class Gem::Resolver

# File lib/rubygems/resolver.rb, line 53
def self.compose_sets(*sets)
  sets.compact!

  sets = sets.flat_map do |set|
    case set
    when Gem::Resolver::BestSet then
      set
    when Gem::Resolver::ComposedSet then
      set.sets
    else
      set
    end
  end

  case sets.length
  when 0 then
    raise ArgumentError, "one set in the composition must be non-nil"
  when 1 then
    sets.first
  else
    Gem::Resolver::ComposedSet.new(*sets)
  end
end

# File lib/rubygems/resolver.rb, line 81
def self.for_current_gems(needed)
  new needed, Gem::Resolver::CurrentSet.new
end

# File lib/rubygems/resolver.rb, line 93
def initialize(needed, set = nil)
  @set = set || Gem::Resolver::IndexSet.new
  @needed = needed

  @development         = false
  @development_shallow = false
  @ignore_dependencies = false
  @skip_gems           = {}
  @soft_missing        = false

  @root_package = RootPackage.new
  @root_version = Gem::PubGrub::Package.root_version

  @packages = {}

  @unfiltered_specs = Hash.new {|h, name| h[name] = find_unfiltered_specs_for(name) }
  @all_specs = Hash.new {|h, name| h[name] = filter_specs(@unfiltered_specs[name]) }
  @all_versions = Hash.new {|h, pkg| h[pkg] = @all_specs[pkg.to_s].map(&:version).uniq.sort }
  @sorted_versions = Hash.new do |h, pkg|
    h[pkg] = Gem::PubGrub::Package.root?(pkg) ? [@root_version] : @all_versions[pkg]
  end
  @cached_dependencies = Hash.new do |h, pkg|
    h[pkg] = if Gem::PubGrub::Package.root?(pkg)
      { @root_version => root_dependencies }
    else
      Hash.new {|v, ver| v[ver] = compute_dependencies(pkg, ver) }
    end
  end
  @version_to_index = Hash.new {|h, pkg| h[pkg] = @sorted_versions[pkg].each_with_index.to_h }
  @versions_for_cache = Hash.new {|h, pkg| h[pkg] = {} }
  @spec_for_cache = Hash.new {|h, name| h[name] = build_spec_for_cache(name) }
end

# File lib/rubygems/resolver.rb, line 180
def all_versions_for(package)
  versions = @sorted_versions[package].reverse # highest first
  name = package.to_s

  if (skip_dep_gems = skip_gems[name]) && !skip_dep_gems.empty?
    # Conservative mode: float the already-installed (skip) versions to the
    # front so the solver prefers them. This sets *preference* only (it feeds
    # the strategy's version-index map); it does not restrict availability, so
    # every version stays selectable via versions_for. When an installed
    # version is made impossible by a downstream conflict, the solver
    # backtracks to a newer version instead of failing. Molinillo instead
    # hard-restricted the candidate set to skip versions and raised.
    #
    # This reaches the same outcome as Bundler (upgrade-over-raise) for the
    # common single-blocked-gem case, though the mechanism differs: Bundler
    # hard-pins locked gems and selectively unlocks + re-solves on conflict,
    # whereas we float as a preference and let PubGrub backtrack in one solve.
    # The float can therefore over-upgrade when several installed gems are
    # jointly involved in a conflict; that outcome-level divergence is
    # accepted (see test_conservative_upgrades_when_installed_blocked).
    skip_versions = skip_dep_gems.map(&:version)
    preferred, rest = versions.partition {|v| skip_versions.include?(v) }
    preferred + rest
  else
    # Prefer already-installed versions to avoid unnecessary upgrades
    installed_versions = @all_specs[name].
      select {|s| s.is_a?(Gem::Resolver::InstalledSpecification) }.
      map(&:version)
    if installed_versions.any?
      preferred, rest = versions.partition {|v| installed_versions.include?(v) }
      preferred + rest
    else
      versions
    end
  end
end

# File lib/rubygems/resolver.rb, line 254
def incompatibilities_for(package, version)
  package_deps = @cached_dependencies[package]
  sorted_versions = @sorted_versions[package]
  package_deps[version].filter_map do |dep_package_name, dep_constraint|
    dep_package = dep_constraint.package

    low = high = @version_to_index[package][version]

