(* https://docs.taler.net/manpages/taler-exchange.conf.5.html
   taler-docs/manpages/taler-exchange.conf.5.rst *)
(* TODO
   - generate `config.ml` from config file (virtual module)?
   - parse config file format
   - no relative path
   - default config: use relevant duration, all set to 1 year for now
   *)

(* TODO unikernel *)
type dir_path
type file_path

(* TODO *)
(* Values that represent a time duration are represented as a series of one or more NUMBER UNIT pairs, e.g. 60 s, 4 weeks 1 day, 5 years 2 minutes. *)
type duration

(* TODO
   make it Amount.t *)
type amount = string
type payto_uri = string

(* TODO
   still need to parse them and tell that its not supported
   some maybe are relevant
   idk *)
type not_relevant
type not_implemented
type url = string
type seconds = int

module Global = struct end

(*
Sections with a name of the form “[currency-$NAME]” (where "$NAME" could
be any unique string) are used to specify details about how currencies
should be handled (and in particularly rendered) by the user interface.
A detailed motivation for this section can be found in DD51.
Different components can have different rules for the same currency. For
example, a bank or merchant may decide to render Euros or Dollars with
always exactly two fractional decimals, while an Exchange for the same
currency may support additional decimals.  The required options in each
currency specification section are: *)
module type Currency = sig
  (*
  Set to YES or NO. If set to NO, the currency specification
  section is ignored. Can be used to disable currencies or
  select alternative sections for the same CODE with different
  choices. *)
  val enabled : [ `YES | `NO ]

  (*
  Code name for the currency. Can be at most 11 characters,
  only the letters A-Z are allowed. Primary way to identify
  the currency in the protocol. *)
  val code : string

  (*
  Long human-readable name for the currency. No restrictions,
  but should match the official name in English. *)
  val name : string

  (*
  Number of fractional digits that users are allowed to enter
  manually in the user interface. *)
  val fractional_input_digits : int

  (*
  Number of fractional digits that will be rendered normally
  (in terms of size and placement).  Digits shown beyond this
  number will typically be rendered smaller and raised (if
  possible). *)
  val fractional_normal_digits : int

  (*
  Number of fractional digits to pad rendered amounts with
  even if these digits are all zero. For example, use 2 to
  render 1 USD as $1.00. *)
  val fractional_trailing_zero_digits : int

  (*
  JSON map determining how to encode very large or very tiny
  amounts in this currency. Maps a base10 logarithm to the
  respective currency symbol. Must include at least an
  entry for 0 (currency unit).  For example, use
  {"0":"€"} for Euros or {"0":"$"} for Dollars. You could
  additionally use {"0":"€","3":"k€"} to render 3000 EUR
  as 3k€. For BTC a typical map would be
  {"0":"BTC","-3":"mBTC"}, informing the UI to render small
  amounts in milli-Bitcoin (mBTC). *)
  val alt_unit_names : (int * string) list
end

(* The following options are from the “[exchange]” section and used by most
   exchange tools. *)
module type Exchange = sig
  (*
  Name of the currency, e.g. “EUR” for Euro. *)
  val currency : string

  (*
  Smallest amount in this currency that can be transferred using the
  underlying RTGS. For example: "EUR:0.01" or "JPY:1". *)
  val currency_round_unit : amount

  (*
  Plugin to use for the database, e.g. “postgres”. *)
  val db : string

  (*
  Attribute encryption key for storing attributes encrypted
  in the database. Should be a high-entropy nonce. *)
  val attribute_encryption_key : string

  (*
  Should the HTTP server listen on a UNIX domain socket (set option to "unix"), or on a TCP socket (set option to "tcp"), or be activated via systemd (set option to "systemd"). *)
  val serve : not_relevant

  (*
  Path to listen on if we "SERVE" is set to "unix". *)
  val unixpath : not_relevant

  (*
  Access permission mask to use for the "UNIXPATH". *)
  val unixpath_mode : not_relevant

  (*
  Port on which the HTTP server listens, e.g. 8080. *)
  val port : int

  (*
  Hostname to which the exchange HTTP server should be bound to, e.g. "localhost". *)
  val bind_to : string

  (*
  Crockford Base32-encoded master public key, public version of the
  exchange's long-time offline signing key.  This configuration option
  is also used by the **auditor** to determine the public key of the
  exchange which it is auditing. *)
  val master_public_key : string

  (*
  Small amount that can be transferred to the exchange for the
  KYC authentication wire transfers. Should be given as a hint
  for merchants what amount they need to transfer to begin the
  KYC transfer. Note that the amount is not enforced by the
  exchange *and* that this option is optional. However, if it is
  not given, merchants will have to guess what amount to transfer,
  so it really should be configured. *)
  val tiny_amount : amount option

