"""
yterm: a simple, standalone interface library for VT100-like terminals on UNIX.
Written by Jacob Welsh for yrc, March 2017.
Tested with Python 2.7 (should support at least 2.4).
"""

__version__ = '9 Kelvin'

from sys import stdout
from fcntl import ioctl
from struct import unpack
import termios as t

NUL = chr(0)
BS = chr(8)
HT = chr(9)
LF = chr(10)
CR = chr(13)
SO = chr(14)
SI = chr(15)
ESC = chr(27)

# VT100 http://vt100.net/docs/vt100-ug/chapter3.html
RESET = ESC + 'c'
CURSOR_SAVE = ESC + '7'
CURSOR_RESTORE = ESC + '8'
KEYPAD_APP = ESC + '=' # keypad produces escape sequences
KEYPAD_NUM = ESC + '>' # keypad produces numbers/symbols
select_g0 = lambda c: ESC + '(' + c
select_g1 = lambda c: ESC + ')' + c
SELECT_G0_ASCII = select_g0('B')
SELECT_G1_SPECIAL = select_g1('0')
CSI = ESC + '['
cseq = lambda code, *params: ''.join((CSI, ';'.join(map(str, params)), code))
# 1-based coordinates, from origin downward
cursor_pos = lambda row, col: cseq('H', row, col)
CURSOR_HOME = cseq('H')
cursor_up = lambda n: cseq('A', n)
CURSOR_UP1 = cseq('A')
cursor_down = lambda n: cseq('B', n)
CURSOR_DOWN1 = cseq('B')
cursor_back = lambda n: cseq('D', n)
CURSOR_BACK1 = cseq('D')
cursor_forward = lambda n: cseq('C', n)
CURSOR_FORWARD1 = cseq('C')
# Top/bottom margins of scrolling region
margins = lambda top, bot: cseq('r', top, bot)
MARGINS_NONE = cseq('r')
set_mode = lambda m: cseq('h', m)
rst_mode = lambda m: cseq('l', m)
set_priv_mode = lambda m: set_mode('?' + str(m))
rst_priv_mode = lambda m: rst_mode('?' + str(m))
LINEFEED_ON = set_mode(20) # LF moves to first column of next row
LINEFEED_OFF = rst_mode(20) # LF moves down only
CURSOR_APP = set_priv_mode(1) # DECCKM
CURSOR_ANSI = rst_priv_mode(1) # implied by KEYPAD_NUM
SCROLL_SMOOTH = set_priv_mode(4) # DECSCLM
SCROLL_JUMP = rst_priv_mode(4)
ORIGIN_MARGIN = set_priv_mode(6) # DECOM: row 1 at top margin, cursor confined
                                 # to scrolling region
ORIGIN_SCREEN = rst_priv_mode(6) # row 1 at top of screen
ERASE_TO_END = cseq('J')
ERASE_FROM_START = cseq('J', 1)
ERASE_FULL = cseq('J', 2)
ERASE_LINE_TO_END = cseq('K')
ERASE_LINE_FROM_START = cseq('K', 1)
ERASE_LINE_FULL = cseq('K', 2)
attrs = lambda *args: cseq('m', *args)
A_NONE = 0
A_BOLD = 1
A_ULINE = 4
A_BLINK = 5
A_REVERSE = 7
ATTR_NONE = attrs()
ATTR_BOLD = attrs(A_BOLD)
ATTR_ULINE = attrs(A_ULINE)
ATTR_BLINK = attrs(A_BLINK)
ATTR_REVERSE = attrs(A_REVERSE)

# DEC special graphics characters http://vt100.net/docs/vt100-ug/table3-9.html
SGC_BLANK = '_'
SGC_DIAMOND = '`'
SGC_CHECKER = 'a'
SGC_HT = 'b'
SGC_FF = 'c'
SGC_CR = 'd'
SGC_LF = 'e'
SGC_DEGREE = 'f'
SGC_PLUSMINUS = 'g'
SGC_NL = 'h'
SGC_VT = 'i' # ACS_LANTERN in ncurses, unclear where that comes from
SGC_LRCORNER = 'j'
SGC_URCORNER = 'k'
SGC_ULCORNER = 'l'
SGC_LLCORNER = 'm'
SGC_CROSSING = 'n'
SGC_HLINE1 = 'o'
SGC_HLINE3 = 'p'
SGC_HLINE5 = 'q'
SGC_HLINE7 = 'r'
SGC_HLINE9 = 's'
SGC_LTEE = 't'
SGC_RTEE = 'u'
SGC_BTEE = 'v'
SGC_TTEE = 'w'
SGC_VBAR = 'x'
SGC_LEQ = 'y'
SGC_GEQ = 'z'
SGC_PI = '{'
SGC_NEQ = '|'
SGC_STERLING = '}'
SGC_CENTERDOT = '~'

