import json
import os
import re
from datetime import datetime, timezone
from typing import Dict, Any, List, Optional

_CURRENT_RUN_NUMBER: Optional[int] = None
DEFAULT_MAX_RUNS = 10


def _get_default_logs_dir() -> str:
    """Return the absolute path to the backend/logs directory."""
    utils_dir = os.path.dirname(os.path.abspath(__file__))
    backend_dir = os.path.dirname(os.path.dirname(utils_dir))
    return os.path.join(backend_dir, "logs")


def _read_counter(counter_file: str) -> Optional[int]:
    """Read the last run number from the counter file if it exists."""
    if not os.path.exists(counter_file):
        return None
    try:
        with open(counter_file, "r", encoding="utf-8") as f:
            content = f.read().strip()
            if content.isdigit():
                return int(content)
    except Exception:
        pass
    return None


def _find_max_existing_run(logs_dir: str) -> int:
    """Scan existing run_*.log files to find the highest run number."""
    if not os.path.exists(logs_dir):
        return 0
    pattern = re.compile(r"^run_(\d+)\.log$")
    max_num = 0
    for name in os.listdir(logs_dir):
        match = pattern.match(name)
        if match:
            max_num = max(max_num, int(match.group(1)))
    return max_num


def prune_old_runs(logs_dir: str, max_runs: int = DEFAULT_MAX_RUNS) -> List[str]:
    """
    Ensure only the latest `max_runs` run files are kept.
    Deletes the oldest run_*.log files exceeding the limit.
    Returns the list of deleted filenames.
    """
    if not os.path.exists(logs_dir) or max_runs <= 0:
        return []

    pattern = re.compile(r"^run_(\d+)\.log$")
    run_files = []
    for name in os.listdir(logs_dir):
        match = pattern.match(name)
        if match:
            run_files.append((int(match.group(1)), name))

    # Sort ascending by run number
    run_files.sort(key=lambda x: x[0])

    deleted = []
    if len(run_files) > max_runs:
        excess_count = len(run_files) - max_runs
        to_delete = run_files[:excess_count]
        for _, name in to_delete:
            file_path = os.path.join(logs_dir, name)
            try:
                os.remove(file_path)
                deleted.append(name)
            except Exception:
                pass

    _prune_history_file(logs_dir, max_runs)
    return deleted


def _prune_history_file(logs_dir: str, max_runs: int):
    """Keep only the last `max_runs` entries in run_history.json."""
    history_file = os.path.join(logs_dir, "run_history.json")
    if not os.path.exists(history_file):
        return
    try:
        with open(history_file, "r", encoding="utf-8") as f:
            history = json.load(f)
        if isinstance(history, list) and len(history) > max_runs:
            history = history[-max_runs:]
            with open(history_file, "w", encoding="utf-8") as f:
                json.dump(history, f, indent=2)
    except Exception:
        pass


def _record_run_history(logs_dir: str, run_number: int, log_file: str, max_runs: int):
    """Append a record for this run in run_history.json and prune older entries."""
    history_file = os.path.join(logs_dir, "run_history.json")
    history = []
    if os.path.exists(history_file):
        try:
            with open(history_file, "r", encoding="utf-8") as f:
                loaded = json.load(f)
                if isinstance(loaded, list):
                    history = loaded
        except Exception:
            history = []

    history.append({
        "run_number": run_number,
        "timestamp": datetime.now(timezone.utc).isoformat(),
        "log_file": os.path.basename(log_file),
    })

    if len(history) > max_runs:
        history = history[-max_runs:]

    try:
        with open(history_file, "w", encoding="utf-8") as f:
            json.dump(history, f, indent=2)
    except Exception:
        pass


def initialize_run(
    logs_dir: Optional[str] = None,
    max_runs: Optional[int] = None,
    force_new: bool = False,
) -> int:
    """
    Initialize the run for this backend execution:
    - Increments the persistent run counter by 1 (or starts at 1).
    - Prunes older runs so only the last `max_runs` (default 10) are kept.
    - Creates/touches the log file for this run.
    - Caches the current run number for the process.
    """
    global _CURRENT_RUN_NUMBER

    if _CURRENT_RUN_NUMBER is not None and not force_new:
        return _CURRENT_RUN_NUMBER

    if logs_dir is None:
        logs_dir = _get_default_logs_dir()

    if max_runs is None:
        env_max = os.getenv("MAX_LOG_RUNS", "").strip()
        max_runs = int(env_max) if env_max.isdigit() else DEFAULT_MAX_RUNS

    os.makedirs(logs_dir, exist_ok=True)
    counter_file = os.path.join(logs_dir, "run_counter.txt")

    last_run = _read_counter(counter_file)
    if last_run is None:
        last_run = _find_max_existing_run(logs_dir)

    new_run = last_run + 1

    # Persist the new run number
    with open(counter_file, "w", encoding="utf-8") as f:
        f.write(str(new_run))

    _CURRENT_RUN_NUMBER = new_run

    # Create run log file
    run_log_file = os.path.join(logs_dir, f"run_{new_run}.log")
    if not os.path.exists(run_log_file):
        with open(run_log_file, "a", encoding="utf-8"):
            pass

    # Prune older runs
    prune_old_runs(logs_dir, max_runs=max_runs)

    # Record in history
    _record_run_history(logs_dir, new_run, run_log_file, max_runs)

    return new_run


def get_current_run_number(logs_dir: Optional[str] = None) -> int:
    """Return the current cached run number, or initialize one if not yet done."""
    global _CURRENT_RUN_NUMBER
    if _CURRENT_RUN_NUMBER is None:
        return initialize_run(logs_dir=logs_dir)
    return _CURRENT_RUN_NUMBER


def get_current_run_log_file(logs_dir: Optional[str] = None) -> str:
    """Return the absolute path to the current run's log file."""
    if logs_dir is None:
        logs_dir = _get_default_logs_dir()
    run_num = get_current_run_number(logs_dir=logs_dir)
    return os.path.join(logs_dir, f"run_{run_num}.log")


def get_run_info(logs_dir: Optional[str] = None, max_runs: Optional[int] = None) -> Dict[str, Any]:
    """Return structured metadata about the current and recent runs."""
    if logs_dir is None:
        logs_dir = _get_default_logs_dir()

    if max_runs is None:
        env_max = os.getenv("MAX_LOG_RUNS", "").strip()
        max_runs = int(env_max) if env_max.isdigit() else DEFAULT_MAX_RUNS

    current_run = get_current_run_number(logs_dir=logs_dir)

    # Inspect present run files
    pattern = re.compile(r"^run_(\d+)\.log$")
    present_runs = []
    if os.path.exists(logs_dir):
        for name in os.listdir(logs_dir):
            match = pattern.match(name)
            if match:
                full_path = os.path.join(logs_dir, name)
                stat = os.stat(full_path)
                present_runs.append({
                    "run_number": int(match.group(1)),
                    "filename": name,
                    "size_bytes": stat.st_size,
                    "modified_at": datetime.fromtimestamp(stat.st_mtime, tz=timezone.utc).isoformat(),
                })

    present_runs.sort(key=lambda x: x["run_number"])

    return {
        "run_number": current_run,
        "max_runs": max_runs,
        "current_log_file": os.path.basename(get_current_run_log_file(logs_dir=logs_dir)),
        "available_runs": present_runs,
    }