#!/usr/bin/python3

# The MIT License (MIT)
#
# Copyright © 2024 pacman64
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the “Software”), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.


from curses import \
    cbreak, curs_set, endwin, initscr, noecho, resetty, savetty, set_escdelay
from curses import A_NORMAL, A_REVERSE
from math import ceil
from os import dup2, getcwd
from os.path import abspath
from re import compile
from sys import argv, exit, stderr, stdin
from typing import Callable, Dict, Iterable, Tuple


info = '''
vb [options...] [filepath/URI...]


View (like a) Book is a text user-interface (TUI) to view/read plain-text,
laying lines out like facing pages in books.


    Escape     Quit this app; quit help-message screen
    F1         Toggle help-message screen; the Escape key also quits it
    F10        Quit this app

    Home       Go to the first pages
    End        Go to the last pages
    Up         Go to the previous pages
    Down       Go to the next pages
    Page Up    Go to the previous pages
    Page Down  Go to the next pages


The right side of the screen also shows little up/down arrow symbols when
there are more entries before/after the ones currently showing.

The only options are one of the help options, which show this message:
these are `-h`, `--h`, `-help`, and `--help`, without the quotes.

You can also view this help message by pressing the F1 key: you can quit
the help screen with the Escape key, or with the F1 key.
'''

# ansi_re matches ANSI-style sequences, so they're ignored
ansi_re = compile('\x1b\\[([0-9]*[A-HJKST]|[0-9;]*m)')


def layout(x: Tuple[str], h: int, i: int = 0) -> Iterable[Tuple[str, str]]:
    maxw = 0
    for k, l in enumerate(x):
        if k % (2 * h) < h:
            maxw = max(maxw, len(l))

    def index(k: int) -> str:
        return x[k] if k < len(x) else ''

    for j in range(h):
        yield f'{index(i + j):{maxw}}', index(i + j + h)


def shortened(s: str, maxlen: int, trail: str = '') -> str:
    maxlen = max(maxlen, 0)
    return s if len(s) <= maxlen else s[:maxlen - len(trail)] + trail


def fix(s: str) -> str:
    return ansi_re.sub('', s).expandtabs(4)


def view_text(screen, title: str, text: str, quit_set, help = None) -> None:
    start = 0

    lines = tuple(fix(l) for l in text.splitlines())
    text = '' # may immediately dealloc a few MBs when viewing big files

    # call func on_resize to properly initialize these variables
    h = w = max_start = inner_width = inner_height = step = 0

    def on_resize() -> None:
        nonlocal h, w, max_start, inner_width, inner_height, step
        h, w = screen.getmaxyx()
        inner_width = w - 1
        inner_height = h - 1
        step = 2 * inner_height
        max_start = max(len(lines) - step, 0)

    def scroll(to: int) -> None:
        nonlocal start
        start = to

    # initialize local variables
    on_resize()

    handlers: Dict[str, Callable] = {
        'KEY_RESIZE': on_resize,
        'KEY_UP': lambda: scroll(max(start - step, 0)),
        'KEY_DOWN': lambda: scroll(min(start + step, max_start)),
        'KEY_NPAGE': lambda: scroll(min(start + step, max_start)),
        'KEY_PPAGE': lambda: scroll(max(start - step, 0)),
        'KEY_HOME': lambda: scroll(0),
        'KEY_END': lambda: scroll(max_start),
    }

    if help:
        handlers[help] = lambda: view_help(screen)

    while True:
        screen.erase()

        screen.addstr(0, 0, shortened(title, inner_width), A_REVERSE)
        at_bottom = len(lines) - start <= step
        if at_bottom:
            msg = f'END ({len(lines):,})' if len(lines) > 0 else '(empty)'
        else:
            msg = f'({start + 1:,} / {len(lines):,})'
        screen.addstr(0, w - 1 - len(msg), shortened(msg, inner_width))

        for i, (left, right) in enumerate(layout(lines, inner_height, start)):
            try:
                line = f'{left} █' if right == '' else f'{left} █ {right}'
                screen.addnstr(i + 1, 0, line, inner_width)
            except Exception:
                # some utf-8 files have lines which upset func addstr
                pass

        # add up/down scrolling arrows
        try:
            if start > 0:
                screen.addstr(1, w - 1, '▲')
            if start < max_start:
                screen.addstr(h - 1, w - 1, '▼')
        except:
            pass

        screen.refresh()

        k = screen.getkey()
        if k in handlers:
            handlers[k]()
            continue
        if k in quit_set:
            return


def view_help(screen) -> None:
    title = 'Help for View like a Book (vb)'
    quit_set = ('\x1b', 'KEY_F(1)', 'KEY_F(10)')
    view_text(screen, title, info.strip(), quit_set)


def enter_ui():
    with open('/dev/tty', 'rb') as newin:
        dup2(newin.fileno(), 0)

    screen = initscr()
    savetty()
    noecho()
    cbreak()
    screen.keypad(True)
    curs_set(0)
    set_escdelay(10)
    return screen


def exit_ui(screen, error_msg) -> None:
    if screen:
        resetty()
        endwin()

    if error_msg:
        # stderr is never tampered with
        print(error_msg, file=stderr)


def run(name: str) -> None:
    screen = None
    help_key = 'KEY_F(1)'
    quit_set = ('\x1b', 'KEY_F(10)')

    try:
        if name == '-':
            # can read piped input only before entering the `ui-mode`
            text = stdin.read()
            # save memory by clearing the variable holding the slurped string
            def free_mem(res: str) -> str:
                nonlocal text
                text = ''
                return res
            screen = enter_ui()
            view_text(screen, '<stdin>', free_mem(text), quit_set, help_key)
        else:
            screen = enter_ui()
            title = abspath(name)
            view_text(screen, title, slurp(name), quit_set, help_key)

        exit_ui(screen, None)
        return 0
    except KeyboardInterrupt:
        exit_ui(screen, None)
        return 1
    except Exception as e:
        exit_ui(screen, f'\x1b[31m{e}\x1b[0m')
        return 1


def slurp(name: str) -> str:
    protocols = ('https://', 'http://', 'file://', 'ftp://', 'data:')
    seems_url = any(name.startswith(p) for p in protocols)

    if seems_url:
        from urllib.request import urlopen
        with urlopen(name) as inp:
            return inp.read().decode('utf-8')

    with open(name) as inp:
        return inp.read()


if len(argv) > 1 and argv[1] in ('-h', '--h', '-help', '--help'):
    print(info.strip(), file=stderr)
    exit(0)

if len(argv) > 2:
    print(info.strip(), file=stderr)
    msg = 'there can only be one (optional) starting-folder argument'
    print(f'\x1b[31m{msg}\x1b[0m', file=stderr)
    exit(4)

# avoid func curses.wrapper, since it calls func curses.start_color, which in
# turn forces a black background even on terminals configured to use any other
# background color

if len(argv) == 2:
    exit(run(argv[1]))
else:
    exit(run('-'))