examples: add simple RIFF parse example

examples/riff.py

@@ -0,0 +1,76 @@
+from __future__ import annotations
+import enum
+from sx import Generic, Struct, parse
+
+
+_Chunk = Generic('Chunk')
+
+class FormatCompression(enum.Enum):
+    Unknown = 0
+    PCM = 1
+    MSADPCM = 2
+    ALaw = 6
+    MuLaw = 7
+    IMAADPCM = 17
+    G723ADPCM = 20
+    GSM610 = 49
+    G721ADPCM = 64
+    MPEG = 80
+    Experimental = 0xFFFF
+
+class FormatChunk(Struct, partial=True):
+    compression:     Enum(FormatCompression, uint16le)
+    channel_count:   uint16le
+    sample_rate:     uint32le
+    bytes_per_sec:   uint32le
+    alignment:       uint16le
+    bits_per_sample: uint16le
+    extra_length:    uint16le
+    extra:           Data(self.extra_length)
+
+class FactChunk(Struct):
+    sample_count: uint32le
+
+class SampleLoop(Struct):
+    id:       uint32le
+    type:     uint32le
+    start:    uint32le
+    end:      uint32le
+    fraction: uint32le
+    count:    uint32le
+
+class SampleChunk(Struct):
+    manufacturer:      uint32le
+    product:           uint32le
+    period:            uint32le
+    unity_note:        uint32le
+    pitch_fraction:    uint32le
+    smtpe_format:      uint32le
+    smpte_offset:      uint32le
+    sample_loop_count: uint32le
+    padding_length:    uint32le
+    sample_loops:      Arr(SampleLoop, count=self.sample_loop_count)
+
+class DataChunk(Struct):
+    data: data
+
+class RIFFChunk(Struct):
+    type: Fixed(b'WAVE')
+    children: Arr(_Chunk)
+
+class Chunk(Struct):
+    type:     Data(4)
+    length:   uint32le
+    contents: Sized(Switch({
+        b'fmt ': FormatChunk,
+        b'fact': FactChunk,
+        b'smpl': SampleChunk,
+        b'data': DataChunk,
+        b'RIFF': RIFFChunk,
+    }, fallback=DataChunk, selector=self.type), self.length)
+
+_Chunk.push(Chunk)
+
+if __name__ == '__main__':
+    import sys
+    print(parse(Chunk, open(sys.argv[1], 'rb')))