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using System;
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using System.Globalization;
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using Implab.Automaton;
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using System.Text;
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using Implab.Components;
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using System.IO;
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namespace Implab.Formats.Json {
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/// <summary>
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/// Сканнер (лексер), разбивающий поток символов на токены JSON.
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/// </summary>
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public abstract class JsonScanner : Disposable {
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readonly InputScanner<JsonGrammar.TokenType> m_jsonContext = JsonGrammar.CreateJsonExpressionScanner();
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readonly InputScanner<JsonGrammar.TokenType> m_stringContext = JsonGrammar.CreateStringExpressionScanner();
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readonly char[] m_unescapeBuf = new char[4];
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readonly char[] m_buffer;
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int m_length;
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int m_pos;
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readonly StringBuilder m_tokenBuilder = new StringBuilder();
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protected JsonScanner(char[] buffer, int pos, int length) {
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m_buffer = buffer;
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m_pos = pos;
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m_length = length;
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}
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bool Read(InputScanner<JsonGrammar.TokenType> scanner, out JsonGrammar.TokenType tokenType) {
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scanner.Reset();
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if (m_pos == m_length) {
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m_pos = 0;
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m_length = Read(m_buffer, 0, m_buffer.Length);
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if (m_length == 0) {
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tokenType = JsonGrammar.TokenType.None;
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return false; // EOF
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}
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}
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while(scanner.Scan(m_buffer, m_pos, m_length - m_pos)) {
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m_tokenBuilder.Append(m_buffer, m_pos, m_length - m_pos);
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m_pos = 0;
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m_length = Read(m_buffer, 0, m_buffer.Length);
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}
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var scannerPos = scanner.Position;
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if (scannerPos != m_pos) {
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m_tokenBuilder.Append(m_buffer, m_pos, scannerPos - m_pos);
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m_pos = scannerPos;
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}
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if (!scanner.IsFinal) {
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if (m_length == 0) {
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// unexpected EOF
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throw new ParserException("Unexpected EOF");
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} else {
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// unecpected character
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throw new ParserException($"Unexpected character '{m_buffer[m_pos + 1]}'");
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}
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}
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tokenType = scanner.Tag;
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return true;
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}
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protected abstract int Read(char[] buffer, int offset, int size);
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/// <summary>
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/// Читает следующий лексический элемент из входных данных.
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/// </summary>
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/// <param name="tokenValue">Возвращает значение прочитанного токена.</param>
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/// <param name="tokenType">Возвращает тип прочитанного токена.</param>
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/// <returns><c>true</c> - чтение произведено успешно. <c>false</c> - достигнут конец входных данных</returns>
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/// <remarks>В случе если токен не распознается, возникает исключение. Значения токенов обрабатываются, т.е.
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/// в строках обрабатываются экранированные символы, числа становтся типа double.</remarks>
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public bool ReadToken(out object tokenValue, out JsonTokenType tokenType) {
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JsonGrammar.TokenType tag;
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m_tokenBuilder.Clear();
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while (Read(m_jsonContext, out tag)) {
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switch (tag) {
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case JsonGrammar.TokenType.StringBound:
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tokenValue = ReadString();
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tokenType = JsonTokenType.String;
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break;
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case JsonGrammar.TokenType.Number:
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tokenValue = Double.Parse(m_tokenBuilder.ToString(), CultureInfo.InvariantCulture);
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tokenType = JsonTokenType.Number;
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break;
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case JsonGrammar.TokenType.Literal:
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tokenType = JsonTokenType.Literal;
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tokenValue = m_tokenBuilder.ToString();
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break;
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case JsonGrammar.TokenType.Whitespace:
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m_tokenBuilder.Clear();
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continue;
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default:
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tokenType = (JsonTokenType)tag;
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tokenValue = null;
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break;
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}
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return true;
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}
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tokenValue = null;
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tokenType = JsonTokenType.None;
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return false;
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}
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string ReadString() {
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JsonGrammar.TokenType tag;
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m_tokenBuilder.Clear();
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while (Read(m_stringContext, out tag)) {
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switch (tag) {
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case JsonGrammar.TokenType.StringBound:
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m_tokenBuilder.Length--;
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return m_tokenBuilder.ToString();
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case JsonGrammar.TokenType.UnescapedChar:
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break;
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case JsonGrammar.TokenType.EscapedUnicode: // \xXXXX - unicode escape sequence
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m_tokenBuilder.CopyTo(m_tokenBuilder.Length - 4, m_unescapeBuf, 0, 4);
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m_tokenBuilder.Length -= 6;
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m_tokenBuilder.Append(StringTranslator.TranslateHexUnicode(m_unescapeBuf, 0));
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break;
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case JsonGrammar.TokenType.EscapedChar: // \t - escape sequence
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var ch = m_tokenBuilder[m_tokenBuilder.Length-1];
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m_tokenBuilder.Length -= 2;
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m_tokenBuilder.Append(StringTranslator.TranslateEscapedChar(ch));
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break;
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}
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}
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throw new ParserException("Unexpected end of data");
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}
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}
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}
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