First public commit.

lenser/spectrum/exporter.py

@@ -0,0 +1,32 @@
+"""Export a ZX Spectrum image as a .SNA snapshot (+ a standard .SCR alongside)."""
+from __future__ import annotations
+
+import os
+
+from . import snapshot
+
+_EXTS = (".sna", ".scr", ".z80")
+
+
+def export_sna(conv, output_path, source_path=None, display="forever",
+               seconds=0, video="pal"):
+    if not output_path.lower().endswith(_EXTS):
+        output_path += ".sna"
+    screen = bytes(conv.data)
+    border = _dominant_paper(screen)
+    sna = snapshot.build_sna(screen, border=border)
+    with open(output_path, "wb") as f:
+        f.write(sna)
+    # also drop the standard raw-screen .scr next to it (interchange format)
+    scr_path = os.path.splitext(output_path)[0] + ".scr"
+    with open(scr_path, "wb") as f:
+        f.write(snapshot.build_scr(screen))
+    return output_path
+
+
+def _dominant_paper(screen: bytes) -> int:
+    """Most common paper colour across the 768 attribute cells -> border colour."""
+    counts = [0] * 8
+    for a in screen[6144:6912]:
+        counts[(a >> 3) & 7] += 1
+    return max(range(8), key=lambda c: counts[c])