EPPlus/Utils/UriHelper.cs

using System;

namespace OfficeOpenXml.Utils;

internal class UriHelper {
  internal static Uri ResolvePartUri(Uri sourceUri, Uri targetUri) {
    if (targetUri.OriginalString.StartsWith("/")) {
      return targetUri;
    }
    string[] source = sourceUri.OriginalString.Split('/');
    string[] target = targetUri.OriginalString.Split('/');

    int t = target.Length - 1;
    int s;
    if (sourceUri.OriginalString.EndsWith(
        "/")) //is the source a directory?
    {
      s = source.Length - 1;
    } else {
      s = source.Length - 2;
    }

    string file = target[t--];

    while (t >= 0) {
      if (target[t] == ".") {
        break;
      }
      if (target[t] == "..") {
        s--;
        t--;
      } else {
        file = target[t--] + "/" + file;
      }
    }
    if (s >= 0) {
      for (int i = s; i >= 0; i--) {
        file = source[i] + "/" + file;
      }
    }
    return new(file, UriKind.RelativeOrAbsolute);
  }

  internal static Uri GetRelativeUri(Uri worksheetUri, Uri uri) {
    string[] source = worksheetUri.OriginalString.Split('/');
    string[] target = uri.OriginalString.Split('/');

    int slen;
    if (worksheetUri.OriginalString.EndsWith("/")) {
      slen = source.Length;
    } else {
      slen = source.Length - 1;
    }
    int i = 0;
    while (i < slen && i < target.Length && source[i] == target[i]) {
      i++;
    }

    string dirUp = "";
    for (int s = i; s < slen; s++) {
      dirUp += "../";
    }
    string file = "";
    for (int t = i; t < target.Length; t++) {
      file += (file == "" ? "" : "/") + target[t];
    }
    return new(dirUp + file, UriKind.Relative);
  }
}