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main.lua (42930 bytes)

 --[[--
 SubRead read-along.
 
 A SubRead subtitle file (.srt) holds the text of the book as cue text, and the
 time when the narrator reads each line as cue times. This plugin runs a clock
 with the audio player and keeps the place of the narration on the screen.
 
 Only crengine documents (EPUB, FB2, TXT, HTML) are supported. PDF and DjVu
 have no xpointer, so the place cannot be followed.
 
 @module koplugin.SubRead
 --]]--
 
 local ButtonDialog = require("ui/widget/buttondialog")
 local DateTimeWidget = require("ui/widget/datetimewidget")
 local Device = require("device")
 local DictQuickLookup = require("ui/widget/dictquicklookup")
 local Dispatcher = require("dispatcher")
 local InfoMessage = require("ui/widget/infomessage")
 local Notification = require("ui/widget/notification")
 local SpinWidget = require("ui/widget/spinwidget")
 local UIManager = require("ui/uimanager")
 local WidgetContainer = require("ui/widget/container/widgetcontainer")
 local datetime = require("datetime")
 local logger = require("logger")
 local time = require("ui/time")
 local util = require("util")
 local _ = require("gettext")
 local C_ = _.pgettext
 local T = require("ffi/util").template
 
 local Clock = require("subread.clock")
 local Cues = require("subread.cues")
 local PlayerState = require("subread.player_state")
 local Srt = require("subread.srt")
 local Text = require("subread.text")
 
 -- Search flags of the crengine full text search. The list is in
 -- frontend/apps/reader/modules/readersearch.lua:33-41.
 -- 0x00FF is every flag except IGNORE_DIACRITICS, the same value that
 -- KOReader itself uses by default (readersearch.lua:50). The plugin needs
 -- MATCH_ACROSS_TEXT_NODES (0x0001), because a cue often runs over an inline
 -- tag, and FOLD_SPACES (0x0020), because the white space of the cue text and
 -- of the book text is not the same.
 local SEARCH_FLAGS = 0x00FF
 -- Stop the search after this many hits. A small number keeps a search that
 -- hits early cheap. See readersearch.lua:61.
 local SEARCH_MAX_HITS = 20
 -- findText origin: -1 whole book, 0 from the current page, 1 after the
 -- current page. See ReaderSearch:searchFromStart and searchFromCurrent,
 -- readersearch.lua:708-724.
 local SEARCH_WHOLE_BOOK = -1
 local SEARCH_FROM_CURRENT_PAGE = 0
 -- findText direction: 0 forward, 1 backward. See readersearch.lua:29.
 local SEARCH_FORWARD = 0
 
 -- The tick never sleeps longer than this, so a change of speed or a device
 -- suspend cannot make the follow late for long.
 local MAX_SLEEP = 30
 local MIN_SLEEP = 0.05
 -- After a cue is not found, the plugin waits this many cues before it
 -- searches again. The wait doubles with each miss. A failed search reads the
 -- book to its end, so this limits the cost when the book misses a stretch.
 local MISS_BACKOFF_MAX = 16
 
 -- Seconds between two reads of the audio player. The player reports its
 -- position and speed, so the clock is exact between two reads. A read only
 -- has to notice a pause, a seek or a new speed.
 local PLAYER_POLL = 2
 -- Seconds between two reads while no player has a media session.
 local PLAYER_POLL_IDLE = 5
 -- A player position this many seconds away from the clock is a seek.
 local PLAYER_JUMP = 3
 -- Seconds between two checks for the end of a dictionary lookup.
 local LOOKUP_POLL = 0.5
 -- The lookup window can open late. Give up the wait for it after this many
 -- checks and start the player again.
 local LOOKUP_WAIT_MAX = 20
 
 -- Characters of cue text shown in a dialog title.
 local TITLE_CHARS = 60
 -- Characters kept from a selection when the user syncs by selecting text.
 -- A long selection can hold the text of more than one cue.
 local SYNC_NEEDLE_CHARS = 24
 
 -- Per book settings, kept in the book's sidecar file.
 local SETTING_FILE = "subread_srt_file"
 local SETTING_POSITION = "subread_position"
 local SETTING_SPEED = "subread_speed"
 local SETTING_OFFSET = "subread_offset"
 -- Global setting: follow the audio player through SubRead Overlay.
 local SETTING_FOLLOW_PLAYER = "subread_follow_player"
 
 local SubRead = WidgetContainer:extend{
     name = "subread",
     is_doc_only = true,
 }
 
 function SubRead:init()
     self.clock = Clock.new()
     self.cues = nil            -- Cues index, built when the file is read
     self.srt_path = nil
     self.current_index = nil   -- cue shown now
     self.located = {}          -- cue index -> { start xpointer, end xpointer }
     self.last_xpointer = nil   -- place of the last found cue
     self.miss_streak = 0
     self.retry_from_index = 0
     self.manual_seek = false
     self.scheduled = false
     self.tick_task = function() self:_tick() end
 
