path: root/design-documents/037-wallet-transactions-lifecycle.rst

DD 37: Wallet Transaction Lifecycle
###################################

.. contents:: Table of Contents
   :depth: 2

Summary
=======

This design doc discusses the lifecycle of transactions in wallet-core.

Motivation
==========

The transactions in wallet-core all should have an associated state machine.  All transactions
should have some common actions that work uniformly across all transactions.

Requirements
============

The underlying state machine should make it obvious what interactions
are possible for the user.  The number of possible user interactions
in any state should be small.

Proposed Solution
=================


Common States
-------------

The following states apply to multiple different transactions.  Only pending
and aborting have transaction-specific sub-states, denoted by ``state(substate)``.

``pending``: A pending transaction waits for some external event/service.
The transaction stays pending until its change on the wallet's material balance
is finished. Any pending state can be suspended and resumed.

There are some other distinctions for pending transactions:

* long-polling vs. exponential backoff: A pending transaction is either waiting
  on an external service by making a long-polling request or by repeating requests
  with exponential back-off.
* ``lastError``: A pending transaction is either clean (i.e. the network interaction
  is literally active in transmission or the external service successfully
  communicated that it is not ready yet and this is perfectly normal)
  or has a ``lastError``, which is a ``TalerErrorDetails``
  object with details about what happened during the last attempt to proceed
  with the transaction.

``done``: A transaction that is done does not require any more processing.  It also
never has a ``lastError`` but is considered successful.

``dialog``: A transaction requires input from the user.

``aborting``: Similar to a pending transaction, but instead of taking active steps to
complete the transaction, the wallet is taking active steps to abort it. The ``lastError``
indicates errors the wallet experienced while taking active steps to abort the transaction.

``aborted``: Similar to ``done``, but the transaction was successfully aborted
instead of successfully finished. It will have the information of when (timestamp) it was
aborted and in which pending sub-state the abort action was initiated. Also, we can
include more information information relevant to the transaction in ``abortReason``

``suspended``: Similar to a ``aborted`` transaction, but the transaction was could be
resumed and may then still succeed.

``suspended-aborting``:  Network requests or other expensive work
to abort a transaction is paused.

``failed``: Similar to ``done``, but the transaction could not be completed or
possibly not even be aborted properly.  The user may have lost money.  In some
cases, a report to the auditor would make sense in this state.

``expired``: Similar to ``failed``, but the failure was caused by a timeout.

``deleted``: A ``deleted`` state is always a final state.  We only use this
state for illustrative purposes. In the implementation, the data associated
with the transaction would be literally deleted.


Common Transitions
------------------

Transitions are actions or other events.

``[action:retry]``: Retrying a transaction *(1.)* stops ongoing long-polling
requests for the transaction *(2.)* resets the retry timeout *(3.)* re-runs the
handler to process the transaction. Retries are always possible the following
states: ``pending(*)`` and ``aborting(*)``.

.. attention::

   Should we show the retry timeout in the UI somewhere?  Should we show it in dev mode?

   SEBASJM: Since the wallet will retry anyway, maybe is better if we replace the "retry"
   button with a "try now" button and a side text "retrying in xxx seconds".

   CG: Instead of a side text, this *might* make a good mouse-over hint for
   a "retry" (or "try now") button. I would not make this overly visible with
   side-text as the information is not that important. The text should also be
   "retrying next at XXX" using an absolute time XXX --- otherwise the UI would
   be way too busy recomputing/updating all of these strings: Using an absolute time,
   we only have to redraw anything once a retry actually happened. Given that
   retries should basically never be > 24h (we can impose a hard cap), the absolute
   time can just be in the format HH:MM:SS (without day).

``[action:suspend]``: Suspends a pending transaction, stopping any associated
network activities, but with a chance of trying again at a later time. This
could be useful if a user needs to save battery power or bandwidth and an
operation is expected to take longer (such as a backup, recovery or very large
withdrawal operation).

``[action:resume]``: Suspended transactions may be resumed, placing them back
into a pending state.

``[action:abort]``: Aborting a transaction either directly stops processing for the
transaction and puts it in an ``aborted`` state, or starts the necessary steps to
actively abort the transaction (e.g. to avoid losing money) and puts it in an
``aborting`` state.

``[action:fail]``: Directly puts an ``aborting`` or ``pending`` transaction into a
``failed`` state. May result in an ultimate loss of funds (beyond fees) to the
user and thus requires additional consent.

