global_exchange/exchange.lua

local sql = require("lsqlite3")
local exports = {}

local init_query = [=[
BEGIN TRANSACTION;
CREATE TABLE if not exists Credit
(
	Owner TEXT PRIMARY KEY NOT NULL,
	Balance INTEGER NOT NULL
);

CREATE TABLE if not exists Log
(
	Id INTEGER PRIMARY KEY AUTOINCREMENT,
	Recipient TEXT NOT NULL,
	Time INTEGER NOT NULL,
	Message TEXT NOT NULL
);

CREATE TABLE if not exists Orders
(
	Id INTEGER PRIMARY KEY AUTOINCREMENT,
	Poster TEXT NOT NULL,
	Exchange TEXT NOT NULL,
v	Type TEXT NOT NULL CHECK(Type IN ("buy", "sell")),
	Time INTEGER NOT NULL,
	Item TEXT NOT NULL,
	Amount INTEGER NOT NULL CHECK(Amount > 0),
	Rate INTEGER NOT NULL CHECK(Rate > 0)
);

CREATE TABLE if not exists Inbox
(
	Id INTEGER PRIMARY KEY AUTOINCREMENT,
	Recipient TEXT NOT NULL,
	Item TEXT NOT NULL,
	Amount INTEGER NOT NULL CHECK(Amount > 0)
);

CREATE INDEX if not exists credit_owner
ON Credit (Owner);

CREATE INDEX if not exists index_log
ON Log (Recipient, Time);

CREATE INDEX if not exists index_orders
ON Orders (Poster, Type, Time, Item, Rate);

CREATE INDEX if not exists index_inbox
ON Inbox (Recipient);

END TRANSACTION;
]=]


local new_act_query = [=[
INSERT INTO Credit (Owner, Balance)
VALUES (:owner,:start_balance);
]=]


local get_balance_query = [[
SELECT Balance FROM Credit
WHERE Owner = ?;
]]


local set_balance_query = [[
UPDATE Credit
SET Balance = ?
WHERE Owner = ?;
]]


local log_query = [[
INSERT INTO Log (Recipient, Time, Message)
VALUES(?, ?, ?);
]]


local search_desc_query = [=[
SELECT * FROM Orders
WHERE Exchange = :ex_name
AND Type = :order_type
AND Item = :item_name
ORDER BY Rate DESC;
]=]


local add_order_query = [=[
INSERT INTO Orders (Poster, Exchange, Type, Time, Item, Amount, Rate)
VALUES (:p_name, :ex_name, :order_type, :time, :item_name, :amount, :rate);
]=]


local del_order_query = [=[
DELETE FROM Orders
WHERE Id = ?;
]=]


local reduce_order_query = [=[
UPDATE Orders
SET Amount = Amount - ?
WHERE Id = ?;
]=]


-- Delete an order while also checking the player.
local cancel_order_query = [=[
DELETE FROM Orders
WHERE Id = :id
AND Poster = :p_name
]=]


local search_asc_query = [=[
SELECT * FROM Orders
WHERE Exchange = :ex_name
AND Type = :order_type
AND Item = :item_name
ORDER BY Rate ASC;
]=]

local search_min_query = [=[
SELECT * FROM Orders
WHERE Exchange = :ex_name
AND Type = :order_type
AND Item = :item_name
AND Rate >= :rate_min
ORDER BY Rate DESC;
]=]


local search_max_query = [=[
SELECT * FROM Orders
WHERE Exchange = :ex_name
AND Type = :order_type
AND Item = :item_name
AND Rate <= :rate_max
ORDER BY Rate ASC;
]=]


local search_own_query = [=[
SELECT * FROM Orders
WHERE Poster = :p_name;
]=]


local insert_inbox_query = [=[
INSERT INTO Inbox(Recipient, Item, Amount)
VALUES(?, ?, ?);
]=]


local view_inbox_query = [=[
SELECT * FROM Inbox
WHERE Recipient = ?;
]=]


local get_inbox_query = [=[
SELECT Amount FROM Inbox
WHERE Id = :id;
]=]

local red_inbox_query = [=[
UPDATE Inbox
SET Amount = Amount - :change
WHERE Id = :id;
]=]

local del_inbox_query = [=[
DELETE FROM Inbox
WHERE Id = :id;
]=]


