defmodule Ravix.RQL.QueryParser do
  @moduledoc false
  require OK

  alias Ravix.RQL.Query

  @non_aliasable_fields ["id()", "count()", "sum()", :"id()", :"count()", :"sum()"]

  @doc """
  Receives a `Ravix.RQL.Query` object and parses it to a RQL query string
  """
  @spec parse(Query.t()) :: {:error, any} | {:ok, Query.t()}
  def parse(%Query{} = query) do
    OK.for do
      parsed_query =
        query
        |> parse_stmt(query.from_token)
        |> parse_stmt(query.group_token)
        |> parse_stmt(query.where_token)
        |> parse_stmt(query.order_token)
        |> parse_stmts(query.and_tokens)
        |> parse_stmts(query.or_tokens)
        |> parse_stmt(query.update_token)
        |> parse_stmt(query.select_token)
        |> parse_stmt(query.limit_token)
    after
      parsed_query
    end
  end

  defp parse_stmts({:ok, query}, stmts), do: parse_stmts(query, stmts)

  defp parse_stmts({:error, err}, _),
    do: {:error, err}

  defp parse_stmts(%Query{} = query, []), do: query

  defp parse_stmts(%Query{} = query, stmts) do
    stmts
    |> Enum.reduce(query, fn stmt, acc ->
      case parse_stmt(acc, stmt) do
        {:ok, stmts} -> Map.merge(acc, stmts)
        {:error, err} -> {:error, err}
      end
    end)
  end

  defp parse_stmt({:ok, query}, stmt), do: parse_stmt(query, stmt)

  defp parse_stmt(%Query{} = query, nil), do: query

  defp parse_stmt({:error, err}, _),
    do: {:error, err}

  defp parse_stmt(%Query{} = query, stmt) do
    case stmt.token do
      :from -> parse_from(query, stmt)
      :from_index -> parse_from_index(query, stmt)
      :select -> parse_select(query, stmt)
      :select_function -> parse_select_function(query, stmt)
      :group_by -> parse_group_by(query, stmt)
      :update -> parse_update(query, stmt)
      :where -> parse_where(query, stmt)
      :and -> parse_and(query, stmt)
      :or -> parse_or(query, stmt)
      :not -> parse_not(query, stmt)
      :order_by -> parse_ordering(query, stmt)
      :limit -> parse_limit(query, stmt)
      _ -> {:error, :invalid_statement}
    end
  end

  defp parse_condition_stmt(%Query{} = query, nil), do: query

  defp parse_condition_stmt(%Query{} = query, condition) do
    query_part =
      case condition.token do
        :greater_than ->
          "#{parse_field(query, condition.field)} > $p#{query.params_count}"

        :eq ->
          "#{parse_field(query, condition.field)} = $p#{query.params_count}"

        :greater_than_or_eq ->
          "#{parse_field(query, condition.field)} >= $p#{query.params_count}"

        :lower_than ->
          "#{parse_field(query, condition.field)} < $p#{query.params_count}"

        :lower_than_or_eq ->
          "#{parse_field(query, condition.field)} <= $p#{query.params_count}"

        :between ->
          "#{parse_field(query, condition.field)} between $p#{query.params_count} and $p#{query.params_count + 1}"

        :in ->
          "#{parse_field(query, condition.field)} in " <>
            "(" <> parse_params_to_positional_string(query, condition.params) <> ")"

        # This one is weird yeah, RavenDB only accepts the NOT in binary operations (OR | AND), so we need
        # to be a little hackish
        :nin ->
          "#{parse_field(query, condition.field)} != null and not #{parse_field(query, condition.field)} in " <>
            "(" <> parse_params_to_positional_string(query, condition.params) <> ")"

        :ne ->
          "#{parse_field(query, condition.field)} != $p#{query.params_count}"

        _ ->
          {:error, :invalid_condition_param}
      end

    case query_part do
      {:error, :invalid_condition_param} -> {:error, :invalid_condition_param}
      _ -> {:ok, query_part}
    end
  end

  defp parse_from(%Query{} = query, from_token) do
    query_fragment =
      "from #{from_token.document_or_index}" <> parse_alias(query, from_token.document_or_index)

    {:ok, append_query_fragment(query, query_fragment)}
  end

  defp parse_from_index(%Query{} = query, from_token) do
    query_fragment =
      "from #{from_token.document_or_index}" <> parse_alias(query, from_token.document_or_index)

    {:ok, append_query_fragment(query, query_fragment)}
  end

  defp parse_select(%Query{} = query, select_token) do
    query_fragment =
      " select " <> Enum.map_join(select_token.fields, ", ", &parse_field(query, &1))

    {:ok, append_query_fragment(query, query_fragment)}
  end

  defp parse_select_function(%Query{} = query, projected_select_token) do
    query_fragment =
      " select { " <>
        Enum.map_join(projected_select_token.fields, "\n", fn {field, projected} ->
          Atom.to_string(field) <> " : " <> projected
        end) <> " }"

