Add a zlib-based compress script

Based on `compress.py` from WebKit#170, with some modifications:
- Can be run as `npm run compress` or simply `node compress.mjs`
- Uses best zlib compression setting.
- Takes arbitrary glob patterns for input files, defaulting to all .z files for decompression.
- Copies the file mode over to avoid spurious git diffs.

Author: danleh

compress.mjs

@@ -0,0 +1,107 @@
+import { globSync } from 'glob';
+import zlib from 'zlib';
+import fs from 'fs';
+
+const isNPM = process.env.npm_config_user_agent !== undefined;
+const command = isNPM ? 'npm run compress --' : 'node compress.mjs';
+
+const usage = `Usage: ${command} [options] <glob>...
+
+Options:
+  -d, --decompress   Decompress files (default: compress).
+  -k, --keep         Keep input files after processing (default: delete).`;
+
+const args = process.argv.slice(2);
+if (args.length === 0) {
+    console.log(usage);
+    process.exit(1);
+}
+
+const keepInputFiles = args.some(arg => arg === '-k' || arg === '--keep');
+const decompressMode = args.some(arg => arg === '-d' || arg === '--decompress');
+
+let globs = args.filter(arg => !arg.startsWith('-'));
+if (globs.length === 0) {
+    if (decompressMode) {
+        const defaultGlob = '**/*.z';
+        console.log(`No input glob pattern given, using default: ${defaultGlob}`);
+        globs = [defaultGlob];
+    } else {
+        // To prevent accidental compression, require explicit input file patterns.
+        console.log(usage);
+        process.exit(1);
+    }
+}
+
+let files = new Set();
+if (globs.length > 0) {
+    for (const glob of globs) {
+        try {
+            const matches = globSync(glob, { nodir: true });
+            for (const match of matches) {
+                files.add(match);
+            }
+        } catch (err) {
+            console.error(`Error processing glob: ${glob}`, err);
+        }
+    }
+}
+files = Array.from(files).sort();
+if (files.length === 0) {
+    console.log(`No files found to process with the given globs: ${globs.join(', ')}`);
+    process.exit(0);
+}
+
+function compress(inputData) {
+    const compressedData = zlib.deflateSync(inputData, { level: zlib.constants.Z_BEST_COMPRESSION });
+
+    const originalSize = inputData.length;
+    const compressedSize = compressedData.length;
+    const compressionRatio = (1 - compressedSize / originalSize) * 100;
+    console.log(`  Original size:   ${String(originalSize).padStart(8)} bytes`);
+    console.log(`  Compressed size: ${String(compressedSize).padStart(8)} bytes`);
+    console.log(`  Compression ratio:  ${compressionRatio.toFixed(2).padStart(8)}%`);
+
+    return compressedData;
+}
+
+function decompress(inputData) {
+    const decompressedData = zlib.inflateSync(inputData);
+
+    const compressedSize = inputData.length;
+    const decompressedSize = decompressedData.length;
+    const expansionRatio = (decompressedSize / compressedSize - 1) * 100;
+    console.log(`  Compressed size:   ${String(compressedSize).padStart(8)} bytes`);
+    console.log(`  Decompressed size: ${String(decompressedSize).padStart(8)} bytes`);
+    console.log(`  Expansion ratio:      ${expansionRatio.toFixed(2).padStart(8)}%`);
+
+    return decompressedData;
+}
+
+const verb = decompressMode ? 'decompress' : 'compress';
+console.log(`Found ${files.length} files to ${verb}...`);
+
+for (const inputFile of files) {
+    try {
+        console.log(inputFile);
+
+        // Copy the mode over to avoid git status entries after a roundtrip.
+        const { mode } = fs.statSync(inputFile);
+        const inputData = fs.readFileSync(inputFile);
+        const outputData = decompressMode ? decompress(inputData) : compress(inputData);
+        let outputFile;
+        if (decompressMode) {
+            outputFile = inputFile.endsWith('.z') ? inputFile.slice(0, -2) : `${inputFile}.decompressed`;
+        } else {
+            outputFile = `${inputFile}.z`;
+        }
+        fs.writeFileSync(outputFile, outputData, { mode });
+
+        if (!keepInputFiles) {
+            fs.unlinkSync(inputFile);
+            console.log(`  Deleted input file.`);
+        }
+    } catch (err) {
+        console.error(`Error ${verb}ing ${inputFile}:`, err);
+    }
+}