require 'kennel'

class HpaDashboard
  SOURCE_METRIC = "datadog.cluster_agent.external_metrics.delay_seconds".freeze
  attr_reader :id

  def initialize(id, timeframe:)
    @id = id
    @api = Kennel::Api.new
    @from = Time.now.to_i - timeframe
  end

  # see https://docs.datadoghq.com/api/latest/metrics/#get-active-metrics-list
  # this has an undocumented limit of 250000 metrics so we can't just use super old @from
  # also tried /api/v2/metrics which returns similar results but is even slower (filtering it with 'queried' + big window did not help)
  def available_metrics
    @api.send(
      :request, :get, "/api/v1/metrics",
      params: { from: @from }
    ).fetch(:metrics).to_set
  end

  def queries_used_by_any_hpa
    @api.send(
      :request, :get, "/api/v1/query",
      params: {
        query: "avg:#{SOURCE_METRIC}{*} by {metric}",
        from: @from,
        to: Time.now.to_i
      }
    ).fetch(:series).map do |data|
      data.fetch(:scope).split(",").to_h { |t| t.split(":", 2) }["metric"]
    end.uniq
  end

  # covert fallout from query normalization to find actual metrics
  # for example default_zero(foo{a:b}) is converted to "default_zero_foo_a:b"
  # this ignores when multiple metrics are in a single query for example a / b * 100
  # since a and b are usually the same
  def extract_metrics(queries)
    queries = queries.dup
    queries.each do |query|
      query.sub!(/\.total_\d+$/, ".total") # math leftover *.total_100 -> *.total
      query.sub!(/^_*(ewma_\d+|default_zero)_*/, "") # remove math
    end
    queries.uniq!
    queries.sort! # for debug printing and to keep the dashboard stable
    queries.to_set
  end

  # since available_metrics is not reliable (hits limit or just has old data)
  # we verify each potentially unknown metric 1-by-1 by hitting this cheap endpoint
  # https://docs.datadoghq.com/api/latest/metrics/?code-lang=curl#get-metric-metadata
  def slow_filter_unknown!(unknown)
    unknown.select! do |metric|
      print "Verifying potentially unknown metric #{metric} ..."
      not_found = @api.send(:request, :get, "/api/v1/metrics/#{metric}", ignore_404: true)[:error]
      print "#{not_found ? "not found" : "found"}\n"
      not_found # keep the truly not found
    end
  end

  def update(used_metrics)
    attributes = {
      title: "HPA metrics used",
      description: <<~DESC,
        1 widget for each metric used in compute maintained kubernetes clusters (anything that reports #{SOURCE_METRIC})
        Automatically filled by a `rake hpa_dashboard` cron from kennel GHA.
        Last updated: #{Time.now} #{$stdout.tty? ? "manually" : RakeHelper.ci_url}
      DESC
      layout_type: "ordered",
      reflow_type: "auto",
      tags: ["team:compute", "team:compute-accelerate"],
      widgets: used_metrics.map do |m|
        {
          definition: {
            title: m,
            type: "timeseries",
            requests: [
              {
                response_format: "timeseries",
                queries: [
                  {
                    name: "query1",
                    data_source: "metrics",
                    query: "avg:#{m}{*}"
                  }
                ],
                display_type: "line"
              }
            ]
          }
        }
      end
    }
    @api.update("dashboard", @id, attributes)
  end
end

desc "Update hpa dashboard to track all currently used external metrics people that change metrics in the UI see that they are used"
task hpa_dashboard: "kennel:environment" do
  dashboard = HpaDashboard.new(DASHBOARD_ID, timeframe: 24 * 60 * 60)

  available_metrics = dashboard.available_metrics
  puts "Found #{available_metrics.size} available metrics"

  used_queries = dashboard.queries_used_by_any_hpa
  puts "Found #{used_queries.size} used queries"

  used_metrics = dashboard.extract_metrics(used_queries)
  puts "Found #{used_metrics.size} used metrics"

  # validate we found everything
  unknown = used_metrics - available_metrics
  dashboard.slow_filter_unknown! unknown if unknown.size < 100
  if unknown.any?
    $stdout.flush # otherwise mixes with stderr in GHA
    abort <<~MSG
      #{unknown.size} unknown metrics found, these would not be displayable on the dashboard, improve parsing code
      usually that means some part of the metrics got mangled and it cannot be found in datadog
      see https://datadoghq.com/metric/summary to find valid metrics

      #{unknown.join("\n")}
    MSG
  end

  dashboard.update used_metrics
  puts "Updated dashboard https://datadoghq.com/dashboard/#{dashboard.id}"
rescue Exception # rubocop:disable Lint/RescueException
  unless $stdout.tty? # do not spam slack when debugging
    send_to_slack <<~MSG
      HPA dashboard update failed #{RakeHelper.ci_url}, fix it!
    MSG
  end
  raise
end