     -- The bridge to the audio player. Only Android has one.
     self.player = nil
     if Device:isAndroid() then
         local ok, module = pcall(require, "subread.android_player")
         if ok then
             self.player = module
         else
             logger.warn("SubRead: no player bridge:", module)
         end
     end
     self.player_on = false      -- true while the follow reads the player
     self.player_status = nil    -- "no_player" while the player has no media session
     self.lookup_paused = false  -- true while the player waits for a dictionary lookup
     self.lookup_external = false
     self.lookup_seen = false
     self.lookup_waited = 0
     self.lookup_task = function() self:_checkLookupDone() end
     self.skip_player_read = false
 
     self:placeInToolsMenu()
     self.ui.menu:registerToMainMenu(self)
     if self:isSupported() then
         self:registerDispatcherActions()
         self:addToHighlightDialog()
     end
 end
 
 function SubRead:isSupported()
     -- self.ui.rolling exists only for crengine documents (readerui.lua:382).
     return self.ui.rolling ~= nil
 end
 
 --- True when the user wants the follow to read the audio player.
 function SubRead:followsPlayer()
     return self.player ~= nil and G_reader_settings:nilOrTrue(SETTING_FOLLOW_PLAYER)
 end
 
 --- Puts the menu entry first in the Tools menu, so it is on the first page.
 -- ReaderMenu sorts the entries with the cached order module
 -- (readermenu.lua:350). An id that is not in the order goes to the end of
 -- the menu, which is the second page.
 function SubRead:placeInToolsMenu()
     local ok, order = pcall(require, "ui/elements/reader_menu_order")
     if ok and type(order) == "table" and type(order.tools) == "table"
         and not util.arrayContains(order.tools, "subread") then
         table.insert(order.tools, 1, "subread")
     end
 end
 
 function SubRead:registerDispatcherActions()
     Dispatcher:registerAction("subread_controls",
         { category = "none", event = "SubReadShowControls",
           title = _("SubRead: controls"), rolling = true })
     Dispatcher:registerAction("subread_toggle",
         { category = "none", event = "SubReadToggle",
           title = _("SubRead: start or pause"), rolling = true })
     Dispatcher:registerAction("subread_sync_page",
         { category = "none", event = "SubReadSyncToPage",
           title = _("SubRead: sync to this page"), rolling = true, separator = true })
 end
 
 --[[-- Settings ]]--
 
 function SubRead:onReadSettings(config)
     self.srt_path = config:readSetting(SETTING_FILE)
     self.clock = Clock.new{
         position = config:readSetting(SETTING_POSITION) or 0,
         speed = config:readSetting(SETTING_SPEED) or 1.0,
         offset = config:readSetting(SETTING_OFFSET) or 0,
     }
 end
 
 function SubRead:onReaderReady()
     if not self:isSupported() then return end
     if self.srt_path and not util.fileExists(self.srt_path) then
         logger.info("SubRead: saved subtitle file is gone:", self.srt_path)
         self.srt_path = nil
     end
     if not self.srt_path then
         self.srt_path = self:findSubtitleBeside(self.ui.document.file)
     end
 end
 
 function SubRead:onSaveSettings()
     self:saveState()
 end
 
 function SubRead:saveState()
     local settings = self.ui.doc_settings
     if not settings then return end
     if not self.srt_path then
         -- Leave no keys in the sidecar file of a book that does not use the
         -- plugin, and clear them when the user forgets the subtitle file.
         settings:delSetting(SETTING_FILE)
         settings:delSetting(SETTING_POSITION)
         settings:delSetting(SETTING_SPEED)
         settings:delSetting(SETTING_OFFSET)
         return
     end
     settings:saveSetting(SETTING_FILE, self.srt_path)
     settings:saveSetting(SETTING_POSITION, self.clock:getPosition(self:_now()))
     settings:saveSetting(SETTING_SPEED, self.clock.speed)
     settings:saveSetting(SETTING_OFFSET, self.clock.offset)
 end
 
 function SubRead:onCloseDocument()
     self:stop()
 end
 
 function SubRead:onCloseWidget()
     self:_unschedule()
     self:_endLookupWait()
     self.tick_task = nil
 end
 
 --- Looks for <book>.srt or <book>.<lang>.srt beside the book file.
 function SubRead:findSubtitleBeside(book_path)
     if not book_path then return nil end
     local directory, file_name = util.splitFilePathName(book_path)
     local base = util.splitFileNameSuffix(file_name)
     if base == "" then return nil end
     local candidate = directory .. base .. ".srt"
     if util.fileExists(candidate) then return candidate end
     -- <book>.<lang>.srt, for example "Dracula.en.srt". The language part is
     -- any name without a dot, so the loop does not need a list of languages.
     local lfs = require("libs/libkoreader-lfs")
     local ok, iterator = pcall(lfs.dir, directory == "" and "." or directory)
     if not ok or type(iterator) ~= "function" then return nil end
     local prefix = base .. "."
     for entry in iterator do
         if entry:sub(1, #prefix) == prefix and entry:sub(-4):lower() == ".srt" then
             local middle = entry:sub(#prefix + 1, -5)
             if middle ~= "" and not middle:find(".", 1, true) then
                 return directory .. entry
             end
         end
     end
     return nil
 end
 
