import fs from "fs/promises";
import path from "path";

const DOCS_ROOT = path.join(process.cwd(), "content", "zhouyi", "docs");
const OTHER_ROOT = path.join(DOCS_ROOT, "other");

export type LearnVariant = "traditional" | "simplified";

function getVariantRoot(variant: LearnVariant): string {
  return variant === "traditional" ? DOCS_ROOT : OTHER_ROOT;
}

export async function listGuaMarks(
  variant: LearnVariant = "traditional",
): Promise<string[]> {
  const dir = getVariantRoot(variant);
  const entries = await fs.readdir(dir, { withFileTypes: true });
  return entries
    .filter((entry) => entry.isDirectory() && /^\d{2}\./.test(entry.name))
    .map((entry) => entry.name)
    .sort();
}

export async function readGuaMarkdown(guaMark: string): Promise<string> {
  const filePath = path.join(DOCS_ROOT, guaMark, "index.md");
  return fs.readFile(filePath, "utf-8");
}

export async function readLearnMarkdown(
  guaMark: string,
  variant: LearnVariant = "traditional",
): Promise<string> {
  const root = getVariantRoot(variant);
  const filePath =
    guaMark === "index"
      ? path.join(root, "index.md")
      : path.join(root, guaMark, "index.md");
  return fs.readFile(filePath, "utf-8");
}

export function stripFrontmatter(content: string): string {
  if (!content.startsWith("---")) {
    return content;
  }
  const end = content.indexOf("---", 3);
  if (end === -1) {
    return content;
  }
  return content.slice(end + 3).trimStart();
}

export function extractZhangMingRen(guaDetail: string): string | undefined {
  return guaDetail
    .match(/(\*\*台灣張銘仁[\s\S]*?)(?=周易第\d+卦)/)?.[1]
    ?.replaceAll("\n\n", "\n");
}

export function extractChangeDetails(
  guaDetail: string,
  guaChange: string,
  guaTitle: string,
): string[] {
  const changeList: string[] = [];
  if (guaChange === "无变爻") {
    return changeList;
  }

  guaChange
    .split(":")[1]
    .trim()
    .split(",")
    .forEach((change) => {
      const detail = guaDetail
        .match(`(\\*\\*${change}變卦[\\s\\S]*?)(?=${guaTitle}|$)`)?.[1]
        ?.replaceAll("\n\n", "\n");
      if (detail) {
        changeList.push(detail.trim());
      }
    });

  return changeList;
}

export function getGuaNumber(guaMark: string): number {
  return parseInt(guaMark.split(".")[0], 10);
}

export function getGuaName(guaMark: string): string {
  return guaMark.split(".").slice(1).join(".");
}