Buildings and levels for the floor map, and make every identifier searchable

shopdb/utils/imagesize.py

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+"""Read an image's pixel dimensions from its header, with no image library.
+
+A level's `mapwidth`/`mapheight` are the coordinate space every marker on it is
+expressed in, so getting them wrong moves every marker relative to the drawing.
+Reading them off the uploaded file removes the most likely way to get them
+wrong, which is somebody typing what they remember.
+
+Pillow would do this in one line and is not a dependency. Adding it would mean a
+new cp314 win_amd64 wheel in the offline installer's hash-pinned wheelhouse -
+built on Windows, verified against bundle-lock.json, shipped in a 240 MB
+installer - to read two integers out of a header. This is the cheaper trade.
+
+Returns (width, height), or (None, None) when the format is not one of these or
+the header is truncated. A caller must treat None as "ask the operator" and
+never as a default.
+"""
+
+import re
+import struct
+
+
+def png_size(data):
+    # An IHDR chunk always follows the 8-byte signature, and its first two
+    # fields are width and height as big-endian 32-bit integers.
+    if len(data) < 24 or data[:8] != b'\x89PNG\r\n\x1a\n':
+        return None, None
+    if data[12:16] != b'IHDR':
+        return None, None
+    width, height = struct.unpack('>II', data[16:24])
+    return width, height
+
+
+def gif_size(data):
+    if len(data) < 10 or data[:6] not in (b'GIF87a', b'GIF89a'):
+        return None, None
+    width, height = struct.unpack('<HH', data[6:10])
+    return width, height
+
+
+def webp_size(data):
+    if len(data) < 30 or data[:4] != b'RIFF' or data[8:12] != b'WEBP':
+        return None, None
+    kind = data[12:16]
+    if kind == b'VP8 ':
+        width, height = struct.unpack('<HH', data[26:30])
+        return width & 0x3FFF, height & 0x3FFF
+    if kind == b'VP8L':
+        bits = struct.unpack('<I', data[21:25])[0]
+        return (bits & 0x3FFF) + 1, ((bits >> 14) & 0x3FFF) + 1
+    if kind == b'VP8X':
+        width = int.from_bytes(data[24:27], 'little') + 1
+        height = int.from_bytes(data[27:30], 'little') + 1
+        return width, height
+    return None, None
+
+
+def jpeg_size(data):
+    """Walk the marker segments to the start-of-frame, which carries the size.
+
+    JPEG has no fixed header offset - the dimensions live in whichever SOF
+    marker the encoder used, after any number of application and comment
+    segments of varying length. So this walks rather than indexes.
+    """
+    if len(data) < 4 or data[:2] != b'\xff\xd8':
+        return None, None
+    index = 2
+    end = len(data)
+    while index < end - 9:
+        if data[index] != 0xFF:
+            index += 1
+            continue
+        marker = data[index + 1]
+        # SOF0 through SOF15, excluding the DHT/JPG/DAC markers interleaved
+        # in that range, all carry height then width at the same offset.
+        if marker in (0xC0, 0xC1, 0xC2, 0xC3, 0xC5, 0xC6, 0xC7,
+                      0xC9, 0xCA, 0xCB, 0xCD, 0xCE, 0xCF):
+            height, width = struct.unpack('>HH', data[index + 5:index + 9])
+            return width, height
+        if marker in (0xD8, 0x01) or 0xD0 <= marker <= 0xD9:
+            index += 2
+            continue
+        segment = struct.unpack('>H', data[index + 2:index + 4])[0]
+        index += 2 + segment
+    return None, None
+
+
+def svg_size(data):
+    """SVG states a size in attributes, or implies one through viewBox.
+
+    Width and height may carry units (mm, in, pt) or be percentages, and a
+    percentage says nothing about pixels - so a unit that is not px falls back to
+    the viewBox, which is unitless user space and is what a renderer scales to.
+    """
+    try:
+        head = data[:4096].decode('utf-8', errors='replace')
+    except Exception:
+        return None, None
+    if '<svg' not in head:
+        return None, None
+
+    def attribute(name):
+        found = re.search(r'\b%s\s*=\s*["\']([^"\']+)["\']' % name, head)
+        return found.group(1).strip() if found else None
+
+    def pixels(value):
+        if not value:
+            return None
+        match = re.match(r'^([0-9.]+)\s*(px)?$', value)
+        return int(round(float(match.group(1)))) if match else None
+
+    width = pixels(attribute('width'))
+    height = pixels(attribute('height'))
+    if width and height:
+        return width, height
+
+    viewbox = attribute('viewBox')
+    if viewbox:
+        parts = re.split(r'[\s,]+', viewbox.strip())
+        if len(parts) == 4:
+            try:
+                return (int(round(float(parts[2]))),
+                        int(round(float(parts[3]))))
+            except ValueError:
+                return None, None
+    return None, None
+
+
+def image_size(data):
+    """Dimensions of PNG, JPEG, GIF, WEBP or SVG data. (None, None) otherwise."""
+    for reader in (png_size, jpeg_size, gif_size, webp_size, svg_size):
+        width, height = reader(data)
+        if width and height:
+            return width, height
+    return None, None