require "rubygems"
require "sequel"

DB = Sequel.mysql('test', :host => 'localhost')

DB << "
create table if not exists items(
  id int primary key,
  component_id int
)
"

DB << "
create table if not exists links(
  first int references items (id),
  second int references items (id),
  key (first),
  key (second),
  unique key (first, second)
)
"

DB << "
create table if not exists components_to_merge(
  component1 int,
  component2 int,
  key(component1)
)
"

# Set up random test data
DB[:items].delete
DB[:links].delete
DB[:items].insert_multiple((0..1000).map{|i| {:id => i}})
DB[:links].insert_multiple(
  (0..800).map{|i| [rand(1000), rand(1000)]}.uniq.map{|x, y| {:first => x, :second => y}}
)

def merge_components_step
  DB[:components_to_merge].delete 
  DB << " insert into components_to_merge
            select distinct t1.component_id c1, t2.component_id c2
            from links
            join items t1
            on links.first = t1.id
            join items t2
            on links.second = t2.id
            where t1.component_id != t2.component_id
          "

  # Ensure symmetricity
  DB << "insert into components_to_merge 
      select component2, component1 from components_to_merge"

  DB << "
    update items 
    join (
      select component1 source, min(component2) target
      from components_to_merge
      group by source
    ) new_components 
    on new_components.source = component_id
    set items.component_id = least(items.component_id, target)
  "

  DB[:components_to_merge].count()
end

DB[:items].update(:component_id => :id)

while merge_components_step > 0
end