# Copyright 2018 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


module Google
  module Cloud
    ##
    # Configuration mechanism for Google Cloud libraries. A Config object
    # contains a list of predefined keys, some of which are values and others
    # of which are subconfigurations, i.e. categories. Field access is
    # generally validated to ensure that the field is defined, and when a
    # a value is set, it is validated for the correct type. Warnings are
    # printed when a validation fails.
    #
    # You generally access fields and subconfigs by calling accessor methods.
    # Methods meant for "administration" such as adding options, are named
    # with a trailing "!" or "?" so they don't pollute the method namespace.
    # It is also possible to access a field using the `[]` operator.
    #
    # Note that config objects inherit from `BasicObject`. This means it does
    # not define many methods you might expect to find in most Ruby objects.
    # For example, `to_s`, `inspect`, `is_a?`, `instance_variable_get`, and so
    # forth.
    #
    # @example
    #   require "google/cloud/config"
    #
    #   config = Google::Cloud::Config.create do |c|
    #     c.add_field! :opt1, 10
    #     c.add_field! :opt2, :one, enum: [:one, :two, :three]
    #     c.add_field! :opt3, "hi", match: [String, Symbol]
    #     c.add_field! :opt4, "hi", match: /^[a-z]+$/, allow_nil: true
    #     c.add_config! :sub do |c2|
    #       c2.add_field! :opt5, false
    #     end
    #   end
    #
    #   config.opt1             #=> 10
    #   config.opt1 = 20        #=> 20
    #   config.opt1             #=> 20
    #   config.opt1 = "hi"      #=> "hi" (but prints a warning)
    #   config.opt1 = nil       #=> nil (but prints a warning)
    #
    #   config.opt2             #=> :one
    #   config.opt2 = :two      #=> :two
    #   config.opt2             #=> :two
    #   config.opt2 = :four     #=> :four (but prints a warning)
    #
    #   config.opt3             #=> "hi"
    #   config.opt3 = "hiho"    #=> "hiho"
    #   config.opt3             #=> "hiho"
    #   config.opt3 = "HI"      #=> "HI" (but prints a warning)
    #
    #   config.opt4             #=> "yo"
    #   config.opt4 = :yo       #=> :yo (Strings and Symbols allowed)
    #   config.opt4             #=> :yo
    #   config.opt4 = 3.14      #=> 3.14 (but prints a warning)
    #   config.opt4 = nil       #=> nil (no warning: nil allowed)
    #
    #   config.sub              #=> <Google::Cloud::Config>
    #
    #   config.sub.opt5         #=> false
    #   config.sub.opt5 = true  #=> true  (true and false allowed)
    #   config.sub.opt5         #=> true
    #   config.sub.opt5 = nil   #=> nil (but prints a warning)
    #
    #   config.opt9 = "hi"      #=> "hi" (warning about unknown key)
    #   config.opt9             #=> "hi" (no warning: key now known)
    #   config.sub.opt9         #=> nil (warning about unknown key)
    #
    class Config < BasicObject
      ##
      # Constructs a Config object. If a block is given, yields `self` to the
      # block, which makes it convenient to initialize the structure by making
      # calls to `add_field!` and `add_config!`.
      #
      # @param [boolean] show_warnings Whether to print warnings when a
      #     validation fails. Defaults to `true`.
      # @return [Config] The constructed Config object.
      #
      def self.create show_warnings: true
        config = new [], show_warnings: show_warnings
        yield config if block_given?
        config
      end

      ##
      # Determines if the given object is a config. Useful because Config
      # does not define the `is_a?` method.
      #
      # @return [boolean]
      #
      def self.config? obj
        Config.send :===, obj
      end

      ##
      # Internal constructor. Generally you should not call `new` directly,
      # but instead use the `Config.create` method. The initializer is used
      # directly by a few older clients that expect a legacy interface.
      #
      # @private
      #
      def initialize legacy_categories = {}, opts = {}
        @show_warnings = opts.fetch :show_warnings, false
        @values = {}
        @defaults = {}
        @validators = {}
        add_options legacy_categories
      end

