require 'kvmultiplex/provider'

require 'logger';
require 'diff-lcs'

module KVMultiplex
  class Multiplexer
    attr_reader :logger

    def initialize(delimiter: ".", logger: Logger.new)
      @logger = logger
      @delimiter = delimiter.dup

      @providers = {}
    end

    def register(prefix, provider, prepend: false)
      raise "provider must be a KVMultiplex::Provider." unless provider.is_a?(KVMultiplex::Provider)

      prefix =
        if prefix.is_a?(String)
          prefix.split(@delimiter).freeze
        elsif prefix.is_a?(Array) && prefix.all? { |i| i.is_a?(String) }
          prefix.map { |i| i.to_s.dup }.freeze
        else
          raise "prefix must be a String or array of Strings."
        end

      @providers[prefix] ||= []

      if prepend
        @providers[prefix].unshift provider
      else
        @providers[prefix].push provider
      end
    end

    def get!(key)
      ret = get(key)
      raise "Value not found for key: #{key}" if ret.nil?
      ret
    end

    def get(key)
      providers, subkey, full_key = find_providers_for_key(key)

      if providers.nil? || providers.empty?
        logger.warn "No providers for '#{full_key.inspect}'."
        nil
      else
        ret = providers.find { |provider| provider.get(subkey, full_key) }
        logger.warn "No values found for '#{full_key.inspect}'." if ret.nil?

        ret
      end
    end

    def set(key, value)
      providers, subkey, full_key = find_providers_for_key(key)

      if providers.nil? || providers.empty?
        logger.warn "No providers for '#{full_key.inspect}'."
        nil
      else
        logger.warn "Multiple providers found for '#{full_key.inspect}'; this might cause surprising behavior!" \
          unless providers.size == 1

        ret = providers.find do |provider|
          logger.debug "Attempting to set into #{provider}."
          p_ret = provider.set(subkey, full_key, value)

          logger.debug "Failed to set into #{provider}." if p_ret.nil?
          !p_ret.nil?
        end

        raise "No provider able to set '#{full_key.inspect}'." unless ret
        ret
      end

      value
    end

    def find_providers_for_key(key)
      logger.debug "Key lookup for '#{key.inspect}'."

      key =
        if key.is_a?(String)
          key.split(@delimiter).freeze
        elsif key.is_a?(Array) && key.all? { |i| i.is_a?(String) }
          key.map(&:to_s).freeze
        else
          raise "key must be a String or array of Strings."
        end

      key_length = key.size

      longest = -1
      longest_prefix = nil
      matched_providers = nil

      @providers.each_pair do |prefix, providers|
        lcs_length = Diff::LCS.LCS(key, prefix).length

        next unless [longest, lcs_length].max == prefix.length

        longest = lcs_length
        longest_prefix = prefix
        matched_providers = providers
        break if key_length == lcs_length # we've matched exactly
      end

      if matched_providers.nil?
        [nil, nil, key]
      else
        subkey = key - longest_prefix

        [matched_providers, subkey, key]
      end
    end
  end
end