From 2da4bc33e7a273e84d32f63db2b8e6f181d96e71 Mon Sep 17 00:00:00 2001
From: Charles Gould <charles@gould.dev>
Date: Thu, 10 Mar 2022 13:10:53 -0500
Subject: [PATCH] fish: add class_version function

---
 fish/functions/class_version.fish | 59 +++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 fish/functions/class_version.fish

diff --git a/fish/functions/class_version.fish b/fish/functions/class_version.fish
new file mode 100644
index 0000000..7f2f95d
--- /dev/null
+++ b/fish/functions/class_version.fish
@@ -0,0 +1,59 @@
+function class_version --argument-name class_file
+
+    if not string match -q '*.class' "$class_file"
+        echo "Expected a Java class file but got: $class_file"
+        return 1
+    end
+
+    # Use the `file` command if available
+    if command -q file
+        command file "$class_file"
+        return 0
+    end
+
+    javap -verbose "$class_file" | string match -rq 'major version: (?<major_version>\d+)'
+
+    set -l version_name
+
+    # https://en.wikipedia.org/wiki/Java_class_file#General_layout
+    switch "$major_version"
+        case 61
+            set version_name 'Java SE 17'
+        case 60
+            set version_name 'Java SE 16'
+        case 59
+            set version_name 'Java SE 15'
+        case 58
+            set version_name 'Java SE 14'
+        case 57
+            set version_name 'Java SE 13'
+        case 56
+            set version_name 'Java SE 12'
+        case 55
+            set version_name 'Java SE 11'
+        case 54
+            set version_name 'Java SE 10'
+        case 53
+            set version_name 'Java SE 9'
+        case 52
+            set version_name 'Java SE 8'
+        case 51
+            set version_name 'Java SE 7'
+        case 50
+            set version_name 'Java SE 6.0'
+        case 49
+            set version_name 'Java SE 5.0'
+        case 48
+            set version_name 'JDK 1.4'
+        case 47
+            set version_name 'JDK 1.3'
+        case 46
+            set version_name 'JDK 1.2'
+        case 45
+            set version_name 'JDK 1.1'
+        case '*'
+            set version_name 'Unknown Java version'
+    end
+
+    echo "$version_name (major version $major_version)"
+end