diff --git a/31-concurrency/xxx-concurrent-downloader/fetch/danger/main.go b/31-concurrency/xxx-concurrent-downloader/fetch/danger/main.go
deleted file mode 100644
index acca60b..0000000
--- a/31-concurrency/xxx-concurrent-downloader/fetch/danger/main.go
+++ /dev/null
@@ -1,46 +0,0 @@
-package main
-
-import (
-	"fmt"
-	"time"
-)
-
-/*
-when the default case exists, messages are not guaranteed
-*/
-func main() {
-	ch := make(chan int)
-
-	// if this GR is fast enough
-	// the main GR can miss the signals
-	go func() {
-		var i int
-
-		for {
-			i++
-
-			select {
-			case ch <- i:
-			default:
-				// message is lost
-				// it doesn't matter whether the chan is buffered or not
-			}
-
-			if i == 10000 {
-				fmt.Println("gopher dies")
-				close(ch)
-				return
-			}
-		}
-	}()
-
-	var total int
-	for i := range ch {
-		// works slower — misses some of the signals
-		time.Sleep(time.Nanosecond)
-		total += i
-	}
-
-	// should be: 50005000
-	fmt.Println(total)
-}
diff --git a/31-concurrency/xxx-concurrent-downloader/fetch/danger2/main.go b/31-concurrency/xxx-concurrent-downloader/fetch/danger2/main.go
deleted file mode 100644
index c937201..0000000
--- a/31-concurrency/xxx-concurrent-downloader/fetch/danger2/main.go
+++ /dev/null
@@ -1,40 +0,0 @@
-package main
-
-import (
-	"fmt"
-	"time"
-)
-
-func main() {
-	a, b := make(chan bool), make(chan bool)
-
-	go func() {
-		for a != nil || b != nil {
-			fmt.Println("loop starts")
-
-			select {
-			case <-a:
-				fmt.Println("recv: a")
-				a = nil
-			case <-b:
-				b = nil
-				fmt.Println("recv: b")
-			}
-
-			fmt.Println("loop ends")
-		}
-		fmt.Println("gopher dies")
-	}()
-
-	time.Sleep(time.Second)
-	// 	a <- true
-	close(a)
-	time.Sleep(time.Second)
-	//b <- true
-	close(b)
-	time.Sleep(time.Second * 2)
-
-	// closed chan never blocks
-	// nil chan always blocks
-	//   if in the loop chans not set to nil, the loop will loop forever
-}
diff --git a/31-concurrency/xxx-concurrent-downloader/fetch/drain.go b/31-concurrency/xxx-concurrent-downloader/fetch/drain.go
deleted file mode 100644
index 98346b4..0000000
--- a/31-concurrency/xxx-concurrent-downloader/fetch/drain.go
+++ /dev/null
@@ -1,12 +0,0 @@
-package fetch
-
-// Drain drains the progress updates and returns the latest progresses
-func Drain(updates <-chan Progress) map[string]Progress {
-	latest := make(map[string]Progress)
-
-	// save the latest progress
-	for p := range updates {
-		latest[p.URL] = p
-	}
-	return latest
-}
diff --git a/31-concurrency/xxx-concurrent-downloader/fetch/httpget.go b/31-concurrency/xxx-concurrent-downloader/fetch/httpget.go
deleted file mode 100644
index 56104fa..0000000
--- a/31-concurrency/xxx-concurrent-downloader/fetch/httpget.go
+++ /dev/null
@@ -1,31 +0,0 @@
-package fetch
-
-import (
-	"fmt"
-	"net/http"
-	"time"
-)
-
-// HTTPGet requests to a url with the specified timeout.
-// And it returns the response with an error.
-// The caller should drain and close the body or it will leak.
