"""This implements a virtual screen. This is used to support ANSI terminal
emulation. The screen representation and state is implemented in this class.
Most of the methods are inspired by ANSI screen control codes. The ANSI class
extends this class to add parsing of ANSI escape codes.

$Id: screen.py 486 2007-07-13 01:04:16Z noah $
"""

import copy

NUL = 0    # Fill character; ignored on input.
ENQ = 5    # Transmit answerback message.
BEL = 7    # Ring the bell.
BS  = 8    # Move cursor left.
HT  = 9    # Move cursor to next tab stop.
LF = 10    # Line feed.
VT = 11    # Same as LF.
FF = 12    # Same as LF.
CR = 13    # Move cursor to left margin or newline.
SO = 14    # Invoke G1 character set.
SI = 15    # Invoke G0 character set.
XON = 17   # Resume transmission.
XOFF = 19  # Halt transmission.
CAN = 24   # Cancel escape sequence.
SUB = 26   # Same as CAN.
ESC = 27   # Introduce a control sequence.
DEL = 127  # Fill character; ignored on input.
SPACE = chr(32) # Space or blank character.

def constrain (n, min, max):

    """This returns a number, n constrained to the min and max bounds. """

    if n < min:
        return min
    if n > max:
        return max
    return n

class screen:

    """This object maintains the state of a virtual text screen as a
    rectangluar array. This maintains a virtual cursor position and handles
    scrolling as characters are added. This supports most of the methods needed
    by an ANSI text screen. Row and column indexes are 1-based (not zero-based,
    like arrays). """

    def __init__ (self, r=24,c=80):

        """This initializes a blank scree of the given dimentions."""

        self.rows = r
        self.cols = c
        self.cur_r = 1
        self.cur_c = 1
        self.cur_saved_r = 1
        self.cur_saved_c = 1
        self.scroll_row_start = 1
        self.scroll_row_end = self.rows
        self.w = [ [SPACE] * self.cols for c in range(self.rows)]

    def __str__ (self):

        """This returns a printable representation of the screen. The end of
        each screen line is terminated by a newline. """

        return '\n'.join ([ ''.join(c) for c in self.w ])

    def dump (self):

        """This returns a copy of the screen as a string. This is similar to
        __str__ except that lines are not terminated with line feeds. """

        return ''.join ([ ''.join(c) for c in self.w ])

    def pretty (self):

        """This returns a copy of the screen as a string with an ASCII text box
        around the screen border. This is similar to __str__ except that it
        adds a box. """

        top_bot = '+' + '-'*self.cols + '+\n'
        return top_bot + '\n'.join(['|'+line+'|' for line in str(self).split('\n')]) + '\n' + top_bot

    def fill (self, ch=SPACE):

        self.fill_region (1,1,self.rows,self.cols, ch)

    def fill_region (self, rs,cs, re,ce, ch=SPACE):

        rs = constrain (rs, 1, self.rows)
        re = constrain (re, 1, self.rows)
        cs = constrain (cs, 1, self.cols)
        ce = constrain (ce, 1, self.cols)
        if rs > re:
            rs, re = re, rs
        if cs > ce:
            cs, ce = ce, cs
        for r in range (rs, re+1):
            for c in range (cs, ce + 1):
                self.put_abs (r,c,ch)

    def cr (self):

        """This moves the cursor to the beginning (col 1) of the current row.
        """

        self.cursor_home (self.cur_r, 1)

    def lf (self):

        """This moves the cursor down with scrolling.
        """

        old_r = self.cur_r
        self.cursor_down()
        if old_r == self.cur_r:
            self.scroll_up ()
            self.erase_line()

    def crlf (self):

        """This advances the cursor with CRLF properties.
        The cursor will line wrap and the screen may scroll.
        """

        self.cr ()
        self.lf ()

    def newline (self):

        """This is an alias for crlf().
        """

        self.crlf()

    def put_abs (self, r, c, ch):

        """Screen array starts at 1 index."""

        r = constrain (r, 1, self.rows)
        c = constrain (c, 1, self.cols)
        ch = str(ch)[0]
        self.w[r-1][c-1] = ch

    def put (self, ch):

        """This puts a characters at the current cursor position.
        """

        self.put_abs (self.cur_r, self.cur_c, ch)

    def insert_abs (self, r, c, ch):

        """This inserts a character at (r,c). Everything under
        and to the right is shifted right one character.
        The last character of the line is lost.
        """

        r = constrain (r, 1, self.rows)
        c = constrain (c, 1, self.cols)
        for ci in range (self.cols, c, -1): 
            self.put_abs (r,ci, self.get_abs(r,ci-1))
        self.put_abs (r,c,ch)

    def insert (self, ch):

        self.insert_abs (self.cur_r, self.cur_c, ch)

    def get_abs (self, r, c):
    
        r = constrain (r, 1, self.rows)
        c = constrain (c, 1, self.cols)
        return self.w[r-1][c-1]

    def get (self):

        self.get_abs (self.cur_r, self.cur_c)

    def get_region (self, rs,cs, re,ce):

