package appbackup

import (
	"bufio"
	"compress/gzip"
	"context"
	"fmt"
	"io"
	"log"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
	"time"

	"gitea.dooplex.hu/admin/felhom-controller/internal/util"
)

// DBType represents a database engine type.
type DBType string

const (
	DBTypePostgres DBType = "postgres"
	DBTypeMariaDB  DBType = "mariadb"
)

// DiscoveredDB holds metadata about a running database container.
type DiscoveredDB struct {
	ContainerName string
	ContainerID   string
	DBType        DBType
	DBUser        string
	DBName        string
	StackName     string
}

// DumpResult holds the outcome of a single database dump.
type DumpResult struct {
	DB         DiscoveredDB
	FilePath   string
	Size       int64
	Duration   time.Duration
	Error      error
	Validation DumpValidation
}

// DumpValidation holds the result of a dump file structural check.
type DumpValidation struct {
	Valid      bool
	TableCount int
	Error      string
	FileSize   int64
	ModTime    time.Time
	// R-44 (v0.148.0) content sniff — a WARN-LEVEL signal, never a gate.
	//
	// Structural validity says nothing about whether a dump holds the customer's data. The immich
	// dump of 2026-07-19 was 52MB, had a valid header and 60+ CREATE TABLEs, and contained zero
	// users and zero assets: its whole bulk was the geodata reference tables immich ships. Size and
	// table count are therefore both useless as emptiness heuristics — but an accounts table with
	// no rows is a strong, cheap, app-agnostic hint that a dump predates the customer entirely.
	//
	// Deliberately NOT a refusal: plenty of legitimate apps have no users table (UserTableFound
	// false → inconclusive → silent), and a false positive that blocked a restore would be far
	// worse than the skew it guards against. The restore confirm shows it as one extra line.
	UserTableFound bool
	UserRows       int
	LooksEmpty     bool // UserTableFound && UserRows == 0
}

// DumpFileInfo holds info about a dump file on disk.
type DumpFileInfo struct {
	FileName   string
	StackName  string
	DBType     DBType
	Size       int64
	ModTime    time.Time
	Validation DumpValidation
	// IsUndo (R-379, v0.220.0) marks a `pre-restore-` safety copy: the undo taken immediately before
	// a reconstitution, not the app's own backup. Its VISIBILITY is a recorded decision — see the
	// comment on preRestoreDumpPrefix, "an undo the customer cannot see is not much of one" — so this
	// flag names it rather than hiding it.
	//
	// It also fixes a real, if latent, naming defect: the filename parse below used to derive
	// StackName by trimming only the engine suffix, so
	// `pre-restore-20260822T140924Z-docmost-postgres.sql` yielded the phantom stack
	// `pre-restore-20260822T140924Z-docmost`. That name reaches the `dbStacks` lookup in
	// web.buildAppBackupRows as a KEY. It renders nothing today because that function iterates
	// DEPLOYED apps and only reads the map by key — verified on the live page 2026-08-22, which
	// contained zero `pre-restore` strings while four such files sat on disk — but any future code
	// that RANGES over that map would surface a stack that does not exist.
	IsUndo bool
	// UndoAt is when the undo copy was taken, parsed from the stamp in its own filename. Zero for a
	// normal dump.
	UndoAt time.Time
}

// UndoDumpPrefix is the marker on a pre-restore safety copy. It is duplicated from
// backup.preRestoreDumpPrefix on purpose — appbackup must not import backup (that direction is the
// dependency, not this one) — and the two are pinned equal by a test.
const UndoDumpPrefix = "pre-restore-"

// trimUndoPrefix splits `pre-restore-<stamp>-<rest>` into (<rest>, <stamp>, true). Returns
// (base, "", false) for anything that is not an undo copy, so a normal dump flows unchanged.
func trimUndoPrefix(base string) (string, string, bool) {
	if !strings.HasPrefix(base, UndoDumpPrefix) {
		return base, "", false
	}
	after := strings.TrimPrefix(base, UndoDumpPrefix)
	i := strings.Index(after, "-")
	if i <= 0 {
		return base, "", false // a prefix with no stamp is not the shape writeSafetyDump writes
	}
	return after[i+1:], after[:i], true
}

