From b9f5658aae1a583235e202bb0bd978cad350381f Mon Sep 17 00:00:00 2001
From: Andrew Dickinson <dickinsa@umich.edu>
Date: Sun, 12 Apr 2020 21:04:43 -0400
Subject: [PATCH] Add functions to query project history

---
 ihatemoney/history.py | 139 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 139 insertions(+)
 create mode 100644 ihatemoney/history.py

diff --git a/ihatemoney/history.py b/ihatemoney/history.py
new file mode 100644
index 00000000..edd7f84a
--- /dev/null
+++ b/ihatemoney/history.py
@@ -0,0 +1,139 @@
+from flask_babel import gettext as _
+from sqlalchemy_continuum import (
+    Operation,
+    parent_class,
+)
+
+from ihatemoney.models import (
+    PersonVersion,
+    ProjectVersion,
+    BillVersion,
+    Person,
+)
+
+
+def get_history_queries(project):
+    """Generate queries for each type of version object for a given project."""
+    person_changes = PersonVersion.query.filter_by(project_id=project.id)
+
+    project_changes = ProjectVersion.query.filter_by(id=project.id)
+
+    bill_changes = (
+        BillVersion.query.with_entities(BillVersion.id.label("bill_version_id"))
+        .join(Person, BillVersion.payer_id == Person.id)
+        .filter(Person.project_id == project.id)
+    )
+    sub_query = bill_changes.subquery()
+    bill_changes = BillVersion.query.filter(BillVersion.id.in_(sub_query))
+
+    return person_changes, project_changes, bill_changes
+
+
+def history_sort_key(history_item_dict):
+    """
+    Return the key necessary to sort history entries. First order sort is time
+    of modification, but for simultaneous modifications we make the re-name
+    modification occur last so that the simultaneous entries make sense using
+    the old name.
+    """
+    second_order = 0
+    if "prop_changed" in history_item_dict:
+        changed_property = history_item_dict["prop_changed"]
+        if changed_property == "name" or changed_property == "what":
+            second_order = 1
+
+    return history_item_dict["time"], second_order
+
+
+def describe_version(version_obj):
+    """Use the base model str() function to describe a version object"""
+    return parent_class(type(version_obj)).__str__(version_obj)
+
+
+def describe_owers_change(version, human_readable_names):
+    """Compute the set difference to get added/removed owers lists."""
+    before_owers = {version.id: version for version in version.previous.owers}
+    after_owers = {version.id: version for version in version.owers}
+
+    added_ids = set(after_owers).difference(set(before_owers))
+    removed_ids = set(before_owers).difference(set(after_owers))
+
+    if not human_readable_names:
+        return added_ids, removed_ids
+
+    added = [describe_version(after_owers[ower_id]) for ower_id in added_ids]
+    removed = [describe_version(before_owers[ower_id]) for ower_id in removed_ids]
+
+    return added, removed
+
+
+def get_history(project, human_readable_names=True):
+    """
+    Fetch history for all models associated with a given project.
+    :param human_readable_names Whether to replace id numbers with readable names
+    :return A sorted list of dicts with history information
+    """
+    person_query, project_query, bill_query = get_history_queries(project)
+    history = []
+    for version_list in [person_query.all(), project_query.all(), bill_query.all()]:
+        for version in version_list:
+            object_type = {
+                "Person": _("Person"),
+                "Bill": _("Bill"),
+                "Project": _("Project"),
+            }[parent_class(type(version)).__name__]
+
+            # Use the old name if applicable
+            if version.previous:
+                object_str = describe_version(version.previous)
+            else:
+                object_str = describe_version(version)
+
+            common_properties = {
+                "time": version.transaction.issued_at,
+                "operation_type": version.operation_type,
+                "object_type": object_type,
+                "object_desc": object_str,
+                "ip": version.transaction.remote_addr,
+            }
+
+            if version.operation_type == Operation.UPDATE:
+                # Only iterate the changeset if the previous version
+                # Was logged
+                if version.previous:
+                    changeset = version.changeset
+                    if isinstance(version, BillVersion):
+                        if version.owers != version.previous.owers:
+                            added, removed = describe_owers_change(
+                                version, human_readable_names
+                            )
+
+                            if added:
+                                changeset["owers_added"] = (None, added)
+                            if removed:
+                                changeset["owers_removed"] = (None, removed)
+
+                    for (prop, (val_before, val_after),) in changeset.items():
+                        if human_readable_names:
+                            if prop == "payer_id":
+                                prop = "payer"
+                                if val_after is not None:
+                                    val_after = describe_version(version.payer)
+                                if version.previous and val_before is not None:
+                                    val_before = describe_version(
+                                        version.previous.payer
+                                    )
+                                else:
+                                    val_after = None
+
+                        next_event = common_properties.copy()
+                        next_event["prop_changed"] = prop
+                        next_event["val_before"] = val_before
+                        next_event["val_after"] = val_after
+                        history.append(next_event)
+                else:
+                    history.append(common_properties)
+            else:
+                history.append(common_properties)
+
+    return sorted(history, key=history_sort_key, reverse=True)