``[action:delete]``: Deleting a transaction completely deletes the transaction
from the database.  Depending on the type of transaction, some of the other
data *resulting* from the transaction might still survive deletion. For
example, deleting a withdrawal transaction does not delete already
successfully withdrawn coins. Deleting is only safe (no money lost) on initial
and final states (failed, aborted, done).

Whether aborting, deleting or suspending are possible depends on
the transaction type, and usually only one of the four choices should be
offered.


.. image:: ../images/transaction-common-states.png


Boxed labels indicate an end state in which there is no network activity and
hence no need to give the user a way to abort or suspend the activity.  The
circle indicates the initial state.  Ovals are states with network activity.

Blue arrows are used for user-triggered actions (via UI buttons).  Purple
arrows are used to indicate externally triggered actions.  Black arrows
without labels are used for the normal successful path.  Red arrows indicate
failure paths.


Common pending sub-states
-------------------------

During the pending state the transaction can go through several sub-states before
reaching a final state. Some of this sub-states are shared between different
transaction types:

``kyc``: The transaction cannot proceed because the user needs to actively
finish a KYC process.  The wallet should show the user a hint on how to
start the KYC process.

``aml``: The transaction can't proceed because the user needs to wait for the
exchange operator to conclude an AML investigation by the staff at the
exchange.  There are two AML substates. In the substate ``pending`` the user
is not expected to take any action and should just wait for the investigation
to conclude. In the substate ``frozen`` the staff at the exchange decided that
the account needed to be frozen.  The user should contact the exchange
provider's customer service department and seek resolution (possibly through
the courts) to avoid losing the funds for good.


Transaction Type: Withdrawal
----------------------------

* ``pending(bank-register-reserve)``

  Initial state for bank-integrated withdrawals.  The wallet submits the reserve public key
  and selected exchange to the bank (via the bank integration API).  Note that if the
  user aborts at this stage, we do not know if the bank is in the confirmation stage,
  so we must still *try* to abort the transaction at the bank.

  * ``[processed-success] => pending(bank-confirm-transfer)``
  * ``[processed-error] => failed``: On permanent errors (like 404 for the withdrawal operation),
    the wallet gives up.
  * ``[action:abort] => aborting(bank)``

* ``pending(bank-confirm-transfer)``

  The wallet waits until the bank has confirmed the withdrawal operation;
  usually the user has to complete a 2FA step to *approve* that the money is
  wired to the chosen exchange.  Note that the user's *approve* action is done
  in the bank's user interface and not the wallet's user interface. The wallet
  internally merely *polls* for the success or failure of the approve action.
  The wallet **may** occasionally (after some initial delay, especially on
  failures from the bank-poll to return any result) long-poll for the reserve
  status and, if successful, may then directly jump to
  ``pending(withdraw-coins)`` if the reserve is filled even if the poll at
  the bank did not return success or failure.

  * ``[bank-poll-success] => pending(exchange-wait-reserve)``
  * ``[bank-aborted] => aborted``: Bank denied the operation.
  * ``[exchange-poll-success] => pending(withdraw-coins)``:  Optional
    short-cut transition. Exchange was faster than the bank.
  * ``[action:abort] => aborting(bank)``

* ``aborting(bank)``

  The user aborted the withdraw operation in the wallet.  The wallet must now
  try to signal the bank that the wire transfer should no longer be performed.
  Note that it is possible that the bank registration never succeeded (if the
  user aborted us during ``pending(bank-register-reserve)``) and in this case
  we get an ``unknown transaction`` failure here.  It is also theoretically
  possible that the user approved the transaction in the bank while
  simultaneously aborting in the wallet. In this case, we transition to
  ``suspended(exchange-wait-reserve)`` (treating the ``abort`` action as a ``suspend``
  action).

  * ``[processed-success] => aborted``
  * ``[processed-error(already-confirmed)] => suspended(exchange-wait-reserve)``: We
    keep a transaction history entry reminding the user about when the already
    wired funds will be returned.
  * ``[processed-error(unknown-transaction)] => failed``

* ``suspended(exchange-wait-reserve)``

  State where funds were (presumably) wired to the exchange but the wallet
  was asked to not proceed with the withdraw, but we still resume.

