import os
import logging
import struct
import time
import collections
import shutil
import lmdb
from pathlib import Path
import PIL.Image

from PySide6.QtCore import (
    QObject, QThread, Signal, QMutex, QSemaphore, QReadWriteLock,
    QMutexLocker, QReadLocker, QWriteLocker, QRunnable
)

import imagehash  # For perceptual hashing

from constants import (
    DUPLICATE_CACHE_PATH, DUPLICATE_HASH_DB_NAME,
    DUPLICATE_EXCEPTIONS_DB_NAME, DUPLICATE_PENDING_DB_NAME,
    MAX_DHASH_DISTANCE, UITexts
)

logger = logging.getLogger(__name__)

# Result structure for duplicate detection
DuplicateResult = collections.namedtuple('DuplicateResult', ['path1', 'path2', 'hash_value', 'is_exception', 'similarity', 'timestamp'])


class BKTree:
    """A Burkhard-Keller tree for efficient similarity searching using Hamming distance."""
    def __init__(self, distance_func):
        self.distance_func = distance_func
        self.tree = None

    def add(self, item):
        if self.tree is None:
            self.tree = (item, {})
            return
        node = self.tree
        while True:
            val, children = node
            dist = self.distance_func(item, val)
            if dist == 0:
                return
            if dist in children:
                node = children[dist]
            else:
                children[dist] = (item, {})
                break

    def query(self, item, max_dist):
        if self.tree is None:
            return []
        results = []
        candidates = [self.tree]
        while candidates:
            val, children = candidates.pop()
            dist = self.distance_func(item, val)
            if dist <= max_dist:
                results.append((val, dist))
            for d in range(max(0, dist - max_dist), dist + max_dist + 1):
                if d in children:
                    candidates.append(children[d])
        return results


class HashWorker(QRunnable):
    """Worker to calculate image hash in a thread pool."""
    def __init__(self, path, detector, result_dict, mutex, semaphore):
        super().__init__()
        self.path = path
        self.detector = detector
        self.result_dict = result_dict
        self.mutex = mutex
        self.semaphore = semaphore

    def run(self):
        if self.detector._is_running:
            try:
                # imagehash requires a PIL/Pillow image object.
                with PIL.Image.open(self.path) as pil_img:
                    # Using dHash from imagehash library as default
                    h = str(imagehash.dhash(pil_img))
                    with QMutexLocker(self.mutex):
                        self.result_dict[self.path] = h
            except Exception as e:
                logger.warning(f"HashWorker failed for {self.path}: {e}")

        self.semaphore.release()


class DuplicateCache(QObject):
    """
    Manages a persistent LMDB cache for perceptual hashes and duplicate relationships.
    Uses (device_id, inode) as primary keys for robustness against file renames/moves.
    """
    def __init__(self):
        super().__init__()
        self._lmdb_env = None
        self._hash_db = None
        self._exceptions_db = None
        self._pending_db = None
        self._db_lock = QMutex()  # Protects LMDB transactions
        # In-memory cache for hashes: (dev, inode) -> (hash_value, path)
        self._hash_cache = {}
        self._hash_cache_lock = QReadWriteLock()

        self.lmdb_open()

    def lmdb_open(self):
        cache_dir = Path(DUPLICATE_CACHE_PATH)
        cache_dir.mkdir(parents=True, exist_ok=True)

        try:
            self._lmdb_env = lmdb.open(
                DUPLICATE_CACHE_PATH,
                map_size=10 * 1024 * 1024 * 1024,  # 10GB default
                max_dbs=3,  # For hashes, exceptions and pending
                readonly=False,
                create=True
            )
            self._hash_db = self._lmdb_env.open_db(DUPLICATE_HASH_DB_NAME)
            self._exceptions_db = self._lmdb_env.open_db(DUPLICATE_EXCEPTIONS_DB_NAME)
            self._pending_db = self._lmdb_env.open_db(DUPLICATE_PENDING_DB_NAME)
            logger.info(f"Duplicate LMDB cache opened: {DUPLICATE_CACHE_PATH}")
        except Exception as e:
            logger.error(f"Failed to open duplicate LMDB cache: {e}")
            self._lmdb_env = None

