If you are interested in this, but would prefer to define reports with a markup language (and SQL), I work on an open source code-based BI tool called Evidence, which might be of interest to you.
It's effectively a static site generator aimed at building automated reports and analysis.
Evidence looks incredible! I would start using it right away except I don't see it having any sort of date range picker / filter capability. Is the concept of being able to let our end users filter / drill into graphs with customized queries at odds with how Evidence works? Or are these things just not built yet?
Big fan of evidence, really elegant design. There is also space for both declarative and imperative approaches when it comes to dashboarding / reporting etc.