#
# Demonstrate how SIGNAL can be used to enforce integrity constraints.
#

# Naming:
# - PO: Purchase Order
# - AB: Address Book
# - IN: Inventory

# Simplified schema:
#
# Relation 1:
# PO_ORDER (PK: po_id) 1:1 <---> 0:N (FK: po_id) PO_ORDER_LINE
#
# Relation 2:
# IN_INVENTORY (PK: item_id) 1:1 <---> 0:N (FK: item_id) PO_ORDER_LINE
#
# Relation 3:
#                               +--> 0:1 (PK: person_id) AB_PHYSICAL_PERSON
# PO_ORDER (FK: cust_id) 1:1 <--|
#                               +--> 0:1 (PK: company_id) AB_MORAL_PERSON
# This is an 'arc' relationship :)
#


--disable_warnings
drop database if exists demo;
--enable_warnings

create database demo;

use demo;

create table ab_physical_person (
  person_id integer,
  first_name VARCHAR(50),
  middle_initial CHAR,
  last_name VARCHAR(50),
  primary key (person_id));

create table ab_moral_person (
  company_id integer,
  name VARCHAR(100),
  primary key (company_id));

create table in_inventory (
  item_id integer,
  descr VARCHAR(50),
  stock integer,
  primary key (item_id));

create table po_order (
  po_id integer auto_increment,
  cust_type char, /* arc relationship, see cust_id */
  cust_id integer, /* FK to ab_physical_person *OR* ab_moral_person */
  primary key (po_id));

create table po_order_line (
  po_id integer, /* FK to po_order.po_id */
  line_no integer,
  item_id integer, /* FK to in_inventory.item_id */
  qty integer);

delimiter $$;

--echo #
--echo # Schema integrity enforcement
--echo #

create procedure check_pk_person(in person_type char, in id integer)
begin
  declare x integer;
  declare msg varchar(128);

  /*
    Test integrity constraints for an 'arc' relationship.
    Based on 'person_type', 'id' points to either a
    physical person, or a moral person.
  */
  case person_type
    when 'P' then
    begin
      select count(person_id) from ab_physical_person
        where ab_physical_person.person_id = id
        into x;

      if (x != 1)
      then
        set msg= concat('No such physical person, PK:', id);
        SIGNAL SQLSTATE '45000' SET
          MESSAGE_TEXT = msg,
          MYSQL_ERRNO = 10000;
      end if;
    end;
    
    when 'M' then
    begin
      select count(company_id) from ab_moral_person
        where ab_moral_person.company_id = id
        into x;

      if (x != 1)
      then
        set msg= concat('No such moral person, PK:', id);
        SIGNAL SQLSTATE '45000' SET
          MESSAGE_TEXT = msg,
          MYSQL_ERRNO = 10000;
      end if;
    end;

    else
    begin
      set msg= concat('No such person type:', person_type);
      SIGNAL SQLSTATE '45000' SET
        MESSAGE_TEXT = msg,
        MYSQL_ERRNO = 20000;
    end;
  end case;
end
$$

create procedure check_pk_inventory(in id integer)
begin
  declare x integer;
  declare msg varchar(128);

  select count(item_id) from in_inventory
    where in_inventory.item_id = id
    into x;

  if (x != 1)
  then
    set msg= concat('Failed integrity constraint, table in_inventory, PK:',
                    id);
    SIGNAL SQLSTATE '45000' SET
      MESSAGE_TEXT = msg,
      MYSQL_ERRNO = 10000;
  end if;
end
$$

create procedure check_pk_order(in id integer)
begin
  declare x integer;
  declare msg varchar(128);

  select count(po_id) from po_order
    where po_order.po_id = id
    into x;

  if (x != 1)
  then
    set msg= concat('Failed integrity constraint, table po_order, PK:', id);
    SIGNAL SQLSTATE '45000' SET
      MESSAGE_TEXT = msg,
      MYSQL_ERRNO = 10000;
  end if;
end
$$

