export type PayloadKind =
  "text" | "url" | "email" | "sms" | "wifi" | "vcard" | "geo";

export interface PayloadFields {
  primary: string;
  secondary?: string;
  tertiary?: string;
  hidden?: boolean;
}

function escapeWifi(value: string): string {
  return value.replace(/[\\;,:"]/gu, (character) => `\\${character}`);
}

function escapeVcard(value: string): string {
  return value
    .replaceAll("\\", "\\\\")
    .replaceAll("\n", "\\n")
    .replaceAll(";", "\\;")
    .replaceAll(",", "\\,");
}

export function buildStructuredPayload(
  kind: PayloadKind,
  fields: PayloadFields,
): string {
  const primary = fields.primary.trim();
  if (!primary) throw new Error("The primary value is required.");
  switch (kind) {
    case "text":
      return fields.primary;
    case "url": {
      const url = new URL(primary);
      if (!["http:", "https:"].includes(url.protocol))
        throw new Error("The URL builder accepts HTTP and HTTPS URLs only.");
      return url.href;
    }
    case "email":
      return `mailto:${encodeURIComponent(primary)}${fields.secondary ? `?subject=${encodeURIComponent(fields.secondary)}` : ""}`;
    case "sms":
      return `SMSTO:${primary}:${fields.secondary ?? ""}`;
    case "wifi": {
      const supplied = (fields.tertiary || "WPA").trim();
      if (!/^(?:WPA|WEP|nopass)$/iu.test(supplied))
        throw new Error("Wi-Fi security must be WPA, WEP, or nopass.");
      const security =
        supplied.toLowerCase() === "nopass" ? "nopass" : supplied.toUpperCase();
      return `WIFI:T:${security};S:${escapeWifi(primary)};P:${escapeWifi(fields.secondary ?? "")};H:${fields.hidden ? "true" : "false"};;`;
    }
    case "vcard":
      return [
        "BEGIN:VCARD",
        "VERSION:3.0",
        `FN:${escapeVcard(primary)}`,
        fields.secondary ? `TEL:${escapeVcard(fields.secondary)}` : "",
        fields.tertiary ? `EMAIL:${escapeVcard(fields.tertiary)}` : "",
        "END:VCARD",
      ]
        .filter(Boolean)
        .join("\r\n");
    case "geo": {
      const latitude = Number(primary);
      const longitude = Number(fields.secondary);
      if (
        !Number.isFinite(latitude) ||
        latitude < -90 ||
        latitude > 90 ||
        !Number.isFinite(longitude) ||
        longitude < -180 ||
        longitude > 180
      )
        throw new Error("Latitude must be −90…90 and longitude −180…180.");
      return `geo:${latitude},${longitude}`;
    }
  }
}

export function gtinCheckDigit(body: string): number {
  if (!/^\d{1,17}$/u.test(body))
    throw new Error("A GTIN body must contain 1–17 decimal digits.");
  let sum = 0;
  for (
    let index = body.length - 1, position = 0;
    index >= 0;
    index -= 1, position += 1
  )
    sum += Number(body[index]) * (position % 2 === 0 ? 3 : 1);
  return (10 - (sum % 10)) % 10;
}

export function validateGtin(value: string): {
  valid: boolean;
  expected: string;
} {
  if (![8, 12, 13, 14].includes(value.length) || !/^\d+$/u.test(value))
    return {
      valid: false,
      expected: "GTIN length must be 8, 12, 13, or 14 digits.",
    };
  const expected = String(gtinCheckDigit(value.slice(0, -1)));
  return { valid: value.endsWith(expected), expected };
}