# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1512242120 -3600
# Node ID 4a33f1cb48ac5b83f21e7b7ee72a223eb2d1932e
# Parent  592a4701a05f064bd3ba0464bfeb4a4d8b1e72b8
Introduced a selector that ensures the inclusion of the main period in the set
of generated occurrences, respecting any COUNT qualifier.
Renamed order_qualifiers to make_selectors.

diff -r 592a4701a05f -r 4a33f1cb48ac vRecurrence.py
--- a/vRecurrence.py	Fri Dec 01 23:09:21 2017 +0100
+++ b/vRecurrence.py	Sat Dec 02 20:15:20 2017 +0100
@@ -244,7 +244,7 @@
 
     return values
 
-def order_qualifiers(qualifiers):
+def make_selectors(qualifiers):
 
     """
     Obtain 'qualifiers' in order of increasing resolution, producing and
@@ -283,6 +283,14 @@
     else:
         return Pattern(freq[qualifier], args, qualifier)
 
+def insert_start_selector(selectors, dt):
+
+    "Return a copy of 'selectors' incorporating 'dt'."
+
+    selectors = selectors + [StartSelector(0, {"start" : dt}, "DTSTART")]
+    selectors.sort(key=selector_sort_key)
+    return selectors
+
 def sort_selectors(selectors):
 
     "Sort 'selectors' in order of increasing resolution."
@@ -309,8 +317,19 @@
     # Other BY... qualifiers sort earlier than selectors at the same resolution
     # even though such things as "FREQ=HOURLY;BYHOUR=10" do not make much sense.
 
-    return (selector.level, not selector.qualifier.startswith("BY") and 2 or
-                            selector.qualifier != "BYSETPOS" and 1 or 0)
+    if not selector.qualifier.startswith("BY"):
+        sublevel = 2
+    elif selector.qualifier != "BYSETPOS":
+        sublevel = 1
+
+    # Make DTSTART sort later than COUNT.
+
+    elif selector.qualifier == "DTSTART":
+        sublevel = 1
+    else:
+        sublevel = 0
+
+    return (selector.level, sublevel)
 
 def get_value_ranges(qualifier):
 
@@ -1031,6 +1050,17 @@
     def set_positions(self, positions):
         self.args["values"] = positions
 
+class StartSelector(Selector):
+
+    "A selector ensuring that the start occurrence is included."
+
+    def materialise_items(self, context, start, end, inclusive=False):
+        return StartIterator(self, context, start, end, inclusive,
+                             self.get_start())
+
+    def get_start(self):
+        return self.args["start"]
+
 special_enum_levels = {
     "BYDAY" : WeekDayFilter,
     "BYMONTHDAY" : MonthDayFilter,
@@ -1373,6 +1403,39 @@
                 else:
                     raise
 
+class StartIterator(SelectorIterator):
+
+    "An iterator ensuring that the start occurrence is included."
+
+    def __init__(self, selector, current, start, end, inclusive, start_dt):
+        SelectorIterator.__init__(self, selector, current, start, end, inclusive)
+        self.waiting = start_dt
+
+    def next(self):
+
+        "Return the next value, initially the start period."
+
+        while not self.at_limit():
+            result = self.next_item(self.start, self.end)
+
+            # Compare with any waiting value.
+
+            if self.waiting:
+
+                # Produce the waiting value, queue the latest result.
+
+                if result != self.waiting:
+                    result, self.waiting = self.waiting, result
+
+                # Remove the waiting value if identical to the latest result.
+
+                else:
+                    self.waiting = None
+
+            return result
+
+        raise StopIteration
+
 def connect_selectors(selectors):
 
     """
@@ -1390,7 +1453,7 @@
         # Allow selectors within the limit selector to act as if they are first
         # in the chain and will operate using the supplied datetime context.
 
-        first = isinstance(current, LimitSelector)
+        first = isinstance(current, (LimitSelector, StartSelector))
 
         current = selector
         current.first = first
@@ -1418,6 +1481,7 @@
     """
 
     dt = to_tuple(dt)
+    selectors = insert_start_selector(selectors, dt)
     return connect_selectors(combine_datetime_with_selectors(dt, selectors))
 
 def get_selectors_for_rule(rule):
@@ -1429,6 +1493,6 @@
 
     if not isinstance(rule, tuple):
         rule = (rule or "").split(";")
-    return order_qualifiers(get_qualifiers(rule))
+    return make_selectors(get_qualifiers(rule))
 
 # vim: tabstop=4 expandtab shiftwidth=4