#!/usr/bin/env python

import copy
import sys
import tty
import termios

NORMAL = 0
EDIT = 1
META = 2

UP = 1000
DOWN = 1001
LEFT = 1002
RIGHT = 1003


class Editor():
    def __init__(self, f):
        lines = [l.replace("\n", "") for l in f]
        self.buffer = Buffer(lines)
        self.cursor = Cursor(0, 0)
        self.mode = NORMAL
        self.history = []

    def set_raw(self):
        fd = sys.stdin.fileno()
        self.old_settings = termios.tcgetattr(fd)
        tty.setraw(fd)

    def unset_raw(self):
        fd = sys.stdin.fileno()
        termios.tcsetattr(fd, termios.TCSADRAIN, self.old_settings)

    def run(self):
        self.running = True
        self.set_raw()
        while self.running:
            self.render()
            if self.mode == NORMAL: self.handle_input()
            if self.mode == EDIT: self.handle_edit()
            if self.mode == META: self.handle_meta()
        self.unset_raw()

    def render(self):
        ANSI.clear_screen()
        ANSI.move_cursor(0, 0)
        self.buffer.render()
        ANSI.move_cursor(self.cursor.row, self.cursor.col)

    def handle_meta(self):
        char = sys.stdin.read(1)

        if char == 'q': self.running = False

    def handle_edit(self):
        char = self.read_input()

        if char == chr(27): # ESC
            self.mode = NORMAL
        elif char == chr(127) and self.cursor.col: # BACK
            self.save_snapshot()
            self.buffer = self.buffer.delete(self.cursor)
            self.cursor = self.cursor.left(self.buffer)
        elif char == '\r':
            self.save_snapshot()
            self.buffer = self.buffer.split_line(self.cursor)
            self.cursor = Cursor(self.cursor.row+1, 0)
        elif char == UP: self.cursor = self.cursor.up(self.buffer)
        elif char == DOWN: self.cursor = self.cursor.down(self.buffer)
        elif char == LEFT: self.cursor = self.cursor.left(self.buffer)
        elif char == RIGHT: self.cursor = self.cursor.right(self.buffer)
        else:
            self.save_snapshot()
            self.buffer = self.buffer.insert(char, self.cursor)
            self.cursor = self.cursor.right(self.buffer)

    def read_input(self):
        char = sys.stdin.read(1)

        if char == '\x1b':
            nchar = sys.stdin.read(1)

            if nchar != '[': return char

            char = sys.stdin.read(1)

            if char == 'A': return UP
            if char == 'B': return DOWN
            if char == 'C': return RIGHT
            if char == 'D': return LEFT

        return char

    def handle_input(self):
        char = self.read_input()

        if char == ':': self.mode = META
        elif char == 'w' or char == UP:
            self.cursor = self.cursor.up(self.buffer)
        elif char == 's' or char == DOWN:
            self.cursor = self.cursor.down(self.buffer)
        elif char == 'a' or char == LEFT:
            self.cursor = self.cursor.left(self.buffer)
        elif char == 'd' or char == RIGHT:
            self.cursor = self.cursor.right(self.buffer)
        elif char == 'u': self.restore_snapshot()
        elif char == 'e': self.mode = EDIT

    def save_snapshot(self):
        self.history.append([self.buffer, self.cursor])

    def restore_snapshot(self):
        if len(self.history): self.buffer, self.cursor = self.history.pop()


class ANSI():
    @staticmethod
    def ansi(s):
        return "\x1b[" + s

    @staticmethod
    def clear_screen():
        sys.stdout.write(ANSI.ansi("2J"))

    @staticmethod
    def move_cursor(x, y):
        sys.stdout.write(ANSI.ansi("{};{}H".format(x+1, y+1)))



class Buffer():
    def __init__(self, lines):
        self.lines = lines

    def render(self):
        for line in self.lines:
            sys.stdout.write(line + "\r\n")

    def line_count(self):
        return len(self.lines)

    def line_length(self, x):
        return len(self.lines[x])

    def insert(self, char, cursor):
        lines = copy.copy(self.lines)
        line = lines[cursor.row]
        lines[cursor.row] = line[:cursor.col] + char + line[cursor.col:]
        return Buffer(lines)

    def delete(self, cursor):
        lines = copy.copy(self.lines)
        line = lines[cursor.row]
        lines[cursor.row] = line[:cursor.col-1] + line[cursor.col:]
        return Buffer(lines)

    def split_line(self, cursor):
        lines = copy.copy(self.lines)
        line = lines[cursor.row]
        before, after = line[:cursor.col], line[cursor.col:]
        lines[cursor.row] = before
        lines.insert(cursor.row+1, after)
        return Buffer(lines)


class Cursor():
    def __init__(self, row=0, col=0):
        self.row = row
        self.col = col

    def up(self, buf):
        return Cursor(self.row-1, self.col).clamp(buf)

    def down(self, buf):
        return Cursor(self.row+1, self.col).clamp(buf)

    def left(self, buf):
        return Cursor(self.row, self.col-1).clamp(buf)

    def right(self, buf):
        return Cursor(self.row, self.col+1).clamp(buf)

    def clamp(self, buf):
        row = max(0, min(self.row, buf.line_count()-1))
        col = max(0, min(self.col, buf.line_length(row)))
        return Cursor(row, col)


with open(sys.argv[1]) as f:
    Editor(f).run()