tree_model.py

# Created By: Virgil Dupras
# Created On: 2009-09-14
# Copyright 2015 Hardcoded Software (http://www.hardcoded.net)
#
# This software is licensed under the "GPLv3" License as described in the "LICENSE" file,
# which should be included with this package. The terms are also available at
# http://www.gnu.org/licenses/gpl-3.0.html

import logging

from PyQt5.QtCore import QAbstractItemModel, QModelIndex


class NodeContainer:
    def __init__(self):
        self._subnodes = None
        self._ref2node = {}

    # --- Protected
    def _create_node(self, ref, row):
        # This returns a TreeNode instance from ref
        raise NotImplementedError()

    def _get_children(self):
        # This returns a list of ref instances, not TreeNode instances
        raise NotImplementedError()

    # --- Public
    def invalidate(self):
        # Invalidates cached data and list of subnodes without resetting ref2node.
        self._subnodes = None

    # --- Properties
    @property
    def subnodes(self):
        if self._subnodes is None:
            children = self._get_children()
            self._subnodes = []
            for index, child in enumerate(children):
                if child in self._ref2node:
                    node = self._ref2node[child]
                    node.row = index
                else:
                    node = self._create_node(child, index)
                    self._ref2node[child] = node
                self._subnodes.append(node)
        return self._subnodes


class TreeNode(NodeContainer):
    def __init__(self, model, parent, row):
        NodeContainer.__init__(self)
        self.model = model
        self.parent = parent
        self.row = row

    @property
    def index(self):
        return self.model.createIndex(self.row, 0, self)


class RefNode(TreeNode):
    """Node pointing to a reference node.

    Use this if your Qt model wraps around a tree model that has iterable nodes.
    """

    def __init__(self, model, parent, ref, row):
        TreeNode.__init__(self, model, parent, row)
        self.ref = ref

    def _create_node(self, ref, row):
        return RefNode(self.model, self, ref, row)

    def _get_children(self):
        return list(self.ref)


# We use a specific TreeNode subclass to easily spot dummy nodes, especially in exception tracebacks.
class DummyNode(TreeNode):
    pass


class TreeModel(QAbstractItemModel, NodeContainer):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self._dummy_nodes = set()  # dummy nodes' reference have to be kept to avoid segfault

    # --- Private
    def _create_dummy_node(self, parent, row):
        # In some cases (drag & drop row removal, to be precise), there's a temporary discrepancy
        # between a node's subnodes and what the model think it has. This leads to invalid indexes
        # being queried. Rather than going through complicated row removal crap, it's simpler to
        # just have rows with empty data replacing removed rows for the millisecond that the drag &
        # drop lasts. Override this to return a node of the correct type.
        return DummyNode(self, parent, row)

    def _last_index(self):
        """Index of the very last item in the tree."""
        current_index = QModelIndex()
        row_count = self.rowCount(current_index)
        while row_count > 0:
            current_index = self.index(row_count - 1, 0, current_index)
            row_count = self.rowCount(current_index)
        return current_index

    # --- Overrides
    def index(self, row, column, parent):
        if not self.subnodes:
            return QModelIndex()
        node = parent.internalPointer() if parent.isValid() else self
        try:
            return self.createIndex(row, column, node.subnodes[row])
        except IndexError:
            logging.debug(
                "Wrong tree index called (%r, %r, %r). Returning DummyNode",
                row,
                column,
                node,
            )
            parent_node = parent.internalPointer() if parent.isValid() else None
            dummy = self._create_dummy_node(parent_node, row)
            self._dummy_nodes.add(dummy)
            return self.createIndex(row, column, dummy)

    def parent(self, index):
        if not index.isValid():
            return QModelIndex()
        node = index.internalPointer()
        if node.parent is None:
            return QModelIndex()
        else:
            return self.createIndex(node.parent.row, 0, node.parent)

    def reset(self):
        super().beginResetModel()
        self.invalidate()
        self._ref2node = {}
        self._dummy_nodes = set()
        super().endResetModel()

    def rowCount(self, parent=QModelIndex()):
        node = parent.internalPointer() if parent.isValid() else self
        return len(node.subnodes)

    # --- Public
    def findIndex(self, row_path):
        """Returns the QModelIndex at `row_path`

        `row_path` is a sequence of node rows. For example, [1, 2, 1] is the 2nd child of the
        3rd child of the 2nd child of the root.
        """
        result = QModelIndex()
        for row in row_path:
            result = self.index(row, 0, result)
        return result

    @staticmethod
    def pathForIndex(index):
        reversed_path = []
        while index.isValid():
            reversed_path.append(index.row())
            index = index.parent()
        return list(reversed(reversed_path))

    def refreshData(self):
        """Updates the data on all nodes, but without having to perform a full reset.

        A full reset on a tree makes us lose selection and expansion states. When all we ant to do
        is to refresh the data on the nodes without adding or removing a node, a call on
        dataChanged() is better. But of course, Qt makes our life complicated by asking us topLeft
        and bottomRight indexes. This is a convenience method refreshing the whole tree.
        """
        column_count = self.columnCount()
        top_left = self.index(0, 0, QModelIndex())
        bottom_left = self._last_index()
        bottom_right = self.sibling(bottom_left.row(), column_count - 1, bottom_left)
        self.dataChanged.emit(top_left, bottom_right)