export const DEFAULT_SOCIAL_MILESTONE_THRESHOLDS = [1000, 10000] as const;

export type SocialMilestoneKind = `unique_scans_${number}`;

/**
 * Staging can set SOCIAL_MILESTONE_THRESHOLDS=1 (or e.g. 1,2) so the complete
 * flow is testable without fabricating thousands of scans. Production keeps
 * the conservative defaults unless its environment explicitly changes them.
 */
export function getSocialMilestoneThresholds(): number[] {
  const configured = process.env.SOCIAL_MILESTONE_THRESHOLDS;
  if (!configured) return [...DEFAULT_SOCIAL_MILESTONE_THRESHOLDS];

  const thresholds = Array.from(new Set(
    configured.split(',')
      .map(value => Number(value.trim()))
      .filter(value => Number.isInteger(value) && value > 0 && value <= 1_000_000)
  )).sort((a, b) => a - b);

  return thresholds.length ? thresholds : [...DEFAULT_SOCIAL_MILESTONE_THRESHOLDS];
}

/**
 * Channels the consent dialog may offer. A channel is only offered where a
 * publisher is actually configured - asking for consent for a post that nobody
 * can publish would be dishonest. Server-side read; the dialog receives the
 * resulting list in its payload.
 */
export function getEnabledSocialChannels(): SocialChannel[] {
  const configured = (process.env.SOCIAL_MILESTONE_CHANNELS || 'x')
    .split(',').map(value => value.trim().toLowerCase()).filter(isSocialChannel);
  return configured.length ? Array.from(new Set(configured)) : ['x'];
}

const useCaseLabels: Record<string, string> = {
  menu_pdf: 'menu QR code',
  marketing_campaign: 'campaign QR code',
  vcard: 'digital business-card QR code',
  event: 'event QR code',
  feedback: 'feedback QR code',
};

export function milestoneKind(threshold: number): SocialMilestoneKind {
  return `unique_scans_${threshold}` as SocialMilestoneKind;
}

export function milestoneThreshold(kind: string): number | null {
  const result = /^unique_scans_(\d+)$/.exec(kind);
  return result ? Number(result[1]) : null;
}

export type SocialLocale = 'en' | 'de';

export type SocialMilestoneCard = {
  version: 'milestone-card-v2';
  language: SocialLocale;
  qrTitle: string;
  label: string;
  title: string;
  totalScans: number;
  totalUniqueScans: number;
  milestoneThreshold: number;
  reachedAt: string;
  trend: {
    points: Array<{ at: string; total: number }>;
    startLabel: string;
    endLabel: string;
    target: number;
    ceiling: number;
  } | null;
};

export function isCompleteSocialMilestoneCard(value: unknown): value is SocialMilestoneCard {
  if (!value || typeof value !== 'object') return false;
  const card = value as Partial<SocialMilestoneCard>;
  const trend = card.trend;
  return card.version === 'milestone-card-v2'
    && typeof card.qrTitle === 'string'
    && typeof card.totalScans === 'number'
    && Number.isFinite(card.totalScans)
    && typeof card.totalUniqueScans === 'number'
    && Number.isFinite(card.totalUniqueScans)
    && Boolean(trend)
    && Array.isArray(trend?.points)
    && trend.points.length >= 2
    && trend.points.every(point => typeof point?.at === 'string' && typeof point?.total === 'number');
}

export function socialLocale(value?: string | null): SocialLocale {
  return value === 'de' ? 'de' : 'en';
}

export function usageLabel(primaryUseCase: string | null, locale: SocialLocale = 'en'): string {
  if (locale === 'de') {
    const german: Record<string, string> = { menu_pdf: 'Speisekarten-QR-Code', marketing_campaign: 'Kampagnen-QR-Code', vcard: 'Visitenkarten-QR-Code', event: 'Event-QR-Code', feedback: 'Feedback-QR-Code' };
    return (primaryUseCase && german[primaryUseCase]) || 'QR-Code';
  }
  return (primaryUseCase && useCaseLabels[primaryUseCase]) || 'QR code';
}

export function buildMilestonePost(primaryUseCase: string | null, threshold: number, xHandle?: string | null, locale: SocialLocale = 'en'): string {
  const count = threshold.toLocaleString(locale === 'de' ? 'de-DE' : 'en-US');
  const base = locale === 'de'
    ? `Ein ${usageLabel(primaryUseCase, locale)} hat gerade ${count} eindeutige Scans erreicht. 🎉`
    : `A ${usageLabel(primaryUseCase, locale)} just reached ${count} unique scans. 🎉`;
  return xHandle ? `${base} By @${xHandle.replace(/^@/, '')}.` : base;
}

export function buildMilestoneCard(primaryUseCase: string | null, threshold: number, locale: SocialLocale) {
  return { version: 'milestone-card-v1', language: locale, threshold, label: usageLabel(primaryUseCase, locale), title: locale === 'de' ? 'Erfolgsmeilenstein' : 'Success milestone' };
}