local ex_methods = {}
local ex_meta = { __index = ex_methods }


local function sql_error(err)
	error("SQL error: " .. err)
end


local function is_integer(num)
	return math.floor(num) == num
end


function exports.open_exchange(path)
	local db = assert(sqlite3.open(path))

	local res = db:exec(init_query)

	if res ~= sqlite3.OK then
		sql_error(db:errmsg())
	end

	local stmts = {
		new_act_stmt = assert(db:prepare(new_act_query)),
		get_balance_stmt = assert(db:prepare(get_balance_query)),
		set_balance_stmt = assert(db:prepare(set_balance_query)),
		log_stmt = assert(db:prepare(log_query)),
		search_desc_stmt = assert(db:prepare(search_desc_query)),
		search_asc_stmt = assert(db:prepare(search_asc_query)),
		search_min_stmt = assert(db:prepare(search_min_query)),
		search_max_stmt = assert(db:prepare(search_max_query)),
		search_own_stmt = assert(db:prepare(search_own_query)),
		add_order_stmt = assert(db:prepare(add_order_query)),
		del_order_stmt = assert(db:prepare(del_order_query)),
		reduce_order_stmt = assert(db:prepare(reduce_order_query)),
		cancel_order_stmt = assert(db:prepare(cancel_order_query)),
		insert_inbox_stmt = assert(db:prepare(insert_inbox_query)),
		view_inbox_stmt = assert(db:prepare(view_inbox_query)),
		get_inbox_stmt = assert(db:prepare(get_inbox_query)),
		red_inbox_stmt = assert(db:prepare(red_inbox_query)),
		del_inbox_stmt = assert(db:prepare(del_inbox_query)),
	}

	
	local ret = { db = db,
		      stmts = stmts,
	}
	setmetatable(ret, ex_meta)

	return ret
end


function ex_methods.close(self)
	for k, v in pairs(self.stmts) do
		v:finalize()
	end

	self.db:close()
end

-- Returns success boolean
function ex_methods.log(self, message, recipient)
	recipient = recipient or ""

	local db = self.db
	local stmt = self.stmts.log_stmt

	stmt:bind_values(recipient, os.time(), message)

	local res = stmt:step()
	stmt:reset()

	if res == sqlite3.ERROR then
		sql_error(db:errmsg())
	elseif res == sqlite3.MISUSE then
		error("Programmer error.")
	elseif res == sqlite3.BUSY then
		return false, "Failed to log message."
	else
		return true
	end
end
		

-- Returns success boolean and error.
function ex_methods.new_account(self, p_name, amt)
	local db = self.db
	amt = amt or 0

	local exists = self:get_balance(p_name)

	if exists then
		return false, "Account already exists."
	end

	db:exec("BEGIN TRANSACTION;")
	
	local stmt = self.stmts.new_act_stmt

	stmt:bind_names({
		owner = p_name,
		start_balance = amt,
		time = os.time(),
	})

	local res = stmt:step()

	if res == sqlite3.MISUSE then
		error("Programmer error.")
	elseif res == sqlite3.BUSY then
		stmt:reset()
		db:exec("ROLLBACK;")
		return false, "Database Busy."
	elseif res ~= sqlite3.DONE then
		sql_error(db:errmsg())
	end

	stmt:reset()

	local log_succ1, log_err1 =
		self:log("Account opened with balance " .. amt, p_name)
	local log_succ2, log_err2 =
		self:log(p_name .. " opened an account with balance " .. amt)

	if not log_succ1 then
		db:exec("ROLLBACK;")
		return false, log_err1
	end

	if not log_succ2 then
		db:exec("ROLLBACK;")
		return false, log_err2
	end

	db:exec("COMMIT;")
	
	return true
end


-- Returns nil if no balance.
function ex_methods.get_balance(self, p_name)
	local db = self.db
	local stmt = self.stmts.get_balance_stmt
	
	stmt:bind_values(p_name)
	local res = stmt:step()

	if res == sqlite3.ERROR then
		sql_error(db:errmsg())
	elseif res == sqlite3.MISUSE then
		error("Programmer error.")
	elseif res == sqlite3.ROW then
		local balance = stmt:get_value(0)
		stmt:reset()

