"""Dependency-free local evaluator. This is process isolation, NOT a security sandbox."""

from __future__ import annotations

import hashlib
import json
import math
import os
import selectors
import shutil
import signal
import subprocess
import sys
import tempfile
import time
from pathlib import Path

DATA = Path(__file__).parent / "data"
MAX_OUTPUT = 1_048_576
EXCLUDED = {".git", ".venv", "venv", "__pycache__", "node_modules", ".env"}


def load_tasks(subset=None, data_dir=None):
    root = Path(data_dir) if data_dir else DATA
    tiers = [subset] if subset else ["easy", "intermediate", "hard", "max"]
    if any(t not in {"easy", "intermediate", "hard", "max"} for t in tiers):
        raise ValueError("Unknown subset")
    for tier in tiers:
        for line in (root / f"{tier}.jsonl").read_text(encoding="utf-8").splitlines():
            if line.strip():
                yield json.loads(line)


def find_task(task_id, data_dir=None):
    for row in load_tasks(data_dir=data_dir):
        if row["task_id"] == task_id:
            return row
    raise ValueError(f"Unknown task: {task_id}")


def equal(actual, expected):
    if isinstance(expected, bool) or expected is None or isinstance(expected, str):
        return type(actual) is type(expected) and actual == expected
    if type(expected) in (int, float):
        if type(actual) not in (int, float):
            return False
        if type(actual) is int and type(expected) is int:
            return actual == expected
        return (
            math.isfinite(actual)
            and math.isfinite(expected)
            and math.isclose(actual, expected, rel_tol=1e-9, abs_tol=1e-9)
        )
    if isinstance(expected, list):
        return (
            isinstance(actual, list)
            and len(actual) == len(expected)
            and all(equal(a, b) for a, b in zip(actual, expected))
        )
    if isinstance(expected, dict):
        return (
            isinstance(actual, dict)
            and actual.keys() == expected.keys()
            and all(equal(actual[k], expected[k]) for k in expected)
        )
    return False


def strict_json(line):
    def invalid(value):
        raise ValueError(f"Nonfinite JSON constant: {value}")

    return json.loads(line, parse_constant=invalid)


def kill_group(process):
    if os.name == "posix":
        try:
            os.killpg(process.pid, signal.SIGKILL)
        except ProcessLookupError:
            pass
    elif process.poll() is None:
        process.kill()
    process.wait()


def child_environment(home):
    # Do not inherit credentials, PYTHONPATH, proxies, or user site configuration.
    return {
        "PATH": os.defpath,
        "HOME": str(home),
        "LANG": "C.UTF-8",
        "LC_ALL": "C.UTF-8",
        "TZ": "UTC",
        "PYTHONHASHSEED": "0",
    }


def copy_project(source, target):
    """No symlinks, special files, or environment files may enter a submission."""
    source = Path(source).resolve()
    if not source.is_dir():
        raise ValueError(f"Solution directory does not exist: {source}")
    count = size = 0
    for root, dirs, files in os.walk(source, followlinks=False):
        base = Path(root)
        dirs[:] = sorted(
            d for d in dirs if d not in EXCLUDED and not (base / d).is_symlink()
        )
        relative = base.relative_to(source)
        (target / relative).mkdir(parents=True, exist_ok=True)
        for name in sorted(files):
            if (
                name in EXCLUDED
                or name.startswith(".env.")
                or name.endswith((".pyc", ".token"))
            ):
                continue
            path = base / name
            if path.is_symlink() or not path.is_file():
                raise ValueError(
                    f"Submission contains a symlink or special file: {relative / name}"
                )
            count += 1
            size += path.stat().st_size
            if count > 2000 or size > 20_000_000:
                raise ValueError("Submission exceeds 2000 files / 20 MB")
            shutil.copyfile(path, target / relative / name)


def run_session(project, state, session, *, durable=False, timeout=10.0):
    if os.name != "posix":
        raise RuntimeError(
            "The local evaluator requires POSIX process groups and pipe selectors"
        )
    argv = [sys.executable, "-E", "-s", "-S", "main.py"]
    if durable:
        argv += ["--state-dir", str(state)]
    start = time.monotonic()
    deadline = start + timeout
    process = subprocess.Popen(
        argv,
        cwd=project,
        env=child_environment(state.parent / "home"),
        stdin=subprocess.PIPE,
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
        start_new_session=True,
        bufsize=0,
    )
    selector = selectors.DefaultSelector()
    for pipe in (process.stdin, process.stdout, process.stderr):
        os.set_blocking(pipe.fileno(), False)
    selector.register(process.stdout, selectors.EVENT_READ, "out")
    selector.register(process.stderr, selectors.EVENT_READ, "err")
    buffer = b""
    stderr = bytearray()
    output_bytes = passed = 0
    failure = None
    actual = None

    def read_events(wait):
        nonlocal buffer, output_bytes
        for key, _ in selector.select(max(0, wait)):
            if key.data == "in":
                continue
            chunk = os.read(key.fileobj.fileno(), 65536)
            if not chunk:
                selector.unregister(key.fileobj)
                continue
            if key.data == "out":
                buffer += chunk
                output_bytes += len(chunk)
                if output_bytes > MAX_OUTPUT:
                    raise ValueError("stdout exceeded 1 MiB")
            elif len(stderr) < 8192:
                stderr.extend(chunk[: 8192 - len(stderr)])