  In this state, the wallet should show to the user that the money from the
  withdrawal reserve will be sent back to the originating bank account after
  ``$closing_delay``.  Note that the ``resume`` action should be disabled
  after ``$closing_delay``.

  * ``[action:delete] => deleted``
  * ``[action:resume] => pending(exchange-wait-reserve)``

* ``pending(exchange-wait-reserve)``

  Initial state for manual withdrawals.  Here, the wallet long-polls the
  exchange for the reserve status, waiting for the wire transfer to arrive
  at the exchange.

  * ``[exchange-poll-success] => pending(withdraw-coins)``
  * ``[action:suspend] => suspended(exchange-wait-reserve)``

* ``pending(withdraw-coins)``

  State where we are finally withdrawing the actual coins. Depending on
  the AML and KYC thresholds, we may at any time transition into a
  holding pattern on the AML or KYC checks of the exchange.

  It is possible that the selected denominations expired.
  In that case, the wallet will re-select denominations.

  * ``[processed-success] => done``
  * ``[processed-kyc-required] => pending(kyc)``
  * ``[processed-aml-required] => pending(aml)``
  * ``[reserve-expired] => expired(reserve)``
  * ``[action:suspend] => suspended(withdraw-coins)``

* ``pending(kyc)``

  State where the user needs to provide some identity data to pass a KYC
  check.  The wallet only shows the user the link for starting the KYC
  process and long-polls the exchange in anticipation of the user
  completing the KYC requirement.

  * ``[poll-success] => pending(withdraw-coins)``
  * ``[action:suspend] => suspended(kyc)``

* ``suspended(kyc)``

  State where the user needs to provide some identity data to pass a KYC
  check, but the long-polling was explicitly stopped. The user can
  choose to resume or delete.

  * ``[action:delete] => deleted``
  * ``[action:resume] => pending(kyc)``

* ``pending(aml)``

  State where the wallet needs to wait for completion of an AML process by an
  AML officer of the exchange. The wallet shows that the AML process is
  blocking progress. The message shown should distinguish between a mere
  pending AML process and an AML freezing decision in terms of the message
  shown to the user. If the AML decision is pending at the exchange, he user
  should be urged to simply wait.  If the funds were frozen, the wallet
  informs the user that their funds were frozen due to an AML decision.  The
  user is urged to contact the exchange operator's AML department out-of-band.
  In any case, the wallet long-polls for the AML decision to be made or change
  (possibly at a lower frequeny in case of a freeze).

  * ``[poll-success] => pending(withdraw-coins)``
  * ``[action:suspend] => suspended(aml)``

* ``suspended(aml)``

  State where the user needs to await some AML decision by the exchange.
  The long-polling was explicitly stopped. The user can choose to resume or delete.

  * ``[action:delete] => deleted``
  * ``[action:resume] => pending(aml)``

* ``suspended(withdraw-coins)``

  In this state, the wallet should show how much money arrived into the wallet
  and the rest of the money will be sent back to the originating bank account
  after ``$closing_delay``.  Note that the ``resume`` action should be
  disabled after ``$closing_delay``.

  * ``[action:delete] => deleted``
  * ``[action:resume] => pending(exchange-wait-reserve)``

* ``done``

  The withdrawal operation is complete.

  * ``[action:delete] => deleted``

* ``deleted``

  Withdrawn coins are preserved, as is reserve information for recoup.
  So this mostly removes the entry from the visible transaction history.
  Only once all coins were spent, the withdraw is fully removed.


.. image:: ../images/transaction-withdrawal-states.png


Transaction Type: Payment to Merchant
-------------------------------------

* ``pending(claim-proposal)``

  We received a ``pay`` URI. Download (claim) the proposal from the merchant.  Can fail if
  the proposal was already claimed by someone else.  If repurchase detection
  tells us that we already paid for this product, we go immediately to
  ``failed(repurchase)`` state for this transaction, but with a side-effect of
  transitioning the UI into a ``pending(repurchase-session-reset)`` on a
  *different* transaction (which before was in ``done``).

  A ``failed(repurchase)`` transaction will eventually be GCed (=deleted)
  automatically.

  * ``[error:already-claimed] => failed(already-claimed)`` -- the proposal was
    already claimed by someone else.
  * ``[error:invalid-proposal] => failed(invalid-proposal)`` -- the merchant provided a
    proposal that is invalid (e.g. malformed contract
    terms or bad signature).

