require 'excon'
require 'json'

module SctCore
    class UpdateChecker
        def self.start_looking_for_update(gem_name)
            begin
                server_results[gem_name] = fetch_latest(gem_name)
            rescue => e
                # ignore possible exceptions
                UI.verbose("error occured fetching latest version #{e.message}")
            end
        end

        def self.server_results
            @results ||= {}
        end

        def self.update_available?(gem_name, current_version)
            latest = server_results[gem_name]
            return (latest and Gem::Version.new(latest) > Gem::Version.new(current_version))
        end

        def self.show_update_status(gem_name, current_version)
            if update_available?(gem_name, current_version)
              show_update_message(gem_name, current_version)
            end
        end

        def self.show_update_message(gem_name, current_version)
            available = server_results[gem_name]
            puts("")
            UI.important('#######################################################################')
            if available
                UI.important("# #{gem_name} #{available} is available. You are on #{current_version}.")
            else
                UI.important("# An update for #{gem_name} is available. You are on #{current_version}.")
            end
            UI.important("# You should use the latest version.")
            UI.important("# Please update by running `#{self.update_command(gem_name: gem_name)}`.")
            UI.important('#######################################################################')

            ensure_rubygems_source
        end

        # Check if RubyGems is set as a gem source
        # on some machines that might not be the case
        # and then users can't find the update when
        # running the specified command
        def self.ensure_rubygems_source
            return if `gem sources`.include?("https://rubygems.org")
            puts("")
            UI.error("RubyGems is not listed as your Gem source")
            UI.error("You can run `gem sources` to see all your sources")
            UI.error("Please run the following command to fix this:")
            UI.command("gem sources --add https://rubygems.org")
        end

        def self.update_command(gem_name: "sct")
            "sudo gem update #{gem_name.downcase}"
        end

        def self.fetch_latest(gem_name)
            JSON.parse(Excon.get(generate_fetch_url(gem_name)).body)["version"]
        end

        def self.generate_fetch_url(gem_name)
            "https://rubygems.org/api/v1/gems/#{gem_name}.json"
        end
    end
end