Pod::Spec.new do |spec|
  spec.name         = 'Reachability'
  spec.version      = '3.1.0'
  spec.license      = { :type => 'BSD' }
  spec.homepage     = 'https://github.com/tonymillion/Reachability'
  spec.authors      = { 'Tony Million' => 'tonymillion@gmail.com' }
  spec.summary      = 'ARC and GCD Compatible Reachability Class for iOS and OS X.'
  spec.source       = { :git => 'https://github.com/tonymillion/Reachability.git', :tag => "v#{spec.version}" }
  spec.source_files = 'Reachability.{h,m}'
  spec.framework    = 'SystemConfiguration'
end

Pod::Spec.new do |spec|
  spec.name         = 'Reachability'
  # 省略与前面相同部分的配置 ...

  spec.module_name   = 'Rich'
  spec.swift_version = '4.0'
  spec.ios.deployment_target  = '9.0'
  spec.osx.deployment_target  = '10.10'
  spec.source_files       = 'Reachability/common/*.swift'
  spec.ios.source_files   = 'Reachability/ios/*.swift', 'Reachability/extensions/*.swift'
  spec.osx.source_files   = 'Reachability/osx/*.swift'
  spec.framework      = 'SystemConfiguration'
  spec.ios.framework  = 'UIKit'
  spec.osx.framework  = 'AppKit'
  spec.dependency 'SomeOtherPod'
end

require 'active_support/core_ext/string/strip.rb'
# 记录对应 platform 上 Spec 的其他 pod 依赖
require 'cocoapods-core/specification/consumer'
# 解析 DSL
require 'cocoapods-core/specification/dsl'
# 校验 Spec 的正确性，并抛出对应的错误和警告
require 'cocoapods-core/specification/linter'
# 用于解析 DSL 内容包含的配置信息
require 'cocoapods-core/specification/root_attribute_accessors'
# 记录一个 Pod 所有依赖的 Spec 来源信息
require 'cocoapods-core/specification/set'
# json 格式数据解析
require 'cocoapods-core/specification/json'

module Pod
  class Specification
    include Pod::Specification::DSL
    include Pod::Specification::DSL::Deprecations
    include Pod::Specification::RootAttributesAccessors
    include Pod::Specification::JSONSupport

    # `subspec` 的父节点
    attr_reader :parent
    # `Spec` 的唯一 id，由 name + version 的 hash 构成
    attr_reader :hash_value
    # 记录 `Spec` 的配置信息 
    attr_accessor :attributes_hash
    # `Spec` 包含的 `subspec`
    attr_accessor :subspecs

    # 递归调用获取 Specification 的根节点
    def root
      parent ? parent.root : self
    end

  def hash
    if @hash_value.nil?
       @hash_value = (name.hash * 53) ^ version.hash
  end
      @hash_value
    end

    # ...
  end
end

Pod::Spec.new do |s|
  s.name             = "QMUIKit"
  s.version          = "4.2.1"
  # ...
  s.subspec 'QMUICore' do |ss|
    ss.source_files = 'QMUIKit/QMUIKit.h', 'QMUIKit/QMUICore', 'QMUIKit/UIKitExtensions'
    ss.dependency 'QMUIKit/QMUIWeakObjectContainer'
    ss.dependency 'QMUIKit/QMUILog'
  end

  s.subspec 'QMUIWeakObjectContainer' do |ss|
    ss.source_files = 'QMUIKit/QMUIComponents/QMUIWeakObjectContainer.{h,m}'
  end

  s.subspec 'QMUILog' do |ss|
    ss.source_files = 'QMUIKit/QMUIComponents/QMUILog/*.{h,m}'
  end

  s.subspec 'QMUIComponents' do |ss|
    ss.dependency 'QMUIKit/QMUICore'

    ss.subspec 'QMUIButton' do |sss|
      sss.source_files = 'QMUIKit/QMUIComponents/QMUIButton/QMUIButton.{h,m}'
    end
    # 此处省略 59 个 Components
  end
  # ...
end