      ##
      # Legacy method of adding subconfigs. This is used by older versions of
      # the stackdriver client libraries but should not be used in new code.
      #
      # @deprecated
      # @private
      #
      def add_options legacy_categories
        [legacy_categories].flatten(1).each do |sub_key|
          case sub_key
          when ::Symbol
            add_config! sub_key, Config.new
          when ::Hash
            sub_key.each do |k, v|
              add_config! k, Config.new(v)
            end
          else
            raise ArgumentError "Category must be a Symbol or Hash"
          end
        end
      end

      ##
      # Add a value field to this configuration.
      #
      # You must provide a key, which becomes the field name in this config.
      # Field names may comprise only letters, numerals, and underscores, and
      # must begin with a letter. This will create accessor methods for the
      # new configuration key.
      #
      # You may pass an initial value (which defaults to nil if not provided).
      #
      # You may also specify how values are validated. Validation is defined
      # as follows:
      #
      # *   If you provide a block or a `:validator` option, it is used as the
      #     validator. A proposed value is passed to the proc, which should
      #     return `true` or `false` to indicate whether the value is valid.
      # *   If you provide a `:match` option, it is compared to the proposed
      #     value using the `===` operator. You may, for example, provide a
      #     class, a regular expression, or a range. If you pass an array,
      #     the value is accepted if _any_ of the elements match.
      # *   If you provide an `:enum` option, it should be an `Enumerable`.
      #     A proposed value is valid if it is included.
      # *   Otherwise if you do not provide any of the above options, then a
      #     default validation strategy is inferred from the initial value:
      #     *   If the initial is `true` or `false`, then either boolean value
      #         is considered valid. This is the same as `enum: [true, false]`.
      #     *   If the initial is `nil`, then any object is considered valid.
      #     *   Otherwise, any object of the same class as the initial value is
      #         considered valid. This is effectively the same as
      #         `match: initial.class`.
      # *   You may also provide the `:allow_nil` option, which, if set to
      #     true, alters any of the above validators to allow `nil` values.
      #
      # In many cases, you may find that the default validation behavior
      # (interpreted from the initial value) is sufficient. If you want to
      # accept any value, use `match: Object`.
      #
      # @param [String, Symbol] key The name of the option
      # @param [Object] initial Initial value (defaults to nil)
      # @param [Hash] opts Validation options
      #
      # @return [Config] self for chaining
      #
      def add_field! key, initial = nil, opts = {}, &block
        key = validate_new_key! key
        opts[:validator] = block if block
        validator = resolve_validator! initial, opts
        validate_value! key, validator, initial
        @values[key] = initial
        @defaults[key] = initial
        @validators[key] = validator
        self
      end

      ##
      # Add a subconfiguration field to this configuration.
      #
      # You must provide a key, which becomes the method name that you use to
      # navigate to the subconfig. Names may comprise only letters, numerals,
      # and underscores, and must begin with a letter.
      #
      # If you provide a block, the subconfig object is passed to the block,
      # so you can easily add fields to the subconfig.
      #
      # You may also pass in a config object that already exists. This will
      # "attach" that configuration in this location.
      #
      # @param [String, Symbol] key The name of the subconfig
      # @param [Config] config A config object to attach here. If not provided,
      #     creates a new config.
      #
      # @return [Config] self for chaining
      #
      def add_config! key, config = nil, &block
        key = validate_new_key! key
        if config.nil?
          config = Config.create(&block)
        elsif block
          yield config
        end
        @values[key] = config
        @defaults[key] = config
        @validators[key] = SUBCONFIG
        self
      end

      ##
      # Cause a key to be an alias of another key. The two keys will refer to
      # the same field.
      #
      def add_alias! key, to_key
        key = validate_new_key! key
        @values.delete key
        @defaults.delete key
        @validators[key] = to_key.to_sym
        self
      end

      ##
      # Restore the original default value of the given key.
      # If the key is omitted, restore the original defaults for all keys,
      # and all keys of subconfigs, recursively.
      #
      # @param [Symbol, nil] key The key to reset. If omitted or `nil`,
      #     recursively reset all fields and subconfigs.
      #
      def reset! key = nil
        if key.nil?
          @values.each_key { |k| reset! k }
        else
          key = key.to_sym
          if @defaults.key? key
            @values[key] = @defaults[key]
            @values[key].reset! if @validators[key] == SUBCONFIG
          elsif @values.key? key
            warn! "Key #{key.inspect} has not been added, but has a value." \
                  " Removing the value."
            @values.delete key
          else
            warn! "Key #{key.inspect} does not exist. Nothing to reset."
          end
        end
        self
      end

