/**
 * Simulator — random-walk driver for the measurement input.
 *
 * Lifted verbatim from Measurement.simulateInput. The orchestrator decides
 * what to do with the returned value (originally written to `inputValue`),
 * so this module owns nothing but the walk and its bounds.
 */
class Simulator {
  constructor({ config, logger } = {}) {
    if (!config || !config.scaling) {
      throw new Error('Simulator requires { config.scaling }');
    }
    this.config = config;
    this.logger = logger || { warn() {}, info() {}, debug() {}, error() {} };

    const s = config.scaling;
    this.inputRange = Math.abs(s.inputMax - s.inputMin);
    this.processRange = Math.abs(s.absMax - s.absMin);
    this.simValue = 0;
  }

  step() {
    const s = this.config.scaling;
    const sign = Math.random() < 0.5 ? -1 : 1;
    let maxStep;

    if (s.enabled) {
      // Step size scales with the live input window; fall back to 1 so a
      // collapsed range still wanders instead of freezing at zero.
      maxStep = this.inputRange > 0 ? this.inputRange * 0.05 : 1;
      if (this.simValue < s.inputMin || this.simValue > s.inputMax) {
        this.logger.warn(`Simulated value ${this.simValue} is outside of input range constraining between min=${s.inputMin} and max=${s.inputMax}`);
        this.simValue = _constrain(this.simValue, s.inputMin, s.inputMax);
      }
    } else {
      maxStep = this.processRange > 0 ? this.processRange * 0.05 : 1;
      if (this.simValue < s.absMin || this.simValue > s.absMax) {
        this.logger.warn(`Simulated value ${this.simValue} is outside of abs range constraining between min=${s.absMin} and max=${s.absMax}`);
        this.simValue = _constrain(this.simValue, s.absMin, s.absMax);
      }
    }

    this.simValue += sign * Math.random() * maxStep;
    return this.simValue;
  }

  reset() {
    this.simValue = 0;
  }

  get current() {
    return this.simValue;
  }
}

function _constrain(v, lo, hi) {
  return Math.min(Math.max(v, lo), hi);
}

module.exports = Simulator;