Added improved help viewer (#595)

- Pagination, with (page) up/down, q(uit) and scrolling support.
 - Render markdown style bullets ('-'/'*') using a '•' instead.

src/main/resources/data/computercraft/lua/rom/programs/help.lua

@@ -15,12 +15,119 @@ end
 
 local sFile = help.lookup(sTopic)
 local file = sFile ~= nil and io.open(sFile) or nil
-if file then
-    local sContents = file:read("*a")
-    file:close()
-
-    local _, nHeight = term.getSize()
-    textutils.pagedPrint(sContents, nHeight - 3)
-else
-    print("No help available")
+if not file then
+    printError("No help available")
+    return
 end
+
+local contents = file:read("*a"):gsub("(\n *)[-*]( +)", "%1\7%2")
+file:close()
+
+local width, height = term.getSize()
+local buffer = window.create(term.current(), 1, 1, width, height, false)
+local old_term = term.redirect(buffer)
+
+local print_height = print(contents) + 1
+
+-- If we fit within the screen, just display without pagination.
+if print_height <= height then
+    term.redirect(old_term)
+    print(contents)
+    return
+end
+
+local function draw_buffer(width)
+    buffer.reposition(1, 1, width, print_height)
+    buffer.clear()
+    buffer.setCursorPos(1, 1)
+    print(contents)
+    term.redirect(old_term)
+end
+
+local offset = 0
+
+local function draw()
+    for y = 1, height - 1 do
+        term.setCursorPos(1, y)
+        if y + offset > print_height then
+             -- Should only happen if we resize the terminal to a larger one
+             -- than actually needed for the current text.
+            term.clearLine()
+        else
+            term.blit(buffer.getLine(y + offset))
+        end
+    end
+end
+
+local function draw_menu()
+    term.setTextColor(colors.yellow)
+    term.setCursorPos(1, height)
+    term.clearLine()
+
+    local tag = "Help: " .. sTopic
+    term.write("Help: " .. sTopic)
+
+    if width >= #tag + 16 then
+        term.setCursorPos(width - 14, height)
+        term.write("Press Q to exit")
+    end
+end
+
+draw_buffer(width)
+draw()
+draw_menu()
+
+while true do
+    local event, param = os.pullEvent()
+    if event == "key" then
+        if param == keys.up and offset > 0 then
+            offset = offset - 1
+            draw()
+        elseif param == keys.down and offset < print_height - height then
+            offset = offset + 1
+            draw()
+        elseif param == keys.pageUp and offset > 0 then
+            offset = math.max(offset - height + 2, 0)
+            draw()
+        elseif param == keys.pageDown and offset < print_height - height then
+            offset = math.min(offset + height - 2, print_height - height)
+            draw()
+        elseif param == keys.home then
+            offset = 0
+            draw()
+        elseif param == keys["end"] then
+            offset = print_height - height
+            draw()
+        elseif param == keys.q then
+            sleep(0) -- Super janky, but consumes stray "char" events.
+            break
+        end
+    elseif event == "mouse_scroll" then
+        if param < 0 and offset > 0 then
+            offset = offset - 1
+            draw()
+        elseif param > 0 and offset < print_height - height then
+            offset = offset + 1
+            draw()
+        end
+    elseif event == "term_resize" then
+        local new_width, new_height = term.getSize()
+
+        if new_width ~= width then
+            buffer.setCursorPos(1, 1)
+            buffer.reposition(1, 1, new_width, print_height)
+            term.redirect(buffer)
+            print_height = print(contents) + 1
+            draw_buffer(new_width)
+        end
+
+        width, height = new_width, new_height
+        offset = math.max(math.min(offset, print_height - height), 0)
+        draw()
+        draw_menu()
+    end
+end
+
+term.redirect(old_term)
+term.setCursorPos(1, 1)
+term.clear()

src/test/resources/test-rom/spec/programs/help_spec.lua

@@ -3,6 +3,6 @@ local capture = require "test_helpers".capture_program
 describe("The help program", function()
     it("errors when there is no such help file", function()
         expect(capture(stub, "help nothing"))
-            :matches { ok = true, output = "No help available\n", error = "" }
+            :matches { ok = true, error = "No help available\n", output = "" }
     end)
 end)