    def lmdb_close(self):
        if self._lmdb_env:
            self._lmdb_env.close()
            self._lmdb_env = None
            self._hash_db = None
            self._exceptions_db = None
            self._pending_db = None

    def get_hash_stats(self):
        """Returns (count, size_bytes) for the hash database."""
        count = 0
        if not self._lmdb_env:
            return 0, 0

        with QMutexLocker(self._db_lock):
            with self._lmdb_env.begin(write=False) as txn:
                count = txn.stat(db=self._hash_db)['entries']

        size = 0
        disk_path = os.path.join(DUPLICATE_CACHE_PATH, "data.mdb")
        if os.path.exists(disk_path):
            size = os.path.getsize(disk_path)

        return count, size

    def clear_hashes(self):
        """Clears all hashes from the database by recreating the environment."""
        with QWriteLocker(self._hash_cache_lock):
            self._hash_cache.clear()

        self.lmdb_close()
        try:
            if os.path.exists(DUPLICATE_CACHE_PATH):
                shutil.rmtree(DUPLICATE_CACHE_PATH)
            self.lmdb_open()
            logger.info("Duplicate hash cache cleared.")
        except Exception as e:
            logger.error(f"Error clearing duplicate LMDB: {e}")

    def __del__(self):
        self.lmdb_close()

    @staticmethod
    def _get_inode_info(path):
        try:
            stat_info = os.stat(path)
            return stat_info.st_dev, struct.pack('Q', stat_info.st_ino)
        except OSError:
            return 0, None

    def _get_lmdb_key(self, dev_id, inode_key_bytes):
        return f"{dev_id}-{inode_key_bytes.hex()}".encode('utf-8')

    def get_hash_and_path(self, dev_id, inode_key_bytes):
        """Retrieves hash, mtime and path for a given (dev_id, inode_key_bytes)."""
        # Check in-memory cache first
        with QReadLocker(self._hash_cache_lock):
            cached_data = self._hash_cache.get((dev_id, inode_key_bytes))
            if cached_data:
                return cached_data  # (hash_value, mtime, path)

        # Check LMDB
        if not self._lmdb_env:
            return None, 0, None

        with QMutexLocker(self._db_lock):
            with self._lmdb_env.begin(write=False) as txn:
                lmdb_key = self._get_lmdb_key(dev_id, inode_key_bytes)
                value_bytes = txn.get(lmdb_key, db=self._hash_db)
                if value_bytes:
                    # Handle format "hash_value_str|mtime|path_str" or old "hash|path"
                    parts = value_bytes.decode('utf-8').split('|', 2)
                    if len(parts) == 3:
                        hash_str, mtime_str, path_str = parts
                        mtime = float(mtime_str)
                    elif len(parts) == 2:
                        hash_str, path_str = parts
                        mtime = 0.0  # Force re-hash
                    else:
                        return None, 0, None

                    with QWriteLocker(self._hash_cache_lock):
                        self._hash_cache[(dev_id, inode_key_bytes)] = (hash_str, mtime, path_str)
                    return hash_str, mtime, path_str
        return None, 0, None

    def get_hash_for_path(self, path, current_mtime, dev_id=None, inode_key_bytes=None):
        if dev_id is None or inode_key_bytes is None:
            dev_id, inode_key_bytes = self._get_inode_info(path)
        if not inode_key_bytes:
            return None
        hash_value, cached_mtime, _ = self.get_hash_and_path(dev_id, inode_key_bytes)
        # Return hash only if mtime matches (with small float tolerance)
        if hash_value and abs(cached_mtime - current_mtime) < 0.001:
            return hash_value
        return None

    def add_hash_for_path(self, path, hash_value, mtime, dev_id=None, inode_key_bytes=None):
        if dev_id is None or inode_key_bytes is None:
            dev_id, inode_key_bytes = self._get_inode_info(path)
        if not inode_key_bytes or not self._lmdb_env:
            return False

        value_str = f"{hash_value}|{mtime}|{path}"
        with QMutexLocker(self._db_lock):
            with self._lmdb_env.begin(write=True) as txn:
                lmdb_key = self._get_lmdb_key(dev_id, inode_key_bytes)
                txn.put(lmdb_key, value_str.encode('utf-8'), db=self._hash_db)

        with QWriteLocker(self._hash_cache_lock):
            self._hash_cache[(dev_id, inode_key_bytes)] = (hash_value, mtime, path)
        return True

    def remove_hash_for_path(self, path, clear_relationships=True):
        """
        Removes the hash entry for a path.

