feat: move clock interface here

Author: AayushSabharwal

Project.toml

@@ -12,6 +12,7 @@ ConstructionBase = "187b0558-2788-49d3-abe0-74a17ed4e7c9"
 Distributed = "8ba89e20-285c-5b6f-9357-94700520ee1b"
 DocStringExtensions = "ffbed154-4ef7-542d-bbb7-c09d3a79fcae"
 EnumX = "4e289a0a-7415-4d19-859d-a7e5c4648b56"
+Expronicon = "6b7a57c9-7cc1-4fdf-b7f5-e857abae3636"
 FunctionWrappersWrappers = "77dc65aa-8811-40c2-897b-53d922fa7daf"
 IteratorInterfaceExtensions = "82899510-4779-5014-852e-03e436cf321d"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
@@ -62,6 +63,7 @@ DataFrames = "1.6"
 Distributed = "1.10"
 DocStringExtensions = "0.9"
 EnumX = "1"
+Expronicon = "0.8"
 ForwardDiff = "0.10.36"
 FunctionWrappersWrappers = "0.1.3"
 IteratorInterfaceExtensions = "^1"

src/SciMLBase.jl

@@ -23,6 +23,7 @@ import RuntimeGeneratedFunctions
 import EnumX
 import ADTypes: AbstractADType
 import Accessors: @set, @reset
+using Expronicon.ADT: @match
 
 using Reexport
 using SciMLOperators
@@ -717,6 +718,7 @@ include("problems/problem_traits.jl")
 include("problems/problem_interface.jl")
 include("problems/optimization_problems.jl")
 
+include("clock.jl")
 include("solutions/basic_solutions.jl")
 include("solutions/nonlinear_solutions.jl")
 include("solutions/ode_solutions.jl")
@@ -835,4 +837,6 @@ export step!, deleteat!, addat!, get_tmp_cache,
 
 export ContinuousCallback, DiscreteCallback, CallbackSet, VectorContinuousCallback
 
+export Clocks, TimeDomain, is_discrete_time_domain, isclock, issolverstepclock, iscontinuous
+
 end

src/clock.jl

@@ -0,0 +1,91 @@
+module Clocks
+
+export TimeDomain
+
+using Expronicon.ADT: @adt, @match
+
+@adt TimeDomain begin
+    Continuous
+    struct PeriodicClock
+        dt::Union{Nothing, Float64, Rational{Int}}
+    end
+    SolverStepClock
+end
+
+Base.Broadcast.broadcastable(d::TimeDomain) = Ref(d)
+
+end
+
+using .Clocks
+
+"""
+    Clock(dt)
+    Clock()
+
+The default periodic clock with tick interval `dt`. If `dt` is left unspecified, it will
+be inferred (if possible).
+"""
+Clock(dt::Union{<:Rational, Float64}) = PeriodicClock(dt)
+Clock(dt) = PeriodicClock(convert(Float64, dt))
+Clock() = PeriodicClock(nothing)
+
+@doc """
+    SolverStepClock
+
+A clock that ticks at each solver step (sometimes referred to as "continuous sample time").
+This clock **does generally not have equidistant tick intervals**, instead, the tick
+interval depends on the adaptive step-size selection of the continuous solver, as well as
+any continuous event handling. If adaptivity of the solver is turned off and there are no
+continuous events, the tick interval will be given by the fixed solver time step `dt`.
+
+Due to possibly non-equidistant tick intervals, this clock should typically not be used with
+discrete-time systems that assume a fixed sample time, such as PID controllers and digital
+filters.
+""" SolverStepClock
+
+isclock(c) = @match c begin
+    PeriodicClock(_) => true
+    _ => false
+end
+
+issolverstepclock(c) = @match c begin
+    &SolverStepClock => true
+    _ => false
+end
+
+iscontinuous(c) = @match c begin
+    &Continuous => true
+    _ => false
+end
+
+is_discrete_time_domain(c) = !iscontinuous(c)
+
+function first_clock_tick_time(c, t0)
+    @match c begin
+        PeriodicClock(dt) => ceil(t0 / dt) * dt
+        &SolverStepClock => t0
+        &Continuous => error("Continuous is not a discrete clock")
+    end
+end
+
+struct IndexedClock{I}
+    clock::TimeDomain
+    idx::I
+end
+
+Base.getindex(c::TimeDomain, idx) = IndexedClock(c, idx)
+
+function canonicalize_indexed_clock(ic::IndexedClock, sol::AbstractTimeseriesSolution)
+    c = ic.clock
+    
+    return @match c begin
+        PeriodicClock(dt) => ceil(sol.prob.tspan[1] / dt) * dt .+ (ic.idx .- 1) .* dt
+        &SolverStepClock => begin
+            ssc_idx = findfirst(eachindex(sol.discretes)) do i
+                !isa(sol.discretes[i].t, AbstractRange)
+            end
+            sol.discretes[ssc_idx].t[ic.idx]
+        end
+        &Continuous => sol.t[ic.idx]
+    end
+end