defmodule VavPipeline.MannaLedgerPersistenceTest do
  @moduledoc """
  What is eaten stays eaten.

  Until 2026-10-04 the ledger lived only in memory. A restart forgot the
  day's consumption and the next cycle gathered the whole provision again.
  That was hidden while manna was an emptyDir (a restart emptied the jar
  too, and the kohen had to refill it by hand); once the provision was put
  on a volume, a crash loop alone would have refilled it.

  These tests restart the ledger process under its real supervisor — a new
  process, an empty state, the same disk — and ask what it remembers.
  """

  use ExUnit.Case, async: false

  alias VavPipeline.{HaltMonitor, Manna, MannaLedger}

  setup do
    if HaltMonitor.halted?(), do: HaltMonitor.resolve("manna persistence test setup")
    MannaLedger.reset()
    write_provision(10)

    on_exit(fn ->
      MannaLedger.reset()
      File.rm(Manna.provision_file())
    end)

    :ok
  end

  describe "the record" do
    test "is written beside the provision, with today's date, when a cycle eats" do
      refute File.exists?(MannaLedger.ledger_file())

      assert {:ok, :loaded} = MannaLedger.load_provision()
      assert {:ok, 7} = MannaLedger.consume(:compute_units, 3)

      assert Path.dirname(MannaLedger.ledger_file()) == Path.dirname(Manna.provision_file())
      record = MannaLedger.ledger_file() |> File.read!() |> Jason.decode!()

      assert record["cycle_date"] == today()
      assert record["consumed"]["compute_units"] == 3
      assert record["consumed"]["api_calls_external"] == 0
    end

    test "is not written by a refused consumption" do
      assert {:ok, :loaded} = MannaLedger.load_provision()
      assert {:error, :provision_exhausted} = MannaLedger.consume(:compute_units, 11)
      refute File.exists?(MannaLedger.ledger_file())
    end
  end

  describe "a restart in the middle of the day" do
    test "resumes the count — the provision is not gathered whole again" do
      assert {:ok, :loaded} = MannaLedger.load_provision()
      assert {:ok, 6} = MannaLedger.consume(:compute_units, 4)

      restart_ledger()

      # The new process takes the day up as it starts — before any cycle
      # asks — so the status never shows an untouched jar.
      ledger = MannaLedger.ledger()
      assert ledger.cycle_date == today()
      assert ledger.allocated.compute_units == 10
      assert ledger.consumed.compute_units == 4

      assert {:ok, :already_loaded} = MannaLedger.load_provision()
      assert MannaLedger.remaining(:compute_units) == 6

      # And it keeps counting from there.
      assert {:ok, 5} = MannaLedger.consume(:compute_units, 1)
    end

    test "an exhausted day stays exhausted — a crash loop does not refill the jar" do
      assert {:ok, :loaded} = MannaLedger.load_provision()
      assert {:ok, 0} = MannaLedger.consume(:compute_units, 10)

      for _ <- 1..3 do
        restart_ledger()
        assert {:waiting, :provision_exhausted} = Manna.gather_for_cycle()
      end
    end

    test "the whole cycle path: gather, restart, gather" do
      assert :ok = Manna.gather_for_cycle()
      assert :ok = Manna.gather_for_cycle()
      restart_ledger()
      assert :ok = Manna.gather_for_cycle()
      assert MannaLedger.ledger().consumed.compute_units == 3
    end
  end

  describe "a restart with nothing to resume" do
    test "no record: the new process holds no day until the first cycle" do
      restart_ledger()
      assert MannaLedger.ledger().cycle_date == nil
      assert {:ok, :loaded} = MannaLedger.load_provision()
      assert MannaLedger.remaining(:compute_units) == 10
    end

    test "a record but no provision: nothing is resumed into an empty day" do
      assert {:ok, :loaded} = MannaLedger.load_provision()
      assert {:ok, 9} = MannaLedger.consume(:compute_units, 1)
      File.rm!(Manna.provision_file())

      restart_ledger()
      assert MannaLedger.remaining(:compute_units) == 0

      # The vessel waits. (Which of the two waiting reasons it gives is
      # the ledger's older behaviour for a day pinned with no provision;
      # the router answers MANNA_DEPLETED for both.)
      assert {:waiting, reason} = Manna.gather_for_cycle()
      assert reason in [:no_provision, :provision_exhausted]
    end
  end

  describe "what the record may not do" do
    test "another day's record is not this day's — it is ignored" do
      write_record(%{"cycle_date" => "2026-01-01", "consumed" => %{"compute_units" => 9}})

