defmodule Firebird.Phoenix.Session do
  @moduledoc """
  WASM-accelerated Phoenix-style session and cookie handling.

  Provides cookie parsing, cookie building, session encoding/decoding,
  flash message management, and secure cookie signing compiled to WebAssembly.

  ## Features

  - Cookie header parsing
  - Set-Cookie header building with options (path, domain, max-age, etc.)
  - Session data encoding/decoding (hex encoding)
  - Flash message management (put/get/clear)
  - Cookie signing and verification (HMAC-like with constant-time comparison)

  ## Examples

      # Parse cookies from header
      {:ok, cookies} = Session.parse_cookies(instance, "session=abc123; theme=dark")
      # => {:ok, %{"session" => "abc123", "theme" => "dark"}}

      # Sign and verify cookies
      {:ok, signed} = Session.sign_cookie(instance, "secret_key", "user_data")
      {:ok, "user_data"} = Session.verify_cookie(instance, "secret_key", signed)
  """

  alias Firebird.Phoenix.FastHelper

  @doc """
  Parse a Cookie header into a key-value map.

  ## Examples

      {:ok, cookies} = Session.parse_cookies(instance, "session_id=abc123; theme=dark; lang=en")
      # => {:ok, %{"session_id" => "abc123", "theme" => "dark", "lang" => "en"}}
  """
  @spec parse_cookies(pid() | reference(), String.t()) :: {:ok, map()} | {:error, term()}
  def parse_cookies(instance, cookie_header) when is_binary(cookie_header) do
    case FastHelper.call_string(instance, "parse_cookies", cookie_header) do
      {:ok, ""} ->
        {:ok, %{}}

      {:ok, result} ->
        cookies =
          result
          |> String.split("\n")
          |> Enum.filter(&(&1 != ""))
          |> Enum.into(%{}, fn line ->
            case String.split(line, "=", parts: 2) do
              [k, v] -> {k, v}
              [k] -> {k, ""}
            end
          end)

        {:ok, cookies}

      {:error, reason} ->
        {:error, reason}
    end
  end

  @doc """
  Build a Set-Cookie header string.

  ## Options

  - `:path` - Cookie path (default: none)
  - `:domain` - Cookie domain
  - `:max_age` - Max age in seconds
  - `:secure` - Secure flag (boolean)
  - `:http_only` - HttpOnly flag (boolean)
  - `:same_site` - SameSite attribute ("Strict", "Lax", "None")

  ## Examples

      {:ok, cookie} = Session.build_cookie(instance, "session", "abc123",
        path: "/",
        http_only: true,
        secure: true,
        same_site: "Strict",
        max_age: "3600"
      )
  """
  @spec build_cookie(pid() | reference(), String.t(), String.t(), keyword()) ::
          {:ok, String.t()} | {:error, term()}
  def build_cookie(instance, name, value, opts \\ [])
      when is_binary(name) and is_binary(value) do
    option_lines =
      opts
      |> Enum.map(fn
        {:path, v} -> "path=#{v}"
        {:domain, v} -> "domain=#{v}"
        {:max_age, v} -> "max_age=#{v}"
        {:expires, v} -> "expires=#{v}"
        {:secure, true} -> "secure=true"
        {:http_only, true} -> "http_only=true"
        {:same_site, v} -> "same_site=#{v}"
        _ -> nil
      end)
      |> Enum.filter(& &1)
      |> Enum.join("\n")

    input = "#{name}\n#{value}\n---OPTIONS---\n#{option_lines}"

    case FastHelper.call_string(instance, "build_cookie", input) do
      {:ok, "error|" <> reason} -> {:error, reason}
      {:ok, cookie} -> {:ok, cookie}
      {:error, reason} -> {:error, reason}
    end
  end

  @doc """
  Encode session data as a cookie-safe string.

  ## Examples

      {:ok, encoded} = Session.encode_session(instance, %{
        "user_id" => "42",
        "role" => "admin"
      })
  """
  @spec encode_session(pid() | reference(), map()) :: {:ok, String.t()} | {:error, term()}
  def encode_session(instance, data) when is_map(data) do
    input =
      data
      |> Enum.map(fn {k, v} -> "#{k}=#{v}" end)
      |> Enum.join("\n")

    FastHelper.call_string(instance, "encode_session", input)
  end

  @doc """
  Decode session data from a cookie-safe string.

  ## Examples

      {:ok, data} = Session.decode_session(instance, encoded)
      # => {:ok, %{"user_id" => "42", "role" => "admin"}}
  """
  @spec decode_session(pid() | reference(), String.t()) :: {:ok, map()} | {:error, term()}
  def decode_session(instance, encoded) when is_binary(encoded) do
    case FastHelper.call_string(instance, "decode_session", encoded) do
      {:ok, "error|" <> reason} ->
        {:error, reason}

      {:ok, result} ->
        data =
          result
          |> String.split("\n")
          |> Enum.filter(&(&1 != ""))
          |> Enum.into(%{}, fn line ->
            case String.split(line, "=", parts: 2) do
              [k, v] -> {k, v}
              [k] -> {k, ""}
            end
          end)

        {:ok, data}

      {:error, reason} ->
        {:error, reason}
    end
  end

  @doc """
  Manage flash messages.

