# Test utilities for fetching & caching assets
#
# Copyright 2024 Red Hat, Inc.
#
# This work is licensed under the terms of the GNU GPL, version 2 or
# later.  See the COPYING file in the top-level directory.

import hashlib
import logging
import os
import stat
import sys
import unittest
import urllib.request
from time import sleep
from pathlib import Path
from shutil import copyfileobj
from urllib.error import HTTPError

class AssetError(Exception):
    def __init__(self, asset, msg, transient=False):
        self.url = asset.url
        self.msg = msg
        self.transient = transient

    def __str__(self):
        return "%s: %s" % (self.url, self.msg)

# Instances of this class must be declared as class level variables
# starting with a name "ASSET_". This enables the pre-caching logic
# to easily find all referenced assets and download them prior to
# execution of the tests.
class Asset:

    def __init__(self, url, hashsum):
        self.url = url
        self.hash = hashsum
        cache_dir_env = os.getenv('QEMU_TEST_CACHE_DIR')
        if cache_dir_env:
            self.cache_dir = Path(cache_dir_env, "download")
        else:
            self.cache_dir = Path(Path("~").expanduser(),
                                  ".cache", "qemu", "download")
        self.cache_file = Path(self.cache_dir, hashsum)
        self.log = logging.getLogger('qemu-test')

    def __repr__(self):
        return "Asset: url=%s hash=%s cache=%s" % (
            self.url, self.hash, self.cache_file)

    def __str__(self):
        return str(self.cache_file)

    def _check(self, cache_file):
        if self.hash is None:
            return True
        if len(self.hash) == 64:
            hl = hashlib.sha256()
        elif len(self.hash) == 128:
            hl = hashlib.sha512()
        else:
            raise AssetError(self, "unknown hash type")

        # Calculate the hash of the file:
        with open(cache_file, 'rb') as file:
            while True:
                chunk = file.read(1 << 20)
                if not chunk:
                    break
                hl.update(chunk)

        return self.hash == hl.hexdigest()

    def valid(self):
        return self.cache_file.exists() and self._check(self.cache_file)

    def fetchable(self):
        return not os.environ.get("QEMU_TEST_NO_DOWNLOAD", False)

    def available(self):
        return self.valid() or self.fetchable()

    def _wait_for_other_download(self, tmp_cache_file):
        # Another thread already seems to download the asset, so wait until
        # it is done, while also checking the size to see whether it is stuck
        try:
            current_size = tmp_cache_file.stat().st_size
            new_size = current_size
        except:
            if os.path.exists(self.cache_file):
                return True
            raise
        waittime = lastchange = 600
        while waittime > 0:
            sleep(1)
            waittime -= 1
            try:
                new_size = tmp_cache_file.stat().st_size
            except:
                if os.path.exists(self.cache_file):
                    return True
                raise
            if new_size != current_size:
                lastchange = waittime
                current_size = new_size
            elif lastchange - waittime > 90:
                return False

        self.log.debug("Time out while waiting for %s!", tmp_cache_file)
        raise

    def fetch(self):
        if not self.cache_dir.exists():
            self.cache_dir.mkdir(parents=True, exist_ok=True)

        if self.valid():
            self.log.debug("Using cached asset %s for %s",
                           self.cache_file, self.url)
            return str(self.cache_file)

        if not self.fetchable():
            raise AssetError(self,
                             "Asset cache is invalid and downloads disabled")

        self.log.info("Downloading %s to %s...", self.url, self.cache_file)
        tmp_cache_file = self.cache_file.with_suffix(".download")

        for retries in range(3):
            try:
                with tmp_cache_file.open("xb") as dst:
                    with urllib.request.urlopen(self.url) as resp:
                        copyfileobj(resp, dst)
                        length_hdr = resp.getheader("Content-Length")

                # Verify downloaded file size against length metadata, if
                # available.
                if length_hdr is not None:
                    length = int(length_hdr)
                    fsize = tmp_cache_file.stat().st_size
                    if fsize != length:
                        self.log.error("Unable to download %s: "
                                       "connection closed before "
                                       "transfer complete (%d/%d)",
                                       self.url, fsize, length)
                        tmp_cache_file.unlink()
                        continue
                break
            except FileExistsError:
                self.log.debug("%s already exists, "
                               "waiting for other thread to finish...",
                               tmp_cache_file)
                if self._wait_for_other_download(tmp_cache_file):
                    return str(self.cache_file)
                self.log.debug("%s seems to be stale, "
                               "deleting and retrying download...",
                               tmp_cache_file)
                tmp_cache_file.unlink()
                continue
            except HTTPError as e:
                tmp_cache_file.unlink()
                self.log.error("Unable to download %s: HTTP error %d",
                               self.url, e.code)
                # Treat 404 as fatal, since it is highly likely to
                # indicate a broken test rather than a transient
                # server or networking problem
                if e.code == 404:
                    raise AssetError(self, "Unable to download: "
                                     "HTTP error %d" % e.code)
                continue
            except Exception as e:
                tmp_cache_file.unlink()
                raise AssetError(self, "Unable to download: " % e)

        if not os.path.exists(tmp_cache_file):
            raise AssetError(self, "Download retries exceeded", transient=True)

        try:
            # Set these just for informational purposes
            os.setxattr(str(tmp_cache_file), "user.qemu-asset-url",
                        self.url.encode('utf8'))
            os.setxattr(str(tmp_cache_file), "user.qemu-asset-hash",
                        self.hash.encode('utf8'))
        except Exception as e:
            self.log.debug("Unable to set xattr on %s: %s", tmp_cache_file, e)
            pass

        if not self._check(tmp_cache_file):
            tmp_cache_file.unlink()
            raise AssetError(self, "Hash does not match %s" % self.hash)
        tmp_cache_file.replace(self.cache_file)
        # Remove write perms to stop tests accidentally modifying them
        os.chmod(self.cache_file, stat.S_IRUSR | stat.S_IRGRP)

        self.log.info("Cached %s at %s" % (self.url, self.cache_file))
        return str(self.cache_file)

    def precache_test(test):
        log = logging.getLogger('qemu-test')
        log.setLevel(logging.DEBUG)
        handler = logging.StreamHandler(sys.stdout)
        handler.setLevel(logging.DEBUG)
        formatter = logging.Formatter(
            '%(asctime)s - %(name)s - %(levelname)s - %(message)s')
        handler.setFormatter(formatter)
        log.addHandler(handler)
        for name, asset in vars(test.__class__).items():
            if name.startswith("ASSET_") and type(asset) == Asset:
                log.info("Attempting to cache '%s'" % asset)
                try:
                    asset.fetch()
                except AssetError as e:
                    if not e.transient:
                        raise
                    log.error("%s: skipping asset precache" % e)

        log.removeHandler(handler)

    def precache_suite(suite):
        for test in suite:
            if isinstance(test, unittest.TestSuite):
                Asset.precache_suite(test)
            elif isinstance(test, unittest.TestCase):
                Asset.precache_test(test)

    def precache_suites(path, cacheTstamp):
        loader = unittest.loader.defaultTestLoader
        tests = loader.loadTestsFromNames([path], None)

        with open(cacheTstamp, "w") as fh:
            Asset.precache_suite(tests)