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####################################################################
# Predictive online PDPS for optical flow with known velocity field
####################################################################

__precompile__()

module AlgorithmPET

identifier = "pet_known_orig"

using Printf

using AlgTools.Util
import AlgTools.Iterate
using ImageTools.Gradient
using ImageTools.Translate
  
using ..Radon   
using ImageTransformations
using Images, CoordinateTransformations, Rotations, OffsetArrays
using ImageCore, Interpolations

using ..OpticalFlow: ImageSize,
                     Image,
                     petpdflow!

#########################
# Iterate initialisation
#########################



function init_rest(x::Image)
    imdim=size(x)

    y = zeros(2, imdim...)
    Δx = copy(x)
    Δy = copy(y)
    x̄ = copy(x)
    radonx = copy(x)

    return x, y, Δx, Δy, x̄, radonx
end

function init_iterates(xinit::Image)
    return init_rest(copy(xinit))
end

function init_iterates(dim::ImageSize)
    return init_rest(zeros(dim...))
end

#########################
# PETscan related
#########################
function petvalue(x, b, c)
    tmp = similar(b)
    radon!(tmp, x)
    return sum(@. tmp - b*log(tmp+c))
end

function petgrad!(res, x, b, c, S)
    tmp = similar(b)
    radon!(tmp, x)
    @. tmp = S .- b/(tmp+c)
    backproject!(res, S.*tmp)
end

function proj_nonneg!(y)
    @inbounds @simd for i=1:length(y)
        if y[i] < 0
            y[i] = 0
        end
    end
    return y
end



############
# Algorithm
############

function step_lengths(params, γ, R_K²)
    ρ̃₀, τ₀, σ₀, σ̃₀ =  params.ρ̃₀, params.τ₀, params.σ₀, params.σ̃₀
    δ = params.δ
    ρ = isdefined(params, :phantom_ρ) ? params.phantom_ρ : params.ρ
    Λ = params.Λ
    Θ = params.dual_flow ? Λ : 1

    τ = τ₀/γ
    @assert(1+γ*τ ≥ Λ)
    σ = σ₀*1/(τ*R_K²)
    #σ = σ₀*min(1/(τ*R_K²), 1/max(0, τ*R_K²/((1+γ*τ-Λ)*(1-δ))-ρ))
    q = δ*(1+σ*ρ)/Θ
    if 1 ≥ q
        σ̃ = σ̃₀*σ/q
        #ρ̃ = ρ̃₀*max(0, ((Θ*σ)/(2*δ*σ̃^2*(1+σ*ρ))+1/(2σ)-1/σ̃))
        ρ̃ = max(0, (1-q)/(2*σ))
    else
        σ̃ = σ̃₀*σ/(q*(1-√(1-1/q)))
        ρ̃ = 0
    end
    
    #println("Step length parameters: τ=$(τ), σ=$(σ), σ̃=$(σ̃), ρ̃=$(ρ̃)")

    return τ, σ, σ̃, ρ̃
end

function solve( :: Type{DisplacementT};
               dim :: ImageSize,
               iterate = AlgTools.simple_iterate,
               params::NamedTuple) where DisplacementT

    ################################                                        
    # Extract and set up parameters
    ################################                    

    α, ρ = params.α, params.ρ
    R_K² = ∇₂_norm₂₂_est²
    γ = 1
    # τ, σ, σ̃, ρ̃ = step_lengths(params, γ, R_K²)
    λ = params.λ
    ω = 1
    c = params.c*ones(params.radondims...)