    # find version low such that all >= low share the same dep
    while low > 0 &&
          package_deps[sorted_versions[low - 1]][dep_package_name] == dep_constraint
      low -= 1
    end
    low =
      if low == 0
        nil
      else
        sorted_versions[low]
      end

    # find version high such that all < high share the same dep
    while high < sorted_versions.length &&
          package_deps[sorted_versions[high]][dep_package_name] == dep_constraint
      high += 1
    end
    high =
      if high == sorted_versions.length
        nil
      else
        sorted_versions[high]
      end

    range = Gem::PubGrub::VersionRange.new(min: low, max: high, include_min: !low.nil?)
    self_constraint = Gem::PubGrub::VersionConstraint.new(package, range: range)

    # No specs anywhere means an unknown package. Check @unfiltered_specs, not
    # the filtered set, so a dep filtered out by platform/Ruby/prerelease falls
    # through to NoVersions for proper hints instead. The band-scoped
    # self_constraint lets clean sibling versions still resolve via backtracking.
    if @unfiltered_specs[dep_package_name].empty?
      cause = Gem::PubGrub::Incompatibility::InvalidDependency.new(dep_package, dep_constraint)
      self_term = Gem::PubGrub::Term.new(self_constraint, true)
      # PubGrub's default InvalidDependency rendering drops the version
      # requirement ("depends on unknown package bar"). Supply a custom
      # explanation so the missing dependency's constraint is preserved
      # ("depends on bar = 0.5 which could not be found in any repository"),
      # matching Molinillo's diagnostics.
      return [Gem::PubGrub::Incompatibility.new(
        [self_term],
        cause: cause,
        custom_explanation: "#{self_term.to_s(allow_every: true)} depends on #{dep_constraint} which could not be found in any repository"
      )]
    end

    # An empty range means the requirement is self-contradictory (e.g. `> 2, < 1`).
    if dep_constraint.range.empty?
      return [Gem::Resolver::Incompatibility.new(
        [Gem::PubGrub::Term.new(self_constraint, true)],
        cause: Gem::PubGrub::Incompatibility::NoVersions.new(dep_constraint),
        custom_explanation: "#{dep_package_name} cannot satisfy contradictory requirements #{dep_constraint.constraint_string}"
      )]
    end

    Gem::PubGrub::Incompatibility.new(
      [Gem::PubGrub::Term.new(self_constraint, true), Gem::PubGrub::Term.new(dep_constraint, false)],
      cause: :dependency
    )
  end
end

# File lib/rubygems/resolver.rb, line 235
def no_versions_incompatibility_for(_package, unsatisfied_term)
  cause = Gem::PubGrub::Incompatibility::NoVersions.new(unsatisfied_term)

  name = unsatisfied_term.package.to_s
  constraint = unsatisfied_term.constraint
  extended_explanation = build_extended_explanation(name, constraint)

  custom_explanation = if extended_explanation
    "#{constraint} could not be found in any repository"
  end

  Gem::Resolver::Incompatibility.new(
    [unsatisfied_term],
    cause: cause,
    custom_explanation: custom_explanation,
    extended_explanation: extended_explanation
  )
end

# File lib/rubygems/resolver.rb, line 129
def resolve
  # Pre-check: raise UnsatisfiableDependencyError for root deps with no
  # platform match. We filter by platform ONLY here (not required_ruby_version
  # / required_rubygems_version): a foreign-platform gem is genuinely "not
  # found", but a gem that exists yet is incompatible with the running Ruby
  # should flow through the solver to a DependencyResolutionError that names
  # the Ruby requirement. That matches Bundler (which models Ruby as a
  # synthetic dependency, so this surfaces as a solve failure) and gives a
  # clearer message than the platform-oriented UnsatisfiableDependencyError.
  @needed.each do |dep|
    next if @soft_missing
    dep_request = DependencyRequest.new(dep, nil)
    all = @set.find_all(dep_request)
    matching = select_local_platforms(all)

    next unless matching.empty?

    exc = Gem::UnsatisfiableDependencyError.new(dep_request, all)
    exc.errors = @set.errors
    raise exc
  end

  solver = Gem::PubGrub::VersionSolver.new(
    source: self,
    root: @root_package,
    strategy: Gem::Resolver::Strategy.new(self),
    logger: make_logger
  )
  result = solver.solve