# lib/cocoapods-core/specification/dsl/attribute_support.rb
SUPPORTED_SPEC_TYPES = [:library, :app, :test].freeze

def self.from_file(path, subspec_name = nil)
  path = Pathname.new(path)
  unless path.exist?
    raise Informative, "No Podspec exists at path `#{path}`."
  end
  string = File.open(path, 'r:utf-8', &:read)
  # Work around for Rubinius incomplete encoding in 1.9 mode
  if string.respond_to?(:encoding) && string.encoding.name != 'UTF-8'
    string.encode!('UTF-8')
  end
  from_string(string, path, subspec_name)
end

def self.from_string(spec_contents, path, subspec_name = nil)
  path = Pathname.new(path).expand_path
  spec = nil
  case path.extname
  when '.podspec'
    Dir.chdir(path.parent.directory? ? path.parent : Dir.pwd) do
      spec = ::Pod._eval_Podspec(spec_contents, path)
      unless spec.is_a?(Specification)
        raise Informative, "Invalid Podspec file at path `#{path}`."
      end
    end
  when '.json'
    spec = Specification.from_json(spec_contents)
  else
    raise Informative, "Unsupported specification format `#{path.extname}` for spec at `#{path}`."
  end

  spec.defined_in_file = path
  spec.subspec_by_name(subspec_name, true)
end

# `lib/cocoapods-core/specification/json.rb`
module Pod
  class Specification
    module JSONSupport
    # ①
    def self.from_json(json)
      require 'json'
      hash = JSON.parse(json)
      from_hash(hash)
    end
    # ②
    def self.from_hash(hash, parent = nil, test_specification: false, app_specification: false)
      attributes_hash = hash.dup
      spec = Spec.new(parent, nil, test_specification, :app_specification => app_specification)
      subspecs = attributes_hash.delete('subspecs')
      testspecs = attributes_hash.delete('testspecs')
      appspecs = attributes_hash.delete('appspecs')

      ## backwards compatibility with 1.3.0
      spec.test_specification = !attributes_hash['test_type'].nil?

      spec.attributes_hash = attributes_hash
      spec.subspecs.concat(subspecs_from_hash(spec, subspecs, false, false))
      spec.subspecs.concat(subspecs_from_hash(spec, testspecs, true, false))
      spec.subspecs.concat(subspecs_from_hash(spec, appspecs, false, true))

      spec
    end
    # ③
    def self.subspecs_from_hash(spec, subspecs, test_specification, app_specification)
      return [] if subspecs.nil?
      subspecs.map do |s_hash|
        Specification.from_hash(s_hash, spec,
                                :test_specification => test_specification,
                                :app_specification => app_specification)
      end
    end
  end
end

Pod::Spec.new do |s|
  s.name             = "QMUIKit"
  s.source_files     = 'QMUIKit/QMUIKit.h'
  # ...
end

# `lib/cocoapods-core/specification/dsl.rb`
module Pod
  class Specification
    module DSL
      extend Pod::Specification::DSL::AttributeSupport
      # Deprecations must be required after include AttributeSupport
      require 'cocoapods-core/specification/dsl/deprecations'

      attribute :name,
                :required => true,
                :inherited => false,
                :multi_platform => false

      root_attribute :version,
                      :required => true
      # ...
    end
  end
end

# `lib/cocoapods-core/specification/attribute_support.rb`
module Pod
  class Specification
    module DSL
      class << self
        attr_reader :attributes
      end

      module AttributeSupport
        def root_attribute(name, options = {})
          options[:root_only] = true
          options[:multi_platform] = false
          store_attribute(name, options)
        end

        def attribute(name, options = {})
          store_attribute(name, options)
        end

        def store_attribute(name, options)
          attr = Attribute.new(name, options)
          @attributes ||= {}
          @attributes[name] = attr
        end
      end
    end
  end
end

# `/lib/coocapods-core/specification`
module Pod
  class Specification
    # ...

    def store_attribute(name, value, platform_name = nil)
      name = name.to_s
      value = Specification.convert_keys_to_string(value) if value.is_a?(Hash)
      value = value.strip_heredoc.strip if value.respond_to?(:strip_heredoc)
      if platform_name
        platform_name = platform_name.to_s
        attributes_hash[platform_name] ||= {}
        attributes_hash[platform_name][name] = value
      else
        attributes_hash[name] = value
      end
    end

    DSL.attributes.values.each do |a|
      define_method(a.writer_name) do |value|
        store_attribute(a.name, value)
      end
      if a.writer_singular_form
        alias_method(a.writer_singular_form, a.writer_name)
      end
    end
  end
end

