import { escapeChar } from "./html.js";

function bufferColToDomOffset(lineText, col) {
  let offset = 0;
  for (let i = 0; i < col && i < lineText.length; i++)
    offset += escapeChar(lineText[i]).length;
  return offset;
}

function findTextNode(parent, targetOffset) {
  let remaining = targetOffset;
  const walker = document.createTreeWalker(parent, NodeFilter.SHOW_TEXT);
  let node;
  while ((node = walker.nextNode())) {
    if (remaining <= node.textContent.length)
      return { node, offset: remaining };
    remaining -= node.textContent.length;
  }
  return { node: parent, offset: parent.childNodes.length };
}

function posToElement(line, col, buffer) {
  const spans = document.querySelectorAll("#text > span");
  if (line >= spans.length) return null;
  const span = spans[line];
  const range = document.createRange();
  const lineText = buffer[line] || "";
  const offset = bufferColToDomOffset(lineText, col);
  const tn = findTextNode(span, offset);
  range.setStart(tn.node, tn.offset);
  range.collapse(true);
  const rect = range.getBoundingClientRect();
  return { x: rect.left, y: rect.top, height: rect.height };
}

export function elementToPos(x, y, buffer) {
  const spans = document.querySelectorAll("#text > span");
  let bestLine = 0;
  let bestDistY = Infinity;

  for (let i = 0; i < spans.length; i++) {
    const rect = spans[i].getBoundingClientRect();
    const midY = rect.top + rect.height / 2;
    const distY = Math.abs(y - midY);
    if (distY < bestDistY) {
      bestDistY = distY;
      bestLine = i;
    }
  }

  let bestCol = 0;
  let bestDistX = Infinity;
  const lineText = buffer[bestLine] || "";
  for (let c = 0; c <= lineText.length; c++) {
    const pos = posToElement(bestLine, c, buffer);
    if (!pos) continue;
    const dist = Math.abs(x - pos.x);
    if (dist < bestDistX) {
      bestDistX = dist;
      bestCol = c;
    }
  }

  return { line: bestLine, col: bestCol };
}