1 files changed, 121 insertions, 0 deletions
diff --git a/lib/bundler/vendor/pub_grub/lib/pub_grub/partial_solution.rb b/lib/bundler/vendor/pub_grub/lib/pub_grub/partial_solution.rb
new file mode 100644
index 0000000000..4c4b8ca844
--- /dev/null
+++ b/lib/bundler/vendor/pub_grub/lib/pub_grub/partial_solution.rb
@@ -0,0 +1,121 @@
+require_relative 'assignment'
+
+module Bundler::PubGrub
+  class PartialSolution
+    attr_reader :assignments, :decisions
+    attr_reader :attempted_solutions
+
+    def initialize
+      reset!
+
+      @attempted_solutions = 1
+      @backtracking = false
+    end
+
+    def decision_level
+      @decisions.length
+    end
+
+    def relation(term)
+      package = term.package
+      return :overlap if !@terms.key?(package)
+
+      @relation_cache[package][term] ||=
+        @terms[package].relation(term)
+    end
+
+    def satisfies?(term)
+      relation(term) == :subset
+    end
+
+    def derive(term, cause)
+      add_assignment(Assignment.new(term, cause, decision_level, assignments.length))
+    end
+
+    def satisfier(term)
+      assignment =
+        @assignments_by[term.package].bsearch do |assignment_by|
+          @cumulative_assignments[assignment_by].satisfies?(term)
+        end
+
+      assignment || raise("#{term} unsatisfied")
+    end
+
+    # A list of unsatisfied terms
+    def unsatisfied
+      @required.keys.reject do |package|
+        @decisions.key?(package)
+      end.map do |package|
+        @terms[package]
+      end
+    end
+
+    def decide(package, version)
+      @attempted_solutions += 1 if @backtracking
+      @backtracking = false;
+
+      decisions[package] = version
+      assignment = Assignment.decision(package, version, decision_level, assignments.length)
+      add_assignment(assignment)
+    end
+
+    def backtrack(previous_level)
+      @backtracking = true
+
+      new_assignments = assignments.select do |assignment|
+        assignment.decision_level <= previous_level
+      end
+
+      new_decisions = Hash[decisions.first(previous_level)]
+
+      reset!
+
+      @decisions = new_decisions
+
+      new_assignments.each do |assignment|
+        add_assignment(assignment)
+      end
+    end
+
+    private
+
+    def reset!
+      # { Array<Assignment> }
+      @assignments = []
+
+      # { Package => Array<Assignment> }
+      @assignments_by = Hash.new { |h,k| h[k] = [] }
+      @cumulative_assignments = {}.compare_by_identity
+
+      # { Package => Package::Version }
+      @decisions = {}
+
+      # { Package => Term }
+      @terms = {}
+      @relation_cache = Hash.new { |h,k| h[k] = {} }
+
+      # { Package => Boolean }
+      @required = {}
+    end
+
+    def add_assignment(assignment)
+      term = assignment.term
+      package = term.package
+
+      @assignments << assignment
+      @assignments_by[package] << assignment
+
+      @required[package] = true if term.positive?
+
+      if @terms.key?(package)
+        old_term = @terms[package]
+        @terms[package] = old_term.intersect(term)
+      else
+        @terms[package] = term
+      end
+      @relation_cache[package].clear
+
+      @cumulative_assignments[assignment] = @terms[package]
+    end
+  end
+end