defmodule ReactPhx do
  @moduledoc """
  See READ.md for installation instructions and examples.
  """

  use Phoenix.Component
  import Phoenix.HTML

  alias Phoenix.LiveView
  alias ReactPhx.SSR
  alias ReactPhx.Slots

  require Logger

  @ssr_default Application.compile_env(:react_phx, :ssr, false)

  @doc """
  Render a React component.
  """
  def react(assigns) do
    # Validate component name looks like a component, not a data value.
    # Catches the common mistake of `<.react name={@name} ...>` where @name is a data prop.
    component_name = Map.get(assigns, :name)

    if is_binary(component_name) and
         component_name != "" and
         String.first(component_name) == String.downcase(String.first(component_name)) do
      Logger.warning(
        "react_phx: name=\"#{component_name}\" looks like a data value, not a component name. " <>
          "Component names should be PascalCase (e.g., \"Counter\"). " <>
          "If you meant to pass a prop called 'name', rename it (e.g., user_name={@name})."
      )
    end

    init = assigns.__changed__ == nil
    dead = assigns[:socket] == nil or not LiveView.connected?(assigns[:socket])
    render_ssr? = init and dead and Map.get(assigns, :ssr, @ssr_default)

    # we manually compute __changed__ for the computed props and slots so it's not sent without reason
    {props, props_changed?} = extract(assigns, :props)
    props = Map.new(props, fn {k, v} -> {k, ReactPhx.Encoder.encode(v)} end)
    {slots, slots_changed?} = extract(assigns, :slots)
    {streams, streams_changed?} = extract(assigns, :streams)
    component_name = Map.get(assigns, :name)

    streams_diff =
      if streams_changed? do
        stream_patches(streams)
      else
        []
      end

    # Generate a stable ID on first render; reuse on subsequent renders.
    # Map.put_new_lazy ensures id/1 is only called when :id is not already set.
    assigns = Map.put_new_lazy(assigns, :id, fn -> id(component_name) end)

    assigns =
      assigns
      |> Map.put_new(:class, nil)
      |> Map.put(:__component_name, component_name)
      |> Map.put(:props, props)
      |> Map.put(:slots, if(slots_changed?, do: Slots.rendered_slot_map(slots), else: %{}))
      |> Map.put(:streams_diff, streams_diff)

    assigns =
      Map.put(assigns, :ssr_render, if(render_ssr?, do: ssr_render(assigns), else: nil))

    computed_changed =
      %{
        props: props_changed?,
        slots: slots_changed?,
        streams_diff: streams_changed?,
        ssr_render: render_ssr?
      }

    assigns =
      update_in(assigns.__changed__, fn
        nil -> nil
        changed -> for {k, true} <- computed_changed, into: changed, do: {k, true}
      end)

    # It's important to not add extra `\n` in the inner div or it will break hydration
    ~H"""
    <div
      id={@id}
      data-name={@__component_name}
      data-props={"#{json(@props)}"}
      data-slots={"#{@slots |> Slots.base_encode_64 |> json}"}
      data-streams-diff={if(@streams_diff != [], do: json(@streams_diff))}
      data-ssr={is_map(@ssr_render)}
      data-props-version={System.unique_integer([:monotonic, :positive])}
      phx-update="ignore"
      phx-hook="ReactHook"
      class={@class}
    ><%= raw(@ssr_render[:html]) %></div>
    <%= if assigns[:uploads] do %>
      <div style="display:none">
        <%= for {_key, upload} <- uploads_list(assigns[:uploads]) do %>
          <.live_file_input upload={upload} />
        <% end %>
      </div>
    <% end %>
    """
  end

  defp extract(assigns, type) do
    Enum.reduce(assigns, {%{}, false}, fn {key, value}, {acc, changed} ->
      case normalize_key(key, value) do
        ^type -> {Map.put(acc, key, value), changed || key_changed(assigns, key)}
        _ -> {acc, changed}
      end
    end)
  end

  defp normalize_key(key, _val)
       when key in ~w(id class ssr name socket uploads __changed__ __given__)a,
       do: :special

  defp normalize_key(_key, %Phoenix.LiveView.LiveStream{}), do: :streams
  defp normalize_key(_key, [%{__slot__: _} | _]), do: :slots
  defp normalize_key(key, val) when is_atom(key), do: key |> to_string() |> normalize_key(val)
  defp normalize_key(_key, _val), do: :props

  defp key_changed(%{__changed__: nil}, _key), do: true
  defp key_changed(%{__changed__: changed}, key), do: changed[key] != nil

  defp ssr_render(assigns) do
    try do
      name = Map.get(assigns, :name)

