defmodule Reader do
    @moduledoc """
    Reads all the files the compiler needs. 
    """
    
    @doc """
    Reads the source code from a file path and a general token list from an XML file. 
    ## Specs  
    ```source_code_path``` is the path to the file to be compiled.          
    ```tokens_path``` is the path to an XML file containing the target language's valid token list.

    Generates the following output:
    + Source Code String (SCS): source code contained in a string.
    + General Token List (GTL): list of target language valid tokens.
    
    ## Examples
    ```
        iex> {scs, gtl} = Reader.read_code_and_tokens('examples/test.c', tokens_path)
    ``` 
    """
    def read_code_and_tokens(source_code_path, tokens_path, verbose \\ false) do
        scs = read_source_code_string(source_code_path)
        gtl = read_general_token_list(tokens_path)
        if verbose do
            Helpers.Printer.print_element(Helpers.StringElements.scs, scs)
            inspect = true
            Helpers.Printer.print_element(Helpers.StringElements.gtl, gtl, inspect)
        end
        {scs, gtl}
    end

    @doc """
    Reads the source code as a string.
    ## Specs  
    ```source_code_path``` is the path to the file to be compiled.  

    Generates the following output:
    + Source Code String (SCS): String.
    
    ## Examples
    ```
        iex> scs = Reader.read_source_code_string(source_code_path)
    ``` 
    """
    def read_source_code_string(source_code_path)           do 
        File.read!(source_code_path) 
        |> _generate_source_code_string()
    end

    def _generate_source_code_string(file_content)          do
        clean_source_code_string(file_content)
    end

    defp clean_source_code_string(file_content)             do
        String.trim(file_content)
        |> String.replace("\n", " ")
        |> String.replace("\t", " ")
    end

    @doc """
    Reads the structure of the target language's valid tokens as a General Token List (GTL).
    ## Specs  
    ```tokens_path``` is the path to an XML file containing the target language's valid token list. 

    Generates the following output:
    + General Token List (GTL): list of target language's valid tokens.
    
    ## Examples
    ```
        iex> gtl = Reader.read_general_token_list(tokens_path)
    ``` 
    """
    def read_general_token_list(tokens_path)                do
        File.read!(tokens_path) 
        |> _generate_general_token_list()
    end

    def _generate_general_token_list(file_content)          do
        XmlToMap.naive_map(file_content)
        |> generate_useful_list()
        |> parse_to_token_list()
        |> add_error_token()
    end

    defp parse_to_token_list(list)                          do
        Enum.map list, fn(token) -> 
            %Structs.Token{
                tag:        token["tag"],
                expression: token["expression"],
                pos_y:      nil,
                pos_x:      nil,
            }
        end
    end

    defp add_error_token(gtl)                               do
        gtl ++ [%Structs.Token{tag: "error", expression: "\\S+", pos_y: nil, pos_x: nil}]
    end

    @doc """
    Reads the structure of the target language's grammar production rules from an XML file.
    ## Specs  
    ```grammar_prod_rules_path``` is the path to an XML file containing the target language's grammar production rules.

    Generates the following output:
    + General Abstract Syntax Treee (GAST): list containing the target language grammar production rules.
    
    ## Examples
    ```
        iex> gast = Reader.read_general_ast(grammar_prod_rules_path)
    ``` 
    """
    def read_general_ast(grammar_prod_rules_path)           do 
        File.read!(grammar_prod_rules_path) 
        |> _generate_general_ast()
    end

    def _generate_general_ast(file_content)                 do
        XmlToMap.naive_map(file_content) 
        |> generate_useful_list()
        |> parse_to_node_list()
    end

    defp generate_useful_list(map)                          do
        [general_list | _] = Map.values map
        [useful_list | _ ] = Map.values general_list
        useful_list
    end

    defp parse_to_node_list(list)                           do
        Enum.map list, fn(node) -> 
            %Structs.Node{
                tag:        node["tag"],
                token:      get_t(node),
                children:   get_c(node),
                class:      node["class"],
                asm:        get_asm(node)
            }
        end
    end

    defp get_c(node)                                        do 
        if node["substructure"] == nil, do: [], else: node["substructure"]
    end

    defp get_t(node)                                        do 
        if node["token"] == %{}, do: nil, else: node["token"]
    end

    defp get_asm(node)                                      do 
        if node["asm"] == %{}, do: "", else: node["asm"]
    end

end