Pod::Spec.new do |s|
  # ...
  s.subspec 'NSURLSession' do |ss|
  # ...
  end
  s.subspec 'UIKit' do |ss|
    ss.ios.deployment_target = '9.0'
    ss.tvos.deployment_target = '9.0'
    ss.dependency 'AFNetworking/NSURLSession'
    ss.source_files = 'UIKit+AFNetworking'
  end
end

def subspec(name, &block)
  subspec = Specification.new(self, name, &block)
  @subspecs << subspec
  subspec
end

def test_spec(name = 'Tests', &block)
  subspec = Specification.new(self, name, true, &block)
  @subspecs << subspec
  subspec
end

def app_spec(name = 'App', &block)
  appspec = Specification.new(self, name, :app_specification => true, &block)
  @subspecs << appspec
  appspec
end

def dependency(*args)
  name, *version_requirements = args
  # dependency args 有效性校验 ...
  attributes_hash['dependencies'] ||= {}
  attributes_hash['dependencies'][name] = version_requirements
  unless whitelisted_configurations.nil?
    # configuration 白名单过滤和校验 ...
    attributes_hash['configuration_pod_whitelist'] ||= {}
    attributes_hash['configuration_pod_whitelist'][name] = whitelisted_configurations
  end
end

$ pod lib create `NAME`

$ pod lib lint `[Podspec_PATHS ...]`

$ pod trunk push `[NAME.podspec]`

$ pod repo push `REPO_NAME` `SPEC_NAME.podspec`

target 'Demo' do
  pod 'QMUIKit/QMUIComponents/QMUILabel', :path => '../QMUI_iOS'
  pod 'QMUIKit/QMUIComponents/QMUIButton', :path => '../QMUI_iOS'
end

target 'Demo2' do
 pod 'QMUIKit/QMUIComponents/QMUILog', :path => '../QMUI_iOS'
end

# 用于检查 spec 是否符合当前 Source 要求
require 'cocoapods-core/source/acceptor'
# 记录本地 source 的集合
require 'cocoapods-core/source/aggregate'
# 用于校验 source 的错误和警告
require 'cocoapods-core/source/health_reporter'
# source 管理器
require 'cocoapods-core/source/manager'
# source 元数据
require 'cocoapods-core/source/metadata'

module Pod
  class Source
    # 仓库默认的 Git 分支
    DEFAULT_SPECS_BRANCH = 'master'.freeze
    # 记录仓库的元数据
    attr_reader :metadata
    # 记录仓库的本地地址
    attr_reader :repo
    # repo 仓库地址 ~/.cocoapods/repos/{repo_name}
    def initialize(repo)
      @repo = Pathname(repo).expand_path
      @versions_by_name = {}
      refresh_metadata
    end
    # 读取 Git 仓库中的 remote url 或 .git 目录
    def url
      @url ||= begin
        remote = repo_git(%w(config --get remote.origin.url))
        if !remote.empty?
          remote
        elsif (repo + '.git').exist?
          "file://#{repo}/.git"
        end
      end
    end

    def type
      git? ? 'git' : 'file system'
    end
    # ...
  end
end

def refresh_metadata
  @metadata = Metadata.from_file(metadata_path)
end

def metadata_path
  repo + 'CocoaPods-version.yml'
end

autoload :Digest, 'digest/md5'
require 'active_support/hash_with_indifferent_access'
require 'active_support/core_ext/hash/indifferent_access'

module Pod
  class Source
    class Metadata
      # 最低可支持的 CocoaPods 版本，对应字段 `min`
      attr_reader :minimum_cocoapods_version
      # 最高可支持的 CocoaPods 版本，对应字段 `max`
      attr_reader :maximum_cocoapods_version
      # 最新 CocoaPods 版本，对应字段 `last`
      attr_reader :latest_cocoapods_version
      # 规定截取的关键字段的前缀长度和数量
      attr_reader :prefix_lengths
      # 可兼容的 CocoaPods 最新版本
      attr_reader :last_compatible_versions
      # ...
    end
  end
end

---
min: 1.0.0
last: 1.10.0.beta.1
prefix_lengths:
- 1
- 1
- 1

def path_fragment(pod_name, version = nil)
  prefixes = if prefix_lengths.empty?
               []
             else
               hashed = Digest::MD5.hexdigest(pod_name)
               prefix_lengths.map do |length|
                 hashed.slice!(0, length)
               end
             end
  prefixes.concat([pod_name, version]).compact
end

$ Digest::MD5.hexdigest('AFNetworking')
"a75d452377f3996bdc4b623a5df25820"

def versions(name)
  return nil unless specs_dir
  raise ArgumentError, 'No name' unless name
  pod_dir = pod_path(name)
  return unless pod_dir.exist?
  @versions_by_name[name] ||= pod_dir.children.map do |v|
    basename = v.basename.to_s
    begin
      Version.new(basename) if v.directory? && basename[0, 1] != '.'
    rescue ArgumentError
    raise Informative, 'An unexpected version directory ...'
    end
  end.compact.sort.reverse
end

class Version < Pod::Vendor::Gem::Version
  METADATA_PATTERN = '(\+[0-9a-zA-Z\-\.]+)'
  VERSION_PATTERN = "[0-9]+(\\.[0-9a-zA-Z\\-]+)*#{METADATA_PATTERN}?"
  # ...
end

