From 5c1364e181dd737f6830382fe203241295e0c344 Mon Sep 17 00:00:00 2001
From: Inanc Gumus <m@inanc.io>
Date: Fri, 17 May 2019 11:14:54 +0300
Subject: [PATCH] add: an exercise to error handling

---
 .../exercises/01-refactor/main.go             | 33 +++++++++++++++++++
 .../exercises/01-refactor/solution/main.go    | 28 ++++++++++++++++
 28-error-handling/exercises/README.md         | 11 +++++++
 internal/magic/detect.go                      |  3 +-
 4 files changed, 74 insertions(+), 1 deletion(-)
 create mode 100644 28-error-handling/exercises/01-refactor/main.go
 create mode 100644 28-error-handling/exercises/01-refactor/solution/main.go
 create mode 100644 28-error-handling/exercises/README.md

diff --git a/28-error-handling/exercises/01-refactor/main.go b/28-error-handling/exercises/01-refactor/main.go
new file mode 100644
index 0000000..414e36c
--- /dev/null
+++ b/28-error-handling/exercises/01-refactor/main.go
@@ -0,0 +1,33 @@
+package main
+
+import "fmt"
+
+// ---------------------------------------------------------
+// EXERCISE: Refactor
+//
+//   In the headerOf function, instead of using a switch,
+//   use a map. Declare it at the package-level.
+//
+// RESTRICTION
+//
+//   For panicking, use a deferred function and a named param.
+//
+// EXPECTED OUTPUT
+//
+//   Please run the solution.
+//
+// ---------------------------------------------------------
+
+func main() {
+	fmt.Println(headerOf("gif"))
+}
+
+func headerOf(format string) string {
+	switch format {
+	case "png":
+		return "\x89PNG\r\n\x1a\n"
+	case "jpg":
+		return "\xff\xd8\xff"
+	}
+	panic("unknown format: " + format)
+}
diff --git a/28-error-handling/exercises/01-refactor/solution/main.go b/28-error-handling/exercises/01-refactor/solution/main.go
new file mode 100644
index 0000000..1eb86b5
--- /dev/null
+++ b/28-error-handling/exercises/01-refactor/solution/main.go
@@ -0,0 +1,28 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println(headerOf("gif"))
+}
+
+var headers = map[string]string{
+	"png": "\x89PNG\r\n\x1a\n",
+	"jpg": "\xff\xd8\xff",
+}
+
+func headerOf(format string) (header string) {
+	defer func() {
+		if header == "" {
+			panic("unknown format: " + format)
+		}
+	}()
+	return headers[format]
+}
diff --git a/28-error-handling/exercises/README.md b/28-error-handling/exercises/README.md
new file mode 100644
index 0000000..64af717
--- /dev/null
+++ b/28-error-handling/exercises/README.md
@@ -0,0 +1,11 @@
+# Header
+
+What you will learn?
+
+1. **[Refactor](https://github.com/inancgumus/learngo/tree/master/28-error-handling/exercises/01-refactor)**
+
+    Refactor the headerOf function with a map + defer + and a named param.
+
+2. **[text](https://github.com/inancgumus/learngo/tree/master/)**
+
+    text
\ No newline at end of file
diff --git a/internal/magic/detect.go b/internal/magic/detect.go
index f67dfc0..60d8dc3 100644
--- a/internal/magic/detect.go
+++ b/internal/magic/detect.go
@@ -14,7 +14,8 @@ import (
 	"os"
 )
 
-// Detect returns only the valid filenames that match to a header of the given format.
+// Detect returns the files that have a valid header (file signature).
+// A valid header is determined by the format.
 func Detect(format string, filenames []string) (valids []string, err error) {
 	defer func() {
 		if rerr := recover(); rerr != nil {