type GreetingPeriod = "morning" | "noon" | "afternoon" | "evening" | "late-night";

type GreetingVariant = {
  readonly salutation: (name: string) => string;
  readonly question: string;
};

const greetingVariants: Record<GreetingPeriod, readonly GreetingVariant[]> = {
  morning: [
    { salutation: (name) => `早上好，${name}。`, question: "今天最想先看什么？" },
    { salutation: (name) => `${name}，早安。`, question: "今天最该关注哪件事？" },
    { salutation: (name) => `早上好，${name}。`, question: "想从哪个问题开始？" },
  ],
  noon: [
    { salutation: (name) => `中午好，${name}。`, question: "现在最想理清哪件事？" },
    { salutation: (name) => `${name}，中午好。`, question: "什么问题最需要方向？" },
    { salutation: (name) => `午间好，${name}。`, question: "事业、关系或选择，想先聊哪个？" },
  ],
  afternoon: [
    { salutation: (name) => `${name}，下午好。`, question: "现在最想推进哪件事？" },
    { salutation: (name) => `下午好，${name}。`, question: "今天想先理清什么？" },
    { salutation: (name) => `${name}，下午好。`, question: "事业、关系或选择，想先聊哪个？" },
  ],
  evening: [
    { salutation: (name) => `晚上好，${name}。`, question: "今天最挂心的是哪件事？" },
    { salutation: (name) => `${name}，晚上好。`, question: "此刻最想聊哪件事？" },
    { salutation: (name) => `晚上好，${name}。`, question: "把心里的问题告诉我吧。" },
  ],
  "late-night": [
    { salutation: (name) => `夜深了，${name}。`, question: "此刻最想问什么？" },
    { salutation: (name) => `${name}，还没休息吗？`, question: "想从哪件事说起？" },
    { salutation: (name) => `这么晚还醒着，${name}。`, question: "直接说说最在意的问题吧。" },
  ],
};

export type StartGreetingParts = {
  readonly salutation: string;
  readonly question: string;
};

export function createStartGreetingParts(
  name: string,
  now = new Date(),
  variantSelection = Math.random(),
): StartGreetingParts {
  const displayName = name.trim() || "你好";
  const hour = now.getHours();
  const period: GreetingPeriod = hour >= 5 && hour < 11
    ? "morning"
    : hour >= 11 && hour < 14
      ? "noon"
      : hour >= 14 && hour < 18
        ? "afternoon"
        : hour >= 18 && hour < 23 ? "evening" : "late-night";
  const variants = greetingVariants[period];
  const index = Math.min(Math.max(Math.floor(variantSelection * variants.length), 0), variants.length - 1);
  const variant = variants[index]!;
  return { salutation: variant.salutation(displayName), question: variant.question };
}

export function createStartGreeting(
  name: string,
  now = new Date(),
  variantSelection = Math.random(),
): string {
  const parts = createStartGreetingParts(name, now, variantSelection);
  return `${parts.salutation}${parts.question}`;
}

export function createOnboardingFallbackGreeting(name: string): string {
  return `${name.trim()}，从你此刻最关心的问题开始吧。`;
}