#
#
#            Nim's Runtime Library
#        (c) Copyright 2020 Nim contributors
#
#    See the file "copying.txt", included in this
#    distribution, for details about the copyright.
#

import macros

macro genEnumCaseStmt*(typ: typedesc, argSym: typed, default: typed, 
            userMin, userMax: static[int], normalizer: static[proc(s :string): string]): untyped =
  # generates a case stmt, which assigns the correct enum field given
  # a normalized string comparison to the `argSym` input.
  # string normalization is done using passed normalizer. 
  # NOTE: for an enum with fields Foo, Bar, ... we cannot generate
  # `of "Foo".nimIdentNormalize: Foo`.
  # This will fail, if the enum is not defined at top level (e.g. in a block).
  # Thus we check for the field value of the (possible holed enum) and convert
  # the integer value to the generic argument `typ`.
  let typ = typ.getTypeInst[1]
  let impl = typ.getImpl[2]
  expectKind impl, nnkEnumTy
  let normalizerNode = quote: `normalizer`
  expectKind normalizerNode, nnkSym
  result = nnkCaseStmt.newTree(newCall(normalizerNode, argSym))
  # stores all processed field strings to give error msg for ambiguous enums
  var foundFields: seq[string] = @[]
  var fStr = "" # string of current field
  var fNum = BiggestInt(0) # int value of current field
  for f in impl:
    case f.kind
    of nnkEmpty: continue # skip first node of `enumTy`
    of nnkSym, nnkIdent: fStr = f.strVal
    of nnkEnumFieldDef:
      case f[1].kind
      of nnkStrLit: fStr = f[1].strVal
      of nnkTupleConstr:
        fStr = f[1][1].strVal
        fNum = f[1][0].intVal
      of nnkIntLit:
        fStr = f[0].strVal
        fNum = f[1].intVal
      else: error("Invalid tuple syntax!", f[1])
    else: error("Invalid node for enum type!", f)
    # add field if string not already added
    if fNum >= userMin and fNum <= userMax:
      fStr = normalizer(fStr)
      if fStr notin foundFields:
        result.add nnkOfBranch.newTree(newLit fStr,  nnkCall.newTree(typ, newLit fNum))
        foundFields.add fStr
      else:
        error("Ambiguous enums cannot be parsed, field " & $fStr &
          " appears multiple times!", f)
    inc fNum
  # finally add else branch to raise or use default
  if default == nil:
    let raiseStmt = quote do:
      raise newException(ValueError, "Invalid enum value: " & $`argSym`)
    result.add nnkElse.newTree(raiseStmt)
  else:
    expectKind(default, nnkSym)
    result.add nnkElse.newTree(default)