defmodule AshPostgres.Predicates.Trigram do
  @moduledoc """
  A filter predicate that filters based on trigram similarity.

  See the postgres docs on [https://www.postgresql.org/docs/9.6/pgtrgm.html](trigram) for more information.

  Requires the pg_trgm extension. Configure which extensions you have installed in your `AshPostgres.Repo`

      # Example

      filter(query, name: [trigram: [text: "geoff", greater_than: 0.4]])
  """

  # alias Ash.Error.Filter.InvalidFilterValue
  defstruct [:field, :text, :greater_than, :less_than, :equals]

  use Ash.Filter.Predicate

  alias Ash.Filter.Predicate

  def new(_resource, attribute, opts) do
    with :ok <- required_options_provided(opts),
         {:ok, value} <- Ash.Type.cast_input(attribute.type, opts[:text]),
         {:ok, less_than} <- validate_similarity(opts[:less_than]),
         {:ok, greater_than} <- validate_similarity(opts[:greater_than]),
         {:ok, equals} <- validate_similarity(opts[:equals]) do
      {:ok,
       %__MODULE__{
         field: attribute.name,
         text: value,
         greater_than: greater_than,
         less_than: less_than,
         equals: equals
       }}
    else
      _ ->
        {:error, "Invalid filter value"}
    end
  end

  defp validate_similarity(nil), do: {:ok, nil}
  defp validate_similarity(1), do: {:ok, 1}
  defp validate_similarity(0), do: {:ok, 0}

  defp validate_similarity(similarity)
       when is_float(similarity) and similarity <= 1.0 and similarity >= 0.0 do
    {:ok, similarity}
  end

  defp validate_similarity(similarity) when is_binary(similarity) do
    sanitized =
      case similarity do
        "." <> decimal_part -> "0." <> decimal_part
        other -> other
      end

    case Float.parse(sanitized) do
      {float, ""} -> {:ok, float}
      _ -> :error
    end
  end

  defp required_options_provided(opts) do
    if Keyword.has_key?(opts, :text) do
      case {opts[:greater_than], opts[:less_than], opts[:equals]} do
        {nil, nil, nil} -> :error
        {nil, nil, _equals} -> :ok
        {_greater_than, nil, nil} -> :ok
        {nil, _less_than, nil} -> :ok
        {_greater_than, _less_than, nil} -> :ok
      end
    else
      :error
    end
  end

  defimpl Inspect do
    import Inspect.Algebra

    def inspect(
          %{field: field, text: text, equals: nil, less_than: nil, greater_than: greater_than},
          opts
        ) do
      concat([
        "similarity(",
        Predicate.add_inspect_path(opts, field),
        ", ",
        to_doc(text, opts),
        ")",
        " > ",
        to_doc(greater_than, opts)
      ])
    end

    def inspect(
          %{field: field, text: text, equals: nil, less_than: less_than, greater_than: nil},
          opts
        ) do
      concat([
        "similarity(",
        Predicate.add_inspect_path(opts, field),
        ", ",
        to_doc(text, opts),
        ")",
        " < ",
        to_doc(less_than, opts)
      ])
    end

    def inspect(
          %{
            field: field,
            text: text,
            equals: nil,
            less_than: less_than,
            greater_than: greater_than
          },
          opts
        ) do
      concat([
        "similarity(",
        Predicate.add_inspect_path(opts, field),
        ", ",
        to_doc(text, opts),
        ") between ",
        to_doc(less_than, opts),
        " and ",
        to_doc(greater_than, opts)
      ])
    end

    def inspect(
          %{field: field, text: text, equals: equals, less_than: nil, greater_than: nil},
          opts
        ) do
      concat([
        Predicate.add_inspect_path(opts, field),
        " trigram similarity to ",
        to_doc(text, opts),
        " == ",
        to_doc(equals, opts)
      ])
    end
  end
end