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Observations are painting a complex picture of massive stars at the end of their lives. Contrary to expectations, massive stars have been found to experience major eruptions in the years preceding their explosion as supernovae (SNe). This sequence of eruptions was \emph{not predicted} on theoretical grounds and is \emph{not explained} by our current understanding of the physical mechanisms that drive the mass loss in evolved massive stars (Smith 2014).   In this respect, two key observational findings are relevant: (i) The direct detection of luminous precursors in the month before the   major explosion of the H-rich SN2009ip associated with the ejection of $\sim0.1\,\rm{M_{\odot}}$ of material (Margutti et al., 2014). (ii) Evidence for significant modulations in the radio light-curves of hydrogen-stripped SNe (i.e. SNe Ib/c; Soderberg Wellons  et al., 2006, 2012,  Milisavljevic et al., 2013). This latter finding indicates that a complex environment, sculpted and enriched by a significantly \emph{non-steady} mass loss of the progenitor system in the years before the explosion, surrounds some Type Ib/c SNe. The two findings above suggest that massive stars might lose their hydrogen envelopes through explosive mass ejections (instead of steady winds, as it has been assumed so far) on time scales of months to decades before the core-collapse (i.e. much shorter than previously thought). To test this idea here we propose a focused collaborative effort to probe the life of massive stars in the last centuries before explosion. Our goal is to reconstruct the density profile in the nearby environment of core-collapse SNe (i) using the entire sample of existing radio observations of core-collapse SNe, (ii) treating the dynamics of the SN shock interaction with the complex medium in a self-consistent way and (iii) by finally connecting our findings to the physics that regulates the time-variable mass loss in massive stars.