Simple key-value datastore. Basic data & transaction commands.

simple_datastore.rb

## SUMMARY
# 	Use Hash($db) to maintain state
# 	Track # open transactions
# 	Memoize modified vars per transaction ($history)

# Be naught, use globals (not thread-safe)
$db = {}
$transactions = 0
$history = {}

# Utility for taking snapshot of var
def memoize k
	$history[$transactions][k] = $history[$transactions].fetch k, get(k)
end

# Data commands
def set k, v
	memoize k if $transactions > 0
	$db[k] = v
end

def get k
	$db.fetch k, "NULL"
end

def unset k
	memoize k if $transactions > 0
	$db.delete k
end

def num_eql_to v
	$db.select { |k,val| v == val  }.length
end

# Transaction commands
def _begin
	$transactions += 1
	$history[$transactions] = {}
end

def rollback
	# Guard against empty transactions
	if $transactions == 0
		puts "NO TRANSACTION"
		return
	end

	# Restore state from last transaction
	$db.merge! $history[$transactions]

	# Scrub this transaction
	$history.delete $transactions
	$transactions -= 1
end

def commit
	if $transactions == 0
		puts "NO TRANSACTION"
	else
		$transactions = 0
		$history = {}
	end
end

# Main runner
while cmd = gets
	case cmd
	when /SET (?<key>\w+) (?<value>\w+)/
		set $~[:key], $~[:value]
	when cmd = /GET (?<key>\w+)/
		puts get $~[:key]
	when /UNSET (?<key>\w+)/
		unset $~[:key]
	when /NUMEQUALTO (?<value>\w+)/
		puts num_eql_to $~[:value]
	when /BEGIN/
		_begin
	when /ROLLBACK/
		rollback
	when /COMMIT/
		commit
	when /END/
		exit 0
	end
end