import type { BlockHandler, IdentifyResult } from "./handler.type.js";
import { ITEM_SEPARATOR, indentWidth, isBlockBoundary, leavesParagraphOpen } from "./identify.js";
import { isLooseList, renderItemContent, serializeItemTail, splitItemHead } from "./list-item.js";

/** Pattern matching the start of a task list item: `- [ ] `, `- [x] `, etc. */
const TASK_ITEM_RE = /^[-*+] \[([ xX])\] /;

export const taskListHandler = {
  identify(lines: string[], index: number): IdentifyResult | null {
    const first = lines[index].trimStart();
    if (!TASK_ITEM_RE.test(first)) return null;

    const items: string[] = [];
    let currentItemLines: string[] = [];
    let column = 0;
    let i = index;

    while (i < lines.length) {
      const cur = lines[i];

      if (cur.trim() === "") {
        // Blank line — continue if next line is another task item or indented
        if (i + 1 < lines.length) {
          const nextTrimmed = lines[i + 1].trimStart();
          const nextIsTask = TASK_ITEM_RE.test(nextTrimmed);
          const nextInItem = currentItemLines.length > 0 && indentWidth(lines[i + 1]) >= column;
          if (nextIsTask || nextInItem) {
            currentItemLines.push("");
            i++;
            continue;
          }
        }
        break;
      }

      if (currentItemLines.length > 0 && indentWidth(cur) >= column) {
        currentItemLines.push(cur);
        i++;
        continue;
      }

      const trimmed = cur.trimStart();
      if (TASK_ITEM_RE.test(trimmed)) {
        if (currentItemLines.length > 0) {
          items.push(currentItemLines.join("\n"));
        }
        // Keep the checkbox prefix (e.g. "[ ] text" or "[x] text")
        currentItemLines = [trimmed.replace(/^[-*+] /, "")];
        column = indentWidth(cur) + 2;
        i++;
      } else if (
        currentItemLines.length > 0 &&
        !isBlockBoundary(cur) &&
        leavesParagraphOpen(currentItemLines[currentItemLines.length - 1])
      ) {
        currentItemLines.push(cur);
        i++;
      } else {
        break;
      }
    }

    if (currentItemLines.length > 0) {
      items.push(currentItemLines.join("\n"));
    }

    if (items.length === 0) return null;

    return {
      raw: items.join(ITEM_SEPARATOR),
      nextIndex: i,
    };
  },

  render(raw: string): string {
    const items = raw.split(ITEM_SEPARATOR);
    const loose = isLooseList(items);
    const inner = items
      .map((itemRaw) => {
        const checked = /^\[x\] /i.test(itemRaw);
        const text = itemRaw.replace(/^\[([ xX])\] /, "");
        const checkedAttr = checked ? " checked" : "";
        return `<li class="task-list-item"><input type="checkbox" disabled${checkedAttr}> ${renderItemContent(text, loose)}</li>`;
      })
      .join("");

    return `<ul class="task-list">${inner}</ul>`;
  },

  serialize(raw: string): string {
    const items = raw.split(ITEM_SEPARATOR);
    const lines: string[] = [];

    for (const itemRaw of items) {
      const checked = /^\[x\] /i.test(itemRaw);
      const text = itemRaw.replace(/^\[([ xX])\] /, "");
      const marker = checked ? "- [x] " : "- [ ] ";
      const [head, tail] = splitItemHead(text);
      lines.push(marker + head);
      lines.push(...serializeItemTail(tail, head));
    }

    return lines.join("\n");
  },
} satisfies BlockHandler;