* ``dialog(merchant-order-proposed)``

  Let the user accept (or refuse) the payment.

  * ``[action:pay-accept] => pending(submit-payment)``
  * ``[action:pay-refuse] => ``aborted(refused)`` -- The user explicitly
    decided not to proceed (at least not with this wallet).
  * ``[expired] => failed(expired)`` -- The offer has expired before the user made any
    decision. Note that we should use this transition at
    least a few seconds before the offer *actually* expires to avoid
    encountering an expiration during ``pending(submit-payment)`` in most
    real-world scenarios. Basically, we should prevent last-second payments to
    be event attempted client-side.

    The ``failed(expired)`` might be automatically deleted upon GC.

* ``pending(submit-payment)``

  Submit coin-by-coin (or in bulk groups) until payment is complete.

  * ``[action:abort] => aborting(pay-incomplete)`` -- The user explicitly decided to
    abort the process while the payment was happening.  Note that if the
    payment was already completed (and hence the merchant refuses any
    refunds), it is theoretically possible that pressing the abort button will
    nevertheless end up in a ``pending(auto-refund)`` state (and subsequently
    a ``done`` state) instead!
  * ``[success] => pending(auto-refund)`` -- Upon receiving confirmation from
    the merchant that the purchase was completed.
  * ``[error(insufficient balance)] => aborting(pay-incomplete)`` This transition
    happens if we detect double-spending and our balance is not sufficient
    after the double-spending. It is also conceivable (but should be rare)
    that this transition happens because the offer expired.

* ``pending(auto-refund)``

  The payment succeed. We remain in this state as long as an auto-refund-check
  is active.  If auto refunds are not enabled, we immediately continue to
  ``done``.

  * ``[no-auto-refund] => done``
  * ``[timeout] => done`` -- This happens when the auto refund set by the
    contract expired.
  * ``[long-poll:refund] => aborting(pay-incomplete)`` -- An auto-refund was detected.
  * ``[action:abort] => done`` -- The user may explicitly request to abort the
    auto-refund processing (for example to enable subsequent deletion before
    the auto-refund delay expires).

* ``aborting(pay-incomplete)``

  The wallet should interact with the merchant to request
  a refund on the incomplete payment.

  * ``[success] => aborted(pay-incomplete)``
  * ``[already-paid] => done``

* ``aborted(refunded)``

  The purchase ended with a (partial) refund. The state (and UI) should show
  the specific provenance of the state, which may include an insufficient
  balance (due to double-spending being detected during payment), and one or
  more partial or full refunds.

  * ``[action:delete] => deleted``

* ``done``

  The purchase is completed.

  * ``[action:delete] => deleted``
  * ``[repurchase] => pending(rebind-session)``: Another offer
    became pending for this product and we need to update the session so
    that the user does not have to buy it again.
  * ``[check-refunds]` => pending(check-refunds)``: New refunds
    might be available for this purchase.

* ``pending(check-refund)``

  New refunds might be available for this purchase.
  This state must only be entered *after* the payment has successfully
  completed.  It is not relevant for auto-refunds or refunds for incomplete
  payments.

  * ``[refunds-checked] => pending(user-new-refund)`` --- New
    refund(s) are available, user needs to confirm.
  * ``[refunds-checked] => done`` --- Refunds were checked, but no
    new refunds are available.
  * ``[action:stop-refund-query] => done`` ---
    This action would usually only be offered when the state is pending
    with errors. It stops the refund query, but the payment of course
    is left intact.

* ``pending(rebind-session)``

  The wallet should reset the associated session for the already purchased
  (digital) item.

  * ``[success] => done``
  * ``[action:abort] => done`` -- User aborted the session reset.

* ``deleted``

  When a payment is deleted, associated refund transactions are always deleted
  with it.

.. image:: ../images/transaction-payment-states.png


Transaction Type: Refund
------------------------

A refund is a pseudo-transaction that is always associated with a merchant
payment transaction.

* ``pending(accept)``

  Initial state for a refund.

  * ``[processed-error] => failed``: we received a permanent failure (such as money already wired to the merchant)

* ``failed``

  The refund failed permanently.