-func HTTPGet(url string, timeout time.Duration) (*http.Response, error) {
-	req, err := http.NewRequest("GET", url, nil)
-	req.Close = true
-	if err != nil {
-		return nil, err
-	}
-
-	c := &http.Client{Timeout: timeout}
-	resp, err := c.Do(req)
-	if err != nil {
-		return nil, err
-	}
-
-	// checkout for the bad urls
-	if s := resp.StatusCode; s < 200 || s > 299 {
-		return resp, fmt.Errorf("bad status: %d", s)
-	}
-
-	return resp, nil
-}
diff --git a/31-concurrency/xxx-concurrent-downloader/fetch/httptransfer.go b/31-concurrency/xxx-concurrent-downloader/fetch/httptransfer.go
deleted file mode 100644
index 1b132d0..0000000
--- a/31-concurrency/xxx-concurrent-downloader/fetch/httptransfer.go
+++ /dev/null
@@ -1,126 +0,0 @@
-package fetch
-
-import (
-	"fmt"
-	"io"
-	"net/http"
-	"os"
-	"path"
-	"time"
-)
-
-// HTTPTransfer uses a fetcher and a storager to fetch and store an url
-type HTTPTransfer struct {
-	Progress
-	r io.ReadCloser
-	w io.WriteCloser
-
-	timeout time.Duration
-
-	done    <-chan bool
-	updates chan<- Progress
-}
-
-// NewHTTPTransfer creates and returns a new transfer
-func NewHTTPTransfer(url string, timeout time.Duration) *HTTPTransfer {
-	return &HTTPTransfer{
-		Progress: Progress{URL: url},
-		timeout:  timeout,
-	}
-}
-
-// Start starts the transfer progress
-// The transfer will send its updates to the update chan
-// and it will stop when receives a signal from the done chan
-//
-// All the t.signal calls are here. I believe this increases the visibility
-// of the Start function (what it does). If the signal calls were in the
-// other funcs of HTTPTransfer, it could easily lead to bugs.
-func (t *HTTPTransfer) Start(updates chan<- Progress, done <-chan bool) {
-	defer t.cleanup()
-
-	t.done, t.updates = done, updates
-
-	t.w, t.Error = os.Create(path.Base(t.URL))
-	if t.Error != nil {
-		t.signal()
-		return
-	}
-
-	t.request()
-	if !t.signal() {
-		return
-	}
-
-	// sniff the on-going transfer until the signal returns false
-	sniff := sniffer(func(p []byte) bool {
-		l := len(p)
-		t.Current = l
-		t.Downloaded += l
-
-		return t.signal()
-	})
-
-	t.transfer(sniff)
-	t.signal()
-}
-
-func (t *HTTPTransfer) cleanup() {
-	if t.r != nil {
-		t.r.Close()
-	}
-	if t.w != nil {
-		t.w.Close()
-	}
-}
-
-func (t *HTTPTransfer) request() {
-	var resp *http.Response
-
-	resp, t.Error = HTTPGet(t.URL, t.timeout)
-	if t.Error != nil {
-		return
-	}
-
-	t.Total = int(resp.ContentLength) // TODO: int(int64)
-	if t.Total <= 0 {
-		t.Error = fmt.Errorf("unknown content length: %d", t.Total)
-	}
-
-	t.r = resp.Body
-}
-
-func (t *HTTPTransfer) transfer(sniff sniffer) {
-	// initiate the transfer and monitor it
-	_, t.Error = io.Copy(io.MultiWriter(t.w, sniff), t.r)
-
-	// if the err is from sniffer ignore it
-	if _, ok := t.Error.(sniffer); ok {
-		t.Error = nil
-	}
-
-	// the next signal will say: "no new bytes received" and its done
-	t.Current = 0
-	t.Done = true
-}
-
-// signal signals the listeners about the last transfer progress.
-// it returns false when the done signal is received or there was an error
-// in the transfer.
-func (t *HTTPTransfer) signal() bool {
-	select {
-	case t.updates <- t.Progress:
-	case <-t.done:
-		// shutting down signal received
-		return false
-	}
-
-	// check the error only after sending the last progress
-	// if this check was above, the last update won't be sent
-	if t.Error != nil {
-		return false
-	}
-
-	// go on your duties
-	return true
-}
diff --git a/31-concurrency/xxx-concurrent-downloader/fetch/httptransfer_fake.go b/31-concurrency/xxx-concurrent-downloader/fetch/httptransfer_fake.go
deleted file mode 100644
index 488b94e..0000000
--- a/31-concurrency/xxx-concurrent-downloader/fetch/httptransfer_fake.go
+++ /dev/null
@@ -1,71 +0,0 @@
-package fetch
-
-import (
-	"errors"
-	"fmt"
-	"math/rand"
-	"time"
-)
-
-func (t *HTTPTransfer) fakeStart() {
-	jitter()
-	t.fakeRequest()
-	t.signal()
-
-	for t.Downloaded < 100 {
-		jitter()
-		t.fakeFetch()
-
-		if !t.signal() {
-			// done signal received or there was an error
-			break
-		}
-	}
-
-	t.fakeFinish()
-	t.signal()
-}
-
-// request requests to the url and adjusts the total length.
