# nimbus-eth1
# Copyright (c) 2023-2024 Status Research & Development GmbH
# Licensed under either of
#  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
#    http://www.apache.org/licenses/LICENSE-2.0)
#  * MIT license ([LICENSE-MIT](LICENSE-MIT) or
#    http://opensource.org/licenses/MIT)
# at your option. This file may not be copied, modified, or distributed
# except according to those terms.

## Aristo DB -- Patricia Trie backend data access
## ==============================================
##

{.push raises: [].}

import
  results,
  "."/[desc_error, desc_identifiers, desc_structural]

type
  GetVtxFn* =
    proc(vid: VertexID): Result[VertexRef,AristoError] {.gcsafe, raises: [].}
      ## Generic backend database retrieval function for a single structural
      ## `Aristo DB` data record.

  GetKeyFn* =
    proc(vid: VertexID): Result[HashKey,AristoError] {.gcsafe, raises: [].}
      ## Generic backend database retrieval function for a single
      ## `Aristo DB` hash lookup value.

  GetTuvFn* =
    proc(): Result[VertexID,AristoError] {.gcsafe, raises: [].}
      ## Generic backend database retrieval function for the top used
      ## vertex ID.

  GetLstFn* =
    proc(): Result[SavedState,AristoError]
      {.gcsafe, raises: [].}
        ## Generic last recorded state stamp retrieval function

  # -------------

  PutHdlRef* = ref object of RootRef
    ## Persistent database transaction frame handle. This handle is used to
    ## wrap any of `PutVtxFn`, `PutKeyFn`, and `PutIdgFn` into and atomic
    ## transaction frame. These transaction frames must not be interleaved
    ## by any library function using the backend.

  PutBegFn* =
    proc(): Result[PutHdlRef,AristoError] {.gcsafe, raises: [].}
      ## Generic transaction initialisation function

  PutVtxFn* =
    proc(hdl: PutHdlRef; vid: VertexID; vtx: VertexRef)
      {.gcsafe, raises: [].}
        ## Generic backend database bulk storage function, `VertexRef(nil)`
        ## values indicate that records should be deleted.

  PutKeyFn* =
    proc(hdl: PutHdlRef; vid: VertexID, key: HashKey)
      {.gcsafe, raises: [].}
        ## Generic backend database bulk storage function, `VOID_HASH_KEY`
        ## values indicate that records should be deleted.

  PutTuvFn* =
    proc(hdl: PutHdlRef; vs: VertexID)
      {.gcsafe, raises: [].}
        ## Generic backend database ID generator storage function for the
        ## top used vertex ID.

  PutLstFn* =
    proc(hdl: PutHdlRef; lst: SavedState)
      {.gcsafe, raises: [].}
        ## Generic last recorded state stamp storage function. This
        ## function replaces the currentlt saved state.

  PutEndFn* =
    proc(hdl: PutHdlRef): Result[void,AristoError] {.gcsafe, raises: [].}
      ## Generic transaction termination function

  # -------------

  CloseFn* =
    proc(eradicate: bool) {.gcsafe, raises: [].}
      ## Generic destructor for the `Aristo DB` backend. The argument
      ## `eradicate` indicates that a full database deletion is requested. If
      ## passed `false` the outcome might differ depending on the type of
      ## backend (e.g. in-memory backends will always eradicate on close.)

  # -------------

  BackendRef* = ref BackendObj
  BackendObj* = object of RootObj
    ## Backend interface.
    getVtxFn*: GetVtxFn              ## Read vertex record
    getKeyFn*: GetKeyFn              ## Read Merkle hash/key
    getTuvFn*: GetTuvFn              ## Read top used vertex ID
    getLstFn*: GetLstFn              ## Read saved state

    putBegFn*: PutBegFn              ## Start bulk store session
    putVtxFn*: PutVtxFn              ## Bulk store vertex records
    putKeyFn*: PutKeyFn              ## Bulk store vertex hashes
    putTuvFn*: PutTuvFn              ## Store top used vertex ID
    putLstFn*: PutLstFn              ## Store saved state
    putEndFn*: PutEndFn              ## Commit bulk store session

    closeFn*: CloseFn                ## Generic destructor

proc init*(trg: var BackendObj; src: BackendObj) =
  trg.getVtxFn = src.getVtxFn
  trg.getKeyFn = src.getKeyFn
  trg.getTuvFn = src.getTuvFn
  trg.getLstFn = src.getLstFn

  trg.putBegFn = src.putBegFn
  trg.putVtxFn = src.putVtxFn
  trg.putKeyFn = src.putKeyFn
  trg.putTuvFn = src.putTuvFn
  trg.putLstFn = src.putLstFn
  trg.putEndFn = src.putEndFn

  trg.closeFn = src.closeFn

# ------------------------------------------------------------------------------
# End
# ------------------------------------------------------------------------------