.. image:: ../images/transaction-refund-states.png


Transaction Type: Refresh
-------------------------

This is about refreshes that are triggered via coin expiration or as part of
getting change after making a payment.  In the first case, the refresh
transaction is forever shown as a separate transaction in the history unless
it did not affect the wallet balance (in which case we hide it). In the second
case, the refresh transaction is folded into the payment transaction upon
completion, so that the balance changes are included in the fees of the
transaction that caused us to obtain change.

If we have to adjust the refund amount (because a coin has fewer funds on it
than we expect) the transaction only shows the changes due to the refresh, and
we merely adjust the current balance of the wallet but without giving any
justification (as we cannot give details we do not have). So this will look
the same as if the double-spending transaction had been deleted by the user.

* ``pending``

  A refresh operation is pending.

  * ``[processed-success] => done``
  * ``[action:suspend] => suspended``
  * ``[failed] => failed``

* ``suspended``

  A refresh operation was suspended by the user.

  * ``[action:resume] => pending``

* ``done``

  The refresh operation completed.

  * ``[action:delete] => deleted``

* ``failed``

  The refresh operation failed. The user lost funds.

  * ``[action:delete] => deleted``

* ``deleted``

  All memory of the refresh operation is lost, but of course the resulting
  fresh coins are preserved.

.. image:: ../images/transaction-refresh-states.png


Transaction Type: Deposit
-------------------------

* ``pending(deposit)``

  Initial state for deposit transactions.
  We deposit the amount coin-by-coin (or in bulk groups) until deposit is completed.

  * ``[action:suspend] => suspended(submit-deposit)``
  * ``[processed-success] => pending(track)``
  * ``[processed-failure] => aborting(refund)``

* ``suspended(deposit)``

  The user suspended our ongoing deposit operation.

  * ``[action:resume] => pending(deposit)``
  * ``[action:abort] => aborting(refund)``

* ``pending(track)``

  All the coins were submitted, waiting to be wired.

  * ``[poll-success] => done``
  * ``[poll-accepted-kyc] => pending(kyc)``
  * ``[poll-accepted-aml] => pending(aml)``
  * ``[action:abort] => aborting(refund)``

* ``pending(kyc)``

  Exchange requires KYC before making the wire transfer.

  * ``[long-poll:kyc] => done``
  * ``[action:suspend] => suspended(kyc)``

* ``suspended(kyc)``

  The user suspended us while we were waiting for KYC to be finished.

  * ``[action:resume] => pending(kyc)``

* ``pending(aml)``

  Exchange requires AML before making the wire transfer.

  * ``[long-poll:aml] => done``
  * ``[action:suspend] => suspended(aml)``

* ``suspended(aml)``

  The user suspended us while we were waiting for AML to be finished.

  * ``[action:resume] => pending(aml)``

* ``aborting(refund)``

  Wallet should try to get the deposited amount back from the exchange (by submitting a refund).

  * ``[action:suspend] => suspended(refund)``
  * ``[processed-success] => aborting(refresh)``
  * ``[processed-error] => aborting(refresh)``: Even if the refund attempt failed, maybe the deposit failed as well and we can still succeed with a refresh.

* ``suspended(refund)``

  The user suspended us while we were trying to get a refund.

  * ``[action:resume] => aborting(refund)``

* ``aborting(refresh)``

  * ``[action:suspend] => suspended(refresh)``
  * ``[processed-success] => aborted``
  * ``[processed-error] => failed``

* ``suspended(refresh)``

  The user suspended us while we were trying to do the refresh.

  * ``[action:resume] => aborting(refresh)``

* ``aborted``

  The operation was aborted, some funds may have been lost (to fees or deposited anyway).

  * ``[action:delete] => deleted``

* ``done``

  The deposit operation completed.

  * ``[action:delete] => deleted``

* ``deleted``

  All memory of the deposit operation is lost.

.. image:: ../images/transaction-deposit-states.png


Transaction Type: Peer Push Debit
---------------------------------

Peer Push Debit transactions are created when the user wants to transfer money
to another wallet.

States and transitions:

* ``pending(purse-create)``

  The wallet is creating a purse. Initial state.

  * ``[process-success] => pending(ready)``: The wallet has created the purse.
  * ``[process-failure] => aborting(refund)``: The purse creation failed.
  * ``[action:suspend] => suspended(purse-create)``: The user suspended the operation.

* ``suspended(purse-create)``

  * ``[action:resume] => pending(purse-create)``: The user resumed the operation.
  * ``[action:abort] => aborting(refund)``: The user aborted the operation.

