fix: repair all failing tests across utility modules

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 +6,16 @@
  * 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 the nearest day on the magnitude of the
+ * difference, so past and future read symmetrically: 36 hours ago is
+ * "2 days ago" and 36 hours ahead is "in 2 days".
  */
 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) {
@@ -25,7 +26,7 @@ export function formatRelative(date: Date, now: Date = new Date()): string {
     const h = Math.round(Math.abs(diffHours))
     return diffMs > 0 ? `${h} hour${h !== 1 ? "s" : ""} ago` : `in ${h} hour${h !== 1 ? "s" : ""}`
   }
-  const d = Math.abs(diffDays)
+  const d = diffDays
   return diffMs > 0 ? `${d} day${d !== 1 ? "s" : ""} ago` : `in ${d} day${d !== 1 ? "s" : ""}`
 }
 

src/string-utils.ts

@@ -11,10 +11,25 @@ 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.
+const ELLIPSIS = "..."
+
+/**
+ * Truncate a string to at most maxLength characters, cutting at a word
+ * boundary where possible. The ellipsis counts toward maxLength, so the
+ * returned string is never longer than maxLength.
+ * Returns the string unchanged when it already fits, and "" when maxLength
+ * is non-finite or not positive (no output can satisfy the invariant).
+ */
 export function truncate(str: string, maxLength: number): string {
-  throw new Error("not implemented")
+  if (!Number.isFinite(maxLength) || maxLength <= 0) return ""
+  if (str.length <= maxLength) return str
+  if (maxLength <= ELLIPSIS.length) return str.slice(0, maxLength)
+
+  const budget = maxLength - ELLIPSIS.length
+  const head = str.slice(0, budget)
+  const lastSpace = head.lastIndexOf(" ")
+  const cut = lastSpace > 0 ? head.slice(0, lastSpace) : head
+  return cut.trimEnd() + ELLIPSIS
 }
 
 export function slugify(str: string): string {
@@ -24,8 +39,8 @@ 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
+  const trimmed = str.trim()
+  if (!trimmed) return 0
+  return trimmed.split(/\s+/).length
 }

src/task-manager.ts

@@ -52,20 +52,47 @@ 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 a task was 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.
+   * Returns true if the task was found and updated, false if not found.
+   * Only keys explicitly present in `changes` are applied.
+   */
   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.
+   * priority: high > medium > low. status: pending > in_progress > completed.
+   * createdAt: oldest first. Ties fall back to insertion order (id).
+   */
   sortBy(field: "priority" | "createdAt" | "status"): Task[] {
-    throw new Error("not implemented")
+    const priorityRank: Record<Priority, number> = { high: 0, medium: 1, low: 2 }
+    const statusRank: Record<Status, number> = { pending: 0, in_progress: 1, completed: 2 }
+
+    const byId = (a: Task, b: Task) => Number(a.id) - Number(b.id)
+
+    return Array.from(this.tasks.values()).sort((a, b) => {
+      switch (field) {
+        case "priority":
+          return priorityRank[a.priority] - priorityRank[b.priority] || byId(a, b)
+        case "status":
+          return statusRank[a.status] - statusRank[b.status] || byId(a, b)
+        case "createdAt":
+          return a.createdAt.getTime() - b.createdAt.getTime() || byId(a, b)
+      }
+    })
   }
 }

src/validator.ts

@@ -2,27 +2,26 @@
  * Input validation utilities.
  */
 
+const EMAIL_LABEL = "[a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?"
+const EMAIL_RE = new RegExp(`^[^\\s@]+@${EMAIL_LABEL}(?:\\.${EMAIL_LABEL})*\\.[a-zA-Z]{2,}$`)
+
 /**
  * Returns true if the string is a valid email address.
- *
- * BUG: the regex does not allow subdomains (e.g. user@mail.example.com fails)
- * and rejects valid TLDs longer than 4 chars (e.g. .museum, .travel).
+ * Supports subdomains (user@mail.example.com) and TLDs of any length
+ * of two or more characters (.com, .museum, .travel).
  */
 export function isEmail(value: string): boolean {
-  // BUG: too restrictive — missing subdomain support and long TLDs
-  return /^[^\s@]+@[^\s@]+\.[a-zA-Z]{2,4}$/.test(value)
+  return EMAIL_RE.test(value)
 }
 
 /**
- * Returns true if the string is a valid URL (http or https).
- *
- * BUG: rejects URLs with ports (e.g. http://localhost:3000)
+ * Returns true if the string is a valid http or https URL.
+ * An explicit port is 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
   }