export const CONSENT_VERSION = 1 as const
export const CONSENT_STORAGE_KEY = 'memento-consent-v1'
export const CONSENT_COOKIE_NAME = 'memento-cookie-consent'
const CONSENT_COOKIE_MAX_AGE = 60 * 60 * 24 * 365

export type ConsentRecord = {
  version: typeof CONSENT_VERSION
  necessary: true
  analytics: boolean
  marketing: boolean
  updatedAt: string
}

export const CONSENT_CHANGE_EVENT = 'memento-consent-change'
export const OPEN_COOKIE_PREFERENCES_EVENT = 'memento-open-cookie-preferences'

function isBrowser(): boolean {
  return typeof window !== 'undefined'
}

function parseRecord(raw: unknown): ConsentRecord | null {
  if (!raw || typeof raw !== 'object') return null
  const o = raw as Partial<ConsentRecord>
  if (o.version !== CONSENT_VERSION) return null
  if (o.necessary !== true) return null
  if (typeof o.analytics !== 'boolean' || typeof o.marketing !== 'boolean') return null
  if (typeof o.updatedAt !== 'string') return null
  return {
    version: CONSENT_VERSION,
    necessary: true,
    analytics: o.analytics,
    marketing: o.marketing,
    updatedAt: o.updatedAt,
  }
}

function readCookie(): ConsentRecord | null {
  if (!isBrowser()) return null
  const match = document.cookie
    .split(';')
    .map((s) => s.trim())
    .find((s) => s.startsWith(`${CONSENT_COOKIE_NAME}=`))
  if (!match) return null
  try {
    const encoded = match.slice(CONSENT_COOKIE_NAME.length + 1)
    const json = decodeURIComponent(atob(encoded))
    return parseRecord(JSON.parse(json))
  } catch {
    return null
  }
}

function writeCookie(record: ConsentRecord): void {
  if (!isBrowser()) return
  const encoded = btoa(encodeURIComponent(JSON.stringify(record)))
  document.cookie = `${CONSENT_COOKIE_NAME}=${encoded};path=/;max-age=${CONSENT_COOKIE_MAX_AGE};samesite=lax`
}

export function getConsent(): ConsentRecord | null {
  if (!isBrowser()) return null
  try {
    const fromStorage = localStorage.getItem(CONSENT_STORAGE_KEY)
    if (fromStorage) {
      const parsed = parseRecord(JSON.parse(fromStorage))
      if (parsed) return parsed
    }
  } catch {
    // ignore corrupt storage
  }
  return readCookie()
}

export function hasConsentChoice(): boolean {
  return getConsent() !== null
}

export function hasAnalyticsConsent(): boolean {
  return getConsent()?.analytics === true
}

export function hasMarketingConsent(): boolean {
  return getConsent()?.marketing === true
}

export function setConsent(partial: Pick<ConsentRecord, 'analytics' | 'marketing'>): ConsentRecord {
  const record: ConsentRecord = {
    version: CONSENT_VERSION,
    necessary: true,
    analytics: partial.analytics,
    marketing: partial.marketing,
    updatedAt: new Date().toISOString(),
  }
  if (isBrowser()) {
    localStorage.setItem(CONSENT_STORAGE_KEY, JSON.stringify(record))
    writeCookie(record)
    window.dispatchEvent(new CustomEvent(CONSENT_CHANGE_EVENT, { detail: record }))
  }
  return record
}

export function acceptEssentialsOnly(): ConsentRecord {
  return setConsent({ analytics: false, marketing: false })
}

export function acceptAllOptional(): ConsentRecord {
  return setConsent({ analytics: true, marketing: false })
}

export function openCookiePreferences(): void {
  if (!isBrowser()) return
  window.dispatchEvent(new CustomEvent(OPEN_COOKIE_PREFERENCES_EVENT))
}