class Molinillo::VersionConflict

def initialize(conflicts, specification_provider)
  pairs = []
  conflicts.values.flat_map(&:requirements).each do |conflicting|
    conflicting.each do |source, conflict_requirements|
      conflict_requirements.each do |c|
        pairs << [c, source]
      end
    end
  end
  super "Unable to satisfy the following requirements:\n\n" \
    "#{pairs.map { |r, d| "- `#{r}` required by `#{d}`" }.join("\n")}"
  @conflicts = conflicts
  @specification_provider = specification_provider
end

def message_with_trees(opts = {})
  solver_name = opts.delete(:solver_name) { self.class.name.split('::').first }
  possibility_type = opts.delete(:possibility_type) { 'possibility named' }
  reduce_trees = opts.delete(:reduce_trees) { proc { |trees| trees.uniq.sort_by(&:to_s) } }
  printable_requirement = opts.delete(:printable_requirement) { proc { |req| req.to_s } }
  additional_message_for_conflict = opts.delete(:additional_message_for_conflict) { proc {} }
  version_for_spec = opts.delete(:version_for_spec) { proc(&:to_s) }
  incompatible_version_message_for_conflict = opts.delete(:incompatible_version_message_for_conflict) do
    proc do |name, _conflict|
      %(#{solver_name} could not find compatible versions for #{possibility_type} "#{name}":)
    end
  end
  conflicts.sort.reduce(''.dup) do |o, (name, conflict)|
    o << "\n" << incompatible_version_message_for_conflict.call(name, conflict) << "\n"
    if conflict.locked_requirement
      o << %(  In snapshot (#{name_for_locking_dependency_source}):\n)
      o << %(    #{printable_requirement.call(conflict.locked_requirement)}\n)
      o << %(\n)
    end
    o << %(  In #{name_for_explicit_dependency_source}:\n)
    trees = reduce_trees.call(conflict.requirement_trees)
    o << trees.map do |tree|
      t = ''.dup
      depth = 2
      tree.each do |req|
        t << '  ' * depth << printable_requirement.call(req)
        unless tree.last == req
          if spec = conflict.activated_by_name[name_for(req)]
            t << %( was resolved to #{version_for_spec.call(spec)}, which)
          end
          t << %( depends on)
        end
        t << %(\n)
        depth += 1
      end
      t
    end.join("\n")
    additional_message_for_conflict.call(o, name, conflict)
    o
  end.strip
end