import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/services.dart';
import 'markdown_editing.dart';

/// Highlighted markdown source that is either read-only or editable.
class MarkdownView extends StatefulWidget {
  final MarkdownController controller;
  final bool readOnly;
  final double fontSize;
  final FocusNode? focusNode;
  final ScrollController? scrollController;

  const MarkdownView({
    super.key,
    required this.controller,
    this.readOnly = true,
    this.fontSize = 16,
    this.focusNode,
    this.scrollController,
  });

  @override
  MarkdownViewState createState() => MarkdownViewState();
}

class MarkdownViewState extends State<MarkdownView> {
  final _fieldKey = GlobalKey();
  final _formatters = [MarkdownInputFormatter()];

  /// Scrolls [offset] into view without focusing the field, so read mode
  /// doesn't bring up the keyboard.
  void revealOffset(int offset) {
    final editable = _findEditable(_fieldKey.currentContext?.findRenderObject());
    if (editable == null) return;
    final caret = editable.getLocalRectForCaret(TextPosition(offset: offset));
    editable.showOnScreen(
      rect: Rect.fromLTRB(
          caret.left, caret.top - 80, caret.right, caret.bottom + 80),
      duration: const Duration(milliseconds: 200),
      curve: Curves.easeOut,
    );
  }

  /// Text offset at the top-left of the visible area.
  int firstVisibleOffset() {
    final box = _fieldKey.currentContext?.findRenderObject() as RenderBox?;
    final editable = _findEditable(box);
    if (box == null || editable == null) return 0;
    return editable
        .getPositionForPoint(box.localToGlobal(const Offset(1, 1)))
        .offset;
  }

  RenderEditable? _findEditable(RenderObject? node) {
    if (node is RenderEditable) return node;
    RenderEditable? found;
    node?.visitChildren((child) => found ??= _findEditable(child));
    return found;
  }

  void _indent({required bool outdent}) {
    final controller = widget.controller;
    controller.value = indentLines(controller.value, outdent: outdent);
  }

  @override
  Widget build(BuildContext context) {
    // Tab would otherwise move focus out of the editor on desktop.
    return CallbackShortcuts(
      bindings: widget.readOnly
          ? const {}
          : {
              const SingleActivator(LogicalKeyboardKey.tab): () =>
                  _indent(outdent: false),
              const SingleActivator(LogicalKeyboardKey.tab, shift: true): () =>
                  _indent(outdent: true),
            },
      child: TextField(
        key: _fieldKey,
        controller: widget.controller,
        focusNode: widget.focusNode,
        scrollController: widget.scrollController,
        readOnly: widget.readOnly,
        showCursor: !widget.readOnly,
        expands: true,
        maxLines: null,
        decoration: null,
        inputFormatters: widget.readOnly ? null : _formatters,
        style: TextStyle(fontSize: widget.fontSize),
      ),
    );
  }
}