#!/usr/bin/env python3
"""Coordinate topology loading, validation, planning, rendering, and execution.

The coordinator is the user-facing entry point of the project.

Normal execution follows this pipeline:

    topology.json
        -> load and parse
        -> validate
        -> plan
        -> render executable Mininet Python
        -> write the generated intermediate artifact
        -> execute that generated artifact

The generated Python file is intentionally preserved so it can be inspected
independently of the declarative topology source.

Author: Christos Choutouridis <cchoutou@ece.auth.gr>
"""

import argparse
from dataclasses import dataclass
import importlib.util
import os
from pathlib import Path
import shutil
import subprocess
import sys
from typing import Optional, Sequence, Tuple, Union

from topology_loader import TopologyLoadError, load_topology
from topology_parser import TopologyParseError, parse_topology
from topology_plan import ExecutionPlan, TopologyPlanError, plan
from topology_renderer import render_python
from topology_validator import TopologyValidationError, validate


# ============================ Types and errors ============================

PathLike = Union[str, Path]


class BuildNetworkError(RuntimeError):
    """Raised for coordinator-level generation or execution failures."""


@dataclass(frozen=True)
class EnvironmentRequirement:
    """Describe one external runtime requirement.

    Args:
        name: Human-readable requirement name.
        available: Whether the requirement is available in the current
            environment.
        detail: Resolved path, explanatory status, or installation hint.
    """

    name: str
    available: bool
    detail: str


@dataclass(frozen=True)
class EnvironmentReport:
    """Contain the result of checking external project dependencies.

    Args:
        requirements: Individual dependency checks.
    """

    requirements: Tuple[EnvironmentRequirement, ...]

    @property
    def ok(self) -> bool:
        """Return whether every required dependency is available."""

        return all(item.available for item in self.requirements)


# =========================== Environment checks ===========================

def _check_python_module(name: str, install_hint: str) -> EnvironmentRequirement:
    """Check whether one Python module is importable.

    Args:
        name: Importable Python module name.
        install_hint: Human-readable installation hint used when missing.

    Returns:
        EnvironmentRequirement describing the result.
    """

    available = importlib.util.find_spec(name) is not None
    detail = "Python module available" if available else install_hint

    return EnvironmentRequirement(
        name="python module %s" % name,
        available=available,
        detail=detail,
    )


def _check_command(
    command: str,
    purpose: str,
    install_hint: str,
) -> EnvironmentRequirement:
    """Check whether one executable is available through PATH.

    Args:
        command: Executable name to locate.
        purpose: Short description of why the executable is required.
        install_hint: Human-readable installation hint used when missing.

    Returns:
        EnvironmentRequirement describing the result.
    """

    path = shutil.which(command)

    if path is not None:
        detail = "%s (%s)" % (path, purpose)
    else:
        detail = "%s; %s" % (purpose, install_hint)

    return EnvironmentRequirement(
        name=command,
        available=path is not None,
        detail=detail,
    )


def check_environment() -> EnvironmentReport:
    """Check dependencies required by the builder and assignment experiments.

    Returns:
        EnvironmentReport containing all required dependency checks.

    Notes:
        This function performs read-only availability checks.
        It does not install packages or modify the system.
    """

    requirements = [
        _check_python_module(
            "mininet",
            "install Mininet, for example: sudo apt install mininet",
        ),
        _check_command(
            "mn",
            "Mininet command-line utilities",
            "install Mininet, for example: sudo apt install mininet",
        ),
        _check_command(
            "ovs-vsctl",
            "Open vSwitch configuration used by Mininet switches",
            "install Open vSwitch, for example: sudo apt install openvswitch-switch",
        ),
        _check_command(
            "ip",
            "interface and route configuration",
            "install iproute2: sudo apt install iproute2",
        ),
        _check_command(
            "tc",
            "traffic-control settings for TCLink",
            "install iproute2: sudo apt install iproute2",
        ),
        _check_command(
            "sysctl",
            "router kernel settings",
            "install procps: sudo apt install procps",
        ),
        _check_command(
            "dnsmasq",
            "DHCP server service",
            "install dnsmasq-base: sudo apt install dnsmasq-base",
        ),
        _check_command(
            "dhclient",
            "manual DHCP client experiment",
            "install isc-dhcp-client: sudo apt install isc-dhcp-client",
        ),
        _check_command(
            "tcpdump",
            "packet capture for DHCP, ARP, and routing experiments",
            "install tcpdump: sudo apt install tcpdump",
        ),
        _check_command(
            "ping",
            "ICMP connectivity experiments",
            "install iputils-ping: sudo apt install iputils-ping",
        ),
    ]

    return EnvironmentReport(requirements=tuple(requirements))


# =================== Compilation and artifact execution ===================

def compile_topology(path: PathLike) -> Tuple[ExecutionPlan, str]:
    """Compile one topology file into a plan and executable Python source.

    Args:
        path: Path to the declarative topology JSON file.

