package e2e

import (
	"context"
	"fmt"
	"io"
	"net"
	"testing"
	"time"

	"github.com/iceBear67/redapricot/client"
)

// startClientWithBandwidth is startClient with an egress cap, for the shaping
// tests. Only the client→hub direction is shaped, which in this harness is the
// leg carrying the mock destination's echo back to the player.
func startClientWithBandwidth(t *testing.T, hubAddr, psk string, maxTunnels int, bandwidth string, mappings []client.Mapping) *client.Client {
	t.Helper()
	cfg := &client.Config{
		Server:         hubAddr,
		PSK:            psk,
		MaxTunnels:     maxTunnels,
		PingIntervalMs: 20000,
		MaxBandwidth:   bandwidth,
		Mappings:       mappings,
	}
	c := client.New(cfg)
	ctx, cancel := context.WithCancel(context.Background())
	t.Cleanup(func() {
		cancel()
		c.Close()
	})
	if err := c.Start(ctx); err != nil {
		t.Fatalf("client start: %v", err)
	}
	time.Sleep(200 * time.Millisecond)
	return c
}

// drain reads a connection until it fails, so a greedy player keeps pulling
// bytes instead of stalling on its own receive window.
func drain(conn net.Conn) {
	go func() { _, _ = io.Copy(io.Discard, conn) }()
}

// TestBandwidthCapIsEnforced pushes a payload that cannot fit in the burst and
// asserts the transfer takes at least as long as the configured rate implies.
// This is the first timing assertion in the suite, so the bounds are wide: the
// unshaped path completes this in well under a second, making the lower bound
// an unambiguous signal rather than a tight measurement.
func TestBandwidthCapIsEnforced(t *testing.T) {
	const psk = "e2e-bwcap"
	port := freePort(t)
	hubAddr := fmt.Sprintf("127.0.0.1:%d", port)
	startHub(t, port, psk)
	dest := newMockDest(t, modeEcho)
	startClientWithBandwidth(t, hubAddr, psk, 1, "1MB/s", []client.Mapping{
		{Pattern: "mc.local", Destination: dest.addr},
	})

	pc := dialPlayer(t, hubAddr, "mc.local")
	defer pc.Close()

	payload := make([]byte, 2*1024*1024)
	for i := range payload {
		payload[i] = byte(i*31 + 7)
	}

	start := time.Now()
	writeErr := make(chan error, 1)
	go func() {
		_, err := pc.Write(payload)
		writeErr <- err
	}()
	got := make([]byte, len(payload))
	_ = pc.SetReadDeadline(time.Now().Add(60 * time.Second))
	if _, err := io.ReadFull(pc, got); err != nil {
		t.Fatalf("read echo: %v", err)
	}
	elapsed := time.Since(start)
	if err := <-writeErr; err != nil {
		t.Fatalf("write payload: %v", err)
	}

	// 2 MiB at 1 MiB/s, minus the 200 KiB the bucket has banked, is ~1.8 s.
	const floor = 1200 * time.Millisecond
	if elapsed < floor {
		t.Errorf("2 MiB echoed back in %v under a 1MB/s cap; expected at least %v, so the cap is not taking effect", elapsed, floor)
	}
	if elapsed > 30*time.Second {
		t.Errorf("transfer took %v, far beyond the ~1.8s the rate implies", elapsed)
	}
}

// TestCappedBandwidthDoesNotStarveLightStreams is the point of the fair queue:
// with the link deliberately capped and three players saturating it, a fourth
// player exchanging small messages must keep round-tripping promptly. A plain
// FIFO token bucket would leave it queued behind the heavy players' backlog,
// which for a real Minecraft client means a keepalive timeout — the exact
// failure this feature exists to prevent.
func TestCappedBandwidthDoesNotStarveLightStreams(t *testing.T) {
	const psk = "e2e-bwfair"
	port := freePort(t)
	hubAddr := fmt.Sprintf("127.0.0.1:%d", port)
	startHub(t, port, psk)
	dest := newMockDest(t, modeEcho)
	// Each player has its own worker conn; the shaper is still the only thing
	// splitting the shared uplink budget.
	startClientWithBandwidth(t, hubAddr, psk, 4, "1MB/s", []client.Mapping{
		{Pattern: "mc.local", Destination: dest.addr},
	})

	// Three greedy players: each writes megabytes and keeps draining the echo,
	// so they compete for the cap for the whole test rather than parking on
	// their own flow-control windows.
	for i := 0; i < 3; i++ {
		heavy := dialPlayer(t, hubAddr, "mc.local")
		defer heavy.Close()
		drain(heavy)
		go func() { _, _ = heavy.Write(make([]byte, 8*1024*1024)) }()
	}
	time.Sleep(500 * time.Millisecond) // let them saturate the shaper

	light := dialPlayer(t, hubAddr, "mc.local")
	defer light.Close()
	payload := make([]byte, 4*1024)
	for i := range payload {
		payload[i] = byte(i*13 + 5)
	}

	var worst time.Duration
	for i := 0; i < 10; i++ {
		start := time.Now()
		playerEcho(t, light, payload)
		if d := time.Since(start); d > worst {
			worst = d
		}
	}

	// Fair sharing puts a 4 KiB round at roughly 4 KiB / (1 MiB/s ÷ 4) ≈ 16 ms of
	// link time. The bound is two orders of magnitude looser so only genuine
	// starvation trips it.
	const limit = 3 * time.Second
	if worst > limit {
		t.Errorf("slowest small round-trip took %v (limit %v); heavy streams are crowding out the light one", worst, limit)
	}
}