#
#
#           The Nim Compiler
#        (c) Copyright 2020 Andreas Rumpf
#
#    See the file "copying.txt", included in this
#    distribution, for details about the copyright.
#

## This module contains 'typeAllowed' and friends which check
## for invalid types like `openArray[var int]`.

import ast, renderer, options, semdata, types
import std/intsets

when defined(nimPreviewSlimSystem):
  import std/assertions

type
  TTypeAllowedFlag* = enum
    taTupField, # field of a tuple
    taObjField, # field of an object
    taHeap,
    taConcept,
    taIsOpenArray,
    taNoUntyped
    taIsTemplateOrMacro
    taProcContextIsNotMacro
    taIsCastable
    taIsDefaultField
    taVoid # only allow direct void fields of objects/tuples

  TTypeAllowedFlags* = set[TTypeAllowedFlag]

proc typeAllowedAux(marker: var IntSet, typ: PType, kind: TSymKind;
                    c: PContext; flags: TTypeAllowedFlags = {}): PType

proc typeAllowedNode(marker: var IntSet, n: PNode, kind: TSymKind,
                     c: PContext; flags: TTypeAllowedFlags = {}): PType =
  if n != nil:
    result = typeAllowedAux(marker, n.typ, kind, c, flags)
    if result == nil:
      case n.kind
      of nkNone..nkNilLit:
        discard
      else:
        #if n.kind == nkRecCase and kind in {skProc, skFunc, skConst}:
        #  return n[0].typ
        for i in 0..<n.len:
          let it = n[i]
          result = typeAllowedNode(marker, it, kind, c, flags)
          if result != nil: break
  else:
    result = nil

proc typeAllowedAux(marker: var IntSet, typ: PType, kind: TSymKind,
                    c: PContext; flags: TTypeAllowedFlags = {}): PType =
  assert(kind in {skVar, skLet, skConst, skProc, skFunc, skParam, skResult})
  # if we have already checked the type, return true, because we stop the
  # evaluation if something is wrong:
  result = nil
  if typ == nil: return nil
  if containsOrIncl(marker, typ.id): return nil
  var t = skipTypes(typ, abstractInst-{tyTypeDesc, tySink})

