Collapse timeline in conflict graphs.

This removes 'inner' timeline nodes that don't carry any useful
information.

src/macrogen/graph.py

@@ -3,11 +3,11 @@
 """
 
 import csv
-from collections import defaultdict, Counter, Sequence
+from collections import defaultdict, Counter
 from dataclasses import dataclass
 from datetime import date, timedelta
 from pathlib import Path
-from typing import List, Callable, Any, Dict, Tuple, Union, Iterable, Generator
+from typing import List, Callable, Any, Dict, Tuple, Union, Iterable, Generator, Sequence, TypeVar
 
 import networkx as nx
 
@@ -249,6 +249,35 @@ def collapse_edges_by_source(graph: nx.MultiDiGraph) -> nx.MultiDiGraph:
     return result
 
 
+T = TypeVar('T')
+S = TypeVar('S')
+
+
+def first(sequence: Iterable[T], default: S = None) -> Union[T, S]:
+    try:
+        return next(iter(sequence))
+    except StopIteration:
+        return default
+
+
+def collapse_timeline(graph: nx.MultiDiGraph) -> nx.MultiDiGraph:
+    """
+    Returns a new graph in which unneeded datetime nodes are removed.
+    """
+    g: nx.MultiDiGraph = graph.copy()
+    timeline = sorted(node for node in g.nodes() if isinstance(node, date))
+    if not timeline:
+        return g  # nothing to do
+    for node in timeline[1:]:
+        pred = first(g.predecessors(node))
+        succ = first(g.successors(node))
+        if g.in_degree(node) == 1 and g.out_degree(node) == 1 \
+                and isinstance(pred, date) and isinstance(succ, date):
+            g.add_edge(pred, succ, **g[pred][node][0])
+            g.remove_node(node)
+    return g
+
+
 @dataclass
 class MacrogenesisInfo:
     base: nx.MultiDiGraph

src/macrogen/report.py

@@ -20,7 +20,7 @@
 
 from .config import config
 from .bibliography import BiblSource
-from .graph import MacrogenesisInfo, pathlink, EARLIEST, LATEST, DAY
+from .graph import MacrogenesisInfo, pathlink, EARLIEST, LATEST, DAY, collapse_timeline
 from .uris import Reference, Witness, Inscription, UnknownRef, AmbiguousRef
 from .visualize import write_dot, simplify_graph
 
@@ -657,10 +657,10 @@ def _report_conflict(graphs: MacrogenesisInfo, u, v):
     except nx.NodeNotFound:
         logger.exception('Node not found!? %s or %s', u, v)
         counter_html = ''
-    subgraph: nx.MultiDiGraph = nx.subgraph(graphs.base, relevant_nodes).copy()
+    subgraph: nx.MultiDiGraph = collapse_timeline(nx.subgraph(graphs.base, relevant_nodes))
 
     # Highlight conflicting edges, counter path and the two nodes of the conflicting edge(s)
-    for v1, v2 in [(u, v)] + list(pairwise(counter_path)):
+    for v1, v2 in [(u, v)] + list(pairwise(nx.shortest_path(subgraph, v, u))):
         for k, attr in subgraph.get_edge_data(v1, v2).items():
             attr['highlight'] = True
     subgraph.node[u]['highlight'] = True