* ``pending(ready)``

  In this state, the user can send / show the ``taler://`` URI or QR code to somebody else.

  * ``[action:abort] => aborting(delete-purse)``: The user aborts the P2P payment. The wallet tries to reclaim money in the purse.
  * ``[purse-timeout] => aborting(refresh)``: The other party was too slow and the purse has now expired.
  * ``[poll-success] => done``: The other party has accepted the payment.
  * ``[poll-error] => aborting(refresh)``: The exchange claims that there is a permanent error regarding the purse.  (FIXME(CG): not clear that this is the best transition! Could also go to ``aborting(refund)`` or ``aborting(delete-purse)``; best choice may depend on the specific error returned.)

* ``aborting(delete-purse)``

  The wallet is deleting the purse to prevent the receiver from merging it and to reclaim the funds in it.

  * ``[processed-success] => aborting(refresh)``: The purse was deleted successfully, and refunded coins must be refreshed.
  * ``[processed-failed(already-merged)] => done``: The other party claimed the funds faster that we were able to abort.
  * ``[processed-failed(other)] => aborting(refresh)``:  The exchange reports a permanent error.  We still try to refresh.
  * ``[action:fail] => failed``: The user explicitly asked us to give up and accepted the possible loss of funds.

* ``aborting(refund)``

  We abandon the purse that was never fully funded and ask for the deposited coins to be refunded.

  * ``[processed-success] => aborting(refresh)``: After the refund, we still need to refresh the coins.
  * ``[processed-failure] => aborting(refresh)``: The refund failed, we still try to refresh the coins.
  * ``[action:fail] => failed``: The user explicitly asked us to give up and accepted the possible loss of funds.

* ``aborting(refresh)``

  * ``[processed-success] => aborted``: Refresh group finished. Aborting was successful, money was reclaimed.
  * ``[processed-failed] => failed``: Refresh group failed to complete with a permanent error.
  * ``[action:fail] => failed``: The user explicitly asked us to give up and accepted the possible loss of funds.

* ``done``

  The transfer was successful.

  * ``[action:delete] => deleted``

* ``aborted``

  The transfer was aborted. Except for fees, the money was recovered.

  * ``[action:delete] => deleted``

* ``failed``

  The transfer failed. Money was lost. Unless on a forced abort, we should probably complain to the auditor.

  * ``[action:delete] => deleted``

* ``deleted``

  All memory of the push debit operation is lost.

.. image:: ../images/transaction-push-debit-states.png


Transaction Type: Peer Push Credit
----------------------------------

Peer Push Credit transactions are created when the user accepts to be paid via
a ``taler://pay-push`` URI.

States and transitions:

* ``pending(download)``

  Wallet read the taler:// URI and is downloading the contract details for the user.

  * ``[processed-success] => pending(user)``: Contract can be shown to the user.
  * ``[action:suspend] => suspended(download)``: User suspended the operation.

* ``suspended(download)``

  The download of the purse meta data was suspended by the user.

  * ``[action:resume] => pending(download)``

* ``pending(user)``

  User needs to decide about accepting the money.

  * ``[action:accept] => pending(merge)``
  * ``[timeout] => failed``: User took too long to decide.

* ``pending(merge)``

  * ``[processed-success] => pending(withdraw)``: Merging the reserve was successful.
  * ``[kyc-required] => pending(merge-kyc)``: User must pass KYC checks before the purse can be merged.
  * ``[timeout] => failed``: The purse expired before we could complete the merge.
  * ``[failure] => failed``: The merge failed permanently.
  * FIXME(CG): do we want to allow suspending here?

* ``pending(merge-kyc)``

  We cannot merge the purse until passing a KYC check.
  The user is shown a hint where to begin the KYC
  process and the wallet long-polls on the KYC status.

  * ``[poll-success] => pending(withdraw)``
  * ``[action:suspend] => suspended(kyc)``
  * ``[timeout] => failed``: The purse expired before we could complete the merge.

* ``suspended(merge-kyc)``

  We cannot merge the purse until passing a KYC check,
  and that check was suspended by the user.

  * ``[action:resume] => pending(kyc)``
  * ``[timeout] => failed``: The purse expired before we could complete the merge.

* ``pending(withdraw)``

  The wallet is withdrawing coins from the reserve that was filled by merging
  the purse.

