import 'dart:convert';
import 'package:xml/xml.dart';
import 'package:yaml/yaml.dart';

/// A syntax problem found by a validator: 1-based line and column.
class Problem {
  final String message;
  final int? line, column;
  const Problem(this.message, {this.line, this.column});
}

/// Which validator applies to a syntax id, if any.
String? validatorFor(String syntax) => switch (syntax) {
  'json' || 'jsonl' => syntax,
  'yaml' => 'yaml',
  'xml' || 'plist' || 'svg' => 'xml',
  _ => null,
};

(int, int) _position(String text, int offset) {
  var line = 1, column = 1;
  for (var i = 0; i < offset && i < text.length; i++) {
    if (text.codeUnitAt(i) == 0x0a) {
      line++;
      column = 1;
    } else {
      column++;
    }
  }
  return (line, column);
}

/// Checks [text] without changing it. Returns null when it is valid.
Problem? validate(String syntax, String text) {
  switch (validatorFor(syntax)) {
    case 'json':
      try {
        jsonDecode(text);
        return null;
      } on FormatException catch (e) {
        final offset = e.offset;
        if (offset == null) return Problem(e.message);
        final (line, column) = _position(text, offset);
        return Problem(e.message, line: line, column: column);
      }
    case 'jsonl':
      final lines = text.split('\n');
      for (var i = 0; i < lines.length; i++) {
        final l = lines[i].trim();
        if (l.isEmpty) continue;
        try {
          jsonDecode(l);
        } on FormatException catch (e) {
          return Problem(e.message, line: i + 1, column: (e.offset ?? 0) + 1);
        }
      }
      return null;
    case 'yaml':
      try {
        loadYamlStream(text);
        return null;
      } on YamlException catch (e) {
        final span = e.span;
        return Problem(
          e.message,
          line: span == null ? null : span.start.line + 1,
          column: span == null ? null : span.start.column + 1,
        );
      }
    case 'xml':
      try {
        XmlDocument.parse(text);
        return null;
      } on XmlParserException catch (e) {
        return Problem(e.message, line: e.line, column: e.column);
      } on XmlTagException catch (e) {
        return Problem(e.message, line: e.line, column: e.column);
      } on XmlException catch (e) {
        return Problem(e.message);
      }
  }
  return null;
}

/// Pretty-printed JSON or XML, produced only when the user asks for it.
/// Returns null when the syntax has no formatter or the text is invalid.
String? formatText(String syntax, String text, {int indent = 2}) {
  try {
    switch (validatorFor(syntax)) {
      case 'json':
        return JsonEncoder.withIndent(' ' * indent).convert(jsonDecode(text));
      case 'xml':
        return XmlDocument.parse(
          text,
        ).toXmlString(pretty: true, indent: ' ' * indent);
    }
  } catch (_) {
    return null;
  }
  return null;
}