplicationController < ActionController::API
+end
+
+# The base controller for all v1 API controllers.
+class API::V1::ApplicationController < API::ApplicationController
+end
+```
+
+This allows us to set base functionality across groups of controllers.
+
+The pattern described in [ADR#6 Controller Structure](/guides/adr/0006-controller-structure.md) details a scalable pattern to managing nested resourceful controllers.
+
+```ruby
+class Find::RecruitmentCycles::CoursesController < Find::ApplicationController
+  # GET /recruitment_cycles/:recruitment_cycle_id/courses
+  def index
+    @courses = recruitment_cycle.courses
+  end
+
+  # GET /recruitment_cycles/:recruitment_cycle_id/courses/:id
+  def show
+    @course = recruitment_cycle.courses.find(params[:id])
+  end
+
+  private
+
+  def recruitment_cycle
+    @recruitment_cycle ||= RecruitmentCycle.find(params[:recruitment_cycle_id])
+  end
+end
+```
+
+The `params[:id]` should always be the ID of the resource being acted upon. Parent resources should always be prefixed, e.g. `params[:recruitment_cycle_id]`.

guides/conventions/namespaces.md

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+[Conventions](/guides/conventions.md) /
+
+# Namespaces
+
+We use namespaces to organise our code into service-specific modules. This provides us with visibility of separation of concerns.
+
+We benefit from this separtation in the following ways:
+
+- Code under a namespace is intended to be used only by the service it belongs to.
+
+  We can easily detect when code is used incorrectly outside of its namespace.
+
+  This limits the blast radius of changes to a single service. For example, we can confidently make changes to a `Find` component and expect that it will only effect the "Find" service.
+
+- Explicit shared code.
+
+  If code is shared, it is in the top-level namespace.
+
+  We can visually determine how much code is shared between services by looking at the non-namespaced files.
+
+## Our namespaces
+
+- `Find`
+- `Publish`
+- `Support`
+- `API`

guides/conventions/rails.md

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+[Conventions](/guides/conventions.md) /
+
+# Rails Architecture
+
+This document describes the Rails conventions of this application.
+
+## 1. File Structure
+
+Learn more about each of the directories' purposes in the [File Structure](conventions/file-structure.md) guide.
+
+```
+.
+└ app
+  ├─ assets
+  ├─ components (View Components)
+  ├─ controllers
+  ├─ forms (Form Objects)
+  ├─ helpers
+  ├─ javascript
+  ├─ jobs
+  ├─ lib
+  ├─ mailers
+  ├─ models
+  ├─ policies
+  ├─ serializers
+  ├─ services (Service Objects)
+  ├─ validators
+  ├─ views
+  └─ wizards
+```
+
+The following directories are deprecated and should be removed:
+
+- `app/decorators`
+
+  We should put decorator-type methods in models themselves.
+
+- `app/view_objects`
+
+  We should use View Components (`app/components`) instead.
+
+## 2. Environments
+
+There are 2 kinds of environments we need to maintain:
+
+1. Rails environment (`RAILS_ENV`)
+
+    There are 3 Rails environments:
+
+    - `production`
+    - `test`
+    - `development`
+
+2. Application environment (`APP_ENV`) - This is commonly known as Hosting environment in other BAT applications.
+
+    This environment is used to determine the settings of the application.
+
+    There are 5 Application environments:
+
+    - `review`
+    - `qa`
+    - `staging`
+    - `sandbox`
+    - `production`
+
+    The `loadtest` and `rollover` environments are deprecated and should be removed. We can use `staging` temporarily for these use-cases.