module RL

export run_rl

using Base: OneTo

using ReinforcementLearning
using Flux: InvDecay
using Intervals
using StaticArrays: SVector
using LoopVectorization: @turbo
using Random: Random
using ProgressMeter: @showprogress

using ..ReCo: ReCo, Particle, angle2, Shape

const INITIAL_REWARD = 0.0
const INITIAL_STATE_IND = 1

function angle_state_space(n_angle_states::Int64)
    angle_range = range(; start=-π, stop=π, length=n_angle_states + 1)

    angle_state_space = Vector{Interval}(undef, n_angle_states)

    @simd for i in 1:n_angle_states
        if i == 1
            bound = Closed
        else
            bound = Open
        end

        angle_state_space[i] = Interval{Float64,bound,Closed}(
            angle_range[i], angle_range[i + 1]
        )
    end

    return angle_state_space
end

mutable struct Env <: AbstractEnv
    n_actions::Int64
    action_space::Vector{SVector{2,Float64}}
    action_ind_space::OneTo{Int64}

    distance_state_space::Vector{Interval}
    direction_angle_state_space::Vector{Interval}

    n_states::Int64
    state_space::Vector{SVector{2,Interval}}
    state_ind_space::OneTo{Int64}
    state_ind::Int64

    reward::Float64
    terminated::Bool

    function Env(;
        max_distance::Float64,
        min_distance::Float64=0.0,
        n_v_actions::Int64=2,
        n_ω_actions::Int64=3,
        max_v::Float64=40.0,
        max_ω::Float64=π / 2,
        n_distance_states::Int64=3,
        n_direction_angle_states::Int64=3,
    )
        @assert min_distance >= 0.0
        @assert max_distance > min_distance
        @assert n_v_actions > 1
        @assert n_ω_actions > 1
        @assert max_v > 0
        @assert max_ω > 0
        @assert n_distance_states > 1
        @assert n_direction_angle_states > 1

        v_action_space = range(; start=0.0, stop=max_v, length=n_v_actions)
        ω_action_space = range(; start=-max_ω, stop=max_ω, length=n_ω_actions)

        n_actions = n_v_actions * n_ω_actions

        action_space = Vector{SVector{2,Float64}}(undef, n_actions)

        ind = 1
        for v in v_action_space
            for ω in ω_action_space
                action_space[ind] = SVector(v, ω)
                ind += 1
            end
        end

        action_ind_space = OneTo(n_actions)

        distance_range = range(;
            start=min_distance, stop=max_distance, length=n_distance_states + 1
        )

        distance_state_space = Vector{Interval}(undef, n_distance_states)

        @simd for i in 1:n_distance_states
            if i == 1
                bound = Closed
            else
                bound = Open
            end

            distance_state_space[i] = Interval{Float64,bound,Closed}(
                distance_range[i], distance_range[i + 1]
            )
        end

        direction_angle_state_space = angle_state_space(n_direction_angle_states)

        n_states = n_distance_states * n_direction_angle_states + 1

        state_space = Vector{SVector{2,Interval}}(undef, n_states - 1)

        ind = 1
        for distance_state in distance_state_space
            for direction_angle_state in direction_angle_state_space
                state_space[ind] = SVector(distance_state, direction_angle_state)
                ind += 1
            end
        end
        # Last state is when no particle is in the skin radius

        state_ind_space = OneTo(n_states)

        return new(
            n_actions,
            action_space,
            action_ind_space,
            distance_state_space,
            direction_angle_state_space,
            n_states,
            state_space,
            state_ind_space,
            INITIAL_STATE_IND,
            INITIAL_REWARD,
            false,
        )
    end
end

function reset!(env::Env)
    env.state_ind = env.n_states
    env.terminated = false

    return nothing
end

RLBase.state_space(env::Env) = env.state_ind_space

RLBase.state(env::Env) = env.state_ind

RLBase.action_space(env::Env) = env.action_ind_space

RLBase.reward(env::Env) = env.reward

RLBase.is_terminated(env::Env) = env.terminated

struct Params{H<:AbstractHook}
    env::Env
    agent::Agent
    hook::H

    old_states_ind::Vector{Int64}
    states_ind::Vector{Int64}

    actions::Vector{SVector{2,Float64}}
    actions_ind::Vector{Int64}

    n_steps_before_actions_update::Int64

    goal_gyration_tensor_eigvals_ratio::Float64

    n_particles::Int64
    max_distance::Float64

    vec_to_neighbour_sums::Vector{SVector{2,Float64}}
    n_neighbours::Vector{Int64}