// DiscoverDatabases finds running database containers via docker ps.
//
// knownStacks is the set of actually-deployed stack names; it is used to attribute each DB container to
// the correct stack (M19). Pass nil/empty for the legacy suffix-strip behaviour.
func DiscoverDatabases(ctx context.Context, logger *log.Logger, debug bool, knownStacks []string) ([]DiscoveredDB, error) {
	known := make(map[string]bool, len(knownStacks))
	for _, s := range knownStacks {
		if s != "" {
			known[s] = true
		}
	}
	if debug {
		logger.Printf("[DEBUG] DiscoverDatabases: running docker ps to find database containers")
	}
	// R-355: the compose PROJECT label is asked for, because it is the stack name BY CONSTRUCTION and
	// the container name is only a guess at it. The controller runs compose with `cmd.Dir` set to
	// `/opt/docker/stacks/<stack>` and never passes `-p` (stacks/manager.go:1218-1226), so compose
	// derives the project from that directory — i.e. from the stack name itself.
	//
	// The label sits in the MIDDLE of the format on purpose: `strings.TrimSpace` is applied to the
	// whole `docker ps` output, so a trailing empty field on the LAST line would be eaten and that
	// row would arrive one column short. Image is never empty, so ending on it keeps every row the
	// same width.
	cmd := exec.CommandContext(ctx, "docker", "ps", "--format",
		"{{.ID}}\t{{.Names}}\t{{.Label \"com.docker.compose.project\"}}\t{{.Image}}", "--filter", "status=running")
	out, err := cmd.Output()
	if err != nil {
		return nil, fmt.Errorf("docker ps failed: %w", err)
	}

	if debug {
		logger.Printf("[DEBUG] DiscoverDatabases: docker ps output: %s", util.TruncateStr(strings.TrimSpace(string(out)), 500))
	}

	var dbs []DiscoveredDB
	var skipped int

	for _, line := range strings.Split(strings.TrimSpace(string(out)), "\n") {
		if line == "" {
			continue
		}
		parts := strings.SplitN(line, "\t", 4)
		if len(parts) < 4 {
			continue
		}

		id, name, project, image := parts[0], parts[1], strings.TrimSpace(parts[2]), strings.ToLower(parts[3])

		// R-47: the same predicate that DBServiceNames applies to compose `image:` values, so a dump
		// that exists is always attributable to a startable service (see dbservices.go).
		dbType, isDB := dbTypeForImage(image)
		if !isDB {
			if debug {
				logger.Printf("[DEBUG] DiscoverDatabases: skipping container %s (image=%s, not a database)", name, image)
			}
			skipped++
			continue
		}

		if debug {
			logger.Printf("[DEBUG] DiscoverDatabases: found %s container: %s (id=%s)", dbType, name, id[:12])
		}

		db := DiscoveredDB{
			ContainerID:   id,
			ContainerName: name,
			DBType:        dbType,
			StackName:     resolveStackName(name, project, known, logger, debug),
		}

		// Get env vars from container
		if err := populateDBEnv(ctx, &db); err != nil {
			logger.Printf("[WARN] [backup] Could not read env vars for %s: %v", name, err)
			if debug {
				logger.Printf("[DEBUG] DiscoverDatabases: skipping %s — env read failed", name)
			}
			continue
		}

		if debug {
			logger.Printf("[DEBUG] DiscoverDatabases: %s → stack=%s, dbUser=%s, dbName=%s", name, db.StackName, db.DBUser, db.DBName)
		}

		dbs = append(dbs, db)
	}

	if debug {
		logger.Printf("[DEBUG] DiscoverDatabases: found %d database(s), skipped %d non-DB container(s)", len(dbs), skipped)
	}

	logger.Printf("[INFO] [backup] Discovered %d databases", len(dbs))
	return dbs, nil
}

// DumpAll dumps all discovered databases.
func DumpAll(ctx context.Context, dbs []DiscoveredDB, dumpDir string, logger *log.Logger, debug bool) []DumpResult {
	// Clean up old .tmp files (older than 1 hour)
	cleanupTmpFiles(dumpDir, logger)

	logger.Printf("[INFO] [backup] Starting DB dump for %d databases", len(dbs))
	var results []DumpResult
	var failed int
	for _, db := range dbs {
		result := DumpOne(ctx, db, dumpDir, logger, debug)
		results = append(results, result)
		if result.Error != nil {
			failed++
		}
	}
	logger.Printf("[INFO] [backup] DB dump complete: %d succeeded, %d failed", len(results)-failed, failed)
	return results
}

// DumpOne dumps a single database.
func DumpOne(ctx context.Context, db DiscoveredDB, dumpDir string, logger *log.Logger, debug bool) DumpResult {
	start := time.Now()
	result := DumpResult{DB: db}

	if debug {
		logger.Printf("[DEBUG] DumpOne: starting dump for container=%s, stack=%s, dbType=%s, dumpDir=%s",
			db.ContainerName, db.StackName, db.DBType, dumpDir)
	}

	// Ensure dump directory exists
	if err := os.MkdirAll(dumpDir, 0755); err != nil {
		result.Error = fmt.Errorf("creating dump dir: %w", err)
		result.Duration = time.Since(start)
		return result
	}

	filename := fmt.Sprintf("%s-%s.sql", db.StackName, db.DBType)
	tmpPath := filepath.Join(dumpDir, filename+".tmp")
	finalPath := filepath.Join(dumpDir, filename)

