local ds = require("DataStructures")
local Dictionary, Stack, WordInfo, State = ds.Dictionary, ds.Stack, ds.WordInfo, ds.State


-- helper functions
function areNumbers(a: any, b: any): boolean
  return a is number and b is number
end

function getActiveDataStack(state: State): Stack
  return state.activeDataStack
end

function isNumber(token: string): boolean
  if tonumber(token) ~= nil then
    return true
  else
    return false
  end
end

function isWhitespace(chr: string): boolean
  return (chr == " " or
          chr == "\t" or
          chr == "\r" or
          chr == "\n" or
          chr == "\v" or
          chr == "\f")
end

function popTwoOperands(state: State): any, any
  local stack = getActiveDataStack(state)
  local b: any = stack:pop()
  local a: any = stack:pop()
  return a, b
end


-- Mathematical operations
function add(state: State)
  local a, b = popTwoOperands(state)
  if areNumbers(a,b) then
    local c = (a as number) + (b as number)
    getActiveDataStack(state):push(c)
  else
    error("invalid operands for add operation!")
  end
end
function sub(state: State)
  local a, b = popTwoOperands(state)
  if areNumbers(a, b) then
    local c = (a as number) - (b as number)
    getActiveDataStack(state):push(c)
  else
    error("invalid operands for sub operation!")
  end
end
function mul(state: State)
  local a, b = popTwoOperands(state)
  if areNumbers(a, b) then
    local c = (a as number) * (b as number)
    getActiveDataStack(state):push(c)
  else
    error("invalid operands for mul operation!")
  end
end
function div(state: State)
  local a, b = popTwoOperands(state)
  if areNumbers(a, b) then
    local c = (a as number) / (b as number)
    getActiveDataStack(state):push(c)
  else
    error("invalid operands for div operation!")
  end
end
-- I/O operations
function dot(state: State)
	local out = state.activeDataStack:pop()
  print(out)

end

function skipWhitespace(state: State)
  local chr = state.activeInputStream:readCurrentCharacter()
  while (isWhitespace(chr)) do
    chr = state.activeInputStream:advanceOffset()
  end
end

function parseToken(state: State): string
  local chr = state.activeInputStream:readCurrentCharacter()
  local token = ""
  while(not isWhitespace(chr)) do
    token = token..chr
    chr = state.activeInputStream:advanceOffset()
  end
end



local CoreWords = Dictionary:new()
local AddInfo = WordInfo:new(add, false)
local SubInfo = WordInfo:new(sub, false)
local MulInfo = WordInfo:new(mul, false)
local DivInfo = WordInfo:new(div, false)

CoreWords:define("+", AddInfo)
CoreWords:define("-", SubInfo)
CoreWords:define("*", MulInfo)
CoreWords:define("/", DivInfo)

return CoreWords