1 files changed, 145 insertions, 0 deletions
diff --git a/source/spots.d b/source/spots.d
new file mode 100644
index 0000000..0f9d8b7
--- /dev/null
+++ b/source/spots.d
@@ -0,0 +1,145 @@
+import std.bigint;
+import std.digest.crc;
+import std.random : unpredictableSeed;
+import std.range;
+import lru : LRUCache;
+import deimos.ncurses;
+
+private BigInt positive(BigInt n)
+{
+    if (n >= 0)
+        return n * 2;
+    else
+        return -n * 2 - 1;
+}
+
+private BigInt pair(BigInt n, BigInt m)
+{
+    // https://stackoverflow.com/a/919661
+    return (positive(n) + positive(m)) * (positive(n) + positive(m) + 1) / 2 + positive(m);
+}
+
+struct Spot
+{
+    private char _contents;
+    this(char c)
+    {
+        _contents = c;
+    }
+
+    @property contents()
+    {
+        return _contents;
+    }
+
+    bool opEqual(const Spot s)
+    {
+        return s._contents == _contents;
+    }
+
+    bool isRock()
+    {
+        return _contents == '*';
+    }
+}
+
+interface SpotSource
+{
+    Spot opIndex(BigInt y, BigInt x);
+}
+
+class RandomSource : SpotSource
+{
+    uint seed;
+    double density = .0025;
+    private LRUCache!(BigInt[2], Spot) cache;
+
+    this()
+    {
+        seed = unpredictableSeed;
+        cache = new LRUCache!(BigInt[2], Spot)(50000);
+    }
+
+    this(uint seed)
+    {
+        this.seed = seed;
+    }
+
+    this(uint seed, double density)
+    {
+        this.density = density;
+        this(seed);
+    }
+
+    private uint hash(BigInt n)
+    {
+        CRC32 crc;
+        crc.start();
+        crc.put((cast(ubyte*)&seed)[0 .. seed.sizeof]);
+        foreach (i; iota(n.ulongLength))
+        {
+            auto digit = n.getDigit(i);
+            crc.put((cast(ubyte*)&digit)[0 .. digit.sizeof]);
+        }
+        auto result = crc.finish();
+        auto hash = *(cast(uint*)&result);
+        return hash;
+    }
+
+    public Spot opIndex(BigInt y, BigInt x)
+    {
+        if ([y, x] in cache)
+            return cache[[y, x]];
+        auto roll = cast(double) hash(pair(y, x)) / uint.max;
+        Spot ret;
+        if (roll < density)
+            ret = Spot('*');
+        else
+            ret = Spot(' ');
+        cache[[y, x]] = ret;
+        return ret;
+    }
+}
+
+class OverlaySource : SpotSource
+{
+    private SpotSource _base;
+    private Spot[BigInt[2]] _overlay;
+
+    this(SpotSource base)
+    {
+        _base = base;
+    }
+
+    void opIndexAssign(Spot spot, BigInt y, BigInt x)
+    {
+        Spot* p = [y, x] in _overlay;
+        if (p !is null && spot == _base[y, x])
+        {
+            _overlay.remove([y, x]);
+        }
+        else
+        {
+            _overlay[[y, x]] = spot;
+        }
+    }
+
+    Spot opIndex(BigInt y, BigInt x)
+    {
+        Spot* p = [y, x] in _overlay;
+        if (p !is null)
+            return *p;
+        else
+            return _base[y, x];
+    }
+
+    unittest
+    {
+        auto base = new RandomSource(0, 0.0);
+        auto src = new OverlaySource(base);
+        src[BigInt(0), BigInt(0)] = Spot('*');
+        src[BigInt(0), BigInt(1)] = Spot('*');
+        assert(src[BigInt(0), BigInt(0)] == Spot('*'));
+        assert(src[BigInt(0), BigInt(1)] == Spot('*'));
+    }
+}