  let flags = if t.kind == tyVoid: flags else: flags-{taVoid}
  case t.kind
  of tyVar, tyLent:
    if kind in {skProc, skFunc, skConst} and (views notin c.features):
      result = t
    elif taIsOpenArray in flags:
      result = t
    elif t.kind == tyLent and (((kind != skResult or taObjField in flags) and views notin c.features) or
      (kind == skParam and {taIsCastable, taObjField, taTupField} * flags == {})): # lent cannot be used as parameters.
                                                       # except in the cast environment and as the field of an object
      result = t
    elif isOutParam(t) and kind != skParam:
      result = t
    else:
      var t2 = skipTypes(t.elementType, abstractInst-{tyTypeDesc, tySink})
      case t2.kind
      of tyVar, tyLent:
        if taHeap notin flags: result = t2 # ``var var`` is illegal on the heap
      of tyOpenArray:
        if (kind != skParam and views notin c.features) or taIsOpenArray in flags: result = t
        else: result = typeAllowedAux(marker, t2[0], kind, c, flags+{taIsOpenArray})
      of tyUncheckedArray:
        if kind != skParam and views notin c.features: result = t
        else: result = typeAllowedAux(marker, t2[0], kind, c, flags)
      of tySink:
        result = t
      else:
        if kind notin {skParam, skResult} and views notin c.features: result = t
        else: result = typeAllowedAux(marker, t2, kind, c, flags)
  of tyProc:
    if kind in {skVar, skLet, skConst} and taIsTemplateOrMacro in flags:
      result = t
    else:
      if isInlineIterator(typ) and kind in {skVar, skLet, skConst, skParam, skResult}:
        # only closure iterators may be assigned to anything.
        result = t
      let f = if kind in {skProc, skFunc}: flags+{taNoUntyped} else: flags
      for _, a in t.paramTypes:
        if result != nil: break
        result = typeAllowedAux(marker, a, skParam, c, f-{taIsOpenArray})
      if result.isNil and t.returnType != nil:
        result = typeAllowedAux(marker, t.returnType, skResult, c, flags)
  of tyTypeDesc:
    if kind in {skVar, skLet, skConst} and taProcContextIsNotMacro in flags:
      result = t
    else:
      # XXX: This is still a horrible idea...
      result = nil
  of tyUntyped, tyTyped:
    if kind notin {skParam, skResult} or taNoUntyped in flags: result = t
  of tyIterable:
    if kind notin {skParam} or taNoUntyped in flags: result = t
      # tyIterable is only for templates and macros.
  of tyStatic:
    if kind notin {skParam}: result = t
  of tyVoid:
    if taVoid notin flags: result = t
  of tyTypeClasses:
    if tfGenericTypeParam in t.flags or taConcept in flags: #or taField notin flags:
      discard
    elif t.isResolvedUserTypeClass:
      result = typeAllowedAux(marker, t.last, kind, c, flags)
    elif kind notin {skParam, skResult}:
      result = t
  of tyGenericBody, tyGenericParam, tyGenericInvocation,
     tyNone, tyForward, tyFromExpr:
    result = t
  of tyNil:
    if kind != skConst and kind != skParam: result = t
  of tyString, tyBool, tyChar, tyEnum, tyInt..tyUInt64, tyCstring, tyPointer:
    result = nil
  of tyOrdinal:
    if kind != skParam: result = t
  of tyGenericInst, tyDistinct, tyAlias, tyInferred:
    result = typeAllowedAux(marker, skipModifier(t), kind, c, flags)
  of tyRange:
    if skipTypes(t.elementType, abstractInst-{tyTypeDesc}).kind notin
      {tyChar, tyEnum, tyInt..tyFloat128, tyInt..tyUInt64, tyRange}: result = t
  of tyOpenArray:
    # you cannot nest openArrays/sinks/etc.
    if (kind != skParam or taIsOpenArray in flags) and views notin c.features:
      result = t
    else:
      result = typeAllowedAux(marker, t.elementType, kind, c, flags+{taIsOpenArray})
  of tyVarargs:
    # you cannot nest openArrays/sinks/etc.
    if kind != skParam or taIsOpenArray in flags:
      result = t
    else:
      result = typeAllowedAux(marker, t.elementType, kind, c, flags+{taIsOpenArray})
  of tySink:
    # you cannot nest openArrays/sinks/etc.
    if kind != skParam or taIsOpenArray in flags or t.elementType.kind in {tySink, tyLent, tyVar}:
      result = t
    else:
      result = typeAllowedAux(marker, t.elementType, kind, c, flags)
  of tyUncheckedArray:
    if kind != skParam and taHeap notin flags:
      result = t
    else:
      result = typeAllowedAux(marker, elementType(t), kind, c, flags-{taHeap})
  of tySequence:
    if t.elementType.kind != tyEmpty:
      result = typeAllowedAux(marker, t.elementType, kind, c, flags+{taHeap})
    elif kind in {skVar, skLet}:
      result = t.elementType
  of tyArray:
    if t.elementType.kind == tyTypeDesc:
      result = t.elementType
    elif t.elementType.kind != tyEmpty:
      result = typeAllowedAux(marker, t.elementType, kind, c, flags)
    elif kind in {skVar, skLet}:
      result = t.elementType
  of tyRef:
    if kind == skConst and taIsDefaultField notin flags: result = t
    else: result = typeAllowedAux(marker, t.elementType, kind, c, flags+{taHeap})
  of tyPtr:
    result = typeAllowedAux(marker, t.elementType, kind, c, flags+{taHeap})
  of tySet:
    result = typeAllowedAux(marker, t.elementType, kind, c, flags)
  of tyObject:
    if kind in {skProc, skFunc, skConst} and
        t.baseClass != nil and taIsDefaultField notin flags:
      result = t
    else:
      let flags = flags+{taObjField, taVoid}
      result = typeAllowedAux(marker, t.baseClass, kind, c, flags)
      if result.isNil and t.n != nil:
        result = typeAllowedNode(marker, t.n, kind, c, flags)
  of tyTuple:
    let flags = flags+{taTupField, taVoid}
    for a in t.kids:
      result = typeAllowedAux(marker, a, kind, c, flags)
      if result != nil: break
    if result.isNil and t.n != nil:
      result = typeAllowedNode(marker, t.n, kind, c, flags)
  of tyEmpty:
    if kind in {skVar, skLet}: result = t
  of tyError:
    # for now same as error node; we say it's a valid type as it should
    # prevent cascading errors:
    result = nil
  of tyOwned:
    if t.hasElementType and t.skipModifier.skipTypes(abstractInst).kind in {tyRef, tyPtr, tyProc}:
      result = typeAllowedAux(marker, t.skipModifier, kind, c, flags+{taHeap})
    else:
      result = t