  (*
  Web URL where users can discover shops that accept digital cash
  offered by this exchange. Optional, but highly recommended. *)
  val shopping_url : url option

  (*
  URL where wallets can find an open banking gateway to
  initiate wire transfers when withdrawing digital cash
  from this exchange. Optional (as obviously not every
  exchange will have an open banking gateway attached). *)
  val open_banking_gateway_url : url option

  (*
  Determines the variant of the AML SPA that should be shown. This
  will determine the set of forms shown to AML staff, statistics to
  be displayed on the main page, and influence the default set of
  properties/events the AML forms show when AML staff makes decisions.
  Possible values for now include "gls", "tops" and "magnet".
  Optional. The AML SPA will only show certain default forms and
  generic decisions if this option is not set. *)
  val aml_spa_dialect : string option

  (*
  Determines the legal language (and possibly other UI/UX aspects)
  wallets should use when providing the user interface for this bank.
  Allows banks to communicate the desired compliance language they
  want to see used to the wallet. Wallets SHOULD follow the guidance
  provided by the bank, but some wallets MAY not understand all compliance
  languages. Optional, if not set wallets will use their default UI/UX. *)
  val bank_compliance_language : string option

  (*
  Absolute amount to add as an offset in the STEFAN fee approximation
  curve (see DD47).  Defaults to CURRENCY:0 if not specified. *)
  val stefan_abs : amount

  (*
  Amount to multiply by the base-2 logarithm of the total amount
  divided by the amount of the smallest denomination
  in the STEFAN fee approximation curve (see DD47).
  Defaults to CURRENCY:0 if not specified. *)
  val stefan_log : amount

  (*
  Linear floating point factor to be multiplied by the total amount
  to use in the STEFAN fee approximation curve (see DD47).
  Defaults to 0.0 if not specified. *)
  val stefan_lin : float

  (*
  The base URL under which the exchange can be reached.
  Added to wire transfers to enable tracking by merchants.
  Used by the KYC logic when interacting with OAuth 2.0. *)
  val base_url : url

  (*
  Where to redirect visitors that access the top-level
  "/" endpoint of the exchange. Should point users to
  information about the exchange operator.
  Optional setting, defaults to "/terms". *)
  val toplevel_redirect_url : string option

  (*
  For how long should the taler-exchange-aggregator sleep when it is idle
  before trying to look for more work? Default is 60 seconds. *)
  val aggregator_idle_sleep_interval : seconds

  (*
  For how long should the taler-exchange-closer sleep when it is idle
  before trying to look for more work? Default is 60 seconds. *)
  val closer_idle_sleep_interval : seconds

  (*
  For how long should the taler-exchange-transfer sleep when it is idle
  before trying to look for more work? Default is 60 seconds. *)
  val transfer_idle_sleep_interval : seconds

  (*
  For how long should the taler-exchange-wirewatch sleep when it is idle
  before trying to look for more work? Default is 60 seconds. *)
  val wirewatch_idle_sleep_interval : seconds

  (*
  Which share of the range from [0,..2147483648] should be processed by one of the shards of the aggregator. Useful only for Taler exchanges with ultra high-performance needs. When changing this value, you must stop all aggregators and run "taler-exchange-dbinit -s" before resuming. Default is 2147483648 (no sharding). *)
  val aggregator_shard_size : int option

  (*
  For how long are signatures with signing keys legally valid? *)
  val signkey_legal_duration : duration

  (*
  For how long should clients cache ``/keys`` responses at most? *)
  val max_keys_caching : duration

  (*
  How many requests should the HTTP server process at most before committing suicide? *)
  val max_requests : int

  (*
  Directory where the terms of service of the exchange operator can be fund.
  The directory must contain sub-directories for every supported language,
  using the two-character language code in lower case, e.g. "en/" or "fr/".
  Each subdirectory must then contain files with the terms of service in
  various formats.  The basename of the file of the current policy must be
  specified under ``TERMS_ETAG``.  The extension defines the mime type.
  Supported extensions include "html", "htm", "txt", "pdf", "jpg", "jpeg",
  "png" and "gif".  For example, using a ``TERMS_ETAG`` of "0", the structure
  could be the following:

  - $TERMS_DIR/en/0.pdf
  - $TERMS_DIR/en/0.html
  - $TERMS_DIR/en/0.txt
  - $TERMS_DIR/fr/0.pdf
  - $TERMS_DIR/fr/0.html
  - $TERMS_DIR/de/0.txt *)
  val terms_dir : dir_path

