defmodule ContentIndexer.Services.Calculator do
  use GenServer

  alias ContentIndexer.Services.{ListCheckerWorker, ListCheckerServer}

  @moduledoc """
    ** Summary **
      calculates the content_indexer weights for a document of tokens against a corpus of tokenized documents

      https://en.wikipedia.org/wiki/Tf-idf

      ** What is Tf-Idf **

      tf–idf, short for term frequency–inverse document frequency, is a numerical statistic that is
      intended to reflect how important a word is to a document in a collection or corpus. It is often
      used as a weighting factor in information retrieval and text mining.

      This library supports calculating large datasets in parallel using the Erlang OTP based server and actors

      Currently the supported file types are plain-text, PDF and DOCX (xml)

      ** Basic Useage **

      Pass it a list of tokens and a corpus of tokens as a list of lists and it will return a list of tokens
      with corresponding content_indexer weights based on the corpus of tokens

      iex> ContentIndexerService.calculate_content_indexer_documents(
        ["bread","butter","jam"],
        [["red","brown","jam"],["blue","green","butter"],["pink","green","bread","jam"]]
      )
      {:ok, [bread: 0.3662040962227032, butter: 0.3662040962227032,jam: 0.3662040962227032]}

  """

  def start_link do
    GenServer.start_link(__MODULE__, :ok, [name: __MODULE__])
  end

  def init(:ok) do
    {:ok, init_calculator()}
  end

  def init_calculator do
    IO.puts "\nInitialising Calculator\n"
  end

  def total(count) do
    GenServer.call(__MODULE__, {:total, count})
  end

  @doc """
    calculates the content_indexer

    ## Parameters

      - content: String of tokens to be indexed
      - corpus: List of String tokens representing the corpus

    ## Example

      iex> ContentIndexerValidateService.calculate_tokens_againts_corpus("bread,butter,jam", ["red,brown,jam","blue,green,butter","pink,green,bread,jam"])
            {:ok,
              [
                {"bread", 0.13515503603605478},
                {"butter", 0.13515503603605478},
                {"jam", 0.0}
              ]
            }
  """
  def calculate_tokens_againts_corpus(content, corpus) do
    token_list = Tfidf.calculate_all(content, corpus, &String.split(&1, ","))
    {:ok, token_list}
  end

  @doc """
    calculates the word count for each token in the list of tokens representing the document
    and returns a list of the tokens with their respective word counts

    ## Parameters

      - tokens: List of tokens to be indexed

    ## Example

      iex> ContentIndexerService.calculate_token_count_document(["bread","butter","jam","jam","bread","bread"])
            {:ok, [bread: 3, butter: 1, jam: 2]}
  """
  def calculate_token_count_document(tokens) do
    token_stream = Stream.map(tokens, fn(token) ->
      {token, word_count(token, tokens)}
    end)
    uniq_tokens = token_stream |> Stream.uniq |> Enum.to_list
    {:ok, uniq_tokens}
  end

  @doc """
    calculates the term frequency for each token in the list of tokens representing the document
    and returns a list of the tokens with their respective term frequencies

    ## Parameters

      - tokens: List of tokens to be indexed

    ## Example

      iex> ContentIndexerService.calculate_tf_document(["bread","butter","jam","jam","bread","bread"])
            {:ok, [bread: 0.5, butter: 0.16666666666666666, jam: 0.3333333333333333]}
  """
  def calculate_tf_document(tokens) do
    token_stream = Stream.map(tokens, fn(token) ->
      {token, tf(token, tokens)}
    end)
    uniq_tokens = token_stream |> Stream.uniq |> Enum.to_list
    {:ok, uniq_tokens}
  end

  @doc """
    calculates the content_indexer weights for each token in the query - weights the query against itself

    ## Parameters

      - tokens: List of tokens to be indexed

    ## Example

      iex> ContentIndexerService.calculate_content_indexer_query(["bread","butter","jam"])
            {:ok, [bread: 0.0, butter: 0.0, jam: 0.0]}
  """
  def calculate_content_indexer_query(tokens) do
    tokenized_tokens = case tokens do
      [_|_] ->
        tokens
      _ ->
        tokenize(tokens)
    end
    token_content_indexer_counts = tokenized_tokens
    |> Enum.uniq
    |> Enum.map(fn(token) ->
      {token, (tf(token, tokenized_tokens) * idf_streamed(token, 1, [tokens]))}
    end)
    {:ok, token_content_indexer_counts}
  end

  @doc """
    calculates the content_indexer weights for each token in the list of tokens against the corpus of tokens

    ## Parameters

      - tokens: List of tokens to be indexed
      - corpus_of_tokens: List of lists representing the corpus of all tokens