        Args:
            path: File path.
            clear_relationships: If True, also wipes all entries in pending and
                               exceptions DBs involving this file.
        """
        dev_id, inode_key_bytes = self._get_inode_info(path)
        if not inode_key_bytes or not self._lmdb_env:
            return False

        with QMutexLocker(self._db_lock):
            with self._lmdb_env.begin(write=True) as txn:
                lmdb_key = self._get_lmdb_key(dev_id, inode_key_bytes)
                txn.delete(lmdb_key, db=self._hash_db)

        with QWriteLocker(self._hash_cache_lock):
            self._hash_cache.pop((dev_id, inode_key_bytes), None)

        # Also remove any exceptions involving this path
        if clear_relationships:
            self._remove_pair_entries_for_path(dev_id, inode_key_bytes, self._exceptions_db)
            self._remove_pair_entries_for_path(dev_id, inode_key_bytes, self._pending_db)
        return True

    def _get_pair_lmdb_key_from_ids(self, dev1, inode1, dev2, inode2):
        # Ensure canonical order for exception keys
        key_parts = sorted([f"{dev1}-{inode1.hex()}", f"{dev2}-{inode2.hex()}"])
        return f"{key_parts[0]}-{key_parts[1]}".encode('utf-8')

    def _get_pair_lmdb_key(self, path1, path2):
        dev1, inode1 = self._get_inode_info(path1)
        dev2, inode2 = self._get_inode_info(path2)
        if not inode1 or not inode2:
            return None
        return self._get_pair_lmdb_key_from_ids(dev1, inode1, dev2, inode2)

    def mark_as_exception(self, path1, path2, is_exception=True, similarity=None, timestamp=None):
        if not self._lmdb_env:
            return False

        dev1, inode1 = self._get_inode_info(path1)
        dev2, inode2 = self._get_inode_info(path2)
        if not inode1 or not inode2:
            return False

        exception_key = self._get_pair_lmdb_key_from_ids(dev1, inode1, dev2, inode2)
        if not exception_key:
            return False

        # Store paths in value to make exception recovery independent of hash DB
        ts = timestamp if timestamp is not None else int(time.time())
        val_str = f"{path1}|{path2}|{similarity if similarity is not None else ''}|{ts}"
        value = val_str.encode('utf-8')

        with QMutexLocker(self._db_lock):
            with self._lmdb_env.begin(write=True) as txn:
                if is_exception:
                    txn.put(exception_key, value, db=self._exceptions_db)
                else:
                    txn.delete(exception_key, db=self._exceptions_db)
        return True

    def is_exception(self, path1, path2):
        if not self._lmdb_env:
            return False

        dev1, inode1 = self._get_inode_info(path1)
        dev2, inode2 = self._get_inode_info(path2)
        if not inode1 or not inode2:
            return False

        exception_key = self._get_pair_lmdb_key_from_ids(dev1, inode1, dev2, inode2)
        if not exception_key:
            return False

        with QMutexLocker(self._db_lock):
            with self._lmdb_env.begin(write=False) as txn:
                return txn.get(exception_key, db=self._exceptions_db) is not None

    def _remove_pair_entries_for_path(self, target_dev, target_inode, db_handle, txn=None):
        """Removes all entries involving a specific (dev, inode) pair from a pair-based DB."""
        if not self._lmdb_env:
            return

        target_inode_hex = target_inode.hex()

