docs: public int getSigInsertionIndex(Sha256Hash hash, ECKey signingKey) {
          // Iterate over existing signatures, skipping the initial OP_0, the final redeem script
          // and any placeholder OP_0 sigs.
          List<ScriptChunk> existingChunks = chunks.subList(1, chunks.size() - 1);
          ScriptChunk redeemScriptChunk = chunks.get(chunks.size() - 1);
          checkNotNull(redeemScriptChunk.data);
          Script redeemScript = new Script(redeemScriptChunk.data);
  
          int sigCount = 0;
          int myIndex = redeemScript.findKeyInRedeem(signingKey);
          for (ScriptChunk chunk : existingChunks) {
              if (chunk.opcode == OP_0) {
                  // OP_0, skip
              } else {
                  checkNotNull(chunk.data);
                  try {
                      if (myIndex < redeemScript.findSigInRedeem(chunk.data, hash))
                          return sigCount;
                  } catch (SignatureDecodeException e) {
                      // ignore
                  }
                  sigCount++;
              }
          }
          return sigCount;
      }