package audit

import (
	"bytes"
	"context"
	"encoding/csv"
	"fmt"
	"net/http"
	"net/http/httptest"
	"os"
	"runtime"
	"strings"
	"testing"
	"time"

	"github.com/jackc/pgx/v5/pgxpool"
)

func setupExportTest(t *testing.T) (*Log, func()) {
	t.Helper()
	adminDSN := os.Getenv("TEST_ADMIN_DSN")
	if adminDSN == "" {
		t.Skip("TEST_ADMIN_DSN nicht gesetzt, Integrationstest uebersprungen")
	}
	ctx := context.Background()

	pool, err := pgxpool.New(ctx, adminDSN)
	if err != nil {
		t.Fatalf("pool: %v", err)
	}
	if _, err := pool.Exec(ctx, `
		CREATE TABLE IF NOT EXISTS audit_events (
			id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
			occurred_at TIMESTAMPTZ NOT NULL DEFAULT now(),
			tenant_slug TEXT NOT NULL CHECK (tenant_slug <> ''),
			actor TEXT NOT NULL CHECK (actor <> ''),
			action TEXT NOT NULL CHECK (action <> ''),
			target TEXT NOT NULL,
			metadata JSONB NOT NULL DEFAULT '{}'::jsonb
		)`); err != nil {
		t.Fatalf("schema: %v", err)
	}

	cleanup := func() { pool.Close() }
	return NewLog(pool), cleanup
}

// Akzeptanzkriterium 1 + Pruefung 2: Filterkombinationen liefern korrekte
// Teilmengen.
func TestExport_FilterCombinations(t *testing.T) {
	log, cleanup := setupExportTest(t)
	defer cleanup()
	ctx := context.Background()

	run := fmt.Sprintf("_%d", time.Now().UnixNano())
	tenantA, tenantB := "test_fa"+run, "test_fb"+run
	alice, bob := "alice"+run, "bob"+run

	events := []Event{
		{TenantSlug: tenantA, Actor: alice, Action: "login", Target: "x"},
		{TenantSlug: tenantA, Actor: bob, Action: "login", Target: "x"},
		{TenantSlug: tenantA, Actor: alice, Action: "logout", Target: "x"},
		{TenantSlug: tenantB, Actor: alice, Action: "login", Target: "x"},
	}
	for _, e := range events {
		if err := log.Record(ctx, e); err != nil {
			t.Fatalf("record: %v", err)
		}
	}

	cases := []struct {
		name    string
		filter  Filter
		wantLen int
	}{
		{"nach tenant", Filter{TenantSlug: tenantA}, 3},
		{"nach tenant+actor", Filter{TenantSlug: tenantA, Actor: alice}, 2},
		{"nach tenant+actor+action", Filter{TenantSlug: tenantA, Actor: alice, Action: "login"}, 1},
		{"nach actor ueber beide tenants", Filter{Actor: alice, Action: "login"}, 2},
	}

	for _, c := range cases {
		t.Run(c.name, func(t *testing.T) {
			var buf bytes.Buffer
			if err := log.StreamCSV(ctx, c.filter, &buf); err != nil {
				t.Fatalf("stream: %v", err)
			}
			rows, err := csv.NewReader(&buf).ReadAll()
			if err != nil {
				t.Fatalf("csv parsen: %v", err)
			}
			got := len(rows) - 1 // Header abziehen
			if got != c.wantLen {
				t.Fatalf("erwartet %d zeilen, habe %d", c.wantLen, got)
			}
		})
	}
}

// Akzeptanzkriterium 1 + Pruefung 2: Zeitraum-Filter.
func TestExport_TimeRangeFilter(t *testing.T) {
	log, cleanup := setupExportTest(t)
	defer cleanup()
	ctx := context.Background()

	tenant := fmt.Sprintf("test_tr_%d", time.Now().UnixNano())
	past := time.Now().Add(-48 * time.Hour)
	future := time.Now().Add(48 * time.Hour)

	if err := log.Record(ctx, Event{TenantSlug: tenant, Actor: "a", Action: "x", Target: "t", OccurredAt: time.Now()}); err != nil {
		t.Fatalf("record: %v", err)
	}

	var buf bytes.Buffer
	if err := log.StreamCSV(ctx, Filter{TenantSlug: tenant, From: &past, To: &future}, &buf); err != nil {
		t.Fatalf("stream (innerhalb range): %v", err)
	}
	if got := countLines(buf.String()) - 1; got != 1 {
		t.Fatalf("erwartet 1 eintrag innerhalb des zeitraums, habe %d", got)
	}

	farPast := time.Now().Add(-96 * time.Hour)
	buf.Reset()
	if err := log.StreamCSV(ctx, Filter{TenantSlug: tenant, From: &farPast, To: &past}, &buf); err != nil {
		t.Fatalf("stream (ausserhalb range): %v", err)
	}
	if got := countLines(buf.String()) - 1; got != 0 {
		t.Fatalf("erwartet 0 eintraege ausserhalb des zeitraums, habe %d", got)
	}
}

func countLines(s string) int {
	s = strings.TrimRight(s, "\n")
	if s == "" {
		return 0
	}
	return len(strings.Split(s, "\n"))
}

