import csv
import json
from pathlib import Path
from typing import Optional


def activity_log_path(activity: str, logs_dir: Optional[Path] = None) -> Path:
    """
    Returns the path of the activity log file in .csv format.
    """
    logs_dir = logs_dir or (Path.cwd() / "activity_logs")
    return logs_dir / f"{activity}.csv"


def activity_units_path(activity: str, units_dir: Optional[Path] = None) -> Path:
    """
    Returns the path of the activity units file in .json format.
    """
    units_dir = units_dir or (Path.cwd() / "activities")
    return units_dir / f"{activity}.json"


def is_convertable(activity: str, units_dir: Optional[Path] = None) -> bool:
    filename = activity_units_path(activity, units_dir)
    with filename.open("r", encoding="utf-8") as f:
        raw_data = json.load(f)
    return bool(raw_data.get("convertable"))


def create_activity_log_file(
    activity: str,
    *,
    units_dir: Optional[Path] = None,
    logs_dir: Optional[Path] = None,
) -> None:
    if not activity_units_path(activity, units_dir).exists():
        raise ValueError(f"{activity} is not a valid activity")

    logs_dir = logs_dir or (Path.cwd() / "activity_logs")
    logs_dir.mkdir(parents=True, exist_ok=True)

    filename = activity_log_path(activity, logs_dir)
    if filename.exists():
        return  # don't re-add headers

    with filename.open("w", newline="", encoding="utf-8") as f:
        writer = csv.writer(f)
        writer.writerow(["timestamp", "username", "value"])


def convert_units(
    activity: str,
    value: int | float,
    unit: str | None,
    *,
    units_dir: Optional[Path] = None,
) -> float:
    filename = activity_units_path(activity, units_dir)
    if not filename.exists():
        raise ValueError(f"{activity} is not a valid activity")

    # Consider None unit value as factor of 1
    if unit is None:
        return float(value)

    with filename.open("r", encoding="utf-8") as f:
        raw_data = json.load(f)

    units_data = raw_data.get("units") or {}
    unit_l = unit.lower()

    for _, data in units_data.items():
        aliases = [a.lower() for a in (data.get("aliases") or [])]
        if unit_l in aliases:
            return float(value) * float(data["factor"])

    raise ValueError(f"{unit} is not a valid unit")


def log_activity(
    timestamp: int,
    username: str,
    activity: str,
    value: int | float,
    unit: str | None,
    *,
    units_dir: Optional[Path] = None,
    logs_dir: Optional[Path] = None,
) -> None:
    
    if not isinstance(value, (int, float)) or value <= 0:
        raise ValueError(f"{value} is not a valid value")

    filename = activity_log_path(activity, logs_dir)
    if not filename.exists():
        create_activity_log_file(activity, units_dir=units_dir, logs_dir=logs_dir)

    if is_convertable(activity, units_dir):
        converted_value = round(convert_units(activity, value, unit, units_dir=units_dir), 2)
    else:
        converted_value = round(float(value), 2)

    with filename.open("a", newline="", encoding="utf-8") as f:
        writer = csv.writer(f)
        writer.writerow([timestamp, username, converted_value])