repos: Add RecursiveBuildReport missing_rating

The plan is to split the recursive_build_report
into more structured and easy-to-operate pieces.
The first part of those pieces is introduction
of a separate class that walks the dependency
trees to build a closure of build requirements
for a given package.

To show what's already possible with it,
we add new report, missing_rating_report,
that shows the most wanted of packages that
are missing from a given repository.

repos_cmp/repos.py

@@ -363,8 +363,8 @@ class TripletReport:
                 return False
         return True
 
-    def __bool__(self):
-        return len(self.triplets) > 0
+    def sources_set(self):
+        return set(p.source_name for k, d, p in self.triplets)
 
     def basic_format(self, title=None, to=None):
         """Format a report
@@ -517,6 +517,75 @@ def _src_name(source):
     return source
 
 
+class RecursiveBuildReport:
+    def __init__(self, from_repo, to_repo, source_names,
+                 stop_names=(), prefer=()):
+        self.from_repo = from_repo
+        self.to_repo = to_repo
+        self.stop_names = frozenset(stop_names)
+        self.prefer = prefer
+        self.requested_names = [_src_name(s) for s in source_names]
+        self.reported_names = self._closure()
+
+    def _build_report(self, name):
+        return build_report(self.from_repo, self.to_repo, name,
+                            prefer=self.prefer)
+
+    def _closure(self):
+        seen = list(self.requested_names)
+        queue = list(self.requested_names)
+        while queue:
+            cur = queue.pop()
+            missing = self._build_report(cur).sources_set()
+            unseen = missing.difference(seen)
+            seen.extend(unseen)
+            # don't recur into packages from stop_names
+            queue.extend(unseen - self.stop_names)
+        return seen
+
+    def format_build_reports(self, to=None):
+        result = []
+        for name in self.reported_names:
+            result.append(f"\n== {name.decode()} ==")
+
+            in_to = self.to_repo.sources.get(name)
+            srpm = in_to.source_rpm.decode() if in_to else 'NONE'
+            result.append(f"{self.to_repo.name} has {srpm}\n")
+
+            if name in self.stop_names:
+                result.append('not going deeper (stop_names)')
+            else:
+                result.append(self._build_report(name).basic_format().strip())
+        return to('\n'.join(result)) if to else '\n'.join(result)
+
+
+def missing_rating(from_repo, to_repo):
+    result = collections.defaultdict(set)
+    for name in from_repo.sources:
+        if name in to_repo.sources or b'gost' in name:
+            continue
+        try:
+            rbr = RecursiveBuildReport(from_repo, to_repo, [name])
+        except Exception:
+            LOG.error("Failed to build recursive build report"
+                      "for %s", name.decode(), exc_info=True)
+        else:
+            for other_name in rbr.reported_names:
+                if other_name != name:
+                    result[other_name].add(name)
+    return sorted(result.items(), key=lambda x: (len(x[1]), x[0]))
+
+
+def missing_rating_report(from_repo, to_repo):
+    rr = list(reversed(missing_rating(from_repo, to_repo)))
+    result = []
+    for name, where in rr:
+        present = '+' if name in to_repo.sources else ''
+        result.append(f"{name.decode()} {present}: {len(where)}")
+        result.append("    " + b' '.join(where).decode())
+    return '\n'.join(result)
+
+
 def recursive_build_report(from_repo, to_repo, *source_names,
                            ignore=(), ignore_sort=(), summary=True):
     reports = []