        def do_remove(t):
            cursor = t.cursor(db=db_handle)
            keys_to_delete = []
            for key_bytes, _ in cursor:
                key_str = key_bytes.decode('utf-8')
                parts = key_str.split('-')
                if len(parts) < 4: continue
                dev1, inode1_hex, dev2, inode2_hex = int(parts[0]), parts[1], int(parts[2]), parts[3]
                if (dev1 == target_dev and inode1_hex == target_inode_hex) or \
                   (dev2 == target_dev and inode2_hex == target_inode_hex):
                    keys_to_delete.append(key_bytes)
            for key in keys_to_delete:
                t.delete(key, db=db_handle)

        if txn:
            do_remove(txn)
        else:
            with QMutexLocker(self._db_lock):
                with self._lmdb_env.begin(write=True) as t:
                    do_remove(t)

    def mark_as_pending(self, path1, path2, is_pending=True, similarity=None, timestamp=None):
        """Marks a pair as pending review."""
        if not self._lmdb_env or self._pending_db is None:
            return False

        key = self._get_pair_lmdb_key(path1, path2)
        if not key:
            return False

        # Store paths in value to allow reconstruction without scanning
        ts = timestamp if timestamp is not None else int(time.time())
        val_str = f"{path1}|{path2}|{similarity if similarity is not None else ''}|{ts}"
        value = val_str.encode('utf-8')

        with QMutexLocker(self._db_lock):
            with self._lmdb_env.begin(write=True) as txn:
                if is_pending:
                    txn.put(key, value, db=self._pending_db)
                else:
                    # Check if it exists before deleting to avoid errors
                    if txn.get(key, db=self._pending_db):
                        txn.delete(key, db=self._pending_db)
        return True

    def get_all_pending_duplicates(self):
        """Retrieves all pending duplicate pairs from the database."""
        results = []
        if not self._lmdb_env or self._pending_db is None:
            return results

        keys_to_delete = []
        with QMutexLocker(self._db_lock):
            with self._lmdb_env.begin(write=False) as txn:
                cursor = txn.cursor(db=self._pending_db)
                for key, value_bytes in cursor:
                    try:
                        parts = value_bytes.decode('utf-8').split('|')
                        p1, p2 = parts[0], parts[1]
                        sim = int(parts[2]) if len(parts) > 2 and parts[2] else None
                        ts = int(parts[3]) if len(parts) > 3 else 0
                        if os.path.exists(p1) and os.path.exists(p2):
                            results.append(DuplicateResult(p1, p2, None, False, sim, ts))
                        else:
                            keys_to_delete.append(key)
                    except Exception:
                        keys_to_delete.append(key)
                        continue

            if keys_to_delete:
                try:
                    with self._lmdb_env.begin(write=True) as txn:
                        for k in keys_to_delete:
                            txn.delete(k, db=self._pending_db)
                    logger.info(f"Cleaned up {len(keys_to_delete)} invalid pending duplicates (files deleted externally)")
                except Exception as e:
                    logger.error(f"Error cleaning up pending duplicates from DB: {e}")

        return results

    def get_all_exceptions(self):
        """Retrieves all duplicate pairs marked as exceptions from the database."""
        results = []
        if not self._lmdb_env or self._exceptions_db is None:
            return results

        with QMutexLocker(self._db_lock):
            with self._lmdb_env.begin(write=False) as txn:
                cursor = txn.cursor(db=self._exceptions_db)
                for key_bytes, value_bytes in cursor:
                    try:
                        p1, p2 = None, None
                        sim = None
                        ts = 0
                        val_str = value_bytes.decode('utf-8')

                        if '|' in val_str:
                            # New format: paths are stored in the value
                            parts = val_str.split('|')
                            if len(parts) >= 2:
                                p1, p2 = parts[0], parts[1]
                                if len(parts) > 2 and parts[2]:
                                    sim = int(parts[2])
                                if len(parts) > 3:
                                    ts = int(parts[3])
                                else:
                                    ts = int(os.path.getmtime(p1)) if os.path.exists(p1) else 0

