Non-leptonic decays of heavy hadrons, such as $B$ and $D$ mesons, have proven to be a rich environment for the study of light meson spectroscopy and also charge-parity violation. For decays of charm hadrons, many problems related to non-perturbative effects arise in the study of strong interactions. Therefore, the usage of hadronic decays to study weak interactions turns out to be a great opportunity to study the dynamics of hadronic interactions and CP violation in these processes via a full amplitude analysis of the corresponding Dalitz Plot. Among the latest LHCb charm amplitude analysis results, the decays $D^+_{(s)} \to \pi^-\pi^+\pi^+$ with a particular emphasis on the measurement of the $\pi^-\pi^+$ S-wave amplitude are presented.