package versioning

import (
	"bytes"
	"context"
	"fmt"
	"os"
	"strings"
	"testing"
	"time"

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

	dmscrypto "gitea.perlbach24.de/scripte/nexarch/dms/internal/crypto"
	"gitea.perlbach24.de/scripte/nexarch/dms/internal/storage"
	"gitea.perlbach24.de/scripte/nexarch/dms/internal/testaudit"
	"gitea.perlbach24.de/scripte/nexarch/dms/internal/testdb"
)

// Akzeptanzkriterium 1: Textunterschiede werden zeilenweise geliefert.
func TestDiffText_LineLevelChanges(t *testing.T) {
	old := "eins\nzwei\ndrei"
	new := "eins\nZWEI\ndrei\nvier"

	got := DiffText(old, new)

	var deletes, inserts, equals []string
	for _, op := range got {
		switch op.Op {
		case DiffDelete:
			deletes = append(deletes, op.Text)
		case DiffInsert:
			inserts = append(inserts, op.Text)
		case DiffEqual:
			equals = append(equals, op.Text)
		}
	}
	if len(deletes) != 1 || deletes[0] != "zwei" {
		t.Fatalf("deletes = %v, want [zwei]", deletes)
	}
	if len(inserts) != 2 || inserts[0] != "ZWEI" || inserts[1] != "vier" {
		t.Fatalf("inserts = %v, want [ZWEI vier]", inserts)
	}
	if len(equals) != 2 {
		t.Fatalf("equals = %v, want 2 unveraenderte zeilen", equals)
	}
}

// Pflichtpruefung 2: Vergleich zweier identischer Revisionen liefert leeres
// Ergebnis (nur DiffEqual-Zeilen, keine Insert/Delete-Operationen).
func TestDiffText_IdenticalTextsProduceNoChanges(t *testing.T) {
	text := "zeile a\nzeile b\nzeile c"
	got := DiffText(text, text)
	for _, op := range got {
		if op.Op != DiffEqual {
			t.Fatalf("erwartet nur DiffEqual bei identischem text, habe: %+v", got)
		}
	}
	if len(got) != 3 {
		t.Fatalf("len = %d, want 3", len(got))
	}
}

func TestDiffText_EmptyInputs(t *testing.T) {
	if got := DiffText("", ""); len(got) != 0 {
		t.Fatalf("leer/leer: %v, want []", got)
	}
	got := DiffText("", "neu")
	if len(got) != 1 || got[0].Op != DiffInsert || got[0].Text != "neu" {
		t.Fatalf("leer/neu: %+v", got)
	}
}

// Akzeptanzkriterium 2: Metadatenänderungen werden als Vorher-Nachher
// ausgegeben.
func TestDiffMetadata_ReportsChangedFieldsOnly(t *testing.T) {
	commentBefore := "erste fassung"
	commentAfter := "zweite fassung"
	before := Revision{MimeType: "application/pdf", SizeBytes: 100, Comment: &commentBefore, CreatedBy: "user-a"}
	after := Revision{MimeType: "application/pdf", SizeBytes: 250, Comment: &commentAfter, CreatedBy: "user-b"}

	got := DiffMetadata(before, after)

	byField := map[string]MetadataDiff{}
	for _, d := range got {
		byField[d.Field] = d
	}
	if _, ok := byField["mime_type"]; ok {
		t.Fatalf("mime_type unveraendert, sollte nicht im diff stehen: %+v", got)
	}
	if d, ok := byField["size_bytes"]; !ok || d.Before != "100" || d.After != "250" {
		t.Fatalf("size_bytes diff falsch: %+v", byField["size_bytes"])
	}
	if d, ok := byField["comment"]; !ok || d.Before != commentBefore || d.After != commentAfter {
		t.Fatalf("comment diff falsch: %+v", byField["comment"])
	}
	if d, ok := byField["created_by"]; !ok || d.Before != "user-a" || d.After != "user-b" {
		t.Fatalf("created_by diff falsch: %+v", byField["created_by"])
	}
}

func TestDiffMetadata_IdenticalRevisionsProduceEmptyResult(t *testing.T) {
	comment := "gleich"
	rev := Revision{MimeType: "application/pdf", SizeBytes: 42, Comment: &comment, CreatedBy: "user-a"}
	got := DiffMetadata(rev, rev)
	if len(got) != 0 {
		t.Fatalf("erwartet leeres ergebnis bei identischen revisionen, habe: %+v", got)
	}
}