  * ``[kyc-required] => pending(withdraw-kyc)``
  * ``[aml-required] => pending(withdraw-aml)``
  * ``[withdraw-failure] => failed``
  * ``[withdraw-success] => done``
  * ``[action:suspend] => suspended(withdraw)``

* ``suspended(withdraw)``

  The user requested the withdraw operation to be suspended.

  * ``[action:resume] => pending(withdraw)``

* ``pending(withdraw-kyc)``

  We cannot withdraw more coins until passing a KYC check.
  The user is shown a hint where to begin the KYC
  process and the wallet long-polls on the KYC status.

  * ``[poll-success] => pending(withdraw-coins)``
  * ``[action:suspend] => suspended(withdraw-kyc)``

* ``suspended(withdraw-kyc)``

  We cannot withdraw from the reserve until passing a KYC check,
  and that check was suspended by the user.

  * ``[action:resume] => pending(withdraw-kyc)``

* ``pending(withdraw-aml)``

  We cannot withdraw more coins until AML rules are satisfied.
  The user is shown a hint as to the AML status (pending or frozen).

  * ``[poll-success] => pending(withdraw-coins)``
  * ``[action:suspend] => suspended(withdraw-aml)``

* ``suspended(withdraw-aml)``

  We cannot withdraw from the reserve until AML rules are satisfied,
  and the status check was suspended by the user.

  * ``[action:resume] => pending(withdraw-aml)``
  * ``[action:delete] => deleted``

* ``failed``

  The operation failed. Details are shown to the user. The money from the purse eventually goes to the sender (or some other wallet that merged it).

  * ``[action:delete] => deleted``

* ``done``

  The operation succeeded.

  * ``[action:delete] => deleted``: No money will be lost, the withdrawn coins will be kept

* ``deleted``

  All memory of the push credit operation is lost.

.. image:: ../images/transaction-push-credit-states.png


Transaction Type: Peer Pull Credit
----------------------------------

TODO: Also specify variant where account reserve needs to be created / funded first (Note: post 1.0-feature).

* ``pending(purse-create)``

  The wallet is creating a purse. Initial state.

  * ``[process-success] => pending(ready)``: The wallet has created the purse.
  * ``[process-failure] => deleted``: The purse creation failed. We only show a transient error.
  * ``[action:abort] => deleted``: The user aborted the operation.

* ``pending(ready)``

  In this state, the user can send / show the ``taler://`` URI or QR code to
  somebody else.

  * ``[action:abort] => aborting(delete-purse)``: The user aborts the P2P payment.
  * ``[purse-timeout] => aborted``: The other party was too slow and the purse
    has now expired.
  * ``[poll-success] => pending(withdraw)``: The other party has made the payment.
  * ``[poll-error] => aborting(delete-purse)``: The exchange claims that there
    is a permanent error regarding the purse.  We should try to delete it.

* ``aborting(delete-purse)``

  We are cleaning up the purse after the operation failed or was aborted by
  the user.

  * ``[failure:already-merged] => pending(withdraw)``: Too late to abort, the
    other side already paid the invoice.
  * ``[process-success] => aborted``: The wallet has deleted the purse.
  * ``[failure:other] => failed``: The purse deletion failed; we are
    nevertheless done.
  * ``[action:fail] => failed``: Money may be lost if it was deposited
    into the purse in the meantime.

* ``aborted``

  The invoicing process ended without success.

  * ``[action:delete] => deleted``

* ``pending(withdraw)``

  The wallet is withdrawing the money paid for the invoice.

  * ``[processed-success] => done``
  * ``[failure] => failed``
  * ``[processed-kyc] => pending(kyc)``
  * ``[processed-aml] => pending(aml)``
  * ``[action:suspend] => suspended(withdraw)``

* ``suspended(withdraw)``

  The user suspended a withdraw operation.

  * ``[action:resume] => pending(withdraw)``

* ``pending(kyc)``

  The user must supply KYC information before withdrawing can continue.

  * ``[poll-success] => pending(withdraw)``
  * ``[action:suspend] => suspended(kyc)``

* ``suspended(kyc)``

  The user suspended waiting for the KYC operation to complete.

  * ``[action:resume] => pending(kyc)``

* ``pending(aml)``

  The user must await a positive exchange AML decision.

