local fs={}

-- 1 : open
-- 2 : read
-- 3 : write
-- 4 : close

function fs.open(path, mode)
    local fd=cororoutine.yield(1,path,mode)
    local ret={
        close=function()
            -- close file
            return coroutine.yield(4,fd)
        end,
        flush=function()
            -- close and reopen file to flush buffers
            coroutine.yield(4,fd)
            fd=coroutine.yield(1,path,mode)
        end
    }
    if mode=="r" then
        ret.read=function(count)
            return coroutine.yield(2,fd,count)
        end
        ret.readAll=function()
            local chunks={} -- to store read chunks
            while true do
                local chunk=coroutine.yield(2,fd,math.huge)
                if chunk==nil or #chunk==0 then break end
                table.insert(chunks,chunk)
            end
            return table.concat(chunks)
        end
        ret.readLine = function()
            local buffer = {}                -- stores leftover data
            local buffer_str = ""            -- concatenated buffer
            local chunk_size = 4096          -- adjust chunk size for performance
            local eof = false

            while true do
                -- Try to find a newline in the current buffer
                local line_end = buffer_str:find("\n")
                if line_end then
                    local line = buffer_str:sub(1, line_end - 1)
                    buffer_str = buffer_str:sub(line_end + 1)
                    return line
                end
            
                -- If EOF was reached previously and buffer is empty, stop
                if eof then
                    if buffer_str ~= "" then
                        local last_line = buffer_str
                        buffer_str = ""
                        return last_line
                    else
                        return nil
                    end
                end
            
                -- Read the next chunk
                local chunk = coroutine.yield(2, fd, chunk_size)
                if not chunk or chunk == "" then
                    eof = true
                else
                    buffer_str = buffer_str .. chunk
                end
            end
        end
    elseif mode=="w" then
        ret.write=function(data)
            -- write data to file
            return coroutine.yield(3,fd,data)
        end
    elseif mode=="a" then
        ret.write=function(data)
            -- append data to file
            return coroutine.yield(3,fd,data)
        end
    else
        error("Invalid mode '"..mode.."'",2)
    end
    return ret
end

function fs.readAllText(path)
    local file=fs.open(path,"r")
    if not file then return false end
    local content=file.readAll()
    file.close()
    return content
end

function fs.writeAllText(path, data)
    local file=fs.open(path,"w")
    file.write(data)
    file.close()
end

function fs.appendAllText(path, data)
    local file=fs.open(path,"a")
    if not file then return false end
    file.write(data)
    file.close()
end

function fs.mkdir(path)
    coroutine.yield(8,path)
end

function fs.remove(path)
    coroutine.yield(9,path)
end

function fs.list(path)
    return coroutine.yield(5,path)
end

function fs.type(path)
    return coroutine.yield(6,path)
end

function fs.attributes(path)
    return coroutine.yield(7,path)
end

function fs.exists(path)
    return coroutine.yield(10, path)
end

function fs.getcwd()
    return coroutine.yield(11)
end

function fs.setcwd(path)
    return coroutine.yield(12, path)
end

return fs