defmodule Plsm.IO.Export do

    @doc """
      Generate the schema field based on the database type
    """
    def type_output (field) do
        case field do
            {name, type} when type == :integer -> four_space "field :#{name}, :integer\n"
            {name, type} when type == :decimal -> four_space "field :#{name}, :decimal\n"
            {name, type} when type == :float -> four_space  "field :#{name}, :float\n"
            {name, type} when type == :string -> four_space "field :#{name}, :string\n"
            {name, type} when type == :text -> four_space "field :#{name}, :text\n"
            {name, type} when type == :map -> four_space("field :#{name}, :map\n")
            {name,type} when type == :date -> four_space "field :#{name}, :naive_datetime\n"
            _ -> ""
        end
    end

  @doc """
    Write the given schema to file.
  """
  @spec write(String.t, String.t, String.t) :: Any
  def write(schema, name, path \\ "") do
    case File.open "#{path}#{name}.ex", [:write] do
      {:ok, file} -> IO.puts "#{path}#{name}.ex"; IO.binwrite file, schema
      {_, msg} -> IO.puts "Could not write #{name} to file: #{msg}"
    end
  end
    
  @doc """
  Format the text of a specific table with the fields that are passed in. This is strictly formatting and will not verify the fields with the database
  """
  @spec prepare(Plsm.Database.Table, String.t) :: {Plsm.Database.TableHeader, String.t}
  def prepare(table, project_name) do
      output = module_declaration(project_name,table.header.name) <> model_inclusion() <> primary_key_declaration(table.columns) <> schema_declaration(table.header.name)
      trimmed_columns = remove_foreign_keys(table.columns)
      column_output = trimmed_columns |> Enum.reduce("",fn(x,a) -> a <> type_output({x.name, x.type}) end)
      output = output <> column_output
      belongs_to_output = Enum.filter(table.columns, fn(column) ->
        column.foreign_table != nil and column.foreign_table != nil
      end)
      |> Enum.reduce("",fn(column, a) ->
        a <> belongs_to_output(project_name, column)
      end)
      output = output <> belongs_to_output <> "\n"

      output = output <> two_space(end_declaration())
      output = output <> changeset(table.columns) <> end_declaration()
      output <> end_declaration()
      {table.header, output}
  end

  @spec primary_key_declaration([Plsm.Database.Column]) :: String.t
  defp primary_key_declaration(columns) do
    Enum.reduce(columns, "", fn(x,acc) -> acc <> create_primary_key(x)  end)
  end
  
  @spec create_primary_key(Plsm.Database.Column) :: String.t
  defp create_primary_key(%Plsm.Database.Column{primary_key: true, name: "id"}), do: ""
  defp create_primary_key(%Plsm.Database.Column{primary_key: true, name: name, type: type}), do: "@primary_key {:#{name}, :#{type}, []}\n" 
  defp create_primary_key(_), do: ""

  defp module_declaration(project_name, table_name) do
    namespace = Plsm.Database.TableHeader.table_name(table_name)
    "defmodule #{project_name}.#{namespace} do\n"
  end

  defp model_inclusion do
    two_space "use Ecto.Schema\n\n"
  end

  defp schema_declaration(table_name) do
    two_space "schema \"#{table_name}\" do\n"
  end

  defp end_declaration do
    "end\n"
  end

  defp four_space(text) do
    "    " <> text
  end

  defp two_space(text) do
    "  " <> text
  end

  defp changeset(columns) do
    output = two_space "def changeset(struct, params \\\\ %{}) do\n"
    output = output <> four_space "struct\n"
    output = output <> four_space "|> cast(params, " <> changeset_list(columns) <> ")\n"
    output <> two_space "end\n"
  end

  defp changeset_list(columns) do
    changelist = Enum.reduce(columns,"", fn(x,acc) -> acc <> ":#{x.name}, " end)
    String.slice(changelist,0,String.length(changelist) - 2)
  end

  @spec prepare(String.t, Plsm.Database.Column) :: String.t
  defp belongs_to_output(project_name, column) do
    column_name = column.name |> String.trim_trailing("_id")
    table_name = Plsm.Database.TableHeader.table_name(column.foreign_table)
    "\n" <> four_space "belongs_to :#{column_name}, #{project_name}.#{table_name}"
  end

  defp remove_foreign_keys(columns) do
    Enum.filter(columns, fn(column) ->
      column.foreign_table == nil and column.foreign_field == nil
    end)
  end
end