    ρ̃₀, τ₀, σ₀, σ̃₀ =  params.ρ̃₀, params.τ₀, params.σ₀, params.σ̃₀

    # Update step length parameters                    
    L = 300.0
    τ = τ₀/L
    σ = σ₀*(1-τ₀)/(R_K²*τ)
    println("Step length parameters: L=$(round(L, digits=4)), τ=$(round(τ, digits=4)), σ=$(round(σ, digits=4))")



    δ = params.δ
    ρ = isdefined(params, :phantom_ρ) ? params.phantom_ρ : params.ρ
    Λ = params.Λ
    Θ = params.dual_flow ? Λ : 1

    q = δ*(1+σ*ρ)/Θ
    if 1 ≥ q
        σ̃ = σ̃₀*σ/q
        #ρ̃ = ρ̃₀*max(0, ((Θ*σ)/(2*δ*σ̃^2*(1+σ*ρ))+1/(2σ)-1/σ̃))
        ρ̃ = max(0, (1-q)/(2*σ))
    else
        σ̃ = σ̃₀*σ/(q*(1-√(1-1/q)))
        ρ̃ = 0
    end

    ######################
    # Initialise iterates
    ######################

    x, y, Δx, Δy, x̄, r∇ = init_iterates(dim)
    
    # L = 1.0
    # oldpetgradx = zeros(size(x)...)
    # petgradx = zeros(size(x))
    # oldx = ones(size(x))

    ####################
    # Run the algorithm
    ####################
                        # THIS IS THE step function inside iterate_visualise
    v = iterate(params) do verbose :: Function,
                           b :: Image,                   # noisy_sinogram
                           v_known :: DisplacementT,
                           theta_known :: DisplacementT,
                           b_true :: Image,
                           S :: Image    
        
        ##################################
        # Update the step length parameter
        ##################################
        # τ = τ₀/L
        # σ = σ₀*(1-τ₀)/(R_K²*τ)
        # println("Step length parameters: L=$(round(L, digits=4)), τ=$(round(τ, digits=4)), σ=$(round(σ, digits=4))") 


        ###################    
        # Prediction steps
        ###################

        petpdflow!(x, Δx, y, Δy, v_known, theta_known, params.dual_flow)                      # Old algorithm
        #pdflow!(x, Δx, y, Δy, v_known, theta_known, params.dual_flow, 1e-2,1e-2)           # Rotation
        #pdflow!(x, Δx, y, Δy, v_known, theta_known, params.dual_flow, 1e-2)                # Adhoc
        #@. oldx = x

        if params.prox_predict
            ∇₂!(Δy, x)
            @. y = (y + σ̃*Δy)/(1 + σ̃*(ρ̃+ρ/α))
            #@. cc = y + 1000000*σ̃*Δy 
            #@. y = (y + σ̃*Δy)/(1 + σ̃*(ρ̃+ρ/α)) + (1 - 1/(1 + ρ̃*σ̃))*cc
            proj_norm₂₁ball!(y, α) 
        end


        ############
        # PDPS step
        ############

        ∇₂ᵀ!(Δx, y)                    # primal step:
        @. x̄ = x                       # | save old x for over-relax
        petgrad!(r∇, x, b, c, S)          # | Calculate gradient of fidelity term

        @. x = x-(τ*λ)*r∇-τ*Δx         # |
        proj_nonneg!(x)                # | non-negativity constaint prox
        @. x̄ = (1+ω)*x - ω*x̄           # over-relax: x̄ = 2x-x_old
        ∇₂!(Δy, x̄)                     # dual step:
        @. y = y + σ*Δy                # |
        proj_norm₂₁ball!(y, α)         # |  prox

        ##########################################
        # Compute for the local Lipschitz constant
        ##########################################
        # petgrad!(petgradx, x, b, c, S)
        # petgrad!(oldpetgradx, oldx, b, c, S)
        # if norm₂(x-oldx)>1e-12
        #    L = max(0.9*norm₂(petgradx - oldpetgradx)/norm₂(x-oldx),L)
        # end   
       
        ################################
        # Give function value if needed
        ################################
        
        v = verbose() do            
            ∇₂!(Δy, x)
            value = λ*petvalue(x, b, c) + params.α*norm₂₁(Δy)
            value, x, [NaN, NaN], nothing
        end 
        
        v
    end

    return x, y, v
end

end # Module