resolver.py: Add CustomPackageProvider class

JIRA: https://issues.redhat.com/browse/RHELAI-3189

The builder project contains code that attempts to satisfy constraints and
package requirements.  This code is effectively replicating
is_satsified_by() of the GenericProvider class and should be removed from
builder in favor of a new class in fromager.

The new class has find_best_match(), which unlike find_matches() returns
the best match in a provided list of versions.

Suggested-by: Doug Hellmann <[email protected]>
Signed-off-by: Prarit Bhargava <[email protected]>

src/fromager/resolver.py

@@ -509,3 +509,52 @@ def _find_tags(
                 yield entry["tarball_url"], version
             # pagination links
             nexturl = resp.links.get("next", {}).get("url")
+
+
+class CustomPackageProvider(BaseProvider):
+    """Get best match"""
+
+    def __init__(
+        self,
+        req: Requirement,
+        constraints: Constraints,
+        versions: dict[Version, str],
+    ):
+        super().__init__(constraints=constraints)
+        self.req = req
+        self.versions = versions
+
+    def get_cache(self) -> dict[str, list[Candidate]]:
+        return GenericProvider.generic_resolver_cache
+
+    def find_best_match(
+        self,
+    ) -> Version:
+        # convert self.versions to candidates
+        candidates = []
+        for version, _ in self.versions.items():
+            # Candidates require a URL for initialization: Use localhost as a place holder
+            # Candidates must match the requirement name in is_satisfied_call below
+            candidate = Candidate(self.req.name, version, "https://localhost")
+            candidates.append(candidate)
+
+        constraint = self.constraints.get_constraint(self.req.name)
+        constraintspec = ""
+        if constraint is not None:
+            constraintspec = str(constraint.specifier)
+
+        for candidate in reversed(candidates):
+            if self.is_satisfied_by(self.req, candidate):
+                logger.info(
+                    f"{self.req.name}{constraintspec} matches {self.req.name} {candidate.version}"
+                )
+                return candidate.version
+            else:
+                if DEBUG_RESOLVER:
+                    logger.debug(
+                        f"find_match {self.req.name} is rejected by {candidate.version}"
+                    )
+
+        raise ValueError(
+            f"{self.req.name}: {self.req.name}{self.req.specifier} and constraint{constraintspec} conflict.  No matches found."
+        )