class Bundler::Resolver

def self.resolve(requirements, index, source_requirements = {}, base = [])
  base = SpecSet.new(base) unless base.is_a?(SpecSet)
  resolver = new(index, source_requirements, base)
  result = catch(:success) do
    resolver.start(requirements)
    raise resolver.version_conflict
    nil
  end
  SpecSet.new(result)
end

def clean_req(req)
  if req.to_s.include?(">= 0")
    req.to_s.gsub(/ \(.*?\)$/, '')
  else
    req.to_s.gsub(/\, (runtime|development)\)$/, ')')
  end
end

def debug
  if ENV['DEBUG_RESOLVER']
    debug_info = yield
    debug_info = debug_info.inpsect unless debug_info.is_a?(String)
    $stderr.puts debug_info
  end
end

def error_message
  output = errors.inject("") do |o, (conflict, (origin, requirement))|
    # origin is the SpecSet of specs from the Gemfile that is conflicted with
    if origin
      o << %{Bundler could not find compatible versions for gem "#{origin.name}":\n}
      o << "  In Gemfile:\n"
      o << gem_message(requirement)
      # If the origin is a LockfileParser, it does not respond_to :required_by
      unless origin.respond_to?(:required_by) && required_by = origin.required_by.first
        o << "  In snapshot (Gemfile.lock):\n"
      end
      o << gem_message(origin)
    # origin is nil if the required gem and version cannot be found in any of
    # the specified sources
    else
      # if the gem cannot be found because of a version conflict between lockfile and gemfile,
      # print a useful error that suggests running `bundle update`, which may fix things
      #
      # @base is a SpecSet of the gems in the lockfile
      # conflict is the name of the gem that could not be found
      if locked = @base[conflict].first
        o << "Bundler could not find compatible versions for gem #{conflict.inspect}:\n"
        o << "  In snapshot (Gemfile.lock):\n"
        o << "    #{clean_req(locked)}\n\n"
        o << "  In Gemfile:\n"
        o << gem_message(requirement)
        o << "Running `bundle update` will rebuild your snapshot from scratch, using only\n"
        o << "the gems in your Gemfile, which may resolve the conflict.\n"
      # the rest of the time, the gem cannot be found because it does not exist in the known sources
      else
        if requirement.required_by.first
          o << "Could not find gem '#{clean_req(requirement)}', required by '#{clean_req(requirement.required_by.first)}', in any of the sources\n"
        else
          o << "Could not find gem '#{clean_req(requirement)} in any of the sources\n"
        end
      end
    end
  end
end

def gem_message(requirement)
  m = ""
  # A requirement that is required by itself is actually in the Gemfile, and does
  # not "depend on" itself
  if requirement.required_by.first && requirement.required_by.first.name != requirement.name
    m << "    #{clean_req(requirement.required_by.first)} depends on\n"
    m << "      #{clean_req(requirement)}\n"
  else
    m << "    #{clean_req(requirement)}\n"
  end
  m << "\n"
end

def initialize(index, source_requirements, base)
  @errors               = {}
  @stack                = []
  @base                 = base
  @index                = index
  @missing_gems         = Hash.new(0)
  @source_requirements  = source_requirements
end