      assert {:ok, :loaded} = MannaLedger.load_provision()
      assert MannaLedger.remaining(:compute_units) == 10
    end

    test "a record that is not a ledger is ignored, and the cycle goes on" do
      for garbage <- [
            "not json",
            Jason.encode!(%{"cycle_date" => today(), "consumed" => "all of it"}),
            Jason.encode!(%{"cycle_date" => today(), "consumed" => %{"compute_units" => -5}}),
            Jason.encode!(%{"cycle_date" => today(), "consumed" => %{"compute_units" => "3"}})
          ] do
        MannaLedger.reset()
        File.write!(MannaLedger.ledger_file(), garbage)

        assert {:ok, :loaded} = MannaLedger.load_provision()
        assert MannaLedger.remaining(:compute_units) == 10
        assert {:ok, 9} = MannaLedger.consume(:compute_units, 1)
      end
    end

    test "it can only take away: a record larger than the provision leaves nothing" do
      write_record(%{"cycle_date" => today(), "consumed" => %{"compute_units" => 500}})

      assert {:ok, :loaded} = MannaLedger.load_provision()
      assert MannaLedger.remaining(:compute_units) == 0
      assert {:error, :provision_exhausted} = MannaLedger.consume(:compute_units, 1)
    end
  end

  describe "release" do
    test "at a day boundary the record goes with the surplus" do
      # The ledger holds no day (cycle_date nil ≠ today), as it does when
      # the day it loaded has passed and been released.
      write_record(%{"cycle_date" => "2026-01-01", "consumed" => %{"compute_units" => 2}})

      assert {:ok, _} = MannaLedger.enforce_cycle_boundary()
      refute File.exists?(MannaLedger.ledger_file())
    end

    test "a release within the same day lets go of the allocation, not the memory" do
      assert {:ok, :loaded} = MannaLedger.load_provision()
      assert {:ok, 8} = MannaLedger.consume(:compute_units, 2)

      # Manna.gather_for_cycle/0 does this when a provision arrives late.
      assert {:ok, _} = MannaLedger.enforce_cycle_boundary()
      assert File.exists?(MannaLedger.ledger_file())

      assert {:ok, :loaded} = MannaLedger.load_provision()
      assert MannaLedger.remaining(:compute_units) == 8
    end

    test "reset forgets the record (tests must not leak a day into each other)" do
      assert {:ok, :loaded} = MannaLedger.load_provision()
      assert {:ok, 9} = MannaLedger.consume(:compute_units, 1)
      assert File.exists?(MannaLedger.ledger_file())

      MannaLedger.reset()
      refute File.exists?(MannaLedger.ledger_file())
    end
  end

  # ------------------------------------------------------------
  # Helpers
  # ------------------------------------------------------------

  defp today, do: Date.utc_today() |> Date.to_iso8601()

  # Bring the ledger down and up again through its own supervisor — a
  # new process with a new, empty state, and the file on disk untouched.
  # That is a restart, not a reset.
  #
  # (Done with terminate_child/restart_child rather than Process.exit:
  # this file restarts the ledger six times in well under five seconds,
  # and a supervisor that sees more than three CRASHES in five seconds
  # gives up and takes the application down with it — as the first
  # version of this test found out.)
  defp restart_ledger do
    old = Process.whereis(MannaLedger)
    :ok = Supervisor.terminate_child(VavPipeline.Supervisor, MannaLedger)
    {:ok, new} = Supervisor.restart_child(VavPipeline.Supervisor, MannaLedger)
    assert new != old
    assert Process.whereis(MannaLedger) == new
  end

  defp write_record(record) do
    File.mkdir_p!(Path.dirname(MannaLedger.ledger_file()))
    File.write!(MannaLedger.ledger_file(), Jason.encode!(record))
  end

  defp write_provision(compute_units) do
    expires = DateTime.utc_now() |> DateTime.add(6 * 3600) |> DateTime.to_iso8601()

    provision = %{
      "date" => today(),
      "provision" => %{
        "compute_units" => compute_units,
        "memory_mb" => 512,
        "api_calls_external" => 5,
        "storage_delta_mb" => 2,
        "sanhedrin_panels_max" => 2
      },
      "type" => "regular",
      "expires_at" => expires,
      "written_by" => "manna_ledger_persistence_test",
      "written_at" => DateTime.utc_now() |> DateTime.to_iso8601()
    }

    path = Manna.provision_file()
    File.mkdir_p!(Path.dirname(path))
    File.write!(path, Jason.encode!(provision))
  end
end