exercism/elixir/community-garden/README.md

# Community Garden

Welcome to Community Garden on Exercism's Elixir Track.
If you need help running the tests or submitting your code, check out `HELP.md`.
If you get stuck on the exercise, check out `HINTS.md`, but try and solve it without using those first :)

## Introduction

## Agent

The `Agent` module facilitates an abstraction for spawning [processes and the _receive-send_ loop][exercism-processes]. From here, we will call processes started using the `Agent` module _'agent processes'_. An _agent process_ might be chosen to represent a central shared state.

To start an _agent process_, `Agent` provides the `start/2` function. The supplied function when `start`_-ing_ the _agent process_ returns the initial state of the process:

```elixir
# Start an agent process with an initial value of an empty list
{:ok, agent_pid} = Agent.start(fn -> [] end)
```

Just like `Map` or `List`, `Agent` provides many functions for working with _agent processes_.

It is customary to organize and encapsulate all `Agent`-related functionality into a module for the domain being modeled.

[exercism-processes]: https://exercism.org/tracks/elixir/concepts/processes

## Instructions

Your community association has asked you to implement a simple registry application to manage the community garden registrations. The `Plot` struct has already been provided for you.

## 1. Open the garden

Implement the `CommunityGarden.start/1` function, it should receive an optional keyword list of options to pass forward to the _agent process_. The garden's initial state should be initialized to represent an empty collection of plots. It should return an `:ok` tuple with the garden's pid.

```elixir
{:ok, pid} = CommunityGarden.start()
# => {:ok, #PID<0.112.0>}
```

## 2. List the registrations

Implement the `CommunityGarden.list_registrations/1` function. It should receive the `pid` for the community garden. It should return a list of the stored plots that are registered.

```elixir
CommunityGarden.list_registrations(pid)
# => []
```

> At this point, we haven't added the ability to register a plot, so this list should be empty

## 3. Register plots to a person

Implement the `CommunityGarden.register/2` function. It should receive the `pid` for the community garden and a name to register the plot. It should return the `Plot` struct with the plot's id and person registered to when it is successful.

The ids should be incremental and unique. You can keep an id counter in the agent's state.

```elixir
CommunityGarden.register(pid, "Emma Balan")
# => %Plot{plot_id: 1, registered_to: "Emma Balan"}
CommunityGarden.list_registrations(pid)
# => [%Plot{plot_id: 1, registered_to: "Emma Balan"}]
```

## 4. Release plots

Implement the `CommunityGarden.release/2` function. It should receive the `pid` and `id` of the plot to be released. It should return `:ok` on success. When a plot is released, the id is not re-used, it is used as a unique identifier only.

```elixir
CommunityGarden.release(pid, 1)
# => :ok
CommunityGarden.list_registrations(pid)
# => []
```

## 5. Get a registered plot

Implement the `CommunityGarden.get_registration/2` function. It should receive the `pid` and `id` of the plot to be checked. It should return the plot if it is registered, and `:not_found` if it is unregistered.

```elixir
CommunityGarden.get_registration(pid, 1)
# => %Plot{plot_id: 1, registered_to: "Emma Balan"}
CommunityGarden.get_registration(pid, 7)
# => {:not_found, "plot is unregistered"}
```

## Source

### Created by

- @neenjaw

### Contributed to by

- @angelikatyborska
- @jrr
- @efx
- @justin-m-morgan
- @cr0t