settled-reach/server/tests/cascade_golden.rs

//! Golden-seed regression for the Layer 0→1 generation cascade (#952, D-200, D-224).
//!
//! Pins two artifacts for one fixed input heightmap, in a single diffable JSON
//! golden (matching the `golden_suite.rs` convention):
//!   - **Layer 0** — SHA-256 of the source `heightmap.png` bytes. Flips if the
//!     Python heightmap generator (or the committed file) changes.
//!   - **Layer 1** — the serialized `Layer1Output` of the cascade run on a
//!     downsampled copy. Flips if the Rust drainage / feature / sub-biome code
//!     changes.
//!
//! The input is a real committed body heightmap (the #963 bake output), so this
//! is an end-to-end determinism guard. The cascade is downsampled to keep the
//! golden small while still exercising the full Layer-1 pipeline.
//!
//! Regenerate after an intended change:
//!   UPDATE_GOLDEN=1 cargo test --test cascade_golden
//!
//! Golden captured on x86_64. The downsample and sub-biome cost use f32, so a
//! different architecture could in principle round differently — regenerate
//! per-arch if CI ever moves off x86_64.
//!
//! **Deliberate re-pin (T-1170 Ruling 2a/2c/3f, A1):** `RiverNetwork` gained
//! an additive `river_downstream: Vec<u8>` field (per-`river_cells`-entry D8
//! downstream pointer + MOUTH/EDGE_DRAIN sentinel), and `extract_river_network`
//! stopped classifying pole-edge D8 exits (flow running off the grid's
//! top/bottom row) as `mouths` — they are grid artifacts, not river-meets-sea
//! events (Ruling 3f, Jeroen's capture question). On this fixture (GJ1c,
//! 256×128 downsample) that drops `mouths` from 19 to 3: 16 of the 19 were
//! pole-edge exits (now `RIVER_DOWNSTREAM_EDGE_DRAIN`), leaving the 3 real
//! sea-adjacent mouths (`RIVER_DOWNSTREAM_MOUTH`). `river_cells`/`attractors`
//! counts are unchanged (93/256) — this is a pure re-classification + one new
//! additive field, not a drainage-algorithm change.
//!
//! **Attractor cascade correction (T-1170 PR #197 review, Hoshe #4):** the A1
//! commit's "pure reclassification" framing overclaimed — `attractors` is
//! count-PARITY (256/256), not byte-identical. Mouths dropping 19→3 shrinks
//! `TerrainAnalysis::water_dist`'s seed set (`compute_water_dist` seeds from
//! `river_network.mouths`), which shifts the water-distance field, which
//! feeds `RawAttractor::strength` scoring in `features::extract_attractors`.
//! This is a principled, in-scope cascade (the pole-edge cells genuinely
//! aren't water-distance sources anymore) — not a bug — but it is a REAL
//! field-level change, not a no-op re-tagging. Restated accurately here so
//! the record doesn't imply byte-identical attractor output.
//!
//! **Second deliberate re-pin (T-1170 PR #197 review, Hoshe #1):**
//! `RiverNetwork` gained a second additive field, `river_seaward:
//! Vec<(u16,u16)>` — the real seaward neighbor position for MOUTH-sentinel
//! river cells, captured in the SAME `extract_river_network` pass (the
//! elevation check that already computes `(nr, nc)` to decide the MOUTH
//! sentinel). Fixes a second instance of the discard-then-need-it-later
//! anti-pattern Ruling 2b's `river_downstream` field fixed for interior D8
//! pointers: `river_course::build_edges` needs a real seaward cell to give
//! Mouth edges a non-degenerate chord (see `river_course.rs`'s
//! `build_edges` doc and `layer_proxy::tests::
//! all_real_gj1c_mouths_resolve_to_mouth_terminus_not_none` for the full
//! bug/fix story). `river_cells`/`mouths`/`attractors` counts unchanged by
//! this second re-pin (93/3/256) — purely the new parallel array, 3 non-
//! placeholder entries (one per real mouth).
//!
