require "date"
#
# Program goal:
# -------------
# Sort a list of date strings in the format "YYYY-MM-DD".
#
# Approach:
# 1. Parse each string into a Date object using Date.strptime.
# 2. Sort using Ruby’s built-in Array#sort (O(n log n)).
# 3. Convert back to strings and print results.
#
# Architecture notes:
# -------------------
# - Parsing is isolated in a dedicated function for clarity and testability.
# - Sorting uses Array#sort, which is stable and efficient.
# - Error handling: invalid formats are detected and reported.
# - Edge cases: malformed strings, invalid ranges, leap years.
# - Performance: Date parsing is fast; sorting is O(n log n).
# - Memory: minimal; only an array of small objects.
# - Security: avoids unsafe parsing; uses strict format matching.
#
#
# Parse a date string into a Date object.
# Returns the Date or raises an exception with a clear message.
#
def parse_date(s)
begin
Date.strptime(s, "%Y-%m-%d")
rescue ArgumentError
raise "Invalid date: #{s}"
end
end
#
# Sort a list of date strings.
# Returns a new sorted array; does not mutate the input.
#
def sort_dates(dates)
parsed = []
# Parse all dates; fail fast on invalid input.
dates.each do |s|
parsed << parse_date(s)
end
# Sort using natural Date ordering.
parsed.sort.map { |d| d.strftime("%Y-%m-%d") }
end
#
# Helper to print a list of strings.
#
def print_list(list)
list.each { |s| puts " #{s}" }
end
#
# Helper to run a named test case.
#
def run_test(name, dates)
puts "\n=== #{name} ==="
begin
sorted = sort_dates(dates)
print_list(sorted)
rescue => e
puts "Error: #{e}"
end
end
#
# Main program with multiple test cases.
#
puts "Ruby Date Sorting Demo"
# Basic chronological order
run_test("Basic chronological order", [
"2024-01-05",
"2023-12-31",
"2024-01-01",
"2022-07-15"
])
# Already sorted input
run_test("Already sorted input", [
"2020-01-01",
"2020-01-02",
"2020-01-03"
])
# Leap year edge cases
run_test("Leap year edge cases", [
"2020-02-29",
"2019-02-28",
"2021-03-01"
])
# Invalid date detection
run_test("Invalid date detection", [
"2024-13-01", # invalid month
"2024-02-30", # invalid day
"not-a-date" # malformed
])
#
# run:
#
# Ruby Date Sorting Demo
#
# === Basic chronological order ===
# 2022-07-15
# 2023-12-31
# 2024-01-01
# 2024-01-05
#
# === Already sorted input ===
# ERROR!
# 2020-01-01
# 2020-01-02
# 2020-01-03
#
# === Leap year edge cases ===
# 2019-02-28
# 2020-02-29
# 2021-03-01
#
# === Invalid date detection ===
# Error: Invalid date: 2024-13-01
#
