using UnityEngine;

public class MainEngine : MonoBehaviour
{
    [Header("References")]
    public FuelTank fuelTank; // Reference to the fuel tank supplying this engine
    public Altimeter altimeter; // Reference to the altimeter for gravity calculations

    [Header("Engine Settings")]
    public float maxThrust = 1000f; // kN
    public float Isp = 300f;        // seconds
    public float throttleRampTime = 2f; // seconds to reach full throttle
    public float minStartupFlow = 0.05f; // minimum fraction of max flow to maintain ignition
    public AnimationCurve throttleCurve = AnimationCurve.Linear(0, 0, 1, 1);

    [Header("Efficiency Settings")]
    [Range(0f, 1f)] public float engineEfficiency = 1f; // e.g., reduce if engine is hot or damaged

    [Header("Engine Status")]
    public bool engineOnline = false;      // true if engine is running
    public bool engineIgnited = false;     // true if ignition completed
    public bool restartable = true;        // if false, engine cannot restart once shut down
    public float throttleInput = 0f;       // 0-1 input from pilot
    public float thrust = 0f;              // kN
    public float fuelFlowRate = 0f;        // kg/s

    private float effectiveThrottle = 0f;  // ramped throttle for smooth startup/shutdown
    private float startupTimer = 0f;
    private bool everStarted = false;      // tracks if engine has ever been started
    private float postIgnitionTimer = 0f;  // timer for post-ignition grace period
    private const float postIgnitionGrace = 0.5f; // seconds to allow ramp-up after ignition
    private float g = 9.81f; // local gravity from altimeter

    void Update()
    {
        HandleEngineState();
        UpdateThrottle();
        // Only calculate thrust and fuel flow if engine is ignited
        if (engineOnline && engineIgnited)
        {
            // Update post-ignition timer
            if (postIgnitionTimer < postIgnitionGrace)
                postIgnitionTimer += Time.deltaTime;
            CalculateThrustAndFuelFlow();
        }
        else
        {
            thrust = 0f;
            fuelFlowRate = 0f;
            postIgnitionTimer = 0f;
        }
    }

    /// <summary>
    /// Handles startup, shutdown, and engine cutout.
    /// </summary>
    private void HandleEngineState()
    {
        g = (float)altimeter.gh; // Update local gravity from altimeter each frame

        // Check if engine is offline and restartable conditions

        if (!engineOnline)
        {
            effectiveThrottle = Mathf.MoveTowards(effectiveThrottle, 0f, Time.deltaTime / throttleRampTime);
            thrust = 0f;
            fuelFlowRate = 0f;

            // Mark engine as having been started
            if (engineIgnited) everStarted = true;

            if (engineIgnited)
                Debug.Log("[MainEngine] Engine shutdown: engineOnline set to false.");
            engineIgnited = false;
            return;
        }

        // Prevent restart if engine is not restartable and was previously started
        if (!restartable && everStarted)
        {
            Debug.Log("[MainEngine] Engine shutdown: not restartable and already started.");
            engineOnline = false;
            effectiveThrottle = 0f;
            thrust = 0f;
            fuelFlowRate = 0f;
            engineIgnited = false;
            return;
        }

        // Engine is commanded online
        if (!engineIgnited)
        {
            // Startup delay / ignition sequence
            startupTimer += Time.deltaTime;
            if (startupTimer >= throttleRampTime)
            {
                engineIgnited = true;
                startupTimer = 0f;
                postIgnitionTimer = 0f; // reset grace period timer
                Debug.Log("[MainEngine] Engine ignition complete.");
            }
            else
            {
                // Slowly ramp effective throttle during startup
                effectiveThrottle = Mathf.Lerp(0f, throttleInput, startupTimer / throttleRampTime);
            }
        }
    }

    /// <summary>
    /// Smooths throttle input over time (fuel ramping)
    /// </summary>
    private void UpdateThrottle()
    {
        if (!engineOnline || !engineIgnited)
            return;

        // Smooth throttle changes to avoid instant jumps
        effectiveThrottle = Mathf.MoveTowards(effectiveThrottle, throttleInput, Time.deltaTime / throttleRampTime);
    }

    /// <summary>
    /// Calculates thrust and fuel flow based on current throttle and efficiency
    /// </summary>
    private void CalculateThrustAndFuelFlow()
    {
        // Base thrust from throttle curve and max thrust
        thrust = throttleCurve.Evaluate(effectiveThrottle) * maxThrust * engineEfficiency;

        // Fuel flow based on thrust and Isp
        fuelFlowRate = thrust / (Isp * g);

        // Request fuel from the tank if assigned
        if (fuelTank != null)
        {
            float fuelRequested = fuelFlowRate * Time.deltaTime;
            float fuelProvided = fuelTank.RequestFuel(fuelRequested);
            if (fuelProvided < fuelRequested)
            {
                Debug.Log($"[MainEngine] Engine flameout: insufficient fuel (requested {fuelRequested:F3}, got {fuelProvided:F3}).");
                engineIgnited = false;
                effectiveThrottle = 0f;
                thrust = 0f;
                fuelFlowRate = 0f;
                return;
            }
        }

        // Only check for flameout if engine is fully ignited and grace period has passed
        float nominalFlow = maxThrust / (Isp * g);
        if (engineIgnited && postIgnitionTimer >= postIgnitionGrace && (fuelFlowRate / nominalFlow) < minStartupFlow)
        {
            Debug.Log($"[MainEngine] Engine flameout: fuel flow below minimum ({fuelFlowRate / nominalFlow:F3} < {minStartupFlow}).");
            engineIgnited = false;   // engine flameout
            effectiveThrottle = 0f;
            thrust = 0f;
            fuelFlowRate = 0f;
        }
    }

    /// <summary>
    /// Call to turn the engine on
    /// </summary>
    public void StartEngine()
    {
        if (!engineOnline)
        {
            // Prevent starting if not restartable and already started
            if (!restartable && everStarted)
            {
                Debug.Log("[MainEngine] StartEngine() called but engine is not restartable and has already started.");
                return;
            }

            Debug.Log("[MainEngine] Engine start command received.");
            engineOnline = true;
            startupTimer = 0f;
        }
    }

    /// <summary>
    /// Call to turn the engine off
    /// </summary>
    public void ShutdownEngine()
    {
        Debug.Log("[MainEngine] Engine shutdown command received.");
        engineOnline = false;
        engineIgnited = false;
    }
    
    public void SetThrottle(float value)
    {
        throttleInput = Mathf.Clamp01(value);
    }
}