import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest'
import { bootstrapTheme, setTheme, getThemePreference } from './theme'

// ── localStorage stub ────────────────────────────────────────────────────────
// Node 25 ships a built-in `localStorage` that is a stub with no methods.
// Replace it with a real in-memory implementation for our tests.

function makeLocalStorageStub(): Storage {
  const store: Record<string, string> = {}
  return {
    getItem: (key: string) => store[key] ?? null,
    setItem: (key: string, val: string) => { store[key] = val },
    removeItem: (key: string) => { delete store[key] },
    clear: () => { Object.keys(store).forEach(k => delete store[k]) },
    key: (index: number) => Object.keys(store)[index] ?? null,
    get length() { return Object.keys(store).length },
  } as Storage
}

// ── matchMedia stub helpers ──────────────────────────────────────────────────

type MediaQueryListener = (e: MediaQueryListEvent) => void

interface MockMQL {
  matches: boolean
  _listeners: MediaQueryListener[]
  addEventListener(type: 'change', fn: MediaQueryListener): void
  removeEventListener(type: 'change', fn: MediaQueryListener): void
  dispatchChange(matches: boolean): void
}

function makeMockMQL(matches: boolean): MockMQL {
  const mql: MockMQL = {
    matches,
    _listeners: [],
    addEventListener(_type: 'change', fn: MediaQueryListener) {
      mql._listeners.push(fn)
    },
    removeEventListener(_type: 'change', fn: MediaQueryListener) {
      mql._listeners = mql._listeners.filter(l => l !== fn)
    },
    dispatchChange(newMatches: boolean) {
      mql.matches = newMatches
      const ev = { matches: newMatches } as MediaQueryListEvent
      mql._listeners.forEach(fn => fn(ev))
    },
  }
  return mql
}

function stubMatchMedia(mql: MockMQL) {
  Object.defineProperty(window, 'matchMedia', {
    writable: true,
    configurable: true,
    value: vi.fn().mockReturnValue(mql),
  })
}

// ── Setup / teardown ─────────────────────────────────────────────────────────

let lsStub: Storage

beforeEach(() => {
  // Install a fresh localStorage stub before each test
  lsStub = makeLocalStorageStub()
  vi.stubGlobal('localStorage', lsStub)

  // Reset data-theme before each test
  delete document.documentElement.dataset['theme']
})

afterEach(() => {
  vi.restoreAllMocks()
  vi.unstubAllGlobals()
})

// ── Tests ────────────────────────────────────────────────────────────────────

describe('bootstrapTheme', () => {
  it('no localStorage.theme + OS=dark → data-theme=dark', () => {
    const mql = makeMockMQL(true)
    stubMatchMedia(mql)

    bootstrapTheme()

    expect(document.documentElement.dataset['theme']).toBe('dark')
  })

  it('localStorage.theme=light + OS=dark → data-theme=light', () => {
    const mql = makeMockMQL(true)
    stubMatchMedia(mql)

    lsStub.setItem('theme', 'light')
    bootstrapTheme()

    expect(document.documentElement.dataset['theme']).toBe('light')
  })

  it('OS theme changes while no override → flips data-theme', () => {
    const mql = makeMockMQL(false) // starts light
    stubMatchMedia(mql)

    bootstrapTheme()
    expect(document.documentElement.dataset['theme']).toBe('light')

    mql.dispatchChange(true) // OS → dark
    expect(document.documentElement.dataset['theme']).toBe('dark')

    mql.dispatchChange(false) // OS → light
    expect(document.documentElement.dataset['theme']).toBe('light')
  })

  it('OS theme changes while override is set → data-theme does NOT change', () => {
    const mql = makeMockMQL(false) // starts light
    stubMatchMedia(mql)

    lsStub.setItem('theme', 'light')
    bootstrapTheme()
    expect(document.documentElement.dataset['theme']).toBe('light')

    mql.dispatchChange(true) // OS → dark, but override active
    expect(document.documentElement.dataset['theme']).toBe('light')
  })
})

describe('setTheme', () => {
  it('setTheme(null) re-syncs with current OS preference (dark)', () => {
    const mql = makeMockMQL(true) // OS = dark
    stubMatchMedia(mql)

    lsStub.setItem('theme', 'light')
    document.documentElement.dataset['theme'] = 'light'

    setTheme(null)

    expect(lsStub.getItem('theme')).toBeNull()
    expect(document.documentElement.dataset['theme']).toBe('dark')
  })

  it('setTheme(null) re-syncs with current OS preference (light)', () => {
    const mql = makeMockMQL(false) // OS = light
    stubMatchMedia(mql)

    lsStub.setItem('theme', 'dark')
    document.documentElement.dataset['theme'] = 'dark'

    setTheme(null)

    expect(lsStub.getItem('theme')).toBeNull()
    expect(document.documentElement.dataset['theme']).toBe('light')
  })

  it('setTheme("dark") writes localStorage and updates data-theme', () => {
    const mql = makeMockMQL(false)
    stubMatchMedia(mql)

    setTheme('dark')

    expect(lsStub.getItem('theme')).toBe('dark')
    expect(document.documentElement.dataset['theme']).toBe('dark')
  })

  it('setTheme("light") writes localStorage and updates data-theme', () => {
    const mql = makeMockMQL(true)
    stubMatchMedia(mql)

    setTheme('light')

    expect(lsStub.getItem('theme')).toBe('light')
    expect(document.documentElement.dataset['theme']).toBe('light')
  })
})

describe('getThemePreference', () => {
  it('no stored key → "system"', () => {
    expect(getThemePreference()).toBe('system')
  })

  it('stored "light" → "light"', () => {
    lsStub.setItem('theme', 'light')
    expect(getThemePreference()).toBe('light')
  })

  it('stored "dark" → "dark"', () => {
    lsStub.setItem('theme', 'dark')
    expect(getThemePreference()).toBe('dark')
  })
})