defmodule Ghostty.Terminal do
  @moduledoc """
  A managed terminal emulator backed by libghostty-vt.

  Each terminal is a GenServer that owns a libghostty-vt terminal instance.
  All operations are serialized through the GenServer to ensure thread safety
  (libghostty-vt terminal instances are not thread-safe).

  ## Examples

      {:ok, term} = Ghostty.Terminal.start_link(cols: 120, rows: 40)
      Ghostty.Terminal.write(term, File.read!("recording.vt"))
      {:ok, html} = Ghostty.Terminal.snapshot(term, :html)

  ## Supervision

      children = [
        {Ghostty.Terminal, name: :main, cols: 80, rows: 24, max_scrollback: 50_000}
      ]

  ## Effects

  Terminal programs can trigger side effects via VT sequences (query
  responses, bell, title changes). These are forwarded as messages to
  the process that called `start_link/1`:

    * `{:pty_write, binary}` — query responses to write back to the PTY
    * `:bell` — BEL character
    * `:title_changed` — title change via OSC 2

  ## Snapshot formats

    * `:plain` — plain text with all styling stripped
    * `:html` — HTML with inline styles preserving all colors and attributes
    * `:vt` — raw VT escape sequences (round-trippable)

  """

  use GenServer

  alias Ghostty.Terminal.Nif

  @type format :: :plain | :html | :vt

  @type rgb :: {byte(), byte(), byte()}

  @type cell ::
          {binary(), rgb() | nil, rgb() | nil, non_neg_integer()}

  @type cursor_style :: :bar | :block | :underline | :block_hollow

  @type cursor_state :: %{
          x: non_neg_integer() | nil,
          y: non_neg_integer() | nil,
          visible: boolean(),
          blinking: boolean(),
          style: cursor_style(),
          wide_tail: boolean(),
          color: rgb() | nil
        }

  @type mouse_modes :: %{
          tracking: boolean(),
          x10: boolean(),
          normal: boolean(),
          button: boolean(),
          any: boolean(),
          sgr: boolean()
        }

  @type scrollbar :: %{
          total: non_neg_integer(),
          offset: non_neg_integer(),
          len: non_neg_integer()
        }

  @type render_state :: %{
          cells: [[cell()]],
          cursor: cursor_state(),
          mouse: mouse_modes(),
          scrollbar: scrollbar(),
          focus_reporting: boolean()
        }

  @type option ::
          {:cols, pos_integer()}
          | {:rows, pos_integer()}
          | {:max_scrollback, non_neg_integer()}
          | {:name, GenServer.name()}

  @unsupported_private_modes ["\e[?1034h", "\e[?1034l"]

  @has_render_state_nif function_exported?(Ghostty.Terminal.Nif, :nif_render_state, 1)

  @enforce_keys [:ref]
  defstruct [:ref, :cols, :rows, :mouse_modes, :focus_reporting]

  @doc """
  Starts a terminal process linked to the caller.

  Effect messages (`:bell`, `:title_changed`, `{:pty_write, data}`)
  are sent to the calling process.

  ## Options

    * `:cols` - number of columns (default: `80`)
    * `:rows` - number of rows (default: `24`)
    * `:max_scrollback` - maximum scrollback lines (default: `10_000`)
    * `:name` - GenServer name registration

  """
  @spec start_link([option()]) :: GenServer.on_start()
  def start_link(opts \\ []) do
    {server_opts, init_opts} = Keyword.split(opts, [:name])
    init_opts = Keyword.put(init_opts, :owner, self())
    GenServer.start_link(__MODULE__, init_opts, server_opts)
  end

  @doc "Returns a child spec for use in supervision trees."
  def child_spec(opts) do
    id = Keyword.get(opts, :id, Keyword.get(opts, :name, __MODULE__))

    %{
      id: id,
      start: {__MODULE__, :start_link, [opts]},
      restart: :permanent,
      shutdown: 5_000
    }
  end

  @doc """
  Writes VT-encoded data to the terminal.

  The terminal's VT parser processes escape sequences and updates
  the internal screen, cursor, and style state. Accepts iodata.

  ## Examples

      Ghostty.Terminal.write(term, "hello world")
      Ghostty.Terminal.write(term, "\\e[31mred\\e[0m")
      Ghostty.Terminal.write(term, ["line 1\\r\\n", "line 2\\r\\n"])

  """
  @spec write(GenServer.server(), iodata()) :: :ok
  def write(terminal, data) do
    case data |> IO.iodata_to_binary() |> drop_unsupported_private_modes() do
      "" -> :ok
      sanitized -> GenServer.call(terminal, {:write, sanitized})
    end
  end

  @doc """
  Resizes the terminal. Text reflow is handled automatically.