		return balance
	end

	stmt:reset()
end


-- Returns success boolean, and error message if false.
function ex_methods.set_balance(self, p_name, new_bal)
	local db = self.db
	local set_stmt = self.stmts.set_balance_stmt

	local bal = self:get_balance(p_name)

	if not bal then
		return false, p_name .. " does not have an account."
	end

	set_stmt:bind_values(new_bal, p_name)
	local res = set_stmt:step()

	if res == sqlite3.ERROR then
		sql_error(db:errmsg())
	elseif res == sqlite3.MISUSE then
		error("Programmer error.")
	elseif res == sqlite3.BUSY then
		set_stmt:reset()
		return false, "Database busy"
	else
		set_stmt:reset()
		return true
	end
end


-- Change balance by the given amount. Returns a success boolean, and error
-- message on fail.
function ex_methods.change_balance(self, p_name, delta)
	if not is_integer(delta)  then
		error("Non-integer credit delta")
	end

	local bal = self:get_balance(p_name)

	if not bal then
		return false, p_name .. " does not have an account."
	end

	if bal + delta < 0 then
		return false, p_name .. " does not have enough money."
	end

	return self:set_balance(p_name, bal + delta)
end


-- Sends credits from one user to another. Returns a success boolean, and error
-- message on fail.
function ex_methods.transfer_credits(self, sender, receiver, amt)
	local db = self.db

	if not is_integer(amt) then
		return false, "Non-integer credit amount"
	end

	db:exec("BEGIN TRANSACTION;")

	local succ_minus, err = self:change_balance(sender, -amt)

	if not succ_minus then
		db:exec("ROLLBACK")
		return false, err
	end

	local succ_plus, err = self:change_balance(receiver, amt)

	if not succ_plus then
		db:exec("ROLLBACK")
		return false, err
	end

	local succ_log1 = self:log("Sent " .. amt .. " credits to " .. receiver, sender)

	if not succ_log1 then
		db:exec("ROLLBACK")
		return false, "Failed to log sender message"
	end

	local succ_log2 = self:log("Received " .. amt .. " credits from " .. sender, receiver)

	if not succ_log2 then
		db:exec("ROLLBACK")
		return false, "Failed to log receiver message"
	end

	db:exec("COMMIT;")

	return true
end


function ex_methods.give_credits(self, p_name, amt, msg)
	local db = self.db

	db:exec("BEGIN TRANSACTION;")

	local succ_change, err = self:change_balance(p_name, amt)

	if not succ_change then
		db:exec("ROLLBACK;")
		return false, err
	end

	local succ_log, err = self:log(msg, p_name)

	if not succ_log then
		db:exec("ROLLBACK;")
		return false, er
	end

	db:exec("COMMIT;")

	return true
end


-- Returns a list of orders, sorted by price.
function ex_methods.search_orders(self, ex_name, order_type, item_name)
	local params = { ex_name = ex_name,
			 order_type = order_type,
			 item_name = item_name,
	}

	local stmt
	if order_type == "buy" then
		stmt = self.stmts.search_asc_stmt
	else
		stmt = self.stmts.search_desc_stmt
	end

	stmt:bind_names(params)

	local orders = {}

	for tab in stmt:nrows() do
		table.insert(orders, tab)
	end

	stmt:reset()
	return orders
end


-- Same as above, except not sorted in any particular order.
function ex_methods.search_player_orders(self, p_name)
	local params = { p_name = p_name,
	}

	local stmt = self.stmts.search_own_stmt

	stmt:bind_names(params)

	local orders = {}

	for tab in stmt:nrows() do
		table.insert(orders, tab)
	end

	stmt:reset()
	return orders
end


-- Adds a new order. Returns success, and an error string if failed.
function ex_methods.add_order(self, p_name, ex_name, order_type, item_name, amount, rate)
	if math.floor(amount) ~= amount then
		return false, "Noninteger quantity"
	end

	if amount <= 0 then
		return false, "Nonpositive quantity"
	end

	if math.floor(rate) ~= rate then
		return false, "Noninteger rate"
	end

	if rate <= 0 then
		return false, "Nonpositive rate"
	end

	local db = self.db
	local stmt = self.stmts.add_order_stmt

	stmt:bind_names({
		p_name = p_name,
		ex_name = ex_name,
		order_type = order_type,
		time = os.time(),
		item_name = item_name,
		amount = amount,
		rate = rate,
	})

