ln

-- ln created by airminer96

------------
-- Fields --
------------

-- The original value of os.unloadAPI
local unloadRaw

---------------
-- Internals --
---------------

-- Checks the fist 8 bytes of the file to see if it's a link
local function isRawLink(path, handle)
  hb = handle.open(path,"rb")
  if handle.exists(path) and not handle.isDir(path) then
    s = {}
    for i = 1, 7 do
      b = hb.read()
      if b then
        s[i] = b
      end
    end
    hb.close()
    if string.char(unpack(s)) == "--link:" then
      return true
    end
  end
  return false
end

-- Quickfix for infinite looping
local loop = 0

-- Resolves a path
local function resolve(path, handle)
  loop = loop + 1
  rp = fs.combine("",path)
  p = rp
  while (p ~= "") and not handle.exists(p) do
    p = p:sub(1,-1*fs.getName(p):len()-2)
  end
  if isRawLink(p, handle) and loop < 100 then
    h = handle.open(p,"r")
    l = h.readLine():sub(8)
    h.close()
    if l:sub(1,1) ~= "/" then
      l = fs.combine(p:sub(1,-1*fs.getName(p):len()-2),l)
    end
    rp = resolve(fs.combine(l,rp:sub(p:len() + 1)),handle)
  end
  loop = 0
  return rp
end

-- Lua shenanigans
isLink = nil

-- The handler passed to fsPlugins.registerHandler
local function handler(path, handle, action)
  if action == "delete" and isLink(path) then
    return fs.combine(resolve(path:sub(1,-1*fs.getName(path):len()-2),handle),fs.getName(path)),handle
  else
    return resolve(path,handle),handle;
  end
end

-- The hook which overrides os.unloadAPI
local function unload(name)
  if name == "fsPlugins" or name == "ln" then
    -- Remove handler
    fsPlugins.removeHandler(handler)
  end
  if (name == "fsPlugins" or name == "ln" or ln == nil) and os.unloadAPI == unload then
    -- Restore os.unloadAPI
    os.unloadAPI = unloadRaw
  end
  unloadRaw(name)
end

----------------
-- Public API --
----------------

-- Checks if the sepcified path is a link (resolves all parent links). A handle can be optionally specified
isLink = function(path, handle)
  if handle then
    return isRawLink(fs.combine(resolve(path:sub(1,-1*fs.getName(path):len()-2),handle),fs.getName(path)),handle)
  else
    if fsPlugins then
      fsPlugins.removeHandler(handler)
    end
    ret = isRawLink(fs.combine(resolve(path:sub(1,-1*fs.getName(path):len()-2),fs),fs.getName(path)),fs)
    if fsPlugins then
      fsPlugins.registerHandler(handler)
    end
    return ret
  end
end

--Creates a link file <name> pointing at the path <target>
function createLink(target, name)
  h = fs.open(name,"w")
  h.write("--link:"..target)
  h.close()
end

-- os.loadAPI sequence
if shell == nil then
  if ln then
    -- Unload API if already loaded
    os.unloadAPI("ln")
  end
  if not fsPlugins then
    -- Try to load fsPlugins API if not already loaded
    os.loadAPI("fsPlugins")
  end
  if fsPlugins then
    -- Register handler
    fsPlugins.registerHandler(handler)
    -- Override os.unloadAPI
    unloadRaw = os.unloadAPI
    os.unloadAPI = unload
  else
    if term.isColor() then
      term.setTextColor(colors.red)
    end
    print("fsPlugins API not found, driver will not be loaded")
  end
-- Shell program sequence
else
  tArgs = {...}
  if tArgs[1] == "load" then
    -- Load API
    os.loadAPI(shell.getRunningProgram())
  elseif tArgs[1] == "unload" then
    -- Unload API
    os.unloadAPI("ln")
  elseif tArgs[1] == "-s" and #tArgs >= 2 then
    if tArgs[3] == nil then
      tArgs[3] = fs.getName(shell.resolve(tArgs[2]))
    end
    -- Create symlink
    createLink(tArgs[2],shell.resolve(tArgs[3]))
  else
    -- Print Usages
    print("Usages:\nln help\nln load\nln unload\nln -s <target> [name]")
  end
end