import os
import time
from pathlib import Path

class CacheMiss(Exception):
    pass

class Cache:
    def __init__(self, name, default_ttl=3600):
        self.default_ttl = default_ttl
        try:
            self.cache_dir = Path(os.environ['XDG_CACHE_HOME'])/name
        except KeyError:
            self.cache_dir = Path(os.environ['HOME'])/'.cache'/name
        self.cache_dir.mkdir(exist_ok=True)

    def write(self, key, value, ttl=None):
        loc = self.cache_dir/key
        loc.write_text(value, errors='ignore')

        # store expiry time as mtime to avoid having anything to do
        ttl = ttl if ttl else self.default_ttl
        stat = loc.stat()
        os.utime(loc, (stat.st_atime, stat.st_mtime + ttl))

    def read(self, key):
        loc = self.cache_dir/key

        if not loc.exists():
            raise CacheMiss

        if time.time() > loc.stat().st_mtime:
            loc.unlink()
            raise CacheMiss
        
        return loc.read_text()