# vim:fileencoding=utf-8
# License: GPL v3 Copyright: 2016, Kovid Goyal <kovid at kovidgoyal.net>
from __python__ import bound_methods, hash_literals

# Notes about flow mode scrolling:
#  All the math in flow mode is based on the block and inline directions.
#  Inline is "the direction lines of text go."
#  In horizontal scripts such as English and Hebrew, the inline is horizontal
#  and the block is vertical.
#  In vertical languages such as Japanese and Mongolian, the inline is vertical
#  and block is horizontal.
#  Regardless of language, flow mode scrolls in the block direction.
#
#  In vertical RTL books, the block position scrolls from right to left. |<------|
#  This means that the viewport positions become negative as you scroll.
#  This is hidden from flow mode by the viewport, which transparently
#  negates any inline coordinates sent in to the viewport_to_document* functions
#  and the various scroll_to/scroll_by functions, as well as the reported X position.
#
#  The result of all this is that flow mode's math can safely pretend that
#  things scroll in the positive block direction.

from dom import set_css
from range_utils import wrap_range, unwrap
from read_book.cfi import scroll_to as cfi_scroll_to
from read_book.globals import current_spine_item, get_boss, rtl_page_progression, ltr_page_progression
from read_book.settings import opts
from read_book.viewport import line_height, rem_size, scroll_viewport


def flow_to_scroll_fraction(frac, on_initial_load):
    scroll_viewport.scroll_to_in_block_direction(scroll_viewport.document_block_size() * frac)


small_scroll_events = v'[]'


def clear_small_scrolls():
    nonlocal small_scroll_events
    small_scroll_events = v'[]'


def dispatch_small_scrolls():
    if small_scroll_events.length:
        now = window.performance.now()
        if now - small_scroll_events[-1].time <= 2000:
            window.setTimeout(dispatch_small_scrolls, 100)
            return
        amt = 0
        for x in small_scroll_events:
            amt += x.amt
        clear_small_scrolls()
        get_boss().report_human_scroll(amt / scroll_viewport.document_block_size())


def add_small_scroll(amt):
    small_scroll_events.push({'amt': amt, 'time': window.performance.now()})
    window.setTimeout(dispatch_small_scrolls, 100)


def report_human_scroll(amt):
    h = scroll_viewport.height()
    is_large_scroll = (abs(amt) / h) >= 0.5
    if amt > 0:
        if is_large_scroll:
            clear_small_scrolls()
            get_boss().report_human_scroll(amt / scroll_viewport.document_block_size())
        else:
            add_small_scroll(amt)
    elif amt is 0 or is_large_scroll:
        clear_small_scrolls()


last_change_spine_item_request = {}


def _check_for_scroll_end(func, obj, args, report):
    before = scroll_viewport.block_pos()
    should_flip_progression_direction = func.apply(obj, args)

    now = window.performance.now()
    scroll_animator.sync(now)

    if scroll_viewport.block_pos() is before:
        csi = current_spine_item()
        if last_change_spine_item_request.name is csi.name and now - last_change_spine_item_request.at < 2000:
            return False
        last_change_spine_item_request.name = csi.name
        last_change_spine_item_request.at = now
        go_to_previous_page = args[0] < 0
        if (should_flip_progression_direction):
            go_to_previous_page = not go_to_previous_page
        get_boss().send_message('next_spine_item', previous=go_to_previous_page)
        return False
    if report:
        report_human_scroll(scroll_viewport.block_pos() - before)
    return True


def check_for_scroll_end(func):
    return def ():
        return _check_for_scroll_end(func, this, arguments, False)


def check_for_scroll_end_and_report(func):
    return def ():
        return _check_for_scroll_end(func, this, arguments, True)


@check_for_scroll_end_and_report
def scroll_by_and_check_next_page(y):
    scroll_viewport.scroll_by_in_block_direction(y)
    # This indicates to check_for_scroll_end_and_report that it should not
    # flip the page progression direction.
    return False

