nondescript/src/ndspkg/chunk.nim

import strformat
import strutils

import types/value

type
  OpCode* = enum
    opReturn, opCall, opCheckArity, opFunctionDef, # functions
    opClosure, # closures
    opPop, opPopSA, opPopA # pop
    opNegate, opNot # unary
    opAdd, opSubtract, opMultiply, opDivide, # math
    opEqual, opGreater, opLess, # comparison
    opTrue, opFalse, opNil, # literal
    opConstant, # constant
    opDefineGlobal, opGetGlobal, opSetGlobal, # globals (uses constants)
    opGetLocal, opSetLocal, # locals
    opGetUpvalue, opSetUpvalue, # upvalues
    opJumpIfFalse, opJump, opLoop, opJumpIfFalsePop, # jumps
    opCreateList, opCreateTable, # collection creation
    opLen, opSetIndex, opGetIndex, # collection operators
    opPrint, opChr, opInt, opPutchar, # temporary opcodes for the brainfuck interpreter TODO move to native funcs

  Chunk* = object
    code*: seq[uint8]
    constants*: seq[NdValue]
    lines*: seq[int]
    name*: string # name of the module/chunk/files

  DoubleUint8* = array[2, uint8]


# WARNING! short args can safely assumed to be 1 byte long outside of chunk.nim
const shortArgSize* = 1
const shortArgMax* = 256 - 1

# modules outside chunk.nim should not assume any length of argSize, however code inside chunk.nim can make such assumptions
const argSize* = 2
const argMax*: int = 256*256 - 1

proc initChunk*(name: string): Chunk =
  Chunk(code: @[], name: name, lines: @[], constants: @[])

proc writeChunk*(ch: var Chunk, code: uint8, line: int) =
  ch.code.add(code)
  ch.lines.add(line)

proc writeChunk*(ch: var Chunk, code: OpCode, line: int) =
  ch.code.add(code.uint8)
  ch.lines.add(line)

proc writeChunk*(ch: var Chunk, code: DoubleUint8, line: int) =
  for c in code:
    ch.code.add(c)
    ch.lines.add(line)

proc len*(ch: Chunk): int =
  ch.code.len

proc toDU8*(integ: int): DoubleUint8 =
  cast[ptr array[2, uint8]](integ.unsafeAddr)[]

proc toInt*(du8: DoubleUint8): int =
  cast[uint16](du8).int

proc DU8ptrToInt*(du8: ptr uint8): int =
  cast[ptr uint16](du8)[].int

proc findConstant(ch: var Chunk, constant: NdValue): int =
  # TODO, if there are a lot of constants that are different, this could be possibly slow, so either use a table lookup or only check for the last x constants
  if ch.constants.len() == 0:
    return -1
  for i in countup(0, ch.constants.high()):
    let current = ch.constants[i]
    if current == constant:
      return i
  return -1

proc addConstant*(ch: var Chunk, constant: NdValue): int =
  let found = ch.findConstant(constant)
  if found == -1:
    ch.constants.add(constant)
    ch.constants.high
  else:
    found

proc writeConstant*(ch: var Chunk, constant: NdValue, line: int): int =
  result = ch.addConstant(constant)
  ch.writeChunk(opConstant, line)
  ch.writeChunk(result.toDU8, line)

const simpleInstructions = {
  opReturn,
  opPop,
  opPrint,
  opNegate, opNot,
  opAdd, opSubtract, opMultiply, opDivide,
  opEqual, opGreater, opLess,
  opTrue, opFalse, opNil,
  opLen, opSetIndex, opGetIndex,
  opChr, opInt, opPutchar,
}
const constantInstructions = {
  opConstant,
  opDefineGlobal, opGetGlobal, opSetGlobal,
}
const shortArgInstructions = {
  opPopSA,
  opCall,
  opCheckArity,
}
const argInstructions = {
  opPopA,
  opGetLocal, opSetLocal,
  opJumpIfFalse, opJump, opLoop, opJumpIfFalsePop,
  opFunctionDef, opClosure,
  opCreateList, opCreateTable,
  opGetUpvalue, opSetUpvalue,
}


proc disassembleChunk*(ch: Chunk) =
  echo &"== Chunk {ch.name} begin =="
  echo "index  line instruction"
  var c: int = 0
  var lastLine = -1
  while c < ch.code.len:
    template instruction: uint8 = ch.code[c]
    template line: int = ch.lines[c]
    template double: DoubleUint8 = [ch.code[c+1], ch.code[c+2]]
    template shortArg: uint8 = ch.code[c+1]
    let cFmt = &"{c:04}"
    let lineFmt =  if lastLine == line: "  | " else: &"{line:04}"
    try:
      write stdout, &"[{cFmt}] {lineFmt} {instruction.OpCode} ({instruction.toHex(2)}"
      case instruction.OpCode:
        of simpleInstructions:
          write stdout, ")\n"
        of shortArgInstructions:
          write stdout, &" {shortArg.toHex(2)}"
          c += 1
        of argInstructions:
          write stdout, &" {double[0].toHex(2)} {double[1].toHex(2)})\n"
          c += 2
        of constantInstructions:
          let i = double.toInt
          write stdout, &" {double[0].toHex(2)} {double[1].toHex(2)})\n"
          echo &"            points to constant {ch.constants[i]} (i: {i})"
          c += 2
    except:
      echo &"[{cFmt}] {lineFmt} Unknown opcode {instruction}"
    c.inc
  echo &"== Chunk {ch.name} end =="