private onSignatureHelp()

in server/src/session.ts [274:323]
40 lines of code
6 McCabe index (conditional complexity)

  private onSignatureHelp(params: lsp.SignatureHelpParams): lsp.SignatureHelp|null {
    const lsInfo = this.getLSAndScriptInfo(params.textDocument);
    if (lsInfo === null) {
      return null;
    }

    const {languageService, scriptInfo} = lsInfo;
    const offset = lspPositionToTsPosition(scriptInfo, params.position);

    const help = languageService.getSignatureHelpItems(scriptInfo.fileName, offset, undefined);
    if (help === undefined) {
      return null;
    }

    return {
      activeParameter: help.argumentCount > 0 ? help.argumentIndex : null,
      activeSignature: help.selectedItemIndex,
      signatures: help.items.map((item: ts.SignatureHelpItem): lsp.SignatureInformation => {
        // For each signature, build up a 'label' which represents the full signature text, as well
        // as a parameter list where each parameter label is a span within the signature label.
        let label = tsDisplayPartsToText(item.prefixDisplayParts);
        const parameters: lsp.ParameterInformation[] = [];
        let first = true;
        for (const param of item.parameters) {
          if (!first) {
            label += tsDisplayPartsToText(item.separatorDisplayParts);
          }
          first = false;

          // Add the parameter to the label, keeping track of its start and end positions.
          const start = label.length;
          label += tsDisplayPartsToText(param.displayParts);
          const end = label.length;

          // The parameter itself uses a range within the signature label as its own label.
          parameters.push({
            label: [start, end],
            documentation: tsDisplayPartsToText(param.documentation),
          });
        }

        label += tsDisplayPartsToText(item.suffixDisplayParts);
        return {
          label,
          documentation: tsDisplayPartsToText(item.documentation),
          parameters,
        };
      }),
    };
  }