  # Convert to Array<ActivationRequest>
  needed_by_name = @needed.group_by(&:name)
  result.filter_map do |package, version|
    next if Gem::PubGrub::Package.root?(package)
    spec = spec_for(package.to_s, version)
    dep = needed_by_name[package.to_s]&.first || Gem::Dependency.new(package.to_s)
    dep_request = DependencyRequest.new(dep, nil)
    ActivationRequest.new(spec, dep_request)
  end
rescue Gem::PubGrub::SolveFailure => e
  extended = extract_extended_explanation(e.incompatibility)
  if extended
    message = "#{e.explanation}\n\n#{extended}"
    raise Gem::DependencyResolutionError, Struct.new(:explanation).new(message)
  else
    raise Gem::DependencyResolutionError, e
  end
end

# File lib/rubygems/resolver.rb, line 217
def versions_for(package, range = Gem::PubGrub::VersionRange.any)
  @versions_for_cache[package][range] ||= begin
    candidates = range.select_versions(@sorted_versions[package])

    if Gem::PubGrub::Package.root?(package) ||
       (@set.respond_to?(:prerelease) && @set.prerelease) ||
       range_admits_prerelease?(range)
      candidates
    elsif @all_versions[package].any? {|v| !v.prerelease? }
      candidates.reject(&:prerelease?)
    else
      # Only prereleases exist for this gem; fall back to them so
      # dependencies like `>= 1.0` can still be satisfied.
      candidates
    end
  end
end

# File lib/rubygems/resolver.rb, line 439
def build_extended_explanation(name, constraint)
  unfiltered = @unfiltered_specs[name]
  return if unfiltered.empty?

  filtered = @all_specs[name]
  pkg = package_for(name)

  # A prerelease hint applies when the source would strip prereleases for
  # this constraint (global prerelease flag off and the constraint's range
  # doesn't itself reach into prerelease territory) AND a prerelease of
  # the gem exists somewhere.
  prerelease_gated = !(@set.respond_to?(:prerelease) && @set.prerelease) &&
                     !range_admits_prerelease?(constraint.range)
  has_prerelease_candidate = prerelease_gated &&
                             @all_versions[pkg].any?(&:prerelease?)

  return if filtered.length == unfiltered.length && !has_prerelease_candidate

  hints = []

  # Check for specs that exist for other platforms
  platform_specs = unfiltered.select do |s|
    !Gem::Platform.installable?(s) && constraint.range.include?(s.version)
  end
  if platform_specs.any?
    label = "#{name} (#{constraint.constraint_string})"
    hints << "The source contains the following gems matching '#{label}':"
    platform_specs.each do |s|
      actual = s.respond_to?(:spec) ? s.spec : s
      hints << "  * #{actual.full_name}"
    end
  end

  # Check for specs filtered by Ruby version
  installable = select_local_platforms(unfiltered)
  ruby_specs = installable.select do |s|
    actual = s.respond_to?(:spec) ? s.spec : s
    constraint.range.include?(s.version) &&
      !actual.required_ruby_version.satisfied_by?(Gem.ruby_version)
  rescue StandardError
    false
  end
  if ruby_specs.any?
    versions = ruby_specs.map(&:version).uniq.sort.reverse.first(3)
    sample = ruby_specs.find {|s| s.version == versions.first }
    actual = sample.respond_to?(:spec) ? sample.spec : sample
    ruby_req = actual.required_ruby_version
    hints << "#{name} #{versions.join(", ")} requires Ruby #{ruby_req} (you have #{Gem.ruby_version})"
  end

  # Check for specs filtered by prerelease status
  if prerelease_gated
    prerelease_versions = @all_versions[pkg].select(&:prerelease?)
    if prerelease_versions.any?
      versions = prerelease_versions.sort.reverse.first(3) # limit to avoid cluttering error output
      hints << "#{name} #{versions.join(", ")} are pre-release versions. Use --prerelease to allow pre-release gems."
    end
  end

  hints.empty? ? nil : hints.join("\n")
end

# File lib/rubygems/resolver.rb, line 383
def build_spec_for_cache(name)
  # Rank sources by the order they were first supplied so that, when multiple
  # sources offer the same version and platform, the earlier source wins.
  source_rank = {}
  @all_specs[name].each do |s|
    source_rank[s.source] ||= source_rank.size
  end

