# frozen_string_literal: true

begin
  gem "redis", ">= 4.0.1"
  require "redis"
  require "redis/distributed"
rescue LoadError
  warn "The Redis cache store requires the redis gem, version 4.0.1 or later. Please add it to your Gemfile: `gem \"redis\", \"~> 4.0\"`"
  raise
end

# Prefer the hiredis driver but don't require it.
begin
  require "redis/connection/hiredis"
rescue LoadError
end

require "digest/sha2"
require "active_support/core_ext/marshal"

module ActiveSupport
  module Cache
    # Redis cache store.
    #
    # Deployment note: Take care to use a *dedicated Redis cache* rather
    # than pointing this at your existing Redis server. It won't cope well
    # with mixed usage patterns and it won't expire cache entries by default.
    #
    # Redis cache server setup guide: https://redis.io/topics/lru-cache
    #
    # * Supports vanilla Redis, hiredis, and Redis::Distributed.
    # * Supports Memcached-like sharding across Redises with Redis::Distributed.
    # * Fault tolerant. If the Redis server is unavailable, no exceptions are
    #   raised. Cache fetches are all misses and writes are dropped.
    # * Local cache. Hot in-memory primary cache within block/middleware scope.
    # * `read_/write_multi` support for Redis mget/mset. Use Redis::Distributed
    #   4.0.1+ for distributed mget support.
    # * `delete_matched` support for Redis KEYS globs.
    class RedisCacheStore < Store
      # Keys are truncated with their own SHA2 digest if they exceed 1kB
      MAX_KEY_BYTESIZE = 1024

      DEFAULT_REDIS_OPTIONS = {
        connect_timeout:    20,
        read_timeout:       1,
        write_timeout:      1,
        reconnect_attempts: 0,
      }

      DEFAULT_ERROR_HANDLER = -> (method:, returning:, exception:) {
        logger.error { "RedisCacheStore: #{method} failed, returned #{returning.inspect}: #{e.class}: #{e.message}" } if logger
      }

      DELETE_GLOB_LUA = "for i, name in ipairs(redis.call('KEYS', ARGV[1])) do redis.call('DEL', name); end"
      private_constant :DELETE_GLOB_LUA

      # Support raw values in the local cache strategy.
      module LocalCacheWithRaw # :nodoc:
        private
          def read_entry(key, options)
            entry = super
            if options[:raw] && local_cache && entry
              entry = deserialize_entry(entry.value)
            end
            entry
          end

          def write_entry(key, entry, options)
            if options[:raw] && local_cache
              raw_entry = Entry.new(entry.value.to_s)
              raw_entry.expires_at = entry.expires_at
              super(key, raw_entry, options)
            else
              super
            end
          end

          def write_multi_entries(entries, options)
            if options[:raw] && local_cache
              raw_entries = entries.map do |key, entry|
                raw_entry = Entry.new(entry.value.to_s)
                raw_entry.expires_at = entry.expires_at
              end.to_h

              super(raw_entries, options)
            else
              super
            end
          end
      end

      prepend Strategy::LocalCache
      prepend LocalCacheWithRaw

      class << self
        # Factory method to create a new Redis instance.
        #
        # Handles four options: :redis block, :redis instance, single :url
        # string, and multiple :url strings.
        #
        #   Option  Class       Result
        #   :redis  Proc    ->  options[:redis].call
        #   :redis  Object  ->  options[:redis]
        #   :url    String  ->  Redis.new(url: …)
        #   :url    Array   ->  Redis::Distributed.new([{ url: … }, { url: … }, …])
        #
        def build_redis(redis: nil, url: nil, **redis_options) #:nodoc:
          urls = Array(url)

          if redis.respond_to?(:call)
            redis.call
          elsif redis
            redis
          elsif urls.size > 1
            build_redis_distributed_client urls: urls, **redis_options
          else
            build_redis_client url: urls.first, **redis_options
          end
        end

        private
          def build_redis_distributed_client(urls:, **redis_options)
            ::Redis::Distributed.new([], DEFAULT_REDIS_OPTIONS.merge(redis_options)).tap do |dist|
              urls.each { |u| dist.add_node url: u }
            end
          end

