using System;
using System.Collections.Generic;
using MinecraftClient.Mapping;
using MinecraftClient.Pathing.Execution.Telemetry;
using MinecraftClient.Physics;

namespace MinecraftClient.Pathing.Execution
{
    public enum PathExecutorState
    {
        InProgress,
        Failed,
        Complete
    }

    /// <summary>
    /// Drives a sequence of PathSegments by instantiating the correct IActionTemplate
    /// for each segment and ticking it every game tick.
    /// </summary>
    public sealed class PathExecutor
    {
        private readonly List<PathSegment> _segments;
        private int _currentIndex;
        private IActionTemplate? _currentTemplate;
        private readonly Action<string>? _debugLog;
        private readonly IPathExecutionObserver? _observer;
        private int _segmentTicks;
        private int _totalTicks;

        public bool IsComplete => _currentIndex >= _segments.Count && _currentTemplate is null;
        public int CurrentIndex => _currentIndex;
        public int TotalSegments => _segments.Count;
        public int TotalTicks => _totalTicks;
        public PathSegment? CurrentSegment =>
            _currentIndex < _segments.Count ? _segments[_currentIndex] : null;
        public PathSegment? LastSegment =>
            _segments.Count > 0 ? _segments[^1] : null;

        public PathExecutor(List<PathSegment> segments, Action<string>? debugLog = null, IPathExecutionObserver? observer = null)
        {
            _segments = segments;
            _currentIndex = 0;
            _debugLog = debugLog;
            _observer = observer;
            _observer?.OnNavigationStarted(segments);
            AdvanceToNextSegment();
        }

        public PathExecutorState Tick(Location pos, PlayerPhysics physics, MovementInput input, World world)
        {
            if (_currentTemplate is null)
            {
                input.Reset();
                return PathExecutorState.Complete;
            }

            _totalTicks++;
            int sameTickAdvanceCount = 0;
            while (_currentTemplate is not null)
            {
                _segmentTicks++;
                var state = _currentTemplate.Tick(pos, physics, input, world);

                switch (state)
                {
                    case TemplateState.Complete:
                        _observer?.OnSegmentCompleted(_currentIndex, _segments.Count, _segments[_currentIndex], _segmentTicks, pos);
                        _debugLog?.Invoke($"[PathExec] Segment {_currentIndex} complete " +
                            $"({_segments[_currentIndex].MoveType}) at ({pos.X:F2},{pos.Y:F2},{pos.Z:F2})");
                        _currentIndex++;
                        _segmentTicks = 0;
                        if (_currentIndex >= _segments.Count)
                        {
                            input.Reset();
                            _currentTemplate = null;
                            _debugLog?.Invoke("[PathExec] All segments complete!");
                            return PathExecutorState.Complete;
                        }

                        AdvanceToNextSegment();

                        // Do not waste the handoff tick when the next segment needs to issue
                        // a jump or braking input immediately.
                        sameTickAdvanceCount++;
                        if (sameTickAdvanceCount > _segments.Count)
                        {
                            input.Reset();
                            _debugLog?.Invoke("[PathExec] Excessive same-tick segment advances; aborting.");
                            return PathExecutorState.Failed;
                        }
                        continue;

                    case TemplateState.Failed:
                        input.Reset();
                        _observer?.OnSegmentFailed(_currentIndex, _segments.Count, _segments[_currentIndex], _segmentTicks, pos);
                        _debugLog?.Invoke($"[PathExec] Segment {_currentIndex} FAILED " +
                            $"({_segments[_currentIndex].MoveType}) at ({pos.X:F2},{pos.Y:F2},{pos.Z:F2}), " +
                            $"target was ({_currentTemplate.ExpectedEnd.X:F2},{_currentTemplate.ExpectedEnd.Y:F2},{_currentTemplate.ExpectedEnd.Z:F2})");
                        return PathExecutorState.Failed;

                    default:
                        return PathExecutorState.InProgress;
                }
            }

            input.Reset();
            return PathExecutorState.Complete;
        }

        private void AdvanceToNextSegment()
        {
            if (_currentIndex < _segments.Count)
            {
                var seg = _segments[_currentIndex];
                PathSegment? next = _currentIndex + 1 < _segments.Count ? _segments[_currentIndex + 1] : null;
                _currentTemplate = ActionTemplateFactory.Create(seg, next);
                _observer?.OnSegmentStarted(_currentIndex, _segments.Count, seg);
                _debugLog?.Invoke($"[PathExec] Starting segment {_currentIndex}/{_segments.Count}: {seg}");
            }
            else
            {
                _currentTemplate = null;
            }
        }
    }
}