    Returns:
        Pair containing the fully resolved ExecutionPlan and rendered Python
        source.

    Raises:
        TopologyLoadError: If the JSON source cannot be loaded.
        TopologyParseError: If the JSON violates the topology grammar.
        TopologyValidationError: If the parsed topology is semantically
            inconsistent.
        TopologyPlanError: If the validated topology cannot be lowered into a
            complete execution plan.
    """

    topology = parse_topology(load_topology(path))
    validate(topology)
    execution_plan = plan(topology)
    source = render_python(execution_plan)

    return execution_plan, source


def default_generated_path(topology_path: PathLike) -> Path:
    """Return the default intermediate Python path for a topology source.

    Args:
        topology_path: Source topology path.

    Returns:
        Path alongside the topology using the `.generated.py` suffix.
    """

    return Path(topology_path).with_suffix(".generated.py")


def write_generated_python(source: str, path: PathLike) -> Path:
    """Write generated executable Python source to disk.

    Args:
        source: Rendered Python program.
        path: Destination path for the generated artifact.

    Returns:
        Destination Path, remaining relative if the supplied path is relative.

    Raises:
        BuildNetworkError: If the artifact cannot be written.
    """

    destination = Path(path)

    try:
        destination.write_text(source, encoding="utf-8")
    except OSError as exc:
        raise BuildNetworkError(
            "failed to write generated Python %s: %s" % (destination, exc)
        ) from exc

    return destination


def execute_generated_python(path: PathLike) -> int:
    """Execute one generated Mininet Python artifact interactively.

    Args:
        path: Generated Python file to execute.

    Returns:
        Exit status returned by the generated process.

    Raises:
        BuildNetworkError: If execution is attempted without root privileges
            or the generated process cannot be started.
    """

    source = Path(path)

    if os.geteuid() != 0:
        raise BuildNetworkError(
            "network execution requires root privileges; rerun with sudo or "
            "use --emit to generate the intermediate Python without executing it"
        )

    try:
        completed = subprocess.run(
            [sys.executable, str(source)],
            check=False,
        )
    except OSError as exc:
        raise BuildNetworkError(
            "failed to execute generated Python %s: %s" % (source, exc)
        ) from exc

    return completed.returncode


# ================== Command-line reporting and arguments ==================

def _print_environment_report(report: EnvironmentReport) -> None:
    """Print an environment report from the command-line layer.

    Args:
        report: Environment report to present to the user.
    """

    print("Environment check:")
    for requirement in report.requirements:
        marker = "OK" if requirement.available else "MISSING"
        print("[%s] %-16s %s" % (marker, requirement.name, requirement.detail))

    if report.ok:
        print("Environment OK.")
    else:
        print("Environment check failed: one or more required dependencies are missing.")


def _build_argument_parser() -> argparse.ArgumentParser:
    """Create the command-line argument parser.

    Returns:
        Configured ArgumentParser instance.
    """

    parser = argparse.ArgumentParser(
        description=(
            "Load, validate, plan, render, and execute a declarative Mininet "
            "topology."
        )
    )
    parser.add_argument(
        "topology",
        nargs="?",
        help="path to topology.json; omitted only with --env-check",
    )
    parser.add_argument(
        "--env-check",
        action="store_true",
        help=(
            "check Mininet, Open vSwitch, dnsmasq, and experiment tools, then exit"
        ),
    )
    parser.add_argument(
        "--emit",
        nargs="?",
        const="",
        metavar="PATH",
        help=(
            "generate the intermediate Python and stop; optionally write it to PATH"
        ),
    )

    return parser


# ======================== Command-line entry point ========================

def main(argv: Optional[Sequence[str]] = None) -> int:
    """Run the coordinator command-line interface.

    Args:
        argv: Optional argument sequence excluding the executable name.

    Returns:
        Process exit status.
    """

    parser = _build_argument_parser()
    args = parser.parse_args(argv)

    if args.env_check:
        report = check_environment()
        _print_environment_report(report)
        return 0 if report.ok else 1

    if args.topology is None:
        parser.error("topology is required unless --env-check is used")

    topology_path = Path(args.topology)

    if args.emit is None:
        generated_path = default_generated_path(topology_path)
        execute = True
    else:
        generated_path = (
            default_generated_path(topology_path)
            if args.emit == ""
            else Path(args.emit)
        )
        execute = False

    try:
        _, source = compile_topology(topology_path)
        generated_path = write_generated_python(source, generated_path)

        print("Generated: %s" % generated_path)

        if not execute:
            return 0

        report = check_environment()
        if not report.ok:
            _print_environment_report(report)
            return 1

        return execute_generated_python(generated_path)

    except (
        TopologyLoadError,
        TopologyParseError,
        TopologyValidationError,
        TopologyPlanError,
        BuildNetworkError,
    ) as exc:
        print("error: %s" % exc, file=sys.stderr)
        return 1


if __name__ == "__main__":
    sys.exit(main())