X-Git-Url: http://club.cc.cmu.edu/~cmccabe/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=pickrand.go;h=e51bf26fbf295bf5ebf246fb6d10ad4beccea485;hb=refs%2Fheads%2Fmaster;hp=a21efdaa80c8b7013e03b02bc1be5c312c4aa188;hpb=fbb7220527c04fb8b07aa777c2f46c26e35f56ed;p=cmccabe-bin

diff --git a/pickrand.go b/pickrand.go
index a21efda..e51bf26 100644
--- a/pickrand.go
+++ b/pickrand.go
@@ -1,23 +1,44 @@
 package main
 
 import (
+	"bytes"
+	"crypto/rand"
+    "flag"
 	"fmt"
+	"math/big"
 	"os"
 	"path/filepath"
-	"math/rand"
 	"time"
 )
 
 func main() {
-	root := "."
-	if len(os.Args) > 1 {
-		root = os.Args[1]
-	}
+    flag.Usage = func() {
+        fmt.Fprintf(os.Stdout, "pickrand.go: picks a random file.\n")
+        fmt.Fprintf(os.Stdout, "\n")
+        flag.PrintDefaults()
+    }
+    prevDays := flag.Int("n", 0, "The number of days back to look.")
+    flag.Parse()
+    var maxDuration time.Duration
+    if (*prevDays != 0) {
+        maxDuration = time.Duration(int64(*prevDays) * (24 * 60 * 60 * 1e9))
+    }
+    
+	root := flag.Arg(0)
+    if (root == "") {
+        root = "."
+    }
 	files := make([]string, 0, 32)
 	err := filepath.Walk(root, func(p string, f os.FileInfo, err error) error {
 		if err != nil {
 			return err
 		}
+        if maxDuration != 0 {
+            var duration = time.Now().Sub(f.ModTime())
+            if duration > maxDuration {
+                return nil
+            }
+        }
 		if !f.IsDir() {
 			files = append(files, p)
 		}
@@ -27,7 +48,23 @@ func main() {
 		fmt.Fprintf(os.Stderr, "** Error: %s\n", err.Error())
 		os.Exit(1)
 	}
-	rand.Seed(time.Now().UTC().UnixNano())
-	i := rand.Int31n(int32(len(files)))
-	fmt.Printf("%s\n", root + "/" + files[i])
+    if len(files) == 0 {
+		fmt.Fprintf(os.Stderr, "No matching files found.\n")
+		os.Exit(1)
+    }
+	var b [16]byte
+	_, err = rand.Read(b[:])
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Failed to access cryptographic randomness.  " +
+			"Error: %s\n\n", err.Error())
+		os.Exit(1)
+	}
+	i, err := rand.Int(bytes.NewReader(b[:]), big.NewInt(int64(len(files))))
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Failed to get a random int.  Error: %s\n", err.Error())
+		os.Exit(1)
+	}
+	j := int(i.Uint64())
+
+	fmt.Printf("%s\n", files[j])
 }