Stackedit/src/services/sectionUtils.js

function SectionDimension(startOffset, endOffset) {
  this.startOffset = startOffset;
  this.endOffset = endOffset;
  this.height = endOffset - startOffset;
}

function dimensionNormalizer(dimensionName) {
  return (editorSvc) => {
    const dimensionList = editorSvc.sectionDescList.map(sectionDesc => sectionDesc[dimensionName]);
    let dimension;
    let i;
    let j;
    for (i = 0; i < dimensionList.length; i += 1) {
      dimension = dimensionList[i];
      if (dimension.height) {
        for (j = i + 1; j < dimensionList.length && dimensionList[j].height === 0; j += 1) {
          // Loop
        }
        const normalizeFactor = j - i;
        if (normalizeFactor !== 1) {
          const normalizedHeight = dimension.height / normalizeFactor;
          dimension.height = normalizedHeight;
          dimension.endOffset = dimension.startOffset + dimension.height;
          for (j = i + 1; j < i + normalizeFactor; j += 1) {
            const startOffset = dimension.endOffset;
            dimension = dimensionList[j];
            dimension.startOffset = startOffset;
            dimension.height = normalizedHeight;
            dimension.endOffset = dimension.startOffset + dimension.height;
          }
          i = j - 1;
        }
      }
    }
  };
}

const normalizeEditorDimensions = dimensionNormalizer('editorDimension');
const normalizePreviewDimensions = dimensionNormalizer('previewDimension');
const normalizeTocDimensions = dimensionNormalizer('tocDimension');

function measureSectionDimensions(editorSvc) {
  let editorSectionOffset = 0;
  let previewSectionOffset = 0;
  let tocSectionOffset = 0;
  let sectionDesc = editorSvc.sectionDescList[0];
  let nextSectionDesc;
  let i = 1;
  for (; i < editorSvc.sectionDescList.length; i += 1) {
    nextSectionDesc = editorSvc.sectionDescList[i];

    // Measure editor section
    let newEditorSectionOffset = nextSectionDesc.editorElt
      ? nextSectionDesc.editorElt.offsetTop
      : editorSectionOffset;
    newEditorSectionOffset = newEditorSectionOffset > editorSectionOffset
      ? newEditorSectionOffset
      : editorSectionOffset;
    sectionDesc.editorDimension = new SectionDimension(editorSectionOffset, newEditorSectionOffset);
    editorSectionOffset = newEditorSectionOffset;

    // Measure preview section
    let newPreviewSectionOffset = nextSectionDesc.previewElt
      ? nextSectionDesc.previewElt.offsetTop
      : previewSectionOffset;
    newPreviewSectionOffset = newPreviewSectionOffset > previewSectionOffset
      ? newPreviewSectionOffset
      : previewSectionOffset;
    sectionDesc.previewDimension = new SectionDimension(
      previewSectionOffset, newPreviewSectionOffset);
    previewSectionOffset = newPreviewSectionOffset;

    // Measure TOC section
    let newTocSectionOffset = nextSectionDesc.tocElt
      ? nextSectionDesc.tocElt.offsetTop + (nextSectionDesc.tocElt.offsetHeight / 2)
      : tocSectionOffset;
    newTocSectionOffset = newTocSectionOffset > tocSectionOffset
      ? newTocSectionOffset
      : tocSectionOffset;
    sectionDesc.tocDimension = new SectionDimension(tocSectionOffset, newTocSectionOffset);
    tocSectionOffset = newTocSectionOffset;

    sectionDesc = nextSectionDesc;
  }

  // Last section
  sectionDesc = editorSvc.sectionDescList[i - 1];
  if (sectionDesc) {
    sectionDesc.editorDimension = new SectionDimension(
      editorSectionOffset, editorSvc.editorElt.scrollHeight);
    sectionDesc.previewDimension = new SectionDimension(
      previewSectionOffset, editorSvc.previewElt.scrollHeight);
    sectionDesc.tocDimension = new SectionDimension(
      tocSectionOffset, editorSvc.tocElt.scrollHeight);
  }

  normalizeEditorDimensions(editorSvc);
  normalizePreviewDimensions(editorSvc);
  normalizeTocDimensions(editorSvc);
}

export default {
  measureSectionDimensions,
};