-func (t *HTTPTransfer) fakeRequest() {
-	t.Total = 100
-
-	if debug {
-		fmt.Printf("[TRANSFER] started: %s\n", t.URL)
-	}
-}
-
-// fetch fetches a bit from the resource
-func (t *HTTPTransfer) fakeFetch() {
-	// TODO: right now hanged goroutine may hang the download completion
-	// needs timeout
-	// if t.URL == "url1" {
-	// 	select {}
-	// }
-
-	// NOTE: burada sayacli io.Writer kullan
-	if t.URL == "url1" && t.Downloaded > rand.Intn(50) {
-		t.Error = errors.New("cekemedim netten")
-	}
-
-	n := rand.Intn(20) + 1
-	if nn := t.Downloaded + n; nn > 100 {
-		n = 100 - t.Downloaded
-	}
-	t.Current = n
-	t.Downloaded += n
-}
-
-// finish signals the finish signal to the listeners
-func (t *HTTPTransfer) fakeFinish() {
-	t.Current = 0
-	t.Done = true
-
-	if debug {
-		fmt.Printf("[TRANSFER] DONE: %s\n", t.URL)
-	}
-}
-
-func jitter() {
-	time.Sleep(time.Millisecond * time.Duration(rand.Intn(500)+1))
-}
diff --git a/31-concurrency/xxx-concurrent-downloader/fetch/progress.go b/31-concurrency/xxx-concurrent-downloader/fetch/progress.go
deleted file mode 100644
index a85eb34..0000000
--- a/31-concurrency/xxx-concurrent-downloader/fetch/progress.go
+++ /dev/null
@@ -1,10 +0,0 @@
-package fetch
-
-// Progress contains data about the downloading progress
-type Progress struct {
-	URL string
-
-	Total, Downloaded, Current int
-	Done                       bool
-	Error                      error
-}
diff --git a/31-concurrency/xxx-concurrent-downloader/fetch/session.go b/31-concurrency/xxx-concurrent-downloader/fetch/session.go
deleted file mode 100644
index 3de9ea3..0000000
--- a/31-concurrency/xxx-concurrent-downloader/fetch/session.go
+++ /dev/null
@@ -1,57 +0,0 @@
-package fetch
-
-import (
-	"fmt"
-	"sync"
-)
-
-const debug = true
-
-// Session manages the downloading process
-type Session struct {
-	done chan bool
-}
-
-// Transfer sends `updates` and terminates when `done` closes
-type Transfer interface {
-	Start(updates chan<- Progress, done <-chan bool)
-}
-
-// NewSession creates a new downloading session
-func NewSession() *Session {
-	return &Session{done: make(chan bool)}
-}
-
-// Start starts the downloading process
-func (s *Session) Start(transfers ...Transfer) <-chan Progress {
-	// a buffered chan may unblock transfers in case of a slow ui
-	updates := make(chan Progress)
-
-	var wg sync.WaitGroup
-	wg.Add(len(transfers))
-
-	for _, t := range transfers {
-		go func(t Transfer) {
-			defer wg.Done()
-			t.Start(updates, s.done)
-		}(t)
-	}
-
-	go func() {
-		wg.Wait()      // wait until all downloads complete
-		close(updates) // let the watchers (ui) know that we're shutting down
-	}()
-
-	return updates
-}
-
-// Shutdown stops the downloading process and sends a signal to all parties
-func (s *Session) Shutdown() {
-	// let the transfers know we're shutting down
-	// when this is done s.updates will be closed in the Start() routine above
-	close(s.done)
-
-	if debug {
-		fmt.Printf("[SESSION ] DONE\n")
-	}
-}
diff --git a/31-concurrency/xxx-concurrent-downloader/fetch/sniffer.go b/31-concurrency/xxx-concurrent-downloader/fetch/sniffer.go
deleted file mode 100644
index 7b87429..0000000
--- a/31-concurrency/xxx-concurrent-downloader/fetch/sniffer.go
+++ /dev/null
@@ -1,27 +0,0 @@
-package fetch
-
-// sniffer converts a function to a sniffer that can sniff from the
-// on-going io.Writer call such as request -> file.
-//
-// This is here just for simplifying the logic of HTTPTransfer.
-type sniffer func(p []byte) bool
-
-// Write satistifes io.Writer interface to sniff from it.
