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"""PySide6 port of the itemviews/fetchmore/fetchmore example from Qt v6.x

Navigate to a directory with many entries by doubleclicking and scroll
down the list to see the model being populated on demand.
"""

import sys

from PySide6.QtCore import (QAbstractListModel, QDir, QFileInfo, QLibraryInfo,
                            QModelIndex, Qt, Signal, Slot)
from PySide6.QtGui import QPalette
from PySide6.QtWidgets import (QApplication, QFileIconProvider, QListView,
                               QPlainTextEdit, QSizePolicy, QVBoxLayout,
                               QWidget)


BATCH_SIZE = 100


class FileListModel(QAbstractListModel):

    number_populated = Signal(str, int, int, int)

    def __init__(self, parent=None):
        super().__init__(parent)

        self._path = ''
        self._file_count = 0
        self._file_list = []
        self._icon_provider = QFileIconProvider()

    def rowCount(self, parent=QModelIndex()):
        return self._file_count

    def data(self, index, role=Qt.DisplayRole):
        if not index.isValid():
            return None

        row = index.row()
        if row >= len(self._file_list) or row < 0:
            return None

        if role == Qt.DisplayRole:
            return self._file_list[row].fileName()

        if role == Qt.BackgroundRole:
            batch = row // BATCH_SIZE
            palette = qApp.palette()
            return palette.base() if batch % 2 == 0 else palette.alternateBase()

        if role == Qt.DecorationRole:
            return self._icon_provider.icon(self._file_list[row])

        return None

    def canFetchMore(self, index):
        return self._file_count < len(self._file_list)

    def fetchMore(self, index):
        start = self._file_count
        total = len(self._file_list)
        remainder = total - start
        items_to_fetch = min(BATCH_SIZE, remainder)

        self.beginInsertRows(QModelIndex(), start, start + items_to_fetch)

        self._file_count += items_to_fetch

        self.endInsertRows()

        self.number_populated.emit(self._path, start, items_to_fetch, total)

    @Slot(str)
    def set_dir_path(self, path):
        self._path = path
        dir = QDir(path)

        self.beginResetModel()
        filter = QDir.AllEntries | QDir.NoDot
        self._file_list = dir.entryInfoList(filter, QDir.Name)
        self._file_count = 0
        self.endResetModel()

    def fileinfo_at(self, index):
        return self._file_list[index.row()]


class Window(QWidget):
    def __init__(self, parent=None):
        super().__init__(parent)

        self._model = FileListModel(self)
        self._model.set_dir_path(QDir.rootPath())

        self._view = QListView()
        self._view.setModel(self._model)

        self._log_viewer = QPlainTextEdit()
        self._log_viewer.setSizePolicy(QSizePolicy(QSizePolicy.Preferred,
                                       QSizePolicy.Preferred))

        self._model.number_populated.connect(self.update_log)
        self._view.activated.connect(self.activated)

        layout = QVBoxLayout(self)
        layout.addWidget(self._view)
        layout.addWidget(self._log_viewer)

        self.setWindowTitle("Fetch More Example")

    @Slot(str, int, int)
    def update_log(self, path, start, number, total):
        native_path = QDir.toNativeSeparators(path)
        last = start + number - 1
        entry = f'{start}..{last}/{total} items from "{native_path}" added.'
        self._log_viewer.appendPlainText(entry)

    @Slot(QModelIndex)
    def activated(self, index):
        fileinfo = self._model.fileinfo_at(index)
        if fileinfo.isDir():
            self._log_viewer.clear()
            self._model.set_dir_path(fileinfo.absoluteFilePath())


if __name__ == '__main__':
    app = QApplication(sys.argv)

    window = Window()
    window.resize(400, 500)
    window.show()

    sys.exit(app.exec_())