planetsim/test_sealevel.cpp

// Headless test for the sea-level controller's runaway guard (no display needed).
//
//   g++ -std=c++17 -O2 -Isrc/sim test_sealevel.cpp src/sim/IcoSphere.cpp
//       src/sim/Planet.cpp src/sim/PlanetTectonics.cpp src/sim/PlanetDrift.cpp
//       src/sim/PlanetErosion.cpp src/sim/PlanetHydrology.cpp
//       src/sim/PlanetBiomes.cpp src/sim/PlanetClimate.cpp src/sim/PlanetLive.cpp
//       src/sim/PlanetOcean.cpp src/sim/PlanetBiota.cpp src/sim/PlanetFloraGen.cpp
//       src/sim/PlanetFaunaGen.cpp src/sim/PlanetFungiGen.cpp src/sim/PlanetIO.cpp
//       -o /tmp/ts && /tmp/ts
//
// Reproduces the bug reported after a long real run: on a world whose buoyant
// (continental) crust area permanently falls short of landFractionTarget (crust
// generation is independent of that geographic target -- nothing guarantees they
// match), the old unbounded adjustSeaLevel() had no way to reach the target using
// real land, so it kept sinking seaLevel to "poach" ageing oceanic crust as fake
// land -- and since that crust keeps deepening with age, the target kept slipping
// away, sinking seaLevel indefinitely (observed: -2900 m after ~1340 My, still
// falling). Verifies the seaLevelMin/seaLevelMax clamp stops the runaway in both
// directions, that it actually engages (proving the mechanism still adjusts, not
// just trivially idle), and that a normal, non-pathological world never comes
// close to the clamp.

#include "Planet.hpp"
#include <cstdio>
#include <cmath>

static int failures = 0;
static void check(bool cond, const char* what) {
    std::printf("  [%s] %s\n", cond ? "PASS" : "FAIL", what);
    if (!cond) ++failures;
}

int main() {
    std::printf("Sea level: runaway guard\n");

    // --- Scenario 1: continental crust structurally short of the target -------
    // 25% of cells continental near continentBase, 75% oceanic spread smoothly
    // across a wide, continuous depth range (mimicking a real mix of young and
    // long-ageing seafloor, not a cliff) -- deliberately short of the 30% default
    // landFractionTarget. With a continuous distribution, each single seaLevelStep
    // nudge always captures more cells and strictly reduces the error, so the
    // pre-fix controller would keep taking that nudge forever, sinking without end.
    {
        PlanetConfig cfg; cfg.subdivisions = 3; cfg.seed = 99;
        Planet planet; planet.generate(cfg);
        const int n = (int)planet.cells.size();
        for (int i = 0; i < n; ++i) {
            bool continental = (i % 4) == 0;   // 25% < landFractionTarget (30%)
            planet.setCrust(i, continental);
            if (continental) planet.setElevation(i, planet.cfg.continentBase + (i % 7) * 10.0);
            else              planet.setElevation(i, -10.0 - 8000.0 * (double)i / n);  // continuous -10..-8010 m
        }
        double startSeaLevel = planet.cfg.seaLevel;
        // erode()'s transport is dtMy-scaled; dt=0 isolates the periodic
        // adjustSeaLevel() call (still triggered by the iteration counter) from
        // any elevation change, so the crafted distribution above stays intact.
        for (int i = 0; i < planet.cfg.seaLevelEvery * 400; ++i) planet.erode(0.0);

        check(planet.cfg.seaLevel < startSeaLevel - 100.0,
              "short-of-target land engages the controller (seaLevel moves down)");
        check(planet.cfg.seaLevel >= planet.cfg.seaLevelMin,
              "seaLevel never sinks past seaLevelMin (the pre-fix bug: it had no floor)");
        check(planet.cfg.seaLevel <= planet.cfg.seaLevelMax, "seaLevel stays within the upper bound too");
    }

    // --- Scenario 2: mirror case, land far in excess of the target ------------
    {
        PlanetConfig cfg; cfg.subdivisions = 3; cfg.seed = 100;
        Planet planet; planet.generate(cfg);
        const int n = (int)planet.cells.size();
        for (int i = 0; i < n; ++i) {
            bool continental = (i % 4) != 0;   // 75% >> landFractionTarget (30%)
            planet.setCrust(i, continental);
            if (continental) planet.setElevation(i, 10.0 + 8000.0 * (double)i / n);   // continuous 10..8010 m
            else              planet.setElevation(i, planet.cfg.oceanBase + (i % 7) * 10.0);
        }
        double startSeaLevel = planet.cfg.seaLevel;
        for (int i = 0; i < planet.cfg.seaLevelEvery * 400; ++i) planet.erode(0.0);

        check(planet.cfg.seaLevel > startSeaLevel + 100.0,
              "excess land engages the controller (seaLevel moves up)");
        check(planet.cfg.seaLevel <= planet.cfg.seaLevelMax,
              "seaLevel never climbs past seaLevelMax (mirror of the sinking bug)");
        check(planet.cfg.seaLevel >= planet.cfg.seaLevelMin, "seaLevel stays within the lower bound too");
    }

    // --- Scenario 3: a normal, freshly-generated world never approaches the ---
    // clamp -- the guard is a safety rail for the pathological case, not
    // something that interferes with ordinary sea-level settling.
    {
        PlanetConfig cfg; cfg.subdivisions = 4; cfg.seed = 42;
        Planet planet; planet.generate(cfg);
        for (int i = 0; i < 40; ++i) planet.step();   // settle Phase-1 relief first
        planet.drifting = true;
        for (int i = 0; i < planet.cfg.seaLevelEvery * 20; ++i) planet.erode(planet.cflDtMy());

        check(planet.cfg.seaLevel > planet.cfg.seaLevelMin * 0.5 && planet.cfg.seaLevel < planet.cfg.seaLevelMax * 0.5,
              "a normal world's sea level settles well clear of the clamp bounds");
    }

    std::printf(failures ? "\nFAILURES: %d\n" : "\nALL SEA LEVEL CHECKS PASSED\n", failures);
    return failures ? 1 : 0;
}