	// 5-minute timeout per dump
	dumpCtx, cancel := context.WithTimeout(ctx, 5*time.Minute)
	defer cancel()

	// Verify container is still running
	checkCmd := exec.CommandContext(dumpCtx, "docker", "inspect", "--format", "{{.State.Running}}", db.ContainerID)
	checkOut, err := checkCmd.Output()
	if err != nil || strings.TrimSpace(string(checkOut)) != "true" {
		result.Error = fmt.Errorf("container %s no longer running", db.ContainerName)
		result.Duration = time.Since(start)
		if debug {
			logger.Printf("[DEBUG] DumpOne: container %s is no longer running — skipping", db.ContainerName)
		}
		return result
	}

	// Build dump command
	var cmd *exec.Cmd
	switch db.DBType {
	case DBTypePostgres:
		cmd = exec.CommandContext(dumpCtx, "docker", "exec", db.ContainerID,
			"pg_dump", "-U", db.DBUser, "-d", db.DBName,
			"--clean", "--if-exists", "--no-owner", "--no-privileges")
		if debug {
			logger.Printf("[DEBUG] DumpOne: pg_dump command: docker exec %s pg_dump -U %s -d %s --clean --if-exists --no-owner --no-privileges",
				db.ContainerID[:12], db.DBUser, db.DBName)
		}
	case DBTypeMariaDB:
		// Get root password from container env
		password := getMariaDBPassword(dumpCtx, db.ContainerID)
		if password == "" {
			result.Error = fmt.Errorf("could not determine MariaDB root password for %s", db.ContainerName)
			result.Duration = time.Since(start)
			if debug {
				logger.Printf("[DEBUG] DumpOne: MariaDB root password not found for %s — skipping", db.ContainerName)
			}
			return result
		}
		cmd = exec.CommandContext(dumpCtx, "docker", "exec", db.ContainerID,
			"mariadb-dump", "-u", "root", "-p***",
			"--single-transaction", "--routines", "--triggers", db.DBName)
		if debug {
			logger.Printf("[DEBUG] DumpOne: mariadb-dump command: docker exec %s mariadb-dump -u root -p*** --single-transaction --routines --triggers %s",
				db.ContainerID[:12], db.DBName)
		}
		// Actual command with real password (not logged)
		cmd = exec.CommandContext(dumpCtx, "docker", "exec", db.ContainerID,
			"mariadb-dump", "-u", "root", "-p"+password,
			"--single-transaction", "--routines", "--triggers", db.DBName)
	default:
		result.Error = fmt.Errorf("unsupported DB type: %s", db.DBType)
		result.Duration = time.Since(start)
		return result
	}

	// Write output to tmp file
	tmpFile, err := os.Create(tmpPath)
	if err != nil {
		result.Error = fmt.Errorf("creating tmp file: %w", err)
		result.Duration = time.Since(start)
		return result
	}
	defer tmpFile.Close()

	cmd.Stdout = tmpFile
	var stderr strings.Builder
	cmd.Stderr = &stderr

	err = cmd.Run()

	if err != nil {
		os.Remove(tmpPath)
		errMsg := stderr.String()
		if len(errMsg) > 200 {
			errMsg = errMsg[:200]
		}
		result.Error = fmt.Errorf("dump failed: %v — %s", err, errMsg)
		result.Duration = time.Since(start)
		if debug {
			logger.Printf("[DEBUG] DumpOne: dump command failed for %s: %v", db.ContainerName, result.Error)
		}
		return result
	}

	// Close and sync tmpFile before rename to ensure data is flushed to disk (H8 fix).
	if err := tmpFile.Sync(); err != nil {
		os.Remove(tmpPath)
		result.Error = fmt.Errorf("syncing dump file: %w", err)
		result.Duration = time.Since(start)
		return result
	}
	if err := tmpFile.Close(); err != nil {
		os.Remove(tmpPath)
		result.Error = fmt.Errorf("closing dump file: %w", err)
		result.Duration = time.Since(start)
		return result
	}

	// Check file size
	stat, err := os.Stat(tmpPath)
	if err != nil || stat.Size() == 0 {
		os.Remove(tmpPath)
		result.Error = fmt.Errorf("dump produced empty file for %s", db.ContainerName)
		result.Duration = time.Since(start)
		if debug {
			logger.Printf("[DEBUG] DumpOne: dump produced empty file for %s", db.ContainerName)
		}
		return result
	}