  ## Examples

      Ghostty.Terminal.resize(term, 120, 40)

  """
  @spec resize(GenServer.server(), pos_integer(), pos_integer()) :: :ok
  def resize(terminal, cols, rows) do
    validate_pos_integer!(:cols, cols)
    validate_pos_integer!(:rows, rows)
    GenServer.call(terminal, {:resize, cols, rows})
  end

  @doc """
  Performs a full terminal reset (RIS — Reset to Initial State).
  """
  @spec reset(GenServer.server()) :: :ok
  def reset(terminal) do
    GenServer.call(terminal, :reset)
  end

  @doc """
  Returns a snapshot of the terminal screen content.

  ## Formats

    * `:plain` — plain text, stripped of all styling (default)
    * `:html` — HTML with inline styles preserving colors and attributes
    * `:vt` — raw VT escape sequences

  ## Examples

      {:ok, text} = Ghostty.Terminal.snapshot(term)
      {:ok, html} = Ghostty.Terminal.snapshot(term, :html)
      {:ok, vt}   = Ghostty.Terminal.snapshot(term, :vt)

  """
  @spec snapshot(GenServer.server(), format()) :: {:ok, binary()}
  def snapshot(terminal, format \\ :plain) do
    GenServer.call(terminal, {:snapshot, format})
  end

  @doc """
  Returns the terminal screen as a grid of cells.

  Each cell is `{grapheme, fg, bg, flags}` where:

    * `grapheme` — UTF-8 binary (empty for blank cells)
    * `fg` / `bg` — `{r, g, b}` tuples or `nil`
    * `flags` — bitmask (see `Ghostty.Terminal.Cell` for helpers)

  ## Examples

      rows = Ghostty.Terminal.cells(term)

      for row <- rows, {char, fg, _bg, flags} <- row, char != "" do
        if Ghostty.Terminal.Cell.bold?({char, fg, nil, flags}), do: IO.write("*")
        IO.write(char)
      end

  """
  @spec cells(GenServer.server()) :: [[cell()]]
  def cells(terminal) do
    GenServer.call(terminal, :cells)
  end

  @doc """
  Encodes a key event into a terminal escape sequence.

  Returns `{:ok, sequence}` with the bytes to send to the PTY,
  or `:none` if the key event produces no output.

  ## Examples

      Ghostty.Terminal.input_key(term, %Ghostty.KeyEvent{key: :enter})
      # => {:ok, "\\r"}

      Ghostty.Terminal.input_key(term, %Ghostty.KeyEvent{key: :c, mods: [:ctrl]})
      # => {:ok, <<3>>}

  """
  @spec input_key(GenServer.server(), Ghostty.KeyEvent.t()) :: {:ok, binary()} | :none
  def input_key(terminal, %Ghostty.KeyEvent{} = event) do
    GenServer.call(terminal, {:input_key, event})
  end

  @doc """
  Encodes a mouse event into a terminal escape sequence.

  Returns `{:ok, sequence}` or `:none` if mouse tracking is not
  enabled by the running program.
  """
  @spec input_mouse(GenServer.server(), Ghostty.MouseEvent.t()) :: {:ok, binary()} | :none
  def input_mouse(terminal, %Ghostty.MouseEvent{} = event) do
    GenServer.call(terminal, {:input_mouse, event})
  end

  @doc """
  Encodes a focus event into a terminal escape sequence.

  ## Examples

      {:ok, seq} = Ghostty.Terminal.encode_focus(true)   # => "\\e[I"
      {:ok, seq} = Ghostty.Terminal.encode_focus(false)  # => "\\e[O"

  """
  @spec encode_focus(boolean()) :: {:ok, binary()} | :none
  def encode_focus(gained?) do
    Nif.nif_encode_focus(gained?)
  end

  @doc """
  Returns the scrollbar state for the terminal viewport.
  """
  @spec scrollbar(GenServer.server()) :: scrollbar()
  def scrollbar(terminal) do
    GenServer.call(terminal, :scrollbar)
  end

  @doc """
  Returns whether focus reporting (DEC mode 1004) is enabled.
  """
  @spec focus_reporting?(GenServer.server()) :: boolean()
  def focus_reporting?(terminal) do
    GenServer.call(terminal, :focus_reporting?)
  end

  @doc """
  Scrolls the terminal viewport.