-// It can be used through a io.MultiWriter.
-func (f sniffer) Write(p []byte) (n int, err error) {
-	n = len(p)
-
-	// if the sniffer returns false, terminate with a non-nil error.
-	// it used to abrupt the sniffing process, such as abrupting the
-	// io.MultiWriter.
-	if !f(p) {
-		err = f
-	}
-	return
-}
-
-// Error satisfies the Error interface. So the returned error from the
-// sniffer.Write func can return itself as an error. This is only used when
-// the sniff.Write wants to terminate. So that we can distinguish it from a
-// real error.
-func (f sniffer) Error() string { return "" }
diff --git a/31-concurrency/xxx-concurrent-downloader/fetch/storage.go b/31-concurrency/xxx-concurrent-downloader/fetch/storage.go
deleted file mode 100644
index b26cf3d..0000000
--- a/31-concurrency/xxx-concurrent-downloader/fetch/storage.go
+++ /dev/null
@@ -1,44 +0,0 @@
-package fetch
-
-import (
-	"fmt"
-	"io"
-)
-
-// TODO: let main func hand the "TransferFactory" to "Session"
-// instead of "StorageFactory"
-//
-// Because: "Session" duplicates almost everything for "Transfer"
-
-// StorageFactory func allows to switch storage implementations
-// When called it may return a FileStore
-// The transfer will call its Write method
-//
-// Why a func rather than an interface?
-// Because: We don't have to store any state
-// Storage will return its own io.Writer and the state will be in it
-//   However, before invoking the storage, we don't need any state
-//   We let us the storage manage its own state, we don't care about it
-type StorageFactory func(url string) io.Writer
-
-// FileStorage is the default storage mechanism for the downloader
-// It writes to files
-type FileStorage struct {
-	url   string
-	saved int
-}
-
-// FileStorageFactory creates and returns a new FileStorage
-func FileStorageFactory(url string) io.Writer {
-	return &FileStorage{url: url}
-}
-
-func (f *FileStorage) Write(p []byte) (int, error) {
-	if debug {
-		fmt.Println("[FILESTORAGE]", string(p), "for", f.url)
-	}
-	// TODO:
-	// if not exists create it
-	// if exists update it
-	return 0, nil
-}
diff --git a/31-concurrency/xxx-concurrent-downloader/fetch/ui.go b/31-concurrency/xxx-concurrent-downloader/fetch/ui.go
deleted file mode 100644
index cd38672..0000000
--- a/31-concurrency/xxx-concurrent-downloader/fetch/ui.go
+++ /dev/null
@@ -1,96 +0,0 @@
-package fetch
-
-import (
-	"fmt"
-	"time"
-
-	"github.com/inancgumus/screen"
-)
-
-const refreshPeriod = time.Second / 10
-
-// uiProgress is the default UI for the downloader
-type uiProgress struct {
-	urls      []string
-	transfers map[string]Progress
-}
-
-// UI listens for the progress updates from the updates chan
-// and it refreshes the ui
-func UI(updates <-chan Progress) {
-	ui := &uiProgress{transfers: make(map[string]Progress)}
-
-	// NOTE: we didn't use time.After here directly
-	// because doing so can create a lot of Timer chans unnecessarily
-	// instead we're just waiting on the same timer value
-	tick := time.After(refreshPeriod)
-	for {
-		select {
-		case p, ok := <-updates:
-			// if no more updates close the ui
-			if !ok {
-				ui.shutdown()
-				return
-			}
-			ui.update(p)
-
-		case <-tick:
-			// `case <-tick:` allows updating the ui independently
-			// from the progress update signals. or the ui would hang
-			// the updaters (transfers).
