defmodule Mix.Tasks.Semver.Increment do
  @moduledoc """
  The semver mix task: `mix semver.increment`
  """
  use Mix.Task

  @semver_line_rx ~r/version: "(\d+)\.(\d+)\.(\d+)(-.*)?",/

  @semver_field_pos 0
  @semver_field_default "patch"
  @increment_amount_pos 1
  @increment_amount_default 1

  @valid_semver_fields ["major", "minor", "patch"]

  @shortdoc "Default task will increment the semver patch version"
  @doc """
  Increment the appropriate field on your project version using Semantic Versioning.

  MAJOR.MINOR.PATCH

  Incrementing a greater value will reset the lower fields unless the --preserve-lower flag is set.

  ## Options

      * `patch` (default)
      * `minor`
      * `major`
      * --preserve [optional csv separated list to preserve (currently only `patch` and `minor`)]
                   Used on its own, only the specified field will be incremented.

  ## Examples

      $ mix semver.increment
      Incremented 0.1.0 -> 0.1.1

      $ mix semver.increment patch
      Incremented 0.1.1 -> 0.1.2

      $ mix semver.increment minor 3
      Incremented 0.1.2 -> 0.4.0

      $ mix semver.increment patch 2
      Incremented 0.4.0 -> 0.4.2

      $ mix semver.increment major --preserve patch
      Incremented 0.4.2 -> 1.0.2
      
  """
  def run(args) do
    {field, amt, opts} = parse_semver_args(args) |> dbg()

    {:ok, mix_data} = File.read("mix.exs")
    semver = get_semver(mix_data)

    next_semver = increment(semver, field, amt, opts)

    new_mix_data =
      String.replace(mix_data, @semver_line_rx, "version: \"#{Version.to_string(next_semver)}\",")

    IO.puts("Incremented #{semver} -> #{next_semver}")
    File.write!("mix.exs", new_mix_data)
    :ok
  end

  @spec increment(Version.t(), atom(), integer(), keyword()) :: Version.t()
  defp increment(semver, field, amount, opts)

  defp increment(semver = %Version{}, :patch, amount, _opts) do
    %Version{semver | patch: semver.patch + amount}
  end

  defp increment(semver = %Version{}, :minor, amount, opts) do
    next_patch = maybe_reset(semver, :patch, Keyword.get(opts, :preserve))
    next_minor = semver.minor + amount

    %Version{semver | minor: next_minor, patch: next_patch}
  end

  defp increment(semver = %Version{}, :major, amount, opts) do
    next_patch = maybe_reset(semver, :patch, Keyword.get(opts, :preserve))
    next_minor = maybe_reset(semver, :minor, Keyword.get(opts, :preserve))
    next_major = semver.major + amount

    %Version{semver | major: next_major, patch: next_patch, minor: next_minor}
  end

  defp coerce_custom_opts({p, nil}) when p in ["--preserve", "-p"],
    do: [preserve: [:patch, :minor]]

  defp coerce_custom_opts({p, fields}) when p in ["--preserve", "-p"] do
    IO.puts("handling custom")

    fields =
      fields
      |> String.split(",", trim: true)
      |> Enum.map(&String.downcase/1)
      |> Enum.map(&String.to_atom/1)

    [preserve: fields]
  end

  defp coerce_custom_opts(opt), do: opt

  defp get_semver(mix_data) do
    [semver_line | _] = Regex.run(@semver_line_rx, mix_data)

    semver_line
    |> String.replace("version: ", "")
    |> String.replace("\"", "")
    |> String.replace(",", "")
    |> Version.parse!()
  end

  defp maybe_reset(_semver, _field, nil), do: 0

  defp maybe_reset(semver, field, preserve_list) do
    if field in preserve_list, do: Map.get(semver, field), else: 0
  end

  defp parse_semver_args(args) do
    {parsed, args, invalid} =
      OptionParser.parse(args,
        strict: [preserve: :string],
        aliases: [p: :preserve]
      )

    opts =
      invalid
      |> Enum.map(&coerce_custom_opts/1)
      |> Enum.reduce(parsed, &Keyword.merge/2)
      |> Keyword.update!(:preserve, fn
        nil ->
          []

        fields when is_binary(fields) ->
          fields
          |> String.downcase()
          |> String.split(",", trim: true)
          |> Enum.map(&String.to_atom/1)

        fields when is_list(fields) ->
          Enum.map(fields, fn
            s when is_binary(s) -> s |> String.downcase() |> String.to_atom()
            a when is_atom(a) -> a
          end)
      end)

    field =
      case Enum.at(args, @semver_field_pos, @semver_field_default) do
        field when field in @valid_semver_fields ->
          String.to_atom(field)

        _ ->
          raise("Invalid semver field selected, must be one of #{inspect(@valid_semver_fields)}")
      end

    amt =
      case Enum.at(args, @increment_amount_pos) do
        delta when is_binary(delta) -> String.to_integer(delta)
        _ -> @increment_amount_default
      end

    {field, amt, opts}
  end
end