def flow_onwheel(evt):
    di = db = 0
    WheelEvent = window.WheelEvent
    # Y deltas always scroll in the previous and next page direction,
    # regardless of writing direction, since doing otherwise would
    # make mouse wheels mostly useless for scrolling in books written
    # vertically.
    if evt.deltaY:
        if evt.deltaMode is WheelEvent.DOM_DELTA_PIXEL:
            db = evt.deltaY
        elif evt.deltaMode is WheelEvent.DOM_DELTA_LINE:
            db = line_height() * evt.deltaY
        if evt.deltaMode is WheelEvent.DOM_DELTA_PAGE:
            db = (scroll_viewport.block_size() - 30) * evt.deltaY
    # X deltas scroll horizontally in both horizontal and vertical books.
    # It's more natural in both cases.
    if evt.deltaX:
        if evt.deltaMode is WheelEvent.DOM_DELTA_PIXEL:
            dx = evt.deltaX
        elif evt.deltaMode is WheelEvent.DOM_DELTA_LINE:
            dx = line_height() * evt.deltaX
        else:
            dx = (scroll_viewport.block_size() - 30) * evt.deltaX

        if scroll_viewport.horizontal_writing_mode:
            di = dx
        else:
            # Left goes forward, so make sure left is positive and right is negative,
            # which is the opposite of what the wheel sends.
            if scroll_viewport.rtl:
                db = -dx
            # Right goes forward, so the sign is correct.
            else:
                db = dx
    if Math.abs(di) >= 1:
        scroll_viewport.scroll_by_in_inline_direction(di)
    if Math.abs(db) >= 1:
        scroll_by_and_check_next_page(db)

@check_for_scroll_end
def goto_boundary(dir):
    position = 0 if dir is DIRECTION.Up else scroll_viewport.document_block_size()
    scroll_viewport.scroll_to_in_block_direction(position)
    get_boss().report_human_scroll()
    return False


@check_for_scroll_end_and_report
def scroll_by_page(direction, flip_if_rtl_page_progression):
    b = scroll_viewport.block_size() - 10
    scroll_viewport.scroll_by_in_block_direction(b * direction)

    # Let check_for_scroll_end_and_report know whether or not it should flip
    # the progression direction.
    return flip_if_rtl_page_progression and rtl_page_progression()


def scroll_to_extend_annotation(backward, horizontal, by_page):
    direction = -1 if backward else 1
    h = line_height()
    if by_page:
        h = (window.innerWidth if horizontal else window.innerHeight) - h
    if horizontal:
        before = window.pageXOffset
        window.scrollBy(h * direction, 0)
        return window.pageXOffset is not before
    before = window.pageYOffset
    window.scrollBy(0, h * direction)
    return window.pageYOffset is not before

def is_auto_scroll_active():
    return scroll_animator.is_active()


def start_autoscroll():
    scroll_animator.start(DIRECTION.Down, True)


def toggle_autoscroll():
    if is_auto_scroll_active():
        cancel_scroll()
        running = False
    else:
        start_autoscroll()
        running = True
    get_boss().send_message('autoscroll_state_changed', running=running)


def handle_shortcut(sc_name, evt):
    if sc_name is 'down':
        scroll_animator.start(DIRECTION.Down, False)
        return True
    if sc_name is 'up':
        scroll_animator.start(DIRECTION.Up, False)
        return True
    if sc_name is 'start_of_file':
        goto_boundary(DIRECTION.Up)
        return True
    if sc_name is 'end_of_file':
        goto_boundary(DIRECTION.Down)
        return True
    if sc_name is 'left':
        scroll_by_and_check_next_page(-15 if ltr_page_progression() else 15, 0)
        return True
    if sc_name is 'right':
        scroll_by_and_check_next_page(15 if ltr_page_progression() else -15, 0)
        return True
    if sc_name is 'start_of_book':
        get_boss().send_message('goto_doc_boundary', start=True)
        return True
    if sc_name is 'end_of_book':
        get_boss().send_message('goto_doc_boundary', start=False)
        return True
    if sc_name is 'pageup':
        scroll_by_page(-1, False)
        return True
    if sc_name is 'pagedown':
        scroll_by_page(1, False)
        return True
    if sc_name is 'toggle_autoscroll':
        toggle_autoscroll()
        return True

    if sc_name.startsWith('scrollspeed_'):
        scroll_animator.sync()

    return False


def layout(is_single_page):
    add_visibility_listener()
    line_height(True)
    rem_size(True)
    set_css(document.body, margin='0', border_width='0', padding='0')
    body_style = window.getComputedStyle(document.body)
    # scroll viewport needs to know if we're in vertical mode,
    # since that will cause scrolling to happen left and right
    scroll_viewport.initialize_on_layout(body_style)
    document.documentElement.style.overflow = 'visible' if scroll_viewport.vertical_writing_mode else 'hidden'

def auto_scroll_resume():
    scroll_animator.wait = False
    scroll_animator.sync()


def add_visibility_listener():
    if add_visibility_listener.done:
        return
    add_visibility_listener.done = True
    # Pause auto-scroll while minimized
    document.addEventListener("visibilitychange", def():
        if (document.visibilityState is 'visible'):
            scroll_animator.sync()
        else:
            scroll_animator.pause()
    )


def cancel_scroll():
    scroll_animator.stop()


def is_scroll_end(pos):
    return not (0 <= pos <= scroll_viewport.document_block_size() - scroll_viewport.block_size())