// Pflichtpruefung 3: Laufzeit bei einem 200-seitigen Dokument gemessen.
// Eine Buchseite hat ueberschlagen ~50 Zeilen Text, 200 Seiten also
// ~10.000 Zeilen je Revision.
func TestDiffText_PerformanceOn200PageDocument(t *testing.T) {
	const linesPerPage = 50
	const pages = 200
	var oldBuf, newBuf strings.Builder
	for i := 0; i < linesPerPage*pages; i++ {
		line := fmt.Sprintf("Zeile %d: lorem ipsum dolor sit amet, konsistenter beispieltext fuer diff-messung.", i)
		oldBuf.WriteString(line)
		oldBuf.WriteByte('\n')
		if i == 5000 {
			newBuf.WriteString("Zeile 5000: GEAENDERT fuer den vergleichstest.\n")
			continue
		}
		newBuf.WriteString(line)
		newBuf.WriteByte('\n')
	}

	start := time.Now()
	got := DiffText(oldBuf.String(), newBuf.String())
	elapsed := time.Since(start)

	t.Logf("200-seitiges Dokument (%d Zeilen je Revision): Diff in %s berechnet", linesPerPage*pages, elapsed)
	if elapsed > 2*time.Second {
		t.Fatalf("diff hat %s gedauert, erwartet deutlich unter 2s fuer 200 seiten", elapsed)
	}

	var changed int
	for _, op := range got {
		if op.Op != DiffEqual {
			changed++
		}
	}
	if changed == 0 {
		t.Fatalf("erwartet mindestens eine erkannte aenderung")
	}
}

func setupDiffTest(t *testing.T) (*pgxpool.Pool, *storage.Service, *dmscrypto.Service, string) {
	t.Helper()
	dsn := os.Getenv("TEST_TENANT_DSN")
	if dsn == "" {
		t.Skip("TEST_TENANT_DSN nicht gesetzt, Integrationstest uebersprungen")
	}
	ctx := context.Background()
	pool := testdb.Pool(t, dsn)
	t.Cleanup(func() { pool.Close() })
	testaudit.Ensure(t, pool)

	if _, err := pool.Exec(ctx, `
		CREATE EXTENSION IF NOT EXISTS pgcrypto;
		CREATE TABLE IF NOT EXISTS users (
			id UUID PRIMARY KEY DEFAULT gen_random_uuid(), email TEXT NOT NULL UNIQUE, name TEXT NOT NULL,
			status TEXT NOT NULL DEFAULT 'active', created_at TIMESTAMPTZ NOT NULL DEFAULT now(), updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
		);
		CREATE TABLE IF NOT EXISTS documents (
			id UUID PRIMARY KEY DEFAULT gen_random_uuid(), folder_id UUID,
			title TEXT NOT NULL, current_revision_id UUID, created_by UUID NOT NULL REFERENCES users(id),
			created_at TIMESTAMPTZ NOT NULL DEFAULT now(), updated_at TIMESTAMPTZ NOT NULL DEFAULT now(), deleted_at TIMESTAMPTZ
		);
		CREATE TABLE IF NOT EXISTS file_revisions (
			id UUID PRIMARY KEY DEFAULT gen_random_uuid(), document_id UUID NOT NULL REFERENCES documents(id) ON DELETE CASCADE,
			revision_number INT NOT NULL, storage_key TEXT NOT NULL, checksum_sha256 TEXT NOT NULL,
			size_bytes BIGINT NOT NULL, mime_type TEXT NOT NULL, created_by UUID NOT NULL REFERENCES users(id),
			created_at TIMESTAMPTZ NOT NULL DEFAULT now(), wrapped_dek BYTEA, comment TEXT,
			UNIQUE (document_id, revision_number)
		);
		CREATE TABLE IF NOT EXISTS document_locks (
			document_id UUID PRIMARY KEY REFERENCES documents(id) ON DELETE CASCADE,
			locked_by UUID NOT NULL REFERENCES users(id), locked_at TIMESTAMPTZ NOT NULL DEFAULT now(),
			lease_until TIMESTAMPTZ NOT NULL
		);
	`); err != nil {
		t.Fatalf("schema: %v", err)
	}
	t.Cleanup(func() {
		_, _ = pool.Exec(context.Background(), `TRUNCATE file_revisions, documents, users CASCADE`)
	})

	storageSvc := storage.NewService(storage.NewLocalDriver(t.TempDir(), []byte("secret"), "https://files.example.test", 0), noopUsageReporter{}, "acme")
	cryptoSvc := dmscrypto.NewService(&fakeKEKProvider{kek: bytes.Repeat([]byte{0x77}, dmscrypto.KEKSize)})

