#include <LittleFS.h>
#include "config.h"
#include "history.h"

static Sample s_buf[HISTORY_SIZE];
static int    s_head  = 0;   // next write position
static int    s_count = 0;

void historyBegin() { s_head = 0; s_count = 0; }

void historyAdd(uint32_t epoch, float mslHpa, float tempC) {
  s_buf[s_head] = Sample{ epoch, mslHpa, tempC };
  s_head = (s_head + 1) % HISTORY_SIZE;
  if (s_count < HISTORY_SIZE) s_count++;
}

int historyCount() { return s_count; }

Sample historyGet(int i) {
  int start = (s_head - s_count + HISTORY_SIZE) % HISTORY_SIZE;
  return s_buf[(start + i) % HISTORY_SIZE];
}

Sample historyLatest() { return historyGet(s_count - 1); }

bool historyTrendDelta(float& outDelta) {
  if (s_count < 2) return false;
  Sample latest = historyLatest();
  if (latest.epoch < 10800UL) return false;
  uint32_t target = latest.epoch - 10800UL;   // 3 h earlier
  // Pick the newest sample at or before `target`. Scan all samples (do not
  // assume epochs are strictly increasing: an NTP correction can shift them).
  int idx = -1;
  uint32_t bestEpoch = 0;
  for (int i = 0; i < s_count; i++) {
    Sample s = historyGet(i);
    if (s.epoch <= target && s.epoch >= bestEpoch) { bestEpoch = s.epoch; idx = i; }
  }
  if (idx < 0) return false;
  Sample past = historyGet(idx);
  if (latest.epoch - past.epoch < 9000UL) return false;  // need >= 2.5 h span
  outDelta = latest.mslHpa - past.mslHpa;
  return true;
}

static const char* HPATH = "/history.dat";

// Binary format: [int32 count][count * Sample], stored oldest-first.
bool historySave() {
  File f = LittleFS.open(HPATH, "w");
  if (!f) return false;
  int32_t n = s_count;
  f.write((const uint8_t*)&n, sizeof(n));
  for (int i = 0; i < s_count; i++) {
    Sample s = historyGet(i);
    f.write((const uint8_t*)&s, sizeof(s));
  }
  f.close();
  return true;
}

bool historyLoad() {
  File f = LittleFS.open(HPATH, "r");
  if (!f) return false;
  int32_t n = 0;
  if (f.read((uint8_t*)&n, sizeof(n)) != sizeof(n)) { f.close(); return false; }
  if (n < 0 || n > HISTORY_SIZE) { f.close(); return false; }
  s_head = 0; s_count = 0;
  for (int i = 0; i < n; i++) {
    Sample s;
    if (f.read((uint8_t*)&s, sizeof(s)) != sizeof(s)) break;
    historyAdd(s.epoch, s.mslHpa, s.tempC);
  }
  f.close();
  return true;
}