using System.Text.Json;
using GameCli;

// Deterministic PRNG for start-pose randomization on reset.
// Seeded fresh on each reset if the caller supplies a seed.
var rng = new Random();

// Current world state and step counter. Reset on {"cmd":"reset"}.
var ship = ShipState.AtCenter();
int stepCount = 0;
int lastAction = 0;

// --- Startup handshake ---------------------------------------------------
var init = new InitMessage
{
    Init = new InitPayload
    {
        World = new[] { 1f, 1f },
        Dt = Physics.Dt,
        ObsDim = Observation.Dim,
        NActions = 4,
    },
};
Console.WriteLine(JsonSerializer.Serialize(init, ProtocolJsonContext.Default.InitMessage));
Console.Out.Flush();

// --- Read-line loop ------------------------------------------------------
string? line;
while ((line = Console.In.ReadLine()) is not null)
{
    if (line.Length == 0) continue;

    StepInput? input;
    try
    {
        input = JsonSerializer.Deserialize(line, ProtocolJsonContext.Default.StepInput);
    }
    catch (JsonException ex)
    {
        Console.Error.WriteLine($"invalid json: {ex.Message}");
        continue;
    }
    if (input is null) continue;

    // Reset command.
    if (input.Cmd == "reset")
    {
        if (input.Seed is int seed) rng = new Random(seed);
        ship = RandomStartPose(rng);
        stepCount = 0;
        lastAction = 0;
        WriteObservation((0.5f, 0.5f), reward: 0f, done: false);
        continue;
    }

    // Step command.
    int action = input.Action ?? 0;
    var target = (input.Target is { Length: >= 2 })
        ? (input.Target[0], input.Target[1])
        : (0.5f, 0.5f);

    ship = Physics.Step(ship, action);
    lastAction = action;
    stepCount++;

    float reward = Reward.Compute(ship, target, action);
    WriteObservation(target, reward, done: false);
}

// --- Helpers -------------------------------------------------------------
void WriteObservation((float X, float Y) target, float reward, bool done)
{
    var output = new StepOutput
    {
        Obs = Observation.Build(ship, target),
        State = new ShipStateDto
        {
            X = ship.X,
            Y = ship.Y,
            Angle = ship.Angle,
            Engine = lastAction,
        },
        Reward = reward,
        Done = done,
        Step = stepCount,
    };
    Console.WriteLine(JsonSerializer.Serialize(output, ProtocolJsonContext.Default.StepOutput));
    Console.Out.Flush();
}

static ShipState RandomStartPose(Random rng)
{
    // Random position in a comfortable box; zero velocity, near-upright.
    float x = 0.2f + (float)rng.NextDouble() * 0.6f;
    float y = 0.2f + (float)rng.NextDouble() * 0.4f;
    float angle = ((float)rng.NextDouble() - 0.5f) * 0.4f;  // ±0.2 rad
    return new ShipState(x, y, 0f, 0f, angle, 0f);
}