feat: zone config loader and static ROI builder

src/zone_config.py

@@ -0,0 +1,73 @@
+"""Zone configuration — load/save counting zone presets from zones.json."""
+
+from __future__ import annotations
+
+import json
+import os
+from typing import Any
+
+from src.truck_roi import TruckROI
+
+
+def load_zone_config(path: str) -> dict[str, Any]:
+    """Load zones.json and return full config dict."""
+    with open(path) as f:
+        return json.load(f)
+
+
+def save_zone_config(config: dict[str, Any], path: str) -> None:
+    """Save zone config dict to zones.json."""
+    with open(path, "w") as f:
+        json.dump(config, f, indent=2)
+
+
+def build_static_roi(zone: dict[str, Any], video_w: int, video_h: int) -> TruckROI:
+    """Build a TruckROI from a zone config dict.
+
+    The zone dict should have:
+      - truck_area: [[x1,y1], [x2,y2], [x3,y3], [x4,y4]] (4-point polygon)
+      - count_line: {"x_start": int, "x_end": int, "y": int}
+    Coordinates are in the video's native resolution (no scaling needed
+    if the zone was calibrated for this resolution).
+    """
+    truck_pts = zone.get("truck_area", [])
+    count_line = zone.get("count_line", {})
+
+    # Compute bounding box of truck_area polygon
+    if truck_pts and len(truck_pts) >= 4:
+        xs = [p[0] for p in truck_pts]
+        ys = [p[1] for p in truck_pts]
+        x1 = max(0, min(xs))
+        y1 = max(0, min(ys))
+        x2 = min(video_w, max(xs))
+        y2 = min(video_h, max(ys))
+    else:
+        # Fallback: use 50% of frame
+        x1, y1 = int(video_w * 0.3), int(video_h * 0.1)
+        x2, y2 = int(video_w * 0.75), int(video_h * 0.95)
+
+    line_y = count_line.get("y", int((y1 + y2) / 2))
+
+    return TruckROI(
+        x1=x1, y1=y1, x2=x2, y2=y2,
+        line_y=line_y,
+        confidence=1.0,
+    )
+
+
+def list_zone_presets(path: str) -> list[dict[str, Any]]:
+    """Return list of preset summaries: [{"name": str, "description": str, ...}]."""
+    config = load_zone_config(path)
+    presets = config.get("presets", {})
+    return [
+        {"name": name, "description": vals.get("description", ""), **vals}
+        for name, vals in presets.items()
+    ]
+
+
+def get_active_zone(path: str, preset_name: str | None = None) -> dict[str, Any] | None:
+    """Get the active preset dict. Falls back to active_preset field if name not given."""
+    config = load_zone_config(path)
+    presets = config.get("presets", {})
+    name = preset_name or config.get("active_preset")
+    return presets.get(name)

tests/test_zone_config.py

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+import json
+import os
+import pytest
+from src.zone_config import load_zone_config, build_static_roi, list_zone_presets
+
+
+def test_load_zone_config_reads_json(tmp_path):
+    cfg = {"presets": {"test": {"count_line": {"x_start": 100, "x_end": 200, "y": 150}}}, "active_preset": "test"}
+    p = tmp_path / "zones.json"
+    p.write_text(json.dumps(cfg))
+    result = load_zone_config(str(p))
+    assert result["active_preset"] == "test"
+    assert result["presets"]["test"]["count_line"]["y"] == 150
+
+
+def test_build_static_roi_from_zone_config():
+    zone = {
+        "truck_area": [[100, 50], [110, 300], [400, 310], [390, 40]],
+        "count_line": {"x_start": 110, "x_end": 400, "y": 150},
+    }
+    roi = build_static_roi(zone, video_w=640, video_h=480)
+    assert roi.line_y == 150
+    assert roi.confidence == 1.0
+    assert roi.x1 < roi.x2
+    assert roi.y1 < roi.y2
+
+
+def test_build_static_roi_scales_coords():
+    zone = {
+        "truck_area": [[600, 385], [609, 1076], [1404, 1078], [1381, 343]],
+        "count_line": {"x_start": 577, "x_end": 1401, "y": 330},
+    }
+    roi = build_static_roi(zone, video_w=1920, video_h=1080)
+    assert roi.line_y == 330
+    assert roi.x1 == 600
+    assert roi.x2 == 1404
+
+
+def test_list_zone_presets(tmp_path):
+    cfg = {"presets": {"p1": {"description": "Zone 1"}, "p2": {"description": "Zone 2"}}}
+    p = tmp_path / "zones.json"
+    p.write_text(json.dumps(cfg))
+    presets = list_zone_presets(str(p))
+    assert len(presets) == 2
+    names = [p["name"] for p in presets]
+    assert "p1" in names
+    assert "p2" in names

zones.json

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+{
+  "presets": {
+    "default": {
+      "truck_area": [[600, 385], [609, 1076], [1404, 1078], [1381, 343]],
+      "counting_area": [[574, 50], [586, 1077], [1418, 1076], [1397, 50]],
+      "count_line": {"x_start": 577, "x_end": 1401, "y": 330},
+      "left_limit": 0.27578,
+      "right_limit": 0.72578,
+      "duplicate_circle_radius": 30,
+      "description": "Default zone for 1920x1080 camera"
+    }
+  },
+  "active_preset": "default"
+}