# `PaperTiger.Plugs.UnflattenParams`
[🔗](https://github.com/EnaiaInc/paper_tiger/blob/v1.2.2/lib/paper_tiger/plugs/unflatten_params.ex#L1)

Converts Stripe's form-encoded nested parameters into proper nested maps.

Stripe's API uses bracket notation for nested parameters in form-encoded requests.
This plug transforms them into nested Elixir maps.

## Examples

    # Single-level nesting
    card[number]=4242424242424242
    => %{card: %{number: "4242424242424242"}}

    # Multi-level nesting
    payment_method_data[billing_details][name]=John Doe
    => %{payment_method_data: %{billing_details: %{name: "John Doe"}}}

    # Arrays
    expand[]=customer
    expand[]=subscription
    => %{expand: ["customer", "subscription"]}

    # Metadata
    metadata[user_id]=123
    metadata[session_id]=abc
    => %{metadata: %{user_id: "123", session_id: "abc"}}

## Usage

    # In router
    plug PaperTiger.Plugs.UnflattenParams

# `convert_indexed_maps_to_lists`

Converts maps with numeric string keys to lists.

## DoS Protection

Validates that array indices are within reasonable bounds (max: 1000)
to prevent memory exhaustion from sparse arrays like items[999999].

## Examples

    convert_indexed_maps_to_lists(%{"0" => "a", "1" => "b"})
    => ["a", "b"]

    convert_indexed_maps_to_lists(%{items: %{"0" => %{price: "p1"}, "1" => %{price: "p2"}}})
    => %{items: [%{price: "p1"}, %{price: "p2"}]}

# `parse_key`

Parses a key like "card[number]" into ["card", "number"].

# `put_nested`

Puts a value into a nested map structure with depth tracking for DoS protection.

## Examples

    put_nested(%{}, ["card", "number"], "4242", 0)
    => %{card: %{number: "4242"}}

    put_nested(%{}, ["expand", ""], "customer", 0)
    => %{expand: ["customer"]}

# `unflatten_params`

Transforms flat params with bracket notation into nested maps.

## DoS Protection

Enforces limits to prevent denial-of-service attacks:
- Maximum nesting depth: 10
- Maximum array index: 1000
- Maximum parameters: 1000

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