Implement wc in JavaScript

Author: Konvaly

implement-shell-tools/package.json

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+{
+  "type": "module"
+}

implement-shell-tools/wc/wc.mjs

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+import process from "node:process";
+import { promises as fs } from "node:fs";
+import { parseArgs } from "node:util";
+
+const { values, positionals } = parseArgs({
+  options: {
+    lines: { type: "boolean", short: "l", default: false },
+    words: { type: "boolean", short: "w", default: false },
+    bytes: { type: "boolean", short: "c", default: false },
+  },
+  allowPositionals: true,
+});
+
+const noFlags = !values.lines && !values.words && !values.bytes;
+const showLines = noFlags || values.lines;
+const showWords = noFlags || values.words;
+const showBytes = noFlags || values.bytes;
+
+if (positionals.length === 0) {
+  console.error("Usage: node wc.mjs [-l] [-w] [-c] <path>...");
+  process.exit(1);
+}
+
+function countLines(content) {
+  let count = 0;
+  for (const character of content) {
+    if (character === "\n") {
+      count++;
+    }
+  }
+  return count;
+}
+
+function countWords(content) {
+  return content.split(/\s+/).filter((word) => word !== "").length;
+}
+
+const results = [];
+const totals = { lines: 0, words: 0, bytes: 0 };
+
+for (const path of positionals) {
+  let buffer;
+  try {
+    buffer = await fs.readFile(path);
+  } catch {
+    console.error(`wc: ${path}: No such file or directory`);
+    process.exitCode = 1;
+    continue;
+  }
+
+  const content = buffer.toString("utf-8");
+  const counts = {
+    lines: countLines(content),
+    words: countWords(content),
+    bytes: buffer.length,
+    name: path,
+  };
+
+  results.push(counts);
+  totals.lines += counts.lines;
+  totals.words += counts.words;
+  totals.bytes += counts.bytes;
+}
+
+if (results.length > 1) {
+  results.push({ ...totals, name: "total" });
+}
+
+const selectedCounts = [showLines, showWords, showBytes].filter(Boolean).length;
+const skipPadding = selectedCounts === 1 && results.length === 1;
+
+let width = 1;
+if (!skipPadding) {
+  for (const result of results) {
+    for (const key of ["lines", "words", "bytes"]) {
+      width = Math.max(width, String(result[key]).length);
+    }
+  }
+}
+
+for (const result of results) {
+  const columns = [];
+  if (showLines) columns.push(String(result.lines).padStart(width));
+  if (showWords) columns.push(String(result.words).padStart(width));
+  if (showBytes) columns.push(String(result.bytes).padStart(width));
+  console.log(`${columns.join(" ")} ${result.name}`);
+}