      ##
      # Remove the given key from the configuration, deleting any validation
      # and value. If the key is omitted, delete all keys. If the key is an
      # alias, deletes the alias but leaves the original.
      #
      # @param [Symbol, nil] key The key to delete. If omitted or `nil`,
      #     delete all fields and subconfigs.
      #
      def delete! key = nil
        if key.nil?
          @values.clear
          @defaults.clear
          @validators.clear
        else
          @values.delete key
          @defaults.delete key
          @validators.delete key
        end
        self
      end

      ##
      # Assign an option with the given name to the given value.
      #
      # @param [Symbol, String] key The option name
      # @param [Object] value The new option value
      #
      def []= key, value
        key = resolve_key! key
        validate_value! key, @validators[key], value
        @values[key] = value
      end

      ##
      # Get the option or subconfig with the given name.
      #
      # @param [Symbol, String] key The option or subconfig name
      # @return [Object] The option value or subconfig object
      #
      def [] key
        key = resolve_key! key
        warn! "Key #{key.inspect} does not exist. Returning nil." unless @validators.key? key
        value = @values[key]
        value = value.call if Config::DeferredValue === value
        value
      end

      ##
      # Check if the given key has been set in this object. Returns true if the
      # key has been added as a normal field, subconfig, or alias, or if it has
      # not been added explicitly but still has a value.
      #
      # @param [Symbol] key The key to check for.
      # @return [boolean]
      #
      def value_set? key
        @values.key? resolve_key! key
      end
      alias option? value_set?

      ##
      # Check if the given key has been explicitly added as a field name.
      #
      # @param [Symbol] key The key to check for.
      # @return [boolean]
      #
      def field? key
        @validators[key.to_sym].is_a? ::Proc
      end
      alias respond_to? field?

      ##
      # Check if the given key has been explicitly added as a subconfig name.
      #
      # @param [Symbol] key The key to check for.
      # @return [boolean]
      #
      def subconfig? key
        @validators[key.to_sym] == SUBCONFIG
      end

      ##
      # Check if the given key has been explicitly added as an alias.
      # If so, return the target, otherwise return nil.
      #
      # @param [Symbol] key The key to check for.
      # @return [Symbol,nil] The alias target, or nil if not an alias.
      #
      def alias? key
        target = @validators[key.to_sym]
        target.is_a?(::Symbol) ? target : nil
      end

      ##
      # Return a list of explicitly added field names.
      #
      # @return [Array<Symbol>] a list of field names as symbols.
      #
      def fields!
        @validators.keys.find_all { |key| @validators[key].is_a? ::Proc }
      end

      ##
      # Return a list of explicitly added subconfig names.
      #
      # @return [Array<Symbol>] a list of subconfig names as symbols.
      #
      def subconfigs!
        @validators.keys.find_all { |key| @validators[key] == SUBCONFIG }
      end

      ##
      # Return a list of alias names.
      #
      # @return [Array<Symbol>] a list of alias names as symbols.
      #
      def aliases!
        @validators.keys.find_all { |key| @validators[key].is_a? ::Symbol }
      end

      ##
      # Returns a string representation of this configuration state, including
      # subconfigs. Only explicitly added fields and subconfigs are included.
      #
      # @return [String]
      #
      def to_s!
        elems = @validators.keys.map do |k|
          v = @values[k]
          vstr = Config.config?(v) ? v.to_s! : v.inspect
          " #{k}=#{vstr}"
        end
        "<Config:#{elems.join}>"
      end
      alias inspect to_s!

      ##
      # Returns a nested hash representation of this configuration state,
      # including subconfigs. Only explicitly added fields and subconfigs are
      # included.
      #
      # @return [Hash]
      #
      def to_h!
        h = {}
        @validators.each_key do |k|
          v = @values[k]
          h[k] = Config.config?(v) ? v.to_h! : v.inspect
        end
        h
      end

      ##
      # Search the given environment variable names for valid credential data
      # that can be passed to `Google::Auth::Credentials.new`.
      # If a variable contains a valid file path, returns that path as a string.
      # If a variable contains valid JSON, returns the parsed JSON as a hash.
      # If no variables contain valid data, returns nil.
      # @private
      #
      def self.credentials_from_env *vars
        vars.each do |var|
          data = ::ENV[var]
          next unless data
          str = data.strip
          return str if ::File.file? str
          json = begin
                   ::JSON.parse str
                 rescue ::StandardError
                   nil
                 end
          return json if json.is_a? ::Hash
        end
        nil
      end

