[UX] Add "Follow Link" in hold/highlight dialog (#3190)

* This way you can disable "tap to follow links" on single tap yet still follow links.
* Change menu as well as per @poire-z's suggestion.

frontend/apps/reader/modules/readerlink.lua

@@ -1,13 +1,17 @@
-local InputContainer = require("ui/widget/container/inputcontainer")
+--[[
+ReaderLink is an abstraction for document-specific link interfaces.
+]]--
+
+local Device = require("device")
+local Event = require("ui/event")
+local Geom = require("ui/geometry")
 local GestureRange = require("ui/gesturerange")
+local InputContainer = require("ui/widget/container/inputcontainer")
 local LinkBox = require("ui/widget/linkbox")
 local UIManager = require("ui/uimanager")
-local Geom = require("ui/geometry")
-local Screen = require("device").screen
-local Device = require("device")
 local logger = require("logger")
-local Event = require("ui/event")
 local _ = require("gettext")
+local Screen = Device.screen
 local T = require("ffi/util").template
 
 local ReaderLink = InputContainer:new{
@@ -55,8 +59,8 @@ function ReaderLink:initGesListener()
     end
 end
 
-local function isFollowLinksOn()
-    return G_reader_settings:readSetting("follow_links") ~= false
+local function isTapToFollowLinksOn()
+    return not G_reader_settings:isFalse("tap_to_follow_links")
 end
 
 local function isSwipeToGoBackEnabled()
@@ -70,22 +74,24 @@ end
 function ReaderLink:addToMainMenu(menu_items)
     -- insert table to main reader menu
     menu_items.follow_links = {
-        text = _("Follow links"),
+        text = _("Links"),
         sub_item_table = {
             {
-                text_func = function()
-                    return isFollowLinksOn() and _("Disable") or _("Enable")
-                end,
-                callback = function()
-                    G_reader_settings:saveSetting("follow_links",
-                        not isFollowLinksOn())
-                end
-            },
-            {
-                text = _("Go back"),
+                text = _("Go back to previous location"),
                 enabled_func = function() return #self.location_stack > 0 end,
                 callback = function() self:onGoBackLink() end,
+                separator = true,
             },
+            {
+                text = _("Tap to follow links"),
+                checked_func = isTapToFollowLinksOn,
+                callback = function()
+                    G_reader_settings:saveSetting("tap_to_follow_links",
+                        not isTapToFollowLinksOn())
+                end,
+                separator = true,
+            },
+
             {
                 text = _("Swipe to go back"),
                 checked_func = isSwipeToGoBackEnabled,
@@ -106,6 +112,48 @@ function ReaderLink:addToMainMenu(menu_items)
     }
 end
 
+--- Gets link from gesture.
+-- `Document:getLinkFromPosition()` behaves differently depending on
+-- document type, so this function provides a wrapper.
+function ReaderLink:getLinkFromGes(ges)
+    if self.ui.document.info.has_pages then
+        local pos = self.view:screenToPageTransform(ges.pos)
+        if pos then
+            -- link box in native page
+            local link, lbox = self.ui.document:getLinkFromPosition(pos.page, pos)
+            if link and lbox then
+                return link, lbox, pos
+            end
+        end
+    else
+        local link = self.ui.document:getLinkFromPosition(ges.pos)
+        if link ~= "" then
+            return link
+        end
+    end
+end
+
+--- Highlights a linkbox if available and goes to it.
+function ReaderLink:showLinkBox(link, lbox, pos)
+    if link and lbox then
+        -- screen box that holds the link
+        local sbox = self.view:pageToScreenTransform(pos.page,
+            self.ui.document:nativeToPageRectTransform(pos.page, lbox))
+        if sbox then
+            UIManager:show(LinkBox:new{
+                box = sbox,
+                timeout = FOLLOW_LINK_TIMEOUT,
+                callback = function() self:onGotoLink(link) end
+            })
+            return true
+        end
+    else
+        if link ~= "" then
+            return self:onGotoLink(link)
+        end
+    end
+end
+
 function ReaderLink:onSetDimensions(dimen)
     -- update listening according to new screen dimen
     if Device:isTouchDevice() then
@@ -114,34 +162,14 @@ function ReaderLink:onSetDimensions(dimen)
 end
 
 function ReaderLink:onTap(_, ges)
-    if not isFollowLinksOn() then return end
-    if self.ui.document.info.has_pages then
-        local pos = self.view:screenToPageTransform(ges.pos)
-        if pos then
-            -- link box in native page
-            local link, lbox = self.ui.document:getLinkFromPosition(pos.page, pos)
-            if link and lbox then
-                -- screen box that holds the link
-                local sbox = self.view:pageToScreenTransform(pos.page,
-                    self.ui.document:nativeToPageRectTransform(pos.page, lbox))
-                if sbox then
-                    UIManager:show(LinkBox:new{
-                        box = sbox,
-                        timeout = FOLLOW_LINK_TIMEOUT,
-                        callback = function() self:onGotoLink(link) end
-                    })
-                    return true
-                end
-            end
-        end
-    else
-        local link = self.ui.document:getLinkFromPosition(ges.pos)
-        if link ~= "" then
-            return self:onGotoLink(link)
-        end
+    if not isTapToFollowLinksOn() then return end
+    local link, lbox, pos = self:getLinkFromGes(ges)
+    if link then
+        self:showLinkBox(link, lbox, pos)
     end
 end
 
+--- Goes to link.
 function ReaderLink:onGotoLink(link)
     logger.dbg("onGotoLink:", link)
     if self.ui.document.info.has_pages then
@@ -196,6 +224,7 @@ function ReaderLink:onGotoLink(link)
     return true
 end
 
+--- Goes back to previous location.
 function ReaderLink:onGoBackLink()
     local saved_location = table.remove(self.location_stack)
     if saved_location then
@@ -216,8 +245,8 @@ function ReaderLink:onSwipe(_, ges)
     end
 end
 
+--- Goes to first link on page.
 function ReaderLink:onGoToFirstLink(ges)
-    if not isFollowLinksOn() then return end
     local firstlink = nil
     if self.ui.document.info.has_pages then
         local pos = self.view:screenToPageTransform(ges.pos)