package server

import (
	"context"
	"encoding/json"
	"net/http"
	"net/http/httptest"
	"runtime"
	"slices"
	"testing"
	"time"

	"git.eeqj.de/sneak/routewatch/internal/config"
	"git.eeqj.de/sneak/routewatch/internal/database"
	"git.eeqj.de/sneak/routewatch/internal/logger"
	"git.eeqj.de/sneak/routewatch/internal/metrics"
	"git.eeqj.de/sneak/routewatch/internal/streamer"
	"github.com/google/uuid"
)

// blockingStatsDB embeds database.Store (left nil) and overrides only
// GetStatsContext, which blocks until release is closed. The stats handlers
// call it in a goroutine; every other Store method is unused on the timeout
// path and would panic if called.
type blockingStatsDB struct {
	database.Store
	release chan struct{}
}

func (d blockingStatsDB) GetStatsContext(_ context.Context) (database.Stats, error) {
	<-d.release

	return database.Stats{}, nil
}

// TestStatsHandlersDoNotLeakOnTimeout drives each stats handler repeatedly with
// a request whose context times out before the database responds, then releases
// the blocked queries and asserts the goroutine count returns to its starting
// value. Before the fix the per-request goroutine sent on an unbuffered channel
// that nothing received once the timeout won, so it blocked forever and every
// poll leaked one goroutine.
func TestStatsHandlersDoNotLeakOnTimeout(t *testing.T) {
	release := make(chan struct{})
	db := blockingStatsDB{release: release}
	s := New(db, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})

	handlers := map[string]http.HandlerFunc{
		"status.json": s.handleStatusJSON(),
		"stats":       s.handleStats(),
	}

	baseline := settledGoroutineCount()

	const (
		iterations     = 20
		requestTimeout = 50 * time.Millisecond
	)
	for _, handler := range handlers {
		for range iterations {
			ctx, cancel := context.WithTimeout(context.Background(), requestTimeout)
			req := httptest.NewRequest(http.MethodGet, "/", nil).WithContext(ctx)
			handler(httptest.NewRecorder(), req)
			cancel()
		}
	}

	// Let the blocked queries finish; with buffered channels each goroutine's
	// send now succeeds and the goroutine exits.
	close(release)

	if !waitForGoroutines(baseline) {
		t.Fatalf("goroutines did not return to baseline %d, got %d",
			baseline, runtime.NumGoroutine())
	}
}

// TestStatsHandlersAnswerFromMemory checks that both stats handlers answer 200
// with the live route counts and the prefix distribution while the database is
// closed, so that any query would fail: the request path reads them from
// memory. The prefix distribution query it used to run read every live route
// and, on a large database, took the whole 4-second deadline, so
// /api/v1/stats answered 500 (https://git.eeqj.de/sneak/routewatch/issues/30).
// The oldest and newest route times still come from one-row lookups at the ends
// of an index; with the database closed they are left out of the answer.
func TestStatsHandlersAnswerFromMemory(t *testing.T) {
	db, err := database.New(&config.Config{StateDir: t.TempDir()}, logger.New())
	if err != nil {
		t.Fatalf("database.New: %v", err)
	}

	ts := time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC)
	start, end, err := database.CalculateIPv4Range("198.51.100.0/24")
	if err != nil {
		t.Fatalf("CalculateIPv4Range: %v", err)
	}
	if err := db.UpsertLiveRouteBatch([]*database.LiveRoute{
		{
			ID: uuid.New(), Prefix: "198.51.100.0/24", MaskLength: 24, IPVersion: 4,
			OriginASN: 64500, PeerIP: "192.0.2.1", ASPath: []int{64500}, NextHop: "192.0.2.1",
			LastUpdated: ts, V4IPStart: &start, V4IPEnd: &end,
		},
		{
			ID: uuid.New(), Prefix: "2001:db8::/32", MaskLength: 32, IPVersion: 6,
			OriginASN: 64501, PeerIP: "2001:db8::1", ASPath: []int{64501}, NextHop: "2001:db8::1",
			LastUpdated: ts,
		},
	}); err != nil {
		t.Fatalf("UpsertLiveRouteBatch: %v", err)
	}
	if err := db.Close(); err != nil {
		t.Fatalf("Close: %v", err)
	}

	s := New(db, streamer.New(logger.New(), metrics.New()), logger.New(), &config.Config{})
	handlers := map[string]http.HandlerFunc{
		"status.json": s.handleStatusJSON(),
		"stats":       s.handleStats(),
	}

	for name, handler := range handlers {
		rec := httptest.NewRecorder()
		handler(rec, httptest.NewRequest(http.MethodGet, "/", nil))
		if rec.Code != http.StatusOK {
			t.Errorf("%s: status %d, want %d; body %s", name, rec.Code, http.StatusOK, rec.Body)

			continue
		}

		var body struct {
			Data struct {
				IPv4Routes             int                           `json:"ipv4_routes"`
				IPv6Routes             int                           `json:"ipv6_routes"`
				IPv4PrefixDistribution []database.PrefixDistribution `json:"ipv4_prefix_distribution"`
				IPv6PrefixDistribution []database.PrefixDistribution `json:"ipv6_prefix_distribution"`
			} `json:"data"`
		}
		if err := json.Unmarshal(rec.Body.Bytes(), &body); err != nil {
			t.Fatalf("%s: decoding the answer: %v", name, err)
		}

		if body.Data.IPv4Routes != 1 || body.Data.IPv6Routes != 1 {
			t.Errorf("%s: routes = (v4 %d, v6 %d), want (1, 1)", name, body.Data.IPv4Routes, body.Data.IPv6Routes)
		}
		wantV4 := []database.PrefixDistribution{{MaskLength: 24, Count: 1}}
		if !slices.Equal(body.Data.IPv4PrefixDistribution, wantV4) {
			t.Errorf("%s: IPv4 distribution = %v, want %v", name, body.Data.IPv4PrefixDistribution, wantV4)
		}
		wantV6 := []database.PrefixDistribution{{MaskLength: 32, Count: 1}}
		if !slices.Equal(body.Data.IPv6PrefixDistribution, wantV6) {
			t.Errorf("%s: IPv6 distribution = %v, want %v", name, body.Data.IPv6PrefixDistribution, wantV6)
		}
	}
}

// settledGoroutineCount lets transient goroutines finish, then reports the
// current count.
func settledGoroutineCount() int {
	prev := runtime.NumGoroutine()
	for range 20 {
		time.Sleep(10 * time.Millisecond)
		cur := runtime.NumGoroutine()
		if cur == prev {
			return cur
		}
		prev = cur
	}

	return prev
}

// waitForGoroutines waits until the goroutine count drops to target or below.
func waitForGoroutines(target int) bool {
	for range 100 {
		if runtime.NumGoroutine() <= target {
			return true
		}
		time.Sleep(10 * time.Millisecond)
	}

	return false
}