import { useEffect, useRef, useState } from "react";
import { Platform } from "react-native";

export type TextSelection = { text: string; x: number; y: number };

// Expand a DOM range outward so its ends land on whitespace boundaries, i.e.
// snap a partial selection to whole words (punctuation stays attached to its
// word). Operates in-place; only touches text nodes (nodeType 3).
function expandRangeToWords(range: any) {
  const startNode: any = range.startContainer;
  if (startNode && startNode.nodeType === 3) {
    const text: string = startNode.textContent || "";
    let s = range.startOffset;
    while (s > 0 && !/\s/.test(text[s - 1])) s--;
    range.setStart(startNode, s);
  }

  const endNode: any = range.endContainer;
  if (endNode && endNode.nodeType === 3) {
    const text: string = endNode.textContent || "";
    let e = range.endOffset;
    while (e < text.length && !/\s/.test(text[e])) e++;
    range.setEnd(endNode, e);
  }
}

// Web-only: tracks the current text selection inside `containerRef` and exposes
// its page position so a floating action (e.g. "Review this passage") can be
// placed next to it. No-op on native, where arbitrary text selection isn't
// available. Pass `enabled=false` to pause tracking (e.g. after submission).
export function useTextSelection(enabled: boolean) {
  const containerRef = useRef<any>(null);
  const popupRef = useRef<any>(null);
  const [selection, setSelection] = useState<TextSelection | null>(null);

  useEffect(() => {
    if (Platform.OS !== "web" || !enabled) {
      setSelection(null);
      return;
    }

    const onMouseUp = (e: any) => {
      // Ignore clicks inside the floating popup so it doesn't clear the selection.
      if (popupRef.current && popupRef.current.contains(e.target)) return;

      const w: any = window;
      const sel = w.getSelection ? w.getSelection() : null;
      if (!sel || sel.isCollapsed || sel.rangeCount === 0) {
        setSelection(null);
        return;
      }

      const range = sel.getRangeAt(0);
      const container = containerRef.current;
      if (container && !container.contains(range.commonAncestorContainer)) {
        setSelection(null);
        return;
      }

      // Snap the selection to whole words and reflect it in the visible highlight.
      expandRangeToWords(range);
      try {
        sel.removeAllRanges();
        sel.addRange(range);
      } catch {
        // Some browsers guard against programmatic selection changes; ignore.
      }

      const text = String(sel.toString()).trim();
      if (!text) {
        setSelection(null);
        return;
      }

      const rect = range.getBoundingClientRect();
      setSelection({
        text,
        x: rect.left + w.scrollX,
        y: rect.bottom + w.scrollY + 4,
      });
    };

    const doc: any = document;
    doc.addEventListener("mouseup", onMouseUp);
    return () => doc.removeEventListener("mouseup", onMouseUp);
  }, [enabled]);

  const clearBrowserSelection = () => {
    if (Platform.OS === "web") {
      const w: any = window;
      w.getSelection?.().removeAllRanges();
    }
    setSelection(null);
  };

  return { selection, setSelection, containerRef, popupRef, clearBrowserSelection };
}