import json
import struct
import tempfile
import unittest
from pathlib import Path
from preflight import inspect_glb

class PreflightTests(unittest.TestCase):
    def write_fixture(self, root, faces, copies=1):
        # Valid unindexed triangles. Repeated triangle vertices exercise the
        # parser with real binary payload, without a 2M-face Python object graph.
        count = faces * 3
        doc = {"asset":{"version":"2.0"}, "buffers":[{"byteLength":count*12}],
               "bufferViews":[{"buffer":0,"byteLength":count*12}],
               "accessors":[{"bufferView":0,"componentType":5126,"count":count,
                             "type":"VEC3","min":[0,0,0],"max":[1,1,0]}],
               "meshes":[{"primitives":[{"attributes":{"POSITION":0}}]}],
               "nodes":[{"mesh":0} for _ in range(copies)],
               "scenes":[{"nodes":list(range(copies))}],"scene":0}
        payload = json.dumps(doc).encode()
        payload += b" " * (-len(payload) % 4)
        p = Path(root)/"fixture.glb"
        with p.open("wb") as stream:
            stream.write(struct.pack("<4sIIII", b"glTF",2,28+len(payload)+count*12,len(payload),0x4E4F534A))
            stream.write(payload)
            stream.write(struct.pack("<II",count*12,0x004E4942))
            triangle = struct.pack("<9f",0,0,0,1,0,0,0,1,0)
            block = triangle * 1000
            for _ in range(faces//1000):
                stream.write(block)
            stream.write(triangle * (faces%1000))
        return p

    def test_normal(self):
        with tempfile.TemporaryDirectory() as root:
            result = inspect_glb(self.write_fixture(root,12))
            self.assertTrue(result["inference_allowed"])
            self.assertEqual(result["triangles"],12)

    def test_two_million_faces_preserved_and_blocked(self):
        with tempfile.TemporaryDirectory() as root:
            path = self.write_fixture(root,2_000_000)
            before = path.stat()
            result = inspect_glb(path)
            self.assertEqual(result["triangles"],2_000_000)
            self.assertFalse(result["inference_allowed"])
            self.assertIn("decimation required",result["warning"])
            self.assertEqual(path.stat().st_size,before.st_size)
            self.assertEqual(path.stat().st_mtime_ns,before.st_mtime_ns)

    def test_instances_count_towards_limit(self):
        with tempfile.TemporaryDirectory() as root:
            result = inspect_glb(self.write_fixture(root,100_000,6))
            self.assertFalse(result["inference_allowed"])
            self.assertEqual(result["instantiated_triangles"],600_000)

    def test_truncated_rejected(self):
        with tempfile.TemporaryDirectory() as root:
            path=Path(root)/"bad.glb"
            path.write_bytes(b"glTF")
            with self.assertRaises(ValueError):
                inspect_glb(path)