  ## Actions

  - `:put` - Add/update flash messages
  - `:get` - Get a specific flash message by key
  - `:clear` - Clear all flash messages

  ## Examples

      # Put flash messages
      {:ok, state} = Session.flash(instance, :put, %{}, %{"info" => "User created"})

      # Get a flash message
      {:ok, msg} = Session.flash(instance, :get, state, "info")

      # Clear flash
      {:ok, %{}} = Session.flash(instance, :clear, state)
  """
  @spec flash(pid() | reference(), :put | :get | :clear, map(), map() | String.t()) ::
          {:ok, map() | String.t()} | {:error, term()}
  def flash(instance, action, current_state \\ %{}, data \\ %{})

  def flash(instance, :put, current_state, data) when is_map(data) do
    flash_lines =
      Enum.map(current_state, fn {k, v} -> "#{k}=#{v}" end)
      |> Enum.join("\n")

    data_lines =
      Enum.map(data, fn {k, v} -> "#{k}=#{v}" end)
      |> Enum.join("\n")

    input = "put\n---FLASH---\n#{flash_lines}\n---DATA---\n#{data_lines}"

    case FastHelper.call_string(instance, "manage_flash", input) do
      {:ok, "error|" <> reason} -> {:error, reason}
      {:ok, result} -> {:ok, parse_flash_state(result)}
      {:error, reason} -> {:error, reason}
    end
  end

  def flash(instance, :get, current_state, key) when is_binary(key) do
    flash_lines =
      Enum.map(current_state, fn {k, v} -> "#{k}=#{v}" end)
      |> Enum.join("\n")

    input = "get\n---FLASH---\n#{flash_lines}\n---DATA---\n#{key}"

    case FastHelper.call_string(instance, "manage_flash", input) do
      {:ok, ""} -> {:ok, nil}
      {:ok, value} -> {:ok, value}
      {:error, reason} -> {:error, reason}
    end
  end

  def flash(instance, :clear, current_state, _data) do
    flash_lines =
      Enum.map(current_state, fn {k, v} -> "#{k}=#{v}" end)
      |> Enum.join("\n")

    input = "clear\n---FLASH---\n#{flash_lines}\n---DATA---\n"

    case FastHelper.call_string(instance, "manage_flash", input) do
      {:ok, _} -> {:ok, %{}}
      {:error, reason} -> {:error, reason}
    end
  end

  @doc """
  Sign a cookie value for tamper protection.

  ## Examples

      {:ok, signed} = Session.sign_cookie(instance, "my_secret_key", "user_id=42")
      # => {:ok, "user_id=42.a1b2c3d4e5f6a7b8"}
  """
  @spec sign_cookie(pid() | reference(), String.t(), String.t()) ::
          {:ok, String.t()} | {:error, term()}
  def sign_cookie(instance, secret, value)
      when is_binary(secret) and is_binary(value) do
    input = "#{secret}\n#{value}"

    case FastHelper.call_string(instance, "sign_cookie", input) do
      {:ok, "error|" <> reason} -> {:error, reason}
      {:ok, signed} -> {:ok, signed}
      {:error, reason} -> {:error, reason}
    end
  end

  @doc """
  Verify a signed cookie value.

  ## Returns

  - `{:ok, original_value}` - Valid signature
  - `{:error, :invalid}` - Invalid signature
  - `{:error, reason}` - Other error

  ## Examples

      {:ok, signed} = Session.sign_cookie(instance, "secret", "data")
      {:ok, "data"} = Session.verify_cookie(instance, "secret", signed)
      {:error, :invalid} = Session.verify_cookie(instance, "wrong_secret", signed)
  """
  @spec verify_cookie(pid() | reference(), String.t(), String.t()) ::
          {:ok, String.t()} | {:error, :invalid | term()}
  def verify_cookie(instance, secret, signed_value)
      when is_binary(secret) and is_binary(signed_value) do
    input = "#{secret}\n#{signed_value}"

    case FastHelper.call_string(instance, "verify_cookie", input) do
      {:ok, "valid|" <> value} -> {:ok, value}
      {:ok, "invalid"} -> {:error, :invalid}
      {:ok, "error|" <> reason} -> {:error, reason}
      {:error, reason} -> {:error, reason}
    end
  end

  defp parse_flash_state(""), do: %{}

  defp parse_flash_state(result) do
    result
    |> String.split("\n")
    |> Enum.filter(&(&1 != ""))
    |> Enum.into(%{}, fn line ->
      case String.split(line, "=", parts: 2) do
        [k, v] -> {k, v}
        [k] -> {k, ""}
      end
    end)
  end
end