#!/usr/bin/env python3

import sys

rip_mode=False

if len(sys.argv)!=2:
    print("Usage: ./rippy.py <file.rip>",file=sys.stderr)
    sys.exit(1)

def error(msg):
    if rip_mode:
        msg="rip"
    print(msg,file=sys.stderr)
    sys.exit(1)

def make_jumpmap(source):
    jm={}
    stk=[]
    for i in range(len(source)):
        if source[i]=="[":
            stk.append(i)
        elif source[i]=="]":
            if len(stk)==0:
                error("Too many ']' in source")
            jm[stk[-1]]=i
            jm[i]=stk[-1]
            stk.pop()
    if len(stk)!=0:
        error("Too many '[' in source")
    return jm

def stack_check(stk,opname,nelems):
    if len(stk)==0:
        error(opname+" needs "+nelems+" element"+("s" if nelems!=1 else "")+" on the stack")

def stack_pop(stk,opname,nelems):
    stack_check(stk,opname,nelems)
    e=stk[-1]
    stk.pop()
    return e


def rip(source,jm):
    ip=0
    stk=[]
    cstk=[]
    lastif=None
    while ip<len(source):
        if source[ip] in " \t\n":
            ip+=1
            continue

        if lastif!=None and source[ip]!="[":
            error("'[' expected after '"+lastif+"'")

        if source[ip] in "0123456789":
            stk.append(int(source[ip]))
        elif source[ip]=="P":
            stack_pop(stk,"Pop",1)
        elif source[ip]=="S":
            stack_check(stk,"Swap",2)
            stk[-2],stk[-1]=stk[-1],stk[-2]
        elif source[ip]=="D":
            stack_check(stk,"Duplicate",1)
            stk.append(stk[-1])
        elif source[ip]=="i":
            stack_check(stk,"Increment",1)
            stk[-1]+=1
        elif source[ip]=="d":
            stack_check(stk,"Decrement",1)
            stk[-1]-=1
        elif source[ip]=="r":
            a=stack_pop(stk,"Roll",1)
            if a<0:
                error("Negative roll amount")
            if a>1:
                stack_check(stk,"Roll("+str(a)+")",a)
                stk[-a],stk[-a+1:-1]=stk[-1],stk[-a:-2]
        elif source[ip]=="R":
            a=stack_pop(stk,"Reverse roll",1)
            if a<0:
                error("Negative reverse roll amount")
            if a>1:
                stack_check(stk,"Reverse roll("+str(a)+")",a)
                stk[-a:-2],stk[-1]=stk[-a+1:-1],stk[-a]
        elif source[ip]=="l":
            stk.append(len(stk))
        elif source[ip] in "asmqMpGLE":
            names={
                "a": "Add", "s": "Subtract", "m": "Multiply", "q": "Quotient",
                "M": "Modulo", "p": "Power", "G": "Greater", "L": "Less", "E": "Equal"
            }
            funcs={
                "a": lambda a,b: a+b, "s": lambda a,b: a-b, "m": lambda a,b: a*b,
                "q": lambda a,b: a//b, "M": lambda a,b: a%b, "p": lambda a,b: a**b,
                "G": lambda a,b: a>b, "L": lambda a,b: a<b, "E": lambda a,b: a==b,
            }
            b=stack_pop(stk,names[source[ip]],2)
            a=stack_pop(stk,names[source[ip]],2)
            stk.append(funcs[source[ip]](a,b))
        elif source[ip]=="n":
            stk.append(stack_pop(stk,"Not",1)!=0)
        elif source[ip] in "IW":
            if lastif!=None:
                error("'"+source[lastif]+" without codeblock")
            lastif=source[ip]
        elif source[ip]=="[":
            if lastif==None:
                error("'[' without I or W")
            if stack_pop(stk,"'[' for '"+lastif+"'",1)!=0:
                cstk.append(lastif)
            else:
                ip=jm[ip]
            lastif=None
        elif source[ip]=="]":
            if cstk[-1]=="W":
                ip=jm[ip]-1
                lastif=cstk[-1]
            else:
                cstk.pop()
        elif source[ip]=="o":
            n=stack_pop(stk,"Output character",1)
            if n<0 or n>255:
                error("Invalid output byte")
            print(chr((n%256+256)%256),end="")
        elif source[ip]=="O":
            n=stack_pop(stk,"Output number",1)
            print(n,end="")
        elif source[ip]=="g":
            c=sys.stdin.read(1)
            if len(c)==0:
                stk.append(-1)
            else:
                stk.append(ord(c))
        elif source[ip]=="'":
            if ip+1>=len(source):
                error("Single-quote at end of file")
            stk.append(ord(source[ip+1]))
            ip+=1
        else:
            error("Unrecognised command '"+source[ip]+"'")

        ip+=1


def main():
    sourcefname=sys.argv[1]
    with open(sourcefname,"r") as f:
        source=f.read()

    jm=make_jumpmap(source)

    rip(source,jm)


if __name__=="__main__":
    main()