defmodule Mix.Tasks.UnusedTest do
  # Mutates `Mix.shell/1` globally; cannot run concurrently with other tests
  # that capture Mix shell output.
  use ExUnit.Case, async: false

  alias Mix.Tasks.Unused

  setup do
    previous_shell = Mix.shell()
    Mix.shell(Mix.Shell.Process)
    on_exit(fn -> Mix.shell(previous_shell) end)
    :ok
  end

  describe "run/1" do
    test "emits human-readable text output by default and returns :ok" do
      assert :ok = Unused.run([])

      # The task either reports "no unused" or a header — both go through
      # `Mix.shell().info/1` which the Process shell captures as messages.
      assert_received_info_matching(fn msg ->
        msg =~ "unused public functions" or msg =~ "No unused public functions"
      end)
    end

    test "honours --format json by emitting valid JSON" do
      assert :ok = Unused.run(["--format", "json"])
      json = collect_info_messages()

      # The task always emits exactly one JSON document via Mix.shell().info/1.
      decoded = Jason.decode!(json)
      refute decoded == []

      for entry <- decoded do
        assert byte_size(entry["module"]) > 0
        assert byte_size(entry["function"]) > 0
        assert is_integer(entry["arity"])
        assert byte_size(entry["file"]) > 0
        assert is_integer(entry["line"])
      end
    end

    test "honours --only by filtering output to a module prefix" do
      # No assertion on contents — just exercise the apply_only/2 branch.
      assert :ok = Unused.run(["--only", "Towerops.NoSuchPrefix"])

      assert_received_info_matching(fn msg ->
        msg =~ "No unused public functions"
      end)
    end

    test "honours --skip by removing modules under a prefix" do
      # Just exercise the apply_skip branch — output depends on the build env.
      assert :ok = Unused.run(["--skip", "Towerops"])

      msg = collect_info_messages()
      # Either we get the "found N" header or the "no unused" message.
      assert msg =~ ~r/unused public functions|No unused public functions/
    end
  end

  # ──────────────────────────────────────────────────────────────────────
  # Helpers

  defp collect_info_messages(acc \\ "") do
    receive do
      {:mix_shell, :info, [msg]} -> collect_info_messages(acc <> msg <> "\n")
    after
      0 -> String.trim(acc)
    end
  end

  defp assert_received_info_matching(predicate) do
    msg = collect_info_messages()
    assert predicate.(msg), "no Mix shell info message matched the predicate. Got: #{inspect(msg)}"
  end
end