  (*
  Basename of the file(s) in the ``TERMS_DIR`` with the current terms of service.
  The value is also used for the "Etag" in the HTTP request to control
  caching.  Whenever the terms of service change, the ``TERMS_ETAG`` MUST also
  change, and old values MUST NOT be repeated.  For example, the date or
  version number of the terms of service SHOULD be used for the Etag.  If
  there are minor (e.g. spelling) fixes to the terms of service, the
  ``TERMS_ETAG`` probably SHOULD NOT be changed. However, whenever users must
  approve the new terms, the ``TERMS_ETAG`` MUST change. *)
  val terms_etag : string

  (*
  Works the same as ``TERMS_DIR``, just for the privacy policy. *)
  val privacy_dir : dir_path

  (*
  Works the same as ``TERMS_ETAG``, just for the privacy policy. *)
  val privacy_etag : string

  (*
  Must be set to ``YES`` to enable AML/KYC rule enforcement. Note that the administrative endpoints will always work, even if the flag is set to ``NO``. *)
  val enable_kyc : [ `YES | `NO ]
end

(* todo: KYC and AML options *)

(*
The functionality of the exchange can be extended by extensions.  Those are
shared libraries which implement the extension-API of the exchange and are
located under ``$LIBDIR``, starting with prefix ``libtaler_extension_``. Each
extension can be enabled by adding a dedicated section
"[exchange-extension-<extensionname>]" and the following option:
  *)
module type Extansions = sig
  (*
  If set to ``YES`` the extension ``<extensionsname>`` is enabled.  Extension-specific
  options might be set in the same section. *)
  val enabled : [ (*`YES|*) `NO ]
end

(* The following options must be in the section "[exchange-offline]". *)
module type Offline_signing = sig
  (*
  Location of the master private key on disk. Only used by tools that
  can be run offline (as the master key is for offline signing).
  Mandatory. *)
  val master_priv_file : file_path

  (* TODO
   - we need two different file
   - there is three, not two, crypto helper modules
     is it only two, because the eddsa one is not comptabilized as a "crypto helper" here? *)
  (*
  Where to store the public keys of both crypto helper modules.
  Used to persist the keys after the first invocation of the tool,
  so that if they ever change in the future, this is detected and
  the tool can abort.
  Mandatory. *)
  val secm_tofu_file : file_path

  (*
  Public key of the (RSA) crypto helper module. Optional. If not given,
  we will rely on TOFU.  Note that once TOFU has been established,
  this option will also be ignored. *)
  val secm_denom_pubkey : string option

  (*
  Public key of the (EdDSA) crypto helper module. Optional. If not given,
  we will rely on TOFU.  Note that once TOFU has been established,
  this option will also be ignored. *)
  val secm_esign_pubkey : string option
end

(* The following options must be in the section "[taler-exchange-secmod-{rsa|cs|eddsa}]". *)
module type Secmod = sig
  (*
  How long do we generate denomination and signing keys ahead of time?
  *)
  val lookahead_sign : duration

  (*
  How much should validity periods for coins overlap?
  Should be long enough to avoid problems with
  wallets picking one key and then due to network latency
  another key being valid.  The ``DURATION_WITHDRAW`` period
  must be longer than this value.
  *)
  val overlap_duration : duration

  (*
  Where should the security module store its long-term private key?
  *)
  val sm_priv_key : file_path

  (*
  Where should the security module store the private keys it manages?
  *)
  val key_dir : dir_path

  (*
  On which path should the security module listen for signing requests?
  *)
  val unixpath : not_relevant
end

module type Secmod_rsa = Secmod
module type Secmod_cs = Secmod
module type Secmod_eddsa = Secmod

(* The following options must be in the section "[exchangedb]". *)
module type Database = sig
  (* TODO not sure about what unit of time/duration is used here *)

  (*
  After which time period should reserves be closed if they are idle? *)
  val idle_reserve_expiration_time : seconds

  (*
  After what time do we forget about (drained) reserves during garbage collection? *)
  val legal_reserve_expiration_time : seconds

  (*
  Delay between a deposit being eligible for aggregation and
  the aggregator actually triggering. *)
  val aggregator_shift : seconds

  (*
  Number of concurrent purses that a reserve may have active
  if it is paid to be opened for a year. *)
  val default_purse_limit : int

  (*
  Maximum time an AML program is allowed to run.
  (Optional for taler-auditor.) *)
  val max_aml_program_runtime : int option

  (*
The following options must be in section “[exchangedb-postgres]” if the
“postgres” plugin was selected for the database. *)
  module type Postgres_backend = sig
    (*
  How to access the database, e.g. “postgres:///taler-exchange” to use the
  “taler-exchange” database. Testcases use “talercheck”. *)
    val config : string
  end
end

(*
An exchange (or merchant) can have multiple bank accounts. The following
options are for sections named “[exchange-account-SOMETHING]”. The ``SOMETHING`` is
arbitrary and should be chosen to uniquely identify the bank account for
the operator.  These options are used by the **taler-exchange-aggregator**, **taler-exchange-closer**, **taler-exchange-transfer** and **taler-exchange-wirewatch** tools. *)
module type Account = sig
  val payto_uri : payto_uri
  val enable_debit : [ `YES | `NO ]
  val enable_credit : [ `YES | `NO ]
end