	local res = stmt:step()

	if res == sqlite3.BUSY then
		stmt:reset()
		return false, "Database Busy"
	elseif res ~= sqlite3.DONE then
		sql_error(db:errmsg())
	end

	stmt:reset()
	return true
end


-- Returns true, or false and an error message.
function ex_methods.cancel_order(self, p_name, id)
	local params = { p_name = p_name,
			 id = id,
	}

	local db = self.db
	local stmt = self.stmts.cancel_order_stmt

	stmt:bind_values(params)

	local res = stmt:step()
	if res == sqlite3.BUSY then
		stmt:reset()
		return false, "Database busy."
	elseif res ~= sqlite3.DONE then
		sql_error(db:errmsg())
	end

	stmt:reset()

	return true
end


-- Puts things in a player's item inbox. Returns success, and also returns an
-- error message if failed.
function ex_methods.put_in_inbox(self, p_name, item_name, amount)
	local db = self.db
	local stmt = self.stmts.insert_inbox_stmt

	stmt:bind_values(p_name, item_name, amount)

	local res = stmt:step()
	if res == sqlite3.BUSY then
		return false, "Database Busy."
	elseif res ~= sqlite3.DONE then
		sql_error(db:errmsg())
	end

	stmt:reset()

	return true
end


-- Tries to buy from orders at the provided rate, and posts an offer with any
-- remaining desired amount. Returns success. If succeeded, also returns amount
-- bought. If failed, returns an error message
function ex_methods.buy(self, p_name, ex_name, item_name, amount, rate)
	if math.floor(amount) ~= amount then
		return false, "Noninteger quantity"
	elseif amount <= 0 then
		return false, "Nonpositive quantity"
	elseif math.floor(rate) ~= rate then
		return false, "Noninteger rate"
	elseif rate <= 0 then
		return false, "Nonpositive rate"
	end

	local db = self.db
	
	local bal = self:get_balance(p_name)
	if bal < amount * rate then
		return false, "Not enough money."
	end
	

	db:exec("BEGIN TRANSACTION");
	
	local remaining = amount

	local del_stmt = self.stmts.del_order_stmt
	local red_stmt = self.stmts.reduce_order_stmt
	local search_stmt = self.stmts.search_max_stmt

	search_stmt:bind_names({
		ex_name = ex_name,
		order_type = "sell",
		item_name = item_name,
		rate_max = rate,
	})

	for row in search_stmt:nrows() do
		local poster = row.Poster
		local row_amount = row.Amount

		if row_amount <= remaining then
			del_stmt:bind_values(row.Id)

			local del_res = del_stmt:step()
			if del_res == sqlite3.BUSY then
				del_stmt:reset()
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, "Database Busy."
			elseif del_res ~= sqlite3.DONE then
				sql_error(db:errmsg())
			end
			del_stmt:reset()

			local ch_succ, ch_err = 
				self:change_balance(poster, rate * row_amount)
			if not ch_succ then
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, ch_err
			end

			local log_succ, log_err = 
				self:log(p_name .. " bought " .. row_amount .. " "
						 .. item_name .. " from you. (+"
						 .. rate * row_amount .. ")", poster)
			if not log_succ then
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, log_err
			end

			local log2_succ, log2_err =
				self:log("Bought " .. row_amount .. " " .. item_name
						 .. " from " .. poster
						 .. "(-" .. rate * row_amount .. ")",p_name)
			if not log2_succ then
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, log2_err
			end

			remaining = remaining - row_amount
		else -- row_amount > remaining
			red_stmt:bind_values(remaining, row.Id)

			local red_res = red_stmt:step()
			if red_res == sqlite3.BUSY then
				red_stmt:reset()
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, "Database Busy."
			elseif red_res ~= sqlite3.DONE then
				red_stmt:reset()
				search_stmt:reset()
				sql_error(db:errmsg())
			end
			red_stmt:reset()

			local ch_succ, ch_err = 
				self:change_balance(poster, rate * remaining)
			if not ch_succ then
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, ch_err
			end

			local log_succ, log_err = 
				self:log(p_name .. " bought " .. remaining .. " "
						 .. item_name .. " from you. (+"
						 .. rate * remaining .. ")", poster)
			if not log_succ then
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, log_err
			end