export function buildMilestonePostForQr(primaryUseCase: string | null, totalUniqueScans: number, xHandle: string | null | undefined, locale: SocialLocale, qrTitle: string): string {
  const count = totalUniqueScans.toLocaleString(locale === 'de' ? 'de-DE' : 'en-US');
  const rawSubject = qrTitle.trim() || usageLabel(primaryUseCase, locale);
  const subject = rawSubject.length > 72 ? `${rawSubject.slice(0, 69).trimEnd()}…` : rawSubject;
  const scanLabel = locale === 'de'
    ? `${count} ${totalUniqueScans === 1 ? 'verifizierten eindeutigen Scan' : 'verifizierte eindeutige Scans'}`
    : `${count} verified unique ${totalUniqueScans === 1 ? 'scan' : 'scans'}`;
  const base = locale === 'de'
    ? `QR-Meilenstein erreicht.\n\n„${subject}“ hat ${scanLabel} erzielt.\n\nErstellt und gemessen mit QR Master.`
    : `QR milestone unlocked.\n\n“${subject}” has reached ${scanLabel}.\n\nCreated and measured with QR Master.`;
  if (!xHandle) return base;
  const mention = locale === 'de' ? 'Glückwunsch' : 'Congratulations';
  return `${base}\n\n${mention} @${xHandle.replace(/^@/, '')}.`;
}

export function buildMilestoneCardSnapshot(input: {
  primaryUseCase: string | null;
  qrTitle: string;
  totalScans: number;
  totalUniqueScans: number;
  milestoneThreshold: number;
  reachedAt: Date;
  trend: SocialMilestoneCard['trend'];
  locale: SocialLocale;
}): SocialMilestoneCard {
  return {
    version: 'milestone-card-v2',
    language: input.locale,
    qrTitle: input.qrTitle,
    label: usageLabel(input.primaryUseCase, input.locale),
    title: input.locale === 'de' ? 'Erfolgsmeilenstein' : 'Success milestone',
    totalScans: input.totalScans,
    totalUniqueScans: input.totalUniqueScans,
    milestoneThreshold: input.milestoneThreshold,
    reachedAt: input.reachedAt.toISOString(),
    trend: input.trend,
  };
}

export function normalizeXHandle(value: string): string | null {
  const handle = value.trim().replace(/^@/, '');
  return /^[A-Za-z0-9_]{1,15}$/.test(handle) ? handle : null;
}

export function normalizeInstagramHandle(value: string): string | null {
  const handle = value.trim().replace(/^@/, '');
  return /^[A-Za-z0-9._]{1,30}$/.test(handle) ? handle : null;
}

/**
 * Publishing channels of the QR Master brand accounts.
 *
 * Consent is bound to a channel: agreeing to a post on X says nothing about
 * Instagram. Every channel therefore carries its own approval, its own text and
 * its own handle.
 */
export const SOCIAL_CHANNELS = ['x', 'instagram'] as const;
export type SocialChannel = typeof SOCIAL_CHANNELS[number];

export function isSocialChannel(value: unknown): value is SocialChannel {
  return typeof value === 'string' && (SOCIAL_CHANNELS as readonly string[]).includes(value);
}

export function normalizeChannelHandle(channel: SocialChannel, value: string): string | null {
  return channel === 'instagram' ? normalizeInstagramHandle(value) : normalizeXHandle(value);
}

function instagramHashtags(locale: SocialLocale): string {
  return locale === 'de'
    ? '#qrcode #qrcodes #marketing #kleinunternehmen #analytics #digitalisierung'
    : '#qrcode #qrcodes #qrcodemarketing #smallbusiness #marketing #analytics';
}

/**
 * The post split into the parts the consent dialog recombines while the
 * customer types a handle. Server and client must never build this text
 * differently - what stands in the preview is what gets published.
 */
export function milestonePostParts(input: {
  channel: SocialChannel;
  primaryUseCase: string | null;
  totalUniqueScans: number;
  locale: SocialLocale;
  qrTitle: string;
  shareUrl: string;
}) {
  return {
    head: buildMilestonePostForQr(input.primaryUseCase, input.totalUniqueScans, null, input.locale, input.qrTitle),
    // A link in an Instagram caption is not clickable, so the share URL would
    // be dead weight there. Hashtags do the reach work instead.
    tail: input.channel === 'instagram' ? `\n\n${instagramHashtags(input.locale)}` : `\n\n${input.shareUrl}`,
    mentionWord: input.locale === 'de' ? 'Glückwunsch' : 'Congratulations',
  };
}

export function buildChannelPost(input: Parameters<typeof milestonePostParts>[0] & { handle: string | null }): string {
  const { head, tail, mentionWord } = milestonePostParts(input);
  const mention = input.handle ? `\n\n${mentionWord} @${input.handle.replace(/^@/, '')}.` : '';
  return `${head}${mention}${tail}`;
}