      SSR.render(name, assigns.props, assigns.slots)
    rescue
      SSR.NotConfigured ->
        nil
    end
  end

  # ---------------------------------------------------------------------------
  # Stream patch generation
  # ---------------------------------------------------------------------------
  # Depends on Phoenix.LiveView.LiveStream internals (>= 1.0.0).
  # The struct fields (inserts, deletes, reset?) are NOT public API and may
  # change across LiveView versions. We wrap processing in try/rescue so that
  # a structural mismatch degrades gracefully rather than crashing the render.
  # ---------------------------------------------------------------------------

  @doc false
  def stream_patches(streams) when is_map(streams) do
    Enum.flat_map(streams, fn {name, %Phoenix.LiveView.LiveStream{} = stream} ->
      stream_to_patches(name, stream)
    end)
  end

  @doc false
  def stream_to_patches(name, %Phoenix.LiveView.LiveStream{} = stream) do
    try do
      path = "/#{name}"

      if stream.reset? do
        # When reset is true, replace the entire stream with current inserts.
        items =
          stream.inserts
          |> deduplicate_inserts()
          |> Enum.map(fn {dom_id, _at, item, _limit, _update_only} ->
            item
            |> encode_stream_item()
            |> Map.put("__dom_id", dom_id)
          end)

        [%{op: "replace", path: path, value: items}]
      else
        insert_ops =
          stream.inserts
          |> deduplicate_inserts()
          |> Enum.flat_map(fn {dom_id, at, item, limit, _update_only} ->
            encoded =
              item
              |> encode_stream_item()
              |> Map.put("__dom_id", dom_id)

            upsert = %{op: "upsert", path: path, match: dom_id, value: encoded}
            upsert = if at != -1, do: Map.put(upsert, :at, at), else: upsert

            if limit do
              [upsert, %{op: "limit", path: path, value: limit}]
            else
              [upsert]
            end
          end)

        delete_ops =
          Enum.map(stream.deletes, fn dom_id ->
            %{op: "delete_by_id", path: path, match: dom_id}
          end)

        insert_ops ++ delete_ops
      end
    rescue
      _ ->
        Logger.warning(
          "react_phx: failed to process stream #{inspect(name)}. " <>
            "LiveStream internals may have changed. Skipping stream patches."
        )

        []
    end
  end

  # Inserts are stored in reverse order and may contain duplicates.
  # We deduplicate keeping only the most recent (first occurrence in reversed list)
  # then reverse to restore insertion order.
  defp deduplicate_inserts(inserts) do
    {deduped, _seen} =
      Enum.reduce(inserts, {[], MapSet.new()}, fn {id, _, _, _, _} = insert, {acc, seen} ->
        if MapSet.member?(seen, id) do
          {acc, seen}
        else
          {[insert | acc], MapSet.put(seen, id)}
        end
      end)

    deduped
  end

  defp encode_stream_item(item) when is_struct(item) do
    item
    |> ReactPhx.Encoder.encode()
    |> ensure_string_keys()
  end

  defp encode_stream_item(item) when is_map(item) do
    item
    |> Map.new(fn {k, v} -> {to_string(k), ReactPhx.Encoder.encode(v)} end)
  end

  defp encode_stream_item(item), do: ReactPhx.Encoder.encode(item)

  defp ensure_string_keys(map) when is_map(map) do
    Map.new(map, fn {k, v} -> {to_string(k), v} end)
  end

  defp ensure_string_keys(other), do: other

  # Normalize uploads into a keyword-like list of {name, config} tuples.
  # Accepts a map (e.g. %{avatar: %UploadConfig{}, photos: %UploadConfig{}})
  # or a single UploadConfig struct.
  defp uploads_list(%{} = uploads) do
    Map.to_list(uploads)
  end

  defp json(data), do: Jason.encode!(data, escape: :html_safe)

  defp id(name) do
    # Deterministic ID based on component name alone.
    # If you render multiple instances of the same component, you MUST pass an
    # explicit `:id` attribute to each one — this matches standard Phoenix
    # component behavior.
    "react-#{name}"
  end
end