local re = require "re"
local path = require "path"

local filenameRegex = re.compile([=[^([0-9]+).*\.sql$]=])

local function throwSqlError(db, prefix)
	local code = db:errcode()
	if code ~= sqlite3.OK and code ~= sqlite3.ROW and code ~= sqlite3.DONE then
		if prefix then
			error(string.format("%s: %s", prefix, db:errmsg()))
		else
			error(db:errmsg())
		end
	end
end

local function transact(db, func, errorPrefix)
	local name = string.format("savepoint_%d", math.abs(math.random(0)))
	db:exec(string.format("savepoint "..name))
	throwSqlError(db, errorPrefix)
	local success, result = pcall(func)
	if not success then
		db:exec("rollback to "..name)
		error(result, errorPrefix)
	end
	db:exec("release "..name)
	return result
end

local function getCurrentMigration(db)
	for seqnum in db:urows("select max(seqnum) from migrations") do return seqnum end
	throwSqlError(db, "failed to get last migration sequence number", db)
	return -1
end

local function recordMigration(db, seqnum)
	local stmt = db:prepare("insert into migrations (seqnum) values (?)")
	stmt:bind_values(seqnum)
	throwSqlError(db, "failed to record migration")
	stmt:step()
end

local function migrate(db)
	local migrations = {}
	local seqnums = {}
	local MIGRATION_PATH = "/migrations/"
	local paths = GetZipPaths(MIGRATION_PATH)
	for _, p in ipairs(paths) do
		-- check that sequence number doesn't already exist
		if p ~= MIGRATION_PATH then
			local basename = path.basename(p)
			local _, seqnum = filenameRegex:search(basename)
			seqnum = tonumber(seqnum)
			if seqnum and not seqnums[seqnum] then
				table.insert(seqnums, seqnum)
				table.insert(migrations, {
					filename = p,
					seqnum = seqnum,
				})
			else
				print(string.format("found weird migration name: %s", p))
			end
		end
	end

	db:exec[[
		create table if not exists migrations (
			seqnum integer primary key
		) without rowid
	]]
	throwSqlError(db, "failed to create migrations table")

	table.sort(migrations, function(a, b) return a.seqnum < b.seqnum end)
	local announced
	for i,mig in ipairs(migrations) do
		local seqnum = mig.seqnum
		local lastSeqnum = getCurrentMigration(db)
		if seqnum > lastSeqnum then
			if not announced then
				print"Applying migrations:"
				announced = true
			end
			print(mig.filename)
			local migsql = LoadAsset(mig.filename)
			transact(db, function()
				db:exec(migsql)
				throwSqlError(db, "migration failed")
				recordMigration(db, seqnum)
				seqnum = seqnum + 1
			end)
		end
	end
end

return {
	migrate = migrate,
}