#!/usr/bin/env python3
'stream.py - by Sean B. Palmer'

import sys, os, itertools, shutil

def exit(*args): 
   for arg in args: 
      if isinstance(arg, int): sys.exit(arg)
      elif hasattr(arg, '__call__'): arg()
      else: print(arg)
   sys.exit()

class Stream(object): 
   def __init__(self, filename): 
      self.oldfn = filename + '.old'
      self.newfn = filename

      if os.path.exists(self.oldfn): 
         exit('File exists: %s' % self.oldfn, 1)
      shutil.copy(self.newfn, self.oldfn)

      self.old = open(self.oldfn, encoding='utf=8')
      self.new = open(self.newfn, 'w', encoding='utf-8')

      self.previous = None
      self.next = None

      self.collection = None
      self.closed = False

   def __enter__(self): 
      return self

   def __exit__(self, exc_type, exc_val, exc_tb): 
      while True: 
         if not self.move(): break   
         self.append(self.previous)
      self.close()
      os.remove(self.oldfn)

   def move(self): 
      try: line = self.old.__next__()
      except StopIteration: line = None
      except ValueError: line = None

      self.previous = self.next
      self.next = line
      return (self.previous is not None) or (self.next is not None)

   def append(self, line): 
      if line is None: return
      if not self.new.closed: 
         self.new.write(line)
      if self.collection is not None: 
         self.collection.append(line)

   def collect(self): 
      self.collection = []

   def collected(self): 
      collection = self.collection
      self.collection = None
      return collection

   def edit(self, ordinal, string, test, skip=False): 
      found = 0
      want = int(ordinal[:-2])
      
      while True: 
         line = getattr(self, test)
         if line and (string in line): 
            found += 1
            if found >= want: 
               if skip: self.move()
               return True

         if not self.move(): break
         self.append(self.previous)
      return False

   def before(self, ordinal, string): 
      return self.edit(ordinal, string, 'next')

   def instead(self, ordinal, string): 
      return self.edit(ordinal, string, 'next', skip=True)

   def after(self, ordinal, string): 
      return self.edit(ordinal, string, 'previous')

   def write(self, text): 
      self.append(text + '\n')

   def close(self): 
      self.old.close()
      self.new.close()
      self.closed = True

if __name__ == '__main__': 
   print(__doc__)