  @all_specs[name].group_by(&:version).transform_values do |candidates|
    next candidates.first if candidates.length == 1

    # Prefer already-installed specs to avoid unnecessary downloads
    installed = candidates.select {|s| s.is_a?(Gem::Resolver::InstalledSpecification) }
    next installed.first if installed.length == 1
    candidates = installed if installed.any?

    # Among remaining candidates, prefer the most specific platform, then the
    # earlier-supplied source.
    candidates.min_by do |s|
      [Gem::Platform.platform_specificity_match(s.platform, Gem::Platform.local),
       source_rank[s.source]]
    end
  end
end

# File lib/rubygems/resolver.rb, line 408
def compute_dependencies(package, version)
  spec = spec_for(package.to_s, version)
  return {} unless spec
  return {} if @ignore_dependencies

  spec.fetch_development_dependencies if @development && spec.respond_to?(:fetch_development_dependencies)

  deps = {}
  root_names = @needed.map(&:name)

  spec.dependencies.each do |d|
    next if d.name == package.to_s
    next if d.type == :development && !@development
    next if d.type == :development && @development_shallow && !root_names.include?(package.to_s)

    dep_package = package_for(d.name)

    # In force mode, skip deps that can't be satisfied - either no
    # specs at all, or no specs matching the version requirement.
    if @soft_missing
      dep_specs = @all_specs[d.name]
      matching = dep_specs.select {|s| d.requirement.satisfied_by?(s.version) }
      next if matching.empty?
    end

    deps[d.name] = Gem::PubGrub::RubyGems.requirement_to_constraint(dep_package, d.requirement)
  end

  deps
end

# File lib/rubygems/resolver.rb, line 501
def extract_extended_explanation(incompatibility)
  while incompatibility.cause.is_a?(Gem::PubGrub::Incompatibility::ConflictCause)
    cause = incompatibility.cause

    [cause.conflict, cause.other].each do |incompat|
      if incompat.cause.is_a?(Gem::PubGrub::Incompatibility::NoVersions) &&
         incompat.respond_to?(:extended_explanation) &&
         incompat.extended_explanation
        return incompat.extended_explanation
      end
    end

    incompatibility = cause.conflict
  end

  nil
end

# File lib/rubygems/resolver.rb, line 364
def filter_specs(specs)
  filtered = select_local_platforms(specs)

  unless @soft_missing
    filtered = filtered.select do |s|
      s.required_ruby_version.satisfied_by?(Gem.ruby_version) &&
        s.required_rubygems_version.satisfied_by?(Gem.rubygems_version)
    rescue StandardError
      true
    end
  end

  filtered
end

# File lib/rubygems/resolver.rb, line 358
def find_unfiltered_specs_for(name)
  dep = Gem::Dependency.new(name, ">= 0.a")
  dep_request = DependencyRequest.new(dep, nil)
  @set.find_all(dep_request)
end

# File lib/rubygems/resolver.rb, line 519
def make_logger
  DEBUG_RESOLVER ? Gem::PubGrub::StderrLogger.new : Gem::PubGrub::NullLogger.new
end

# File lib/rubygems/resolver.rb, line 335
def package_for(name)
  @packages[name] ||= Gem::PubGrub::Package.new(name)
end

# File lib/rubygems/resolver.rb, line 351
def range_admits_prerelease?(range)
  range.ranges.any? do |r|
    next false if r.empty?
    r.min&.prerelease?
  end
end

# File lib/rubygems/resolver.rb, line 339
def root_dependencies
  deps = {}
  @needed.each do |dep|
    constraint = Gem::PubGrub::RubyGems.requirement_to_constraint(package_for(dep.name), dep.requirement)
    deps[dep.name] = deps.key?(dep.name) ? deps[dep.name].intersect(constraint) : constraint
  end
  deps
end

# File lib/rubygems/resolver.rb, line 379
def spec_for(name, version)
  @spec_for_cache[name][version]
end