DIRECTION = {'Up': -1, 'up': -1, 'Down': 1, 'down': 1, 'UP': -1, 'DOWN': 1}


class ScrollAnimator:
    DURATION = 100 # milliseconds

    def __init__(self):
        self.animation_id = None
        self.auto = False
        self.auto_timer = None
        self.paused = False

    def is_running(self):
        return self.animation_id is not None or self.auto_timer is not None

    def is_active(self):
        return self.is_running() and (self.auto or self.auto_timer is not None)

    def start(self, direction, auto):
        cancel_drag_scroll()
        if self.wait:
            return

        now = window.performance.now()
        self.end_time = now + self.DURATION
        self.stop_auto_spine_transition()

        if not self.is_running() or direction is not self.direction or auto is not self.auto:
            if self.auto and not auto:
                self.pause()
            self.stop()
            self.auto = auto
            self.direction = direction
            self.start_time = now
            self.start_offset = scroll_viewport.block_pos()
            self.csi_idx = current_spine_item().index
            self.animation_id = window.requestAnimationFrame(self.auto_scroll if auto else self.smooth_scroll)

    def smooth_scroll(self, ts):
        duration = self.end_time - self.start_time
        if duration <= 0:
            self.animation_id = None
            return
        progress = max(0, min(1, (ts - self.start_time) / duration)) # max/min to account for jitter
        scroll_target = self.start_offset
        scroll_target += Math.trunc(self.direction * progress * duration * line_height() * opts.lines_per_sec_smooth) / 1000

        scroll_viewport.scroll_to_in_block_direction(scroll_target)
        amt = scroll_viewport.block_pos() - self.start_offset

        if is_scroll_end(scroll_target) and (not opts.scroll_stop_boundaries or (abs(amt) < 3 and duration is self.DURATION)):
            # "Turn the page" if stop at boundaries option is false or
            # this is a new scroll action and we were already at the end
            self.animation_id = None
            self.wait = True
            report_human_scroll(amt)
            get_boss().send_message('next_spine_item', previous=self.direction is DIRECTION.Up)
        elif progress < 1:
            self.animation_id = window.requestAnimationFrame(self.smooth_scroll)
        elif self.paused:
            self.resume()
        else:
            self.animation_id = None
            report_human_scroll(amt)

    def auto_scroll(self, ts):
        elapsed = max(0, ts - self.start_time) # max to account for jitter
        scroll_target = self.start_offset
        scroll_target += Math.trunc(self.direction * elapsed * line_height() * opts.lines_per_sec_auto) / 1000

        scroll_viewport.scroll_to_in_block_direction(scroll_target)
        scroll_finished = is_scroll_end(scroll_target)

        # report every second
        if elapsed >= 1000:
            self.sync(ts)

        if scroll_finished:
            self.pause()
            if opts.scroll_auto_boundary_delay >= 0:
                self.auto_timer = setTimeout(self.request_next_spine_item, opts.scroll_auto_boundary_delay * 1000)
        else:
            self.animation_id = window.requestAnimationFrame(self.auto_scroll)

    def request_next_spine_item(self):
        self.auto_timer = None
        get_boss().send_message('next_spine_item', previous=self.direction is DIRECTION.Up)

    def report(self):
        amt = scroll_viewport.block_pos() - self.start_offset
        if abs(amt) > 0 and self.csi_idx is current_spine_item().index:
            report_human_scroll(amt)

    def sync(self, ts):
        if self.auto:
            self.report()
            self.csi_idx = current_spine_item().index
            self.start_time = ts or window.performance.now()
            self.start_offset = scroll_viewport.block_pos()
        else:
            self.resume()

    def stop(self):
        self.auto = False
        if self.animation_id is not None:
            window.cancelAnimationFrame(self.animation_id)
            self.animation_id = None
            self.report()
        self.stop_auto_spine_transition()

    def stop_auto_spine_transition(self):
        if self.auto_timer is not None:
            clearTimeout(self.auto_timer)
            self.auto_timer = None
            self.paused = False

    def pause(self):
        if self.auto:
            self.paused = self.direction
            self.stop()
        else:
            self.paused = False

