From 77c71bd5962368b931e479123a155e825485f119 Mon Sep 17 00:00:00 2001
From: Harshavardhana <harsha@harshavardhana.net>
Date: Thu, 17 Sep 2015 16:44:31 -0700
Subject: [PATCH] Add trie to verify wrong inputs, and provide meaningful
 messages

---
 commands.go |   4 ++
 main.go     |  18 ++++++++-
 trie.go     | 112 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 133 insertions(+), 1 deletion(-)
 create mode 100644 trie.go

diff --git a/commands.go b/commands.go
index f3618673b..d03a693f7 100644
--- a/commands.go
+++ b/commands.go
@@ -21,7 +21,11 @@ import "github.com/minio/cli"
 // Collection of minio commands currently supported are
 var commands = []cli.Command{}
 
+// Collection of minio commands currently supported in a trie tree
+var commandsTree = newTrie()
+
 // registerCommand registers a cli command
 func registerCommand(command cli.Command) {
 	commands = append(commands, command)
+	commandsTree.Insert(command.Name)
 }
diff --git a/main.go b/main.go
index c69a0ea92..a1d91c93d 100644
--- a/main.go
+++ b/main.go
@@ -87,6 +87,14 @@ func getFormattedVersion() string {
 	return t.Format(http.TimeFormat)
 }
 
+func findClosestCommands(command string) []string {
+	var closestCommands []string
+	for _, value := range commandsTree.PrefixMatch(command) {
+		closestCommands = append(closestCommands, value.(string))
+	}
+	return closestCommands
+}
+
 func registerApp() *cli.App {
 	// register all commands
 	registerCommand(donutCmd)
@@ -132,7 +140,15 @@ VERSION:
 {{end}}
 `
 	app.CommandNotFound = func(ctx *cli.Context, command string) {
-		Fatalf("Command not found: ‘%s’\n", command)
+		msg := fmt.Sprintf("‘%s’ is not a mc command. See ‘minio help’.", command)
+		closestCommands := findClosestCommands(command)
+		if len(closestCommands) > 0 {
+			msg += fmt.Sprintf("\n\nDid you mean one of these?\n")
+			for _, cmd := range closestCommands {
+				msg += fmt.Sprintf("        ‘%s’\n", cmd)
+			}
+		}
+		Fatalln(msg)
 	}
 
 	return app
diff --git a/trie.go b/trie.go
new file mode 100644
index 000000000..844458aa7
--- /dev/null
+++ b/trie.go
@@ -0,0 +1,112 @@
+/*
+ * Minio Cloud Storage, (C) 2015 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package main
+
+// This package borrows idea from - https://godoc.org/golang.org/x/text/internal/triegen
+
+// Trie trie container
+type Trie struct {
+	root *trieNode
+	size int
+}
+
+// newTrie get new trie
+func newTrie() *Trie {
+	return &Trie{
+		root: newTrieNode(),
+		size: 0,
+	}
+}
+
+// trieNode trie tree node container carries value and children
+type trieNode struct {
+	exists bool
+	value  interface{}
+	child  map[rune]*trieNode // runes as child
+}
+
+func newTrieNode() *trieNode {
+	return &trieNode{
+		exists: false,
+		value:  nil,
+		child:  make(map[rune]*trieNode),
+	}
+}
+
+// Insert insert a key
+func (t *Trie) Insert(key string) {
+	curNode := t.root
+	for _, v := range key {
+		if curNode.child[v] == nil {
+			curNode.child[v] = newTrieNode()
+		}
+		curNode = curNode.child[v]
+	}
+
+	if !curNode.exists {
+		// increment when new rune child is added
+		t.size++
+		curNode.exists = true
+	}
+	// value is stored for retrieval in future
+	curNode.value = key
+}
+
+// PrefixMatch - prefix match
+func (t *Trie) PrefixMatch(key string) []interface{} {
+	node, _ := t.findNode(key)
+	if node != nil {
+		return t.walk(node)
+	}
+	return []interface{}{}
+}
+
+// walk the tree
+func (t *Trie) walk(node *trieNode) (ret []interface{}) {
+	if node.exists {
+		ret = append(ret, node.value)
+	}
+	for _, v := range node.child {
+		ret = append(ret, t.walk(v)...)
+	}
+	return
+}
+
+// find nodes corresponding to key
+func (t *Trie) findNode(key string) (node *trieNode, index int) {
+	curNode := t.root
+	f := false
+	for k, v := range key {
+		if f {
+			index = k
+			f = false
+		}
+		if curNode.child[v] == nil {
+			return nil, index
+		}
+		curNode = curNode.child[v]
+		if curNode.exists {
+			f = true
+		}
+	}
+
+	if curNode.exists {
+		index = len(key)
+	}
+
+	return curNode, index
+}