docs: AGENTS

AGENTS.md

@@ -0,0 +1,79 @@
+This is a Nostr server written using Elixir and PostgreSQL.
+
+## Project guidelines
+
+- Use `mix precommit` alias when you are done with all changes and fix any pending issues
+- Use the already included and available `:req` (`Req`) library for HTTP requests, **avoid** `:httpoison`, `:tesla`, and `:httpc`.
+
+<!-- usage-rules-start -->
+
+<!-- phoenix:elixir-start -->
+## Elixir guidelines
+
+- Elixir lists **do not support index based access via the access syntax**
+
+  **Never do this (invalid)**:
+
+      i = 0
+      mylist = ["blue", "green"]
+      mylist[i]
+
+  Instead, **always** use `Enum.at`, pattern matching, or `List` for index based list access, ie:
+
+      i = 0
+      mylist = ["blue", "green"]
+      Enum.at(mylist, i)
+
+- Elixir variables are immutable, but can be rebound, so for block expressions like `if`, `case`, `cond`, etc
+  you *must* bind the result of the expression to a variable if you want to use it and you CANNOT rebind the result inside the expression, ie:
+
+      # INVALID: we are rebinding inside the `if` and the result never gets assigned
+      if connected?(socket) do
+        socket = assign(socket, :val, val)
+      end
+
+      # VALID: we rebind the result of the `if` to a new variable
+      socket =
+        if connected?(socket) do
+          assign(socket, :val, val)
+        end
+
+- **Never** nest multiple modules in the same file as it can cause cyclic dependencies and compilation errors
+- **Never** use map access syntax (`changeset[:field]`) on structs as they do not implement the Access behaviour by default. For regular structs, you **must** access the fields directly, such as `my_struct.field` or use higher level APIs that are available on the struct if they exist, `Ecto.Changeset.get_field/2` for changesets
+- Elixir's standard library has everything necessary for date and time manipulation. Familiarize yourself with the common `Time`, `Date`, `DateTime`, and `Calendar` interfaces by accessing their documentation as necessary. **Never** install additional dependencies unless asked or for date/time parsing (which you can use the `date_time_parser` package)
+- Don't use `String.to_atom/1` on user input (memory leak risk)
+- Predicate function names should not start with `is_` and should end in a question mark. Names like `is_thing` should be reserved for guards
+- Elixir's builtin OTP primitives like `DynamicSupervisor` and `Registry`, require names in the child spec, such as `{DynamicSupervisor, name: MyApp.MyDynamicSup}`, then you can use `DynamicSupervisor.start_child(MyApp.MyDynamicSup, child_spec)`
+- Use `Task.async_stream(collection, callback, options)` for concurrent enumeration with back-pressure. The majority of times you will want to pass `timeout: :infinity` as option
+
+## Mix guidelines
+
+- Read the docs and options before using tasks (by using `mix help task_name`)
+- To debug test failures, run tests in a specific file with `mix test test/my_test.exs` or run all previously failed tests with `mix test --failed`
+- `mix deps.clean --all` is **almost never needed**. **Avoid** using it unless you have good reason
+
+## Test guidelines
+
+- **Always use `start_supervised!/1`** to start processes in tests as it guarantees cleanup between tests
+- **Avoid** `Process.sleep/1` and `Process.alive?/1` in tests
+  - Instead of sleeping to wait for a process to finish, **always** use `Process.monitor/1` and assert on the DOWN message:
+
+      ref = Process.monitor(pid)
+      assert_receive {:DOWN, ^ref, :process, ^pid, :normal}
+
+   - Instead of sleeping to synchronize before the next call, **always** use `_ = :sys.get_state/1` to ensure the process has handled prior messages
+<!-- phoenix:elixir-end -->
+
+<!-- phoenix:ecto-start -->
+## Ecto Guidelines
+
+- **Always** preload Ecto associations in queries when they'll be accessed in templates, ie a message that needs to reference the `message.user.email`
+- Remember `import Ecto.Query` and other supporting modules when you write `seeds.exs`
+- `Ecto.Schema` fields always use the `:string` type, even for `:text`, columns, ie: `field :name, :string`
+- `Ecto.Changeset.validate_number/2` **DOES NOT SUPPORT the `:allow_nil` option**. By default, Ecto validations only run if a change for the given field exists and the change value is not nil, so such as option is never needed
+- You **must** use `Ecto.Changeset.get_field(changeset, :field)` to access changeset fields
+- Fields which are set programmatically, such as `user_id`, must not be listed in `cast` calls or similar for security purposes. Instead they must be explicitly set when creating the struct
+- **Always** invoke `mix ecto.gen.migration migration_name_using_underscores` when generating migration files, so the correct timestamp and conventions are applied
+<!-- phoenix:ecto-end -->
+
+<!-- usage-rules-end -->