    # Resume auto-scroll
    def resume(self):
        if self.paused:
            self.start(self.paused, True)
            self.paused = False

scroll_animator = ScrollAnimator()


class FlickAnimator:

    SPEED_FACTOR = 0.04
    DECEL_TIME_CONSTANT = 325  # milliseconds
    VELOCITY_HISTORY = 300  # milliseconds
    MIMUMUM_VELOCITY = 100  # pixels/sec

    def __init__(self):
        self.animation_id = None

    def start(self, gesture):
        cancel_drag_scroll()
        self.vertical = gesture.axis is 'vertical'
        now = window.performance.now()
        points = times = None
        for i, t in enumerate(gesture.times):
            if now - t < self.VELOCITY_HISTORY:
                points, times = gesture.points[i:], gesture.times[i:]
                break
        if times and times.length > 1:
            elapsed = (times[-1] - times[0]) / 1000
            if elapsed > 0 and points.length > 1:
                delta = points[0] - points[-1]
                velocity = delta / elapsed
                if abs(velocity) > self.MIMUMUM_VELOCITY:
                    self.amplitude = self.SPEED_FACTOR * velocity
                    self.start_time = now
                    self.animation_id = window.requestAnimationFrame(self.auto_scroll)

    def auto_scroll(self, ts):
        if self.animation_id is None:
            return
        elapsed = window.performance.now() - self.start_time
        delta = self.amplitude * Math.exp(-elapsed / self.DECEL_TIME_CONSTANT)
        if abs(delta) >= 1:
            delta = Math.round(delta)
            if self.vertical:
                window.scrollBy(0, delta)
            else:
                window.scrollBy(delta, 0)
            self.animation_id = window.requestAnimationFrame(self.auto_scroll)

    def stop(self):
        if self.animation_id is not None:
            window.cancelAnimationFrame(self.animation_id)
            self.animation_id = None

flick_animator = FlickAnimator()


class DragScroller:

    DURATION = 100 # milliseconds

    def __init__(self):
        self.animation_id = None
        self.direction = 1
        self.speed_factor = 1
        self.start_time = self.end_time = 0
        self.start_offset = 0

    def is_running(self):
        return self.animation_id is not None

    def smooth_scroll(self, ts):
        duration = self.end_time - self.start_time
        if duration <= 0:
            self.animation_id = None
            self.start(self.direction, self.speed_factor)
            return
        progress = max(0, min(1, (ts - self.start_time) / duration)) # max/min to account for jitter
        scroll_target = self.start_offset
        scroll_target += Math.trunc(self.direction * progress * duration * line_height() * opts.lines_per_sec_smooth * self.speed_factor) / 1000
        scroll_viewport.scroll_to_in_block_direction(scroll_target)

        if progress < 1:
            self.animation_id = window.requestAnimationFrame(self.smooth_scroll)
        else:
            self.animation_id = None
            self.start(self.direction, self.speed_factor)

    def start(self, direction, speed_factor):
        now = window.performance.now()
        self.end_time = now + self.DURATION
        if not self.is_running() or direction is not self.direction or speed_factor is not self.speed_factor:
            self.stop()
            self.direction = direction
            self.speed_factor = speed_factor
            self.start_time = now
            self.start_offset = scroll_viewport.block_pos()
            self.animation_id = window.requestAnimationFrame(self.smooth_scroll)

    def stop(self):
        if self.animation_id is not None:
            window.cancelAnimationFrame(self.animation_id)
            self.animation_id = None


drag_scroller = DragScroller()


def cancel_drag_scroll():
    drag_scroller.stop()


def start_drag_scroll(delta):
    limit = opts.margin_top if delta < 0 else opts.margin_bottom
    direction = 1 if delta >= 0 else -1
    speed_factor = min(abs(delta), limit) / limit
    speed_factor *= (2 - speed_factor)  # QuadOut Easing curve
    drag_scroller.start(direction, 2 * speed_factor)


