parse.js

// The parser is from Mozilla's iodide project:
// https://github.com/iodide-project/iodide/blob/master/src/editor/iomd-tools/iomd-parser.js

function hashCode(str) {
    // this is an implementation of java's hashcode method
    // https://stackoverflow.com/questions/7616461/generate-a-hash-from-string-in-javascript
    let hash = 0;
    let chr;
    if (str.length !== 0) {
        for (let i = 0; i < str.length; i++) {
            chr = str.charCodeAt(i);
            hash = (hash << 5) - hash + chr; // eslint-disable-line
            hash |= 0; // eslint-disable-line
        }
    }
    return hash.toString();
}

export function iomdParser(fullIomd) {
    const iomdLines = fullIomd.split('\n');
    const chunks = [];
    let currentChunkLines = [];
    let currentEvalType = '';
    let evalFlags = [];
    let currentChunkStartLine = 1;

    const newChunkId = (str) => {
        const hash = hashCode(str);
        let hashNum = '0';
        for (const chunk of chunks) {
            const [prevHash, prevHashNum] = chunk.chunkId.split('_');
            if (hash === prevHash) {
                hashNum = (parseInt(prevHashNum, 10) + 1).toString();
            }
        }
        return `${hash}_${hashNum}`;
    };

    const pushChunk = (endLine) => {
        const chunkContent = currentChunkLines.join('\n');
        chunks.push({
            chunkContent,
            chunkType: currentEvalType,
            chunkId: newChunkId(chunkContent),
            evalFlags,
            startLine: currentChunkStartLine,
            endLine,
        });
    };

    for (const [i, line] of iomdLines.entries()) {
        const lineNum = i + 1; // uses 1-based indexing
        if (line.slice(0, 2) === '%%') {
            // if line start with '%%', a new chunk has started
            // push the current chunk (unless it's on line 1), then reset
            if (lineNum !== 1) {
                // DON'T push a chunk if we're only on line 1
                pushChunk(lineNum - 1);
            }
            // reset the currentChunk state
            currentChunkStartLine = lineNum;
            currentChunkLines = [];
            evalFlags = [];
            // find the first char on this line that isn't '%'
            let lineColNum = 0;
            while (line[lineColNum] === '%') {
                lineColNum += 1;
            }
            const chunkFlags = line
                .slice(lineColNum)
                .split(/[ \t]+/)
                .filter((s) => s !== '');
            if (chunkFlags.length > 0) {
                // if there is a captured group, update the eval type
                [currentEvalType, ...evalFlags] = chunkFlags;
            }
        } else {
            // if there is no match, then the line is not a
            // chunk delimiter line, so add the line to the currentChunk
            currentChunkLines.push(line);
        }
    }
    // this is what's left over in the final chunk
    pushChunk(iomdLines.length);
    return chunks;
}