  Positive `delta` scrolls down (towards newer content),
  negative scrolls up (towards scrollback history).
  """
  @spec scroll(GenServer.server(), integer()) :: :ok
  def scroll(terminal, delta) do
    GenServer.call(terminal, {:scroll, delta})
  end

  @doc """
  Returns the current cursor position as `{col, row}` (0-indexed).
  """
  @spec cursor(GenServer.server()) :: {non_neg_integer(), non_neg_integer()}
  def cursor(terminal) do
    GenServer.call(terminal, :cursor)
  end

  @doc """
  Returns the current terminal dimensions as `{cols, rows}`.
  """
  @spec size(GenServer.server()) :: {pos_integer(), pos_integer()}
  def size(terminal) do
    GenServer.call(terminal, :size)
  end

  @doc """
  Returns the current render-state cursor metadata for the visible viewport.
  """
  @spec cursor_state(GenServer.server()) :: cursor_state()
  def cursor_state(terminal) do
    terminal
    |> render_state()
    |> Map.fetch!(:cursor)
  end

  @doc """
  Returns the current visible render-state cells together with cursor metadata.
  """
  @spec render_state(GenServer.server()) :: render_state()
  def render_state(terminal) do
    terminal
    |> GenServer.call(:render_state)
    |> render_state_from_nif()
  end

  @doc """
  Returns the current terminal mouse reporting mode state.
  """
  @spec mouse_modes(GenServer.server()) :: mouse_modes()
  def mouse_modes(terminal) do
    terminal
    |> render_state()
    |> Map.fetch!(:mouse)
  end

  # --- GenServer Callbacks ---

  @impl true
  def init(opts) do
    cols = Keyword.get(opts, :cols, 80)
    rows = Keyword.get(opts, :rows, 24)
    max_scrollback = Keyword.get(opts, :max_scrollback, 10_000)

    validate_pos_integer!(:cols, cols)
    validate_pos_integer!(:rows, rows)
    validate_non_neg_integer!(:max_scrollback, max_scrollback)

    ref = Nif.nif_new(cols, rows, max_scrollback)
    Nif.nif_set_effect_pid(ref, Keyword.fetch!(opts, :owner))

    {:ok,
     %__MODULE__{
       ref: ref,
       cols: cols,
       rows: rows,
       mouse_modes: default_mouse_modes(),
       focus_reporting: false
     }}
  rescue
    e in ErlangError ->
      {:stop, {:nif_not_loaded, Exception.message(e)}}

    e in ArgumentError ->
      {:stop, {:invalid_option, Exception.message(e)}}
  end

  defp validate_pos_integer!(_name, value) when is_integer(value) and value > 0, do: :ok

  defp validate_pos_integer!(name, value) do
    raise ArgumentError, "expected #{name} to be a positive integer, got: #{inspect(value)}"
  end

  defp validate_non_neg_integer!(_name, value) when is_integer(value) and value >= 0, do: :ok

  defp validate_non_neg_integer!(name, value) do
    raise ArgumentError,
          "expected #{name} to be a non-negative integer, got: #{inspect(value)}"
  end

  @impl true
  def handle_call({:write, data}, _from, state) do
    Nif.nif_vt_write(state.ref, data)

    {:reply, :ok,
     %{
       state
       | mouse_modes: update_mouse_modes(state.mouse_modes, data),
         focus_reporting: update_focus_reporting(state.focus_reporting, data)
     }}
  end

  def handle_call({:resize, cols, rows}, _from, state) do
    Nif.nif_resize(state.ref, cols, rows)
    {:reply, :ok, %{state | cols: cols, rows: rows}}
  end

  def handle_call(:reset, _from, state) do
    Nif.nif_reset(state.ref)
    {:reply, :ok, %{state | mouse_modes: default_mouse_modes(), focus_reporting: false}}
  end

  def handle_call({:snapshot, format}, _from, state) do
    result = Nif.nif_snapshot(state.ref, Atom.to_string(format))
    {:reply, {:ok, result}, state}
  end

  def handle_call({:scroll, delta}, _from, state) do
    Nif.nif_scroll(state.ref, delta)
    {:reply, :ok, state}
  end

  def handle_call(:cursor, _from, state) do
    {:reply, Nif.nif_get_cursor(state.ref), state}
  end

  def handle_call(:size, _from, state) do
    {:reply, {state.cols, state.rows}, state}
  end

  def handle_call(:cells, _from, state) do
    {:reply, Nif.nif_render_cells(state.ref), state}
  end

  def handle_call(:scrollbar, _from, state) do
    {:reply, scrollbar_from_nif(Nif.nif_scrollbar(state.ref)), state}
  end

  def handle_call(:focus_reporting?, _from, state) do
    {:reply, state.focus_reporting, state}
  end

  def handle_call(:render_state, _from, state) do
    raw =
      if @has_render_state_nif do
        Nif.nif_render_state(state.ref)
      else
        fallback_render_state(state.ref)
      end

