defmodule Localize.Mf2.TreeSitter do
  @moduledoc """
  Elixir bindings to the tree-sitter-mf2 grammar.

  Produces a concrete, position-aware CST for ICU MessageFormat 2 (MF2)
  source. Complements the NimbleParsec parser in
  [`localize`](https://hexdocs.pm/localize/) — that parser is strict,
  fast, and aborts on the first error; this one is resilient and
  error-recovering, which is what editor tooling and an LSP need.

  The NIF embeds a vendored copy of the tree-sitter C runtime and the
  generated `tree-sitter-mf2` parser, so no Rust toolchain and no
  system `libtree-sitter` are required to build.

  ### Primary API

  * `parse/1` — parse a source binary into a `Tree`.
  * `root/1` — obtain the root `Node`.

  Walk from the root using the functions in
  `Localize.Mf2.TreeSitter.Node`.
  """

  alias Localize.Mf2.TreeSitter.{Edit, Nif, Node, Tree}

  @doc """
  Parse an MF2 source binary.

  Tree-sitter is error-recovering: invalid input still yields a tree,
  with `ERROR` or `MISSING` nodes placed at the failure points. Use
  `Localize.Mf2.TreeSitter.Node.has_error?/1` on the root to detect
  whether recovery was needed.

  ### Arguments

  * `source` is a UTF-8 binary containing MF2 source.

  ### Returns

  * `{:ok, tree}` on success.

  * `{:error, :parse_failed}` if the underlying parser could not be
    constructed (out-of-memory or library misconfiguration). Invalid
    MF2 input does **not** produce this — it produces an `{:ok, tree}`
    with `ERROR` nodes.

  ### Examples

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

  """
  @spec parse(binary()) :: {:ok, Tree.t()} | {:error, :parse_failed}
  def parse(source) when is_binary(source) do
    case Nif.parse(source) do
      {:ok, ref} -> {:ok, %Tree{ref: ref, source: source}}
      {:error, reason} -> {:error, reason}
    end
  end

  @doc """
  Return the root node of a parse tree.

  ### Arguments

  * `tree` is a `Localize.Mf2.TreeSitter.Tree` returned by `parse/1`.

  ### Returns

  * A `Localize.Mf2.TreeSitter.Node` struct.

  ### Examples

      iex> {:ok, tree} = Localize.Mf2.TreeSitter.parse("")
      iex> Localize.Mf2.TreeSitter.Node.type(Localize.Mf2.TreeSitter.root(tree))
      "source_file"

  """
  @spec root(Tree.t()) :: Node.t()
  def root(%Tree{ref: ref, source: source}) do
    %Node{handle: Nif.tree_root_node(ref), source: source}
  end

  @doc """
  Reparse a source binary incrementally, reusing subtrees from a
  previous parse.

  This is the LSP / editor case: the user made a small text change,
  and we want to produce a new tree without redoing the full parse.
  The old tree is not mutated — internally a copy is taken, each
  edit is applied to that copy, and the parser is fed the
  edited-old-tree plus the new source. Unchanged subtrees are reused
  byte-for-byte.

  ### Arguments

  * `old_tree` is a `Localize.Mf2.TreeSitter.Tree` from a previous
    `parse/1` or `parse_incremental/3` call.

  * `edits` is a list of `Localize.Mf2.TreeSitter.Edit` structs
    describing the text change(s) from the old source to the new.

  * `new_source` is the updated UTF-8 binary.

  ### Returns

  * `{:ok, new_tree}` with the new tree wrapping `new_source`.

  * `{:error, :parse_failed}` on allocation or language failure.

  ### Examples

      iex> {:ok, old} = Localize.Mf2.TreeSitter.parse("hello {$name}")
      iex> # user appended "!" at the end
      iex> edit = %Localize.Mf2.TreeSitter.Edit{
      ...>   start_byte: byte_size("hello {$name}"),
      ...>   old_end_byte: byte_size("hello {$name}"),
      ...>   new_end_byte: byte_size("hello {$name}!"),
      ...>   start_point: {0, byte_size("hello {$name}")},
      ...>   old_end_point: {0, byte_size("hello {$name}")},
      ...>   new_end_point: {0, byte_size("hello {$name}!")}
      ...> }
      iex> {:ok, new} = Localize.Mf2.TreeSitter.parse_incremental(old, [edit], "hello {$name}!")
      iex> Localize.Mf2.TreeSitter.Node.text(Localize.Mf2.TreeSitter.root(new))
      "hello {$name}!"