	// Rename tmp to final
	if err := os.Rename(tmpPath, finalPath); err != nil {
		os.Remove(tmpPath)
		result.Error = fmt.Errorf("renaming dump file: %w", err)
		result.Duration = time.Since(start)
		return result
	}

	result.FilePath = finalPath
	result.Size = stat.Size()
	result.Duration = time.Since(start)

	// Run validation on the dump file
	result.Validation = ValidateDump(finalPath, db.DBType)

	if debug {
		logger.Printf("[DEBUG] DumpOne: completed %s → %s (size=%s, valid=%v, tables=%d, duration=%s)",
			db.ContainerName, filename, humanizeBytes(stat.Size()),
			result.Validation.Valid, result.Validation.TableCount, result.Duration.Round(time.Millisecond))
	}

	logger.Printf("[INFO] [backup] DB dump: %s → %s (%s, %s, %d tables)", db.ContainerName, filename,
		humanizeBytes(stat.Size()), result.Duration.Round(time.Millisecond), result.Validation.TableCount)

	return result
}

// ValidateDump checks a SQL dump file for basic structural integrity.
func ValidateDump(filePath string, dbType DBType) DumpValidation {
	stat, err := os.Stat(filePath)
	if err != nil {
		return DumpValidation{Error: fmt.Sprintf("stat failed: %v", err)}
	}

	v := DumpValidation{
		FileSize: stat.Size(),
		ModTime:  stat.ModTime(),
	}

	if stat.Size() < 100 {
		v.Error = "dump file too small (< 100 bytes)"
		log.Printf("[WARN] [backup] ValidateDump FAIL: %s — %s", filePath, v.Error)
		return v
	}

	// H1: Use bufio.Scanner to read line-by-line instead of loading entire file into memory.
	// Large dumps (500MB+) would cause massive allocations on every 5-min cache refresh.
	f, err := os.Open(filePath)
	if err != nil {
		v.Error = fmt.Sprintf("read failed: %v", err)
		log.Printf("[WARN] [backup] ValidateDump FAIL: %s — %s", filePath, v.Error)
		return v
	}
	defer f.Close()

	// Use bufio.Reader instead of Scanner: ReadLine gracefully handles lines
	// longer than the buffer (isPrefix=true) so we can skip them. Only short
	// lines matter (headers, CREATE TABLE). Long COPY/INSERT data lines
	// (e.g., Immich's binary-encoded image data) are skipped without allocating.
	reader := bufio.NewReaderSize(f, 256*1024)

	lineNum := 0
	headerFound := false
	tableCount := 0
	// R-44 sniff state. inUserCopy tracks a postgres `COPY … FROM stdin;` block for an accounts
	// table; rows are counted until the `\.` terminator.
	inUserCopy := false
	for {
		lineBytes, isPrefix, err := reader.ReadLine()
		if err != nil {
			if err != io.EOF {
				v.Error = fmt.Sprintf("hiba az olvasás közben: %v", err)
				log.Printf("[WARN] [backup] ValidateDump FAIL: %s — read error: %v", filePath, err)
				return v
			}
			break // EOF
		}
		if isPrefix {
			// Line exceeds buffer — skip remainder (COPY data, large INSERTs).
			// A long line inside a user COPY block is still a ROW: count it before discarding it,
			// or a table whose rows happen to be wide would sniff as empty and raise a false alarm.
			if inUserCopy {
				v.UserRows++
			}
			for isPrefix && err == nil {
				_, isPrefix, err = reader.ReadLine()
			}
			continue
		}

		line := string(lineBytes)
		lineNum++

		// R-44 content sniff (warn-level; see DumpValidation).
		if inUserCopy {
			if line == `\.` {
				inUserCopy = false
			} else {
				v.UserRows++
			}
		} else if isUserCopyStart(line, dbType) {
			inUserCopy = true
			v.UserTableFound = true
		} else if dbType == DBTypeMariaDB && isUserInsert(line) {
			// mysqldump writes multi-row `INSERT INTO \`users\` VALUES (…),(…);` — the row count is
			// not worth parsing out of it, and presence alone answers the only question asked here.
			v.UserTableFound = true
			v.UserRows++
		}

		// Header check — scan first 10 lines for expected dump header
		// MariaDB 11.4+ prepends a sandbox comment before the header line
		if lineNum <= 10 && !headerFound {
			switch dbType {
			case DBTypeMariaDB:
				if strings.HasPrefix(line, "-- MariaDB dump") ||
					strings.HasPrefix(line, "-- MySQL dump") ||
					strings.HasPrefix(line, "-- mysqldump") {
					headerFound = true
				}
			case DBTypePostgres:
				if strings.HasPrefix(line, "-- PostgreSQL database dump") {
					headerFound = true
				}
			}
		}