(*
Additionally, for each enabled account there MUST be another matching section named “[exchange-accountcredentials-SOMETHING]”.  This section SHOULD be in a ``secret/`` configuration file that is only readable for the **taler-exchange-wirewatch** and **taler-exchange-transfer** processes. It contains the credentials to access the bank account: *)
module type Account_secret = sig
  val wire_gateway_url : url
  val wire_gateway_auth_method : string
  val username : string
  val password : string
  val token : string
end

(* -- ********************************** -- *)
let currency = `Eur
let currency_to_string = function `Eur -> "EUR"

(* Values that represent an amount are in the usual amount syntax: CURRENCY:VALUE.FRACTION,
   e.g. EUR:1.50. The FRACTION portion may extend up to 8 places. *)
type value = {
  currency: [ `Eur ];
  value: int;
  fraction: int;
}

let currency_round_unit = { currency= `Eur; value= 0; fraction= 1 }

let value_to_string v =
  Fmt.str "%s:%d.%d" (currency_to_string v.currency) v.value v.fraction

(* https://docs.taler.net/manpages/taler-exchange.conf.5.html#exchange-coin-options *)
module Coin = struct
  (* How much is the coin worth, the format is CURRENCY:VALUE.FRACTION. For
     example, a 10 cent piece is “EUR:0.10”. *)
  let value = { currency= `Eur; value= 0; fraction= 1 }

  (*How long can a coin of this type be withdrawn? This limits the losses
    incurred by the exchange when a denomination key is compromised.*)
  let duration_withdraw = Duration.of_year 1

  (*How long is a coin of the given type valid? Smaller values result in lower
    storage costs for the exchange.*)
  let duration_spend = Duration.of_year 1

  (*How long is the coin of the given type legal?*)
  let duration_legal = Duration.of_year 1

  (*What does it cost to withdraw this coin? Specified using the same format as
    value.*)
  let fee_withdraw = { currency= `Eur; value= 0; fraction= 0 }

  (*What does it cost to deposit this coin? Specified using the same format as
    value.*)
  let fee_deposit = { currency= `Eur; value= 0; fraction= 0 }

  (*What does it cost to refresh this coin? Specified using the same format as
    value.*)
  let fee_refresh = { currency= `Eur; value= 0; fraction= 0 }

  (*What does it cost to refund this coin? Specified using the same format as
    value.*)
  let fee_refund = { currency= `Eur; value= 0; fraction= 0 }

  (*Which cipher to use for this coin? Must be either RSA or CS.*)
  let cipher : [ `RSA | `CS ] = `RSA

  (*How many bits should the RSA modulus (product of the two primes) have for
    this type of coin.*)
  let rsa_keysize = -1

  (*Set to YES to make this a denomination with support*)
  let age_restricted : [ `YES | `NO ] = `NO
end

(* Crockford Base32-encoded master public key, public version of the exchange’s long-time offline signing key. *)
let master_public_key = "uhuh"

(* module type for CS/EDDSA/RSA config *)
module Secmod = struct
  (* Note that the taler-exchange-secmod-rsa also evaluates the [coin_*] configuration sections described below. *)

  (*How long do we generate denomination and signing keys ahead of time?*)
  let lookahead_sign = Duration.of_year 1

  (*How much should validity periods for coins overlap? Should be long enough to avoid problems with wallets picking one key and then due to network latency another key being valid. The DURATION_WITHDRAW period must be longer than this value.*)
  let overlap_duration = Duration.of_year 1

  (*
    Where should the security module store its long-term private key?
SM_PRIV_KEY

    Where should the security module store the private keys it manages?
KEY_DIR

    On which path should the security module listen for signing requests?
UNIXPATH
*)
end

module Database = struct
  (*After which time period should reserves be closed if they are idle?*)
  let idle_reserve_expiration_time = -1

  (*After what time do we forget about (drained) reserves during garbage collection?*)
  let legal_reserve_expiration_time = -1

  (*Delay between a deposit being eligible for aggregation and the aggregator actually triggering.*)
  let aggregator_shift = -1

  (*Number of concurrent purses that a reserve may have active if it is paid to be opened for a year.*)
  let default_purse_limit = -1

  (*Maximum time an AML program is allowed to run. (Optional for taler-auditor.)*)
  let max_aml_program_runtime = -1

  module Postgres = struct
    (*How to access the database, e.g. “postgres:///taler-exchange” to use the “taler-exchange” database. Testcases use “talercheck”.*)
    let config = "uhuh"
  end
end