defmodule Microwaveprop.Radio.CsvImport do
  @moduledoc false

  alias Microwaveprop.Radio
  alias Microwaveprop.Workers.ContactWeatherEnqueueWorker

  @expected_columns 7
  @columns ~w(station1 station2 grid1 grid2 band mode qso_timestamp)

  @doc """
  Imports contacts from a CSV string. The first line is treated as a header.
  Each valid row is inserted via `Radio.create_contact/1` and enrichment is enqueued.
  The submitter_email is added to each row's attributes.

  Returns:
    - `{:ok, %{imported: [%Contact{}, ...], errors: [{row_num, [error_string]}]}}`
    - `{:error, :empty_csv}` if the input is empty or whitespace-only
    - `{:error, :no_data_rows}` if there are no data rows after the header
  """
  def import(csv_string, submitter_email) do
    numbered_lines =
      csv_string
      |> String.replace("\r\n", "\n")
      |> String.split("\n")
      |> Enum.with_index(1)

    non_blank = Enum.reject(numbered_lines, fn {line, _num} -> blank?(line) end)

    case non_blank do
      [] ->
        {:error, :empty_csv}

      [{_header, _}] ->
        {:error, :no_data_rows}

      [{_header, _} | data_lines] ->
        import_data_lines(data_lines, submitter_email)
    end
  end

  defp blank?(line), do: String.trim(line) == ""

  defp import_data_lines(data_lines, submitter_email) do
    result =
      Enum.reduce(data_lines, %{imported: [], errors: []}, fn {line, row_num}, acc ->
        case parse_and_import_row(line, submitter_email) do
          {:ok, contact} ->
            %{acc | imported: [contact | acc.imported]}

          {:error, error_messages} ->
            %{acc | errors: [{row_num, error_messages} | acc.errors]}
        end
      end)

    {:ok, %{imported: Enum.reverse(result.imported), errors: Enum.reverse(result.errors)}}
  end

  defp parse_and_import_row(line, submitter_email) do
    fields = line |> String.split(",") |> Enum.map(&String.trim/1)

    if length(fields) == @expected_columns do
      attrs =
        @columns
        |> Enum.zip(fields)
        |> Map.new()
        |> Map.put("submitter_email", submitter_email)

      case normalize_timestamp(attrs["qso_timestamp"]) do
        {:ok, iso_timestamp} ->
          attrs = Map.put(attrs, "qso_timestamp", iso_timestamp)

          case Radio.create_contact(attrs) do
            {:ok, contact} ->
              ContactWeatherEnqueueWorker.enqueue_for_contact(contact)
              {:ok, contact}

            {:error, changeset} ->
              {:error, changeset_error_strings(changeset)}
          end

        {:error, msg} ->
          {:error, [msg]}
      end
    else
      {:error, ["expected #{@expected_columns} columns, got #{length(fields)}"]}
    end
  end

  @doc """
  Parses various date/time formats into ISO 8601 UTC strings.

  Accepted formats:
    - ISO 8601: 2024-06-15T14:30:00Z, 2024-06-15 14:30:00Z, 2024-06-15T14:30:00
    - US date: 06/15/2024 14:30, 6/15/2024 2:30 PM
    - US date: 06-15-2024 14:30
    - EU date: 15/06/2024 14:30
    - Date only: 2024-06-15 (assumes 00:00 UTC)
    - Compact: 20240615 1430, 20240615T143000
  """
  def normalize_timestamp(raw) do
    trimmed = String.trim(raw)

    cond do
      # Already ISO 8601 with timezone
      match?({:ok, _, _}, DateTime.from_iso8601(trimmed)) ->
        {:ok, trimmed}

      # ISO-ish without Z: 2024-06-15T14:30:00 or 2024-06-15 14:30:00
      Regex.match?(~r/^\d{4}-\d{2}-\d{2}[T ]\d{2}:\d{2}(:\d{2})?$/, trimmed) ->
        {:ok, trimmed <> "Z"}

      # Date only: 2024-06-15
      Regex.match?(~r/^\d{4}-\d{2}-\d{2}$/, trimmed) ->
        {:ok, trimmed <> "T00:00:00Z"}

      # US format with AM/PM: 6/15/2024 2:30 PM or 06/15/2024 02:30 PM
      match = Regex.run(~r"^(\d{1,2})/(\d{1,2})/(\d{4})\s+(\d{1,2}):(\d{2})\s*(AM|PM)$"i, trimmed) ->
        [_, m, d, y, h, min, ampm] = match
        hour = parse_12h(String.to_integer(h), String.upcase(ampm))
        format_iso(y, m, d, hour, min)

      # US format 24h: 6/15/2024 14:30 or 06/15/2024 14:30:00
      match = Regex.run(~r"^(\d{1,2})/(\d{1,2})/(\d{4})\s+(\d{1,2}):(\d{2})(:\d{2})?$", trimmed) ->
        [_, m, d, y, h, min | _] = match
        format_iso(y, m, d, String.to_integer(h), min)

      # US format with dashes: 06-15-2024 14:30
      match = Regex.run(~r"^(\d{1,2})-(\d{1,2})-(\d{4})\s+(\d{1,2}):(\d{2})(:\d{2})?$", trimmed) ->
        [_, m, d, y, h, min | _] = match
        format_iso(y, m, d, String.to_integer(h), min)

      # Compact: 20240615 1430 or 20240615T143000
      match = Regex.run(~r"^(\d{4})(\d{2})(\d{2})[T ]?(\d{2})(\d{2})(\d{2})?$", trimmed) ->
        [_, y, m, d, h, min | _] = match
        format_iso(y, m, d, String.to_integer(h), min)

      true ->
        {:error, "qso_timestamp could not be parsed: #{trimmed}"}
    end
  end

  defp parse_12h(12, "AM"), do: 0
  defp parse_12h(12, "PM"), do: 12
  defp parse_12h(h, "PM"), do: h + 12
  defp parse_12h(h, "AM"), do: h

  defp format_iso(y, m, d, hour, min) do
    y = String.pad_leading(to_string(y), 4, "0")
    m = String.pad_leading(to_string(m), 2, "0")
    d = String.pad_leading(to_string(d), 2, "0")
    h = String.pad_leading(to_string(hour), 2, "0")
    min = String.pad_leading(to_string(min), 2, "0")
    {:ok, "#{y}-#{m}-#{d}T#{h}:#{min}:00Z"}
  end

  defp changeset_error_strings(changeset) do
    changeset
    |> Ecto.Changeset.traverse_errors(fn {message, opts} ->
      Regex.replace(~r"%{(\w+)}", message, fn _, key ->
        opts |> Keyword.get(String.to_existing_atom(key), key) |> to_string()
      end)
    end)
    |> Enum.flat_map(fn {field, messages} ->
      Enum.map(messages, &"#{field} #{&1}")
    end)
  end
end