    ## Example

      iex> ContentIndexerService.calculate_content_indexer_documents(
              ["bread","butter","jam"],
              [
                ["red","brown","jam"],
                ["blue","green","butter"],
                ["pink","green","bread","jam"]
              ])
            {:ok, [bread: 0.3662040962227032, butter: 0.3662040962227032,jam: 0.3662040962227032]}
  """
  def calculate_content_indexer_documents(tokens, corpus_of_tokens) do
    corpus_size = length(corpus_of_tokens) # this is so we can avoid calculating it again!
    case corpus_size do
      1 ->
        calculate_content_indexer_documents_single(tokens, corpus_of_tokens)
      _ ->
        calculate_content_indexer_documents_multiple(tokens, corpus_of_tokens, corpus_size)
    end
  end

  @doc """
    calculates the content_indexer weights for each token in the list of tokens against the corpus of tokens

    ## Parameters

      - tokens: List of tokens to be indexed
      - corpus_of_tokens: List of lists representing the corpus of all tokens
      - corpus_size: Integer with the size of the corpus_of_tokens - just so we can avoid re-calculating it

    ## Example

      iex> ContentIndexerService.calculate_content_indexer_documents(
            ["bread","butter","jam"],
            [
              ["red","brown","jam"],
              ["blue","green","butter"],
              ["pink","green","bread","jam"]
            ])
            {:ok, [bread: 0.3662040962227032, butter: 0.3662040962227032,jam: 0.3662040962227032]}
  """
  def calculate_content_indexer_documents(tokens, corpus_of_tokens, corpus_size) do
    case corpus_size do
      1 ->
        calculate_content_indexer_documents_single(tokens, corpus_of_tokens)
      _ ->
        calculate_content_indexer_documents_multiple(tokens, corpus_of_tokens, corpus_size)
    end
  end

  @doc """
    simple function to check if an item is contained in the list

    ## Parameters

      - list: List of any type
      - item: Any type of item stored in the list

    ## Example

      iex> ContentIndexerService.calculate_content_indexer_documents(
            ["bread","butter","jam"],
            [
              ["red","brown","jam"],
              ["blue","green","butter"],
              ["pink","green","bread","jam"]
            ])
            {:ok, [bread: 0.3662040962227032, butter: 0.3662040962227032,jam: 0.3662040962227032]}
  """
  def list_contains(list, item), do: Enum.find(list, &(item == &1)) != nil

  # - internal genserver call handler methods

  def handle_call({:state}, _from, state) do
    {:reply, {:ok, state}, state}
  end

  def handle_call({:total, _count}, _from, state) do
    {:reply, {:ok, state}, state}
  end

  # - private methods

  defp calculate_content_indexer_documents_single(tokens, corpus_of_tokens) do
    token_content_indexer_counts = tokens
    |> Enum.uniq
    |> Enum.map(fn(token) ->
      {token, (tf(token, tokens) * idf(token, corpus_of_tokens))}
    end)

    {:ok, token_content_indexer_counts}
  end

  # The corpus_of_tokens has more than one document in it
  defp calculate_content_indexer_documents_multiple(tokens, corpus_of_tokens, corpus_size) do
    token_content_indexer_counts = tokens
    |> Enum.uniq
    |> Enum.map(fn(token) ->
      {to_string(token), (tf(token, tokens) * idf_streamed(token, corpus_size, corpus_of_tokens))}
    end)
    {:ok, token_content_indexer_counts}
  end

  defp idf_streamed(word, corpus_size, corpus_of_tokens) do
    :math.log(corpus_size / (1 + n_containing_calc(word, corpus_of_tokens, corpus_size)))
  end

  # Corpus of tokens is a list of tuples with the index being the second item in the tuple
  defp n_containing_calc(word, corpus_of_tokens, collection_size) do
    ListCheckerServer.initialise_collection(collection_size, self())
    indexed_stream = Stream.with_index(corpus_of_tokens)
    indexed_stream |> Enum.each(fn(streamed_item) ->
      {tokens, index} = streamed_item
      ListCheckerWorker.list(index, word, tokens)
    end)

    total = receive do
      {:total, count} ->
        count
    end
    total
  end

  defp idf(word, corpus_of_tokens) do
    :math.log(length(corpus_of_tokens) / (1 + n_containing(word, corpus_of_tokens)))
  end

  defp tf(word, tokens) do
    word_count(word, tokens) / length(tokens)
  end

  defp word_count(word, tokens) do
    Enum.reduce(tokens, 0, fn(cur_word, acc) ->
      if cur_word == word, do: acc + 1, else: acc
    end)
  end

  defp n_containing(word, corpus_of_tokens) do
    Enum.reduce(corpus_of_tokens, 0, fn(text, acc) ->
      if list_contains(text, word), do: acc + 1, else: acc
    end)
  end

  defp tokenize(text, split_char \\ ",") do
    split_str = String.split(text, split_char)
    split_str |> Enum.filter(fn x -> x != "" end) # remove empty elements
  end
end