def resolve(reqs, activated)
  # If the requirements are empty, then we are in a success state. Aka, all
  # gem dependencies have been resolved.
  throw :success, successify(activated) if reqs.empty?
  debug { print "\e[2J\e[f" ; "==== Iterating ====\n\n" }
  # Sort dependencies so that the ones that are easiest to resolve are first.
  # Easiest to resolve is defined by:
  #   1) Is this gem already activated?
  #   2) Do the version requirements include prereleased gems?
  #   3) Sort by number of gems available in the source.
  reqs = reqs.sort_by do |a|
    [ activated[a.name] ? 0 : 1,
      a.requirement.prerelease? ? 0 : 1,
      @errors[a.name]   ? 0 : 1,
      activated[a.name] ? 0 : search(a).size ]
  end
  debug { "Activated:\n" + activated.values.map { |a| "  #{a.name} (#{a.version})" }.join("\n") }
  debug { "Requirements:\n" + reqs.map { |r| "  #{r.name} (#{r.requirement})"}.join("\n") }
  activated = activated.dup
  # Pull off the first requirement so that we can resolve it
  current = reqs.shift
  debug { "Attempting:\n  #{current.name} (#{current.requirement})"}
  # Check if the gem has already been activated, if it has, we will make sure
  # that the currently activated gem satisfies the requirement.
  existing = activated[current.name]
  if existing || current.name == 'bundler'
    # Force the current
    if current.name == 'bundler' && !existing
      existing = search(DepProxy.new(Gem::Dependency.new('bundler', VERSION), Gem::Platform::RUBY)).first
      activated['bundler'] = existing
      raise GemNotFound, %Q{Bundler could not find gem "bundler" (#{VERSION})} unless existing
    end
    if current.requirement.satisfied_by?(existing.version)
      debug { "    * [SUCCESS] Already activated" }
      @errors.delete(existing.name)
      # Since the current requirement is satisfied, we can continue resolving
      # the remaining requirements.
      # I have no idea if this is the right way to do it, but let's see if it works
      # The current requirement might activate some other platforms, so let's try
      # adding those requirements here.
      reqs.concat existing.activate_platform(current.__platform)
      resolve(reqs, activated)
    else
      debug { "    * [FAIL] Already activated" }
      @errors[existing.name] = [existing, current]
      debug { current.required_by.map {|d| "      * #{d.name} (#{d.requirement})" }.join("\n") }
      # debug { "    * All current conflicts:\n" + @errors.keys.map { |c| "      - #{c}" }.join("\n") }
      # Since the current requirement conflicts with an activated gem, we need
      # to backtrack to the current requirement's parent and try another version
      # of it (maybe the current requirement won't be present anymore). If the
      # current requirement is a root level requirement, we need to jump back to
      # where the conflicting gem was activated.
      parent = current.required_by.last
      # `existing` could not respond to required_by if it is part of the base set
      # of specs that was passed to the resolver (aka, instance of LazySpecification)
      parent ||= existing.required_by.last if existing.respond_to?(:required_by)
      # We track the spot where the current gem was activated because we need
      # to keep a list of every spot a failure happened.
      debug { "    -> Jumping to: #{parent.name}" }
      if parent
        throw parent.name, existing.respond_to?(:required_by) && existing.required_by.last.name
      else
        # The original set of dependencies conflict with the base set of specs
        # passed to the resolver. This is by definition an impossible resolve.
        raise version_conflict
      end
    end
  else
    # There are no activated gems for the current requirement, so we are going
    # to find all gems that match the current requirement and try them in decending
    # order. We also need to keep a set of all conflicts that happen while trying
    # this gem. This is so that if no versions work, we can figure out the best
    # place to backtrack to.
    conflicts = Set.new
    # Fetch all gem versions matching the requirement
    #
    # TODO: Warn / error when no matching versions are found.
    matching_versions = search(current)
    if matching_versions.empty?
      if current.required_by.empty?
        if current.source
          name = current.name
          versions = @source_requirements[name][name].map { |s| s.version }
          message  = "Could not find gem '#{current}' in #{current.source}.\n"
          if versions.any?
            message << "Source contains '#{name}' at: #{versions.join(', ')}"
          else
            message << "Source does not contain any versions of '#{current}'"
          end
        else
          message = "Could not find gem '#{current}' "
          if @index.sources.include?(Bundler::Source::Rubygems)
            message << "in any of the gem sources."
          else
            message << "in the gems available on this machine."
          end
        end
        raise GemNotFound, message
      else
        if @missing_gems[current] >= 5
          message =  "Bundler could not find find gem #{current.required_by.last},"
          message << "which is required by gem #{current}."
          raise GemNotFound, message
        end
        @missing_gems[current] += 1
        debug { "    Could not find #{current} by #{current.required_by.last}" }
        @errors[current.name] = [nil, current]
      end
    end
    matching_versions.reverse_each do |spec_group|
      conflict = resolve_requirement(spec_group, current, reqs.dup, activated.dup)
      conflicts << conflict if conflict
    end
    # If the current requirement is a root level gem and we have conflicts, we
    # can figure out the best spot to backtrack to.
    if current.required_by.empty? && !conflicts.empty?
      # Check the current "catch" stack for the first one that is included in the
      # conflicts set. That is where the parent of the conflicting gem was required.
      # By jumping back to this spot, we can try other version of the parent of
      # the conflicting gem, hopefully finding a combination that activates correctly.
      @stack.reverse_each do |savepoint|
        if conflicts.include?(savepoint)
          debug { "    -> Jumping to: #{savepoint}" }
          throw savepoint
        end
      end
    end
  end
end

def resolve_requirement(spec_group, requirement, reqs, activated)
  # We are going to try activating the spec. We need to keep track of stack of
  # requirements that got us to the point of activating this gem.
  spec_group.required_by.replace requirement.required_by
  spec_group.required_by << requirement
  activated[spec_group.name] = spec_group
  debug { "  Activating: #{spec_group.name} (#{spec_group.version})" }
  debug { spec_group.required_by.map { |d| "    * #{d.name} (#{d.requirement})" }.join("\n") }
  dependencies = spec_group.activate_platform(requirement.__platform)
  # Now, we have to loop through all child dependencies and add them to our
  # array of requirements.
  debug { "    Dependencies"}
  dependencies.each do |dep|
    next if dep.type == :development
    debug { "    * #{dep.name} (#{dep.requirement})" }
    dep.required_by.replace(requirement.required_by)
    dep.required_by << requirement
    reqs << dep
  end
  # We create a savepoint and mark it by the name of the requirement that caused
  # the gem to be activated. If the activated gem ever conflicts, we are able to
  # jump back to this point and try another version of the gem.
  length = @stack.length
  @stack << requirement.name
  retval = catch(requirement.name) do
    resolve(reqs, activated)
  end
  # Since we're doing a lot of throw / catches. A push does not necessarily match
  # up to a pop. So, we simply slice the stack back to what it was before the catch
  # block.
  @stack.slice!(length..-1)
  retval
end

def search(dep)
  if base = @base[dep.name] and base.any?
    d = Gem::Dependency.new(base.first.name, *[dep.requirement.as_list, base.first.version].flatten)
  else
    d = dep.dep
  end
  index = @source_requirements[d.name] || @index
  results = index.search_for_all_platforms(d, @base[d.name])
  if results.any?
    version = results.first.version
    nested  = [[]]
    results.each do |spec|
      if spec.version != version
        nested << []
        version = spec.version
      end
      nested.last << spec
    end
    nested.map { |a| SpecGroup.new(a) }.select { |sg| sg.for?(dep.__platform) }
  else
    []
  end
end

def start(reqs)
  activated = {}
  resolve(reqs, activated)
end

def successify(activated)
  activated.values.map { |s| s.to_specs }.flatten.compact
end

def version_conflict
  VersionConflict.new(errors.keys, error_message)
end