def handle_gesture(gesture):
    flick_animator.stop()
    if gesture.type is 'swipe':
        if gesture.points.length > 1 and not gesture.is_held:
            delta = gesture.points[-2] - gesture.points[-1]
            if Math.abs(delta) >= 1:
                if gesture.axis is 'vertical':
                    # Vertical writing scrolls left and right,
                    # so doing a vertical flick shouldn't change pages.
                    if scroll_viewport.vertical_writing_mode:
                        scroll_viewport.scroll_by(delta, 0)
                    # However, it might change pages in horizontal writing
                    else:
                        scroll_by_and_check_next_page(delta)
                else:
                    # A horizontal flick should check for new pages in
                    # vertical modes, since they flow left and right.
                    if scroll_viewport.vertical_writing_mode:
                        scroll_by_and_check_next_page(delta)
                    # In horizontal modes, just move by the delta.
                    else:
                        scroll_viewport.scroll_by(delta, 0)
        if not gesture.active and not gesture.is_held:
            flick_animator.start(gesture)
    elif gesture.type is 'prev-page':
        # should flip = False - previous is previous whether RTL or LTR.
        # flipping of this command is handled higher up
        scroll_by_page(-1, False)
    elif gesture.type is 'next-page':
        # should flip = False - next is next whether RTL or LTR.
        # flipping of this command is handled higher up
        scroll_by_page(1, False)


anchor_funcs = {
    'pos_for_elem': def pos_for_elem(elem):
        if not elem:
            return {'block': 0, 'inline': 0}
        br = elem.getBoundingClientRect()

        # Start of object in the scrolling direction
        return {
            'block': scroll_viewport.viewport_to_document_block(scroll_viewport.rect_block_start(br), elem.ownerDocument),
            'inline': scroll_viewport.viewport_to_document_inline(scroll_viewport.rect_inline_start(br), elem.ownerDocument)
        }
    ,
    'visibility': def visibility(pos):
        q = pos.block
        # Have to negate X if in RTL for the math to be correct,
        # as the value that the scroll viewport returns is negated
        if scroll_viewport.vertical_writing_mode and scroll_viewport.rtl:
            q = -q

        if q + 1 < scroll_viewport.block_pos():
            # the + 1 is needed for visibility when top aligned, see: https://bugs.launchpad.net/calibre/+bug/1924890
            return -1
        if q <= scroll_viewport.block_pos() + scroll_viewport.block_size():
            return 0
        return 1
    ,
    'cmp': def cmp(a, b):
        return (a.block - b.block) or (a.inline - b.inline)
    ,
}


def auto_scroll_action(action):
    if action is 'toggle':
        toggle_autoscroll()
    elif action is 'start':
        if not is_auto_scroll_active():
            toggle_autoscroll()
    elif action is 'stop':
        if is_auto_scroll_active():
            toggle_autoscroll()
    elif action is 'resume':
        auto_scroll_resume()
    return is_auto_scroll_active()


def closest_preceding_element(p):
    while p and not p.scrollIntoView:
        p = p.previousSibling or p.parentNode
    return p


def ensure_selection_visible():
    s = window.getSelection()
    p = s.anchorNode
    if not p:
        return
    p = closest_preceding_element(p)
    if p?.scrollIntoView:
        p.scrollIntoView()
    r = s.getRangeAt(0)
    if not r:
        return
    rect = r.getBoundingClientRect()
    if not rect:
        return
    if rect.top < 0 or rect.top >= window.innerHeight or rect.left < 0 or rect.left >= window.innerWidth:
        wrapper = document.createElement('span')
        wrap_range(r, wrapper)
        wrapper.scrollIntoView()
        unwrap(wrapper)


def ensure_selection_boundary_visible(use_end):
    sel = window.getSelection()
    try:
        rr = sel.getRangeAt(0)
    except:
        rr = None
    if rr:
        r = rr.getBoundingClientRect()
        if r:
            node = sel.focusNode if use_end else sel.anchorNode
            x = scroll_viewport.rect_inline_end(r) if use_end else scroll_viewport.rect_inline_start(r)
            if x < 0 or x >= window.innerWidth:
                x = scroll_viewport.viewport_to_document_inline(x, doc=node.ownerDocument)
                if use_end:
                    x -= line_height()
                scroll_viewport.scroll_to_in_inline_direction(x, True)
            y = scroll_viewport.rect_block_end(r) if use_end else scroll_viewport.rect_block_start(r)
            if y < 0 or y >= window.innerHeight:
                y = scroll_viewport.viewport_to_document_block(y, doc=node.ownerDocument)
                if use_end:
                    y -= line_height()
                scroll_viewport.scroll_to_in_block_direction(y, True)


def jump_to_cfi(cfi):
    # Jump to the position indicated by the specified conformal fragment
    # indicator.
    cfi_scroll_to(cfi, def(x, y):
        # block is vertical if text is horizontal
        if scroll_viewport.horizontal_writing_mode:
            scroll_viewport.scroll_to_in_block_direction(y)
        # block is horizontal if text is vertical
        else:
            scroll_viewport.scroll_to_in_block_direction(x)
    )
