From 9ba485b789af82b8d939481da7f5b56404218f08 Mon Sep 17 00:00:00 2001
From: Sebastian Morr <sebastian@morr.cc>
Date: Sun, 13 Sep 2020 21:55:51 +0200
Subject: [PATCH] Add levels for refs and symrefs

---
 levels/00-empty/description  | 1 +
 levels/05-ref/description    | 9 +++++++++
 levels/05-ref/start          | 5 +++++
 levels/05-ref/win            | 3 +++
 levels/06-symref/description | 9 +++++++++
 levels/06-symref/start       | 4 ++++
 levels/06-symref/win         | 1 +
 7 files changed, 32 insertions(+)
 create mode 100644 levels/00-empty/description
 create mode 100644 levels/05-ref/description
 create mode 100644 levels/05-ref/start
 create mode 100644 levels/05-ref/win
 create mode 100644 levels/06-symref/description
 create mode 100644 levels/06-symref/start
 create mode 100644 levels/06-symref/win

diff --git a/levels/00-empty/description b/levels/00-empty/description
new file mode 100644
index 0000000..0e18f97
--- /dev/null
+++ b/levels/00-empty/description
@@ -0,0 +1 @@
+This is an empty level without any winning condition - you can use it as a playground!
diff --git a/levels/05-ref/description b/levels/05-ref/description
new file mode 100644
index 0000000..097ae6b
--- /dev/null
+++ b/levels/05-ref/description
@@ -0,0 +1,9 @@
+Let's take a look at "refs", short for "references"! Refs are not objects, but rather very simple *pointers* to objects! They can help you keep track of what's where.
+
+You can create or update a ref with
+
+    git update-ref refs/<refname> <newvalue>
+
+Make sure to start a ref's name with "refs/"! That's a convention that helps Git find all refs you create.
+
+Create refs that point to all objects in this repository!
diff --git a/levels/05-ref/start b/levels/05-ref/start
new file mode 100644
index 0000000..1c9caca
--- /dev/null
+++ b/levels/05-ref/start
@@ -0,0 +1,5 @@
+echo hello > hello
+echo world > world
+git add .
+TREE=$(git write-tree)
+git commit-tree $TREE -m "Initial commit"
diff --git a/levels/05-ref/win b/levels/05-ref/win
new file mode 100644
index 0000000..76a1f24
--- /dev/null
+++ b/levels/05-ref/win
@@ -0,0 +1,3 @@
+OBJECTS=$(git cat-file --batch-check='%(objectname)' --batch-all-objects | sort)
+REF_TARGETS=$(git show-ref -s | sort | uniq)
+test "$OBJECTS" = "$REF_TARGETS"
diff --git a/levels/06-symref/description b/levels/06-symref/description
new file mode 100644
index 0000000..41eedd3
--- /dev/null
+++ b/levels/06-symref/description
@@ -0,0 +1,9 @@
+Instead of pointing directly to objects, refs can also point to other refs!
+
+When that happens, they are called "symbolic refs". You can create or update a symbolic ref using
+
+    git symbolic-ref <name> <ref>
+
+Usually, you will only encounter a special symbolic ref called "HEAD". This ref is special in that it doesn't start with "refs/"!
+
+Try pointing HEAD to the refs in this repository!
diff --git a/levels/06-symref/start b/levels/06-symref/start
new file mode 100644
index 0000000..d1373ab
--- /dev/null
+++ b/levels/06-symref/start
@@ -0,0 +1,4 @@
+TREE=$(git write-tree)
+COMMIT=$(git commit-tree $TREE -m "Initial commit")
+git update-ref refs/best_commit $COMMIT
+git update-ref refs/worst_commit $COMMIT
diff --git a/levels/06-symref/win b/levels/06-symref/win
new file mode 100644
index 0000000..2dab745
--- /dev/null
+++ b/levels/06-symref/win
@@ -0,0 +1 @@
+git symbolic-ref HEAD | grep _commit