## Multi-level state 
abstract type HierarchicalState <: AbstractState end

#=
# by default, the multilevel state wraps a tuple of states
struct MultilevelState{T <: Tuple} <: HierarchicalState
    levels :: T
end  
MultilevelState(levels...; kwargs...) = MultilevelState(levels)

course(::MultilevelState) = MultilevelState(s.levels[1:end-1])
fine(s::MultilevelState)   = s.levels[end]
combine(s::MultilevelState, fine_state) = MultilevelState(s.levels..., fine_state)
level(s::MultilevelState) = length(s.levels)

# Multi-level log density
abstract type HierarchicalLogDensity{S <: HierarchicalState} <: AbstractLogDensity{S} end

struct MultilevelLogDensity{F, S} <: HierarchicalLogDensity{S}
    logdensities :: F
end

logdensity(d::HierarchicalLogDensity, state::HierarchicalState; level=length(state)) = logdensity(d, state)
=#
#level(s::MultilevelState) = length(s.states)
#Base.eltype(states::MultilevelState) = eltype(states.states)

## construct from single level states
#MultilevelState(states::State ... ) = MultilevelState(getindex.([states ... ], :state))

## recursive construction
#course(states::MultilevelState) = MultilevelState(states[1:end-1])
#fine(states::MultilevelState)   = states[end]
#combine(states::MultilevelState, state) = MultilevelState(vcat(states.states ... , state)) 



#=
## Multi-level log density
abstract type HierarchicalLogDensity{S} <: AbstractLogDensity{S} end
struct MultilevelLogDensity{F, S} <: HierarchicalLogDensity{S}
    logdensities :: F
end
logdensity(d::MultilevelLogDensity, state::MultilevelState) = logdensity(d.logdensities, state.states


#logdensity(d::HierarchicalLogDensity, state::HierarchicalState, level::Int)

function logdensity(d::MultilevelLogDensity, state::HierarchicalState, level::Int)
    logdensity(d.logdensities[level], state.states[level]
    
end
#MultilevelLogDensity(logdensities::AbstractVector{<:AbstractLogDensity}) = MultilevelLogDensity(logdensities

=#

#abstract type AbstractMultilevelLogDensity <: LogDensity{S} end

#abstract type AbstractMultilevelLogDensity <: LogDensity{S} end

#struct MultilevelLogDensity <: AbstractMultilevelLogDensity
#end