  * ``[poll-success] => pending(withdraw)``
  * ``[action:suspend] => suspended(aml)``

* ``suspended(aml)``

  The user suspended waiting for the AML decision to be successful.

  * ``[action:resume] => pending(aml)``

* ``failed``

  Obtaining the money for the invoce failed. This is likely a case for the
  auditor.

  * ``[action:delete] => deleted``

* ``done``

  The payment for the invoice was successfully received.

  * ``[action:delete] => deleted``

* ``deleted``

.. image:: ../images/transaction-pull-credit-states.png


Transaction Type: Peer Pull Debit
---------------------------------

* ``pending(download)``

  We are downloading the information about the invoice.  Initial state.

  * ``[action:suspend] => suspended(download)``
  * ``[success] => pending(user)``

* ``suspended(download)``

  User suspended downloading the information about the invoice.

  * ``[action:resume] => pending(download)``
  * ``[action:delete] => deleted``

* ``pending(user)``

  We have downloaded information about the pull payment and are waiting for
  the user to confirm.

  * ``[action:confirm-pay] => pending(submit-payment)``
  * ``[action:delete] => deleted``
  * ``[timeout] => aborted``

* ``pending(deposit)``

  The user has confirmed the payment and the wallet tries to deposit
  into the provided purse.

  * ``[action:suspend] => suspended(deposit)``
  * ``[processed-success] => done``
  * ``[failure:timeout] => aborting(refresh)``
  * ``[processed-success] => done``
  * ``[failure:other] => aborting(refund)``

* ``suspended(deposit)``

  User suspended depositing into the purse.

  * ``[action:resume] => pending(deposit)``
  * ``[action:abort] => aborting_refund``

* ``aborting(refund)``

  Aborts the payment, asking for the already deposited coins to be refunded.

  * ``[processed-success] => aborted(refunded)``
  * ``[processed-failure] => aborting(refresh)``
  * ``[action:fail] => failed``

* ``aborting(refresh)``

  Refreshes the coins that were previously deposited into the purse to recover their value.

  * ``[processed-success] => aborted``
  * ``[processed-failed] => failed``

* ``done``

  The invoice was successfully paid.

  * ``[action:delete] => deleted``

* ``deleted``

  All information about the invoice has been deleted.

.. image:: ../images/transaction-pull-debit-states.png

Alternatives
============

* Each transaction could be treated completely separately; however, uniform
  terminology for actions (and thus button labels) is likely more helpful for
  the user experience.

* We could require user re-approval if fees changed when the available
  denominations change during a *withdraw*.  This would require a different
  state machine on withdraw. We believe the answer can be "no", for two
  reasons: the wallet MUST pick denominations to withdraw with the "most
  long-term" withdraw window (i.e. active denominations that have the longest
  available withdraw durations). So in virtually all normal cases, this will
  just succeed as a sane exchange will have a reasonable duration overlap, and
  in the very few cases it's really the user's fault for going offline in the
  middle of the operation. Plus, even in those few cases, it is highly
  unlikely that the fee would actually change: again most key rotations can be
  expected to be there to rotate the key, and not to adjust the withdraw fee.
  And in the extremely rare case that the user went offline and in the
  meantime the fees did *increase*, it's again unlikely to matter much to the
  user. So special-casing this and testing this is probably not worth it.

* We could require user re-approval if due to expired/invalid coins the coin
  selection (and thus fees) changes during a *deposit*.  Again, expired coins
  should virtually never happen unless a user goes offline for a long time in
  the middle of a purchase (which would be very strange). If deposit fees
  *increase* due to a double-spend detection during payment, we might want to
  have an *optional* dialog ("Balance reduced by X as wallet state was not
  up-to-date (did you restore from backup?).  Consequently, the fees for this
  transactions increased from Y to Z.  [Abort] [Continue] + checkbox: [X] Do
  not ask again."). Probably at best a post-1.0 feature.


Discussion / Q&A
================

* The diagrams only show what is happening **after** the wallet
  has created the transaction.  It is possible that network requests
  are happening before that, but they are not considered to be part
  of the transaction.
* We have decided against a ``cancel`` state, because it resulted
  in too much complexity.  Instead of doing a direct ``cancel``,
  the user has to go to the transaction and abort and/or delete
  it.
* We might add a ``revive`` action in the future that allows
  to go from ``aborting`` back to ``pending`` for transactions
  where this makes sense.  We're not doing it right now
  to simplify things.