package main

import (
	"bytes"
	"context"
	"database/sql"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"
)

const maxDatabaseRestoreBytes int64 = 2 << 30

type postgresToolConfig struct {
	dbURL string
	env   []string
}

func postgresToolConfigFromSettings() (postgresToolConfig, string, error) {
	dsn, err := buildPostgresDSNFromSettings()
	if err != nil {
		return postgresToolConfig{}, "", err
	}

	dbURL, env, err := postgresToolConnection(dsn)
	if err != nil {
		return postgresToolConfig{}, "", err
	}

	return postgresToolConfig{
		dbURL: dbURL,
		env:   env,
	}, dsn, nil
}

func postgresToolConnection(dsn string) (string, []string, error) {
	dsn = strings.TrimSpace(dsn)
	if dsn == "" {
		return "", nil, errors.New("databaseUrl ist leer")
	}

	u, err := url.Parse(dsn)
	if err != nil {
		return "", nil, appErrorf("databaseUrl ungueltig: %w", err)
	}

	switch strings.ToLower(strings.TrimSpace(u.Scheme)) {
	case "postgres", "postgresql":
	default:
		return "", nil, appErrorf("databaseUrl muss postgres:// oder postgresql:// verwenden")
	}

	env := os.Environ()

	if u.User != nil {
		user := u.User.Username()
		if pw, ok := u.User.Password(); ok && strings.TrimSpace(pw) != "" {
			env = upsertEnv(env, "PGPASSWORD", pw)
		}
		if strings.TrimSpace(user) != "" {
			u.User = url.User(user)
		} else {
			u.User = nil
		}
	}

	if sslMode := strings.TrimSpace(u.Query().Get("sslmode")); sslMode != "" {
		env = upsertEnv(env, "PGSSLMODE", sslMode)
	}
	env = upsertEnv(env, "PGCONNECT_TIMEOUT", "10")

	return u.String(), env, nil
}

func postgresToolPath(name string) (string, error) {
	path, err := exec.LookPath(name)
	if err == nil && strings.TrimSpace(path) != "" {
		return path, nil
	}

	return "", appErrorf("%s wurde nicht gefunden. Installiere postgresql-client oder nimm %s in PATH auf.", name, name)
}

func runPostgresTool(ctx context.Context, tool string, cfg postgresToolConfig, args ...string) (string, error) {
	toolPath, err := postgresToolPath(tool)
	if err != nil {
		return "", err
	}

	cmd := exec.CommandContext(ctx, toolPath, args...)
	cmd.Env = cfg.env
	hideCommandWindow(cmd)

	var stderr bytes.Buffer
	cmd.Stderr = &stderr

	if err := cmd.Run(); err != nil {
		msg := strings.TrimSpace(stderr.String())
		if msg == "" {
			msg = err.Error()
		}
		return trimCommandOutput(msg), err
	}

	return trimCommandOutput(stderr.String()), nil
}

func trimCommandOutput(s string) string {
	s = strings.TrimSpace(s)
	const maxLen = 4000
	if len(s) <= maxLen {
		return s
	}
	return s[:maxLen] + "\n..."
}

func settingsDatabaseBackupHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		http.Error(w, "Nur GET erlaubt", http.StatusMethodNotAllowed)
		return
	}

	storeConfig, err := buildModelStoreConfigFromSettings()
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	if storeConfig.Type == databaseTypeSQLite {
		settingsSQLiteDatabaseBackupHandler(w, r, storeConfig)
		return
	}

	cfg, _, err := postgresToolConfigFromSettings()
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}

	tmp, err := os.CreateTemp("", "nsfwapp-db-backup-*.dump")
	if err != nil {
		http.Error(w, "Backup-Datei konnte nicht erstellt werden: "+err.Error(), http.StatusInternalServerError)
		return
	}
	tmpPath := tmp.Name()
	defer os.Remove(tmpPath)

	ctx, cancel := context.WithTimeout(r.Context(), 10*time.Minute)
	defer cancel()

	toolPath, err := postgresToolPath("pg_dump")
	if err != nil {
		_ = tmp.Close()
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}

	cmd := exec.CommandContext(
		ctx,
		toolPath,
		"--format=custom",
		"--blobs",
		"--no-owner",
		"--no-privileges",
		"--dbname="+cfg.dbURL,
	)
	cmd.Env = cfg.env
	cmd.Stdout = tmp
	hideCommandWindow(cmd)

	var stderr bytes.Buffer
	cmd.Stderr = &stderr

	runErr := cmd.Run()
	closeErr := tmp.Close()
	if runErr != nil {
		msg := trimCommandOutput(stderr.String())
		if msg == "" {
			msg = runErr.Error()
		}
		http.Error(w, "pg_dump fehlgeschlagen: "+msg, http.StatusInternalServerError)
		return
	}
	if closeErr != nil {
		http.Error(w, "Backup-Datei konnte nicht geschlossen werden: "+closeErr.Error(), http.StatusInternalServerError)
		return
	}