//! **Third deliberate re-pin (T-1185, D-227 amendment (4) — basin-outlet →
//! D8 river-network wiring):** `run_layer1`/`run_layer1_with_moisture` now
//! extends the D8-extracted `RiverNetwork` with every `BasinOutcome::
//! Overflow` basin's `outlet_path` as new river cells (the endorheic cue:
//! outflow-course PRESENCE). `attractors` (256) and `drainage_basins` are
//! UNCHANGED — the extension runs strictly after
//! `features::extract_attractors`, by design, so basin-outlet cells never
//! perturb geographic attractor placement. `mouths`/`confluences` also
//! unchanged (T-1185 never rewrites those arrays).
//!
//! **This golden pins the FALLBACK moisture path, not production — stated
//! explicitly so nobody cites its basin-outcome split as what a player
//! actually sees (PR #202 review, Hoshe finding 2).**
//! `run_cascade_from_heightmap`'s `body_params: None` argument here means
//! `run_layer1`'s `DEFAULT_HYDROLOGY_MOISTURE_Q = 55` fallback is what
//! solves this fixture's hydrology, not GJ1c's REAL body params
//! (`wiki/star-systems/GJ-1/bodies/GJ1c/index.md`: `hydrosphere:
//! liquid_water`, `atmosphere: standard` → `derive_moisture_ceiling_q`
//! yields **moisture_q=80**, well above `ENDORHEIC_MOISTURE_CEILING=60`).
//! At the fallback `moisture_q=55` this fixture's 53 real working-grid
//! basins split 51 Overflow / 2 Endorheic; verified directly (a scratch
//! probe, not committed) that at the PRODUCTION `moisture_q=80` the SAME
//! 53 basins are **53/53 all-Overflow — zero Endorheic** (moisture is the
//! only thing that moves; `filled_scaled`/basin geometry itself is
//! moisture-independent, per `run_layer1_with_moisture_changes_
//! endorheic_split_not_lake_extent`'s own invariant). A materially
//! different picture: on the real body, every one of these basins shows an
//! exit river on the map — this fixture happening to include 2 Endorheic
//! basins is an artifact of testing at the body-agnostic fallback
//! constant, not a fact about GJ1c itself.
//!
//! **Cell count (post PR #202 review fix — the i==1/spill-collision
//! regression, Hoshe finding 1):** `river_cells` 93→192 (+99). Every one of
//! the 51 real `Overflow` basins now has its spill cell wired as a real
//! river-network entry, unconditionally — the earlier landing (143, now
//! superseded) silently dropped a basin's ENTIRE outlet whenever
//! `outlet_path[1]` collided with a pre-existing river cell (the loop broke
//! on its first iteration having pushed nothing), which on THIS fixture
//! happened for 1 basin outright and would have made it visually
//! indistinguishable from Endorheic — exactly the cue this ticket must
//! never break. Verified directly against this fixture (scratch probe, not
//! committed): all 51 real `Overflow` basins now build into a real,
//! readable `RiverEdge` via `river_course::build_edges` — zero basins
//! missing an outlet edge. One pre-existing baseline cell (`(28, 14)`) is
//! overwritten in place (its `river_downstream` sentinel changes from
//! `RIVER_DOWNSTREAM_EDGE_DRAIN` to a real D8 direction) rather than
//! duplicated — the other real spill-cell collision on this fixture lands
//! among the newly-appended range, not the original 93-cell baseline.
//! Confirmed by direct position-identity diff (not raw array-index
//! comparison, which is misleading once the fix reshuffles positions
//! within each basin's block): zero positions are ever REMOVED between the
//! pre-fix and post-fix goldens, only added-or-overwritten — the fix is
//! additive at the position level, exactly as designed. No duplicate
//! `(row, col)` positions exist in the final array (verified — the
//! `edge_ids_are_unique` invariant `build_edges` depends on holds).

