# `PhoenixKit.Install.ChildOrder`
[🔗](https://github.com/BeamLabEU/phoenix_kit/blob/v2.13.9/lib/phoenix_kit/install/child_order.ex#L1)

Reads a host application's `application.ex` and checks that the Ecto Repo
starts BEFORE `PhoenixKit.Supervisor` and `Oban` in the supervision
`children` list.

`PhoenixKit.Supervisor` reads Settings / OAuth configuration from the
database as it boots, and Oban opens a connection pool against the same
Repo — so both MUST appear after the Repo in the children list. A
mis-ordered list crashes the app at startup (typically an Oban crash-loop:
the pool has no database to reach yet).

`mix phoenix_kit.install` positions its child after the detected Repo, but a
hand-edited `application.ex` — or an Igniter anchor miss that prepends the
child instead of inserting it after the Repo — can regress the order. This
module is the deterministic safety net: `mix phoenix_kit.doctor` runs
`check/2` against the host's source so both fresh and existing installs are
caught, independent of how the children ended up ordered.

Everything here is a pure function over source text — no application boot,
no database — so it is unit-testable in isolation.

# `child`

```elixir
@type child() :: module() | nil
```

A module extracted from a child spec, or `nil` when unrecognized.

# `check`

```elixir
@spec check(String.t(), module()) ::
  {:ok, String.t()}
  | {:misordered, [module()]}
  | :no_repo_in_children
  | :no_children
```

Checks the child ordering in `source` relative to `repo_module`.

Returns:

  * `{:ok, detail}` — the Repo precedes every Repo-dependent child that is
    present (or none are present); `detail` is a human-readable summary.
  * `{:misordered, [module]}` — the listed Repo-dependent modules appear
    *before* the Repo. This is the crash case.
  * `:no_repo_in_children` — `repo_module` wasn't found in the children list,
    so ordering can't be judged (verify manually).
  * `:no_children` — no `children` list could be located in the source.

# `ordered_children`

```elixir
@spec ordered_children(String.t()) :: {:ok, [child()]} | :error
```

Extracts the ordered list of head modules from the host's `children` list.

Each element is the module heading a child spec (`MyApp.Repo`,
`{Oban, opts}` → `Oban`, `{Phoenix.PubSub, ...}` → `Phoenix.PubSub`), or
`nil` for a spec whose module can't be read cheaply (e.g. a `%{}` map spec).
Returns `:error` if no children list can be found.

---

*Consult [api-reference.md](api-reference.md) for complete listing*