From 1a3115b9b75ed1f9a380b59c80d51fabdc811a2a Mon Sep 17 00:00:00 2001
From: Jason Woofenden <jason@jasonwoof.com>
Date: Tue, 29 Mar 2016 00:11:55 -0400
Subject: [PATCH] implement page-down key

---
 editor.coffee |   97 +++++++++++++++++++++++++++++++++++----------------------
 1 file changed, 60 insertions(+), 37 deletions(-)

diff --git a/editor.coffee b/editor.coffee
index a02e278..c78151a 100644
--- a/editor.coffee
+++ b/editor.coffee
@@ -955,6 +955,7 @@ class PeachHTML5Editor
 				@on_page_up_key e
 				return false
 			when KEY_PAGE_DOWN
+				@on_page_down_key e
 				return false
 			when KEY_TAB
 				return false
@@ -1076,47 +1077,69 @@ class PeachHTML5Editor
 				@kill_cursor()
 		return
 	on_page_up_key: (e) ->
+		if @cursor?
+			screen_y = @cursor.y - @wrap2.scrollTop
 		scroll_amount = @wrap2_height - breathing_room
-		# scroll up a page
 		@wrap2.scrollTop = Math.max 0, @wrap2.scrollTop - scroll_amount
-		# note: if cursor innacuracy causes it no not be within new scroll,
-		# @move_cursor will adjust the scroll a bit.
 		if @cursor?
-			# move cursor up approximately scroll_amount
-			was = @cursor
-			y_target = @cursor.y - scroll_amount
-			y_min = Math.min y_target, @wrap2.scrollTop
-			y_max = Math.min y_target, @wrap2.scrollTop - scroll_amount
-			y_target = Math.min y_target, y_max
-			y_target = Math.max y_target, y_min
-			loop
-				cur = find_up_cursor_position @tree, was, @cursor_ideal_x
-				break unless cur?
-				break if cur.y <= y_target
-				was = cur
-			if was is @cursor
-				if cur?
-					new_cursor = cur
-				else
-					# should this move the cursor to the beginning of the line?
-					new_cursor = null
+			@move_cursor_into_view screen_y + @wrap2.scrollTop
+	on_page_down_key: (e) ->
+		if @cursor?
+			screen_y = @cursor.y - @wrap2.scrollTop
+		scroll_amount = @wrap2_height - breathing_room
+		lowest_scrollpos = @wrap2.scrollHeight - @wrap2_height
+		@wrap2.scrollTop = Math.min lowest_scrollpos, @wrap2.scrollTop + scroll_amount
+		if @cursor?
+			@move_cursor_into_view screen_y + @wrap2.scrollTop
+		return
+	move_cursor_into_view: (y_target) ->
+		return if y_target is @cursor.y
+		was = @cursor
+		y_min = @wrap2.scrollTop + breathing_room
+		y_max = @wrap2.scrollTop + @wrap2_height - 2 * breathing_room
+		y_target = Math.min y_target, y_max
+		y_target = Math.max y_target, y_min
+		if y_target < @cursor.y
+			finder = find_up_cursor_position
+			far_enough = (a, b) ->
+				return a <= b
+		else
+			finder = find_down_cursor_position
+			far_enough = (a, b) ->
+				return a >= b
+		loop
+			cur = finder @tree, was, @cursor_ideal_x
+			break unless cur?
+			break if far_enough cur.y, y_target
+			was = cur
+		if was is @cursor
+			was = null
+		if was?
+			if was.y > y_max
+				was = null
+			else if was.y < y_min
+				was = null
+		if cur?
+			if cur.y > y_max
+				cur = null
+			else if cur.y < y_min
+				cur = null
+		if cur? and was?
+			# both valid, pick best
+			if cur.y < y_min
+				new_cursor = was
+			else if was.y > y_max
+				new_cursor = cur
+			else if cur.y - y_target < y_target - was.y
+				new_cursor = cur
 			else
-				if cur?
-					# both valid, pick best
-					if cur.y < y_min
-						new_cursor = was
-					else if was.y > y_max
-						new_cursor = cur
-					else if cur.y - y_target < y_target - was.y
-						new_cursor = cur
-					else
-						new_cursor = was
-				else
-					new_cursor = was
-			if new_cursor?
-				saved_ideal_x = @cursor_ideal_x
-				@move_cursor new_cursor
-				@cursor_ideal_x = saved_ideal_x
+				new_cursor = was
+		else
+			new_cursor = was ? cur
+		if new_cursor?
+			saved_ideal_x = @cursor_ideal_x
+			@move_cursor new_cursor
+			@cursor_ideal_x = saved_ideal_x
 		return
 	clear_dom: -> # remove all the editable content (and cursor, overlays, etc)
 		while @idoc.body.childNodes.length
-- 
1.7.10.4