package membership

// Migration from the local SQLite control plane to replicated JetStream KV
// (issue 0003c). It is the one-time, idempotent data move that decentralization
// needs: read the entire SQLite state, write it into the KV buckets. Re-running
// it is safe (every KV write is an overwrite), so a partial/interrupted run is
// recovered by running again, and a parity test can assert the two stores hold
// the same state before and after.

import (
	"database/sql"
	"fmt"
	"strings"
	"time"

	"github.com/nats-io/nats.go/jetstream"
)

// SealedKeyRecord is one row of room_keys: the sealed room key for an endpoint
// at a given epoch. It is the unit the snapshot carries so a backend can be
// imported with the exact epoch history (CreateRoom/AddMember alone could not
// reproduce a multi-epoch room).
type SealedKeyRecord struct {
	RoomID   string
	Endpoint string
	Epoch    int
	Sealed   []byte
}

// Snapshot is the complete control-plane state, backend-agnostic. It is what
// ExportSnapshot produces and importSnapshot consumes, so the SQLite->KV
// migration and the parity test both work in terms of it.
type Snapshot struct {
	Rooms   []RoomInfo
	Members map[string][]Member // roomID -> members
	Keys    []SealedKeyRecord
	Users   []User
}

// MigrateReport summarizes what a migration moved, for the operator log.
type MigrateReport struct {
	BackupPath string
	Rooms      int
	Members    int
	Keys       int
	Users      int
}

// MigrateSQLiteToKV reads the SQLite store at sqlitePath and writes its entire
// state into the JetStream KV buckets on js (created with cfg.Replicas). It is
// idempotent: re-running converges to the same state. The caller is responsible
// for backing up the SQLite file first (BackupSQLite) — this function only
// reads it.
func MigrateSQLiteToKV(sqlitePath string, js jetstream.JetStream, cfg JetStreamConfig) (*MigrateReport, error) {
	src, err := openSQLite(sqlitePath)
	if err != nil {
		return nil, fmt.Errorf("migrate: open sqlite %q: %w", sqlitePath, err)
	}
	defer src.Close()

	snap, err := src.ExportSnapshot()
	if err != nil {
		return nil, fmt.Errorf("migrate: export sqlite: %w", err)
	}

	dst, err := OpenJetStream(js, cfg)
	if err != nil {
		return nil, fmt.Errorf("migrate: open kv: %w", err)
	}
	kv := dst.(*jetstreamStore)
	if err := kv.importSnapshot(snap); err != nil {
		return nil, fmt.Errorf("migrate: import to kv: %w", err)
	}

	members := 0
	for _, ms := range snap.Members {
		members += len(ms)
	}
	return &MigrateReport{
		Rooms:   len(snap.Rooms),
		Members: members,
		Keys:    len(snap.Keys),
		Users:   len(snap.Users),
	}, nil
}

// BackupSQLite makes a consistent copy of the SQLite database next to it,
// named "<path>.bak.<unixnano>", using SQLite's own VACUUM INTO (which writes a
// transactionally-consistent snapshot even with a live WAL). It returns the
// backup path. Always call this before MigrateSQLiteToKV so a botched migration
// can be undone.
func BackupSQLite(path string) (string, error) {
	dst := fmt.Sprintf("%s.bak.%d", path, time.Now().UnixNano())
	db, err := sql.Open("sqlite", "file:"+path+"?_pragma=busy_timeout(5000)")
	if err != nil {
		return "", fmt.Errorf("backup: open %q: %w", path, err)
	}
	defer db.Close()
	if err := db.Ping(); err != nil {
		return "", fmt.Errorf("backup: ping %q: %w", path, err)
	}
	// VACUUM INTO writes a fresh, consistent database file; the literal path is
	// safely single-quoted (it is operator-supplied, never network input).
	if _, err := db.Exec("VACUUM INTO '" + strings.ReplaceAll(dst, "'", "''") + "'"); err != nil {
		return "", fmt.Errorf("backup: VACUUM INTO %q: %w", dst, err)
	}
	return dst, nil
}

// ---- SQLite export --------------------------------------------------------

// ExportSnapshot reads the entire SQLite control-plane state into a Snapshot.
func (s *sqliteStore) ExportSnapshot() (*Snapshot, error) {
	snap := &Snapshot{Members: map[string][]Member{}}

	rows, err := s.db.Query(`SELECT room_id, subject, key_epoch, encrypt, persist, sign_msgs, owner_endpoint FROM rooms ORDER BY room_id`)
	if err != nil {
		return nil, fmt.Errorf("export: query rooms: %w", err)
	}
	for rows.Next() {
		var r RoomInfo
		var enc, per, sgn int
		if err := rows.Scan(&r.RoomID, &r.Subject, &r.Epoch, &enc, &per, &sgn, &r.OwnerEndpoint); err != nil {
			rows.Close()
			return nil, fmt.Errorf("export: scan room: %w", err)
		}
		r.Encrypt, r.Persist, r.SignMsgs = enc != 0, per != 0, sgn != 0
		snap.Rooms = append(snap.Rooms, r)
	}
	rows.Close()
	if err := rows.Err(); err != nil {
		return nil, err
	}

	mrows, err := s.db.Query(`SELECT room_id, endpoint, role, sign_pub, kex_pub FROM members ORDER BY room_id, endpoint`)
	if err != nil {
		return nil, fmt.Errorf("export: query members: %w", err)
	}
	for mrows.Next() {
		var roomID string
		var m Member
		if err := mrows.Scan(&roomID, &m.Endpoint, &m.Role, &m.SignPub, &m.KexPub); err != nil {
			mrows.Close()
			return nil, fmt.Errorf("export: scan member: %w", err)
		}
		snap.Members[roomID] = append(snap.Members[roomID], m)
	}
	mrows.Close()
	if err := mrows.Err(); err != nil {
		return nil, err
	}

	krows, err := s.db.Query(`SELECT room_id, epoch, endpoint, sealed_key FROM room_keys ORDER BY room_id, endpoint, epoch`)
	if err != nil {
		return nil, fmt.Errorf("export: query room_keys: %w", err)
	}
	for krows.Next() {
		var rec SealedKeyRecord
		if err := krows.Scan(&rec.RoomID, &rec.Epoch, &rec.Endpoint, &rec.Sealed); err != nil {
			krows.Close()
			return nil, fmt.Errorf("export: scan room_key: %w", err)
		}
		snap.Keys = append(snap.Keys, rec)
	}
	krows.Close()
	if err := krows.Err(); err != nil {
		return nil, err
	}

	users, err := s.ListUsers()
	if err != nil {
		return nil, fmt.Errorf("export: list users: %w", err)
	}
	snap.Users = users
	return snap, nil
}