module ReCoRL

using ReinforcementLearning
using Flux: InvDecay
using Intervals
using StaticArrays: SVector

import Base: run

struct DistanceState{L<:Bound}
    interval::Interval{Float64,L,Closed}

    function DistanceState{L}(lower::Float64, upper::Float64) where {L<:Bound}
        return new(Interval{Float64,L,Closed}(lower, upper))
    end
end

struct DirectionState
    interval::Interval{Float64,Open,Closed}

    function DirectionState(lower::Float64, upper::Float64)
        return new(Interval{Float64,Closed,Open}(lower, upper))
    end
end

mutable struct EnvParams
    action_space::Vector{Tuple{Float64,Float64}}
    distance_state_space::Vector{DistanceState}
    direction_state_space::Vector{DirectionState}
    state_space::Vector{Tuple{Union{DistanceState,Nothing},Union{DirectionState,Nothing}}}
    reward::Float64

    function EnvParams(
        min_distance::Float64,
        max_distance::Float64;
        n_v_actions::Int64=2,
        n_ω_actions::Int64=3,
        max_v::Float64=20.0,
        max_ω::Float64=π / 1.5,
        n_distance_states::Int64=3,
        n_direction_states::Int64=4,
    )
        @assert min_distance > 0.0
        @assert max_distance > min_distance
        @assert n_v_actions > 1
        @assert n_ω_actoins > 1
        @assert max_v > 0
        @assert max_ω > 0

        v_action_space = 0.0:(max_v / (n_v_actions - 1)):max_v
        ω_action_space = (-max_ω):(2 * max_ω / (n_ω_actions - 1)):max_ω

        n_actions = n_v_actions * n_ω_actions

        action_space = Vector{Tuple{Float64,Float64}}(undef, n_actions)

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

        distance_range =
            min_distance:((max_distance - min_distance) / n_distance_states):max_distance

        distance_state_space = Vector{DistanceState}(undef, n_distance_states)

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

            distance_state_space[i] = DistanceState{bound}(
                distance_range[i], distance_range[i + 1]
            )
        end

        direction_range = 0.0:(2 * π / n_direction_states):(2 * π)

        direction_state_space = Vector{DirectionState}(undef, n_direction_states)

        for i in 1:n_direction_states
            direction_state_space[i] = DirectionState(
                direction_range[i], direction_range[i + 1]
            )
        end

        state_space = Vector{
            Tuple{Union{DistanceState,Nothing},Union{DirectionState,Nothing}}
        }(
            undef, n_states
        )

        ind = 1
        for distance_state in distance_state_space
            for direction_state in direction_state_space
                state_space[ind] = (distance_state, direction_state)
                ind += 1
            end
        end
        state_space[ind] = (nothing, nothing)

        return new(
            action_space, distance_state_space, direction_state_space, state_space, 0.0
        )
    end
end

mutable struct Env <: AbstractEnv
    params::EnvParams
    particle::Particle
    state::Tuple{Union{DistanceState,Nothing},Union{DirectionState,Nothing}}

    function Env(params::EnvParams, particle::Particle)
        return new(params, particle, (nothing, nothing))
    end
end

function gen_policy(n_states, n_actions)
    return QBasedPolicy(;
        learner=MonteCarloLearner(;
            approximator=TabularQApproximator(;
                n_state=n_states, n_action=n_actions, opt=InvDecay(1.0)
            ),
        ),
        explorer=EpsilonGreedyExplorer(0.1),
    )
end

struct Params{H<:AbstractHook}
    envs::Vector{Env}
    agents::Vector{Agent}
    hooks::Vector{H}
    actions::Vector{Tuple{Float64,Float64}}
    env_params::EnvParams
    n_steps_before_actions_update::Int64
    min_distance²::Vector{Float64}
    r⃗₁₂_to_min_distance_particle::Vector{SVector{2,Float64}}

    function Params{H}(
        n_particles::Int64, env_params::EnvParams, n_steps_before_actions_update::Int64
    ) where {H<:AbstractHook}
        policies = [
            gen_policy(
                length(rl_params.env_params.state_space),
                length(rl_params.env_params.action_space),
            ) for i in 1:n_particles
        ]
        agents = [
            Agent(; policy=policy, trajectory=VectorSARTTrajectory()) for policy in policies
        ]
        return new(
            [Env(env_params, gen_tmp_particle()) for i in 1:n_particles],
            agents,
            [H() for i in 1:n_particles],
            Vector{Tuple{Float64,Float64}}(undef, n_particles),
            env_params,
            n_steps_before_actions_update,
            zeros(n_particles),
            fill(SVector(0.0, 0.0), n_particles),
        )
    end
end

