local shell=require("shell")

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')

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
stream.buffer[#stream.buffer+1]=line
if stream.capacity<0 then
table.remove(stream.buffer,1)
stream.capacity=0
end
else
stream.buffer=stream.buffer..line
if stream.capacity<0 then
stream.buffer=stream.buffer:sub(-stream.capacity+1)
stream.capacity=0
end
end
end

end

for i=1,#args do
local arg=args[i]
local file,reason
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