frontend/trace-buffer.ts

import { TraceData } from './types';

export type PlaybackMode = 'live' | 'paused' | 'slow' | 'fast' | 'catchup';

export interface BufferState {
  mode: PlaybackMode;
  speed: number; // Multiplier: 0.25, 0.5, 1, 2, 4
  bufferSize: number;
  currentSize: number;
  writePosition: number;
  readPosition: number;
  droppedCount: number;
  isPaused: boolean;
}

export interface TraceBufferConfig {
  maxSize?: number;
  updateInterval?: number;
  batchSize?: number;
}

type BufferListener = (traces: TraceData[], state: BufferState) => void;

export class TraceBuffer {
  private buffer: (TraceData | null)[];
  private maxSize: number;
  private writePos: number = 0;
  private readPos: number = 0;
  private currentSize: number = 0;
  private droppedCount: number = 0;
  
  private mode: PlaybackMode = 'live';
  private speed: number = 1;
  private isPaused: boolean = false;
  
  private listeners: Set<BufferListener> = new Set();
  private updateTimer: NodeJS.Timeout | null = null;
  private updateInterval: number;
  private batchSize: number;
  
  private pendingTraces: TraceData[] = [];
  private lastUpdateTime: number = 0;
  private targetFPS: number = 60;
  
  constructor(config: TraceBufferConfig = {}) {
    this.maxSize = config.maxSize || 10000;
    this.updateInterval = config.updateInterval || 16; // ~60fps
    this.batchSize = config.batchSize || 10;
    this.buffer = new Array(this.maxSize).fill(null);
    
    this.startUpdateLoop();
  }
  
  private startUpdateLoop(): void {
    const update = () => {
      const now = Date.now();
      const deltaTime = now - this.lastUpdateTime;
      
      if (!this.isPaused && this.pendingTraces.length > 0) {
        const effectiveInterval = this.updateInterval / this.speed;
        
        if (deltaTime >= effectiveInterval) {
          this.processPendingTraces();
          this.lastUpdateTime = now;
        }
      }
      
      this.updateTimer = setTimeout(update, Math.max(1, this.updateInterval));
    };
    
    update();
  }
  
  private processPendingTraces(): void {
    if (this.pendingTraces.length === 0) return;
    
    let tracesToProcess: TraceData[];
    
    switch (this.mode) {
      case 'live':
        // Process in real-time batches
        tracesToProcess = this.pendingTraces.splice(0, this.batchSize);
        break;
        
      case 'slow':
        // Process one at a time for slow motion
        tracesToProcess = this.pendingTraces.splice(0, 1);
        break;
        
      case 'fast':
        // Process larger batches for fast forward
        tracesToProcess = this.pendingTraces.splice(0, this.batchSize * 4);
        break;
        
      case 'catchup':
        // Process all pending to catch up
        tracesToProcess = this.pendingTraces.splice(0, this.pendingTraces.length);
        this.mode = 'live'; // Return to live after catching up
        break;
        
      default:
        tracesToProcess = [];
    }
    
    if (tracesToProcess.length > 0) {
      this.notifyListeners(tracesToProcess);
    }
  }
  
  public push(trace: TraceData): void {
    // Add to ring buffer
    if (this.currentSize >= this.maxSize) {
      // Buffer is full, overwrite oldest
      this.droppedCount++;
    } else {
      this.currentSize++;
    }
    
    this.buffer[this.writePos] = trace;
    this.writePos = (this.writePos + 1) % this.maxSize;
    
    // Add to pending traces for processing
    if (!this.isPaused) {
      this.pendingTraces.push(trace);
    }
  }
  
  public setMode(mode: PlaybackMode): void {
    this.mode = mode;
    
    switch (mode) {
      case 'paused':
        this.isPaused = true;
        break;
        
      case 'catchup':
        this.isPaused = false;
        // Will process all pending traces
        break;
        
      default:
        this.isPaused = false;
    }
  }
  
  public setSpeed(speed: number): void {
    this.speed = Math.max(0.25, Math.min(4, speed));
  }
  
  public pause(): void {
    this.isPaused = true;
    this.mode = 'paused';
  }
  
  public resume(): void {
    this.isPaused = false;
    this.mode = 'live';
  }
  
  public clear(): void {
    this.buffer.fill(null);
    this.writePos = 0;
    this.readPos = 0;
    this.currentSize = 0;
    this.droppedCount = 0;
    this.pendingTraces = [];
    this.notifyListeners([]);
  }
  
  public getState(): BufferState {
    return {
      mode: this.mode,
      speed: this.speed,
      bufferSize: this.maxSize,
      currentSize: this.currentSize,
      writePosition: this.writePos,
      readPosition: this.readPos,
      droppedCount: this.droppedCount,
      isPaused: this.isPaused,
    };
  }
  
  public getRecentTraces(count: number = 100): TraceData[] {
    const traces: TraceData[] = [];
    let pos = (this.writePos - 1 + this.maxSize) % this.maxSize;
    let collected = 0;
    
    while (collected < count && collected < this.currentSize) {
      const trace = this.buffer[pos];
      if (trace) {
        traces.unshift(trace);
        collected++;
      }
      pos = (pos - 1 + this.maxSize) % this.maxSize;
    }
    
    return traces;
  }
  
  public subscribe(listener: BufferListener): () => void {
    this.listeners.add(listener);
    
    // Send current state immediately
    listener(this.getRecentTraces(), this.getState());
    
    // Return unsubscribe function
    return () => {
      this.listeners.delete(listener);
    };
  }
  
  private notifyListeners(newTraces: TraceData[]): void {
    const state = this.getState();
    this.listeners.forEach(listener => {
      try {
        listener(newTraces, state);
      } catch (error) {
        console.error('Error in buffer listener:', error);
      }
    });
  }
  
  public destroy(): void {
    if (this.updateTimer) {
      clearTimeout(this.updateTimer);
      this.updateTimer = null;
    }
    this.listeners.clear();
    this.buffer = [];
    this.pendingTraces = [];
  }
}

// Singleton instance
let bufferInstance: TraceBuffer | null = null;

export function getTraceBuffer(config?: TraceBufferConfig): TraceBuffer {
  if (!bufferInstance) {
    bufferInstance = new TraceBuffer(config);
  }
  return bufferInstance;
}

export function destroyTraceBuffer(): void {
  if (bufferInstance) {
    bufferInstance.destroy();
    bufferInstance = null;
  }
}