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/mv/membership_fees/cycle_generator.ex

@@ -0,0 +1,317 @@
+defmodule Mv.MembershipFees.CycleGenerator do
+  @moduledoc """
+  Module for generating membership fee cycles for members.
+
+  This module provides functions to automatically generate membership fee cycles
+  based on a member's fee type, start date, and exit date.
+
+  ## Algorithm
+
+  1. Load member with relationships (membership_fee_type, membership_fee_cycles)
+  2. Determine membership_fee_start_date (calculate if nil)
+  3. Find the last existing cycle start date (or use membership_fee_start_date)
+  4. Generate all cycle starts from last to today (or left_at)
+  5. Filter out existing cycles (idempotency)
+  6. Create new cycles with the current amount from membership_fee_type
+
+  ## Concurrency
+
+  Uses PostgreSQL advisory locks to prevent race conditions when generating
+  cycles for the same member concurrently.
+
+  ## Examples
+
+      # Generate cycles for a single member
+      {:ok, cycles} = CycleGenerator.generate_cycles_for_member(member)
+
+      # Generate cycles for all active members
+      {:ok, results} = CycleGenerator.generate_cycles_for_all_members()
+
+  """
+
+  alias Mv.MembershipFees.CalendarCycles
+  alias Mv.MembershipFees.MembershipFeeCycle
+  alias Mv.MembershipFees.Changes.SetMembershipFeeStartDate
+  alias Mv.Membership.Member
+  alias Mv.Repo
+
+  require Ash.Query
+  require Logger
+
+  @type generate_result :: {:ok, [MembershipFeeCycle.t()]} | {:error, term()}
+
+  @doc """
+  Generates membership fee cycles for a single member.
+
+  Uses an advisory lock to prevent concurrent generation for the same member.
+
+  ## Parameters
+
+    - `member` - The member struct or member ID
+    - `opts` - Options:
+      - `:today` - Override today's date (useful for testing)
+
+  ## Returns
+
+    - `{:ok, cycles}` - List of newly created cycles
+    - `{:error, reason}` - Error with reason
+
+  ## Examples
+
+      {:ok, cycles} = CycleGenerator.generate_cycles_for_member(member)
+      {:ok, cycles} = CycleGenerator.generate_cycles_for_member(member_id)
+      {:ok, cycles} = CycleGenerator.generate_cycles_for_member(member, today: ~D[2024-12-31])
+
+  """
+  @spec generate_cycles_for_member(Member.t() | String.t(), keyword()) :: generate_result()
+  def generate_cycles_for_member(member_or_id, opts \\ [])
+
+  def generate_cycles_for_member(member_id, opts) when is_binary(member_id) do
+    case load_member(member_id) do
+      {:ok, member} -> generate_cycles_for_member(member, opts)
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  def generate_cycles_for_member(%Member{} = member, opts) do
+    today = Keyword.get(opts, :today, Date.utc_today())
+
+    # Use advisory lock to prevent concurrent generation
+    with_advisory_lock(member.id, fn ->
+      do_generate_cycles(member, today)
+    end)
+  end
+
+  @doc """
+  Generates membership fee cycles for all active members.
+
+  Active members are those who:
+  - Have a membership_fee_type assigned
+  - Have a join_date set
+  - Either have no exit_date or exit_date >= today
+
+  ## Parameters
+
+    - `opts` - Options:
+      - `:today` - Override today's date (useful for testing)
+      - `:batch_size` - Number of members to process in parallel (default: 10)
+
+  ## Returns
+
+    - `{:ok, results}` - Map with :success and :failed counts
+    - `{:error, reason}` - Error with reason
+
+  """
+  @spec generate_cycles_for_all_members(keyword()) :: {:ok, map()} | {:error, term()}
+  def generate_cycles_for_all_members(opts \\ []) do
+    today = Keyword.get(opts, :today, Date.utc_today())
+    batch_size = Keyword.get(opts, :batch_size, 10)
+
+    # Query active members with fee type assigned
+    query =
+      Member
+      |> Ash.Query.filter(not is_nil(membership_fee_type_id))
+      |> Ash.Query.filter(not is_nil(join_date))
+      |> Ash.Query.filter(is_nil(exit_date) or exit_date >= ^today)
+
+    case Ash.read(query) do
+      {:ok, members} ->
+        results = process_members_in_batches(members, batch_size, today)
+        {:ok, build_results_summary(results)}
+
+      {:error, reason} ->
+        {:error, reason}
+    end
+  end
+
+  defp process_members_in_batches(members, batch_size, today) do
+    members
+    |> Enum.chunk_every(batch_size)
+    |> Enum.flat_map(&process_batch(&1, today))
+  end
+
+  defp process_batch(batch, today) do
+    batch
+    |> Task.async_stream(fn member ->
+      {member.id, generate_cycles_for_member(member, today: today)}
+    end)
+    |> Enum.map(fn {:ok, result} -> result end)
+  end
+
+  defp build_results_summary(results) do
+    success_count = Enum.count(results, fn {_id, result} -> match?({:ok, _}, result) end)
+    failed_count = Enum.count(results, fn {_id, result} -> match?({:error, _}, result) end)
+
+    %{success: success_count, failed: failed_count, total: length(results)}
+  end
+
+  # Private functions
+
+  defp load_member(member_id) do
+    Member
+    |> Ash.Query.filter(id == ^member_id)
+    |> Ash.Query.load([:membership_fee_type, :membership_fee_cycles])
