/**
 * Flock「按密度估算货运等级」= NMFTA Docket 2025-1 十三档密度表（2025-07-19 生效）
 *
 * 权威来源（禁止臆造区间）：
 * - NMFTA Disposition Bulletin / Docket 2025-1（13-sub density scale）
 * - Flock 官网 i 弹层：Total Volume / Density / Density-based Freight Class
 *   实测样例：6×48×40×48、2000 lb → 320 ft³、6.25 PCF → Class 125
 *
 * 关系（与「参数越小等级越高」的正确表述）：
 * - 密度 PCF = 总重(lb) ÷ 总体积(ft³)
 * - 体积越大或重量越轻 → PCF ↓ → 货运等级数字 ↑（越贵，占车容多）
 * - 体积越小或重量越重 → PCF ↑ → 货运等级数字 ↓（越便宜，装得下更多重量）
 *
 * 公式：
 *   cuFt = (L_in × W_in × H_in × 件数) / 1728
 *   PCF  = 总重_lb / cuFt
 *   等级 = 下表查表（区间均为「≥min 且 <max」，末档 ≥50 → 50）
 *
 * 密度推算只会落到下表 13 档。下拉中的 77.5 / 110 / 150 / 200 / 500
 * 属于商品条件分等（handling/stowability/liability），不能由密度公式算出。
 */

export const CUBIC_INCHES_PER_CU_FT = 1728;

/**
 * NMFTA 2025 十三档：自高密度→低密度。
 * 文案口径：Sub N · min – <max pcf → Class C（与 NMFTA “X but less than Y” 一致）
 */
export const NMFC_DENSITY_CLASS_BANDS: ReadonlyArray<{
  sub: number;
  minPcf: number;
  maxPcf: number;
  freightClass: string;
  /** 中文区间说明，供 tip / 单测展示 */
  rangeLabelZh: string;
}> = [
  {
    sub: 13,
    minPcf: 50,
    maxPcf: Number.POSITIVE_INFINITY,
    freightClass: "50",
    rangeLabelZh: "≥50",
  },
  {
    sub: 12,
    minPcf: 35,
    maxPcf: 50,
    freightClass: "55",
    rangeLabelZh: "35 – <50",
  },
  {
    sub: 11,
    minPcf: 30,
    maxPcf: 35,
    freightClass: "60",
    rangeLabelZh: "30 – <35",
  },
  {
    sub: 10,
    minPcf: 22.5,
    maxPcf: 30,
    freightClass: "65",
    rangeLabelZh: "22.5 – <30",
  },
  {
    sub: 9,
    minPcf: 15,
    maxPcf: 22.5,
    freightClass: "70",
    rangeLabelZh: "15 – <22.5",
  },
  {
    sub: 8,
    minPcf: 12,
    maxPcf: 15,
    freightClass: "85",
    rangeLabelZh: "12 – <15",
  },
  {
    sub: 7,
    minPcf: 10,
    maxPcf: 12,
    freightClass: "92.5",
    rangeLabelZh: "10 – <12",
  },
  {
    sub: 6,
    minPcf: 8,
    maxPcf: 10,
    freightClass: "100",
    rangeLabelZh: "8 – <10",
  },
  {
    sub: 5,
    minPcf: 6,
    maxPcf: 8,
    freightClass: "125",
    rangeLabelZh: "6 – <8",
  },
  {
    sub: 4,
    minPcf: 4,
    maxPcf: 6,
    freightClass: "175",
    rangeLabelZh: "4 – <6",
  },
  {
    sub: 3,
    minPcf: 2,
    maxPcf: 4,
    freightClass: "250",
    rangeLabelZh: "2 – <4",
  },
  {
    sub: 2,
    minPcf: 1,
    maxPcf: 2,
    freightClass: "300",
    rangeLabelZh: "1 – <2",
  },
  {
    sub: 1,
    minPcf: 0,
    maxPcf: 1,
    freightClass: "400",
    rangeLabelZh: "<1",
  },
];