    function Params(
        env::Env,
        agent::Agent,
        hook::H,
        n_steps_before_actions_update::Int64,
        goal_gyration_tensor_eigvals_ratio::Float64,
        n_particles::Int64,
        max_distance::Float64,
    ) where {H<:AbstractHook}
        n_states = env.n_states

        return new{H}(
            env,
            agent,
            hook,
            fill(0, n_particles),
            fill(n_states, n_particles),
            fill(SVector(0.0, 0.0), n_particles),
            fill(0, n_particles),
            n_steps_before_actions_update,
            goal_gyration_tensor_eigvals_ratio,
            n_particles,
            max_distance,
            fill(SVector(0.0, 0.0), n_particles),
            fill(0, n_particles),
        )
    end
end

function pre_integration_hook(rl_params::Params)
    @simd for id in 1:(rl_params.n_particles)
        rl_params.vec_to_neighbour_sums[id] = SVector(0.0, 0.0)
        rl_params.n_neighbours[id] = 0
    end

    return nothing
end

function state_update_helper_hook(
    rl_params::Params, id1::Int64, id2::Int64, r⃗₁₂::SVector{2,Float64}
)
    rl_params.vec_to_neighbour_sums[id1] += r⃗₁₂
    rl_params.vec_to_neighbour_sums[id2] -= r⃗₁₂

    rl_params.n_neighbours[id1] += 1
    rl_params.n_neighbours[id2] += 1

    return nothing
end

function find_state_ind(state::S, state_space::Vector{S}) where {S<:SVector{2,Interval}}
    return findfirst(x -> x == state, state_space)
end

function find_state_interval(value::Float64, state_space::Vector{Interval})::Interval
    for state in state_space
        if value in state
            return state
        end
    end
end

function state_update_hook(rl_params::Params, particles::Vector{Particle})
    @turbo for id in 1:(rl_params.n_particles)
        rl_params.old_states_ind[id] = rl_params.states_ind[id]
    end

    env = rl_params.env

    for id in 1:(rl_params.n_particles)
        n_neighbours = rl_params.n_neighbours[id]

        if n_neighbours == 0
            state_ind = env.n_states
        else
            vec_to_local_center_of_mass = rl_params.vec_to_neighbour_sums[id] / n_neighbours

            distance = sqrt(
                vec_to_local_center_of_mass[1]^2 + vec_to_local_center_of_mass[2]^2
            )

            distance_state = find_state_interval(distance, env.distance_state_space)

            si, co = sincos(particles[id].φ)

            direction_angle = angle2(SVector(co, si), vec_to_local_center_of_mass)

            direction_angle_state = find_state_interval(
                direction_angle, env.direction_angle_state_space
            )

            state = SVector{2,Interval}(distance_state, direction_angle_state)
            state_ind = find_state_ind(state, env.state_space)
        end

        rl_params.states_ind[id] = state_ind
    end

    return nothing
end

function get_env_agent_hook(rl_params::Params)
    return (rl_params.env, rl_params.agent, rl_params.hook)
end

function update_reward!(env::Env, rl_params::Params, particle::Particle)
    id = particle.id

    normalization = (rl_params.max_distance * rl_params.n_particles)

    n_neighbours = rl_params.n_neighbours[id]
    if n_neighbours == 0
        env.reward = -(rl_params.max_distance^2) / normalization
    else
        vec_to_local_center_of_mass = rl_params.vec_to_neighbour_sums[id] / n_neighbours # TODO: Reuse vec_to_local_center_of_mass from state_update_hook
        env.reward =
            -(vec_to_local_center_of_mass[1]^2 + vec_to_local_center_of_mass[2]^2) /
            normalization
    end

    return nothing
end

function update_table_and_actions_hook(
    rl_params::Params, particle::Particle, first_integration_step::Bool
)
    env, agent, hook = get_env_agent_hook(rl_params)

    id = particle.id

    if !first_integration_step
        # Old state
        env.state_ind = rl_params.old_states_ind[id]

        action_ind = rl_params.actions_ind[id]