 --[[-- Subtitle file ]]--
 
 --- Reads the subtitle file. Returns true when the index is ready.
 function SubRead:loadSubtitles()
     if self.cues then return true end
     if not self.srt_path then
         self:showMessage(_("No SubRead subtitle file is loaded for this book."))
         return false
     end
     local list, err = Srt.parseFile(self.srt_path)
     if not list then
         self:showMessage(T(_("Could not read the subtitle file:\n%1"), tostring(err)))
         return false
     end
     if #list == 0 then
         self:showMessage(_("The subtitle file holds no cues."))
         return false
     end
     self.cues = Cues.new(list)
     self.located = {}
     logger.info("SubRead: loaded", #list, "cues from", self.srt_path)
     return true
 end
 
 function SubRead:setSubtitleFile(path)
     self:stop()
     self.srt_path = path
     self.cues = nil
     self.located = {}
     self.current_index = nil
     self.last_xpointer = nil
     self:saveState()
 end
 
 function SubRead:chooseSubtitleFile(touchmenu_instance)
     local PathChooser = require("ui/widget/pathchooser")
     local directory = util.splitFilePathName(self.ui.document.file)
     UIManager:show(PathChooser:new{
         title = _("Select a SubRead subtitle file"),
         path = directory,
         select_directory = false,
         -- With a file_filter set, FileChooser shows only the files that pass
         -- it, even if they are not a book (filechooser.lua:92).
         file_filter = function(file_name)
             return file_name:sub(-4):lower() == ".srt"
         end,
         onConfirm = function(file_path)
             self:setSubtitleFile(file_path)
             if touchmenu_instance then touchmenu_instance:updateItems() end
         end,
     })
 end
 
 --[[-- The clock ]]--
 
 --- Returns a monotonic time in seconds.
 -- getElapsedTimeSinceBoot adds the time in standby and in suspend
 -- (uimanager.lua:1133), so the follow stays right when the device sleeps
 -- while the audio player runs on.
 function SubRead:_now()
     return time.to_number(UIManager:getElapsedTimeSinceBoot())
 end
 
 --[[-- The audio player ]]--
 
 --- Reads the state of the audio player through SubRead Overlay.
 -- @return the state table of PlayerState.parse, or nil and an error name:
 --   "not_installed", "no_notification_access" or "no_player".
 function SubRead:_readPlayer()
     local line = self.player.query()
     if not line then return nil, "not_installed" end
     return PlayerState.parse(line)
 end
 
 --- Sets the clock from the audio player.
 -- Returns true when the follow can go on with the player. Returns false when
 -- the player cannot be reached at all; the follow then runs its own clock.
 function SubRead:_syncClockToPlayer(now)
     local state, err = self:_readPlayer()
     if not state then
         if err == "no_player" then
             -- The player app is closed, or it has no session yet. Keep the
             -- place and read again later.
             self.player_status = err
             self.clock:pause(now)
             return true
         end
         self.player_on = false
         self.player_status = nil
         self:showMessage(self:playerProblemText(err))
         return false
     end
     self.player_status = nil
     if state.position then
         -- A seek in the player app can go backward. The normal search runs
         -- forward from the current page, so treat a jump like a seek that
         -- the user asked for here.
         local jumped = math.abs(state.position - self.clock:getPosition(now)) > PLAYER_JUMP
         self.clock:setSpeed(state.speed, now)
         self.clock:seek(state.position, now)
         if jumped then self:_manualSeek() end
     end
     if state.playing then
         self.clock:start(now)
     else
         self.clock:pause(now)
     end
     return true
 end
 
 function SubRead:playerProblemText(err)
     if err == "no_notification_access" then
         return _("SubRead Overlay has no notification access, so the audio player cannot be read. Give it the access in its app. Until then the plugin runs its own clock.")
     end
     return _("SubRead Overlay was not found. Install it and give it notification access, so the plugin can follow the audio player. Until then the plugin runs its own clock.")
 end
 
 --- Sends play or pause to the player when the follow reads it.
 function SubRead:_playerCall(method)
     if not self.player_on then return end
     self.player.call(method)
     self.skip_player_read = true
 end
 
 --- Moves the clock, and the player when the follow reads it.
 -- The player takes a moment for a seek or a play. The read that comes at
 -- once after would bring the old state back, so that one read is skipped.
 function SubRead:_seekTo(position, now)
     self.clock:seek(position, now)
     if self.player_on then
         self.player.call("seek", PlayerState.seekArgument(self.clock:getPosition(now)))
         self.skip_player_read = true
     end
 end
 