		// Count CREATE TABLE statements
		upper := strings.ToUpper(strings.TrimSpace(line))
		if strings.HasPrefix(upper, "CREATE TABLE") {
			tableCount++
		}
	}

	v.TableCount = tableCount

	if !headerFound {
		switch dbType {
		case DBTypeMariaDB:
			v.Error = "MariaDB dump missing comment header"
		case DBTypePostgres:
			v.Error = "PostgreSQL dump missing comment header"
		}
		log.Printf("[WARN] [backup] ValidateDump FAIL: %s — %s", filePath, v.Error)
		return v
	}

	if tableCount == 0 {
		v.Error = "no CREATE TABLE statements found"
		log.Printf("[WARN] [backup] ValidateDump FAIL: %s — %s (header was found, scanned %d lines)", filePath, v.Error, lineNum)
		return v
	}

	v.LooksEmpty = v.UserTableFound && v.UserRows == 0
	if v.LooksEmpty {
		log.Printf("[WARN] [backup] ValidateDump: %s is structurally valid (%d tables) but its accounts table has NO rows — the dump may predate the customer's data", filePath, tableCount)
	}

	v.Valid = true
	return v
}

// userTableNames are the table names treated as "the accounts table" by the R-44 sniff. Kept
// deliberately short: a wider net (anything containing "user") would match join/audit tables like
// `user_metadata` or `album_user`, which are legitimately empty on a healthy single-user install
// and would produce exactly the false alarm this signal must not raise.
var userTableNames = []string{"user", "users", "account", "accounts"}

// isUserCopyStart reports whether a line opens a postgres `COPY <accounts-table> … FROM stdin;`
// block. pg_dump writes the table qualified and optionally quoted — `COPY public."user" (…)`,
// `COPY public.users (…)` — so both forms are matched.
func isUserCopyStart(line string, dbType DBType) bool {
	if dbType != DBTypePostgres || !strings.HasPrefix(line, "COPY ") {
		return false
	}
	rest := strings.TrimPrefix(line, "COPY ")
	sp := strings.IndexByte(rest, ' ')
	if sp < 0 {
		return false
	}
	return matchesUserTable(rest[:sp])
}

// isUserInsert reports whether a line is a mysqldump INSERT into an accounts table.
func isUserInsert(line string) bool {
	const pfx = "INSERT INTO "
	if !strings.HasPrefix(line, pfx) {
		return false
	}
	rest := strings.TrimPrefix(line, pfx)
	sp := strings.IndexByte(rest, ' ')
	if sp < 0 {
		return false
	}
	return matchesUserTable(rest[:sp])
}

// matchesUserTable strips schema qualification and quoting from a dumped table reference and
// reports whether the bare name is an accounts table.
func matchesUserTable(ref string) bool {
	if dot := strings.LastIndexByte(ref, '.'); dot >= 0 {
		ref = ref[dot+1:]
	}
	ref = strings.Trim(ref, "\"`")
	for _, n := range userTableNames {
		if strings.EqualFold(ref, n) {
			return true
		}
	}
	return false
}

// ListDumpFiles returns info about SQL dump files on disk.
//
// M18: ValidateDump scans the dump line-by-line; on a customer with hundreds-of-MB dumps that is wasted
// disk I/O + CPU on every ~5-min scheduler cycle. `cached` is an optional lookup that returns a
// previously-computed DumpValidation for a file whose (name, size, modtime) match — when it returns ok,
// the expensive ValidateDump is skipped. Pass nil to always validate (legacy fast path / other callers).
func ListDumpFiles(dumpDir string, cached func(name string, size int64, mod time.Time) (DumpValidation, bool)) ([]DumpFileInfo, error) {
	entries, err := os.ReadDir(dumpDir)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, nil
		}
		return nil, fmt.Errorf("reading dump dir: %w", err)
	}

	var files []DumpFileInfo
	for _, e := range entries {
		// M2: Check .tmp before .sql to correctly skip ".sql.tmp" temp files (was dead code before).
		if e.IsDir() || strings.HasSuffix(e.Name(), ".tmp") {
			continue
		}
		if !strings.HasSuffix(e.Name(), ".sql") {
			continue
		}

		info, err := e.Info()
		if err != nil {
			continue
		}

		f := DumpFileInfo{
			FileName: e.Name(),
			Size:     info.Size(),
			ModTime:  info.ModTime(),
		}