        # Pre act
        agent(PRE_ACT_STAGE, env, action_ind)
        hook(PRE_ACT_STAGE, agent, env, action_ind)

        # Update to current state
        env.state_ind = rl_params.states_ind[id]

        # Update reward
        update_reward!(env, rl_params, particle)

        # Post act
        agent(POST_ACT_STAGE, env)
        hook(POST_ACT_STAGE, agent, env)
    end

    # Update action
    action_ind = agent(env)
    action = env.action_space[action_ind]

    rl_params.actions[id] = action
    rl_params.actions_ind[id] = action_ind

    return nothing
end

act_hook(::Nothing, args...) = nothing

function act_hook(
    rl_params::Params, particle::Particle, δt::Float64, si::Float64, co::Float64
)
    # Apply action
    action = rl_params.actions[particle.id]

    vδt = action[1] * δt
    particle.tmp_c += SVector(vδt * co, vδt * si)
    particle.φ += action[2] * δt

    return nothing
end

function gen_agent(n_states::Int64, n_actions::Int64, ϵ_stable::Float64)
    # TODO: Optimize warmup and decay
    warmup_steps = 200_000
    decay_steps = 1_000_000

    policy = QBasedPolicy(;
        learner=MonteCarloLearner(;
            approximator=TabularQApproximator(;
                n_state=n_states, n_action=n_actions, opt=InvDecay(1.0)
            ),
        ),
        explorer=EpsilonGreedyExplorer(;
            kind=:linear,
            ϵ_init=1.0,
            ϵ_stable=ϵ_stable,
            warmup_steps=warmup_steps,
            decay_steps=decay_steps,
        ),
    )

    return Agent(; policy=policy, trajectory=VectorSARTTrajectory())
end

function run_rl(;
    goal_gyration_tensor_eigvals_ratio::Float64,
    n_episodes::Int64=200,
    episode_duration::Float64=50.0,
    update_actions_at::Float64=0.1,
    n_particles::Int64=100,
    seed::Int64=42,
    ϵ_stable::Float64=0.0001,
    parent_dir::String="",
)
    @assert 0.0 <= goal_gyration_tensor_eigvals_ratio <= 1.0
    @assert n_episodes > 0
    @assert episode_duration > 0
    @assert update_actions_at in 0.001:0.001:episode_duration
    @assert n_particles > 0
    @assert 0.0 < ϵ_stable < 1.0

    # Setup
    Random.seed!(seed)

    sim_consts = ReCo.gen_sim_consts(
        n_particles, 0.0; skin_to_interaction_r_ratio=2.0, packing_ratio=0.22
    )
    n_particles = sim_consts.n_particles

    max_distance = sim_consts.skin_r
    env = Env(; max_distance=max_distance)

    agent = gen_agent(env.n_states, env.n_actions, ϵ_stable)

    n_steps_before_actions_update = round(Int64, update_actions_at / sim_consts.δt)

    hook = TotalRewardPerEpisode()

    rl_params = Params(
        env,
        agent,
        hook,
        n_steps_before_actions_update,
        goal_gyration_tensor_eigvals_ratio,
        n_particles,
        max_distance,
    )

    parent_dir = "RL" * parent_dir

    # Pre experiment
    hook(PRE_EXPERIMENT_STAGE, agent, env)
    agent(PRE_EXPERIMENT_STAGE, env)

    @showprogress 0.6 for episode in 1:n_episodes
        dir = ReCo.init_sim_with_sim_consts(sim_consts; parent_dir=parent_dir)

        # Reset
        reset!(env)

        # Pre espisode
        hook(PRE_EPISODE_STAGE, agent, env)
        agent(PRE_EPISODE_STAGE, env)

        # Episode
        ReCo.run_sim(
            dir; duration=episode_duration, seed=rand(1:typemax(Int64)), rl_params=rl_params
        )

        env.terminated = true

        # Post episode
        hook(POST_EPISODE_STAGE, agent, env)
        agent(POST_EPISODE_STAGE, env)

        # TODO: Replace with live plot
        display(hook.rewards)
        display(agent.policy.explorer.step)
    end

    # Post experiment
    hook(POST_EXPERIMENT_STAGE, agent, env)

    return rl_params
end

end # module