1 files changed, 132 insertions, 0 deletions
diff --git a/resources/libraries/python/MLRsearch/strategy/base.py b/resources/libraries/python/MLRsearch/strategy/base.py
new file mode 100644
index 0000000000..0724f882bf
--- /dev/null
+++ b/resources/libraries/python/MLRsearch/strategy/base.py
@@ -0,0 +1,132 @@
+# Copyright (c) 2023 Cisco and/or its affiliates.
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at:
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Module defining StrategyBase class."""
+
+
+from abc import ABC, abstractmethod
+from dataclasses import dataclass, field
+from typing import Callable, Optional, Tuple
+
+from ..discrete_interval import DiscreteInterval
+from ..discrete_load import DiscreteLoad
+from ..discrete_width import DiscreteWidth
+from ..expander import TargetedExpander
+from ..limit_handler import LimitHandler
+from ..relevant_bounds import RelevantBounds
+from ..target_spec import TargetSpec
+
+
+@dataclass
+class StrategyBase(ABC):
+    """Abstract class encompassing data common to most strategies.
+
+    A strategy is one piece of logic a selector may use
+    when nominating a candidate according to its current target.
+
+    The two initial bound arguments may not be bounds at all.
+    For initial targets, the two values are usually mrr and mrr2.
+    For subsequent targets, the initial values are usually
+    the relevant bounds of the preceding target,
+    but one of them may be None if hitting min or max load.
+
+    The initial values are mainly used as stable alternatives
+    to relevant bounds of preceding target,
+    because those bounds may have been unpredictably altered
+    by nominations from unrelated search goals.
+    This greatly simplifies reasoning about strategies making progress.
+    """
+
+    target: TargetSpec
+    """The target this strategy is focusing on."""
+    expander: TargetedExpander
+    """Instance to track width expansion during search (if applicable)."""
+    initial_lower_load: Optional[DiscreteLoad]
+    """Smaller of the two loads distinguished at instance creation.
+    Can be None if upper bound is the min load."""
+    initial_upper_load: Optional[DiscreteLoad]
+    """Larger of the two loads distinguished at instance creation.
+    Can be None if lower bound is the max load."""
+    handler: LimitHandler = field(repr=False)
+    """Reference to the limit handler instance."""
+    debug: Callable[[str], None] = field(repr=False)
+    """Injectable function for debug logging."""
+
+    @abstractmethod
+    def nominate(
+        self, bounds: RelevantBounds
+    ) -> Tuple[Optional[DiscreteLoad], Optional[DiscreteWidth]]:
+        """Nominate a load candidate if the conditions activate this strategy.
+
+        A complete candidate refers also to the nominating selector.
+        To prevent circular dependence (selector refers to nominating strategy),
+        this function returns only duration and width.
+
+        Width should only be non-None if global current width should be updated
+        when the candidate based on this becomes winner.
+        But currently all strategies return non-None width
+        if they return non-None load.
+
+        :param bounds: Freshly updated bounds relevant for current target.
+        :type bounds: RelevantBounds
+        :returns: Two nones or candidate intended load and duration.
+        :rtype: Tuple[Optional[DiscreteLoad], Optional[DiscreteWidth]]
+        """
+        return None, None
+
+    def won(self, bounds: RelevantBounds, load: DiscreteLoad) -> None:
+        """Notify the strategy its candidate became the winner.
+
+        Most strategies have no use for this information,
+        but some strategies may need to update their private information.
+
+        :param bounds: Freshly updated bounds relevant for current target.
+        :param load: The current load, so strategy does not need to remember.
+        :type bounds: RelevantBounds
+        :type load: DiscreteLoad
+        """
+        return
+
+    def not_worth(self, bounds: RelevantBounds, load: DiscreteLoad) -> bool:
+        """A check on bounds common for multiple strategies.
+
+        The load is worth measuring only if it can create or improve
+        either relevant bound.
+
+        Each strategy is designed to create a relevant bound for current target,
+        which is only needed if that (or better) bound does not exist yet.
+        Conversely, if a strategy does not nominate, it is because
+        the load it would nominate (if any) is found not worth by this method.
+
+        :param bounds: Current relevant bounds.
+        :param load: Load of a possible candidate.
+        :type bounds: RelevantBounds
+        :type load: DiscreteLoad
+        :returns: True if the load should NOT be nominated.
+        :rtype: bool
+        """
+        if bounds.clo and bounds.clo >= load:
+            return True
+        if bounds.chi and bounds.chi <= load:
+            return True
+        if bounds.clo and bounds.chi:
+            # We are not hitting min nor max load.
+            # Measuring at this load will create or improve clo or chi.
+            # The only reason not to nominate is if interval is narrow already.
+            wig = DiscreteInterval(
+                lower_bound=bounds.clo,
+                upper_bound=bounds.chi,
+            ).width_in_goals(self.target.discrete_width)
+            if wig <= 1.0:
+                return True
+        return False