      ##
      # @private
      # Create a configuration value that will be invoked when retrieved.
      #
      def self.deferred &block
        DeferredValue.new(&block)
      end

      ##
      # @private
      # Dynamic methods accessed as keys.
      #
      def method_missing name, *args
        name_str = name.to_s
        super unless name_str =~ /^[a-zA-Z]\w*=?$/
        if name_str.end_with? "="
          self[name_str[0...-1]] = args.first
        else
          self[name]
        end
      end

      ##
      # @private
      # Dynamic methods accessed as keys.
      #
      def respond_to_missing? name, include_private
        return true if value_set? name.to_s.chomp("=")
        super
      end

      ##
      # @private
      # Implement standard nil check
      #
      # @return [false]
      #
      def nil?
        false
      end

      private

      ##
      # @private A validator that allows all values
      #
      OPEN_VALIDATOR = ::Proc.new { true }

      ##
      # @private a list of key names that are technically illegal because
      # they clash with method names.
      #
      ILLEGAL_KEYS = [:add_options,
                      :initialize,
                      :inspect,
                      :instance_eval,
                      :instance_exec,
                      :method_missing,
                      :send,
                      :singleton_method_added,
                      :singleton_method_removed,
                      :singleton_method_undefined].freeze

      ##
      # @private sentinel indicating a subconfig in the validators hash
      #
      SUBCONFIG = ::Object.new

      def resolve_key! key
        key = key.to_sym
        alias_target = @validators[key]
        alias_target.is_a?(::Symbol) ? alias_target : key
      end

      def validate_new_key! key
        key_str = key.to_s
        key = key.to_sym
        if key_str !~ /^[a-zA-Z]\w*$/ || ILLEGAL_KEYS.include?(key)
          warn! "Illegal key name: #{key_str.inspect}. Method dispatch will" \
                " not work for this key."
        end
        warn! "Key #{key.inspect} already exists. It will be replaced." if @validators.key? key
        key
      end

      def resolve_validator! initial, opts
        allow_nil = initial.nil? || opts[:allow_nil]
        if opts.key? :validator
          build_proc_validator! opts[:validator], allow_nil
        elsif opts.key? :match
          build_match_validator! opts[:match], allow_nil
        elsif opts.key? :enum
          build_enum_validator! opts[:enum], allow_nil
        elsif [true, false].include? initial
          build_enum_validator! [true, false], allow_nil
        elsif initial.nil?
          OPEN_VALIDATOR
        else
          klass = Config.config?(initial) ? Config : initial.class
          build_match_validator! klass, allow_nil
        end
      end

      def build_match_validator! matches, allow_nil
        matches = ::Kernel.Array(matches)
        matches += [nil] if allow_nil && !matches.include?(nil)
        ->(val) { matches.any? { |m| m.send :===, val } }
      end

      def build_enum_validator! allowed, allow_nil
        allowed = ::Kernel.Array(allowed)
        allowed += [nil] if allow_nil && !allowed.include?(nil)
        ->(val) { allowed.include? val }
      end

      def build_proc_validator! proc, allow_nil
        ->(val) { proc.call(val) || (allow_nil && val.nil?) }
      end

      def validate_value! key, validator, value
        value = value.call if Config::DeferredValue === value
        case validator
        when ::Proc
          unless validator.call value
            warn! "Invalid value #{value.inspect} for key #{key.inspect}." \
                  " Setting anyway."
          end
        when Config
          if value != validator
            warn! "Key #{key.inspect} refers to a subconfig and shouldn't" \
                  " be changed. Setting anyway."
          end
        else
          warn! "Key #{key.inspect} has not been added. Setting anyway."
        end
      end

      def warn! msg
        return unless @show_warnings
        location = ::Kernel.caller_locations.find do |s|
          !s.to_s.include? "/google/cloud/config.rb:"
        end
        ::Kernel.warn "#{msg} at #{location}"
      end

      ##
      # @private
      #
      class DeferredValue
        def initialize &block
          @callback = block
        end

        def call
          @callback.call
        end
      end
    end
  end
end
