Highlight file changes as they happen

watchfile.py

import curses, sys, difflib
import time, os.path
import watchdog.events, watchdog.observers

class Drawer:
    def __init__(self, win):
        self.xoffset = self.yoffset = 0
        self.win = win

    def draw(self, event_handler):
        self.win.erase()
        height, width = self.win.getmaxyx()
        first_column = 0 if curses.has_colors() else 1
        if not event_handler.first:
            for tag, i1, i2, j1, j2 in event_handler.matcher.get_opcodes():
                if curses.has_colors():
                    self.win.attrset(curses.color_pair({'replace': 1,
                                                        'insert': 2,
                                                        'delete': 3,
                                                        'equal': 0
                                                       }[tag]))
                for i in range(j1, j2):
                    if i-self.yoffset < 0: continue
                    if i-self.yoffset >= height: break
                    if not curses.has_colors():
                        self.win.addnstr(i-self.yoffset, 0, {'replace': '*',
                                                             'insert': '+',
                                                             'delete': '-',
                                                             'equal': ' '
                                                            }[tag], 1)
                    self.win.addnstr(i-self.yoffset, first_column, event_handler.contents[i][self.xoffset:], width-first_column)
        else:
            for i, line in enumerate(event_handler.contents):
                if i-self.yoffset < 0: continue
                if i-self.yoffset >= height: break
                self.win.addnstr(i-self.yoffset, first_column, line[self.xoffset:], width-first_column)
        self.win.refresh()

    def input(self, linecount):
        c = self.win.getch()
        height, width = self.win.getmaxyx()
        if 0 < c < 256 and chr(c) in 'Qq':
            return True
        elif c == curses.KEY_UP:
            if self.yoffset > 0:
                self.yoffset -= 1
            else:
                curses.beep()
        elif c == curses.KEY_DOWN:
            if self.yoffset+height < linecount:
                self.yoffset += 1
            else:
                curses.beep()
        elif c == curses.KEY_LEFT:
            if self.xoffset > 0:
                self.xoffset -= 1
            else:
                curses.beep()
        elif c == curses.KEY_RIGHT:
            self.xoffset += 1

class Handler(watchdog.events.PatternMatchingEventHandler):
    def __init__(self, path):
        super().__init__(patterns=[path])
        self.path = os.path.abspath(path)
        self.matcher = difflib.SequenceMatcher(isjunk=lambda s: s.isspace())
        self.contents = None
        self.first = True
        self.read()

    def read(self):
        old = self.contents
        with open(self.path) as f:
            self.contents = f.read().splitlines()
        if old is not None:
            self.matcher.set_seqs(old, self.contents)
            self.first = False

    def on_deleted(self, event):
        self.path = None

    def on_modified(self, event):
        if self.path is None: return
        self.read()
        self.drawer.draw(self)

    def on_moved(self, event):
        if self.path is None: return
        self.path = event.dest_path
        self.patterns[:] = [event.dest_path]
        # TODO: restart the observer if it moved to a different directory

event_handler = Handler(sys.argv[1])
observer = watchdog.observers.Observer()
observer.schedule(event_handler, os.path.dirname(event_handler.path))

def mainloop(win):
    curses.curs_set(0)
    if curses.has_colors():
        curses.init_pair(1, 0, curses.COLOR_BLUE)
        curses.init_pair(2, 0, curses.COLOR_GREEN)
        curses.init_pair(3, 0, curses.COLOR_RED)
    win.nodelay(False)
    drawer = Drawer(win)
    event_handler.drawer = drawer
    observer.start()
    while event_handler.path is not None:
        drawer.draw(event_handler)
        if drawer.input(len(event_handler.contents)):
            break
    observer.stop()
    curses.curs_set(1)

curses.wrapper(mainloop)
observer.join()