fix: repair failing utility tests and implement missing functions

src/calculator.ts

@@ -15,7 +15,7 @@ export function multiply(a: number, b: number): number {
   return a * b
 }
 
-// BUG: Division by zero is not handled
 export function divide(a: number, b: number): number {
+  if (b === 0) throw new Error("Division by zero")
   return a / b
 }

src/date-utils.ts

@@ -6,15 +6,14 @@
  * Format a date as a human-readable relative string.
  * e.g. "2 days ago", "just now", "in 3 hours"
  *
- * BUG: off-by-one — uses Math.floor where Math.round is needed for days,
- * causing "1 day ago" to appear for anything from 12h to 47h.
+ * Day counts are rounded to nearest, so 36h ago reads "2 days ago".
  */
 export function formatRelative(date: Date, now: Date = new Date()): string {
   const diffMs = now.getTime() - date.getTime()
   const diffSec = diffMs / 1000
   const diffMin = diffSec / 60
   const diffHours = diffMin / 60
-  const diffDays = Math.floor(diffHours / 24) // BUG: should be Math.round
+  const diffDays = Math.round(Math.abs(diffHours) / 24)
 
   if (Math.abs(diffSec) < 60) return "just now"
   if (Math.abs(diffMin) < 60) {

src/string-utils.ts

@@ -11,10 +11,32 @@ export function reverse(str: string): string {
   return str.split("").reverse().join("")
 }
 
-// TODO: implement truncate — should truncate at a word boundary, with "..."
-// counting toward maxLength. Return unchanged if str.length <= maxLength.
+/**
+ * Truncate a string to at most maxLength characters, cutting at a word
+ * boundary and appending an ellipsis. The ellipsis counts toward maxLength,
+ * so the result is never longer than maxLength.
+ */
 export function truncate(str: string, maxLength: number): string {
-  throw new Error("not implemented")
+  if (!str || str.length <= maxLength) return str
+
+  const ellipsis = "..."
+  if (maxLength <= ellipsis.length) return str.slice(0, Math.max(maxLength, 0))
+
+  // Leading whitespace would otherwise eat the character budget and could
+  // reduce the result to a bare ellipsis. Trim it here rather than at entry so
+  // a within-limit string is still returned byte-for-byte unchanged above.
+  const source = str.trimStart()
+  if (source.length <= maxLength) return source
+
+  const budget = maxLength - ellipsis.length
+  const candidate = source.slice(0, budget)
+  const lastSpace = candidate.lastIndexOf(" ")
+  // `source` starts with a non-whitespace character, so `candidate` does too:
+  // whichever branch is taken, the body keeps that character and survives
+  // trimEnd() non-empty. Content can therefore never be lost entirely.
+  const body = lastSpace > 0 ? candidate.slice(0, lastSpace) : candidate
+
+  return body.trimEnd() + ellipsis
 }
 
 export function slugify(str: string): string {
@@ -24,8 +46,7 @@ export function slugify(str: string): string {
     .replace(/^-|-$/g, "")
 }
 
-// BUG: This doesn't handle multiple consecutive spaces
 export function wordCount(str: string): number {
   if (!str.trim()) return 0
-  return str.split(" ").length
+  return str.trim().split(/\s+/).length
 }

src/task-manager.ts

@@ -52,20 +52,46 @@ export class TaskManager {
     return true
   }
 
-  // TODO: implement — remove a task by id, return true if removed, false if not found
+  /** Remove a task by id. Returns true if removed, false if not found. */
   remove(id: string): boolean {
-    throw new Error("not implemented")
+    return this.tasks.delete(id)
   }
 
-  // TODO: implement — update title/description/priority of a task
-  // return true if updated, false if not found
+  /**
+   * Update the title, description and/or priority of a task.
+   *
+   * Omitted keys are always left untouched. An explicit `undefined` behaves
+   * differently per field, because `title` and `priority` are required on Task
+   * while `description` is optional:
+   *   - `title` / `priority`: an explicit `undefined` is ignored, so a required
+   *     field can never be blanked out.
+   *   - `description`: an explicit `undefined` clears it.
+   *
+   * Returns true if updated, false if the task was not found.
+   */
   update(id: string, changes: Partial<Pick<Task, "title" | "description" | "priority">>): boolean {
-    throw new Error("not implemented")
+    const task = this.tasks.get(id)
+    if (!task) return false
+    if ("title" in changes && changes.title !== undefined) task.title = changes.title
+    if ("description" in changes) task.description = changes.description
+    if ("priority" in changes && changes.priority !== undefined) task.priority = changes.priority
+    return true
   }
 
-  // TODO: implement — return all tasks sorted by the given field
-  // priority sort order: high > medium > low
+  /** Return all tasks sorted by the given field, without mutating internal order. */
   sortBy(field: "priority" | "createdAt" | "status"): Task[] {
-    throw new Error("not implemented")
+    const priorityOrder: Record<Priority, number> = { high: 0, medium: 1, low: 2 }
+    const statusOrder: Record<Status, number> = { in_progress: 0, pending: 1, completed: 2 }
+
+    return Array.from(this.tasks.values()).sort((a, b) => {
+      switch (field) {
+        case "priority":
+          return priorityOrder[a.priority] - priorityOrder[b.priority]
+        case "status":
+          return statusOrder[a.status] - statusOrder[b.status]
+        case "createdAt":
+          return a.createdAt.getTime() - b.createdAt.getTime()
+      }
+    })
   }
 }

src/validator.ts

@@ -4,25 +4,23 @@
 
 /**
  * Returns true if the string is a valid email address.
- *
- * BUG: the regex does not allow subdomains (e.g. user@mail.example.com fails)
- * and rejects valid TLDs longer than 4 chars (e.g. .museum, .travel).
+ * Supports subdomains (user@mail.example.com) and TLDs of any length (.museum).
  */
 export function isEmail(value: string): boolean {
-  // BUG: too restrictive — missing subdomain support and long TLDs
-  return /^[^\s@]+@[^\s@]+\.[a-zA-Z]{2,4}$/.test(value)
+  // Bound the input before matching so the regex cannot be driven into
+  // pathological backtracking (RFC 5321 caps a forward path at 254 chars).
+  if (!value || value.length > 254) return false
+  return /^[^\s@]+@[^\s@]+\.[a-zA-Z]{2,}$/.test(value)
 }
 
 /**
  * Returns true if the string is a valid URL (http or https).
- *
- * BUG: rejects URLs with ports (e.g. http://localhost:3000)
+ * Ports are permitted (e.g. http://localhost:3000).
  */
 export function isUrl(value: string): boolean {
   try {
     const url = new URL(value)
-    // BUG: only allows http/https but also rejects valid port usage
-    return (url.protocol === "http:" || url.protocol === "https:") && url.port === ""
+    return url.protocol === "http:" || url.protocol === "https:"
   } catch {
     return false
   }