        """This returns a list of lines representing the region.
        """

        rs = constrain (rs, 1, self.rows)
        re = constrain (re, 1, self.rows)
        cs = constrain (cs, 1, self.cols)
        ce = constrain (ce, 1, self.cols)
        if rs > re:
            rs, re = re, rs
        if cs > ce:
            cs, ce = ce, cs
        sc = []
        for r in range (rs, re+1):
            line = ''
            for c in range (cs, ce + 1):
                ch = self.get_abs (r,c)
                line = line + ch
            sc.append (line)
        return sc

    def cursor_constrain (self):

        """This keeps the cursor within the screen area.
        """

        self.cur_r = constrain (self.cur_r, 1, self.rows)
        self.cur_c = constrain (self.cur_c, 1, self.cols)

    def cursor_home (self, r=1, c=1): # <ESC>[{ROW};{COLUMN}H

        self.cur_r = r
        self.cur_c = c
        self.cursor_constrain ()

    def cursor_back (self,count=1): # <ESC>[{COUNT}D (not confused with down)

        self.cur_c = self.cur_c - count
        self.cursor_constrain ()

    def cursor_down (self,count=1): # <ESC>[{COUNT}B (not confused with back)

        self.cur_r = self.cur_r + count
        self.cursor_constrain ()

    def cursor_forward (self,count=1): # <ESC>[{COUNT}C

        self.cur_c = self.cur_c + count
        self.cursor_constrain ()

    def cursor_up (self,count=1): # <ESC>[{COUNT}A

        self.cur_r = self.cur_r - count
        self.cursor_constrain ()

    def cursor_up_reverse (self): # <ESC> M   (called RI -- Reverse Index)

        old_r = self.cur_r
        self.cursor_up()
        if old_r == self.cur_r:
            self.scroll_up()

    def cursor_force_position (self, r, c): # <ESC>[{ROW};{COLUMN}f

        """Identical to Cursor Home."""

        self.cursor_home (r, c)

    def cursor_save (self): # <ESC>[s

        """Save current cursor position."""

        self.cursor_save_attrs()

    def cursor_unsave (self): # <ESC>[u

        """Restores cursor position after a Save Cursor."""

        self.cursor_restore_attrs()

    def cursor_save_attrs (self): # <ESC>7

        """Save current cursor position."""

        self.cur_saved_r = self.cur_r
        self.cur_saved_c = self.cur_c

    def cursor_restore_attrs (self): # <ESC>8

        """Restores cursor position after a Save Cursor."""

        self.cursor_home (self.cur_saved_r, self.cur_saved_c)

    def scroll_constrain (self):

        """This keeps the scroll region within the screen region."""

        if self.scroll_row_start <= 0:
            self.scroll_row_start = 1
        if self.scroll_row_end > self.rows:
            self.scroll_row_end = self.rows

    def scroll_screen (self): # <ESC>[r

        """Enable scrolling for entire display."""

        self.scroll_row_start = 1
        self.scroll_row_end = self.rows

    def scroll_screen_rows (self, rs, re): # <ESC>[{start};{end}r

        """Enable scrolling from row {start} to row {end}."""

        self.scroll_row_start = rs
        self.scroll_row_end = re
        self.scroll_constrain()

    def scroll_down (self): # <ESC>D

        """Scroll display down one line."""

        # Screen is indexed from 1, but arrays are indexed from 0.
        s = self.scroll_row_start - 1
        e = self.scroll_row_end - 1
        self.w[s+1:e+1] = copy.deepcopy(self.w[s:e])

    def scroll_up (self): # <ESC>M

        """Scroll display up one line."""

        # Screen is indexed from 1, but arrays are indexed from 0.
        s = self.scroll_row_start - 1
        e = self.scroll_row_end - 1
        self.w[s:e] = copy.deepcopy(self.w[s+1:e+1])

    def erase_end_of_line (self): # <ESC>[0K -or- <ESC>[K

        """Erases from the current cursor position to the end of the current
        line."""

        self.fill_region (self.cur_r, self.cur_c, self.cur_r, self.cols)

    def erase_start_of_line (self): # <ESC>[1K

        """Erases from the current cursor position to the start of the current
        line."""

        self.fill_region (self.cur_r, 1, self.cur_r, self.cur_c)

    def erase_line (self): # <ESC>[2K

        """Erases the entire current line."""

        self.fill_region (self.cur_r, 1, self.cur_r, self.cols)

    def erase_down (self): # <ESC>[0J -or- <ESC>[J

        """Erases the screen from the current line down to the bottom of the
        screen."""

        self.erase_end_of_line ()
        self.fill_region (self.cur_r + 1, 1, self.rows, self.cols)

    def erase_up (self): # <ESC>[1J

        """Erases the screen from the current line up to the top of the
        screen."""

        self.erase_start_of_line ()
        self.fill_region (self.cur_r-1, 1, 1, self.cols)

    def erase_screen (self): # <ESC>[2J

        """Erases the screen with the background color."""

        self.fill ()

    def set_tab (self): # <ESC>H

        """Sets a tab at the current position."""

        pass

    def clear_tab (self): # <ESC>[g

        """Clears tab at the current position."""

        pass

    def clear_all_tabs (self): # <ESC>[3g

        """Clears all tabs."""

        pass

#        Insert line             Esc [ Pn L
#        Delete line             Esc [ Pn M
#        Delete character        Esc [ Pn P
#        Scrolling region        Esc [ Pn(top);Pn(bot) r