'use strict';

/**
 * Shared helpers for AppDetail record processing.
 * Used by both api_pub.js and api_export.js to avoid duplication.
 */

const { RateUnits } = require('./constants');
const utils = require('./utils');

/**
 * Compute appRateApplied from raw fields.
 * Formula: lminApp / (grSpeed_m_s × swath_m) × 10000
 * Returns null on zero-division to avoid Infinity.
 */
function computeAppRateApplied(lminApp, grSpeed, swath) {
  if (!utils.isNumber(lminApp) || !utils.isNumber(grSpeed) || !utils.isNumber(swath)) return null;
  if (grSpeed === 0 || swath === 0) return null;
  return lminApp / (grSpeed * swath) * 10000;
}

/**
 * Convert app rate (L/ha or Kg/ha) + speed + swath to per-minute flow value.
 * For liquid this is L/min; for dry this is material/min.
 */
function flowRateFromAppRate(appRate, grSpeed, swath) {
  if (!utils.isNumber(appRate) || !utils.isNumber(grSpeed) || !utils.isNumber(swath)) return null;
  if (grSpeed <= 0 || swath <= 0) return null;
  return appRate * grSpeed * swath / 10000 * 60;
}

function isPositiveNumber(v) {
  return utils.isNumber(v) && v > 0;
}

/**
 * Resolve the rate unit code from session metadata or job fallback.
 */
function inferRateUnitCode(sessionMeta, job) {
  if (utils.isNumber(sessionMeta?.appRateUnit)) return sessionMeta.appRateUnit;
  if (typeof sessionMeta?.appRateUnitStr === 'string' && sessionMeta.appRateUnitStr.trim()) {
    const code = utils.rateStringToCode(sessionMeta.appRateUnitStr);
    if (utils.isNumber(code)) return code;
  }
  if (utils.isNumber(job?.appRateUnit)) return job.appRateUnit;
  return null;
}

/**
 * Determine whether the session material is liquid (vs dry/granular).
 * Returns true for liquid, false for dry, based on matType string or rate unit.
 */
function isLikelyLiquidMaterial(sessionMeta, rateUnitCode) {
  if (typeof sessionMeta?.matType === 'string') {
    const matType = sessionMeta.matType.trim().toLowerCase();
    if (matType === 'wet') return true;
    if (matType === 'dry') return false;
  }

  return rateUnitCode === RateUnits.OZ_PER_ACRE
    || rateUnitCode === RateUnits.GAL_PER_ACRE
    || rateUnitCode === RateUnits.LIT_PER_HA;
}

/**
 * Resolve a session target app rate into metric-per-hectare units.
 * Returns L/ha for liquid or Kg/ha for dry depending on source unit.
 */
function resolveTargetRatePerHa(sessionMeta, job) {
  const rawRate = utils.isNumber(sessionMeta?.appRate)
    ? sessionMeta.appRate
    : (utils.isNumber(job?.appRate) ? job.appRate : null);
  if (!utils.isNumber(rawRate)) return null;

  const unitCode = inferRateUnitCode(sessionMeta, job);
  if (!utils.isNumber(unitCode)) return rawRate;

  return utils.toMetricRate(rawRate, unitCode).value;
}

module.exports = {
  computeAppRateApplied,
  flowRateFromAppRate,
  isPositiveNumber,
  inferRateUnitCode,
  isLikelyLiquidMaterial,
  resolveTargetRatePerHa
};