// Akzeptanzkriterium 3 + Pruefung 1: Export mit hoher Eintragszahl ohne
// uebermaessigen Speicherverbrauch — Stichprobe per runtime.MemStats.
func TestExport_StreamsLargeResultWithoutExcessiveMemory(t *testing.T) {
	log, cleanup := setupExportTest(t)
	defer cleanup()
	ctx := context.Background()

	tenant := fmt.Sprintf("test_large_%d", time.Now().UnixNano())
	const n = 20000
	for i := 0; i < n; i++ {
		if err := log.Record(ctx, Event{TenantSlug: tenant, Actor: "bulk", Action: "test.bulk", Target: fmt.Sprintf("obj-%d", i)}); err != nil {
			t.Fatalf("record %d: %v", i, err)
		}
	}

	runtime.GC()
	var before runtime.MemStats
	runtime.ReadMemStats(&before)

	lineCount := 0
	cw := &countingWriter{onWrite: func(p []byte) { lineCount += strings.Count(string(p), "\n") }}
	if err := log.StreamCSV(ctx, Filter{TenantSlug: tenant}, cw); err != nil {
		t.Fatalf("stream: %v", err)
	}

	runtime.GC()
	var after runtime.MemStats
	runtime.ReadMemStats(&after)

	if lineCount != n+1 { // +1 Header
		t.Fatalf("erwartet %d zeilen (inkl. header), habe %d", n+1, lineCount)
	}

	// Grobe Stichprobe: ein NICHT streamender Export haette hier locker
	// mehrere MB an einmal gehaltenen Zeilen/Strings erzeugt. Grosszuegige
	// Schwelle, da Go-Heap-Messungen naturgemaess rauschen.
	const maxAcceptableGrowth = 3 * 1024 * 1024 // 3 MB
	growth := int64(after.HeapAlloc) - int64(before.HeapAlloc)
	t.Logf("heap-wachstum waehrend export von %d zeilen: %d bytes (schwelle: %d)", n, growth, maxAcceptableGrowth)
	if growth > maxAcceptableGrowth {
		t.Fatalf("heap ist um %d bytes gewachsen, erwartet unter %d (hinweis auf vollstaendige pufferung statt streaming)", growth, maxAcceptableGrowth)
	}
}

type countingWriter struct {
	onWrite func(p []byte)
}

func (w *countingWriter) Write(p []byte) (int, error) {
	w.onWrite(p)
	return len(p), nil
}

// Akzeptanzkriterium 2 + Pruefung 3: Zugriff ohne passende Berechtigung wird abgewiesen.
func TestExportHandler_RejectsWithoutAuthorization(t *testing.T) {
	log, cleanup := setupExportTest(t)
	defer cleanup()

	handler := NewExportHandler(log, func(ctx context.Context, caller string) bool {
		return caller == "berechtigte-person@example.com"
	})

	req := httptest.NewRequest(http.MethodGet, "/audit/export?caller=unberechtigt@example.com", nil)
	rec := httptest.NewRecorder()
	handler.Export(rec, req)
	if rec.Code != http.StatusForbidden {
		t.Fatalf("unberechtigt: status = %d, want 403", rec.Code)
	}

	reqNoCaller := httptest.NewRequest(http.MethodGet, "/audit/export", nil)
	recNoCaller := httptest.NewRecorder()
	handler.Export(recNoCaller, reqNoCaller)
	if recNoCaller.Code != http.StatusForbidden {
		t.Fatalf("ohne caller: status = %d, want 403", recNoCaller.Code)
	}

	reqOK := httptest.NewRequest(http.MethodGet, "/audit/export?caller=berechtigte-person@example.com", nil)
	recOK := httptest.NewRecorder()
	handler.Export(recOK, reqOK)
	if recOK.Code != http.StatusOK {
		t.Fatalf("berechtigt: status = %d, want 200", recOK.Code)
	}
}