open Base

let _unary = [ "@SP"; "A=M-1" ]
let _binary = [ "@SP"; "AM=M-1"; "D=M"; "A=A-1" ]
let _add = _binary @ [ "M=M+D" ]
let _sub = _binary @ [ "M=M-D" ]
let _neg = _unary @ [ "M=-M" ]
let _and = _binary @ [ "M=D&M" ]
let _or = _binary @ [ "M=D|M" ]
let _not = _unary @ [ "M=!M" ]

let _eq loc =
  _binary
  @ [ "D=M-D"
    ; "M=-1"
    ; "@END_EQ_" ^ loc
    ; "D;JEQ"
    ; "@SP"
    ; "A=M-1"
    ; "M=0"
    ; "(END_EQ_" ^ loc ^ ")"
    ]
;;

let _gt loc =
  _binary
  @ [ "D=M-D"
    ; "M=-1"
    ; "@END_GT_" ^ loc
    ; "D;JGT"
    ; "@SP"
    ; "A=M-1"
    ; "M=0"
    ; "(END_GT_" ^ loc ^ ")"
    ]
;;

let _lt loc =
  _binary
  @ [ "D=M-D"
    ; "M=-1"
    ; "@END_LT_" ^ loc
    ; "D;JLT"
    ; "@SP"
    ; "A=M-1"
    ; "M=0"
    ; "(END_LT_" ^ loc ^ ")"
    ]
;;

let a_command ?(loc = 0) a =
  let suffix = Int.to_string loc in
  match a with
  | "add" -> _add
  | "sub" -> _sub
  | "neg" -> _neg
  | "eq" -> _eq suffix
  | "gt" -> _gt suffix
  | "lt" -> _lt suffix
  | "and" -> _and
  | "or" -> _or
  | "not" -> _not
  | _ -> failwith "a_command: Invalid Command"
;;

let addr a = [ String.concat [ "@"; a ] ]
let push_constant = [ "D=A"; "@SP"; "A=M"; "M=D"; "@SP"; "M=M+1" ]

let _end = ["(TERMINATE)"; "@TERMINATE"; "0;JMP"]

let _process_push s a =
  match s with
  | "constant" -> addr a @ push_constant
  | _ -> failwith "Invalid Segment"
;;

let m_command (c, s, a) =
  match c with
  | "push" -> _process_push s a
  | _ -> failwith "m_command: Invalid Command"
;;