# XTerm http://invisible-island.net/xterm/ctlseqs/ctlseqs.html
ALT_SCREEN_ON = set_priv_mode(47)
ALT_SCREEN_OFF = rst_priv_mode(47)
BRACKETED_PASTE_ON = set_priv_mode(2004)
BRACKETED_PASTE_OFF = rst_priv_mode(2004)
BRACKETED_PASTE_START = cseq('~', 200)
BRACKETED_PASTE_END = cseq('~', 201)

def init(term_file=stdout, nonblock_read=False):
    """
    Initialize the terminal for full-screen graphics and raw input,
    returning a cleanup function to be called to restore it at exit.

    Parameters:
    term_file -- file object representing the terminal, default stdout (must
            support write, flush, and fileno methods)
    nonblock_read -- if false (default), reading from the terminal is blocking
            and returns at least one character (except on EOF); otherwise it is
            nonblocking and may return no characters.

    Details:
    - Sets terminal driver attributes for raw input: no line buffering; no flow
      control (^S/^Q), signal (^C etc.), or EOF (^D) characters; no CR/LF
      translation; 8-bit character size; no echo
    - Saves terminal cursor, attribute, and character set state (DECSC)
    - Initializes terminal character sets: G0 to ASCII and G1 to the DEC
      special graphics characters, initially selecting G0 (SI selects G0; SO
      selects G1)
    - Selects the alternate screen (to preserve XTerm scrollback)
    - Initializes terminal modes: standard linefeed handling (LNM); keypad
      produces ASCII characters (DECKPNM); jump scrolling (DECSCLM); no scroll
      margins (DECSTBM); no character attributes

    Cleanup details:
    - Selects G0 character set
    - Disables the alternate screen
    - Restores terminal cursor, attribute, and character set state (DECRC)
    - Restores original terminal driver state
    """
    old_attrs = t.tcgetattr(term_file.fileno())
    # "It's a bad idea to simply initialize a struct termios structure to a
    # chosen set of attributes and pass it directly to tcsetattr. Your program
    # may be run years from now, on systems that support members not
    # documented in this manual. The way to avoid setting these members to
    # unreasonable values is to avoid changing them."
    #   -- glibc manual
    #
    # Nope. It's 2017; we don't need new pheaturez in termios. If forcing them
    # to zero does something "unreasonable", then blindly accepting prior state
    # is worse as it could just as well do the same, but unpredictably.
    iflag = oflag = lflag = 0
    cflag = t.CS8 | t.CREAD
    ispeed, ospeed = old_attrs[4:6]
    cc = [NUL]*t.NCCS
    if nonblock_read:
        cc[t.VMIN] = 0
    else:
        cc[t.VMIN] = 1
    cc[t.VTIME] = 0
    t.tcsetattr(term_file.fileno(), t.TCSANOW,
                [iflag, oflag, cflag, lflag, ispeed, ospeed, cc])
    term_file.write(''.join((
        CURSOR_SAVE, ALT_SCREEN_ON,
        SELECT_G0_ASCII, SI, SELECT_G1_SPECIAL,
        LINEFEED_OFF, KEYPAD_NUM, SCROLL_JUMP,
        ATTR_NONE, MARGINS_NONE, ERASE_FULL,
    )))
    term_file.flush()
    def cleanup():
        term_file.write(''.join((
            SI, ALT_SCREEN_OFF, CURSOR_RESTORE,
        )))
        term_file.flush()
        t.tcsetattr(term_file.fileno(), t.TCSANOW, old_attrs)
    return cleanup

def screen_size(term_file=stdout):
    """
    Return the screen size (rows, columns) of the given terminal as reported by
    the driver.
    """
    rows, cols = unpack('HH', ioctl(term_file.fileno(), t.TIOCGWINSZ, ' '*4))
    return rows, cols

def render(tree, stack=None):
    """
    Render a text attribute tree to a single string with escape sequences.

    A node is either:
    - a string, or
    - a sequence of attribute code followed by zero or more child nodes

    An attribute code is an integer (e.g. the A_* constants).

    Example:
    >>> t = (A_NONE, 'normal, ',
    ...              (A_REVERSE, 'reverse, ', (A_BOLD, 'bold reverse,'),
    ...                          ' reverse again,'),
    ...              ' and back to normal.')
    >>> print render(t)
    """
    if isinstance(tree, str):
        return tree
    if stack is None:
        stack = [A_NONE]
    tag, children = tree[0], tree[1:]
    stack.append(tag)
    body = ''.join(render(c, stack) for c in children)
    stack.pop()
    return ''.join((attrs(tag), body, attrs(*stack)))