_getPageAdvance()

in web/pdf_viewer.js [2147:2239]
90 lines of code
31 McCabe index (conditional complexity)

  _getPageAdvance(currentPageNumber, previous = false) {
    switch (this._scrollMode) {
      case ScrollMode.WRAPPED: {
        const { views } = this._getVisiblePages(),
          pageLayout = new Map();

        // Determine the current (visible) page layout.
        for (const { id, y, percent, widthPercent } of views) {
          if (percent === 0 || widthPercent < 100) {
            continue;
          }
          let yArray = pageLayout.get(y);
          if (!yArray) {
            pageLayout.set(y, (yArray ||= []));
          }
          yArray.push(id);
        }
        // Find the row of the current page.
        for (const yArray of pageLayout.values()) {
          const currentIndex = yArray.indexOf(currentPageNumber);
          if (currentIndex === -1) {
            continue;
          }
          const numPages = yArray.length;
          if (numPages === 1) {
            break;
          }
          // Handle documents with varying page sizes.
          if (previous) {
            for (let i = currentIndex - 1, ii = 0; i >= ii; i--) {
              const currentId = yArray[i],
                expectedId = yArray[i + 1] - 1;
              if (currentId < expectedId) {
                return currentPageNumber - expectedId;
              }
            }
          } else {
            for (let i = currentIndex + 1, ii = numPages; i < ii; i++) {
              const currentId = yArray[i],
                expectedId = yArray[i - 1] + 1;
              if (currentId > expectedId) {
                return expectedId - currentPageNumber;
              }
            }
          }
          // The current row is "complete", advance to the previous/next one.
          if (previous) {
            const firstId = yArray[0];
            if (firstId < currentPageNumber) {
              return currentPageNumber - firstId + 1;
            }
          } else {
            const lastId = yArray[numPages - 1];
            if (lastId > currentPageNumber) {
              return lastId - currentPageNumber + 1;
            }
          }
          break;
        }
        break;
      }
      case ScrollMode.HORIZONTAL: {
        break;
      }
      case ScrollMode.PAGE:
      case ScrollMode.VERTICAL: {
        if (this._spreadMode === SpreadMode.NONE) {
          break; // Normal vertical scrolling.
        }
        const parity = this._spreadMode - 1;

        if (previous && currentPageNumber % 2 !== parity) {
          break; // Left-hand side page.
        } else if (!previous && currentPageNumber % 2 === parity) {
          break; // Right-hand side page.
        }
        const { views } = this._getVisiblePages(),
          expectedId = previous ? currentPageNumber - 1 : currentPageNumber + 1;

        for (const { id, percent, widthPercent } of views) {
          if (id !== expectedId) {
            continue;
          }
          if (percent > 0 && widthPercent === 100) {
            return 2;
          }
          break;
        }
        break;
      }
    }
    return 1;
  }