 --[[-- Start, pause and stop ]]--
 
 function SubRead:start()
     if not self:checkSupported() then return end
     if not self:loadSubtitles() then return end
     local now = self:_now()
     if self:followsPlayer() then
         self.player_on = true
         if self:_syncClockToPlayer(now) then
             self:_playerCall("play")
         end
     end
     if not self.player_on then
         if self.clock:getPosition(now) <= 0 then
             local index = self:cueIndexForCurrentPage()
             if index then
                 self.clock:seekCueTime(self.cues:get(index).start, now)
             end
         end
     end
     -- The player takes a moment to start. The next read confirms the state.
     if self.player_status ~= "no_player" then
         self.clock:start(now)
     end
     -- The reader may have moved the view since the last pause, so drop the
     -- lower limit and let the search start at the page that is shown.
     self.last_xpointer = nil
     self.miss_streak = 0
     self.retry_from_index = 0
     self.current_index = nil -- force a redraw of the cue that is on
     self:_tick()
 end
 
 function SubRead:pause()
     local now = self:_now()
     self.clock:pause(now)
     self:_playerCall("pause")
     if self.player_on then
         -- Keep the reads, so a start from the player app is seen.
         self:_schedule(now, self.clock:getCueTime(now))
     else
         self:_unschedule()
     end
     self:saveState()
 end
 
 function SubRead:stop()
     if self.clock:isRunning() then
         self.clock:pause(self:_now())
     end
     self:_endLookupWait()
     self.player_on = false
     self.player_status = nil
     self:_unschedule()
     if self:isSupported() and self.ui.document then
         self.ui.document:clearSelection()
     end
     self:saveState()
 end
 
 --- True when the follow runs: the clock, or the reads of the player.
 function SubRead:isActive()
     return self.clock:isRunning() or self.player_on
 end
 
 function SubRead:toggle()
     if self.clock:isRunning() then
         self:pause()
     else
         self:start()
     end
 end
 
 --- Prepares for a jump that the user asked for.
 -- The user can jump backward, but the normal search only runs forward from
 -- the current page. After a manual jump the next search reads the whole book
 -- and uses the place of the nearest cue found before as its lower limit.
 function SubRead:_manualSeek()
     self.manual_seek = true
     self.miss_streak = 0
     self.retry_from_index = 0
     self.current_index = nil
 end
 
 --- Moves the clock and shows the new place at once.
 function SubRead:seekAndShow(position)
     local now = self:_now()
     self:_seekTo(position, now)
     self:_manualSeek()
     self:_tick()
 end
 
 function SubRead:skipCues(count)
     if not self:loadSubtitles() then return end
     local now = self:_now()
     local index = self.cues:findNearest(self.clock:getCueTime(now))
     if not index then return end
     index = index + count
     if index < 1 then index = 1 end
     if index > self.cues:count() then index = self.cues:count() end
     self:_seekTo(self.cues:get(index).start + self.clock.offset, now)
     self:_manualSeek()
     self:_tick()
 end
 
 --[[-- The follow loop ]]--
 
 function SubRead:_unschedule()
     if self.scheduled then
         UIManager:unschedule(self.tick_task)
         self.scheduled = false
     end
 end
 
 --- One step of the follow loop.
 -- The screen is only touched when the cue changes, never on a bare timer tick.
 function SubRead:_tick()
     self.scheduled = false
     if not self.cues then return end
     local now = self:_now()
     if self.player_on and not self.skip_player_read then
         self:_syncClockToPlayer(now)
     end
     self.skip_player_read = false
     local cue_time = self.clock:getCueTime(now)
     local index = self.cues:findByTime(cue_time)
     if index and index ~= self.current_index then
         self.current_index = index
         self:showCue(index)
     end
     self:_schedule(now, cue_time)
 end
 
 --- Sleeps until the next cue starts, or the next read of the player, or
 --- MAX_SLEEP, whichever is first.
 function SubRead:_schedule(now, cue_time)
     self:_unschedule()
     local delay = MAX_SLEEP
     if self.player_on then
         delay = self.player_status == "no_player" and PLAYER_POLL_IDLE or PLAYER_POLL
     elseif not self.clock:isRunning() then
         return
     end
     local next_index = self.cues:nextAfter(cue_time)
     if next_index then
         local wait = self.clock:realSecondsUntilCueTime(self.cues:get(next_index).start, now)
         if wait and wait < delay then delay = wait end
     end
     if delay < MIN_SLEEP then delay = MIN_SLEEP end
     UIManager:scheduleIn(delay, self.tick_task)
     self.scheduled = true
 end
 
 --- True when the xpointer is at or after the lower limit.
 function SubRead:_isAtOrAfter(floor_xpointer, xpointer)
     if not floor_xpointer then return true end
     -- compareXPointers returns 1 when xp2 is after xp1, 0 when they are the
     -- same, -1 when not, nil when one of them is not valid
     -- (credocument.lua:750-754).
     local order = self.ui.document:compareXPointers(floor_xpointer, xpointer)
     return order == nil or order >= 0
 end
 
 -- How many cues back to look for a place that is already known.
 local FLOOR_LOOKBACK = 50
 
 --- Returns the place of the nearest cue before index that is already found.
 function SubRead:_floorFor(index)
     local first = index - FLOOR_LOOKBACK
     if first < 1 then first = 1 end
     for at = index - 1, first, -1 do
         local found = self.located[at]
         if found then return found[1] end
     end
     return nil
 end
 