proc typeAllowed*(t: PType, kind: TSymKind; c: PContext; flags: TTypeAllowedFlags = {}): PType =
  # returns 'nil' on success and otherwise the part of the type that is
  # wrong!
  var marker = initIntSet()
  result = typeAllowedAux(marker, t, kind, c, flags)

type
  ViewTypeKind* = enum
    noView, immutableView, mutableView

proc combine(dest: var ViewTypeKind, b: ViewTypeKind) {.inline.} =
  case dest
  of noView, mutableView:
    dest = b
  of immutableView:
    if b == mutableView: dest = b

proc classifyViewTypeAux(marker: var IntSet, t: PType): ViewTypeKind

proc classifyViewTypeNode(marker: var IntSet, n: PNode): ViewTypeKind =
  case n.kind
  of nkSym:
    result = classifyViewTypeAux(marker, n.typ)
  of nkOfBranch:
    result = classifyViewTypeNode(marker, n.lastSon)
  else:
    result = noView
    for child in n:
      result.combine classifyViewTypeNode(marker, child)
      if result == mutableView: break

proc classifyViewTypeAux(marker: var IntSet, t: PType): ViewTypeKind =
  if containsOrIncl(marker, t.id): return noView
  case t.kind
  of tyVar:
    result = mutableView
  of tyLent, tyOpenArray, tyVarargs:
    result = immutableView
  of tyGenericInst, tyDistinct, tyAlias, tyInferred, tySink, tyOwned,
     tyUncheckedArray, tySequence, tyArray, tyRef, tyStatic:
    result = classifyViewTypeAux(marker, skipModifier(t))
  of tyFromExpr:
    if t.hasElementType:
      result = classifyViewTypeAux(marker, skipModifier(t))
    else:
      result = noView
  of tyTuple:
    result = noView
    for a in t.kids:
      result.combine classifyViewTypeAux(marker, a)
      if result == mutableView: break
  of tyObject:
    result = noView
    if t.n != nil:
      result = classifyViewTypeNode(marker, t.n)
    if t.baseClass != nil:
      result.combine classifyViewTypeAux(marker, t.baseClass)
  else:
    # it doesn't matter what these types contain, 'ptr openArray' is not a
    # view type!
    result = noView

proc classifyViewType*(t: PType): ViewTypeKind =
  var marker = initIntSet()
  result = classifyViewTypeAux(marker, t)

proc directViewType*(t: PType): ViewTypeKind =
  # does classify 't' without looking recursively into 't'.
  case t.kind
  of tyVar:
    result = mutableView
  of tyLent, tyOpenArray:
    result = immutableView
  of abstractInst-{tyTypeDesc}:
    result = directViewType(t.skipModifier)
  else:
    result = noView

proc requiresInit*(t: PType): bool =
  (t.flags * {tfRequiresInit, tfNeedsFullInit, tfNotNil} != {}) or
  classifyViewType(t) != noView