          def build_redis_client(url:, **redis_options)
            ::Redis.new DEFAULT_REDIS_OPTIONS.merge(redis_options.merge(url: url))
          end
      end

      attr_reader :redis_options
      attr_reader :max_key_bytesize

      # Creates a new Redis cache store.
      #
      # Handles three options: block provided to instantiate, single URL
      # provided, and multiple URLs provided.
      #
      #   :redis Proc   -> options[:redis].call
      #   :url   String -> Redis.new(url: …)
      #   :url   Array  -> Redis::Distributed.new([{ url: … }, { url: … }, …])
      #
      # No namespace is set by default. Provide one if the Redis cache
      # server is shared with other apps: `namespace: 'myapp-cache'`.
      #
      # Compression is enabled by default with a 1kB threshold, so cached
      # values larger than 1kB are automatically compressed. Disable by
      # passing `cache: false` or change the threshold by passing
      # `compress_threshold: 4.kilobytes`.
      #
      # No expiry is set on cache entries by default. Redis is expected to
      # be configured with an eviction policy that automatically deletes
      # least-recently or -frequently used keys when it reaches max memory.
      # See https://redis.io/topics/lru-cache for cache server setup.
      #
      # Race condition TTL is not set by default. This can be used to avoid
      # "thundering herd" cache writes when hot cache entries are expired.
      # See <tt>ActiveSupport::Cache::Store#fetch</tt> for more.
      def initialize(namespace: nil, compress: true, compress_threshold: 1.kilobyte, expires_in: nil, race_condition_ttl: nil, error_handler: DEFAULT_ERROR_HANDLER, **redis_options)
        @redis_options = redis_options

        @max_key_bytesize = MAX_KEY_BYTESIZE
        @error_handler = error_handler

        super namespace: namespace,
          compress: compress, compress_threshold: compress_threshold,
          expires_in: expires_in, race_condition_ttl: race_condition_ttl
      end

      def redis
        @redis ||= self.class.build_redis(**redis_options)
      end

      def inspect
        instance = @redis || @redis_options
        "<##{self.class} options=#{options.inspect} redis=#{instance.inspect}>"
      end

      # Cache Store API implementation.
      #
      # Read multiple values at once. Returns a hash of requested keys ->
      # fetched values.
      def read_multi(*names)
        if mget_capable?
          read_multi_mget(*names)
        else
          super
        end
      end

      # Cache Store API implementation.
      #
      # Supports Redis KEYS glob patterns:
      #
      #   h?llo matches hello, hallo and hxllo
      #   h*llo matches hllo and heeeello
      #   h[ae]llo matches hello and hallo, but not hillo
      #   h[^e]llo matches hallo, hbllo, ... but not hello
      #   h[a-b]llo matches hallo and hbllo
      #
      # Use \ to escape special characters if you want to match them verbatim.
      #
      # See https://redis.io/commands/KEYS for more.
      #
      # Failsafe: Raises errors.
      def delete_matched(matcher, options = nil)
        instrument :delete_matched, matcher do
          case matcher
          when String
            redis.eval DELETE_GLOB_LUA, [], [namespace_key(matcher, options)]
          else
            raise ArgumentError, "Only Redis glob strings are supported: #{matcher.inspect}"
          end
        end
      end

      # Cache Store API implementation.
      #
      # Increment a cached value. This method uses the Redis incr atomic
      # operator and can only be used on values written with the :raw option.
      # Calling it on a value not stored with :raw will initialize that value
      # to zero.
      #
      # Failsafe: Raises errors.
      def increment(name, amount = 1, options = nil)
        instrument :increment, name, amount: amount do
          redis.incrby normalize_key(name, options), amount
        end
      end

      # Cache Store API implementation.
      #
      # Decrement a cached value. This method uses the Redis decr atomic
      # operator and can only be used on values written with the :raw option.
      # Calling it on a value not stored with :raw will initialize that value
      # to zero.
      #
      # Failsafe: Raises errors.
      def decrement(name, amount = 1, options = nil)
        instrument :decrement, name, amount: amount do
          redis.decrby normalize_key(name, options), amount
        end
      end