/** 密度公式绝不会给出的档（仅商品条件分等；Flock 下拉仍可手选） */
export const NMFC_NON_DENSITY_FREIGHT_CLASSES = [
  "77.5",
  "110",
  "150",
  "200",
  "500",
] as const;

export type FreightDensityInput = {
  lengthIn: number;
  widthIn: number;
  heightIn: number;
  quantity: number;
  totalWeightLb: number;
};

export type FreightDensityResult = {
  cubicFeet: number;
  densityPcf: number;
  /** 查表得到的密度分等（仅 13 档之一） */
  suggestedClass: string;
  rangeLabelZh: string;
};

export function computeFreightDensity(
  input: FreightDensityInput,
): FreightDensityResult | null {
  const { lengthIn, widthIn, heightIn, quantity, totalWeightLb } = input;
  if (
    !(lengthIn > 0) ||
    !(widthIn > 0) ||
    !(heightIn > 0) ||
    !(quantity > 0) ||
    !(totalWeightLb > 0)
  ) {
    return null;
  }
  const cubicInches = lengthIn * widthIn * heightIn * quantity;
  const cubicFeet = cubicInches / CUBIC_INCHES_PER_CU_FT;
  if (!(cubicFeet > 0)) return null;
  const densityPcf = totalWeightLb / cubicFeet;
  if (!Number.isFinite(densityPcf) || densityPcf <= 0) return null;
  const matched = matchDensityBand(densityPcf);
  if (!matched) return null;
  return {
    cubicFeet,
    densityPcf,
    suggestedClass: matched.freightClass,
    rangeLabelZh: matched.rangeLabelZh,
  };
}

export function matchDensityBand(pcf: number) {
  if (!Number.isFinite(pcf) || pcf < 0) return null;
  for (const band of NMFC_DENSITY_CLASS_BANDS) {
    if (pcf >= band.minPcf && pcf < band.maxPcf) {
      return band;
    }
  }
  return null;
}

export function densityPcfToFreightClass(pcf: number): string | null {
  return matchDensityBand(pcf)?.freightClass ?? null;
}

/** 完整十三档表（密度↑ → 等级数字↓） */
export function formatNmfcDensityClassChartZh(): string {
  const rows = [...NMFC_DENSITY_CLASS_BANDS]
    .slice()
    .reverse()
    .map(
      (b) =>
        `${b.rangeLabelZh} lbs/ft³ → 等级 ${b.freightClass}`,
    );
  return [
    "密度越高 → 等级数字越低（越便宜）；体积大/重量轻 → 等级越高。",
    "NMFTA 2025 十三档（与 Flock 密度推算一致）：",
    ...rows,
    "注：77.5 / 110 / 150 / 200 / 500 不能由密度算出，仅商品条件分等可选手选。",
  ].join("\n");
}

/** 官网 i 弹层：有尺寸重量时三行明细；否则公式 + 完整分档表 */
export function formatFreightClassDensityTip(
  density: FreightDensityResult | null,
): string {
  if (!density) {
    return [
      "总体积 = (长×宽×高×件数) ÷ 1728（立方英尺）",
      "密度 = 总重(磅) ÷ 总体积",
      formatNmfcDensityClassChartZh(),
    ].join("\n");
  }
  return [
    `总体积：${density.cubicFeet.toFixed(2)} ft³`,
    `密度：${density.densityPcf.toFixed(2)} lbs/ft³（区间 ${density.rangeLabelZh}）`,
    `基于密度的货运等级：${density.suggestedClass}`,
  ].join("\n");
}

/** 手选等级与密度推算不一致时返回提示；一致或「按密度估算」则 null */
export function freightClassDensityMismatchMessage(
  selectedClass: string,
  density: FreightDensityResult | null,
): string | null {
  if (!density) return null;
  if (!selectedClass || selectedClass === "density") return null;
  const selected = selectedClass.trim();
  if (selected === density.suggestedClass) return null;
  return `根据货物尺寸与重量推算，请选择货运等级 ${density.suggestedClass}。`;
}

export function parsePositiveNumber(raw: string): number | null {
  const n = Number(String(raw).replace(/,/g, "").trim());
  return Number.isFinite(n) && n > 0 ? n : null;
}