-			ui.refresh()
-			tick = time.After(refreshPeriod)
-		}
-	}
-
-}
-
-// shutdown refreshes the ui for the last time and closes it
-func (ui *uiProgress) shutdown() {
-	ui.refresh()
-
-	if debug {
-		fmt.Printf("[ UI ] DONE\n")
-	}
-}
-
-// update updates the progress data from the received message
-func (ui *uiProgress) update(p Progress) {
-	if _, ok := ui.transfers[p.URL]; !ok {
-		ui.urls = append(ui.urls, p.URL)
-	}
-
-	// update the latest progress for the url
-	ui.transfers[p.URL] = p
-}
-
-// refresh refreshes the UI with the latest progress
-func (ui *uiProgress) refresh() {
-	if !debug {
-		screen.Clear()
-		screen.MoveTopLeft()
-	}
-
-	var total, downloaded int
-
-	for _, u := range ui.urls {
-		p := ui.transfers[u]
-
-		msg := "Downloading"
-		if p.Done && p.Error == nil {
-			msg = "👍 Completed"
-		}
-		if p.Error != nil {
-			msg = fmt.Sprintf("❌ %s", p.Error)
-		}
-
-		fmt.Println(p.URL)
-		fmt.Printf("\t%d/%d\n", p.Downloaded, p.Total)
-		fmt.Printf("\t%s\n", msg)
-
-		total += p.Total
-		downloaded += p.Downloaded
-	}
-
-	fmt.Printf("\n%s %d/%d\n", "TOTAL DOWNLOADED BYTES:", downloaded, total)
-}
diff --git a/31-concurrency/xxx-concurrent-downloader/main.go b/31-concurrency/xxx-concurrent-downloader/main.go
deleted file mode 100644
index e01a639..0000000
--- a/31-concurrency/xxx-concurrent-downloader/main.go
+++ /dev/null
@@ -1,103 +0,0 @@
-package main
-
-import (
-	"time"
-
-	dl "github.com/inancgumus/learngo/31-concurrency/xxx-concurrent-downloader/fetch"
-)
-
-//
-//       +--- transfer #1 (on done/error signals and quits)
-//       |
-// UI <--+--- transfer #2
-//       |
-//       +--- transfer #N
-//               ^
-//               |
-// SESSION ------+ launches goroutines
-//
-
-//
-//       +--- transfer #1
-//       |
-// UI <--+--- transfer #2
-//       |
-//       +--- transfer #N
-//               ^
-//               |
-// SESSION ------+ launches goroutines
-//
-
-//
-//       +--- transfer #1
-//       |
-// UI <--+--- transfer #2
-// ^     |
-// |     +--- transfer #N
-// |             ^
-// |             |
-// +--------- SESSION
-//
-// Session can close the transfers with session.Shutdown()
-// (through session.done chan)
-//
-// Session closes the watcher chan when the transfers end
-// Possible problem: If any of the transfers never quit, session will hang.
-// I think, I'm going to manage that using context.Context in the transfers.
-//
-
-func main() {
-	// ========================================================================
-
-	// to := time.Second * 5
-	// res, err := dl.HTTPGet("https://jsonplaceholder.typicode.com/todos/1", to)
-	// if err != nil {
-	// 	fmt.Println(err)
-	// 	return
-	// }
-	// defer res.Body.Close()
-
-	// io.Copy(os.Stdout, res.Body)
-
-	// return
-
-	// ========================================================================
-
-	sess := dl.NewSession()
-
-	// simulate a manual shutdown
-	// time.AfterFunc(time.Second, func() {
-	// 	sess.Shutdown()
-	// })
-
-	to := time.Second * 5
-	transfers := []dl.Transfer{
-		dl.NewHTTPTransfer("https://inancgumus.github.io/samples/jpg-beach-1020x670-160kb.jpg", to),
-		dl.NewHTTPTransfer("https://inancgumus.github.io/samples/jpg-beach-1020x670-610kb.jpg", to),
-		dl.NewHTTPTransfer("https://inancgumus.github.io/samples/jpg-beach-1020x670-80kb.jpg", to),
-		dl.NewHTTPTransfer("https://inancgumus.github.io/samples/jpg-beach-1900x1250-1700kb.jpg", to),
-	}
-
-	// transfers := []dl.Transfer{
-	// 	dl.NewHTTPTransfer(ctx, "http://inanc.io/1"),
-	// 	dl.NewHTTPTransfer(ctx, "http://inanc.io/2"),
-	// 	dl.NewHTTPTransfer(ctx, "http://inanc.io/3"),
-	// }
-
-	dl.UI(sess.Start(transfers...))
-
-	// results := dl.Drain(sess.Start(urls))
-	// for _, r := range results {
-	// 	fmt.Printf("%s [err: %v — %d/%d]\n",
-	// 		r.URL, r.Error, r.Downloaded, r.Total)
-	// }
-
-	// how to handle ctrl+c signals?
-	//   register a signal
-	//   let the downloader now that the operation halts
-	//   with Downloader.onCancel or "context.Context"
-
-	// run with: GOTRACEBACK=all go run -race main.go
-	// time.Sleep(time.Second * 2)
-	// panic("give me the stack trace")
-}