using UnityEngine;

namespace MazeGen
{
    /// <summary>
    /// Top-down camera rig: smoothly glides to focus on newly entered rooms, and can be
    /// freely panned with WASD or by holding the middle mouse button and dragging. Any
    /// manual pan input cancels whatever auto-focus is currently in progress.
    /// </summary>
    public class MazeCameraController : MonoBehaviour
    {
        [SerializeField] private float panSpeed = 8f;
        [SerializeField] private float focusSharpness = 6f;
        [SerializeField] private float dragSensitivity = 1f;

        private Camera _camera;
        private Vector2? _focusTarget;
        private Vector2 _lastPointerScreenPos;
        private bool _isDragging;

        private void Awake()
        {
            _camera = GetComponent<Camera>();
            if (_camera == null) _camera = Camera.main;
        }

        /// <summary>Smoothly glides the camera to look at worldPosition.</summary>
        public void FocusOn(Vector2 worldPosition)
        {
            _focusTarget = worldPosition;
        }

        /// <summary>Instantly moves the camera to worldPosition, no smoothing.</summary>
        public void SnapTo(Vector2 worldPosition)
        {
            _focusTarget = null;
            transform.position = new Vector3(worldPosition.x, worldPosition.y, transform.position.z);
        }

        private void Update()
        {
            HandleDrag();
            HandleKeyboardPan();
            HandleAutoFocus();
        }

        private void HandleKeyboardPan()
        {
            Vector2 input = MazeInput.ReadWasdAxis();
            if (input.sqrMagnitude <= 0f) return;

            _focusTarget = null; // manual input takes over from auto-focus
            transform.position += new Vector3(input.x, input.y, 0f) * (panSpeed * Time.deltaTime);
        }

        private void HandleDrag()
        {
            bool middleHeldNow = MazeInput.IsMiddleMouseHeld();
            Vector2 pointerNow = MazeInput.GetPointerScreenPosition();

            if (middleHeldNow && !_isDragging)
            {
                _isDragging = true;
                _lastPointerScreenPos = pointerNow;
                return;
            }

            if (middleHeldNow)
            {
                Vector2 screenDelta = pointerNow - _lastPointerScreenPos;
                if (screenDelta.sqrMagnitude > 0f)
                {
                    _focusTarget = null; // manual input takes over from auto-focus
                    Vector2 worldDelta = ScreenDeltaToWorldDelta(screenDelta);
                    transform.position -= new Vector3(worldDelta.x, worldDelta.y, 0f);
                }
                _lastPointerScreenPos = pointerNow;
            }
            else
            {
                _isDragging = false;
            }
        }

        private void HandleAutoFocus()
        {
            if (!_focusTarget.HasValue) return;

            Vector2 current = transform.position;
            Vector2 target = _focusTarget.Value;

            // Framerate-independent exponential smoothing rather than a constant-speed move,
            // so the glide eases in and settles instead of arriving abruptly.
            float t = 1f - Mathf.Exp(-focusSharpness * Time.deltaTime);
            Vector2 next = Vector2.Lerp(current, target, t);
            transform.position = new Vector3(next.x, next.y, transform.position.z);

            if (Vector2.Distance(next, target) < 0.01f)
                _focusTarget = null;
        }

        private Vector2 ScreenDeltaToWorldDelta(Vector2 screenDelta)
        {
            if (_camera == null || Screen.height <= 0) return Vector2.zero;

            float worldUnitsPerPixel;
            if (_camera.orthographic)
            {
                worldUnitsPerPixel = (_camera.orthographicSize * 2f) / Screen.height;
            }
            else
            {
                // Rooms sit on the z = 0 plane; use the camera's distance to it as the
                // reference plane for converting a screen-space drag into world units.
                float distance = Mathf.Abs(transform.position.z);
                worldUnitsPerPixel = (2f * distance * Mathf.Tan(_camera.fieldOfView * 0.5f * Mathf.Deg2Rad)) / Screen.height;
            }

            return screenDelta * worldUnitsPerPixel * dragSensitivity;
        }
    }
}