			local log2_succ, log2_err =
				self:log("Bought " .. remaining .. " " .. item_name
						 .. " from " .. poster .. " (-"
						 .. rate * remaining .. ")", p_name)
			if not log2_succ then
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, log2_err
			end

			remaining = 0
		end

		if remaining == 0 then break end
	end

	search_stmt:reset()

	local bought = amount - remaining
	local cost = amount * rate
	local ch_succ, ch_err = self:change_balance(p_name, -cost)
	if not ch_succ then
		db:exec("ROLLBACK;")
		return false, ch_err
	end

	if remaining > 0 then
		local add_succ, add_err =
			self:add_order(p_name, ex_name, "buy", item_name, remaining, rate)

		if not add_succ then
			db:exec("ROLLBACK;")
			return false, add_err
		end

		local log_succ, log_err =
		self:log("Posted buy offer for "
				 .. remaining .. " " .. item_name .. " at "
				 .. rate .. "/item (-"
				 .. remaining * rate .. ")", p_name)

		if not log_succ then
			db:exec("ROLLBACK;")
			return false, log_err
		end
	end

	db:exec("COMMIT;")

	return true, bought
end


-- Tries to sell to orders at the provided rate, and posts an offer with any
-- remaining desired amount. Returns success. If failed, returns an error message.
function ex_methods.sell(self, p_name, ex_name, item_name, amount, rate)
	if math.floor(amount) ~= amount then
		return false, "Noninteger quantity"
	elseif amount <= 0 then
		return false, "Nonpositive quantity"
	elseif math.floor(rate) ~= rate then
		return false, "Noninteger rate"
	elseif rate <= 0 then
		return false, "Nonpositive rate"
	end

	local db = self.db
	
	db:exec("BEGIN TRANSACTION");
	
	local remaining = amount

	local del_stmt = self.stmts.del_order_stmt
	local red_stmt = self.stmts.reduce_order_stmt
	local search_stmt = self.stmts.search_min_stmt

	search_stmt:bind_names({
		ex_name = ex_name,
		order_type = "buy",
		item_name = item_name,
		rate_min = rate,
	})

	for row in search_stmt:nrows() do
		local poster = row.Poster
		local row_amount = row.Amount

		if row_amount <= remaining then
			del_stmt:bind_values(row.Id)

			local del_res = del_stmt:step()
			if del_res == sqlite3.BUSY then
				del_stmt:reset()
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, "Database Busy."
			elseif del_res ~= sqlite3.DONE then
				sql_error(db:errmsg())
			end
			del_stmt:reset()

			local in_succ, in_err = 
				self:put_in_inbox(poster, item_name, row_amount)
			if not in_succ then
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, in_err
			end

			local log_succ, log_err = 
				self:log(p_name .. " sold " .. row_amount .. " "
						 .. item_name .. " to you." , poster)
			if not log_succ then
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, log_err
			end

			local log2_succ, log2_err =
				self:log("Sold " .. row_amount .. " " .. item_name
						 .. " to " .. poster
						 .. "(+" .. rate * row_amount .. ")",p_name)
			if not log2_succ then
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, log2_err
			end

			remaining = remaining - row_amount
		else -- row_amount > remaining
			red_stmt:bind_values(remaining, row.Id)

			local red_res = red_stmt:step()
			if red_res == sqlite3.BUSY then
				red_stmt:reset()
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, "Database Busy."
			elseif red_res ~= sqlite3.DONE then
				red_stmt:reset()
				search_stmt:reset()
				sql_error(db:errmsg())
			end
			red_stmt:reset()

			local in_succ, in_err = 
				self:put_in_inbox(poster, item_name, remaining)
			if not in_succ then
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, in_err
			end

			local log_succ, log_err = 
				self:log(p_name .. " sold " .. remaining .. " "
						 .. item_name .. " to you.", poster)
			if not log_succ then
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, log_err
			end

			local log2_succ, log2_err =
				self:log("Sold " .. row_amount .. " " .. item_name
						 .. " to " .. poster .. " (+"
						 .. rate * remaining .. ")", p_name)
			if not log2_succ then
				search_stmt:reset()
				db:exec("ROLLBACK;")
				return false, log2_err
			end

