class Kredis::Migration

def delete_all(*key_patterns)
  log_migration "DELETE ALL #{key_patterns.inspect}" do
    if key_patterns.length > 1
      @redis.del(*key_patterns)
    else
      each_key_batch_matching(key_patterns.first) do |keys, pipeline|
        pipeline.del(*keys)
      end
    end
  end
end

def each_key_batch_matching(key_pattern, &block)
  cursor = "0"
  begin
    cursor, keys = @redis.scan(cursor, match: key_pattern, count: SCAN_BATCH_SIZE)
    @redis.multi { |pipeline| yield keys, pipeline }
  end until cursor == "0"
end

def initialize(config = :shared)
  @redis = Kredis.configured_for config
  # TODO: Replace script loading with `copy` command once Redis 6.2+ is the minimum supported version.
  @copy_sha = @redis.script "load", "redis.call('SETNX', KEYS[2], redis.call('GET', KEYS[1])); return 1;"
end

def log_migration(message, &block)
  Kredis.instrument :migration, message: message, &block
end

def migrate(from:, to:, pipeline: nil)
  namespaced_to = Kredis.namespaced_key(to)
  if to.present? && from != namespaced_to
    log_migration "Migrating key #{from} to #{namespaced_to}" do
      (pipeline || @redis).evalsha @copy_sha, keys: [ from, namespaced_to ]
    end
  else
    log_migration "Skipping blank/unaltered migration key #{from} → #{to}"
  end
end

def migrate_all(key_pattern)
  each_key_batch_matching(key_pattern) do |keys, pipeline|
    keys.each do |key|
      ids = key.scan(/\d+/).map(&:to_i)
      migrate from: key, to: yield(key, *ids), pipeline: pipeline
    end
  end
end