# `ClaudeAgentSDK.Hooks.Registry`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/hooks/registry.ex#L1)

Hook callback registration and ID management.

Maintains bidirectional mapping between callback functions and unique IDs
for use with the Claude Code CLI hooks system.

## Purpose

- Assigns unique IDs to callback functions for CLI initialization
- Enables lookup of callbacks by ID when CLI triggers hooks
- Provides idempotent registration (re-registering same callback returns same ID)

## Usage

This module is primarily used internally by `ClaudeAgentSDK.Client`, but can
be used directly for testing hooks or building custom integrations.

    registry = Registry.new()
    callback = fn _input, _id, _ctx -> Output.allow() end

    registry = Registry.register(registry, callback)
    id = Registry.get_id(registry, callback)  # => "hook_0"

    {:ok, ^callback} = Registry.get_callback(registry, id)

# `t`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/hooks/registry.ex#L38)

```elixir
@type t() :: %ClaudeAgentSDK.Hooks.Registry{
  callbacks: %{required(String.t()) => ClaudeAgentSDK.Hooks.hook_callback()},
  counter: non_neg_integer(),
  reverse_map: %{required(ClaudeAgentSDK.Hooks.hook_callback()) => String.t()}
}
```

Registry state containing callback mappings.

Fields:
- `callbacks` - Map from ID string to callback function
- `reverse_map` - Map from callback function to ID string (for quick lookup)
- `counter` - Next ID number to assign

# `all_callbacks`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/hooks/registry.ex#L196)

```elixir
@spec all_callbacks(t()) :: %{
  required(String.t()) => ClaudeAgentSDK.Hooks.hook_callback()
}
```

Returns all registered callbacks.

## Parameters

- `registry` - Registry to query

## Returns

Map from ID string to callback function.

## Examples

    registry = Registry.new()
    registry = Registry.register(registry, fn _, _, _ -> %{} end)

    Registry.all_callbacks(registry)
    # => %{"hook_0" => #Function<...>}

# `count`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/hooks/registry.ex#L222)

```elixir
@spec count(t()) :: non_neg_integer()
```

Returns count of registered callbacks.

## Parameters

- `registry` - Registry to query

## Returns

Non-negative integer count.

## Examples

    registry = Registry.new()
    Registry.count(registry)
    # => 0

    registry = Registry.register(registry, fn _, _, _ -> %{} end)
    Registry.count(registry)
    # => 1

# `get_callback`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/hooks/registry.ex#L138)

```elixir
@spec get_callback(t(), String.t()) ::
  {:ok, ClaudeAgentSDK.Hooks.hook_callback()} | :error
```

Gets callback function by ID.

## Parameters

- `registry` - Registry to query
- `id` - Callback ID string (e.g., "hook_0")

## Returns

- `{:ok, callback}` if ID found
- `:error` if ID not found

## Examples

    registry = Registry.new()
    callback = fn _, _, _ -> %{} end
    registry = Registry.register(registry, callback)

    {:ok, retrieved} = Registry.get_callback(registry, "hook_0")
    retrieved == callback
    # => true

    Registry.get_callback(registry, "hook_999")
    # => :error

# `get_id`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/hooks/registry.ex#L172)

```elixir
@spec get_id(t(), ClaudeAgentSDK.Hooks.hook_callback()) :: String.t() | nil
```

Gets ID for a callback function.

## Parameters

- `registry` - Registry to query
- `callback` - Callback function to look up

## Returns

- ID string if callback registered
- `nil` if callback not found

## Examples

    registry = Registry.new()
    callback = fn _, _, _ -> %{} end
    registry = Registry.register(registry, callback)

    Registry.get_id(registry, callback)
    # => "hook_0"

    other_callback = fn _, _, _ -> %{other: :callback} end
    Registry.get_id(registry, other_callback)
    # => nil

# `new`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/hooks/registry.ex#L58)

```elixir
@spec new() :: t()
```

Creates a new empty registry.

## Examples

    iex> registry = Registry.new()
    iex> Registry.count(registry)
    0

# `register`
[🔗](https://github.com/nshkrdotcom/claude_agent_sdk/blob/v0.9.2/lib/claude_agent_sdk/hooks/registry.ex#L92)

```elixir
@spec register(t(), ClaudeAgentSDK.Hooks.hook_callback()) :: t()
```

Registers a callback and returns updated registry.

If the callback is already registered, returns the existing registry
without modification (idempotent operation).

## Parameters

- `registry` - Current registry state
- `callback` - Callback function to register (must be 3-arity function)

## Returns

Updated registry with callback registered.

## Examples

    registry = Registry.new()
    callback = fn _input, _tool_use_id, _context -> %{} end

    registry = Registry.register(registry, callback)
    Registry.get_id(registry, callback)
    # => "hook_0"

    # Registering again is idempotent
    registry = Registry.register(registry, callback)
    Registry.count(registry)
    # => 1

---

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