package web

import (
	"io"
	"log"
	"sync"
	"sync/atomic"
	"testing"
	"time"
)

// R-695 (v0.275.0) — the file-browser sync is single-flight: callers that queued behind a running sync
// are covered by ONE sync that read the state after they asked, not by one restart each; a caller whose
// request came after a sync began reading is never dropped.
//
// COMPANION RED-PROOF (REPORT.md): remove the `fbDoneGen >= mine` early return — five queued callers
// then run five syncs.
func TestR695_QueuedSyncsCoalesceIntoOne(t *testing.T) {
	s := &Server{logger: log.New(io.Discard, "", 0)}
	var runs int32
	release := make(chan struct{})
	first := true
	var fmu sync.Mutex
	s.syncFileBrowserHook = func() {
		atomic.AddInt32(&runs, 1)
		fmu.Lock()
		f := first
		first = false
		fmu.Unlock()
		if f {
			<-release // the first sync is slow: everything below queues behind it
		}
	}
	var wg sync.WaitGroup
	wg.Add(1)
	go func() { defer wg.Done(); s.SyncFileBrowserMounts() }()
	time.Sleep(50 * time.Millisecond) // the first sync holds the lock
	for i := 0; i < 5; i++ {
		wg.Add(1)
		go func() { defer wg.Done(); s.SyncFileBrowserMounts() }()
	}
	time.Sleep(50 * time.Millisecond) // all five are queued
	close(release)
	wg.Wait()
	if got := atomic.LoadInt32(&runs); got != 2 {
		t.Fatalf("%d syncs ran for 6 requests (1 running + 5 queued) — want 2: the running one and ONE that re-reads for the queue", got)
	}
	// A request after everything finished is never dropped.
	s.SyncFileBrowserMounts()
	if got := atomic.LoadInt32(&runs); got != 3 {
		t.Fatalf("a new request after the queue drained ran %d syncs in total, want 3", got)
	}
}