/**
 * Tests for src/utils/datetime.ts
 *
 * Key invariants verified (timezone-agnostic where possible):
 * 1. A tz-less string is parsed identically to the same string with "Z" appended
 *    (i.e. treated as UTC regardless of the machine's local timezone).
 * 2. Formatted output never contains AM / PM / am / pm (always 24-hour).
 * 3. Strings that already carry a timezone marker are NOT double-offset.
 * 4. Invalid / empty input does not throw — returns original string or safe fallback.
 * 5. Pure date strings (no T) are handled without crashing.
 */

import { describe, it, expect } from 'vitest'
import {
  parseBackendTimestamp,
  formatLocalDateTime,
  formatLocalTime,
  formatLocalDate,
} from './datetime'

// ---------------------------------------------------------------------------
// parseBackendTimestamp — core UTC-fallback logic
// ---------------------------------------------------------------------------

describe('parseBackendTimestamp', () => {
  it('returns the same Date for tz-less and Z-suffixed strings (UTC equivalence)', () => {
    const noTz = parseBackendTimestamp('2026-06-24T10:27:00')
    const withZ = parseBackendTimestamp('2026-06-24T10:27:00Z')
    // Both must represent the exact same UTC instant.
    expect(noTz.getTime()).toBe(withZ.getTime())
  })

  it('does not double-offset a string that already has Z', () => {
    const d1 = parseBackendTimestamp('2026-06-24T10:27:00Z')
    const d2 = parseBackendTimestamp('2026-06-24T10:27:00')
    expect(d1.getTime()).toBe(d2.getTime())
  })

  it('correctly parses a string with +HH:MM offset', () => {
    // 2026-06-24T12:27:00+02:00 == 2026-06-24T10:27:00Z
    const withOffset = parseBackendTimestamp('2026-06-24T12:27:00+02:00')
    const utc = parseBackendTimestamp('2026-06-24T10:27:00Z')
    expect(withOffset.getTime()).toBe(utc.getTime())
  })

  it('correctly parses a string with -HH:MM offset', () => {
    // 2026-06-24T02:27:00-08:00 == 2026-06-24T10:27:00Z
    const withOffset = parseBackendTimestamp('2026-06-24T02:27:00-08:00')
    const utc = parseBackendTimestamp('2026-06-24T10:27:00Z')
    expect(withOffset.getTime()).toBe(utc.getTime())
  })

  it('handles pure date strings (no T) without crashing', () => {
    const d = parseBackendTimestamp('2026-06-24')
    expect(isNaN(d.getTime())).toBe(false)
  })

  it('returns Invalid Date for empty string', () => {
    const d = parseBackendTimestamp('')
    expect(isNaN(d.getTime())).toBe(true)
  })

  it('returns Invalid Date for garbage input', () => {
    const d = parseBackendTimestamp('not-a-date')
    expect(isNaN(d.getTime())).toBe(true)
  })
})

// ---------------------------------------------------------------------------
// formatLocalDateTime — no AM/PM, 24-hour
// ---------------------------------------------------------------------------

describe('formatLocalDateTime', () => {
  it('produces the same output for tz-less and Z-suffixed strings (UTC equivalence)', () => {
    const noTz = formatLocalDateTime('2026-06-24T10:27:00')
    const withZ = formatLocalDateTime('2026-06-24T10:27:00Z')
    // Both should format to the same local representation.
    expect(noTz).toBe(withZ)
  })

  it('does not contain AM or PM (24-hour enforcement)', () => {
    // Use noon UTC — a time where AM/PM distinction matters.
    const result = formatLocalDateTime('2026-06-24T14:30:00Z')
    expect(result).not.toMatch(/[Aa][Mm]|[Pp][Mm]/)
  })

  it('does not throw or return undefined for empty string', () => {
    const result = formatLocalDateTime('')
    expect(result).toBe('')
  })

  it('does not throw or return undefined for invalid string', () => {
    const result = formatLocalDateTime('not-a-date')
    // Should return the original string as a safe fallback.
    expect(result).toBe('not-a-date')
  })

  it('returns a non-empty string for a valid timestamp', () => {
    const result = formatLocalDateTime('2026-06-24T10:27:00Z')
    expect(typeof result).toBe('string')
    expect(result.length).toBeGreaterThan(0)
  })
})

// ---------------------------------------------------------------------------
// formatLocalTime — compact HH:mm, no AM/PM
// ---------------------------------------------------------------------------

describe('formatLocalTime', () => {
  it('produces the same output for tz-less and Z-suffixed strings', () => {
    const noTz = formatLocalTime('2026-06-24T10:27:00')
    const withZ = formatLocalTime('2026-06-24T10:27:00Z')
    expect(noTz).toBe(withZ)
  })

  it('does not contain AM or PM', () => {
    const result = formatLocalTime('2026-06-24T14:30:00Z')
    expect(result).not.toMatch(/[Aa][Mm]|[Pp][Mm]/)
  })

  it('returns a non-empty string for a valid timestamp', () => {
    const result = formatLocalTime('2026-06-24T10:27:00Z')
    expect(typeof result).toBe('string')
    expect(result.length).toBeGreaterThan(0)
  })

  it('does not throw for empty string', () => {
    expect(() => formatLocalTime('')).not.toThrow()
    expect(formatLocalTime('')).toBe('')
  })

  it('does not throw for invalid string', () => {
    expect(() => formatLocalTime('bad')).not.toThrow()
    expect(formatLocalTime('bad')).toBe('bad')
  })
})

// ---------------------------------------------------------------------------
// formatLocalDate — date only
// ---------------------------------------------------------------------------

describe('formatLocalDate', () => {
  it('produces the same output for tz-less and Z-suffixed strings', () => {
    // Pick a time that won't cross a date boundary in any timezone
    // (noon UTC — safe for UTC-12 through UTC+14).
    const noTz = formatLocalDate('2026-06-24T12:00:00')
    const withZ = formatLocalDate('2026-06-24T12:00:00Z')
    expect(noTz).toBe(withZ)
  })

  it('handles pure date strings without crashing', () => {
    expect(() => formatLocalDate('2026-06-24')).not.toThrow()
    const result = formatLocalDate('2026-06-24')
    expect(typeof result).toBe('string')
    expect(result.length).toBeGreaterThan(0)
  })

  it('does not throw for empty string', () => {
    expect(() => formatLocalDate('')).not.toThrow()
    expect(formatLocalDate('')).toBe('')
  })

  it('does not throw for invalid string', () => {
    expect(() => formatLocalDate('not-a-date')).not.toThrow()
    expect(formatLocalDate('not-a-date')).toBe('not-a-date')
  })

  it('returns a non-empty string for a valid date', () => {
    const result = formatLocalDate('2026-06-01T00:00:00Z')
    expect(result.length).toBeGreaterThan(0)
  })
})
