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module S = Saturation_repr

module S_syntax = struct
  let log2 x = S.safe_int (1 + S.numbits x)

  let ( + ) = S.add

  let ( * ) = S.mul

  let ( lsr ) = S.shift_right
end

module Constants = struct
  (* TODO: https://gitlab.com/tezos/tezos/-/issues/2648
     Fill in real benchmarked values.
     Need to create benchmark and fill in values.
  *)
  let cost_add_message_base = S.safe_int 430

  let cost_add_message_per_byte = S.safe_int 15

  let cost_add_inbox_per_level = S.safe_int 15

  let cost_update_num_and_size_of_messages = S.safe_int 15

  (* equal to Michelson_v1_gas.Cost_of.Unparsing.contract_optimized *)
  let cost_decoding_contract_optimized = S.safe_int 70

  (* equal to Michelson_v1_gas.Cost_of.Unparsing.key_hash_optimized *)
  let cost_decoding_key_hash_optimized = S.safe_int 50

  (* Set to the cost of encoding a pkh defined in {!Michelson_v1_gas} divided
     by the number of characters of a pkh, i.e. 70/35. To be updated when
     benchmarking is completed. *)
  let cost_encode_string_per_byte = S.safe_int 2

  (* Cost of serializing a state hash. *)
  let cost_serialize_state_hash =
    let len = S.safe_int State_hash.size in
    S_syntax.(cost_encode_string_per_byte * len)

  (* Cost of serializing a commitment hash. *)
  let cost_serialize_commitment_hash =
    let len = S.safe_int Sc_rollup_commitment_repr.Hash.size in
    S_syntax.(cost_encode_string_per_byte * len)

  (* Cost of serializing a commitment. The cost of serializing the level and
     number of ticks (both int32) is negligible. *)
  let cost_serialize_commitment =
    S_syntax.(cost_serialize_state_hash + cost_serialize_commitment_hash)

  (* Cost of serializing an operation hash. *)
  let cost_serialize_operation_hash =
    let len = S.safe_int Operation_hash.size in
    S_syntax.(cost_encode_string_per_byte * len)

  (* Cost of serializing a nonce. The cost of serializing the index (an int32)
     is negligible. *)
  let cost_serialize_nonce = cost_serialize_operation_hash
end

(* We assume that the gas cost of adding messages [[ m_1; ... ; m_n]] at level
   [l] is linear in the sum of lengths of the messages, and it is logarithmic
   in [l]. That is, [cost_add_serialized_messages([m_1; .. ; m_n], l)] =
   `n * cost_add_message_base +
    cost_add_message_per_bytes * \sum_{i=1}^n length(m_i) +
    cost_add_inbox_per_level * l`.
*)
let cost_add_serialized_messages ~num_messages ~total_messages_size l =
  let open S_syntax in
  let log_level =
    if Int32.equal l Int32.zero then Saturation_repr.safe_int 0
    else log2 @@ S.safe_int (Int32.to_int l)
  in
  let level_cost = log_level * Constants.cost_add_inbox_per_level in
  (S.safe_int num_messages * Constants.cost_add_message_base)
  + level_cost
  + (Constants.cost_add_message_per_byte * S.safe_int total_messages_size)

(* Reusing model from {!Ticket_costs.has_tickets_of_ty_cost}. *)
let is_valid_parameters_ty_cost ~ty_size =
  let fixed_cost = S.safe_int 10 in
  let coeff = S.safe_int 6 in
  S.add fixed_cost (S.mul coeff ty_size)

let cost_serialize_internal_inbox_message
    Sc_rollup_inbox_message_repr.{payload; sender = _; source = _} =
  let lexpr = Script_repr.lazy_expr payload in
  let expr_cost = Script_repr.force_bytes_cost lexpr in
  S_syntax.(
    expr_cost + Constants.cost_decoding_contract_optimized
    + Constants.cost_decoding_key_hash_optimized)

(** TODO: #3212
    Confirm gas cost model.
    We here assume that the cost of deserializing an expression of [bytes_len]
    is proportional to deserializing a script expression of size [bytes_len].
    This may not be the case and in particular, the cost depends on the specific
    structure used for the PVM. We may thus need to split the cost function.
  *)
let cost_deserialize_output_proof ~bytes_len =
  Script_repr.deserialization_cost_estimated_from_bytes bytes_len

let cost_serialize_external_inbox_message ~bytes_len =
  let len = S.safe_int bytes_len in
  S_syntax.(Constants.cost_encode_string_per_byte * len)

(* Equal to Michelson_v1_gas.Cost_of.Interpreter.blake2b. *)
let cost_hash_bytes ~bytes_len =
  let open S_syntax in
  let v0 = S.safe_int bytes_len in
  S.safe_int 430 + v0 + (v0 lsr 3)