	info, err := os.Stat(tmpPath)
	if err != nil {
		http.Error(w, "Backup-Datei konnte nicht gelesen werden: "+err.Error(), http.StatusInternalServerError)
		return
	}

	f, err := os.Open(tmpPath)
	if err != nil {
		http.Error(w, "Backup-Datei konnte nicht geöffnet werden: "+err.Error(), http.StatusInternalServerError)
		return
	}
	defer f.Close()

	filename := "nsfwapp-db-backup-" + time.Now().Format("20060102-150405") + ".dump"
	w.Header().Set("Content-Type", "application/octet-stream")
	w.Header().Set("Content-Disposition", fmt.Sprintf(`attachment; filename="%s"`, filename))
	w.Header().Set("Cache-Control", "no-store")
	w.Header().Set("Content-Length", fmt.Sprintf("%d", info.Size()))

	http.ServeContent(w, r, filename, info.ModTime(), f)
}

func settingsSQLiteDatabaseBackupHandler(w http.ResponseWriter, r *http.Request, storeConfig ModelStoreConfig) {
	tmp, err := os.CreateTemp("", "nsfwapp-db-backup-*.sqlite")
	if err != nil {
		http.Error(w, "Backup-Datei konnte nicht erstellt werden: "+err.Error(), http.StatusInternalServerError)
		return
	}
	tmpPath := tmp.Name()
	_ = tmp.Close()
	_ = os.Remove(tmpPath)
	defer os.Remove(tmpPath)

	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Minute)
	defer cancel()

	db, err := sql.Open("sqlite", storeConfig.SQLitePath)
	if err != nil {
		http.Error(w, "SQLite konnte nicht geöffnet werden: "+err.Error(), http.StatusInternalServerError)
		return
	}
	defer db.Close()

	if _, err := db.ExecContext(ctx, `PRAGMA busy_timeout = 5000;`); err != nil {
		http.Error(w, "SQLite Backup konnte nicht vorbereitet werden: "+err.Error(), http.StatusInternalServerError)
		return
	}
	if _, err := db.ExecContext(ctx, "VACUUM INTO "+sqliteLiteral(tmpPath)); err != nil {
		http.Error(w, "SQLite Backup fehlgeschlagen: "+err.Error(), http.StatusInternalServerError)
		return
	}

	info, err := os.Stat(tmpPath)
	if err != nil {
		http.Error(w, "Backup-Datei konnte nicht gelesen werden: "+err.Error(), http.StatusInternalServerError)
		return
	}

	f, err := os.Open(tmpPath)
	if err != nil {
		http.Error(w, "Backup-Datei konnte nicht geöffnet werden: "+err.Error(), http.StatusInternalServerError)
		return
	}
	defer f.Close()

	filename := "nsfwapp-db-backup-" + time.Now().Format("20060102-150405") + ".sqlite"
	w.Header().Set("Content-Type", "application/vnd.sqlite3")
	w.Header().Set("Content-Disposition", fmt.Sprintf(`attachment; filename="%s"`, filename))
	w.Header().Set("Cache-Control", "no-store")
	w.Header().Set("Content-Length", fmt.Sprintf("%d", info.Size()))

	http.ServeContent(w, r, filename, info.ModTime(), f)
}

func settingsDatabaseRestoreHandler(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodPost {
		http.Error(w, "Nur POST erlaubt", http.StatusMethodNotAllowed)
		return
	}

	storeConfig, err := buildModelStoreConfigFromSettings()
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}

	r.Body = http.MaxBytesReader(w, r.Body, maxDatabaseRestoreBytes)
	if err := r.ParseMultipartForm(32 << 20); err != nil {
		http.Error(w, "Restore-Datei konnte nicht gelesen werden: "+err.Error(), http.StatusBadRequest)
		return
	}
	if r.MultipartForm != nil {
		defer r.MultipartForm.RemoveAll()
	}

	file, header, err := r.FormFile("backup")
	if err != nil {
		http.Error(w, "Form-Feld 'backup' fehlt: "+err.Error(), http.StatusBadRequest)
		return
	}
	defer file.Close()

	tmp, err := os.CreateTemp("", "nsfwapp-db-restore-*.dump")
	if err != nil {
		http.Error(w, "Restore-Datei konnte nicht vorbereitet werden: "+err.Error(), http.StatusInternalServerError)
		return
	}
	tmpPath := tmp.Name()
	defer os.Remove(tmpPath)