      # Cache Store API implementation.
      #
      # Removes expired entries. Handled natively by Redis least-recently-/
      # least-frequently-used expiry, so manual cleanup is not supported.
      def cleanup(options = nil)
        super
      end

      # Clear the entire cache on all Redis servers. Safe to use on
      # shared servers if the cache is namespaced.
      #
      # Failsafe: Raises errors.
      def clear(options = nil)
        failsafe :clear do
          if namespace = merged_options(options)[namespace]
            delete_matched "*", namespace: namespace
          else
            redis.flushdb
          end
        end
      end

      def mget_capable? #:nodoc:
        set_redis_capabilities unless defined? @mget_capable
        @mget_capable
      end

      def mset_capable? #:nodoc:
        set_redis_capabilities unless defined? @mset_capable
        @mset_capable
      end

      private
        def set_redis_capabilities
          case redis
          when Redis::Distributed
            @mget_capable = true
            @mset_capable = false
          else
            @mget_capable = true
            @mset_capable = true
          end
        end

        # Store provider interface:
        # Read an entry from the cache.
        def read_entry(key, options = nil)
          failsafe :read_entry do
            deserialize_entry redis.get(key)
          end
        end

        def read_multi_mget(*names)
          options = names.extract_options!
          options = merged_options(options)

          keys_to_names = names.map { |name| [ normalize_key(name, options), name ] }.to_h
          values = redis.mget(*keys_to_names.keys)

          keys_to_names.zip(values).each_with_object({}) do |((key, name), value), results|
            if value
              entry = deserialize_entry(value)
              unless entry.nil? || entry.expired? || entry.mismatched?(normalize_version(name, options))
                results[name] = entry.value
              end
            end
          end
        end

        # Write an entry to the cache.
        #
        # Requires Redis 2.6.12+ for extended SET options.
        def write_entry(key, entry, unless_exist: false, raw: false, expires_in: nil, race_condition_ttl: nil, **options)
          value = raw ? entry.value.to_s : serialize_entry(entry)

          # If race condition TTL is in use, ensure that cache entries
          # stick around a bit longer after they would have expired
          # so we can purposefully serve stale entries.
          if race_condition_ttl && expires_in && expires_in > 0 && !raw
            expires_in += 5.minutes
          end

          failsafe :write_entry do
            if unless_exist || expires_in
              modifiers = {}
              modifiers[:nx] = unless_exist
              modifiers[:px] = (1000 * expires_in.to_f).ceil if expires_in

              redis.set key, value, modifiers
            else
              redis.set key, value
            end
          end
        end

        # Delete an entry from the cache.
        def delete_entry(key, options)
          failsafe :delete_entry, returning: false do
            redis.del key
          end
        end

        # Nonstandard store provider API to write multiple values at once.
        def write_multi_entries(entries, expires_in: nil, **options)
          if entries.any?
            if mset_capable? && expires_in.nil?
              failsafe :write_multi_entries do
                redis.mapped_mset(entries)
              end
            else
              super
            end
          end
        end

        # Truncate keys that exceed 1kB.
        def normalize_key(key, options)
          truncate_key super
        end

        def truncate_key(key)
          if key.bytesize > max_key_bytesize
            suffix = ":sha2:#{Digest::SHA2.hexdigest(key)}"
            truncate_at = max_key_bytesize - suffix.bytesize
            "#{key.byteslice(0, truncate_at)}#{suffix}"
          else
            key
          end
        end

        def deserialize_entry(raw_value)
          if raw_value
            entry = Marshal.load(raw_value) rescue raw_value
            entry.is_a?(Entry) ? entry : Entry.new(entry)
          end
        end

        def serialize_entry(entry)
          Marshal.dump(entry)
        end

        def failsafe(method, returning: nil)
          yield
        rescue ::Redis::BaseConnectionError => e
          handle_exception exception: e, method: method, returning: returning
          returning
        end

        def handle_exception(exception:, method:, returning:)
          if @error_handler
            @error_handler.(method: method, exception: exception, returning: returning)
          end
        rescue => failsafe
          warn "RedisCacheStore ignored exception in handle_exception: #{failsafe.class}: #{failsafe.message}\n  #{failsafe.backtrace.join("\n  ")}"
        end
    end
  end
end