3.0.0
3.0.0-beta.1
3.0.0-beta.2
3.0.0-beta.3
3.0.1

require 'cocoapods-core/source'
# ...
module Pod
  class CDNSource < Source
    def initialize(repo)
      # 标记是否正在同步文件
      @check_existing_files_for_update = false
      # 记录时间用于对比下载文件的新旧程度，以确认是否需要更新保存所下的资源
      @startup_time = Time.new
      # 缓存查询过的 PodSpec 资源
      @version_arrays_by_fragment_by_name = {}
      super(repo)
    end

    def url
      @url ||= File.read(repo.join('.url')).chomp.chomp('/') + '/'
    end

    def type
      'CDN'
    end
    # ...
  end
end

module Pod
  class TrunkSource < CDNSource
    # 新版落盘后仓库名称
    TRUNK_REPO_NAME = 'trunk'.freeze
    TRUNK_REPO_URL = 'https://cdn.cocoapods.org/'.freeze
    def url
      @url ||= TRUNK_REPO_URL
      super
    end
  end
end

module Pod
  class Source
    class Manager
      attr_reader :repos_dir

      def initialize(repos_dir)
        @repos_dir = Pathname(repos_dir).expand_path
      end

      def source_repos
        return [] unless repos_dir.exist?
        repos_dir.children.select(&:directory?).sort_by { |d| d.basename.to_s.downcase }
      end

      def aggregate
        aggregate_with_repos(source_repos)
      end

      def aggregate_with_repos(repos)
        sources = repos.map { |path| source_from_path(path) }
        @aggregates_by_repos ||= {}
        @aggregates_by_repos[repos] ||= Source::Aggregate.new(sources)
      end

      def all
        aggregate.sources
      end
      # ...
    end
  end
end

def source_from_path(path)
  @sources_by_path ||= Hash.new do |hash, key|
    hash[key] = case
                when key.basename.to_s == Pod::TrunkSource::TRUNK_REPO_NAME
                  TrunkSource.new(key)
                when (key + '.url').exist?
                  CDNSource.new(key)
                else
                  Source.new(key)
                end
  end
  @sources_by_path[path]
end

module Pod
  class Source
    class Aggregate
      attr_reader :sources

      def initialize(sources)
        raise "Cannot initialize an aggregate with a nil source: (#{sources})" if sources.include?(nil)
        @sources = sources
      end

      # 查询依赖对应的 specs
      def search(dependency) ... end

      # 查询某个 pod 以发布的 specs
      def search_by_name(query, full_text_search = false) ... end

      # ...
  end
end

source 'https://github.com/CocoaPods/Specs.git'
source 'https://github.com/artsy/Specs.git'

# lib/cocoapods/installer/analyzer.rb
def sources
  @sources ||= begin
    # 省略获取 podfile、plugins、dependencies 的 source url ...
    sources = ...

    result = sources.uniq.map do |source_url|
      sources_manager.find_or_create_source_with_url(source_url)
    end
    unless plugin_sources.empty?
      result.insert(0, *plugin_sources)
      plugin_sources.each do |source|
        sources_manager.add_source(source)
      end
    end
    result
  end
end

# lib/cocoapods/sources_manager.rb
module Pod
  class Source
    class Manager

      def find_or_create_source_with_url(url)
        source_with_url(url) || create_source_with_url(url)
      end

      def create_source_with_url(url)
        name = name_for_url(url)
        is_cdn = cdn_url?(url)
    # ...
        begin
          if is_cdn
            Command::Repo::AddCDN.parse([name, url]).run
          else
            Command::Repo::Add.parse([name, url]).run
          end
        rescue Informative => e
          raise Informative, # ...
        ensure
          UI.title_level = previous_title_level
        end
        source = source_with_url(url)
        raise "Unable to create a source with URL #{url}" unless source
        source
      end
      # ...
    end
  end
end

# lib/cocoapods-core/source/manager.rb

def source_with_url(url)
  url = canonic_url(url)
  url = 'https://github.com/cocoapods/specs' if url =~ %r{github.com[:/]+cocoapods/specs}
  all.find do |source|
    source.url && canonic_url(source.url) == url
  end
end

def canonic_url(url)
  url.downcase.gsub(/\.git$/, '').gsub(%r{\/$}, '')
end

# lib/cocoapods-core/source/aggregate.rb

def search(dependency)
  found_sources = sources.select { |s| s.search(dependency) }
  unless found_sources.empty?
    Specification::Set.new(dependency.root_name, found_sources)
  end
end

