1 files changed, 22 insertions, 0 deletions
diff --git a/lua/laskuri/refnum.lua b/lua/laskuri/refnum.lua
new file mode 100644
index 0000000..ecd83de
--- /dev/null
+++ b/lua/laskuri/refnum.lua
@@ -0,0 +1,22 @@
+-- Calculate the Finnish reference number
+local refnum = function(invoicenr)
+    local reversed = string.reverse(invoicenr)
+    local weights = {7, 3, 1}
+    local counter = 0
+    local sum = 0
+    for digit in string.gmatch(reversed, "%d") do
+        local n = tonumber(digit)
+        local w = weights[(counter % 3) + 1]
+        counter = counter + 1
+        sum = sum + n * w
+    end
+    local check = (sum + (10 - (sum % 10))) - sum
+    if check == 10 then
+        check = 0
+    end
+    return invoicenr .. tostring(math.tointeger(check))
+end
+
+return {
+    refnum = refnum
+}