using UnityEngine;
#if ENABLE_INPUT_SYSTEM
using UnityEngine.InputSystem;
#endif

/// <summary>
/// Gravity-free "insect" surface walker: crawls along any surface (floors, ramps,
/// walls, ceilings, around convex/concave edges) regardless of slope. No
/// CharacterController, no Rigidbody — the transform is moved kinematically and
/// re-stuck to the surface every frame via sphere casts.
///
/// Each step: WASD is taken camera-relative (the camera stays world-up) and
/// projected onto the current surface tangent plane, the body advances along that
/// plane, then a small set of probes re-finds the surface to follow:
///   1. a wall directly ahead (concave corner) becomes the new ground,
///   2. otherwise a down-cast (into the surface) keeps the body stuck on
///      flat/ramped/concave ground,
///   3. otherwise a forward-sweeping cast wraps the body over a convex edge.
/// The body's up is aligned to the surface normal; its forward faces the move
/// direction. Designed to coexist with <see cref="PlayerCharacterController"/> on
/// the same GameObject, toggled by the GameModeManager (only one is enabled).
/// </summary>
[DisallowMultipleComponent]
public class InsectController : MonoBehaviour
{
    [Header("Movement")]
    [Tooltip("Crawl speed along the surface (units/second).")]
    public float moveSpeed = 4f;

    [Tooltip("Speed multiplier while the sprint key (Left Shift) is held.")]
    public float sprintSpeedMultiplier = 1.8f;

    [Tooltip("How snappily the body re-aligns its up to the surface normal and turns toward the move direction (1/second; higher = tighter).")]
    public float alignSmoothing = 16f;

    [Header("Camera")]
    [Tooltip("Interpret WASD relative to the camera (projected onto the surface). Off = world X/Z axes projected onto the surface.")]
    public bool cameraRelative = true;

    [Tooltip("Camera used for camera-relative movement. Empty = Camera.main.")]
    public Transform cameraTransform;

    [Header("Surface Sticking")]
    [Tooltip("Distance kept between the transform origin and the surface it walks on (tune to the character's pivot; 0 = origin sits on the surface).")]
    public float hoverHeight = 0f;

    [Tooltip("Radius of the probe spheres. Roughly the body's half-width; keeps the walker off sharp edges.")]
    public float probeRadius = 0.3f;

    [Tooltip("How far the body can step up onto a rise or drop down a dip while staying stuck.")]
    public float stepHeight = 0.4f;

    [Tooltip("Surfaces the walker can stick to.")]
    public LayerMask groundMask = ~0;

    [Header("Edge Wrapping")]
    [Tooltip("A surface ahead steeper than this (degrees from the current up) is treated as a wall to climb into (concave corner).")]
    [Range(5f, 90f)]
    public float wallWrapAngle = 35f;

    [Tooltip("How far ahead to look for a wall to climb into.")]
    public float wallProbeDistance = 0.6f;

    [Tooltip("Largest angle the body wraps around a convex edge in one step (degrees). Higher = follows sharper outside corners.")]
    [Range(30f, 170f)]
    public float maxWrapAngle = 150f;

    [Header("Animation (optional)")]
    public Animator animator;

    [Tooltip("Animator bool set true while crawling.")]
    public string runningParameter = "Running";

    /// <summary>When false, input is ignored (the body holds its surface pose).</summary>
    public bool ControlEnabled { get; set; } = true;

    /// <summary>True after the last step found a surface to stick to.</summary>
    public bool OnSurface => _onSurface;

    /// <summary>Surface normal the body is currently stuck to (its up).</summary>
    public Vector3 SurfaceNormal => _surfaceNormal;

    private const float RunningSpeedThresholdSqr = 0.04f; // (0.2 m/s)^2
    private const float Eps = 1e-5f;

    private int _runningHash;
    private bool _onSurface;
    private Vector3 _surfaceNormal = Vector3.up;
    private Vector3 _lastMove;
    private readonly RaycastHit[] _hits = new RaycastHit[16];

    void Awake()
    {
        _runningHash = Animator.StringToHash(runningParameter);
        if (!cameraTransform && Camera.main)
            cameraTransform = Camera.main.transform;
        if (groundMask.value == 0)
            groundMask = ~0;
        _surfaceNormal = transform.up;
    }

    void Update()
    {
        float h = 0f, v = 0f;
        bool sprinting = false;

        if (ControlEnabled)
        {
#if ENABLE_INPUT_SYSTEM
            var keyboard = Keyboard.current;
            if (keyboard != null)
            {
                if (keyboard.aKey.isPressed) h -= 1f;
                if (keyboard.dKey.isPressed) h += 1f;
                if (keyboard.sKey.isPressed) v -= 1f;
                if (keyboard.wKey.isPressed) v += 1f;
                sprinting = keyboard.leftShiftKey.isPressed;
            }
#else
            h = Input.GetAxisRaw("Horizontal");
            v = Input.GetAxisRaw("Vertical");
            sprinting = Input.GetKey(KeyCode.LeftShift);
#endif
        }