 --- Finds the place of a cue in the book.
 -- The search starts at the current page and runs forward, so the plugin never
 -- reads the whole book for every cue. Hits before the last found place are
 -- dropped, so a word that comes again on the same page cannot pull the
 -- follow backward.
 -- @return start xpointer, end xpointer, or nil
 function SubRead:_locate(index)
     local cached = self.located[index]
     if cached then
         self.manual_seek = false
         return cached[1], cached[2]
     end
     local cue = self.cues:get(index)
     if not cue or cue.no_place then return nil end
 
     local origin, floor = SEARCH_FROM_CURRENT_PAGE, self.last_xpointer
     if self.manual_seek then
         self.manual_seek = false
         origin, floor = SEARCH_WHOLE_BOOK, self:_floorFor(index)
     end
 
     local document = self.ui.document
     for _, anchor in ipairs(Text.anchors(cue.norm)) do
         -- findText(pattern, origin, direction, case_insensitive, page, regex,
         -- max_hits, search_flags) (credocument.lua:1442). Each hit holds the
         -- xpointers "start" and "end" (readersearch.lua:446-447).
         local hits = document:findText(anchor, origin, SEARCH_FORWARD,
             true, self.view.state.page, false, SEARCH_MAX_HITS, SEARCH_FLAGS)
         if hits then
             for _, hit in ipairs(hits) do
                 if hit.start and self:_isAtOrAfter(floor, hit.start) then
                     local pos1 = hit["end"]
                     if Text.len(anchor) < Text.len(cue.norm) then
                         pos1 = self:_cueEnd(cue, hit.start, pos1)
                     end
                     self.located[index] = { hit.start, pos1 }
                     return hit.start, pos1
                 end
             end
         end
     end
     return nil
 end
 
 -- The text between the start of a cue and the end of its tail may hold ruby
 -- text, so it can be longer than the cue. A hit further away than this
 -- factor is a tail that belongs to another line.
 local CUE_END_SLACK = 2
 
 --- Finds the end of the cue text, so the mark covers the whole line.
 -- The anchor is only the first characters of the cue. The tail of the cue is
 -- searched forward from the current page, and the first hit after the start
 -- that lies close to it gives the end. When the tail is not found, the end
 -- of the anchor stays.
 function SubRead:_cueEnd(cue, pos0, anchor_end)
     local tail = Text.tail(cue.norm)
     if not tail then return anchor_end end
     local document = self.ui.document
     local hits = document:findText(tail, SEARCH_FROM_CURRENT_PAGE, SEARCH_FORWARD,
         true, self.view.state.page, false, SEARCH_MAX_HITS, SEARCH_FLAGS)
     if not hits then return anchor_end end
     local limit = Text.len(cue.norm) * CUE_END_SLACK + Text.TAIL_LENGTH
     for _, hit in ipairs(hits) do
         if hit.start and hit["end"] and self:_isAtOrAfter(pos0, hit.start) then
             local between = document:getTextFromXPointers(pos0, hit["end"], false)
             if between and Text.len(Text.normalize(between)) <= limit then
                 return hit["end"]
             end
             -- The first hit after the start is already too far.
             return anchor_end
         end
     end
     return anchor_end
 end
 
 --- Brings the cue on screen and marks it.
 function SubRead:showCue(index)
     local cue = self.cues:get(index)
     if not cue or cue.no_place then return end
     -- After a miss, do not search again for the next few cues.
     if index < self.retry_from_index then return end
 
     local pos0, pos1 = self:_locate(index)
     if not pos0 then
         self.miss_streak = self.miss_streak + 1
         local step = math.floor(2 ^ (self.miss_streak - 1))
         if step > MISS_BACKOFF_MAX then step = MISS_BACKOFF_MAX end
         self.retry_from_index = index + step
         logger.dbg("SubRead: cue", index, "not found, next try at", self.retry_from_index)
         return
     end
     self.miss_streak = 0
     self.retry_from_index = 0
     self.last_xpointer = pos0
     self:drawCue(pos0, pos1)
     -- Open controls show the clock and the cue of the time when they were built.
     if self.controls_dialog then self:showControls() end
 end
 
 --- Turns the page if needed and draws the mark.
 -- The mark is the crengine selection, the same one that KOReader draws for a
 -- full text search hit (readersearch.lua:946). crengine draws it itself, so
 -- it costs no extra widget, it survives a page turn, and it is never written
 -- into the book's annotations.
 function SubRead:drawCue(pos0, pos1)
     local document = self.ui.document
     local was_visible = document:isXPointerInCurrentPage(pos0)
     if not was_visible then
         self.ui.rolling:onGotoXPointer(pos0)
     end
     if pos1 then
         document:getTextFromXPointers(pos0, pos1, true)
     end
     -- A page turn needs a partial refresh. A mark that moves inside the same
     -- page only needs the light "ui" refresh.
     UIManager:setDirty(self.view.dialog, was_visible and "ui" or "partial")
 end
 
 --- Draws the cue that is on again, after something else used the selection.
 function SubRead:redrawCurrentCue()
     if not self.current_index then return end
     local pos0, pos1 = self:_locate(self.current_index)
     if pos0 then self:drawCue(pos0, pos1) end
 end
 
 --[[-- Page and time ]]--
 
 --- Returns the text of the current page, or nil.
 function SubRead:currentPageText()
     local document = self.ui.document
     local page = document:getCurrentPage()
     if not page then return nil end
     -- getPageXPointer gives the xpointer of the first line of a page
     -- (credocument.lua:888).
     local from_xpointer = document:getPageXPointer(page)
     local to_xpointer = document:getPageXPointer(page + 1)
     if not from_xpointer or not to_xpointer then return nil end
     return document:getTextFromXPointers(from_xpointer, to_xpointer, false)
 end
 
