// api/session-stats.prg — Compute session statistics (FLOAT MATH IN PRG)
//
// ctx:
//   session_id  — session ID
//   duration_sec — duration in seconds (from server.js)
//   record_count — total records
//   rows         — JSON array of records [{sensor: {tempC, batteryMv, ...}, channels: [...]}]
//
// PRG handles all numeric aggregation: mean, min, max, stddev for 6 channels.
// Float computation is done here (Harbour double precision) — easier maintenance
// than maintaining SQL JSONB aggregates in server.js.
//
// Copyright (c) 2026 Charles KWON OhJun

FUNCTION Main()
   LOCAL aRows, hRow, nDuration, nCount, hSensor, aChannels, hCh
   LOCAL nTempSum, nTempMin, nTempMax, nTempCnt
   LOCAL nBatStart, nBatEnd
   LOCAL aChStats, i, ch, peakSums, peakMins, peakMaxs, peakCounts, peakSqs
   LOCAL nMean, nVar, nStdDev, hOutCh, aChOut
   LOCAL cDur, nH, nM, nS

   aRows     := hb_jsonDecode(ctx_get("rows", "[]"))
   nDuration := Val(ctx_get("duration_sec", "0"))
   nCount    := Val(ctx_get("record_count", "0"))

   IF ! HB_ISARRAY(aRows) ; aRows := {} ; ENDIF

   // ─ Init accumulators ──
   nTempSum := 0
   nTempMin := 999.9
   nTempMax := -999.9
   nTempCnt := 0
   nBatStart := NIL
   nBatEnd := NIL

   // 6 channels: peak sum / min / max / count / sum-of-squares (for stddev)
   peakSums   := { 0, 0, 0, 0, 0, 0 }
   peakMins   := { 99999, 99999, 99999, 99999, 99999, 99999 }
   peakMaxs   := { -99999, -99999, -99999, -99999, -99999, -99999 }
   peakCounts := { 0, 0, 0, 0, 0, 0 }
   peakSqs    := { 0, 0, 0, 0, 0, 0 }

   // ─ Iterate records ──
   FOR EACH hRow IN aRows
      // sensor
      hSensor := fn_HGet(hRow, "sensor")
      IF HB_ISHASH(hSensor)
         IF hb_HHasKey(hSensor, "tempC") .AND. ValType(hSensor["tempC"]) == "N"
            nTempSum += hSensor["tempC"]
            nTempCnt++
            IF hSensor["tempC"] < nTempMin ; nTempMin := hSensor["tempC"] ; ENDIF
            IF hSensor["tempC"] > nTempMax ; nTempMax := hSensor["tempC"] ; ENDIF
         ENDIF
         IF hb_HHasKey(hSensor, "batteryMv") .AND. ValType(hSensor["batteryMv"]) == "N"
            IF nBatStart == NIL ; nBatStart := hSensor["batteryMv"] ; ENDIF
            nBatEnd := hSensor["batteryMv"]
         ENDIF
      ENDIF

      // channels
      aChannels := fn_HGet(hRow, "channels")
      IF HB_ISARRAY(aChannels)
         FOR EACH hCh IN aChannels
            IF HB_ISHASH(hCh) .AND. hb_HHasKey(hCh, "ch") .AND. hb_HHasKey(hCh, "peak")
               i := hCh["ch"] + 1   // 1-based
               IF i >= 1 .AND. i <= 6 .AND. ValType(hCh["peak"]) == "N"
                  peakSums[i]   += hCh["peak"]
                  peakSqs[i]    += hCh["peak"] * hCh["peak"]
                  peakCounts[i]++
                  IF hCh["peak"] < peakMins[i] ; peakMins[i] := hCh["peak"] ; ENDIF
                  IF hCh["peak"] > peakMaxs[i] ; peakMaxs[i] := hCh["peak"] ; ENDIF
               ENDIF
            ENDIF
         NEXT
      ENDIF
   NEXT

   // ─ Compute per-channel stats (mean, stddev) ──
   aChOut := {}
   FOR i := 1 TO 6
      ch := i - 1
      IF peakCounts[i] > 0
         nMean := peakSums[i] / peakCounts[i]
         // population variance: E[x^2] - (E[x])^2
         nVar := (peakSqs[i] / peakCounts[i]) - (nMean * nMean)
         IF nVar < 0 ; nVar := 0 ; ENDIF
         nStdDev := Sqrt(nVar)
         hOutCh := { ;
            "ch"         => ch, ;
            "peakAvg"    => Round(nMean, 2), ;
            "peakMin"    => peakMins[i], ;
            "peakMax"    => peakMaxs[i], ;
            "peakStdDev" => Round(nStdDev, 2), ;
            "samples"    => peakCounts[i] ;
         }
      ELSE
         hOutCh := { "ch" => ch, "peakAvg" => NIL, "peakMin" => NIL, "peakMax" => NIL, "peakStdDev" => NIL, "samples" => 0 }
      ENDIF
      AAdd(aChOut, hOutCh)
   NEXT

   // ─ Format duration HH:MM:SS ──
   nH := Int(nDuration / 3600)
   nM := Int((nDuration % 3600) / 60)
   nS := Int(nDuration % 60)
   cDur := iif(nDuration > 0, ;
      StrZero(nH, 2) + ":" + StrZero(nM, 2) + ":" + StrZero(nS, 2), ;
      "")

   AP_JSONRESPONSE({ ;
      "sessionId"   => ctx_get("session_id", ""), ;
      "recordCount" => nCount, ;
      "duration"    => cDur, ;
      "channels"    => aChOut, ;
      "temperature" => { ;
         "avg" => iif(nTempCnt > 0, Round(nTempSum / nTempCnt, 2), NIL), ;
         "min" => iif(nTempCnt > 0, nTempMin, NIL), ;
         "max" => iif(nTempCnt > 0, nTempMax, NIL) ;
      }, ;
      "battery" => { ;
         "startMv"        => nBatStart, ;
         "endMv"          => nBatEnd, ;
         "drainMv"        => iif(nBatStart != NIL .AND. nBatEnd != NIL, nBatStart - nBatEnd, NIL), ;
         "drainPctPerHour" => iif(nBatStart != NIL .AND. nBatEnd != NIL .AND. nDuration > 0, ;
                                   Round(((nBatStart - nBatEnd) / nBatStart) * 3600 / nDuration * 100, 2), NIL) ;
      } ;
   })

RETURN NIL

STATIC FUNCTION fn_HGet(h, k)
   IF HB_ISHASH(h) .AND. hb_HHasKey(h, k) ; RETURN h[k] ; ENDIF
RETURN NIL