                        if not p1 or not p2:
                            # Legacy format fallback: lookup paths in hash db
                            key_str = key_bytes.decode('utf-8')
                            kp = key_str.split('-')
                            if len(kp) == 4:
                                k1, k2 = f"{kp[0]}-{kp[1]}".encode(), f"{kp[2]}-{kp[3]}".encode()
                                v1, v2 = txn.get(k1, db=self._hash_db), txn.get(k2, db=self._hash_db)
                                if v1 and v2:
                                    # Format is hash|mtime|path|dist... path is always index 2
                                    p1 = v1.decode('utf-8').split('|')[2]
                                    p2 = v2.decode('utf-8').split('|')[2]

                        if p1 and p2:
                            if os.path.exists(p1) and os.path.exists(p2):
                                results.append(DuplicateResult(p1, p2, None, True, sim, ts))
                    except Exception:
                        continue
        return results

    def clean_stale_hashes(self):
        """
        Removes hash entries from the database for files that no longer exist on disk.
        """
        if not self._lmdb_env or self._hash_db is None:
            return 0

        keys_to_delete = []
        with QMutexLocker(self._db_lock):
            with self._lmdb_env.begin(write=False) as txn:
                cursor = txn.cursor(db=self._hash_db)
                for key, value_bytes in cursor:
                    try:
                        # value_bytes is "hash|mtime|path|last_dist"
                        parts = value_bytes.decode('utf-8').split('|')
                        if len(parts) >= 3:
                            path = parts[2]
                            if not os.path.exists(path):
                                keys_to_delete.append(key)
                    except Exception:
                        keys_to_delete.append(key)  # Corrupted entry
                        continue

            if keys_to_delete:
                with self._lmdb_env.begin(write=True) as txn:
                    for k in keys_to_delete:
                        txn.delete(k, db=self._hash_db)
                logger.info(f"Cleaned up {len(keys_to_delete)} stale hash entries (files deleted externally)")
        return len(keys_to_delete)

    def get_all_hashes_with_paths(self):
        """Retrieves all hashes from the database along with their associated paths and inode info."""
        # hash_value -> [(path, dev_id, inode_key_bytes)]
        all_hashes = collections.defaultdict(list)
        if not self._lmdb_env:
            return all_hashes

        with QMutexLocker(self._db_lock):
            with self._lmdb_env.begin(write=False) as txn:
                cursor = txn.cursor(db=self._hash_db)
                for key_bytes, value_bytes in cursor:
                    # key_bytes is like "dev_id-inode_hex"
                    key_str = key_bytes.decode('utf-8')
                    parts = key_str.split('-')
                    dev_id = int(parts[0])
                    inode_key_bytes = bytes.fromhex(parts[1])

                    # value_bytes is "hash|mtime|path|last_dist"
                    parts_val = value_bytes.decode('utf-8').split('|')
                    if len(parts_val) >= 3:
                        hash_value = parts_val[0]
                        path = parts_val[2]
                    else:
                        continue

                    all_hashes[hash_value].append((path, dev_id, inode_key_bytes))
        return all_hashes

    def rename_entry(self, old_path, new_path):
        """
        Updates the cache entry for a file that has been renamed or moved.
        This involves deleting the old (dev, inode) entry and adding a new one
        with the new (dev, inode) and path, preserving the hash value.
        """
        old_dev, old_inode_key_bytes = self._get_inode_info(old_path)
        new_dev, new_inode_key_bytes = self._get_inode_info(new_path)

        if not old_inode_key_bytes or not new_inode_key_bytes or not self._lmdb_env:
            return False

        # If the (dev, inode) pair is the same, only the path in the value needs updating.
        # This happens if the file is renamed within the same filesystem.
        if (old_dev, old_inode_key_bytes) == (new_dev, new_inode_key_bytes):
            hash_value, mtime, _ = self.get_hash_and_path(old_dev, old_inode_key_bytes)
            if hash_value:
                self.add_hash_for_path(new_path, hash_value, mtime)
                self._update_pair_paths(old_path, new_path, self._pending_db)
                return True
            return False

