neiam /gitgud

defmodule GitGud.Repositories.Numbering do
  @moduledoc """
  Allocates the next `#N` for a repository. The number space is shared
  between issues and pull requests, matching GitHub semantics.

  Call inside a transaction; the two MAX(...) queries lock nothing on
  their own, so concurrent inserts can race. The per-repo
  `unique_index(:issues, [:repository_id, :number])` and the matching
  one on `:pull_requests` are the safety net — on conflict, retry.
  """

  import Ecto.Query, warn: false
  alias GitGud.Issues.Issue
  alias GitGud.PullRequests.PullRequest
  alias GitGud.Repo

  @doc "Returns the next free `number` for the repo (≥ 1)."
  def next_for(repository_id) when is_integer(repository_id) do
    issue_max =
      from(i in Issue, where: i.repository_id == ^repository_id, select: max(i.number))
      |> Repo.one()

    pr_max =
      from(p in PullRequest, where: p.repository_id == ^repository_id, select: max(p.number))
      |> Repo.one()

    Enum.max([issue_max || 0, pr_max || 0]) + 1
  end
end