	written, err := io.Copy(tmp, file)
	closeErr := tmp.Close()
	if err != nil {
		http.Error(w, "Restore-Datei konnte nicht gespeichert werden: "+err.Error(), http.StatusBadRequest)
		return
	}
	if closeErr != nil {
		http.Error(w, "Restore-Datei konnte nicht geschlossen werden: "+closeErr.Error(), http.StatusInternalServerError)
		return
	}
	if written <= 0 {
		http.Error(w, "Restore-Datei ist leer", http.StatusBadRequest)
		return
	}

	if storeConfig.Type == databaseTypeSQLite {
		if err := restoreSQLiteDatabase(storeConfig, tmpPath); err != nil {
			http.Error(w, "SQLite Restore fehlgeschlagen: "+err.Error(), http.StatusInternalServerError)
			return
		}

		refreshedStore := NewModelStore(storeConfig)
		if err := refreshedStore.Load(); err != nil {
			appLogln("Models DB nach Restore konnte nicht neu verbunden werden:", err)
		} else {
			setModelStore(refreshedStore)
		}

		writeJSON(w, http.StatusOK, map[string]any{
			"ok":       true,
			"fileName": strings.TrimSpace(header.Filename),
			"bytes":    written,
		})
		return
	}

	cfg, dsn, err := postgresToolConfigFromSettings()
	if err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}

	ctx, cancel := context.WithTimeout(r.Context(), 15*time.Minute)
	defer cancel()

	stderr, err := runPostgresTool(
		ctx,
		"pg_restore",
		cfg,
		"--clean",
		"--if-exists",
		"--no-owner",
		"--no-privileges",
		"--single-transaction",
		"--dbname="+cfg.dbURL,
		filepath.Clean(tmpPath),
	)
	if err != nil {
		http.Error(w, "pg_restore fehlgeschlagen: "+stderr, http.StatusInternalServerError)
		return
	}

	refreshedStore := NewModelStore(ModelStoreConfig{Type: databaseTypePostgres, DSN: dsn})
	if err := refreshedStore.Load(); err != nil {
		appLogln("⚠️ Models DB nach Restore konnte nicht neu verbunden werden:", err)
	} else {
		setModelStore(refreshedStore)
	}

	writeJSON(w, http.StatusOK, map[string]any{
		"ok":       true,
		"fileName": strings.TrimSpace(header.Filename),
		"bytes":    written,
	})
}

func restoreSQLiteDatabase(storeConfig ModelStoreConfig, restorePath string) error {
	restorePath = filepath.Clean(strings.TrimSpace(restorePath))
	if restorePath == "" {
		return errors.New("restore path fehlt")
	}
	if err := validateSQLiteDatabaseFile(restorePath); err != nil {
		return err
	}

	targetPath := filepath.Clean(strings.TrimSpace(storeConfig.SQLitePath))
	if targetPath == "" {
		return errors.New("sqlite path fehlt")
	}
	if err := os.MkdirAll(filepath.Dir(targetPath), 0755); err != nil {
		return err
	}

	oldStore := getModelStore()
	if oldStore != nil && oldStore.isSQLite() && oldStore.db != nil {
		_, _ = oldStore.db.Exec(`PRAGMA wal_checkpoint(TRUNCATE);`)
		_ = oldStore.Close()
	}

	if _, err := os.Stat(targetPath); err == nil {
		backupPath := targetPath + ".before-restore-" + time.Now().Format("20060102-150405") + ".bak"
		if _, err := copyDatabaseFile(targetPath, backupPath); err != nil {
			return appErrorf("Sicherung der bisherigen SQLite-Datei fehlgeschlagen: %w", err)
		}
	}

	_ = os.Remove(targetPath + "-wal")
	_ = os.Remove(targetPath + "-shm")
	_ = os.Remove(targetPath)

	if _, err := copyDatabaseFile(restorePath, targetPath); err != nil {
		return err
	}
	return nil
}

func validateSQLiteDatabaseFile(path string) error {
	db, err := sql.Open("sqlite", path)
	if err != nil {
		return err
	}
	defer db.Close()

	if err := db.Ping(); err != nil {
		return err
	}

	var name string
	err = db.QueryRow(`SELECT name FROM sqlite_master WHERE type='table' AND name='models' LIMIT 1;`).Scan(&name)
	if errors.Is(err, sql.ErrNoRows) {
		return errors.New("SQLite-Datei enthaelt keine models-Tabelle")
	}
	return err
}

func copyDatabaseFile(src, dst string) (int64, error) {
	in, err := os.Open(src)
	if err != nil {
		return 0, err
	}
	defer in.Close()

	out, err := os.OpenFile(dst, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
	if err != nil {
		return 0, err
	}
	written, copyErr := io.Copy(out, in)
	closeErr := out.Close()
	if copyErr != nil {
		return written, copyErr
	}
	if closeErr != nil {
		return written, closeErr
	}
	return written, nil
}

func sqliteLiteral(value string) string {
	return "'" + strings.ReplaceAll(value, "'", "''") + "'"
}