refactor parallel code

openos/head.lua

@@ -0,0 +1,137 @@
+local shell = require("openos.shell")
+local fs = require("openos.filesystem")
+
+local args, options = shell.parse(...)
+local error_code = 0
+
+local function pop(key, convert)
+  local result = options[key]
+  options[key] = nil
+  if result and convert then
+    local c = tonumber(result)
+    if not c then
+      io.stderr:write(string.format("use --%s=n where n is a number\n", key))
+      options.help = true
+      error_code = 1
+    end
+    result = c
+  end
+  return result
+end
+
+local bytes = pop('bytes', true)
+local lines = pop('lines', true)
+local quiet = {pop('q'), pop('quiet'), pop('silent')}
+quiet = quiet[1] or quiet[2] or quiet[3]
+local verbose = {pop('v'), pop('verbose')}
+verbose = verbose[1] or verbose[2]
+local help = pop('help')
+local invalid_key = next(options)
+
+if bytes and lines then
+  invalid_key = 'bytes and lines both specified'
+end
+
+if help or next(options) then
+  local invalid_key = next(options)
+  if invalid_key then
+    invalid_key = string.format('invalid option: %s\n', invalid_key)
+    error_code = 1
+  else
+    invalid_key = ''
+  end
+  print(invalid_key .. [[Usage: head [--lines=n] file
+Print the first 10 lines of each FILE to stdout.
+For more info run: man head]])
+  os.exit(error_code)
+end
+
+if #args == 0 then
+  args = {'-'}
+end
+
+if quiet and verbose then
+  quiet = false
+end
+
+local function new_stream()
+  return
+  {
+    open=true,
+    capacity=math.abs(lines or bytes or 10),
+    bytes=bytes,
+    buffer=(lines and lines < 0 and {}) or (bytes and bytes < 0 and '')
+  }
+end
+
+local function close(stream)
+  if stream.buffer then
+    if type(stream.buffer) == 'table' then
+      stream.buffer = table.concat(stream.buffer)
+    end
+    io.stdout:write(stream.buffer)
+    stream.buffer = nil
+  end
+  stream.open = false
+end
+
+local function push(stream, line)
+  if not line then
+    return close(stream)
+  end
+
+  local cost = stream.bytes and line:len() or 1
+  stream.capacity = stream.capacity - cost
+
+  if not stream.buffer then
+    if stream.bytes and stream.capacity < 0 then
+      line = line:sub(1,stream.capacity-1)
+    end
+    io.write(line)
+    if stream.capacity <= 0 then
+      return close(stream)
+    end
+  else
+    if type(stream.buffer) == 'table' then -- line storage
+      stream.buffer[#stream.buffer+1] = line
+      if stream.capacity < 0 then
+        table.remove(stream.buffer, 1)
+        stream.capacity = 0 -- zero out
+      end
+    else -- byte storage
+      stream.buffer = stream.buffer .. line
+      if stream.capacity < 0 then
+        stream.buffer = stream.buffer:sub(-stream.capacity+1)
+        stream.capacity = 0 -- zero out
+      end
+    end
+  end
+
+end
+
+for i=1,#args do
+  local arg = args[i]
+  local file
+  if arg == '-' then
+    arg = 'standard input'
+    file = io.stdin
+  else
+    file, reason = io.open(arg, 'r')
+    if not file then
+      io.stderr:write(string.format([[head: cannot open '%s' for reading: %s]], arg, reason))
+    end
+  end
+  if file then
+    if verbose or #args > 1 then
+      io.write(string.format('==> %s <==\n', arg))
+    end
+
+    local stream = new_stream()
+
+    while stream.open do
+      push(stream, file:read('*L'))
+    end
+
+    file:close()
+  end
+end