        # If (dev, inode) changed (cross-filesystem move), we need to:
        # 1. Get the hash from the old entry.
        # 2. Remove the old entry.
        # 3. Add a new entry with the new (dev, inode) and path, using the old hash.
        hash_value, mtime, _ = self.get_hash_and_path(old_dev, old_inode_key_bytes)
        if hash_value:
            self.remove_hash_for_path(old_path)  # This removes the old (dev, inode) entry
            self.add_hash_for_path(new_path, hash_value, mtime)  # Adds new (dev, inode) entry
            self._update_pair_paths(old_path, new_path, self._pending_db)
            return True
        return False

    def _update_pair_paths(self, old_path, new_path, db_handle):
        """Updates stored paths in a pair-based DB value when a file is renamed."""
        if not self._lmdb_env or db_handle is None:
            return
        with QMutexLocker(self._db_lock):
            with self._lmdb_env.begin(write=True) as txn:
                cursor = txn.cursor(db=db_handle)
                for key, value_bytes in cursor:
                    val_str = value_bytes.decode('utf-8')
                    if old_path in val_str:
                        p1, p2 = val_str.split('|')
                        np1 = new_path if p1 == old_path else p1
                        np2 = new_path if p2 == old_path else p2
                        txn.put(key, f"{np1}|{np2}".encode('utf-8'), db=db_handle)


class DuplicateDetector(QThread):
    """
    Worker thread for detecting duplicate images using perceptual hashing.
    """
    progress_update = Signal(int, int, str)  # current, total, message
    duplicates_found = Signal(list)  # List of DuplicateResult
    detection_finished = Signal()

    def __init__(self, paths_to_scan, duplicate_cache, pool_manager, method="histogram_hashing", threshold=90, force_full=False):
        super().__init__()
        self.paths_to_scan = paths_to_scan
        self.duplicate_cache = duplicate_cache
        self.pool_manager = pool_manager
        self.method = method
        self.threshold = threshold  # Similarity percentage (50-100)
        self.force_full = force_full
        self._is_running = True

    def stop(self):
        self._is_running = False
        self.wait() # Add this line

    def run(self):
        total_files = len(self.paths_to_scan)
        found_duplicates = []
        unique_duplicate_pairs = set()  # To store frozenset((path1, path2)) for uniqueness
        last_update_time = 0

        pool = self.pool_manager.get_pool()

        # 1. Load existing pending duplicates from cache to avoid recalculation (unless force_full)
        if not self.force_full:
            pending = self.duplicate_cache.get_all_pending_duplicates()
            for p in pending:
                if p.path1 in self.paths_to_scan and p.path2 in self.paths_to_scan:
                    if p.similarity is None or p.similarity >= self.threshold:
                        found_duplicates.append(p)
                        unique_duplicate_pairs.add(frozenset((p.path1, p.path2)))

        # Convert similarity threshold (percentage) to Hamming distance
        distance_threshold = int(MAX_DHASH_DISTANCE * (100 - self.threshold) / 100)
        logger.info(f"Duplicate detection: Method={self.method}, Similarity Threshold={self.threshold}%, Hamming Distance Threshold={distance_threshold}")

        # 2. Phase 1: Hash Collection (Parallelized)
        path_to_hash = {}
        dirty_hashes_objs = set()
        dirty_paths = set()
        paths_to_hash_parallel = []

        for path in self.paths_to_scan:
            try:
                stat_info = os.stat(path)
                mtime = stat_info.st_mtime
                dev, inode = stat_info.st_dev, struct.pack('Q', stat_info.st_ino)

                cached_h = \
                    self.duplicate_cache.get_hash_for_path(path, mtime, dev, inode)

                if cached_h:
                    path_to_hash[path] = (cached_h, dev, inode)
                else:
                    dirty_paths.add(path)
                    paths_to_hash_parallel.append((path, mtime, dev, inode))
            except OSError:
                continue