create trigger po_order_bi before insert on po_order
for each row
begin
  call check_pk_person(NEW.cust_type, NEW.cust_id);
end
$$

create trigger po_order_bu before update on po_order
for each row
begin
  call check_pk_person(NEW.cust_type, NEW.cust_id);
end
$$

create trigger po_order_line_bi before insert on po_order_line
for each row
begin
  call check_pk_order(NEW.po_id);
  call check_pk_inventory(NEW.item_id);
end
$$

create trigger po_order_line_bu before update on po_order_line
for each row
begin
  call check_pk_order(NEW.po_id);
  call check_pk_inventory(NEW.item_id);
end
$$

--echo #
--echo # Application helpers
--echo #

create procedure po_create_order(
  in p_cust_type char,
  in p_cust_id integer,
  out id integer)
begin
  insert into po_order set cust_type = p_cust_type, cust_id = p_cust_id;
  set id = last_insert_id();
end
$$

create procedure po_add_order_line(
  in po integer,
  in line integer,
  in item integer,
  in q integer)
begin
  insert into po_order_line set
    po_id = po, line_no = line, item_id = item, qty = q;
end
$$

delimiter ;$$

--echo #
--echo # Create sample data
--echo #

insert into ab_physical_person values
  ( 1, "John", "A", "Doe"),
  ( 2, "Marry", "B", "Smith")
;

insert into ab_moral_person values
  ( 3, "ACME real estate, INC"),
  ( 4, "Local school")
;

insert into in_inventory values
  ( 100, "Table, dinner", 5),
  ( 101, "Chair", 20),
  ( 200, "Table, coffee", 3),
  ( 300, "School table", 25),
  ( 301, "School chairs", 50)
;

select * from ab_physical_person order by person_id;
select * from ab_moral_person order by company_id;
select * from in_inventory order by item_id;

--echo #
--echo # Entering an order
--echo #

set @my_po = 0;

/* John Doe wants 1 table and 4 chairs */
call po_create_order("P", 1, @my_po);

call po_add_order_line (@my_po, 1, 100, 1);
call po_add_order_line (@my_po, 2, 101, 4);

/* Marry Smith wants a coffee table */
call po_create_order("P", 2, @my_po);

call po_add_order_line (@my_po, 1, 200, 1);

--echo #
--echo # Entering bad data in an order
--echo #

# There is no item 999 in in_inventory
--error 10000
call po_add_order_line (@my_po, 1, 999, 1);

--echo #
--echo # Entering bad data in an unknown order
--echo #

# There is no order 99 in po_order
--error 10000
call po_add_order_line (99, 1, 100, 1);

--echo #
--echo # Entering an order for an unknown company
--echo #

# There is no moral person of id 7
--error 10000
call po_create_order("M", 7, @my_po);

--echo #
--echo # Entering an order for an unknown person type
--echo #

# There is no person of type X
--error 20000
call po_create_order("X", 1, @my_po);

/* The local school wants 10 class tables and 20 chairs */
call po_create_order("M", 4, @my_po);

call po_add_order_line (@my_po, 1, 300, 10);
call po_add_order_line (@my_po, 2, 301, 20);

# Raw data
select * from po_order;
select * from po_order_line;

# Creative reporting ...

select po_id as "PO#",
  ( case cust_type
  when "P" then concat (pp.first_name,
                   " ",
                   pp.middle_initial,
                   " ",
                   pp.last_name)
  when "M" then mp.name
  end ) as "Sold to"
  from po_order po
  left join ab_physical_person pp on po.cust_id = pp.person_id
  left join ab_moral_person mp on po.cust_id = company_id
;

select po_id as "PO#",
  ol.line_no as "Line",
  ol.item_id as "Item",
  inv.descr as "Description",
  ol.qty as "Quantity"
  from po_order_line ol, in_inventory inv
  where inv.item_id = ol.item_id
  order by ol.item_id, ol.line_no;

drop database demo;