        Step(h, v, sprinting, Time.deltaTime);
    }

    /// <summary>
    /// Advances the body one frame: projects the (h,v) input onto the surface,
    /// moves along it, re-sticks to the surface and re-orients. Public so it can be
    /// driven deterministically in tests (set <see cref="cameraRelative"/> false to
    /// map input to world axes without a camera).
    /// </summary>
    public void Step(float h, float v, bool sprinting, float dt)
    {
        Vector3 up = transform.up;
        Vector3 wish = InputToWorld(up, h, v);
        float inputMag = Mathf.Clamp01(new Vector2(h, v).magnitude);
        float speed = sprinting ? moveSpeed * sprintSpeedMultiplier : moveSpeed;

        Vector3 move = wish * (speed * inputMag * dt);
        Vector3 tentative = transform.position + move;
        _lastMove = move;

        if (ProbeSurface(tentative, up, wish, out Vector3 point, out Vector3 normal)
            && normal.sqrMagnitude > Eps)
        {
            normal.Normalize();
            transform.position = point + normal * hoverHeight;
            _surfaceNormal = normal;
            _onSurface = true;
            OrientTo(normal, wish, dt);
        }
        else
        {
            // No surface within reach (e.g. ran off the end of geometry): keep
            // crawling along the last tangent instead of falling.
            transform.position = tentative;
            _onSurface = false;
        }

        if (animator)
            animator.SetBool(_runningHash, _onSurface && inputMag > 0f
                && _lastMove.sqrMagnitude / Mathf.Max(dt * dt, 1e-8f) > RunningSpeedThresholdSqr);
    }

    /// <summary>
    /// Immediately probes straight into the current surface and places the body on
    /// it (no smoothing). Used when entering insect mode so the first frame is stuck.
    /// </summary>
    public void SnapToSurface()
    {
        Vector3 up = transform.up;
        if (ProbeSurface(transform.position, up, Vector3.zero, out Vector3 point, out Vector3 normal)
            && normal.sqrMagnitude > Eps)
        {
            normal.Normalize();
            transform.position = point + normal * hoverHeight;
            _surfaceNormal = normal;
            _onSurface = true;
            Vector3 fwd = Vector3.ProjectOnPlane(transform.forward, normal);
            if (fwd.sqrMagnitude < Eps) fwd = Vector3.ProjectOnPlane(transform.right, normal);
            if (fwd.sqrMagnitude > Eps)
                transform.rotation = Quaternion.LookRotation(fwd.normalized, normal);
        }
    }

    /// <summary>
    /// Maps WASD to a world-space direction in the surface tangent plane. The camera
    /// stays world-up, so its axes are projected onto the plane; if an axis is nearly
    /// parallel to the surface normal (on a wall/ceiling) it is rebuilt from the other
    /// axis so the mapping never collapses.
    /// </summary>
    private Vector3 InputToWorld(Vector3 up, float h, float v)
    {
        Vector3 right, fwd;
        if (cameraRelative && cameraTransform)
        {
            right = Vector3.ProjectOnPlane(cameraTransform.right, up);
            fwd = Vector3.ProjectOnPlane(cameraTransform.forward, up);
        }
        else
        {
            right = Vector3.ProjectOnPlane(Vector3.right, up);
            fwd = Vector3.ProjectOnPlane(Vector3.forward, up);
        }

        if (fwd.sqrMagnitude < Eps) fwd = Vector3.Cross(right, up);
        if (right.sqrMagnitude < Eps) right = Vector3.Cross(up, fwd);
        if (fwd.sqrMagnitude < Eps || right.sqrMagnitude < Eps)
            return Vector3.zero;

        Vector3 dir = right.normalized * h + fwd.normalized * v;
        return dir.sqrMagnitude > 1f ? dir.normalized : dir;
    }

    /// <summary>
    /// Finds the surface the body should stick to at <paramref name="pos"/>, trying in
    /// order: a wall ahead (concave corner), the ground below (flat/ramp/concave), a
    /// convex edge wrap. Returns the surface contact point and normal.
    /// </summary>
    private bool ProbeSurface(Vector3 pos, Vector3 up, Vector3 moveDir, out Vector3 point, out Vector3 normal)
    {
        bool moving = moveDir.sqrMagnitude > Eps;
        // Lift the sideways/edge probes clear of the surface we are already on, so the
        // probe sphere never starts penetrating it (which would self-hit or, worse, make
        // SphereCast report a bogus point at the world origin on an initial overlap).
        Vector3 probeOrigin = pos + up * Mathf.Max(hoverHeight, probeRadius + 0.05f);

