"""
Canopy-R3 Best-Practice Checkpointing, Resumption, Atomic Writes,
Storage Safety, and System Resource Monitoring.
"""

import os
import gc
import glob
import shutil
import random
import logging
from pathlib import Path
from typing import Optional, Dict, Any, Tuple, List, Union

import numpy as np
import psutil
import torch
import torch.nn as nn
from safetensors.torch import save_file

logger = logging.getLogger("canopy.checkpoint")


class ResourceMonitor:
    """Monitors CPU RAM, GPU VRAM, and Filesystem Disk Space."""

    @staticmethod
    def get_system_ram_gib() -> Dict[str, float]:
        vm = psutil.virtual_memory()
        return {
            "total_gib": vm.total / (1024 ** 3),
            "available_gib": vm.available / (1024 ** 3),
            "used_gib": vm.used / (1024 ** 3),
            "percent": vm.percent,
        }

    @staticmethod
    def get_disk_free_gib(path: Union[str, Path] = ".") -> Dict[str, float]:
        usage = shutil.disk_usage(path)
        return {
            "total_gib": usage.total / (1024 ** 3),
            "used_gib": usage.used / (1024 ** 3),
            "free_gib": usage.free / (1024 ** 3),
            "percent": (usage.used / usage.total) * 100.0,
        }

    @staticmethod
    def get_gpu_vram_gib(device: Union[int, str, torch.device] = "cuda") -> Dict[str, float]:
        if not torch.cuda.is_available():
            return {"allocated_gib": 0.0, "reserved_gib": 0.0, "max_gib": 0.0}
        return {
            "allocated_gib": torch.cuda.memory_allocated(device) / (1024 ** 3),
            "reserved_gib": torch.cuda.memory_reserved(device) / (1024 ** 3),
            "max_gib": torch.cuda.max_memory_allocated(device) / (1024 ** 3),
        }

    @classmethod
    def get_status_string(cls, path: Union[str, Path] = ".", device: str = "cuda") -> str:
        ram = cls.get_system_ram_gib()
        disk = cls.get_disk_free_gib(path)
        vram = cls.get_gpu_vram_gib(device)
        return (
            f"RAM: {ram['used_gib']:.1f}/{ram['total_gib']:.1f}G ({ram['percent']:.0f}%) | "
            f"Disk: {disk['free_gib']:.1f}G free | "
            f"VRAM: {vram['allocated_gib']:.1f}G"
        )


class CheckpointManager:
    """
    Manages robust, atomic checkpoint saving, automatic rotation/pruning of older checkpoints,
    lightweight weights export (safetensors + pt), and exact state restoration.
    """

    def __init__(
        self,
        output_dir: Union[str, Path],
        keep_last_k: int = 3,
        min_free_disk_gb: float = 10.0,
        save_weights_only: bool = True,
        save_safetensors: bool = True,
    ):
        self.output_dir = Path(output_dir)
        self.output_dir.mkdir(parents=True, exist_ok=True)
        self.keep_last_k = max(1, keep_last_k)
        self.min_free_disk_gb = min_free_disk_gb
        self.save_weights_only = save_weights_only
        self.save_safetensors = save_safetensors

    def check_disk_space(self) -> float:
        """Verifies sufficient disk space remains on the storage volume."""
        free_gb = ResourceMonitor.get_disk_free_gib(self.output_dir)["free_gib"]
        if free_gb < self.min_free_disk_gb:
            logger.warning(
                f"WARNING: Low disk space detected on {self.output_dir}: "
                f"{free_gb:.2f} GiB remaining (threshold: {self.min_free_disk_gb} GiB)."
            )
        return free_gb

    def save_checkpoint(
        self,
        step: int,
        model: nn.Module,
        optimizer: Optional[torch.optim.Optimizer] = None,
        scheduler: Optional[Any] = None,
        sampler: Optional[Any] = None,
        tokens_seen: int = 0,
        metrics: Optional[Dict[str, Any]] = None,
        is_best: bool = False,
        config_dict: Optional[Dict[str, Any]] = None,
    ) -> Path:
        """
        Atomically saves complete training state, exports weights, and prunes old checkpoints.
        """
        self.check_disk_space()

        # Capture RNG states for bit-for-bit reproducibility
        rng_state = {
            "python": random.getstate(),
            "numpy": np.random.get_state(),
            "torch_cpu": torch.get_rng_state(),
            "torch_cuda": torch.cuda.get_rng_state() if torch.cuda.is_available() else None,
        }

        # Handle unwrapped models (e.g. torch.compile or DDP)
        raw_model = getattr(model, "_orig_mod", model)
        model_state = raw_model.state_dict()

        payload = {
            "step": step,
            "tokens_seen": tokens_seen,
            "model_state": model_state,
            "optimizer_state": optimizer.state_dict() if optimizer else None,
            "scheduler_state": scheduler.state_dict() if scheduler else None,
            "sampler_state": sampler.state_dict() if (sampler and hasattr(sampler, "state_dict")) else None,
            "rng_state": rng_state,
            "metrics": metrics or {},
            "config": config_dict or {},
        }

        # 1. Atomic write of full training checkpoint (via temporary file)
        target_path = self.output_dir / f"checkpoint_step_{step:08d}.pt"
        tmp_path = self.output_dir / f"checkpoint_step_{step:08d}.pt.tmp"

        torch.save(payload, tmp_path)
        os.replace(tmp_path, target_path)

