const iconv = require('iconv-lite');
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// ============================================================================
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// framing.js 负责“分帧”而不是“解析”
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// - 输入：连续文本/字节流（可能粘包、半包、多帧）
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// - 输出：完整 XML 帧数组 + 未完成尾部余量
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// 解析工作交给 index.js 的 parseAndPrintData。
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// ============================================================================
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const ROOT_SPECS = [
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{ open: '<ORU_R31', close: '</ORU_R31>' },
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{ open: '<ORF_R04', close: '</ORF_R04>' },
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];
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function findNextRoot(text, fromIndex) {
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// 从当前位置向后找下一个根节点起点（ORU_R31 / ORF_R04），取最早出现者。
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let best = null;
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for (const spec of ROOT_SPECS) {
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const idx = text.indexOf(spec.open, fromIndex);
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if (idx === -1) continue;
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if (!best || idx < best.idx) best = { idx, spec };
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}
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return best;
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}
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function maybeIncludeXmlDecl(text, frameStart, searchFloor) {
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// 若根节点前存在同一帧的 XML 声明 `<?xml ...?>`，则把声明一起纳入帧起点。
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const idxXml = text.lastIndexOf('<?xml', frameStart);
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if (idxXml < searchFloor) return frameStart;
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const endDecl = text.indexOf('?>', idxXml);
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if (endDecl === -1) return frameStart;
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if (endDecl >= frameStart) return frameStart;
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return idxXml;
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}
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function extractFramesFromText(text) {
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// 文本分帧：按根节点和闭合标签切片，找不到闭合则保留余量等待下次补齐。
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const frames = [];
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let cursor = 0;
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while (cursor < text.length) {
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const next = findNextRoot(text, cursor);
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if (!next) break;
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let start = next.idx;
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start = maybeIncludeXmlDecl(text, start, cursor);
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const endClose = text.indexOf(next.spec.close, next.idx);
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if (endClose === -1) {
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// Incomplete frame: keep from `start` as remainder.
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return { frames, remainderText: text.slice(start) };
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}
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const end = endClose + next.spec.close.length;
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frames.push(text.slice(start, end));
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cursor = end;
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}
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return { frames, remainderText: text.slice(cursor) };
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}
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function extractFramesFromUtf16leBuffer(buffer) {
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// 字节分帧：先按 UTF-16LE 解码成文本分帧，再把 remainder 映射回字节余量。
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const frames = [];
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// UTF-16LE requires even bytes; keep a tail byte if needed.
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let oddTail = Buffer.alloc(0);
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let work = buffer;
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if (work.length % 2 === 1) {
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oddTail = work.slice(work.length - 1);
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work = work.slice(0, work.length - 1);
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}
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const text = iconv.decode(work, 'utf16le');
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const { frames: found, remainderText } = extractFramesFromText(text);
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frames.push(...found);
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// Convert remainderText length (code units) back to bytes.
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// This assumes the decoded text maps 1:1 to UTF-16 code units, which is valid here.
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const consumedChars = text.length - remainderText.length;
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const consumedBytes = consumedChars * 2;
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const remainderBuffer = Buffer.concat([work.slice(consumedBytes), oddTail]);
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return { frames, remainderBuffer };
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}
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function guessTextEncodingFromBuffer(buffer) {
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// 编码猜测：透析机报文常见 UTF-16LE（奇数字节位置大量 0x00）。
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if (!buffer || buffer.length < 4) return 'utf16le';
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// Heuristic: UTF-16LE XML often looks like 3C 00 4F 00 ... (lots of zeros on odd bytes)
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const sampleLen = Math.min(buffer.length, 512);
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let oddPositions = 0;
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let oddZeros = 0;
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for (let i = 1; i < sampleLen; i += 2) {
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oddPositions++;
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if (buffer[i] === 0x00) oddZeros++;
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}
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const ratio = oddPositions ? oddZeros / oddPositions : 0;
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return ratio >= 0.25 ? 'utf16le' : 'utf8';
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}
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module.exports = {
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extractFramesFromText,
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extractFramesFromUtf16leBuffer,
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guessTextEncodingFromBuffer,
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};
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