defmodule ToweropsWeb.ChangelogParser do
  @moduledoc "Parses priv/static/changelog.txt into structured entries."

  @doc "Returns a list of %{date: Date.t(), title: String.t(), items: [String.t()]}"
  def parse do
    path = Application.app_dir(:towerops, "priv/static/changelog.txt")

    case File.read(path) do
      {:ok, content} -> parse_content(content)
      {:error, _} -> []
    end
  end

  defp parse_content(content) do
    content
    |> String.split("\n")
    |> Enum.reduce([], fn line, acc ->
      cond do
        # Date header with title: "2026-02-13 — Title"
        Regex.match?(~r/^\d{4}-\d{2}-\d{2}\s+[—–]\s+.+/, line) ->
          [date_str | rest] = String.split(line, ~r/\s+[—–]\s+/, parts: 2)
          title = List.first(rest, "")
          entry = %{date: Date.from_iso8601!(String.trim(date_str)), title: String.trim(title), items: []}
          [entry | acc]

        # Date header without title: "2026-02-13"
        Regex.match?(~r/^\d{4}-\d{2}-\d{2}\s*$/, line) ->
          date = Date.from_iso8601!(String.trim(line))
          entry = %{date: date, title: nil, items: []}
          [entry | acc]

        # Bullet point
        String.starts_with?(String.trim(line), "* ") ->
          add_item_to_current(acc, line |> String.trim() |> String.trim_leading("* "))

        true ->
          acc
      end
    end)
    |> Enum.reverse()
  end

  defp add_item_to_current([current | rest], item), do: [%{current | items: current.items ++ [item]} | rest]

  defp add_item_to_current([], _item), do: []
end