    try:
        if len(session["requests"]) != len(session["expected"]):
            raise ValueError("Invalid acceptance session lengths")
        for index, (request, expected) in enumerate(
            zip(session["requests"], session["expected"])
        ):
            actual = None
            wire = (
                request
                if isinstance(request, str)
                else json.dumps(request, ensure_ascii=True, allow_nan=False)
            ) + "\n"
            pending = memoryview(wire.encode("utf-8"))
            selector.register(process.stdin, selectors.EVENT_WRITE, "in")
            while pending:
                if time.monotonic() >= deadline:
                    raise TimeoutError("session timeout while sending request")
                try:
                    written = os.write(process.stdin.fileno(), pending)
                    pending = pending[written:]
                except BlockingIOError:
                    read_events(min(0.02, deadline - time.monotonic()))
            selector.unregister(process.stdin)
            while b"\n" not in buffer:
                remaining = deadline - time.monotonic()
                if remaining <= 0:
                    raise TimeoutError(
                        "session timeout waiting for flushed JSON response"
                    )
                read_events(min(0.05, remaining))
                if process.poll() is not None and b"\n" not in buffer:
                    raise ValueError(
                        f"process exited before response (code {process.returncode})"
                    )
            line, buffer = buffer.split(b"\n", 1)
            actual = strict_json(line.decode("utf-8"))
            if not equal(actual, expected):
                failure = {
                    "request_index": index,
                    "reason": "response mismatch",
                    "expected": expected,
                    "actual": actual,
                }
                break
            passed += 1
        if failure is None:
            if durable:
                # Test persistence after acknowledgement without graceful shutdown hooks.
                kill_group(process)
            else:
                process.stdin.close()
                while process.poll() is None or selector.get_map():
                    if time.monotonic() >= deadline:
                        raise TimeoutError("process did not exit cleanly on EOF")
                    read_events(min(0.02, deadline - time.monotonic()))
                if process.returncode:
                    raise ValueError(f"nonzero exit code {process.returncode}")
            # Catch extra lines even if the child has exited or was force-killed.
            read_events(0)
            if buffer:
                raise ValueError("extra stdout beyond one JSON response per request")
    except (ValueError, OSError, TimeoutError, UnicodeError) as error:
        failure = {
            "request_index": passed,
            "reason": str(error),
            "timed_out": isinstance(error, TimeoutError),
        }
    finally:
        kill_group(process)
        selector.close()
        for pipe in (process.stdin, process.stdout, process.stderr):
            if not pipe.closed:
                pipe.close()
    return {
        "passed": failure is None,
        "assertions_passed": passed,
        "assertions": len(session["expected"]),
        "duration": time.monotonic() - start,
        "failure": failure,
        "stderr": stderr.decode("utf-8", errors="replace") if failure else "",
    }


def evaluate(task, solution, *, timeout=None, tests=None, fail_fast=False):
    """A task passes only when every scenario and every restart session passes."""
    traces = tests if tests is not None else json.loads(task["acceptance_tests"])
    if not traces:
        raise ValueError("Refusing an empty acceptance suite")
    source = Path(solution).resolve()
    reports = []
    began = time.monotonic()
    with tempfile.TemporaryDirectory(prefix="klein-bench-") as temporary:
        root = Path(temporary)
        clean = root / "submission"
        clean.mkdir()
        rejection = None
        try:
            copy_project(source, clean)
        except ValueError as error:
            rejection = str(error)
        if rejection or not (clean / "main.py").is_file():
            return {
                "task_id": task["task_id"],
                "subset": task["subset"],
                "passed": False,
                "resolved": False,
                "reason": rejection or "main.py is missing",
                "scenarios": [],
                "duration": time.monotonic() - began,
            }
        source_hash = hashlib.sha256()
        for file in sorted(p for p in clean.rglob("*") if p.is_file()):
            source_hash.update(str(file.relative_to(clean)).encode())
            source_hash.update(b"\0" + file.read_bytes() + b"\0")
        for index, trace in enumerate(traces):
            scenario = root / str(index)
            project, state = scenario / "project", scenario / "state"
            project.mkdir(parents=True)
            state.mkdir()
            (scenario / "home").mkdir()
            copy_project(clean, project)
            sessions = []
            for session in trace["sessions"]:
                report = run_session(
                    project,
                    state,
                    session,
                    durable=task["subset"] == "max",
                    timeout=timeout or task["timeout_seconds"],
                )
                sessions.append(report)
                if not report["passed"]:
                    break
            reports.append(
                {
                    "name": trace["name"],
                    "passed": all(s["passed"] for s in sessions),
                    "sessions": sessions,
                }
            )
            if fail_fast and not reports[-1]["passed"]:
                break
    passed = len(reports) == len(traces) and all(r["passed"] for r in reports)
    return {
        "task_id": task["task_id"],
        "subset": task["subset"],
        "passed": passed,
        "resolved": passed,
        "scenarios_passed": sum(r["passed"] for r in reports),
        "scenarios_total": len(traces),
        "assertions_passed": sum(
            s["assertions_passed"] for r in reports for s in r["sessions"]
        ),
        "assertions_total": sum(
            len(s["expected"]) for t in traces for s in t["sessions"]
        ),
        "source_sha256": source_hash.hexdigest(),
        "duration": time.monotonic() - began,
        "scenarios": reports,
    }