        # Phase 1 starts with files already found in cache or skipped
        processed_hashing = total_files - len(paths_to_hash_parallel)

        if paths_to_hash_parallel and self._is_running:
            batch_size = pool.maxThreadCount() * 2
            results_mutex = QMutex()
            new_hashes = {}
            sem = QSemaphore(0)

            for i in range(0, len(paths_to_hash_parallel), batch_size):
                if not self._is_running:
                    break
                current_batch = paths_to_hash_parallel[i : i + batch_size]
                for p_data in current_batch:
                    pool.start(HashWorker(p_data[0], self, new_hashes, results_mutex, sem))

                for _ in range(len(current_batch)):
                    while not sem.tryAcquire(1, 100):
                        if not self._is_running:
                            break
                    if not self._is_running:
                        break
                    processed_hashing += 1
                    if time.perf_counter() - last_update_time > 0.05:
                        self.progress_update.emit(processed_hashing, total_files * 2, UITexts.DUPLICATE_MSG_HASHING.format(filename="..."))
                        last_update_time = time.perf_counter()

            for p, mtime, dev, inode in paths_to_hash_parallel:
                h = new_hashes.get(p)
                if h:
                    path_to_hash[p] = (h, dev, inode)
                    dirty_hashes_objs.add(imagehash.hex_to_hash(h))
                    self.duplicate_cache.add_hash_for_path(p, h, mtime, dev, inode)

        if not self._is_running:
            self.detection_finished.emit()
            return

        # Signal phase transition to exactly 50%
        self.progress_update.emit(total_files, total_files * 2, UITexts.DUPLICATE_MSG_ANALYZING.format(filename="..."))

        # 3. Phase 2: Comparison (Optimized with BK-Tree)
        hash_map = collections.defaultdict(list)
        bk_tree = BKTree(lambda a, b: a - b)

        for p, (h_str, dev, inode) in path_to_hash.items():
            h_obj = imagehash.hex_to_hash(h_str)
            if h_obj not in hash_map:
                bk_tree.add(h_obj)
            hash_map[h_obj].append((p, dev, inode))
            if self.force_full or p in dirty_paths:
                dirty_hashes_objs.add(h_obj)

        # Optimization: Only query the tree for hashes associated with new or modified files.
        # This finds pairs (Dirty, Clean) and (Dirty, Dirty). (Clean, Clean) were handled in previous runs.
        hashes_to_query = list(dirty_hashes_objs) if not self.force_full else list(hash_map.keys())
        total_queries = len(hashes_to_query)

        for i, h1 in enumerate(hashes_to_query):
            if not self._is_running:
                break

            items1 = hash_map[h1]

            if time.perf_counter() - last_update_time > 0.1:
                # Scale Phase 2 progress to the 50%-100% range
                phase2_progress = int(((i + 1) / total_queries) * total_files) if total_queries > 0 else total_files
                self.progress_update.emit(total_files + phase2_progress, total_files * 2, UITexts.DUPLICATE_MSG_ANALYZING.format(filename="..."))
                last_update_time = time.perf_counter()

            # Query tree for similar hashes
            for h2, distance in bk_tree.query(h1, distance_threshold):
                items2 = hash_map[h2]

                for p1, dev1, ino1 in items1:
                    for p2, dev2, ino2 in items2:
                        if not self._is_running:
                            break
                        if (dev1, ino1) == (dev2, ino2):
                            continue

                        # Optimization: Skip pair if BOTH were already verified
                        if not self.force_full and p1 not in dirty_paths and p2 not in dirty_paths:
                            continue

                        canonical = frozenset((p1, p2))
                        if not self._is_running:
                            break
                        if canonical not in unique_duplicate_pairs:
                            if not self.duplicate_cache.is_exception(p1, p2):
                                sim = int((1.0 - (distance / MAX_DHASH_DISTANCE)) * 100)
                                ts = int(time.time())
                                res = DuplicateResult(p1, p2, str(h1), False, sim, ts)
                                found_duplicates.append(res)
                                unique_duplicate_pairs.add(canonical)
                                self.duplicate_cache.mark_as_pending(p1, p2, True, similarity=sim, timestamp=ts)

        self.duplicates_found.emit(found_duplicates)
        self.detection_finished.emit()