use std::path::PathBuf;

use serde_json::{json, Value};
use settled_reach_server::atlas::cascade::{run_cascade_from_heightmap, CascadeLayer};
use settled_reach_server::atlas::heightmap::load_heightmap_png;
use settled_reach_server::seed::SeedChain;
use sha2::{Digest, Sha256};

/// Source heightmap — a real committed body, relative to the server manifest dir.
const SOURCE_HEIGHTMAP: &str = "../wiki/star-systems/GJ-1/bodies/GJ1c/heightmap.png";
/// Downsample target: large enough that GJ1c's drainage produces a real river
/// network (not just attractors), small enough for a compact golden.
const DOWNSAMPLE: (u32, u32) = (256, 128);
/// World seed for the run. Cosmetic here — Layers 0–1 are RNG-free, so changing
/// it does not change the golden; it is carried only to exercise the SeedChain
/// contract end-to-end (D-224). Seed-sensitivity gets pinned once Layer 3+ lands.
const WORLD_SEED: u64 = 42;
const GOLDEN: &str = "tests/golden/cascade_layer1.json";

#[test]
fn cascade_layer0_to_1_matches_golden() {
    let manifest = PathBuf::from(env!("CARGO_MANIFEST_DIR"));
    let src = manifest.join(SOURCE_HEIGHTMAP);

    // ── Layer 0 — load + hash the source heightmap.png. ─────────────────────
    let png_bytes = std::fs::read(&src)
        .unwrap_or_else(|e| panic!("read source heightmap {}: {e}", src.display()));
    let mut hasher = Sha256::new();
    hasher.update(&png_bytes);
    let sha = format!("{:x}", hasher.finalize());

    let heightmap = load_heightmap_png(&src, "GJ1c", 0.3).expect("decode source heightmap");

    // ── Layer 1 — downsample, then run the cascade to topography. ───────────
    let small = heightmap.downsample(DOWNSAMPLE.0, DOWNSAMPLE.1);
    let body_seed = SeedChain::for_body(WORLD_SEED, "GJ1c");
    let snapshot =
        run_cascade_from_heightmap(body_seed, small, &[], None, None, CascadeLayer::Topography);
    let layer1 = snapshot.layer1.expect("Layer 1 ran");

    let actual = json!({
        "source_heightmap": SOURCE_HEIGHTMAP,
        "source_sha256": sha,
        "downsample": [DOWNSAMPLE.0, DOWNSAMPLE.1],
        "layer1": serde_json::to_value(&layer1).expect("serialize Layer1Output"),
    });
    let actual_json = serde_json::to_string_pretty(&actual).expect("format JSON") + "\n";

    let golden_path = manifest.join(GOLDEN);

    if std::env::var("UPDATE_GOLDEN").is_ok() {
        std::fs::create_dir_all(golden_path.parent().unwrap()).expect("mkdir golden");
        std::fs::write(&golden_path, &actual_json).expect("write golden");
        eprintln!(
            "Golden written: {} ({} bytes)",
            golden_path.display(),
            actual_json.len()
        );
        return;
    }

    let golden_json = std::fs::read_to_string(&golden_path).unwrap_or_else(|e| {
        panic!(
            "Golden not found: {}. Run: UPDATE_GOLDEN=1 cargo test --test cascade_golden\n{e}",
            golden_path.display()
        )
    });

    // Compare as parsed JSON so whitespace/formatting never causes spurious diffs.
    let actual_v: Value = serde_json::from_str(&actual_json).expect("reparse actual JSON");
    let golden_v: Value = serde_json::from_str(&golden_json).expect("parse golden JSON");

    if actual_v != golden_v {
        let count =
            |v: &Value, ptr: &str| v.pointer(ptr).and_then(Value::as_array).map_or(0, Vec::len);
        panic!(
            "Cascade golden mismatch.\n  \
             source_sha256: golden={} actual={}\n  \
             river_cells:   golden={} actual={}\n  \
             attractors:    golden={} actual={}\n\
             To update: UPDATE_GOLDEN=1 cargo test --test cascade_golden\n  Golden: {}",
            golden_v["source_sha256"],
            actual_v["source_sha256"],
            count(&golden_v, "/layer1/river_network/river_cells"),
            count(&actual_v, "/layer1/river_network/river_cells"),
            count(&golden_v, "/layer1/attractors"),
            count(&actual_v, "/layer1/attractors"),
            golden_path.display(),
        );
    }
}