Rewrite the shell to use a wrapper script

 - Instead of reimplementing the entire shell API, just handle the REPL
   loop.
 - As we want to "appear" as a separate shell, we add a wrapper script
   which just launches a new shell with our "actual" shell program.
 - This removes support for strict mode and custom package paths. The
   first of these is definitely a shame, but should hopefully give me a
   kick up the backside to actually get this into CC:T.

 - Also change when we allow scrolling - it's now supported whenever the
   cursor is blinking, instead of just inside the read/readline functions.

   It's probably still a bit silly, but hopefully should be fine.
   Maybe??

Closes SquidDev-CC#32

bin/shell-worker.lua

@@ -0,0 +1,179 @@
+local history = {}
+do
+  local history_file = settings.get("mbs.shell.history_file", ".shell_history")
+  if history_file and fs.exists(history_file) then
+    local handle = fs.open(history_file, "r")
+    if handle then
+      for line in handle.readLine do history[#history + 1] = line end
+      handle.close()
+    end
+  end
+
+  local max = tonumber(settings.get("mbs.shell.history_max", 1e4)) or 1e4
+  if #history > max then
+    while #history > max do table.remove(history, 1) end
+
+    local history_file = settings.get("mbs.shell.history_file", ".shell_history")
+    if history_file then
+      local handle = fs.open(history_file, "w")
+      if handle then
+        for i = 1, #history do handle.writeLine(history[i]) end
+        handle.close()
+      end
+    end
+  end
+end
+
+-- Nasty! Thankfully we don't actually need to worry about this, as
+-- we'll always be launched by our shell bootstrap.
+shell.exit()
+local running = true
+function shell.exit() running = false end
+
+local promptColour, textColour, bgColour
+if term.isColour() then
+  promptColour = colours.yellow
+  textColour = colours.white
+  bgColour = colours.black
+else
+  promptColour = colours.white
+  textColour = colours.white
+  bgColour = colours.black
+end
+
+local parent = term.current()
+local redirect = scroll_window.create(parent)
+
+local function get_first_startup()
+  if fs.exists("startup.lua") and not fs.isDir("startup.lua") then
+    return "startup.lua"
+  end
+  if fs.isDir("startup")  then
+    local first = fs.list("startup")[1]
+    if first then return fs.combine("startup", first) end
+  end
+
+  return nil
+end
+
+local scroll_offset = 0
+
+local worker = coroutine.create(function()
+  -- Print the header
+  term.redirect(redirect)
+  term.setCursorPos(1, 1)
+  term.setBackgroundColor(bgColour)
+  term.setTextColour(promptColour)
+  print(os.version() .. " (+MBS)")
+  term.setTextColour(textColour)
+
+  if shell.getRunningProgram() == get_first_startup() then
+    -- If we're currently in the first startup file, then run all the others.
+    local current = shell.getRunningProgram()
+
+    if settings.get("motd.enable") then shell.run("motd") end
+
+    -- Run /startup or /startup.lua
+    local root_startup = shell.resolveProgram("startup")
+    if root_startup and root_startup ~= current then shell.run("/" .. root_startup) end
+
+    -- Run startup/*
+    if fs.isDir("startup") then
+      for _, file in ipairs(fs.list("startup")) do
+        local sub_startup = fs.combine("startup", file)
+        if sub_startup ~= current and not fs.isDir(sub_startup) then
+          shell.run("/" .. sub_startup)
+        end
+      end
+    end
+  end
+
+  -- The main interaction loop
+  while running do
+    local scrollback = tonumber(settings.get("mbs.shell.scroll_max", 1e3))
+    if scrollback then redirect.setMaxScrollback(scrollback) end
+
+    term.setBackgroundColor(bgColour)
+    term.setTextColour(promptColour)
+    if term.getCursorPos() ~= 1 then print() end
+    write(shell.dir() .. "> ")
+    term.setTextColour(textColour)
+
+    local line
+    if settings.get("shell.autocomplete") then
+      line = read(nil, history, shell.complete)
+    else
+      line = read(nil, history)
+    end
+
+    if not line then break end
+
+    if line:match("%S") and history[#history] ~= line then
+      -- Add item to history
+      history[#history + 1] = line
+
+      -- Write history file
+      local history_file = settings.get("mbs.shell.history_file", ".shell_history")
+      if history_file then
+        local handle = fs.open(history_file, "a")
+        handle.writeLine(line)
+        handle.close()
+      end
+    end
+
+    local _, y = term.getCursorPos()
+    redirect.setCursorThreshold(y)
+
+    local ok = shell.run(line)
+
+    term.redirect(redirect)
+    redirect.endPrivateMode(not ok)
+    redirect.draw(0)
+  end
+
+  term.redirect(parent)
+end)
+
+local ok, filter = coroutine.resume(worker)
+
+-- We run the main worker inside a coroutine, catching any potential scroll
+-- events.
+while coroutine.status(worker) ~= "dead" do
+  local event = table.pack(coroutine.yield())
+  local e = event[1]
+
+  -- Run the main REPL worker
+  if filter == nil or e == filter or e == "terminate" then
+    ok, filter = coroutine.resume(worker, table.unpack(event, 1, event.n))
+  end
+
+  -- Resize the terminal if required
+  if e == "term_resize" then
+    redirect.updateSize()
+    redirect.draw(scroll_offset or 0, true)
+  end
+
+  -- If we're in some interactive function, allow scrolling the input
+  if redirect.getCursorBlink() then
+    local change = 0
+    if e == "mouse_scroll" then
+      change = event[2]
+    elseif e == "key" and event[2] == keys.pageDown then
+      change = 10
+    elseif e == "key" and event[2] == keys.pageUp then
+      change = -10
+    elseif e == "key" or e == "paste" then
+      -- Reset offset if another key is pressed
+      change = -scroll_offset
+    end
+
+    if change ~= 0 and term.current() == redirect and not redirect.isPrivateMode() then
+      scroll_offset = scroll_offset + change
+      if scroll_offset > 0 then scroll_offset = 0 end
+      if scroll_offset < -redirect.getTotalHeight() then scroll_offset = -redirect.getTotalHeight() end
+      redirect.draw(scroll_offset)
+    end
+  end
+end
+
+if not ok then error(filter, 0) end