# lib/cocoapods-core/cdn_source.rb

def search(query)
  unless specs_dir
    raise Informative, "Unable to find a source named: `#{name}`"
  end
  if query.is_a?(Dependency)
    query = query.root_name
  end

  fragment = pod_shard_fragment(query)
  ensure_versions_file_loaded(fragment)
  version_arrays_by_name = @version_arrays_by_fragment_by_name[fragment] || {}

  found = version_arrays_by_name[query].nil? ? nil : query

  if found
    set = set(query)
    set if set.specification_name == query
  end
end

AFNetworking/0.10.0/0.10.1/.../4.0.1
AppseeAnalytics/2.4.7/2.4.8/2.4.8.0/...
DynamsoftBarcodeReader/7.1.0/...
...

def ensure_versions_file_loaded(fragment)
  return if !@version_arrays_by_fragment_by_name[fragment].nil? && !@check_existing_files_for_update
  index_file_name = index_file_name_for_fragment(fragment)
  download_file(index_file_name)
  versions_raw = local_file(index_file_name, &:to_a).map(&:chomp)
  @version_arrays_by_fragment_by_name[fragment] = versions_raw.reduce({}) do |hash, row|
    row = row.split('/')
    pod = row.shift
    versions = row
    hash[pod] = versions
    hash
  end
end

def index_file_name_for_fragment(fragment)
  fragment_joined = fragment.join('_')
  fragment_joined = '_' + fragment_joined unless fragment.empty?
  "all_pods_versions#{fragment_joined}.txt"
end

module Pod
  class Specification
    class Set
      attr_reader :name
      attr_reader :sources

      def specification_name
        versions_by_source.each do |source, versions|
          next unless version = versions.first
          return source.specification(name, version).name
        end
        nil
      end

      def versions_by_source
        @versions_by_source ||= sources.each_with_object({}) do |source, result|
          result[source] = source.versions(name)
        end
      end
      # ...
    end
  end
end

$ pod search `QUERY`

# lib/cocoapods/installer/analyzer.rb

def update_repositories
  sources.each do |source|
    if source.updateable?
      sources_manager.update(source.name, true)
    else
      UI.message "Skipping ..."
    end
  end
  @specs_updated = true
end

# lib/cocoapods/sources_managers.rb

def update(source_name = nil, show_output = false)
  if source_name
    sources = [updateable_source_named(source_name)]
  else
    sources = updateable_sources
  end

  changed_spec_paths = {}

  # Do not perform an update if the repos dir has not been setup yet.
  return unless repos_dir.exist?

  File.open("#{repos_dir}/Spec_Lock", File::CREAT) do |f|
    f.flock(File::LOCK_EX)
    sources.each do |source|
      UI.p "Updating spec repo `#{source.name}`" do
        changed_source_paths = source.update(show_output)
        changed_spec_paths[source] = changed_source_paths if changed_source_paths.count > 0
        source.verify_compatibility!
      end
    end
  end
  update_search_index_if_needed_in_background(changed_spec_paths)
end

def update(show_output)
  return [] if unchanged_github_repo?
  prev_commit_hash = git_commit_hash
  update_git_repo(show_output)
  @versions_by_name.clear
  refresh_metadata
  if version = metadata.last_compatible_version(Version.new(CORE_VERSION))
    tag = "v#{version}"
    CoreUI.warn "Using the ..."
    repo_git(['checkout', tag])
  end
  diff_until_commit_hash(prev_commit_hash)
end

def update(_show_output)
  @check_existing_files_for_update = true
  begin
    preheat_existing_files
  ensure
    @check_existing_files_for_update = false
  end
  []
end

def preheat_existing_files
  files_to_update = files_definitely_to_update + deprecated_local_podspecs - ['deprecated_podspecs.txt']
  concurrent_requests_catching_errors do
    loaders = files_to_update.map do |file|
      download_file_async(file)
    end
    Promises.zip_futures_on(HYDRA_EXECUTOR, *loaders).wait!
  end
end

$ pod repo update `[NAME]`

# lib/cocoapods/command/repo/update.rb
module Pod
  class Command
    class Repo < Command
      class Update < Repo
        def run
          show_output = !config.silent?
          config.sources_manager.update(@name, show_output)
          exclude_repos_dir_from_backup
        end
        # ...
      end
    end
  end
end