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

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

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

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

function pre_integration_hook!(rl_params::Params, n_particles::Int64)
    for i in 1:n_particles
        env = rl_params.envs[i]
        agent = rl_params.agents[i]
        action = agent(env)
        rl_params.actions[i] = action

        agent(PRE_ACT_STAGE, env, action)
        rl_params.hooks[i](PRE_ACT_STAGE, agent, env, action)
    end

    return nothing
end

function state_hook(
    id1::Int64, id2::Int64, r⃗₁₂::SVector{2,Float64}, distance²::Float64, rl_params::Params
)
    if rl_params.min_distance²[id1] > distance²
        rl_params.min_distance²[id1] = distance²

        rl_params.r⃗₁₂_to_min_distance_particle[id1] = r⃗₁₂
    end

    if rl_params.min_distance²[id2] > distance²
        rl_params.min_distance²[id2] = distance²

        rl_params.r⃗₁₂_to_min_distance_particle[id2] = -r⃗₁₂
    end

    return nothing
end

function integration_hook(particle::Particle, rl_params::Params, δt::Float64)
    action = rl_params.actions[particle.id]

    particle.tmp_c += action[1] * δt
    particle.φ += action[2] * δt

    return nothing
end

function post_integration_hook(
    rl_params::Params, n_particles::Int64, particles::Vector{Particle}
)
    env_direction_state = rl_params.env_params.direction_state_space[1]

    for i in 1:n_particles
        env = rl_params.envs[i]
        agent = rl_params.agents[i]

        min_distance = sqrt(rl_params.min_distance²[i])

        env_distance_state::Union{DistanceState,Nothing} = nothing

        for distance_state in rl_params.env_params.distance_state_space
            if min_distance in distance_state.interval
                env_distance_state = distance_state
                break
            end
        end

        if isnothing(env_distance_state)
            env.state = (nothing, nothing)
        else
            r⃗₁₂ = rl_params.r⃗₁₂_to_min_distance_particle[i]
            si, co = sincos(particles[i].φ)

            #=
            Angle between two vectors
            e = (co, si)
            angle = acos(dot(r⃗₁₂, e) / (norm(r⃗₁₂) * norm(e)))
            norm(r⃗₁₂) == min_distance
            norm(e) == 1
            =#
            direction = acos((r⃗₁₂[1] * co + r⃗₁₂[2] * si) / min_distance)

            for direction_state in rl_params.env_params.direction_state_space
                if direction in direction_state
                    env_direction_state = direction_state
                end
            end

            env.state = (env_distance_state, env_direction_state)
        end

        agent(POST_ACT_STAGE, env)
        rl_params.hooks[i](POST_ACT_STAGE, agent, env)
    end

    return nothing
end

function run(
    n_episodes::Int64=100,
    episode_duration::Float64=5.0,
    update_actions_at::Float64=0.1,
    n_particles::Int64=10,
)
    @assert n_episodes > 0
    @assert episode_duration > 0
    @assert update_actions_at in 0.01:0.01:episode_duration
    @assert episode_duration % update_actions_at == 0
    @assert n_particles > 0

    Random.seed!(42)

    sim_consts = gen_sim_consts(n_particles, v₀)

    env_params = EnvParams(sim_consts.particle_radius, sim_consts.skin_r)

    rl_params = Params{TotalRewardPerEpisode}(
        n_particles, env_params, n_steps_before_actions_update
    )

    for i in 1:n_particles
        env = rl_params.envs[i]
        agent = rl_params.agents[i]

        rl_params.hooks[i](PRE_EXPERIMENT_STAGE, agent, env)
        agent(PRE_EXPERIMENT_STAGE, env)
    end

    for episode in 1:n_episodes
        dir, particles = init_sim_with_sim_consts(; sim_consts, parent_dir="RL")

        for i in 1:n_particles
            env = rl_params.envs[i]
            agent = rl_params.agents[i]

            rl_params.hooks[i](PRE_EPISODE_STAGE, agent, env)
            agent(PRE_EPISODE_STAGE, env)
        end

        for i in 1:n_particles
            rl_params.envs[i].particle = particles[i]
            rl_params.envs[i].state = (nothing, nothing)
        end

        rl_params.env_params.reward = 0.0

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

        for i in 1:n_particles
            env = rl_params.envs[i]
            agent = rl_params.agents[i]

            rl_params.hooks[i](POST_EPISODE_STAGE, agent, env)
            agent(POST_EPISODE_STAGE, env)
        end
    end

    for i in 1:n_particles
        env = rl_params.envs[i]
        agent = rl_params.agents[i]

        rl_params.hooks[i](POST_EXPERIMENT_STAGE, agent, env)
    end

    return rl_params.hooks
end

end # module