feat: implement automatic cycle generation for members

- Add CycleGenerator module with advisory lock mechanism
- Add SetMembershipFeeStartDate change for auto-calculation
- Extend Settings with include_joining_cycle and default_membership_fee_type_id
- Add scheduled job skeleton for future Oban integration

lib/membership_fees/changes/set_membership_fee_start_date.ex

@@ -0,0 +1,154 @@
+defmodule Mv.MembershipFees.Changes.SetMembershipFeeStartDate do
+  @moduledoc """
+  Ash change module that automatically calculates and sets the membership_fee_start_date.
+
+  ## Logic
+
+  1. Only executes if `membership_fee_start_date` is not manually set
+  2. Requires both `join_date` and `membership_fee_type_id` to be present
+  3. Reads `include_joining_cycle` setting from global Settings
+  4. Reads `interval` from the assigned `membership_fee_type`
+  5. Calculates the start date:
+     - If `include_joining_cycle = true`: First day of the joining cycle
+     - If `include_joining_cycle = false`: First day of the next cycle after joining
+
+  ## Usage
+
+  In a Member action:
+
+      create :create_member do
+        # ...
+        change Mv.MembershipFees.Changes.SetMembershipFeeStartDate do
+          where [present(:membership_fee_type_id), present(:join_date)]
+        end
+      end
+
+  """
+  use Ash.Resource.Change
+
+  alias Mv.MembershipFees.CalendarCycles
+
+  @impl true
+  def change(changeset, _opts, _context) do
+    # Only calculate if membership_fee_start_date is not already set
+    if has_start_date?(changeset) do
+      changeset
+    else
+      calculate_and_set_start_date(changeset)
+    end
+  end
+
+  # Check if membership_fee_start_date is already set (either in changeset or data)
+  defp has_start_date?(changeset) do
+    # Check if it's being set in this changeset
+    case Ash.Changeset.fetch_change(changeset, :membership_fee_start_date) do
+      {:ok, date} when not is_nil(date) ->
+        true
+
+      _ ->
+        # Check if it already exists in the data (for updates)
+        case changeset.data do
+          %{membership_fee_start_date: date} when not is_nil(date) -> true
+          _ -> false
+        end
+    end
+  end
+
+  defp calculate_and_set_start_date(changeset) do
+    with {:ok, join_date} <- get_join_date(changeset),
+         {:ok, membership_fee_type_id} <- get_membership_fee_type_id(changeset),
+         {:ok, interval} <- get_interval(membership_fee_type_id),
+         {:ok, include_joining_cycle} <- get_include_joining_cycle() do
+      start_date = calculate_start_date(join_date, interval, include_joining_cycle)
+      Ash.Changeset.force_change_attribute(changeset, :membership_fee_start_date, start_date)
+    else
+      {:error, _reason} ->
+        # If we can't calculate the start date (missing required fields), just return unchanged
+        changeset
+    end
+  end
+
+  defp get_join_date(changeset) do
+    # First check the changeset for changes
+    case Ash.Changeset.fetch_change(changeset, :join_date) do
+      {:ok, date} when not is_nil(date) ->
+        {:ok, date}
+
+      _ ->
+        # Then check existing data
+        case changeset.data do
+          %{join_date: date} when not is_nil(date) -> {:ok, date}
+          _ -> {:error, :join_date_not_set}
+        end
+    end
+  end
+
+  defp get_membership_fee_type_id(changeset) do
+    # First check the changeset for changes
+    case Ash.Changeset.fetch_change(changeset, :membership_fee_type_id) do
+      {:ok, id} when not is_nil(id) ->
+        {:ok, id}
+
+      _ ->
+        # Then check existing data
+        case changeset.data do
+          %{membership_fee_type_id: id} when not is_nil(id) -> {:ok, id}
+          _ -> {:error, :membership_fee_type_not_set}
+        end
+    end
+  end
+
+  defp get_interval(membership_fee_type_id) do
+    case Ash.get(Mv.MembershipFees.MembershipFeeType, membership_fee_type_id) do
+      {:ok, %{interval: interval}} -> {:ok, interval}
+      {:error, _} -> {:error, :membership_fee_type_not_found}
+    end
+  end
+
+  defp get_include_joining_cycle do
+    case Mv.Membership.get_settings() do
+      {:ok, %{include_joining_cycle: include}} -> {:ok, include}
+      {:error, _} -> {:ok, true}
+    end
+  end
+
+  @doc """
+  Calculates the membership fee start date based on join date, interval, and settings.
+
+  ## Parameters
+
+    - `join_date` - The date the member joined
+    - `interval` - The billing interval (:monthly, :quarterly, :half_yearly, :yearly)
+    - `include_joining_cycle` - Whether to include the joining cycle
+
+  ## Returns
+
+    The calculated start date (first day of the appropriate cycle).
+
+  ## Examples
+
+      iex> calculate_start_date(~D[2024-03-15], :yearly, true)
+      ~D[2024-01-01]
+
+      iex> calculate_start_date(~D[2024-03-15], :yearly, false)
+      ~D[2025-01-01]
+
+      iex> calculate_start_date(~D[2024-03-15], :quarterly, true)
+      ~D[2024-01-01]
+
+      iex> calculate_start_date(~D[2024-03-15], :quarterly, false)
+      ~D[2024-04-01]
+
+  """
+  @spec calculate_start_date(Date.t(), atom(), boolean()) :: Date.t()
+  def calculate_start_date(join_date, interval, include_joining_cycle) do
+    if include_joining_cycle do
+      # Start date is the first day of the joining cycle
+      CalendarCycles.calculate_cycle_start(join_date, interval)
+    else
+      # Start date is the first day of the next cycle after joining
+      join_cycle_start = CalendarCycles.calculate_cycle_start(join_date, interval)
+      CalendarCycles.next_cycle_start(join_cycle_start, interval)
+    end
+  end
+end