defmodule Localize.Mf2.TreeSitter.Node do
  @moduledoc """
  A single node in a tree-sitter MF2 parse tree.

  Nodes are value structs that hold the opaque NIF node handle plus
  the tree's source binary, so that span-addressing (`text/1`) is a
  pure Elixir operation and does not round-trip through the NIF.

  Child traversal (`children/1`, `named_children/1`) is implemented in
  Elixir on top of indexed NIF accessors. Each accessor call is O(1).
  """

  alias Localize.Mf2.TreeSitter.Nif

  @enforce_keys [:handle, :source]
  defstruct [:handle, :source]

  @typedoc """
  A tree-sitter node. Opaque — the `:handle` field is a NIF resource
  handle whose internal representation is unspecified. Always
  interact with a node via the functions on this module rather than
  pattern-matching on its fields.
  """
  @opaque t :: %__MODULE__{handle: Nif.node_handle(), source: binary()}

  @type point :: {row :: non_neg_integer(), column :: non_neg_integer()}
  @type range :: {point(), point()}

  @doc "Return the node's grammar symbol name (e.g. `\"variable\"`)."
  @spec type(t()) :: binary()
  def type(%__MODULE__{handle: h}), do: Nif.node_type(h)

  @doc "Return the node's byte offset in the source."
  @spec start_byte(t()) :: non_neg_integer()
  def start_byte(%__MODULE__{handle: h}), do: Nif.node_start_byte(h)

  @doc "Return the byte offset just past the node's last byte."
  @spec end_byte(t()) :: non_neg_integer()
  def end_byte(%__MODULE__{handle: h}), do: Nif.node_end_byte(h)

  @doc "Return the node's `{row, column}` start position."
  @spec start_point(t()) :: point()
  def start_point(%__MODULE__{handle: h}), do: Nif.node_start_point(h)

  @doc "Return the node's `{row, column}` end position."
  @spec end_point(t()) :: point()
  def end_point(%__MODULE__{handle: h}), do: Nif.node_end_point(h)

  @doc "Return `{start_point, end_point}` for the node."
  @spec range(t()) :: range()
  def range(%__MODULE__{} = node), do: {start_point(node), end_point(node)}

  @doc "Whether the node is a named grammar node (not anonymous punctuation)."
  @spec named?(t()) :: boolean()
  def named?(%__MODULE__{handle: h}), do: Nif.node_is_named(h)

  @doc """
  Whether the node or any descendant is an `ERROR` / `MISSING` node.

  This is the LSP-relevant predicate: after parsing partially invalid
  input, tree-sitter's GLR recovery produces a tree with `ERROR` /
  `MISSING` nodes at the failure points rather than aborting. Use this
  to decide whether to surface diagnostics.
  """
  @spec has_error?(t()) :: boolean()
  def has_error?(%__MODULE__{handle: h}), do: Nif.node_has_error(h)

  @doc "Return the total number of children (named and anonymous)."
  @spec child_count(t()) :: non_neg_integer()
  def child_count(%__MODULE__{handle: h}), do: Nif.node_child_count(h)

  @doc "Return the number of named children."
  @spec named_child_count(t()) :: non_neg_integer()
  def named_child_count(%__MODULE__{handle: h}), do: Nif.node_named_child_count(h)

  @doc "Return the child at `index`, or `nil` if the index is out of range."
  @spec child(t(), non_neg_integer()) :: t() | nil
  def child(%__MODULE__{handle: h, source: src}, index) do
    case Nif.node_child(h, index) do
      nil -> nil
      child_handle -> %__MODULE__{handle: child_handle, source: src}
    end
  end

  @doc "Return the named child at `index`, or `nil` if the index is out of range."
  @spec named_child(t(), non_neg_integer()) :: t() | nil
  def named_child(%__MODULE__{handle: h, source: src}, index) do
    case Nif.node_named_child(h, index) do
      nil -> nil
      child_handle -> %__MODULE__{handle: child_handle, source: src}
    end
  end

  @doc "Return all children (named and anonymous) as a list."
  @spec children(t()) :: [t()]
  def children(%__MODULE__{} = node) do
    for i <- 0..(child_count(node) - 1)//1, do: child(node, i)
  end

  @doc "Return only named children as a list."
  @spec named_children(t()) :: [t()]
  def named_children(%__MODULE__{} = node) do
    for i <- 0..(named_child_count(node) - 1)//1, do: named_child(node, i)
  end

  @doc """
  Return the slice of the source binary spanned by the node.