	var userID string
	if err := pool.QueryRow(ctx, `INSERT INTO users (email, name) VALUES ($1, 'A') RETURNING id`, fmt.Sprintf("diff-%d@example.test", time.Now().UnixNano())).Scan(&userID); err != nil {
		t.Fatalf("user: %v", err)
	}

	return pool, storageSvc, cryptoSvc, userID
}

// Pflichtpruefung 1: Diff an Referenzpaaren gegen erwartetes Ergebnis
// geprueft — Ende-zu-Ende ueber echte Check-in-Revisionen inkl.
// Ver-/Entschluesselung.
func TestDiffRevisions_ReferencePairMatchesExpectedResult(t *testing.T) {
	pool, storageSvc, cryptoSvc, userID := setupDiffTest(t)
	ctx := context.Background()

	var documentID string
	if err := pool.QueryRow(ctx, `INSERT INTO documents (title, created_by) VALUES ('vertrag.txt', $1) RETURNING id`, userID).Scan(&documentID); err != nil {
		t.Fatalf("dokument anlegen: %v", err)
	}

	if _, err := CheckOut(ctx, pool, documentID, userID, DefaultLeaseDuration); err != nil {
		t.Fatalf("checkout 1: %v", err)
	}
	revA, err := CheckIn(ctx, pool, storageSvc, cryptoSvc, "acme", documentID, userID, "erste fassung", "text/plain", strings.NewReader("Zeile 1\nZeile 2\nZeile 3"))
	if err != nil {
		t.Fatalf("checkin 1: %v", err)
	}

	if _, err := CheckOut(ctx, pool, documentID, userID, DefaultLeaseDuration); err != nil {
		t.Fatalf("checkout 2: %v", err)
	}
	revB, err := CheckIn(ctx, pool, storageSvc, cryptoSvc, "acme", documentID, userID, "zweite fassung", "text/plain", strings.NewReader("Zeile 1\nZeile 2 geaendert\nZeile 3\nZeile 4"))
	if err != nil {
		t.Fatalf("checkin 2: %v", err)
	}

	textDiff, metadataDiff, err := DiffRevisions(ctx, pool, storageSvc, cryptoSvc, "acme", documentID, revA.ID, revB.ID)
	if err != nil {
		t.Fatalf("DiffRevisions: %v", err)
	}

	var deletes, inserts int
	for _, op := range textDiff {
		switch op.Op {
		case DiffDelete:
			deletes++
		case DiffInsert:
			inserts++
		}
	}
	if deletes != 1 || inserts != 2 {
		t.Fatalf("erwartet 1 loeschung, 2 einfuegungen (geaenderte + neue zeile), habe deletes=%d inserts=%d: %+v", deletes, inserts, textDiff)
	}

	byField := map[string]MetadataDiff{}
	for _, d := range metadataDiff {
		byField[d.Field] = d
	}
	if d, ok := byField["comment"]; !ok || d.Before != "erste fassung" || d.After != "zweite fassung" {
		t.Fatalf("comment-diff falsch: %+v", byField["comment"])
	}
	if d, ok := byField["size_bytes"]; !ok {
		t.Fatalf("size_bytes haette sich aendern muessen: %+v", metadataDiff)
	} else if d.Before == d.After {
		t.Fatalf("size_bytes vorher/nachher identisch, erwartet unterschied: %s", d.Before)
	}
}

func TestDiffRevisions_UnknownRevisionReturnsNotFound(t *testing.T) {
	pool, storageSvc, cryptoSvc, userID := setupDiffTest(t)
	ctx := context.Background()

	var documentID string
	if err := pool.QueryRow(ctx, `INSERT INTO documents (title, created_by) VALUES ('x.txt', $1) RETURNING id`, userID).Scan(&documentID); err != nil {
		t.Fatalf("dokument anlegen: %v", err)
	}
	if _, err := CheckOut(ctx, pool, documentID, userID, DefaultLeaseDuration); err != nil {
		t.Fatalf("checkout: %v", err)
	}
	revA, err := CheckIn(ctx, pool, storageSvc, cryptoSvc, "acme", documentID, userID, "c", "text/plain", strings.NewReader("a"))
	if err != nil {
		t.Fatalf("checkin: %v", err)
	}

	_, _, err = DiffRevisions(ctx, pool, storageSvc, cryptoSvc, "acme", documentID, revA.ID, "00000000-0000-0000-0000-000000000000")
	if err != ErrRevisionNotFound {
		t.Fatalf("err = %v, want ErrRevisionNotFound", err)
	}
}