Accepts a file path and creates an index.

index.erl

% Does not properly formate index
% Does not remove duplicates

-module(index).
-export([get_file_contents/1,
         show_file_contents/1,
         map_to_words/1,
         index/1]).

% Used to read a file into a list of lines.
% Example files available in:
%   gettysburg-address.txt (short)
%   dickens-christmas.txt  (long)


% Get the contents of a text file into a list of lines.
% Each line has its trailing newline removed.

get_file_contents(Name) ->
    {ok,File} = file:open(Name,[read]),
    Rev = get_all_lines(File,[]),
lists:reverse(Rev).

% Auxiliary function for get_file_contents.
% Not exported.

get_all_lines(File,Partial) ->
    case io:get_line(File,"") of
        eof -> file:close(File),
               Partial;
        Line -> {Strip,_} = lists:split(length(Line)-1,Line),
                get_all_lines(File,[Strip|Partial])
    end.

% Show the contents of a list of strings.
% Can be used to check the results of calling get_file_contents.

show_file_contents([L|Ls]) ->
    io:format("~s~n",[L]),
    show_file_contents(Ls);
 show_file_contents([]) ->
    ok.

% Get the contents of a line as a list of words.
get_all_words([], _LineNumber) ->
    [];

get_all_words(Line, LineNumber) ->
    get_all_words(Line, [], [], LineNumber).

get_all_words([], [], Words, _LineNumber) ->
    lists:reverse(remove_empty(Words));

get_all_words([], Word, Words, LineNumber) ->
    get_all_words([], [], [ { lists:reverse(Word), LineNumber } | Words], LineNumber);

get_all_words([X | Xs], Word, Words, LineNumber) ->
    case lists:member(X, ".,\ ;:\t\n\"") of
        true ->
            get_all_words(Xs, [], [{ lists:reverse(Word), LineNumber } | Words], LineNumber);
        false ->
            get_all_words(Xs, [X | Word], Words, LineNumber)
    end.

% Removes empty words from list
remove_empty([]) ->
    [];

remove_empty(ListOfWords) ->
    remove_empty(ListOfWords, []).

remove_empty([], NewWordList) ->
    NewWordList;

remove_empty([{Word, LineNumber} | Words], NewWordList) ->
    case Word of
        [] ->
            remove_empty(Words, NewWordList);
        _ ->
            remove_empty(Words, [{Word, LineNumber} | NewWordList])
    end.

% Maps each line into a list of words
map_to_words([]) ->
    [];

map_to_words(List) ->
    map_to_words(List, [], 1).

map_to_words([], ListOfWords, _StartLine) ->
    lists:reverse(ListOfWords);

map_to_words([X | Xs], ListOfWords, StartLine) ->
    map_to_words(Xs, [get_all_words(X, StartLine) | ListOfWords], StartLine + 1).


% Index each word
% Data structure: [[{word, line-number}, ..., {word, line-number},...], ..., [...]]

index(Name) ->
    index(map_to_words(get_file_contents(Name)), []).

index([], Index) ->
    lists:reverse(Index);

index([[] | ListOfListsOfWordLineNumberTuples], Index) ->
    index(ListOfListsOfWordLineNumberTuples, Index);

index([[{Word, Line}|ListOfWordLineNumberTuple] | ListOfListsOfWordLineNumberTuples], Index) ->
    index([ListOfWordLineNumberTuple | ListOfListsOfWordLineNumberTuples], [traverse_list_of_tuples({Word, Line}, ListOfListsOfWordLineNumberTuples) | Index]).


% Traverse and modify one tuple on one list of tuples
traverse_and_transform({Word, Line}, ListOfTuples) ->
    traverse_and_transform({Word, Line}, ListOfTuples, []). % [{Line}]

traverse_and_transform({_Word, _Line}, [], WordIndex) ->
    lists:reverse(WordIndex);

traverse_and_transform({Word, _Line}, [{Word, OtherLine} | RestOfTuples], WordIndex) ->
    traverse_and_transform({Word, _Line}, RestOfTuples, [{OtherLine} | WordIndex]);

traverse_and_transform({Word, _Line}, [{_OtherWord, _OtherLIne} | RestOfTuples], WordIndex) ->
    traverse_and_transform({Word, _Line}, RestOfTuples, WordIndex).


% Recursively applies traverse_and_transform function to all lists of tuples in a greater list
traverse_list_of_tuples({Word, Line}, ListOfListsOfTuples) ->
    traverse_list_of_tuples({Word, Line}, ListOfListsOfTuples, []).

traverse_list_of_tuples({Word, Line}, [], ListOfLines) ->
    {Word, lists:flatten([{Line} | lists:reverse(ListOfLines)])};

traverse_list_of_tuples({Word, Line}, [ListOfTuples | ListOfListsOfTuples], ListOfLines) ->
    traverse_list_of_tuples({Word, Line}, ListOfListsOfTuples, [traverse_and_transform({Word, Line}, ListOfTuples) | ListOfLines]).