        // 1) Concave corner: a wall right in front becomes the new ground to climb into.
        if (moving)
        {
            Vector3 d = moveDir.normalized;
            if (CastBest(probeOrigin, d, probeRadius + wallProbeDistance, out Vector3 wp, out Vector3 wn)
                && Vector3.Angle(wn, up) > wallWrapAngle)
            {
                point = wp; normal = wn; return true;
            }
        }

        // 2) Ground follow: cast from above the body straight into the surface.
        float startUp = hoverHeight + stepHeight;
        float downDist = startUp + hoverHeight + stepHeight + probeRadius;
        if (CastBest(pos + up * startUp, -up, downDist, out Vector3 gp, out Vector3 gn))
        {
            point = gp; normal = gn; return true;
        }

        // 3) Convex edge: the surface curved away ahead. Sweep the down-probe forward,
        //    pitching it over the edge until it catches the wrapped surface.
        if (moving)
        {
            Vector3 axis = Vector3.Cross(moveDir.normalized, up);
            if (axis.sqrMagnitude > Eps)
            {
                axis.Normalize();
                float reach = hoverHeight + stepHeight + probeRadius + 0.5f;
                for (float ang = 20f; ang <= maxWrapAngle; ang += 20f)
                {
                    Vector3 d = Quaternion.AngleAxis(ang, axis) * (-up);
                    if (CastBest(probeOrigin, d, reach, out Vector3 ep, out Vector3 en))
                    {
                        point = ep; normal = en; return true;
                    }
                }
            }
        }

        point = pos; normal = up; return false;
    }

    /// <summary>
    /// Sphere-casts and returns the nearest hit that is not our own collider and has a
    /// usable (non-zero) normal. False if nothing valid was hit.
    /// </summary>
    private bool CastBest(Vector3 origin, Vector3 dir, float dist, out Vector3 point, out Vector3 normal)
    {
        point = origin;
        normal = Vector3.zero;
        if (dir.sqrMagnitude < Eps)
            return false;

        int n = Physics.SphereCastNonAlloc(
            origin, probeRadius, dir.normalized, _hits, dist, groundMask, QueryTriggerInteraction.Ignore);

        float best = float.MaxValue;
        bool found = false;
        for (int i = 0; i < n; i++)
        {
            RaycastHit hit = _hits[i];
            if (!hit.collider || hit.collider.transform.IsChildOf(transform))
                continue;
            // A zero distance means the sphere started inside the collider; Unity then
            // reports point=(0,0,0) and normal=-dir, which would teleport us — discard it.
            if (hit.distance <= 1e-4f || hit.normal.sqrMagnitude < Eps)
                continue;
            if (hit.distance < best)
            {
                best = hit.distance;
                point = hit.point;
                normal = hit.normal;
                found = true;
            }
        }
        return found;
    }

    /// <summary>Eases the body's up toward the surface normal and its forward toward the move direction.</summary>
    private void OrientTo(Vector3 normal, Vector3 wish, float dt)
    {
        Vector3 fwd = Vector3.ProjectOnPlane(wish, normal);
        // When the move/forward is parallel to the new normal (walking straight into a
        // wall), fall back to the old up projected onto the surface: that points "up the
        // wall", so the body keeps climbing instead of snapping a 90-degree yaw.
        if (fwd.sqrMagnitude < Eps) fwd = Vector3.ProjectOnPlane(transform.forward, normal);
        if (fwd.sqrMagnitude < Eps) fwd = Vector3.ProjectOnPlane(transform.up, normal);
        if (fwd.sqrMagnitude < Eps) fwd = Vector3.ProjectOnPlane(transform.right, normal);
        if (fwd.sqrMagnitude < Eps)
            return;

        Quaternion target = Quaternion.LookRotation(fwd.normalized, normal);
        float t = alignSmoothing > 0f ? 1f - Mathf.Exp(-alignSmoothing * dt) : 1f;
        transform.rotation = Quaternion.Slerp(transform.rotation, target, t);
    }

    void OnDrawGizmosSelected()
    {
        Gizmos.color = Color.cyan;
        Vector3 c = transform.position + transform.up * hoverHeight;
        Gizmos.DrawWireSphere(c, probeRadius);
        Gizmos.color = Color.green;
        Gizmos.DrawLine(c, c + _surfaceNormal * 0.5f);
    }
}