+    |> Ash.read_one()
+    |> case do
+      {:ok, nil} -> {:error, :member_not_found}
+      {:ok, member} -> {:ok, member}
+      {:error, reason} -> {:error, reason}
+    end
+  end
+
+  defp with_advisory_lock(member_id, fun) do
+    # Convert UUID to integer for advisory lock (use hash)
+    lock_key = :erlang.phash2(member_id)
+
+    Repo.transaction(fn ->
+      # Acquire advisory lock for this transaction
+      Ecto.Adapters.SQL.query!(Repo, "SELECT pg_advisory_xact_lock($1)", [lock_key])
+
+      case fun.() do
+        {:ok, result} -> result
+        {:error, reason} -> Repo.rollback(reason)
+      end
+    end)
+  end
+
+  defp do_generate_cycles(member, today) do
+    # Reload member with relationships to ensure fresh data
+    case load_member(member.id) do
+      {:ok, member} ->
+        cond do
+          is_nil(member.membership_fee_type_id) ->
+            {:error, :no_membership_fee_type}
+
+          is_nil(member.join_date) ->
+            {:error, :no_join_date}
+
+          true ->
+            generate_missing_cycles(member, today)
+        end
+
+      {:error, reason} ->
+        {:error, reason}
+    end
+  end
+
+  defp generate_missing_cycles(member, today) do
+    fee_type = member.membership_fee_type
+    interval = fee_type.interval
+    amount = fee_type.amount
+    existing_cycles = member.membership_fee_cycles || []
+
+    # Determine start date
+    start_date = determine_start_date(member, interval)
+
+    # Determine end date (today or exit_date, whichever is earlier)
+    end_date = determine_end_date(member, today)
+
+    # Generate all cycle starts from start_date to end_date
+    all_cycle_starts = generate_cycle_starts(start_date, end_date, interval)
+
+    # Filter out existing cycles
+    existing_starts = MapSet.new(existing_cycles, & &1.cycle_start)
+    missing_starts = Enum.reject(all_cycle_starts, &MapSet.member?(existing_starts, &1))
+
+    # Create missing cycles
+    create_cycles(missing_starts, member.id, fee_type.id, amount)
+  end
+
+  defp determine_start_date(member, interval) do
+    if member.membership_fee_start_date do
+      member.membership_fee_start_date
+    else
+      # Calculate from join_date using global settings
+      include_joining_cycle = get_include_joining_cycle()
+
+      SetMembershipFeeStartDate.calculate_start_date(
+        member.join_date,
+        interval,
+        include_joining_cycle
+      )
+    end
+  end
+
+  defp determine_end_date(member, today) do
+    if member.exit_date && Date.compare(member.exit_date, today) == :lt do
+      # Member has left - use the cycle that contains the exit date
+      member.exit_date
+    else
+      today
+    end
+  end
+
+  defp get_include_joining_cycle do
+    case Mv.Membership.get_settings() do
+      {:ok, %{include_joining_cycle: include}} -> include
+      {:error, _} -> true
+    end
+  end
+
+  @doc """
+  Generates all cycle start dates from a start date to an end date.
+
+  ## Parameters
+
+    - `start_date` - The first cycle start date
+    - `end_date` - The date up to which cycles should be generated
+    - `interval` - The billing interval
+
+  ## Returns
+
+    List of cycle start dates.
+
+  ## Examples
+
+      iex> generate_cycle_starts(~D[2024-01-01], ~D[2024-12-31], :quarterly)
+      [~D[2024-01-01], ~D[2024-04-01], ~D[2024-07-01], ~D[2024-10-01]]
+
+  """
+  @spec generate_cycle_starts(Date.t(), Date.t(), atom()) :: [Date.t()]
+  def generate_cycle_starts(start_date, end_date, interval) do
+    # Ensure start_date is aligned to cycle boundary
+    aligned_start = CalendarCycles.calculate_cycle_start(start_date, interval)
+
+    generate_cycle_starts_acc(aligned_start, end_date, interval, [])
+  end
+
+  defp generate_cycle_starts_acc(current_start, end_date, interval, acc) do
+    if Date.compare(current_start, end_date) == :gt do
+      # Current cycle start is after end date - stop
+      Enum.reverse(acc)
+    else
+      # Include this cycle and continue to next
+      next_start = CalendarCycles.next_cycle_start(current_start, interval)
+      generate_cycle_starts_acc(next_start, end_date, interval, [current_start | acc])
+    end
+  end
+
+  defp create_cycles(cycle_starts, member_id, fee_type_id, amount) do
+    cycles =
+      Enum.map(cycle_starts, fn cycle_start ->
+        attrs = %{
+          cycle_start: cycle_start,
+          member_id: member_id,
+          membership_fee_type_id: fee_type_id,
+          amount: amount,
+          status: :unpaid
+        }
+
+        case Ash.create(MembershipFeeCycle, attrs) do
+          {:ok, cycle} -> {:ok, cycle}
+          {:error, reason} -> {:error, {cycle_start, reason}}
+        end
+      end)
+
+    errors = Enum.filter(cycles, &match?({:error, _}, &1))
+
+    if Enum.empty?(errors) do
+      {:ok, Enum.map(cycles, fn {:ok, cycle} -> cycle end)}
+    else
+      Logger.warning("Some cycles failed to create: #{inspect(errors)}")
+      # Return successfully created cycles anyway
+      successful = Enum.filter(cycles, &match?({:ok, _}, &1)) |> Enum.map(fn {:ok, c} -> c end)
+      {:ok, successful}
+    end
+  end
+end