    {:reply, {raw, state.mouse_modes, Nif.nif_scrollbar(state.ref), state.focus_reporting}, state}
  end

  def handle_call({:input_key, event}, _from, state) do
    result =
      with {:ok, action} <- Ghostty.KeyEvent.action_to_int(event.action),
           {:ok, key} <- Ghostty.KeyEvent.key_to_int(event.key) do
        Nif.nif_encode_key(
          state.ref,
          action,
          key,
          Ghostty.Mods.to_bitmask(event.mods),
          event.utf8 || "",
          event.unshifted_codepoint || 0
        )
      else
        :error -> {:error, :invalid_key_event}
      end

    {:reply, result, state}
  end

  def handle_call({:input_mouse, event}, _from, state) do
    result =
      with {:ok, action} <- Ghostty.MouseEvent.action_to_int(event.action),
           {:ok, button} <- Ghostty.MouseEvent.button_to_int(event.button) do
        Nif.nif_encode_mouse(
          state.ref,
          action,
          button,
          Ghostty.Mods.to_bitmask(event.mods),
          event.x,
          event.y
        )
      else
        :error -> {:error, :invalid_mouse_event}
      end

    {:reply, result, state}
  end

  defp drop_unsupported_private_modes(data) do
    Enum.reduce(@unsupported_private_modes, data, &:binary.replace(&2, &1, "", [:global]))
  end

  defp render_state_from_nif({raw_render_state, mouse_modes, scrollbar_tuple, focus_reporting}) do
    raw_render_state
    |> render_state_from_nif_raw()
    |> Map.put(:mouse, mouse_modes_from_nif(mouse_modes))
    |> Map.put(:scrollbar, scrollbar_from_nif(scrollbar_tuple))
    |> Map.put(:focus_reporting, focus_reporting)
  end

  defp render_state_from_nif_raw({cells, cursor_tuple, _mouse_tuple}) do
    %{cells: cells, cursor: cursor_state_from_nif(cursor_tuple)}
  end

  defp render_state_from_nif_raw({cells, cursor_tuple}) do
    %{cells: cells, cursor: cursor_state_from_nif(cursor_tuple)}
  end

  defp fallback_render_state(ref) do
    {x, y} = Nif.nif_get_cursor(ref)

    {Nif.nif_render_cells(ref), {true, x, y, true, false, :block, false, nil}, fallback_mouse_modes(ref)}
  end

  defp scrollbar_from_nif({total, offset, len}) do
    %{total: total, offset: offset, len: len}
  end

  defp cursor_state_from_nif({has_position, x, y, visible, blinking, style, wide_tail, color}) do
    %{
      x: if(has_position, do: x, else: nil),
      y: if(has_position, do: y, else: nil),
      visible: visible,
      blinking: blinking,
      style: style,
      wide_tail: has_position and wide_tail,
      color: color
    }
  end

  defp mouse_modes_from_nif(%{} = mouse_modes), do: mouse_modes

  defp mouse_modes_from_nif({tracking, x10, normal, button, any, sgr}) do
    %{
      tracking: tracking,
      x10: x10,
      normal: normal,
      button: button,
      any: any,
      sgr: sgr
    }
  end

  defp fallback_mouse_modes(ref) do
    Nif.nif_mouse_modes(ref) |> mouse_modes_from_nif()
  rescue
    ErlangError -> default_mouse_modes()
  end

  defp default_mouse_modes do
    %{tracking: false, x10: false, normal: false, button: false, any: false, sgr: false}
  end

  defp update_focus_reporting(focus_reporting, data) do
    focus_reporting = if String.contains?(data, "\ec"), do: false, else: focus_reporting

    Regex.scan(~r/\e\[\?1004(h|l)/, data)
    |> Enum.reduce(focus_reporting, fn [_, value], _acc ->
      value == "h"
    end)
  end

  defp update_mouse_modes(mouse_modes, data) do
    mouse_modes =
      if String.contains?(data, "\ec") do
        default_mouse_modes()
      else
        mouse_modes
      end

    Regex.scan(~r/\e\[\?(9|1000|1002|1003|1006)(h|l)/, data)
    |> Enum.reduce(mouse_modes, fn [_, mode, value], acc ->
      enabled? = value == "h"

      case mode do
        "9" -> %{acc | x10: enabled?} |> normalize_mouse_modes()
        "1000" -> %{acc | normal: enabled?} |> normalize_mouse_modes()
        "1002" -> %{acc | button: enabled?} |> normalize_mouse_modes()
        "1003" -> %{acc | any: enabled?} |> normalize_mouse_modes()
        "1006" -> %{acc | sgr: enabled?} |> normalize_mouse_modes()
      end
    end)
  end

  defp normalize_mouse_modes(mouse_modes) do
    %{
      mouse_modes
      | tracking: mouse_modes.x10 or mouse_modes.normal or mouse_modes.button or mouse_modes.any
    }
  end
end