// The interface shared by the CPU and the GPU time loops.
export interface ChunkResult {
  firstSample: number;            // audio index of pressureFront[0]
  pressureFront: Float32Array;    // baffled Rayleigh pressure [Pa]
  pressureBack: Float32Array;     // diffracted back term [Pa]; unbaffled = front - back
  frames: Float32Array[];         // displacement w at every node, captured every `movieEvery` audio samples
  frameSamples: number[];         // audio sample index of each frame
  /** Normal acceleration of every node [m/s^2] for the samples [firstSample, firstSample + count), row-major (count, N); present when recording. */
  acceleration: Float32Array | null;
  dispFrames: Float32Array[];     // displacement w for the .cymsim record, every `dispEvery` audio samples
  dispSamples: number[];
}

export interface HitState { peakForce: number; contactTime: number; velocity: number; height: number }

export interface Diagnostics {
  time: number; kinetic: number; membrane: number; bending: number; exciters: number; maxWoverH: number; hits: HitState[];
}

/** What a backend needs to continue a run: its own arrays, opaque to everything but the same backend kind. */
export interface BackendState {
  kind: "cpu" | "gpu";
  step: number;                   // sub-steps done
  samplesDone: number;
  arrays: Record<string, Float32Array | Float64Array | Uint32Array>;
}

export interface BackendOptions {
  /** > 0 captures w for the replay movie every that many audio samples. */
  movieEvery?: number;
  /** > 0 captures w for the .cymsim displacement record every that many audio samples. */
  dispEvery?: number;
  /** Keep the audio-rate normal acceleration of every node (returned per chunk). */
  recordAcceleration?: boolean;
}

export interface SimulatorBackend {
  readonly kind: "cpu" | "gpu";
  readonly samplesDone: number;
  /** Largest chunk (audio samples) runChunk accepts. */
  readonly maxChunk: number;
  /** Advance by nSamples audio samples and return the pressure samples completed meanwhile. */
  runChunk(nSamples: number): Promise<ChunkResult>;
  diagnostics(): Promise<Diagnostics>;
  /** Transverse displacement w at every node, for the plate view. */
  displacement(): Promise<Float32Array>;
  /** The integrator state, for a .cymsim file; ``importState`` continues from one (same backend kind and set-up). */
  exportState(): Promise<BackendState>;
  importState(state: BackendState): Promise<void>;
  dispose(): void;
}

/** Sub-steps per audio sample times audio samples between file displacement frames, for a frame rate [fps]. */
export function dispEveryFor(fs: number, rate: number): number {
  return rate > 0 ? Math.max(1, Math.round(fs / rate)) : 0;
}