  ### Examples

      iex> {:ok, tree} = Localize.Mf2.TreeSitter.parse("hello {$name}")
      iex> root = Localize.Mf2.TreeSitter.root(tree)
      iex> Localize.Mf2.TreeSitter.Node.text(root)
      "hello {$name}"

  """
  @spec text(t()) :: binary()
  def text(%__MODULE__{source: src} = node) do
    start_b = start_byte(node)
    end_b = end_byte(node)
    binary_part(src, start_b, end_b - start_b)
  end

  @doc "Return the parent node, or `nil` if this is the root."
  @spec parent(t()) :: t() | nil
  def parent(%__MODULE__{handle: h, source: src}) do
    case Nif.node_parent(h) do
      nil -> nil
      handle -> %__MODULE__{handle: handle, source: src}
    end
  end

  @doc "Return the next sibling (including anonymous nodes), or `nil`."
  @spec next_sibling(t()) :: t() | nil
  def next_sibling(%__MODULE__{handle: h, source: src}) do
    case Nif.node_next_sibling(h) do
      nil -> nil
      handle -> %__MODULE__{handle: handle, source: src}
    end
  end

  @doc "Return the previous sibling (including anonymous nodes), or `nil`."
  @spec previous_sibling(t()) :: t() | nil
  def previous_sibling(%__MODULE__{handle: h, source: src}) do
    case Nif.node_prev_sibling(h) do
      nil -> nil
      handle -> %__MODULE__{handle: handle, source: src}
    end
  end

  @doc "Return the next named sibling, or `nil`."
  @spec next_named_sibling(t()) :: t() | nil
  def next_named_sibling(%__MODULE__{handle: h, source: src}) do
    case Nif.node_next_named_sibling(h) do
      nil -> nil
      handle -> %__MODULE__{handle: handle, source: src}
    end
  end

  @doc "Return the previous named sibling, or `nil`."
  @spec previous_named_sibling(t()) :: t() | nil
  def previous_named_sibling(%__MODULE__{handle: h, source: src}) do
    case Nif.node_prev_named_sibling(h) do
      nil -> nil
      handle -> %__MODULE__{handle: handle, source: src}
    end
  end

  @doc """
  Return the smallest node that spans the given byte range.

  Includes anonymous nodes. Useful for answering "what is under the
  cursor?" — pass the cursor's start and end byte offsets (equal for
  a caret, different for a selection).

  ### Examples

      iex> {:ok, tree} = Localize.Mf2.TreeSitter.parse("hello {$name}")
      iex> root = Localize.Mf2.TreeSitter.root(tree)
      iex> node = Localize.Mf2.TreeSitter.Node.descendant_for_byte_range(root, 8, 8)
      iex> Localize.Mf2.TreeSitter.Node.type(node)
      "name"

  """
  @spec descendant_for_byte_range(t(), non_neg_integer(), non_neg_integer()) :: t() | nil
  def descendant_for_byte_range(%__MODULE__{handle: h, source: src}, start_byte, end_byte) do
    case Nif.node_descendant_for_byte_range(h, start_byte, end_byte) do
      nil -> nil
      handle -> %__MODULE__{handle: handle, source: src}
    end
  end

  @doc """
  Like `descendant_for_byte_range/3` but restricted to named nodes.
  """
  @spec named_descendant_for_byte_range(t(), non_neg_integer(), non_neg_integer()) :: t() | nil
  def named_descendant_for_byte_range(%__MODULE__{handle: h, source: src}, start_byte, end_byte) do
    case Nif.node_named_descendant_for_byte_range(h, start_byte, end_byte) do
      nil -> nil
      handle -> %__MODULE__{handle: handle, source: src}
    end
  end

  @doc """
  Whether this exact node is an `ERROR` node.

  Non-recursive — unlike `has_error?/1`, this returns `false` for a
  well-formed node whose descendants contain errors. Used together
  with tree traversal to collect the precise ranges of parse failures
  for editor diagnostics.
  """
  @spec error?(t()) :: boolean()
  def error?(%__MODULE__{handle: h}), do: Nif.node_is_error(h)

  @doc """
  Whether this node is `MISSING`.

  A missing node is synthesised by tree-sitter's error recovery when
  a required child was absent in the input (e.g. the `}}` that closes
  a quoted pattern). Missing nodes have zero-byte span at the point
  where the parser expected the token.
  """
  @spec missing?(t()) :: boolean()
  def missing?(%__MODULE__{handle: h}), do: Nif.node_is_missing(h)

  @doc "Return the node's S-expression form (see `Tree.to_sexp/1`)."
  @spec to_sexp(t()) :: binary()
  def to_sexp(%__MODULE__{handle: h}), do: Nif.node_to_sexp(h)

  defimpl Inspect do
    def inspect(%Localize.Mf2.TreeSitter.Node{} = node, _opts) do
      "#Localize.Mf2.TreeSitter.Node<" <>
        Localize.Mf2.TreeSitter.Node.type(node) <>
        " " <>
        inspect(Localize.Mf2.TreeSitter.Node.range(node)) <> ">"
    end
  end
end