		// Parse stack name and DB type from filename: "paperless-ngx-postgres.sql"
		base := strings.TrimSuffix(e.Name(), ".sql")
		// R-379: strip the `pre-restore-<stamp>-` head FIRST, so an undo copy resolves to the app it
		// belongs to instead of a phantom stack named after its own timestamp.
		if rest, stamp, ok := trimUndoPrefix(base); ok {
			base = rest
			f.IsUndo = true
			if t, err := time.Parse("20060102T150405Z", stamp); err == nil {
				f.UndoAt = t
			}
		}
		if strings.HasSuffix(base, "-postgres") {
			f.StackName = strings.TrimSuffix(base, "-postgres")
			f.DBType = DBTypePostgres
		} else if strings.HasSuffix(base, "-mariadb") {
			f.StackName = strings.TrimSuffix(base, "-mariadb")
			f.DBType = DBTypeMariaDB
		} else {
			f.StackName = base
		}

		// M18: reuse a cached validation when the file is unchanged (name+size+modtime), else validate.
		if cached != nil {
			if v, ok := cached(e.Name(), info.Size(), info.ModTime()); ok {
				f.Validation = v
				files = append(files, f)
				continue
			}
		}
		fullPath := filepath.Join(dumpDir, e.Name())
		f.Validation = ValidateDump(fullPath, f.DBType)

		files = append(files, f)
	}

	return files, nil
}

func populateDBEnv(ctx context.Context, db *DiscoveredDB) error {
	cmd := exec.CommandContext(ctx, "docker", "inspect", db.ContainerID,
		"--format", "{{range .Config.Env}}{{println .}}{{end}}")
	out, err := cmd.Output()
	if err != nil {
		return err
	}

	env := make(map[string]string)
	for _, line := range strings.Split(string(out), "\n") {
		if idx := strings.IndexByte(line, '='); idx > 0 {
			env[line[:idx]] = line[idx+1:]
		}
	}

	switch db.DBType {
	case DBTypePostgres:
		db.DBUser = env["POSTGRES_USER"]
		if db.DBUser == "" {
			db.DBUser = "postgres"
		}
		db.DBName = env["POSTGRES_DB"]
		if db.DBName == "" {
			db.DBName = db.DBUser
		}
	case DBTypeMariaDB:
		db.DBName = env["MYSQL_DATABASE"]
		if db.DBName == "" {
			db.DBName = env["MARIADB_DATABASE"]
		}
		if db.DBName == "" {
			db.DBName = "mysql" // fallback to dump all
		}
		db.DBUser = "root"
	}

	return nil
}

// ImportDump replays a (possibly gzipped) SQL dump into a RUNNING database container — the read-side
// counterpart to DumpOne (F17). It reuses the per-engine clients (psql / mariadb) and the DiscoveredDB's
// OWN credentials (discovered from the live container env), so the caller needs no external env map. The
// container must already be running (the restore flow brings the stack up first); ImportDump briefly
// waits for the engine to accept connections, then pipes the dump in. The backup dumps are produced with
// DROP/CREATE (pg_dump --clean --if-exists; mariadb-dump's default --add-drop-table), so a replay fully
// reconstructs the captured logical state.
func ImportDump(ctx context.Context, db DiscoveredDB, dumpPath string, logger *log.Logger, debug bool) error {
	if err := waitDBReady(ctx, db, 30*time.Second); err != nil {
		return fmt.Errorf("waiting for %s (%s) readiness: %w", db.ContainerName, db.DBType, err)
	}

	f, err := os.Open(dumpPath)
	if err != nil {
		return fmt.Errorf("opening dump %s: %w", dumpPath, err)
	}
	defer f.Close()

	var reader io.Reader = f
	if strings.HasSuffix(dumpPath, ".gz") {
		gr, err := gzip.NewReader(f)
		if err != nil {
			return fmt.Errorf("opening gzip %s: %w", dumpPath, err)
		}
		defer gr.Close()
		reader = gr
	}

	impCtx, cancel := context.WithTimeout(ctx, 30*time.Minute)
	defer cancel()

	var cmd *exec.Cmd
	switch db.DBType {
	case DBTypePostgres:
		user := db.DBUser
		if user == "" {
			user = "postgres"
		}
		dbName := db.DBName
		if dbName == "" {
			dbName = user
		}
		// ON_ERROR_STOP=1: a real import error must FAIL (and surface), not silently half-apply.
		//
		// --single-transaction (R-380, v0.220.0) is a BELT, not the fix. It makes a Postgres replay
		// all-or-nothing at the engine, so the emptied-and-crash-looping state measured on `docmost`
		// on 2026-08-22 stops being reachable on this engine. It does NOT make MariaDB atomic —
		// MariaDB's DDL is not transactional, so a partial apply there is unavoidable at the engine
		// and is why the rollback in offbox_reconstitute.go exists and is the actual fix. Do not
		// read this flag as making the rollback optional.
		cmd = exec.CommandContext(impCtx, "docker", "exec", "-i", db.ContainerID,
			"psql", "-v", "ON_ERROR_STOP=1", "--single-transaction", "-U", user, "-d", dbName)
	case DBTypeMariaDB:
		password := getMariaDBPassword(impCtx, db.ContainerID)
		if password == "" {
			return fmt.Errorf("could not determine MariaDB root password for %s", db.ContainerName)
		}
		cmd = exec.CommandContext(impCtx, "docker", "exec", "-i", db.ContainerID,
			"mariadb", "-u", "root", "-p"+password, db.DBName)
	default:
		return fmt.Errorf("unsupported DB type: %s", db.DBType)
	}

