"""Security-focused tests for the attestation chain.

Tests concurrent access, oversized records, and edge cases that could
compromise chain integrity.
"""

from __future__ import annotations

import hashlib
import struct
import threading
from pathlib import Path

import pytest
from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey

from fieldwitness.exceptions import ChainError
from fieldwitness.federation.chain import MAX_RECORD_SIZE, ChainStore


def test_concurrent_append_no_fork(chain_dir: Path):
    """Concurrent appends must not fork the chain — indices must be unique."""
    private_key = Ed25519PrivateKey.generate()
    num_threads = 8
    records_per_thread = 5
    results: list[list] = [[] for _ in range(num_threads)]
    errors: list[Exception] = []

    def worker(thread_id: int):
        try:
            store = ChainStore(chain_dir)
            for i in range(records_per_thread):
                content = hashlib.sha256(f"t{thread_id}-r{i}".encode()).digest()
                record = store.append(content, "test/plain", private_key)
                results[thread_id].append(record.chain_index)
        except Exception as e:
            errors.append(e)

    threads = [threading.Thread(target=worker, args=(t,)) for t in range(num_threads)]
    for t in threads:
        t.start()
    for t in threads:
        t.join()

    assert not errors, f"Thread errors: {errors}"

    # Collect all indices
    all_indices = []
    for r in results:
        all_indices.extend(r)

    # Every index must be unique (no fork)
    assert len(all_indices) == len(set(all_indices)), (
        f"Duplicate chain indices detected — chain forked! " f"Indices: {sorted(all_indices)}"
    )

    # Indices should be 0..N-1 contiguous
    total = num_threads * records_per_thread
    assert sorted(all_indices) == list(range(total))

    # Full chain verification should pass
    store = ChainStore(chain_dir)
    assert store.verify_chain() is True
    assert store.state().record_count == total


def test_oversized_record_rejected(chain_dir: Path):
    """A corrupted length prefix exceeding MAX_RECORD_SIZE must raise ChainError."""
    chain_file = chain_dir / "chain.bin"

    # Write a length prefix claiming a 100 MB record
    bogus_length = 100 * 1024 * 1024
    chain_file.write_bytes(struct.pack(">I", bogus_length) + b"\x00" * 100)

    store = ChainStore(chain_dir)

    with pytest.raises(ChainError, match="exceeds maximum"):
        list(store._iter_raw())


def test_max_record_size_boundary(chain_dir: Path):
    """Records at exactly MAX_RECORD_SIZE should be rejected (real records are <1KB)."""
    chain_file = chain_dir / "chain.bin"

    chain_file.write_bytes(struct.pack(">I", MAX_RECORD_SIZE + 1) + b"\x00" * 100)

    store = ChainStore(chain_dir)
    with pytest.raises(ChainError, match="exceeds maximum"):
        list(store._iter_raw())


def test_truncated_chain_file(chain_dir: Path, private_key: Ed25519PrivateKey):
    """A truncated chain.bin still yields complete records before the truncation."""
    store = ChainStore(chain_dir)
    for i in range(3):
        store.append(hashlib.sha256(f"c-{i}".encode()).digest(), "test/plain", private_key)

    # Truncate the file mid-record
    chain_file = chain_dir / "chain.bin"
    data = chain_file.read_bytes()
    chain_file.write_bytes(data[: len(data) - 50])

    store2 = ChainStore(chain_dir)
    records = list(store2._iter_raw())
    # Should get at least the first 2 complete records
    assert len(records) >= 2
    assert records[0].chain_index == 0
    assert records[1].chain_index == 1


def test_empty_chain_file(chain_dir: Path):
    """An empty chain.bin (0 bytes) yields no records without error."""
    chain_file = chain_dir / "chain.bin"
    chain_file.write_bytes(b"")

    store = ChainStore(chain_dir)
    records = list(store._iter_raw())
    assert records == []


def test_concurrent_read_during_write(chain_dir: Path):
    """Reading the chain while appending should not crash."""
    private_key = Ed25519PrivateKey.generate()
    store = ChainStore(chain_dir)

    # Seed with some records
    for i in range(5):
        store.append(hashlib.sha256(f"seed-{i}".encode()).digest(), "test/plain", private_key)

    read_errors: list[Exception] = []
    write_errors: list[Exception] = []

    def reader():
        try:
            s = ChainStore(chain_dir)
            for _ in range(20):
                list(s.iter_records())
        except Exception as e:
            read_errors.append(e)

    def writer():
        try:
            s = ChainStore(chain_dir)
            for i in range(10):
                s.append(hashlib.sha256(f"w-{i}".encode()).digest(), "test/plain", private_key)
        except Exception as e:
            write_errors.append(e)

    threads = [
        threading.Thread(target=reader),
        threading.Thread(target=reader),
        threading.Thread(target=writer),
    ]
    for t in threads:
        t.start()
    for t in threads:
        t.join()

    assert not read_errors, f"Read errors during concurrent access: {read_errors}"
    assert not write_errors, f"Write errors during concurrent access: {write_errors}"