defmodule SqlParserEx do
  @moduledoc """
  Elixir NIF wrapper for the `sqlparser` Rust crate.

  Parses SQL into an AST (as a decoded map) and reconstructs SQL from an AST.

  ## Dialects

  Pass a dialect atom as the `dialect:` option. Defaults to `:generic`.

  ## Limitations

  `to_sql/2` accepts a `dialect:` option for API consistency, but the underlying Rust
  serializer uses a dialect-agnostic Display implementation. The dialect argument is
  validated but does not affect the reconstructed SQL output.

  ## Examples

      iex> {:ok, ast} = SqlParserEx.parse("SELECT 1")
      iex> is_map(ast) and map_size(ast) > 0
      true

  """

  alias SqlParserEx.Native

  @valid_dialects ~w(
    generic ansi postgres mysql sqlite mssql bigquery
    clickhouse duckdb databricks hive redshift snowflake
  )a

  @type dialect ::
          :generic
          | :ansi
          | :postgres
          | :mysql
          | :sqlite
          | :mssql
          | :bigquery
          | :clickhouse
          | :duckdb
          | :databricks
          | :hive
          | :redshift
          | :snowflake

  @type sql_opt :: {:dialect, dialect()}
  @type sql_string :: String.t()

  @type parse_error ::
          String.t()
          | {:unknown_dialect, atom()}
          | {:encode_error, Jason.EncodeError.t() | String.t()}

  @doc """
  Parses a SQL string and returns the single statement as an AST map.

  Returns `{:error, reason}` if zero or multiple statements are found.
  Use `parse_many/2` for multi-statement SQL.
  """
  @spec parse(sql_string(), [sql_opt()]) :: {:ok, map()} | {:error, parse_error()}
  def parse(sql, opts \\ []) do
    case parse_many(sql, opts) do
      {:ok, [statement]} -> {:ok, statement}
      {:ok, []} -> {:error, "no statements found in SQL input"}
      {:ok, _many} -> {:error, "expected exactly one statement; use parse_many/2 for multiple"}
      {:error, _} = error -> error
    end
  end

  @doc """
  Parses a SQL string and returns all statements as a list of AST maps.
  """
  @spec parse_many(sql_string(), [sql_opt()]) :: {:ok, [map()]} | {:error, parse_error()}
  def parse_many(sql, opts \\ []) do
    dialect = Keyword.get(opts, :dialect, :generic)

    with :ok <- validate_dialect(dialect),
         {:ok, json} <- Native.parse_sql(sql, dialect_to_string(dialect)),
         {:ok, statements} <- Jason.decode(json),
         :ok <- validate_statements(statements) do
      {:ok, statements}
    end
  end

  @doc """
  Reconstructs a SQL string from an AST map returned by `parse/2` or `parse_many/2`.

  Note: the `dialect:` option is validated but does not affect output. The underlying
  Rust serializer uses a dialect-agnostic Display implementation.
  """
  @spec to_sql(map(), [sql_opt()]) :: {:ok, sql_string()} | {:error, parse_error()}
  def to_sql(ast, opts \\ []) do
    dialect = Keyword.get(opts, :dialect, :generic)

    with :ok <- validate_dialect(dialect),
         {:ok, json} <- encode_ast(ast) do
      Native.to_sql(json, dialect_to_string(dialect))
    end
  end

  @doc "Returns all supported dialect atoms."
  @spec dialects() :: [dialect()]
  def dialects, do: @valid_dialects

  defp validate_dialect(d) when d in @valid_dialects, do: :ok
  defp validate_dialect(d), do: {:error, {:unknown_dialect, d}}

  defp validate_statements(stmts) when is_list(stmts) do
    if Enum.all?(stmts, &is_map/1),
      do: :ok,
      else: {:error, "unexpected NIF output: statements must be a list of maps"}
  end

  defp validate_statements(_), do: {:error, "unexpected NIF output: expected a JSON array"}

  defp encode_ast(ast) when is_map(ast) do
    case Jason.encode([ast]) do
      {:ok, _} = ok -> ok
      {:error, reason} -> {:error, {:encode_error, reason}}
    end
  end

  defp encode_ast(ast), do: {:error, {:encode_error, "expected a map, got: #{inspect(ast)}"}}

  defp dialect_to_string(dialect), do: Atom.to_string(dialect)
end