	cmd.Stdin = reader
	var stderr strings.Builder
	cmd.Stderr = &stderr
	if debug && logger != nil {
		logger.Printf("[DEBUG] [backup] ImportDump: importing %s into %s (%s)", dumpPath, db.ContainerName, db.DBType)
	}
	if err := cmd.Run(); err != nil {
		// R-381: the engine's stderr goes to the OPERATOR LOG, in full. It used to be truncated to
		// 300 chars and folded into the returned error, which the restore surface then rendered to
		// the customer — measured 2026-08-22 at 407 bytes (Postgres, a caret diagram and
		// `exit status 3`) and 615 bytes (MariaDB, whose middle was an `INSERT INTO migrations
		// VALUES (...)` listing, i.e. ROWS OUT OF THE CUSTOMER'S OWN DATABASE, HTML-escaped, on
		// their dashboard).
		//
		// The diagnostic is ADDED here, not removed: previously nothing logged the full text at all,
		// so this is strictly more for the operator and strictly less for the customer.
		full := strings.TrimSpace(stderr.String())
		if logger != nil {
			logger.Printf("[ERROR] [backup] %s import into %s FAILED: %v — engine output follows:\n%s",
				db.DBType, db.ContainerName, err, full)
		}
		return fmt.Errorf("%s import into %s failed: %w", db.DBType, db.ContainerName, err)
	}
	if logger != nil {
		logger.Printf("[INFO] [backup] Imported DB dump %s into %s (%s)", filepath.Base(dumpPath), db.ContainerName, db.DBType)
	}
	return nil
}

// waitDBReady polls until the database accepts connections (pg_isready / mariadb-admin ping).
func waitDBReady(ctx context.Context, db DiscoveredDB, timeout time.Duration) error {
	deadline := time.Now().Add(timeout)
	for {
		c, cancel := context.WithTimeout(ctx, 5*time.Second)
		var cmd *exec.Cmd
		switch db.DBType {
		case DBTypePostgres:
			user := db.DBUser
			if user == "" {
				user = "postgres"
			}
			cmd = exec.CommandContext(c, "docker", "exec", db.ContainerID, "pg_isready", "-U", user)
		case DBTypeMariaDB:
			pw := getMariaDBPassword(c, db.ContainerID)
			cmd = exec.CommandContext(c, "docker", "exec", db.ContainerID, "mariadb-admin", "ping", "-u", "root", "-p"+pw)
		default:
			cancel()
			return fmt.Errorf("unsupported DB type: %s", db.DBType)
		}
		err := cmd.Run()
		cancel()
		if err == nil {
			return nil
		}
		if time.Now().After(deadline) {
			return fmt.Errorf("timeout after %s", timeout)
		}
		time.Sleep(2 * time.Second)
	}
}

func getMariaDBPassword(ctx context.Context, containerID string) string {
	cmd := exec.CommandContext(ctx, "docker", "inspect", containerID,
		"--format", "{{range .Config.Env}}{{println .}}{{end}}")
	out, err := cmd.Output()
	if err != nil {
		return ""
	}

	for _, line := range strings.Split(string(out), "\n") {
		if strings.HasPrefix(line, "MYSQL_ROOT_PASSWORD=") {
			return strings.TrimPrefix(line, "MYSQL_ROOT_PASSWORD=")
		}
		if strings.HasPrefix(line, "MARIADB_ROOT_PASSWORD=") {
			return strings.TrimPrefix(line, "MARIADB_ROOT_PASSWORD=")
		}
	}
	return ""
}