        # 2. Save standalone lightweight weights (for inference / evaluation without optimizer memory)
        if self.save_weights_only:
            weights_path = self.output_dir / f"weights_step_{step:08d}.pt"
            weights_tmp = self.output_dir / f"weights_step_{step:08d}.pt.tmp"
            torch.save({"model_state": model_state, "config": config_dict or {}}, weights_tmp)
            os.replace(weights_tmp, weights_path)

        # 3. Save Safetensors format
        if self.save_safetensors:
            st_path = self.output_dir / f"model_step_{step:08d}.safetensors"
            cloned_state = {}
            for k, v in model_state.items():
                if isinstance(v, torch.Tensor):
                    cloned_state[k] = v.clone().cpu()
            save_file(cloned_state, str(st_path))

        # 4. Update latest checkpoint pointer
        latest_record = self.output_dir / "latest_checkpoint.txt"
        with open(latest_record, "w", encoding="utf-8") as f:
            f.write(str(target_path.name) + "\n")

        # 5. If best model, save dedicated copy
        if is_best:
            best_target = self.output_dir / "best_model.pt"
            torch.save({"model_state": model_state, "step": step, "metrics": metrics}, best_target)

        # 6. Prune old checkpoints to maintain bounded disk footprint
        self.prune_old_checkpoints()

        return target_path

    def prune_old_checkpoints(self):
        """Keeps only the last keep_last_k checkpoints and removes older ones."""
        ckpts = sorted(self.output_dir.glob("checkpoint_step_*.pt"), key=os.path.getmtime)
        if len(ckpts) > self.keep_last_k:
            to_delete = ckpts[: -self.keep_last_k]
            for ckpt in to_delete:
                try:
                    step_str = ckpt.stem.replace("checkpoint_step_", "")
                    ckpt.unlink(missing_ok=True)

                    # Also prune corresponding weights file if present
                    w_file = self.output_dir / f"weights_step_{step_str}.pt"
                    w_file.unlink(missing_ok=True)

                    st_file = self.output_dir / f"model_step_{step_str}.safetensors"
                    st_file.unlink(missing_ok=True)
                except Exception as e:
                    logger.warning(f"Failed to delete old checkpoint {ckpt}: {e}")

    @staticmethod
    def find_latest_checkpoint(dir_path: Union[str, Path]) -> Optional[Path]:
        """Finds the most recent checkpoint in directory, using latest_checkpoint.txt or max step."""
        p = Path(dir_path)
        if not p.exists():
            return None

        # Check latest_checkpoint.txt first
        pointer = p / "latest_checkpoint.txt"
        if pointer.exists():
            with open(pointer, "r", encoding="utf-8") as f:
                name = f.read().strip()
                target = p / name
                if target.exists():
                    return target

        # Fallback to scanning
        ckpts = sorted(p.glob("checkpoint_step_*.pt"))
        if ckpts:
            return ckpts[-1]
        return None

    @staticmethod
    def load_checkpoint(
        checkpoint_path: Union[str, Path],
        model: nn.Module,
        optimizer: Optional[torch.optim.Optimizer] = None,
        scheduler: Optional[Any] = None,
        sampler: Optional[Any] = None,
        device: str = "cpu",
        strict: bool = True,
    ) -> Dict[str, Any]:
        """
        Safely restores model weights, optimizer moments, scheduler, sampler, and RNG states.
        """
        ckpt_path = Path(checkpoint_path)
        if not ckpt_path.exists():
            raise FileNotFoundError(f"Checkpoint not found at: {ckpt_path}")

        print(f" Loading checkpoint from: {ckpt_path} (target device: {device})...")
        ckpt = torch.load(ckpt_path, map_location=device, weights_only=False)

        # Restore model weights
        raw_model = getattr(model, "_orig_mod", model)
        raw_model.load_state_dict(ckpt["model_state"], strict=strict)

        # Restore optimizer
        if optimizer and ckpt.get("optimizer_state"):
            optimizer.load_state_dict(ckpt["optimizer_state"])

        # Restore scheduler
        if scheduler and ckpt.get("scheduler_state"):
            scheduler.load_state_dict(ckpt["scheduler_state"])

        # Restore sampler
        if sampler and ckpt.get("sampler_state") and hasattr(sampler, "load_state_dict"):
            sampler.load_state_dict(ckpt["sampler_state"])

        # Restore RNG states
        if "rng_state" in ckpt:
            rng = ckpt["rng_state"]
            if "python" in rng and rng["python"]:
                random.setstate(rng["python"])
            if "numpy" in rng and rng["numpy"]:
                np.random.set_state(rng["numpy"])
            if "torch_cpu" in rng and rng["torch_cpu"] is not None:
                cpu_state = rng["torch_cpu"]
                if isinstance(cpu_state, torch.Tensor):
                    cpu_state = cpu_state.cpu().to(torch.uint8)
                torch.set_rng_state(cpu_state)
            if "torch_cuda" in rng and rng["torch_cuda"] is not None and torch.cuda.is_available():
                cuda_state = rng["torch_cuda"]
                if isinstance(cuda_state, torch.Tensor):
                    cuda_state = cuda_state.cpu().to(torch.uint8)
                torch.cuda.set_rng_state(cuda_state)

        step = ckpt.get("step", 0)
        tokens_seen = ckpt.get("tokens_seen", 0)
        metrics = ckpt.get("metrics", {})

        print(f" Resumed successfully from Step {step:,} ({tokens_seen:,} tokens seen).")
        return {
            "step": step,
            "tokens_seen": tokens_seen,
            "metrics": metrics,
            "config": ckpt.get("config", {}),
        }