#include <math.h>
#include "config.h"
#include "forecast.h"

// Full Zambretti phrases, index 0='A' .. 25='Z'.
static const char* const ZTEXT[26] = {
  "Settled fine weather",                    // A
  "Fine weather",                            // B
  "Becoming fine",                           // C
  "Fine, becoming less settled",             // D
  "Fine, possibly showers",                  // E
  "Fairly fine, improving",                  // F
  "Fairly fine, possibly showers early",     // G
  "Fairly fine, showers later",              // H
  "Showery early, improving",                // I
  "Changeable, improving",                   // J
  "Fairly fine, showers likely",             // K
  "Rather unsettled, clearing later",        // L
  "Unsettled, probably improving",           // M
  "Showery, bright intervals",               // N
  "Showery, becoming unsettled",             // O
  "Changeable, some rain",                   // P
  "Unsettled, short fine intervals",         // Q
  "Unsettled, rain later",                   // R
  "Unsettled, rain at times",                // S
  "Very unsettled, finer at times",          // T
  "Rain at times, worse later",              // U
  "Rain at times, becoming very unsettled",  // V
  "Rain at frequent intervals",              // W
  "Very unsettled, rain",                    // X
  "Stormy, possibly improving",              // Y
  "Stormy, much rain"                        // Z
};

// Map a constrained Zambretti number to a letter, per trend (G6EJD tables).
static char letterRising(int z)  { const char* m = "ABCFGIJLMQTYZ"; return m[z - 1]; } // z 1..13
static char letterFalling(int z) { const char* m = "ABDHORUXZ";     return m[z - 1]; } // z 1..9
static char letterSteady(int z)  { const char* m = "ABEKNPSWXZ";    return m[z - 1]; } // z 1..10

static int clampi(int v, int lo, int hi) { return v < lo ? lo : (v > hi ? hi : v); }

static WxCategory categoryOf(char letter) {
  switch (letter) {
    case 'A': case 'B': case 'C': case 'F':                       return WX_FINE;
    case 'E': case 'G': case 'I': case 'J': case 'K':
    case 'M': case 'N': case 'Q':                                 return WX_FAIR;
    case 'D': case 'H': case 'L': case 'O': case 'P':             return WX_CHANGEABLE;
    case 'R': case 'S': case 'T': case 'U': case 'V': case 'W':
    case 'X':                                                     return WX_RAIN;
    case 'Y': case 'Z':                                           return WX_STORM;
    default:                                                      return WX_UNKNOWN;
  }
}

Trend classifyTrend(float d) {
  if (d >  TREND_THRESHOLD_HPA) return TREND_RISING;
  if (d < -TREND_THRESHOLD_HPA) return TREND_FALLING;
  return TREND_STEADY;
}

Forecast computeForecast(float p, Trend trend, int month) {
  bool winter = (month < 4 || month > 9);   // northern hemisphere
  int z;
  char letter;

  if (trend == TREND_RISING) {
    z = (int)lround(-0.1449 * p + 150.18);
    if (winter) z += 1;
    z = clampi(z, 1, 13);
    letter = letterRising(z);
  } else if (trend == TREND_FALLING) {
    z = (int)lround(0.0000257935 * p * p * p
                    - 0.078482105 * p * p
                    + 79.4582219457 * p
                    - 26762.7164899421);
    if (winter) z -= 1;
    z = clampi(z, 1, 9);
    letter = letterFalling(z);
  } else {
    z = (int)lround(0.0000258964 * p * p * p
                    - 0.07753778137 * p * p
                    + 77.2287820569 * p
                    - 25582.130426005);
    z = clampi(z, 1, 10);
    letter = letterSteady(z);
  }

  return Forecast{ letter, ZTEXT[letter - 'A'], categoryOf(letter) };
}

const char* forecastTextForLetter(char letter) {
  if (letter < 'A' || letter > 'Z') return "";
  return ZTEXT[letter - 'A'];
}

const char* categoryShort(WxCategory c) {
  switch (c) {
    case WX_FINE:       return "Fine";
    case WX_FAIR:       return "Fair";
    case WX_CHANGEABLE: return "Changeable";
    case WX_RAIN:       return "Rain";
    case WX_STORM:      return "Storm";
    default:            return "...";
  }
}