// deriveStackName maps a DB container name to its owning stack name.
//
// M19: the old logic pure-suffix-stripped on `-` (postgres/db/mariadb/mysql/database/redis/cache),
// which misattributes a stack whose real slug ENDS in a role token (e.g. a stack literally named
// `my-cache` → stripped to `my`). When the set of actually-deployed stack names is known, cross-reference
// it so the result is a real stack:
//   - candidate := suffix-strip result.
//   - known[candidate]            → candidate (a real DB-role suffix of a real stack, e.g. romm-postgres→romm).
//   - else known[containerName]   → containerName (the container name IS the stack — don't strip, e.g. my-cache).
//   - else longest known prefix   → handles <stack>_postgres / <stack>-1 / compose-suffixed names.
//   - else                        → candidate (fall back to today's suffix-strip; preserves behaviour when
//     the stack list is empty/unavailable, so nothing regresses).
//
// A nil/empty `known` map = the legacy fast path (pure suffix-strip).
// resolveStackName attributes a running DB container to the stack that owns it.
//
// R-355, and the reason this exists rather than more string-munging: the container name is a GUESS at
// the stack name and the compose project label is the ANSWER. `paperless-ngx` runs a container called
// `paperless-postgres`; no amount of suffix-stripping or prefix-matching can bridge that, and
// deriveStackName's last line returns its unresolved candidate as though it had resolved it. The dump
// then went to `backups/primary/paperless/db-dumps/` — a directory for a stack that does not exist, on
// the system drive — while the app's own recovery unit recorded `db_dumps: null`. Nothing collected it,
// nothing off-sited it, nothing restored it, and because writeSafetyDump filters on this same value the
// destructive restore took NO undo copy and told the customer the app had no database. Measured live
// 2026-08-21: 284 617 bytes, 72 tables, valid, and unreachable.
//
// The label is authoritative BY CONSTRUCTION — see the note on the `docker ps` format above — so it is
// preferred whenever it names a stack we know. It is not trusted blindly: a project label naming an
// unknown stack would write into an unknown app's directory, which is the very fault being fixed.
//
// The fallback is unchanged, so every container whose name already resolves keeps its exact previous
// attribution (pinned by TestResolveStackName_UnaffectedAppsAreUnchanged).
//
// When NEITHER route resolves to a known stack we still return the old candidate — refusing here would
// change behaviour for any container legitimately relying on the legacy path — but we say so loudly,
// because the silent version of this line is what hid R-355 for the life of the feature.
func resolveStackName(containerName, composeProject string, known map[string]bool, logger *log.Logger, debug bool) string {
	if composeProject != "" && (len(known) == 0 || known[composeProject]) {
		if debug && composeProject != deriveStackName(containerName, known) {
			logger.Printf("[DEBUG] DiscoverDatabases: %s → stack %q from the compose project label (the container name would have given %q)",
				containerName, composeProject, deriveStackName(containerName, known))
		}
		return composeProject
	}
	fallback := deriveStackName(containerName, known)
	if len(known) > 0 && !known[fallback] {
		logger.Printf("[WARN] [backup] DB container %q could not be attributed to any deployed stack (compose project %q, name gives %q) — its dump will be written under %q, which no recovery unit reads. This is the R-355 shape; investigate before trusting that app's backup.",
			containerName, composeProject, fallback, fallback)
	}
	return fallback
}

func deriveStackName(containerName string, known map[string]bool) string {
	candidate := suffixStripStackName(containerName)

	if len(known) == 0 {
		return candidate
	}
	if known[candidate] {
		return candidate
	}
	if known[containerName] {
		return containerName
	}
	// Longest known stack name that is a prefix of the container name (tie-break: longest wins).
	best := ""
	for name := range known {
		if name == "" || len(name) >= len(containerName) {
			continue
		}
		// boundary char so "rom" doesn't match "romm-..."; compose/role separators are - or _.
		sep := containerName[len(name)]
		if strings.HasPrefix(containerName, name) && (sep == '-' || sep == '_') && len(name) > len(best) {
			best = name
		}
	}
	if best != "" {
		return best
	}
	return candidate
}

// suffixStripStackName is the legacy pure suffix-strip (the M19 fallback when no stack list is known).
func suffixStripStackName(containerName string) string {
	knownSuffixes := []string{"postgres", "db", "mariadb", "mysql", "database", "redis", "cache"}

	parts := strings.Split(containerName, "-")
	if len(parts) <= 1 {
		return containerName
	}

	last := strings.ToLower(parts[len(parts)-1])
	for _, suffix := range knownSuffixes {
		if last == suffix {
			return strings.Join(parts[:len(parts)-1], "-")
		}
	}
	return containerName
}

func cleanupTmpFiles(dumpDir string, logger *log.Logger) {
	entries, err := os.ReadDir(dumpDir)
	if err != nil {
		return
	}

	cutoff := time.Now().Add(-1 * time.Hour)
	for _, e := range entries {
		if !strings.HasSuffix(e.Name(), ".tmp") {
			continue
		}
		info, err := e.Info()
		if err != nil {
			continue
		}
		if info.ModTime().Before(cutoff) {
			path := filepath.Join(dumpDir, e.Name())
			os.Remove(path)
			logger.Printf("[INFO] [backup] Cleaned up stale tmp file: %s", e.Name())
		}
	}
}

// M1: formatBytes removed — use humanizeBytes() from appdata.go (same package, no duplication).