 --- Returns the index of the first cue on the current page, or nil.
 function SubRead:cueIndexForCurrentPage()
     if not self.cues then return nil end
     local page_text = self:currentPageText()
     if not page_text or page_text == "" then return nil end
     local index = self.cues:findIndexForText(page_text)
     -- getTextFromXPointers with draw_selection false can drop the mark, so
     -- put it back.
     if self.clock:isRunning() then self:redrawCurrentCue() end
     return index
 end
 
 function SubRead:showPageTime()
     if not self:checkSupported() then return end
     if not self:loadSubtitles() then return end
     local index = self:cueIndexForCurrentPage()
     if not index then
         self:showMessage(_("No cue of the subtitle file was found on this page."))
         return
     end
     local cue = self.cues:get(index)
     local player_time = cue.start + self.clock.offset
     self:showMessage(T(_("This page starts at %1 in the audio.\n\n%2"),
         datetime.secondsToClock(player_time, false),
         Text.ellipsize(cue.text, TITLE_CHARS)))
 end
 
 function SubRead:syncToPage()
     if not self:checkSupported() then return end
     if not self:loadSubtitles() then return end
     local index = self:cueIndexForCurrentPage()
     if not index then
         self:showMessage(_("No cue of the subtitle file was found on this page."))
         return
     end
     self:syncToCue(index)
 end
 
 --- Sets the clock to the start of a cue. When the follow reads the player,
 --- the audio moves there too.
 function SubRead:syncToCue(index)
     local cue = self.cues:get(index)
     if not cue then return end
     local now = self:_now()
     if self:followsPlayer() and not self.player_on then
         -- "Move the audio to this page" before a start: begin the follow of
         -- the player, so the seek reaches it.
         self.player_on = true
         self:_syncClockToPlayer(now)
     end
     local position = cue.start + self.clock.offset
     self:_seekTo(position, now)
     self:_manualSeek()
     self:_tick()
     local clock_text = datetime.secondsToClock(position, false)
     self:showNotification(self.player_on and T(_("Audio moved to %1"), clock_text)
                                           or T(_("Synced to %1"), clock_text))
 end
 
 --- Text of the action that sets the place: it moves the audio when the
 --- follow reads the player, else the clock of the plugin.
 function SubRead:syncToPageText()
     if self:followsPlayer() then
         return _("Move the audio to this page")
     end
     return _("Sync the clock to this page")
 end
 
 --[[-- Dictionary lookup ]]--
 
 --- ReaderDictionary sends this before it looks a word up
 --- (readerdictionary.lua:1429). The player pauses while the user reads.
 function SubRead:onWordLookedUp()
     if not self.player_on or self.lookup_paused then return end
     local state = self:_readPlayer()
     if not state or not state.playing then return end
     self:_playerCall("pause")
     self.clock:pause(self:_now())
     self.lookup_paused = true
     self.lookup_seen = false
     self.lookup_waited = 0
     -- An external dictionary is another app. KOReader gets a Resume event
     -- when the user comes back (device/android/device.lua:179).
     self.lookup_external = Device:canExternalDictLookup()
         and G_reader_settings:isTrue("external_dict_lookup")
     if not self.lookup_external then
         UIManager:scheduleIn(LOOKUP_POLL, self.lookup_task)
     end
 end
 
 --- Starts the player again when the last lookup window is closed.
 -- DictQuickLookup keeps its open windows in window_list
 -- (dictquicklookup.lua:176) and sends no event when the last one closes.
 function SubRead:_checkLookupDone()
     if not self.lookup_paused then return end
     local open = #DictQuickLookup.window_list > 0
     if open then
         self.lookup_seen = true
     elseif not self.lookup_seen then
         -- The lookup runs before the window opens. Wait for the window.
         self.lookup_waited = self.lookup_waited + 1
         if self.lookup_waited >= LOOKUP_WAIT_MAX then
             self:_resumeAfterLookup()
             return
         end
     end
     if open or not self.lookup_seen then
         UIManager:scheduleIn(LOOKUP_POLL, self.lookup_task)
         return
     end
     self:_resumeAfterLookup()
 end
 
 function SubRead:_endLookupWait()
     UIManager:unschedule(self.lookup_task)
     self.lookup_paused = false
 end
 
 function SubRead:_resumeAfterLookup()
     self:_endLookupWait()
     if not self.player_on then return end
     self:_playerCall("play")
     self.clock:start(self:_now())
     self:_tick()
 end
 
 function SubRead:onResume()
     if self.lookup_paused and self.lookup_external then
         self:_resumeAfterLookup()
     end
 end
 
