fixed bug in lastIndexOf

Signed-off-by: Matt Butcher <matt.butcher@microsoft.com>

lib/mediatype.gr

@@ -6,6 +6,7 @@ import {lastIndexOf, reverse} from "./lib/stringutil"
 
 export let default_mt = "application/octet-stream"
 
+// A giant map of all of the media types we know about.
 let mut mediatypes = Map.make()
 
 // Text formats
@@ -102,7 +103,12 @@ Map.set("woff", "font/woff", mediatypes)
 Map.set("woff2", "font/woff2", mediatypes)
 
 // Guess the media type of this file
+//
+// Per recommendation, if no media type is found for an extension,
+// this returns `application/octet-stream`.
+//
 // @param filename: The name of the file
+// @returns String a media type
 export let guess = (filename: String) => {
     match (lastIndexOf(".", filename)) {
         Some(extOffset) => {

lib/stringutil.gr

@@ -2,6 +2,9 @@ import String from "string"
 import Array from "array"
 
 // Return a String that is the reverse of the given String.
+//
+// @param str: The string to reverse.
+// @return String A reversed version of the given string
 export let reverse = (str: String) => {
     let chars = String.explode(str)
     let clen = Array.length(chars)
@@ -15,9 +18,11 @@ export let reverse = (str: String) => {
 // Get the index of the last appearance of needle in the haystack.
 // @param needle: The string to search for
 // @param haystack: The string to be searched
+// @return Option<Number> The offset, if found, or a number
 export let lastIndexOf = (needle: String, haystack: String) => {
     let rev = reverse(haystack)
-    let i = String.indexOf(needle, rev)
+    let revNeedle = reverse(needle)
+    let i = String.indexOf(revNeedle, rev)
     match (i) {
         Some(offset) => Some(String.length(haystack) - 1 - offset),
         None => None,   

tests.gr

@@ -35,7 +35,7 @@ let report = () => {
 
 expect(("a", "b"), Env.splitEnvVar("a=b"), "Env.splitEnvVar should parse")
 expect("gfedcba", Util.reverse("abcdefg"), "Util.reverse should reverse string")
-expect(Some(5), Util.lastIndexOf("..", "aaaa.."), "UtillastIndexOf should find Some")
+expect(Some(5), Util.lastIndexOf("/.", "aaaa/."), "UtillastIndexOf should find Some")
 expect(None, Util.lastIndexOf("??", "aaaa.."), "Util.lastIndexOf should find None")
 expect("text/plain", Mediatype.guess("foo.txt"), "Mediatype.guess should find text/plain")
 expect("application/octet-stream", Mediatype.guess("foo.MADEUP"), "Mediatype.guess should find default type")