Time Zone Converter

Level: Beginner 15–30 min

Concepts: Edge CasesAlgorithms

Solutions: C# | TypeScript | Python

Implement a time zone converter that can convert times between different time zones, handle daylight saving time, and format dates according to various standards.

Requirements

  1. Convert times between different time zones
    • Support major time zones (UTC, EST, PST, etc.)
    • Handle daylight saving time transitions
    • Support custom time zone offsets
  2. Format dates and times
    • Support different date/time formats (ISO 8601, RFC 3339, etc.)
    • Handle different locale-specific formats
    • Support relative time formats (e.g., “2 hours ago”)
  3. Validate time zone inputs
    • Check for valid time zone names
    • Validate date/time strings
    • Handle invalid inputs gracefully

Hint

Start by implementing basic time zone conversions using fixed offsets, then add support for daylight saving time. Consider using a time zone database or library for accurate conversions. Think about edge cases like:

  • Times during daylight saving time transitions
  • Times near midnight that cross date boundaries
  • Invalid or ambiguous times
  • Non-integer time zone offsets (e.g., UTC+5:30)
  • Invalid or unknown time zone names
  • Conversions across the International Date Line

Bonus

  • Add support for historical time zone data
  • Implement time zone abbreviation resolution
  • Add support for recurring time conversions
  • Create a time zone database manager
  • Implement time zone-aware scheduling

Reference Walkthrough

Reference implementations in C#, TypeScript, and Python live at tddbuddy-reference-katas/time-zone-converter. The reference follows the kata hint’s “start by implementing basic time zone conversions using fixed offsets” and stays there — IANA zones, daylight saving rules, and ambiguous/skipped local times around DST transitions are explicitly out of scope. Widening the kata to full IANA handling swaps it from an F1 algorithmic exercise (one-line arithmetic) to an F3 domain-modelling one (injected clock, zone registry, disambiguation policy for the repeated hour in fall-back); the hint’s phrasing calls for the narrower first step. Twelve scenarios cover the identity case, westward / eastward shifts from UTC, a cross-zone conversion that doesn’t touch UTC, forward / backward midnight roll-overs, half-hour (+05:30) and quarter-hour (+05:45) offsets, month / year / leap-day boundaries, and a twenty-four-hour swing across the international date line.

  • C# (.NET 8, xUnit, FluentAssertions 6.12.0) — walkthrough — public static DateTime Convert(DateTime local, TimeSpan fromOffset, TimeSpan toOffset) with a one-expression body (local - fromOffset + toOffset); DateTime / TimeSpan arithmetic carries across minute / hour / day / month / year boundaries
  • TypeScript (Node 20, Vitest 1.6, TS 5 strict) — walkthrough — LocalDateTime / Offset shape-only interfaces; conversion normalises to a UTC millisecond instant via Date.UTC(...), shifts by the offset delta in milliseconds, and reads calendar components back via getUTC* for host-time-zone-independence
  • Python (3.11, pytest) — walkthrough — naive datetime plus timedelta offsets; convert is a single expression and the package __init__.py re-exports it so tests import from time_zone_converter import convert

This kata ships in Agent Full-Bake mode at high gear (F1 tier): the algorithm is small enough to land as one commit per language, with walkthroughs noting there are no builders because the date-time types come from the standard library and the inputs / outputs are the domain. See the repo’s Gears section for when high gear is the right call.