 --- Sets the clock from a piece of text that the user selected.
 function SubRead:syncToSelectedText(selected)
     if not self:checkSupported() then return end
     if not self:loadSubtitles() then return end
     local needle = Text.normalize(selected or "")
     if Text.len(needle) < 4 then
         self:showMessage(_("Select a few more words, so the line can be found."))
         return
     end
     -- A long selection can hold text of more than one cue, so cut it down.
     if Text.len(needle) > SYNC_NEEDLE_CHARS then
         needle = Text.sub(needle, 1, SYNC_NEEDLE_CHARS)
     end
     local index = self.cues:findIndexContaining(needle)
     if not index then
         self:showMessage(_("That text was not found in the subtitle file."))
         return
     end
     self:syncToCue(index)
 end
 
 function SubRead:addToHighlightDialog()
     -- "13_" sorts after the last button that KOReader itself adds
     -- (readerhighlight.lua:246-261, qrclipboard.koplugin/main.lua:30).
     self.ui.highlight:addToHighlightDialog("13_subread_sync", function(this)
         return {
             text = _("SubRead: sync here"),
             callback = function()
                 local selected = this.selected_text and this.selected_text.text
                 this:onClose(true)
                 self:syncToSelectedText(selected)
             end,
         }
     end)
 end
 
 --[[-- Dialogs ]]--
 
 function SubRead:checkSupported()
     if self:isSupported() then return true end
     self:showMessage(_("SubRead read-along needs an EPUB, FB2, TXT or HTML book. PDF and DjVu are not supported."))
     return false
 end
 
 function SubRead:showMessage(text)
     UIManager:show(InfoMessage:new{ text = text })
 end
 
 function SubRead:showNotification(text)
     UIManager:show(Notification:new{ text = text, timeout = 2 })
 end
 
 function SubRead:statusText()
     local now = self:_now()
     local clock_text = datetime.secondsToClock(self.clock:getPosition(now), false)
     local line
     if self.player_on and self.player_status == "no_player" then
         line = _("No audio player is open")
     elseif self.player_on then
         line = self.clock:isRunning() and T(_("Player: %1, playing"), clock_text)
                                       or T(_("Player: %1, paused"), clock_text)
     else
         line = self.clock:isRunning() and T(_("Clock: %1, running"), clock_text)
                                       or T(_("Clock: %1, paused"), clock_text)
     end
     if self.cues and self.current_index then
         local cue = self.cues:get(self.current_index)
         if cue then
             line = line .. "\n" .. Text.ellipsize(cue.text, TITLE_CHARS)
         end
     end
     return line
 end
 
 function SubRead:closeControls()
     if self.controls_dialog then
         UIManager:close(self.controls_dialog)
         self.controls_dialog = nil
     end
 end
 
 --- Shows the read-along controls. The dialog is built again after each
 --- button, so the title always shows the clock as it is now.
 function SubRead:showControls()
     if not self:checkSupported() then return end
     if not self:loadSubtitles() then return end
     self:closeControls()
 
     local function again(action)
         return function()
             action()
             self:showControls()
         end
     end
 
     self.controls_dialog = ButtonDialog:new{
         title = self:statusText(),
         title_align = "center",
         buttons = {
             {
                 { text = _("Prev. cue"),
                   callback = again(function() self:skipCues(-1) end) },
                 { text = _("-10 s"),
                   callback = again(function() self:seekAndShow(self.clock:getPosition(self:_now()) - 10) end) },
                 { text = _("+10 s"),
                   callback = again(function() self:seekAndShow(self.clock:getPosition(self:_now()) + 10) end) },
                 { text = _("Next cue"),
                   callback = again(function() self:skipCues(1) end) },
             },
             {
                 { text = self.clock:isRunning() and _("Pause") or _("Start"),
                   callback = again(function() self:toggle() end) },
                 { text = _("Stop"),
                   callback = function()
                       self:stop()
                       self:closeControls()
                   end },
             },
             {
                 { text = self:syncToPageText(),
                   callback = again(function() self:syncToPage() end) },
                 { text = _("Go to time…"),
                   callback = function()
                       self:closeControls()
                       self:showGoToTime()
                   end },
             },
             {
                 { text = T(_("Speed: %1"), string.format("%.2f", self.clock.speed)),
                   callback = function()
                       self:closeControls()
                       self:showSpeed()
                   end },
                 { text = T(_("Offset: %1 s"), string.format("%+d", self.clock.offset)),
                   callback = function()
                       self:closeControls()
                       self:showOffset()
                   end },
             },
             {
                 { text = _("What time is this page?"),
                   callback = again(function() self:showPageTime() end) },
             },
         },
     }
     UIManager:show(self.controls_dialog)
 end
 
 function SubRead:showGoToTime()
     if not self:checkSupported() then return end
     if not self:loadSubtitles() then return end
     local position = self.clock:getPosition(self:_now())
     local hour = math.floor(position / 3600)
     local minute = math.floor(position / 60) % 60
     local second = math.floor(position) % 60
     UIManager:show(DateTimeWidget:new{
         title_text = _("Go to time"),
         info_text = _("Enter the position of the audio player."),
         hour = hour,
         hour_max = 99,
         min = minute,
         sec = second,
         ok_text = _("Go"),
         callback = function(widget)
             -- The widget writes the picked values back into itself before it
             -- calls us (datetimewidget.lua:396-406).
             self:seekAndShow(widget.hour * 3600 + widget.min * 60 + widget.sec)
             self:saveState()
         end,
     })
 end
 
