#!/usr/bin/env python3
"""
A simple clang-tidy caching application.

Prefix calls to clang-tidy to cache
their results for faster static code analysis.

Source: https://github.com/freedick/cltcache
"""
import configparser
import gzip
import hashlib
import os
import pathlib
import re
import subprocess
import sys
import time


def save_to_file_raw(data, filename):
    with open(filename, "wb") as f:
        f.write(data)


def save_to_file(string, filename):
    save_to_file_raw(string.encode("utf-8"), filename)


def compress_to_file(data, filename):
    save_to_file_raw(gzip.compress(data), filename)


def read_from_file_raw(filename):
    with open(filename, "rb") as f:
        return f.read()


def read_from_file(filename):
    return read_from_file_raw(filename).decode("utf-8")


def decompress_from_file(filename):
    return gzip.decompress(read_from_file_raw(filename))


def sha256(string):
    m = hashlib.sha256()
    m.update(string.encode('utf-8'))
    return m.hexdigest()


def file_age(filepath):
    return time.time() - os.path.getmtime(filepath)


def run_command(command):
    return subprocess.run(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, check=False)


def run_get_stdout(command, ignore_errors=False):
    """
    Run a command and forward its stdout and stderr if exit code is nonzero,
    otherwise return stdout.
    """
    result = run_command(command)
    if not ignore_errors and result.returncode != 0:
        raise Exception(f"Bad exit code when running: {command}")
    return result.stdout.decode("utf-8")


def remove_o_flag(compile_args):
    if "-o" in compile_args:
        oflag_index = compile_args.index('-o')
        return compile_args[:oflag_index] + compile_args[oflag_index + 2 :]
    return compile_args


def get_preproc_hash(compile_args, config):
    compile_args = remove_o_flag(compile_args)
    preproc_flag = "-E"
    keep_comments_flag = config.get("preprocessor", "preserve_comments", fallback="-C")
    preproc_command = config.get("preprocessor", "command", fallback="c++")
    preproc_source = run_get_stdout(
        [preproc_command] + compile_args + [preproc_flag, keep_comments_flag],
        config.getboolean("preprocessor", "ignore_errors", fallback=False),
    )
    verbose = config.getboolean("behavior", "verbose", fallback=False)
    if verbose:
        print("cltcache length of preproccesed source:", len(preproc_source))
    preproc_hash = sha256(preproc_source)
    return preproc_hash


def compute_cache_key(clang_tidy_call, config):
    clang_tidy = clang_tidy_call[0]
    if "--" not in clang_tidy_call:
        raise Exception("Missing '--' flag in compiler options")

    forwardflag_index = clang_tidy_call.index("--")
    compile_args = clang_tidy_call[forwardflag_index + 1 :]
    clang_tidy_args = clang_tidy_call[1:forwardflag_index]

    preproc_hash = get_preproc_hash(compile_args, config)

    version_out = run_get_stdout([clang_tidy] + ["--version"])
    version = ",".join(re.findall(r'[0-9]+\.[0-9]+\.?[0-9]*', version_out))
    version_hash = sha256(version)

    enabled_checks = run_get_stdout([clang_tidy] + clang_tidy_args + ["--list-checks"])
    enabled_checks_hash = sha256(enabled_checks)

    return sha256(preproc_hash + enabled_checks_hash + version_hash)[:-16]


def init_cltcache():
    cltcache_path = os.environ.get("CLTCACHE_DIR", pathlib.Path().home() / ".cltcache")
    cltcache_path.mkdir(parents=True, exist_ok=True)
    config = configparser.ConfigParser()
    config.read(cltcache_path / "cltcache.cfg")
    return cltcache_path, config


def cache_clang_tidy(clang_tidy_call):
    print(f"000Running CLang Tidy: ${clang_tidy_call}")
    cltcache_path, config = init_cltcache()
    cache_path, cat_path, out_path, err_path = (None, None, None, None)
    verbose = config.getboolean("behavior", "verbose", fallback=False)
    if verbose:
        print("cltcache computing cache key")
    try:
        cache_key = compute_cache_key(clang_tidy_call, config)
        if verbose:
            print("cltcache key:", cache_key)
        cat_path = cltcache_path / cache_key[0]
        cache_path = cat_path / cache_key
        out_path = cache_path.with_suffix(".out.gz")
        err_path = cache_path.with_suffix(".err.gz")
        if os.path.exists(cache_path):
            if verbose:
                print("cltcache hit!")
            if os.path.exists(out_path):
                clang_tidy_stdout = decompress_from_file(out_path)
                if clang_tidy_stdout:
                    print(
                        clang_tidy_stdout.decode("utf-8"),
                    )
            if os.path.exists(err_path):
                clang_tidy_stderr = decompress_from_file(err_path)
                if clang_tidy_stderr:
                    print(
                        clang_tidy_stderr.decode("utf-8"),
                        file=sys.stderr,
                    )
            sys.exit(int(read_from_file(cache_path)))
        elif verbose:
            print("cltcache miss...")
    except Exception as e:
        if verbose:
            print("cltcache", e)
            print("cltcache Preprocessing failed! Forwarding call without caching...", file=sys.stderr)
    print(f"Running CLang Tidy: ${clang_tidy_call}")
    result = run_command(clang_tidy_call)

    clt_success = result.returncode == 0
    preproc_success = cache_path is not None
    cache_results = (clt_success or config.getboolean("behavior", "cache_failure", fallback=True)) and preproc_success
    if cache_results:
        cat_path.mkdir(parents=True, exist_ok=True)
    if result.stdout:
        print(
            result.stdout.decode("utf-8"),
        )
        if cache_results:
            compress_to_file(result.stdout, out_path)
    if result.stderr:
        print(
            result.stderr.decode("utf-8"),
            file=sys.stderr,
        )
        if cache_results:
            compress_to_file(result.stderr, err_path)
    if cache_results:
        if verbose:
            print("cltcache caching results...")
        save_to_file(str(result.returncode), cache_path)
    sys.exit(result.returncode)


def main():
    if len(sys.argv) <= 1:
        command = sys.argv[0]
        helptext = (
            "Usage:\n"
            f"    {command}\n"
            f"    {command} clang-tidy [clang-tidy options] -- "
            "-o output [compiler options]"
        )
        print(helptext)
    else:
        cache_clang_tidy(sys.argv[1:])


if __name__ == "__main__":
    main()