			remaining = 0
		end

		if remaining == 0 then break end
	end

	search_stmt:reset()

	local sold = amount - remaining
	local revenue = sold * rate
	local ch_succ, ch_err = self:change_balance(p_name, revenue)
	if not ch_succ then
		db:exec("ROLLBACK;")
		return false, ch_err
	end

	if remaining > 0 then
		local add_succ, add_err =
			self:add_order(p_name, ex_name, "sell", item_name, remaining, rate)

		if not add_succ then
			db:exec("ROLLBACK;")
			return false, add_err
		end

	end

	db:exec("COMMIT;")

	return true
end


-- On success, returns true and a list of inbox entries.
-- On failure, returns false and an error message.
function ex_methods.view_inbox(self, p_name)
	local db = self.db
	local stmt = self.stmt.view_inbox_stmt

	stmt:bind_values(p_name)

	local res = {}

	for row in stmt:nrows() do
		table.insert(res, row)
	end

	stmt:reset()

	return true, res
end


-- Returns success boolean. On success, also returns the number actually
-- taken. On failure, also returns an error message
function ex_methods.take_inbox(self, id, amount)
	local db = self.db
	local get_stmt = self.stmts.get_inbox_stmt
	local red_stmt = self.stmts.red_inbox_stmt
	local del_stmt = self.stmts.del_inbox_stmt

	get_stmt:bind_names({
		id = id,
		change = amount
	})
	
	local res = get_stmt:step()

	if res == sqlite3.BUSY then
		get_stmt:reset()
		return false, "Database Busy."
	elseif res == sqlite3.DONE then
		get_stmt:reset()
		return false, "Order does not exist."
	elseif res ~= sqlite3.ROW then
		sql_error(db:errmsg())
	end

	local available = get_stmt:get_value(0)
	get_stmt:reset()

	db:exec("BEGIN TRANSACTION;")
	
	if available > amount then
		red_stmt:bind_names({
			id = id,
			change = amount
		})

		local red_res = red_stmt:step()

		if red_res == sqlite3.BUSY then
			red_stmt:reset()
			db:exec("ROLLBACK;")
			return false, "Database Busy."
		elseif red_res ~= sqlite3.DONE then
			sql_error(db:errmsg())
		end

		red_stmt:reset()
	else
		del_stmt:bind_names({
			id = id,
		})

		local del_res = del_stmt:step()

		if del_res == sqlite3.BUSY then
			del_stmt:reset()
			db:exec("ROLLBACK;")
			return false, "Database Busy."
		elseif del_res ~= sqlite3.DONE then
			sql_error(db:errmsg())
		end

		del_stmt:reset()
	end

	db:exec("COMMIT;")
	return true, math.min(amount, available)

end
	


function exports.test()
	local ex = exports.open_exchange("test.db")

	local alice_bal = ex:get_balance("Alice")
	local bob_bal = ex:get_balance("Bob")


	local function print_balances()
		print("Alice: ", ex:get_balance("Alice"))
		print("Bob: ", ex:get_balance("Bob"))
	end

	
	-- Initialize balances
	if alice_bal then
		ex:set_balance("Alice", 420)
	else
		ex:new_account("Alice", 420)
	end

	if bob_bal then
		ex:set_balance("Bob", 2015)
	else
		ex:new_account("Bob", 2015)
	end

	print_balances()

	
	-- Transfer a valid amount
	print("Transfering 1000 credits from Bob to Alice")

	local succ, err = ex:transfer_credits("Bob", "Alice", 1000)

	print("Success: ", succ, " ", err)
	print_balances()


	-- Transfer an invalid amount
	print("Transfering 3000 credits from Alice to Bob")

	local succ, err = ex:transfer_credits("Alice", "Bob", 3000)

	print("Success: ", succ, " ", err)
	print_balances()


	-- Simulate a transaction
	print("Alice posting an offer to buy 10 cobble at 2 credits each")
	local succ, err = ex:buy("Alice", "", "default:cobble", 10, 2)
	print("Success: ", succ, " ", err)
	print_balances()

	print("Bob posting an offer to sell 20 cobble at 1 credits each")
	local succ, err = ex:sell("Bob", "", "default:cobble", 20, 1)
	print("Success: ", succ, " ", err)
	print_balances()
	
	ex:close()
end


return exports