 function SubRead:showSpeed()
     UIManager:show(SpinWidget:new{
         title_text = _("Player speed"),
         info_text = _("Set this to the speed of your audio player."),
         value = self.clock.speed,
         value_min = Clock.SPEED_MIN,
         value_max = Clock.SPEED_MAX,
         value_step = 0.05,
         value_hold_step = 0.25,
         precision = "%.2f",
         default_value = 1.0,
         callback = function(widget)
             self.clock:setSpeed(widget.value, self:_now())
             self:saveState()
             self:_tick()
         end,
     })
 end
 
 function SubRead:showOffset()
     UIManager:show(SpinWidget:new{
         title_text = _("Audio offset"),
         info_text = _("Seconds to add to the subtitle times. Use a positive value when the audio file starts with an intro."),
         value = self.clock.offset,
         value_min = -600,
         value_max = 600,
         value_step = 1,
         value_hold_step = 10,
         default_value = 0,
         unit = C_("Time", "s"),
         callback = function(widget)
             self.clock:setOffset(widget.value)
             self:saveState()
             self:_tick()
         end,
     })
 end
 
 --[[-- Events from a gesture or a key ]]--
 
 function SubRead:onSubReadShowControls()
     self:showControls()
     return true
 end
 
 function SubRead:onSubReadToggle()
     if not self:checkSupported() then return true end
     if not self:loadSubtitles() then return true end
     self:toggle()
     if self.player_on then
         self:showNotification(self.clock:isRunning() and _("Audio playing") or _("Audio paused"))
     else
         self:showNotification(self.clock:isRunning() and _("Read-along running") or _("Read-along paused"))
     end
     return true
 end
 
 function SubRead:onSubReadSyncToPage()
     self:syncToPage()
     return true
 end
 
 --[[-- Menu ]]--
 
 function SubRead:subtitleMenuText()
     if not self.srt_path then
         return _("Subtitle file: none")
     end
     local _directory, file_name = util.splitFilePathName(self.srt_path)
     return T(_("Subtitle file: %1"), file_name)
 end
 
 function SubRead:addToMainMenu(menu_items)
     local items = {
         {
             text_func = function() return self:subtitleMenuText() end,
             keep_menu_open = true,
             callback = function(touchmenu_instance)
                 if self:checkSupported() then
                     self:chooseSubtitleFile(touchmenu_instance)
                 end
             end,
             hold_callback = function(touchmenu_instance)
                 self:setSubtitleFile(nil)
                 touchmenu_instance:updateItems()
             end,
             separator = true,
         },
         {
             text_func = function()
                 return self:isActive() and _("Read-along controls")
                                         or _("Start read-along")
             end,
             callback = function(touchmenu_instance)
                 touchmenu_instance:onClose()
                 if not self:checkSupported() then return end
                 if not self:isActive() then
                     -- The controls would cover the line that the narrator reads.
                     -- They open with the same menu entry when the user wants them.
                     self:start()
                     if self:isActive() then
                         self:showNotification(_("Read-along started. The controls are in this menu."))
                     end
                     return
                 end
                 self:showControls()
             end,
         },
         {
             text_func = function() return self:syncToPageText() end,
             callback = function(touchmenu_instance)
                 touchmenu_instance:onClose()
                 self:syncToPage()
             end,
         },
         {
             text = _("Go to time…"),
             keep_menu_open = true,
             callback = function() self:showGoToTime() end,
         },
         {
             text = _("What time is this page?"),
             keep_menu_open = true,
             callback = function() self:showPageTime() end,
             separator = true,
         },
     }
     if self.player then
         table.insert(items, {
             text = _("Follow the audio player"),
             help_text = _("Reads the position of the audio player through the SubRead Overlay app, which needs notification access. Start, pause and the seeks then control the player. When off, the plugin runs its own clock."),
             checked_func = function() return G_reader_settings:nilOrTrue(SETTING_FOLLOW_PLAYER) end,
             callback = function()
                 G_reader_settings:flipNilOrTrue(SETTING_FOLLOW_PLAYER)
                 self:stop()
             end,
             separator = true,
         })
     end
     menu_items.subread = {
         -- placeInToolsMenu puts the id first in the Tools order. The hint is
         -- for a user order file that does not list the id
         -- (menusorter.lua:161-182).
         sorting_hint = "tools",
         text = _("SubRead read-along"),
         sub_item_table = items,
     }
     table.insert(items, {
         text_func = function()
             return T(_("Player speed: %1"), string.format("%.2f", self.clock.speed))
         end,
         -- The player reports its speed, so the setting is for the own clock.
         enabled_func = function() return not self:followsPlayer() end,
         keep_menu_open = true,
         callback = function(touchmenu_instance)
             self:showSpeed()
             if touchmenu_instance then touchmenu_instance:updateItems() end
         end,
     })
     table.insert(items, {
         text_func = function()
             return T(_("Audio offset: %1 s"), string.format("%+d", self.clock.offset))
         end,
         keep_menu_open = true,
         callback = function(touchmenu_instance)
             self:showOffset()
             if touchmenu_instance then touchmenu_instance:updateItems() end
         end,
     })
 end
 
 return SubRead