#!/usr/bin/perl

################################################################################
# JavaInfo - Java Class File Version Analyzer
#
# This utility extracts Java version information from compiled class files by
# reading their bytecode headers. It recursively processes files and directories
# to identify Java class files and report their compilation version.
#
# The script reads the first 8 bytes of each file, checks for the Java class
# file magic number (0xCAFEBABE), and extracts the major/minor version numbers
# which indicate the Java version used to compile the class.
#
# Usage: JavaInfo <file or directory> [<file or directory> ...]
#
# Examples:
#   JavaInfo MyClass.class
#   JavaInfo /path/to/project/bin
#   JavaInfo target/classes lib/*.jar
#
# Author: Thomas
# License: See LICENSE file
################################################################################

use strict;
use warnings;
use File::Spec::Functions;

#
# Main entry point - processes all command-line arguments
#
# Parameters:
#   @_ - List of file or directory paths to process
#
sub main {
    foreach my $node (@_) {
	process_node($node);
    }
}

#
# Process a filesystem node (file or directory)
#
# Determines whether the given path is a file or directory and dispatches
# to the appropriate handler function.
#
# Parameters:
#   $node - Path to the filesystem node to process
#
sub process_node {
    my $node = shift();
    if (-f $node) {
	process_file($node);
    } elsif (-d $node) {
	process_dir($node);
    }
}

#
# Recursively process all files in a directory
#
# Reads all entries in the directory (excluding . and ..) and recursively
# processes each one by calling process_node.
#
# Parameters:
#   $dir - Path to the directory to process
#
# Dies on error:
#   - If the directory cannot be opened
#   - If the directory contents cannot be read
#
sub process_dir {
    my $dir = shift();
    if (opendir(my $DIR, $dir)) {
	if (my @nodes = readdir(DIR)) {
	    foreach my $node (no_upwards(@nodes)) {
		process_node(catfile($dir, $node));
	    }
	} else {
	    die "$dir: could not read directory ($!)\n";
	}
	closedir(DIR);
    } else {
	die "$dir: could not open directory ($!)\n";
    }
}

#
# Process a single file and extract Java version information
#
# Reads the first 8 bytes of a file to check if it's a valid Java class file
# (identified by the magic number 0xCAFEBABE) and extracts version information
# from the bytecode header.
#
# Java class file format (first 8 bytes):
#   Bytes 0-3: Magic number (0xCAFEBABE)
#   Bytes 4-5: Minor version
#   Bytes 6-7: Major version
#
# Version mapping:
#   Major 45 (minor <=3): Java 1.0.2
#   Major 45 (minor >3):  Java 1.1.8
#   Major 46:             Java 1.2.2
#   Major 47:             Java 1.3.1
#   Major 48:             Java 1.4.2
#   Major 49+:            Java (major - 44)  [e.g., 52 = Java 8, 61 = Java 17]
#
# Parameters:
#   $file - Path to the file to process
#
# Dies on error:
#   - If the file cannot be opened
#   - If the file cannot be read
#   - If the file is not a valid Java class file
#
sub process_file {
    my $file = shift();
    if (open(my $FILE, '<', $file)) {
	binmode($FILE);
	my $buffer;
	if (read(FILE, $buffer, 8)) {
	    # Unpack the first 8 bytes as two 32-bit unsigned integers (big-endian)
	    my @fields = unpack('NN', $buffer);

	    # Check for Java class file magic number (0xCAFEBABE)
	    if ($fields[0] == 0xCAFEBABE) {
		# Extract minor and major version numbers from the second 32-bit value
		my $minor = ($fields[1] & 0xFF00) >> 16; ## no critic [Use of bitwise operator]: indeed
		my $major = $fields[1] & 0x00FF; ## no critic [Use of bitwise operator]: indeed
		my $version = '';

		# Map major/minor version to Java release version
		if ($major == 45) {
		    if ($minor <= 3) {
			$version = '1.0.2';
		    } else {
			$version = '1.1.8';
		    }
		} elsif ($major == 46) {
		    $version = '1.2.2';
		} elsif ($major == 47) {
		    $version = '1.3.1';
		} elsif ($major == 48) {
		    $version = '1.4.2';
		} elsif ($major >= 49) {
		    # Java 5 and later: version = major - 44
		    $version = ($major - 44);
		}
		print "$file: Java " . $version . " [" . $minor . "/" . $major . "]\n";
	    } else {
		die "$file: not a java class file\n";
	    }
	} else {
	    die "$file: could not read file ($!)\n";
	}
	close($FILE);
    } else {
	die "$file: could not open file ($!)\n";
    }
}

main(@ARGV);