    {:ok, append_query_fragment(query, query_fragment)}
  end

  defp parse_update(%Query{} = query, update_token) do
    fields_to_update =
      update_token.fields
      |> Enum.reduce(%{updates: [], current_position: query.params_count}, fn field, acc ->
        %{
          acc
          | updates:
              acc.updates ++
                [
                  "#{parse_field(query, field.name)} #{parse_assignment_operation(field.operation)} $p#{acc.current_position}"
                ],
            current_position: acc.current_position + 1
        }
      end)

    field_values = Enum.map(update_token.fields, fn field -> field.value end)
    positional_params = parse_params_to_positional(query, field_values)

    query_params =
      Map.merge(
        query.query_params,
        positional_params
      )

    {:ok,
     %Query{
       query
       | query_params: query_params,
         params_count: fields_to_update.current_position
     }
     |> append_query_fragment(" update{ " <> Enum.join(fields_to_update.updates, ", ") <> " }")}
  end

  defp parse_assignment_operation(operation) do
    case operation do
      :set -> "="
      :inc -> "+="
      :dec -> "-="
    end
  end

  defp parse_where(%Query{} = query, where_token) do
    parse_locator_stmt(query, where_token, "where", false)
  end

  defp parse_and(%Query{} = query, and_token, negated \\ false) do
    parse_locator_stmt(query, and_token, "and", negated)
  end

  defp parse_or(%Query{} = query, or_token, negated \\ false) do
    parse_locator_stmt(query, or_token, "or", negated)
  end

  defp parse_not(%Query{} = query, not_token) do
    case not_token.condition do
      %Ravix.RQL.Tokens.And{} = and_token -> parse_and(query, and_token, true)
      %Ravix.RQL.Tokens.Or{} = or_token -> parse_or(query, or_token, true)
    end
  end

  defp parse_ordering(%Query{} = query, order_by_token) do
    query_fragment =
      " order by " <>
        Enum.map_join(order_by_token.fields, ",", fn {field, order} ->
          "#{parse_field(query, field)} #{Atom.to_string(order)}"
        end)

    {:ok, append_query_fragment(query, query_fragment)}
  end

  defp parse_group_by(%Query{} = query, group_by_token) do
    query_fragment = " group by " <> Enum.map_join(group_by_token.fields, &parse_field(query, &1))

    {:ok, append_query_fragment(query, query_fragment)}
  end

  defp parse_limit(%Query{} = query, limit_token) do
    query_fragment = " limit #{limit_token.skip}, #{limit_token.next}"

    {:ok, append_query_fragment(query, query_fragment)}
  end

  defp parse_locator_stmt(%Query{} = query, stmt, locator, negated) do
    OK.for do
      condition <- parse_condition_stmt(query, stmt.condition)
      positional_params = parse_params_to_positional(query, stmt.condition.params)
      params_count = query.params_count + length(stmt.condition.params)

      negated =
        case negated do
          true -> " not "
          false -> " "
        end

      query_params =
        Map.merge(
          query.query_params,
          positional_params
        )
    after
      %Query{
        query
        | query_string: query.query_string <> " #{locator}#{negated}#{condition}",
          query_params: query_params,
          params_count: params_count
      }
    end
  end

  defp parse_params_to_positional(query, params) do
    query.params_count..(query.params_count + length(params) - 1)
    |> Enum.reduce(%{}, fn position, acc ->
      Map.put(acc, "p#{position}", Enum.at(params, position - query.params_count))
    end)
  end

  defp parse_params_to_positional_string(query, params) do
    parse_params_to_positional(query, params)
    |> Map.keys()
    |> Enum.map_join(",", fn key -> "$#{key}" end)
  end

  defp parse_alias(%Query{aliases: aliases}, document) do
    case Map.has_key?(aliases, document) do
      true -> " as " <> Map.get(aliases, document)
      false -> ""
    end
  end

  defp parse_field(%Query{}, {field_name, field_alias})
       when field_name in @non_aliasable_fields do
    field_name <> " as #{field_alias}"
  end

  defp parse_field(%Query{aliases: aliases, from_token: from_token}, {field_name, field_alias}) do
    case Map.has_key?(aliases, from_token.document_or_index) do
      true -> Map.get(aliases, from_token.document_or_index) <> ".#{field_name} as #{field_alias}"
      false -> field_name <> " as #{field_alias}"
    end
  end

  defp parse_field(%Query{}, field) when field in @non_aliasable_fields, do: field

  defp parse_field(%Query{aliases: aliases, from_token: from_token}, field) do
    case Map.has_key?(aliases, from_token.document_or_index) do
      true -> Map.get(aliases, from_token.document_or_index) <> ".#{field}"
      false -> field
    end
  end

  defp append_query_fragment(%Query{} = query, append) do
    %Query{
      query
      | query_string: query.query_string <> "#{append}"
    }
  end
end