"""Narrow field projection model, not an Avro serializer. Python standard library."""
import csv
import json
from pathlib import Path

ROOT = Path(__file__).parent
SCHEMAS = {
    "v1": {"account": None, "region": "unknown"},
    "v2": {"account": None},
    "v3": {"account": None, "region": None},
}
MESSAGES = {
    "v1": {"account": "a1", "region": "west"},
    "v2": {"account": "a1"},
    "v3": {"account": "a1", "region": "east"},
}

def project(reader, message):
    result = {}
    for field, default in SCHEMAS[reader].items():
        if field in message:
            result[field] = message[field]
        elif default is not None:
            result[field] = default
        else:
            return {"status": "reject", "reason": "missing " + field}
    return {"status": "read", "value": result}

rows = []
for reader in SCHEMAS:
    for writer, message in MESSAGES.items():
        out = project(reader, message)
        rows.append({"reader": reader, "writer": writer, **out})
assert len(rows) == 9
assert sum(r["status"] == "reject" for r in rows) == 1
assert project("v1", MESSAGES["v2"])["value"]["region"] == "unknown"
assert project("v3", MESSAGES["v2"]) == {"status": "reject", "reason": "missing region"}
assert "region" not in project("v2", MESSAGES["v1"])["value"]
(ROOT / "results.json").write_text(json.dumps(rows, indent=2) + "\n")
with (ROOT / "compatibility.csv").open("w", newline="") as f:
    writer = csv.writer(f)
    writer.writerow(["reader", "writer", "result", "detail"])
    for r in rows:
        writer.writerow([r["reader"], r["writer"], r["status"], json.dumps(r.get("value", r.get("reason")))])
print("9 reader/writer pairs: 8 read, 1 rejects; defaults and ignored fields checked")