  """
  @spec parse_incremental(Tree.t(), [Edit.t()], binary()) ::
          {:ok, Tree.t()} | {:error, :parse_failed}
  def parse_incremental(%Tree{ref: old_ref}, edits, new_source)
      when is_list(edits) and is_binary(new_source) do
    edit_tuples = Enum.map(edits, &Edit.to_tuple/1)

    case Nif.parse_incremental(old_ref, edit_tuples, new_source) do
      {:ok, ref} -> {:ok, %Tree{ref: ref, source: new_source}}
      {:error, reason} -> {:error, reason}
    end
  end

  @doc """
  Return the byte/point ranges that differ between two trees.

  Intended to be called with a previous tree and the tree returned by
  `parse_incremental/3` for the same source sequence. The result is a
  list of `{start_byte, end_byte, start_point, end_point}` ranges that
  a consumer (editor highlight pass, LSP semantic-tokens) needs to
  redraw.

  ### Arguments

  * `old_tree` and `new_tree` are `Localize.Mf2.TreeSitter.Tree`
    structs.

  ### Returns

  * A list of `{start_byte, end_byte, start_point, end_point}` tuples.

  ### Examples

      iex> {:ok, old} = Localize.Mf2.TreeSitter.parse("hello")
      iex> {:ok, new} = Localize.Mf2.TreeSitter.parse("hello")
      iex> Localize.Mf2.TreeSitter.changed_ranges(old, new)
      []

  """
  @spec changed_ranges(Tree.t(), Tree.t()) :: [
          {non_neg_integer(), non_neg_integer(), Node.point(), Node.point()}
        ]
  def changed_ranges(%Tree{ref: old}, %Tree{ref: new}) do
    Nif.tree_get_changed_ranges(old, new)
  end

  @doc """
  Walk a tree and return every `ERROR` or `MISSING` node as a
  diagnostic descriptor.

  Each diagnostic is `{kind, node}` where `kind` is `:error` or
  `:missing`. Read the range with `Localize.Mf2.TreeSitter.Node.start_byte/1`,
  `end_byte/1`, `start_point/1`, `end_point/1` to render a squiggle
  or emit an LSP `textDocument/publishDiagnostics` notification.

  The traversal is depth-first, pre-order; diagnostics appear in
  source order. Well-formed trees return `[]`.

  ### Arguments

  * `tree` is a `Localize.Mf2.TreeSitter.Tree`.

  ### Returns

  * A list of `{:error | :missing, Localize.Mf2.TreeSitter.Node.t()}`
    tuples in source order, possibly empty.

  ### Examples

      iex> {:ok, tree} = Localize.Mf2.TreeSitter.parse("hello {$")
      iex> [{kind, _node} | _] = Localize.Mf2.TreeSitter.diagnostics(tree)
      iex> kind in [:error, :missing]
      true

      iex> {:ok, tree} = Localize.Mf2.TreeSitter.parse("hello")
      iex> Localize.Mf2.TreeSitter.diagnostics(tree)
      []

  """
  @spec diagnostics(Tree.t()) :: [{:error | :missing, Node.t()}]
  def diagnostics(%Tree{} = tree) do
    root = root(tree)

    if Node.has_error?(root) do
      root |> collect_diagnostics([]) |> Enum.reverse()
    else
      []
    end
  end

  # Depth-first pre-order walk, collecting ERROR and MISSING nodes.
  # Accumulates in reverse (cons-onto-head) and the public function
  # reverses once at the end. Descent is pruned at subtrees that have
  # no errors anywhere beneath them.
  defp collect_diagnostics(%Node{} = node, acc) do
    acc =
      cond do
        Node.missing?(node) -> [{:missing, node} | acc]
        Node.error?(node) -> [{:error, node} | acc]
        true -> acc
      end

    if Node.has_error?(node) do
      node
      |> Node.children()
      |> Enum.reduce(acc, &collect_diagnostics/2)
    else
      acc
    end
  end
end