import { allMountainNames } from "./mountains.ts";

/**
 * One client property datum — the dwelling input each 风水 art reads its
 * slice of: xuankong needs `sitting` plus a completion date (period 运),
 * bazhai needs `sitting` alone (宅卦). Facing is always derived as the
 * opposite mountain, never stored.
 */
export interface PropertyDatum {
  /** Display label, e.g. "太古城 3座 12A". */
  readonly label: string;
  /** 坐山 — one of the 二十四山 characters. */
  readonly sitting: string;
  /** Completion (落成) Gregorian year; anchors the 玄空 period 运. */
  readonly completionYear: number;
  /** Optional exact completion date for 立春-accurate period resolution. */
  readonly completionMonth?: number;
  readonly completionDay?: number;
  readonly notes?: string;
}

export function describe(value: unknown): string {
  if (value === null) return "null";
  if (value === undefined) return "missing";
  if (typeof value === "string") return JSON.stringify(value);
  if (typeof value === "object") return Array.isArray(value) ? "an array" : "an object";
  return String(value);
}

function propertyInt(value: unknown, min: number, max: number): value is number {
  return typeof value === "number" && Number.isInteger(value) && value >= min && value <= max;
}

/**
 * Validate an untrusted value (parsed JSON, request body) into a
 * `PropertyDatum`. Throws with an actionable message on the first invalid
 * field; `path` prefixes messages so callers can point at e.g. `properties[2]`.
 */
export function validatePropertyDatum(value: unknown, path = "property"): PropertyDatum {
  if (typeof value !== "object" || value === null || Array.isArray(value)) {
    throw new Error(`${path} must be an object, got ${describe(value)}`);
  }
  const obj = value as Record<string, unknown>;

  const label = obj["label"];
  if (typeof label !== "string" || label.trim() === "") {
    throw new Error(`${path}.label must be a non-empty string, got ${describe(label)}`);
  }

  const sitting = obj["sitting"];
  if (typeof sitting !== "string" || !allMountainNames().includes(sitting)) {
    throw new Error(
      `${path}.sitting must be one of the 二十四山 (${allMountainNames().join(" ")}), got ${describe(sitting)}`,
    );
  }

  const completionYear = obj["completionYear"];
  if (!propertyInt(completionYear, 1, 9999)) {
    throw new Error(
      `${path}.completionYear must be an integer year, got ${describe(completionYear)}`,
    );
  }

  const month = obj["completionMonth"] ?? undefined;
  const day = obj["completionDay"] ?? undefined;
  if ((month === undefined) !== (day === undefined)) {
    throw new Error(
      `${path}: completionMonth and completionDay travel together (both needed for 立春-accurate period resolution)`,
    );
  }
  if (month !== undefined && !propertyInt(month, 1, 12)) {
    throw new Error(`${path}.completionMonth must be an integer 1-12, got ${describe(month)}`);
  }
  if (day !== undefined && !propertyInt(day, 1, 31)) {
    throw new Error(`${path}.completionDay must be an integer 1-31, got ${describe(day)}`);
  }

  const notes = obj["notes"] ?? undefined;
  if (notes !== undefined && typeof notes !== "string") {
    throw new Error(`${path}.notes must be a string when present, got ${describe(notes)}`);
  }

  return {
    label: label.trim(),
    sitting,
    completionYear,
    ...(month !== undefined && day !== undefined
      ? { completionMonth: month, completionDay: day }
      : {}),
    ...(notes !== undefined && notes.trim() !== "" ? { notes: notes.trim() } : {}),
  };
}