import argparse
import collections
import configparser
from datetime import datetime
from fnmatch import fnmatch
import hashlib
from math import ceil
import os
import re
import sys
import zlib

argparser = argparse.ArgumentParser(description="The stupidest content tracker")

argsubparsers = argparser.add_subparsers(title="Commands", dest="command")
argsubparsers.required = True

def main(argv=sys.argv[1:]):
    args = argparser.parse_args(argv)
    match args.command:
        case "add"          : cmd_add(args)
        case "cat-file"     : cmd_cat_file(args)
        case "check-ignore" : cmd_check_ignore(args)
        case "checkout"     : cmd_checkout(args)
        case "commit"       : cmd_commit(args)
        case "hash-object"  : cmd_hash_object(args)
        case "init"         : cmd_init(args)
        case "log"          : cmd_log(args)
        case "ls-files"     : cmd_ls_files(args)
        case "ls-tree"      : cmd_ls_tree(args)
        case "rev-parse"    : cmd_rev_parse(args)
        case "rm"           : cmd_rm(args)
        case "show-ref"     : cmd_show_ref(args)
        case "status"       : cmd_status(args)
        case "tag"          : cmd_tag(args)
        case _              : print("Bad command.")

class GitRepository (object):
    """A git repo"""

    worktree = None
    gitdir = None
    conf = None

    def __init__(self, path, force=False):
        self.worktree = path
        self.gitdir = os.path.join(path, ".git")

        if not (force or os.path.isdir(self.gitdir)):
            raise Exception(f"Not a git repository {path}")

        # Read configuration file in .git/config
        self.conf = configparser.ConfigParser()
        cf = GitRepository.repo_file(self, "config")

        if cf and os.path.exists(cf):
            self.conf.read([cf])
        elif not force:
            raise Exception("Configuration file missing")

        if not force:
            vers = int(self.conf.get("core", "repositoryformatversion"))
            if vers != 0:
                raise Exception(f"Unsupported repositoryformatversion {vers}")

    def repo_path(repo, *path):
        """Compute path under repo's gitdir."""
        return os.path.join(repo.gitdir, *path)

    def repo_file(repo, *path, mkdir=False):
        """Same as repo_path, but create dirname(*path) if absent. For
        example, repo_file(r, \"refs\", \"remotes\", \"origin\", \"HEAD\") will create
        .git/refs/remotes/origin."""

        if GitRepository.repo_dir(repo, *path[:-1], mkdir=mkdir):
            return GitRepository.repo_path(repo, *path)

    def repo_dir(repo, *path, mkdir=False):
        """Same as repo_path, bt mkdir *path if absent if mkdir"""

        path = GitRepository.repo_path(repo, *path)

        if (os.path.exists(path)):
            if (os.path.isdir(path)):
                return path
            else:
                raise Exception(f"Not a directory {path}")

        if mkdir:
            os.makedirs(path)
            return path
        else:
            return None

def repo_create(path):
    """Create a new repository at path."""

    repo = GitRepository(path, True)

    # First, we make sure the path either doesn't exist or is an
    # empty dir.

    if os.path.exists(repo.worktree):
        if not os.path.isdir(repo.worktree):
            raise Exception(f"{path} is not a directory!")
        if os.path.exists(repo.gitdir) and os.listdir(repo.gitdir):
            raise Exception(f"{path} is not empty!")
    else:
        os.makedirs(repo.worktree)

    assert GitRepository.repo_dir(repo, "branches", mkdir=True)
    assert GitRepository.repo_dir(repo, "objects", mkdir=True)
    assert GitRepository.repo_dir(repo, "refs", "tags", mkdir=True)
    assert GitRepository.repo_dir(repo, "refs", "heads", mkdir=True)

    # .git/description
    with open(GitRepository.repo_file(repo, "description"), "w") as f:
        f.write("Unnamed repository; edit this file 'description' to name the repository")

    with open(GitRepository.repo_file(repo, "HEAD"), "w") as f:
        f.write("ref: refs/heads/master\n")

    with open(GitRepository.repo_file(repo, "config"), "w") as f:
        config = repo_default_config()
        config.write(f)

    return repo

def repo_default_config():
    ret = configparser.ConfigParser()

    ret.add_section("core")
    ret.set("core", "repositoryformatVersion", "0")
    ret.set("core", "filemode", "false")
    ret.set("core", "bare", "false")

    return ret

argsp = argsubparsers.add_parser("init", help="Initialize a new, empty repository.")

argsp.add_argument("path",
                   metavar="directory",
                   nargs="?",
                   default=".",
                   help="Where to create the repository.")

def cmd_init(args):
    repo_create(args.path)

def repo_find(path=".", required=True):
    path = os.path.realpath(path)

    if os.path.isdir(os.path.join(path, ".git")):
        return GitRepository(path)

    # If we haven't returned, recurse in parent
    parent = os.path.realpath(os.path.join(path, ".."))

    match os.name:
        case "nt":
            is_root = os.path.splitdrive(path)[1] == "\\"
        case "posix":
            # If parent==path, then path is root.
            is_root = parent == path
        case _:
            raise Exception(f"Unsupported os {os.name}")

    if is_root:
        if required:
            raise Exception("No git directory.")
        else:
            return None

    # Recursive case
    return repo_find(parent, required)

argsp = argsubparsers.add_parser("status", help="Get the status of the repo")

argsp.add_argument("path",
                   metavar="directory",
                   nargs="?",
                   default=".",
                   help="Which directory")

def cmd_status(args):
    # TODO: actually get status
    print(repo_find(args.path).worktree)

class GitObject (object):
    def __init__(self, data=None):
        if data != None:
            self.deserialize(data)
        else:
            self.init()

    def serialize(self, repo):
        """This function MUST be implemented by subclasses.

It must read the object's contents from self.data, a byte string, and
do whatever it takes to convert it into a meaningful representation. What exactly that means depends on each subclass."""
        raise Exception("Unimplemented!")

    def deserialize(self, repo):
        raise Exception("Unimplemented!")

    def init(self):
        pass # other implementations might do something here

def object_read(repo, sha):
    """Read object sha from Git repository repo. Return a
    GitObject whose exact type depends on the object."""

    path = GitRepository.repo_file(repo, "objects", sha[0:2], sha[2:])

    if not os.path.isfile(path):
        return None

    with open(path, "rb") as f:
        raw = zlib.decompress(f.read())

        # Read object type
        x = raw.find(b' ')
        fmt = raw[0:x]

        # Read and validate object size
        y = raw.find(b'\x00', x)
        size = int(raw[x:y].decode("ascii"))
        if size != len(raw)-y-1:
            raise Exception(f"Malformed object {sha}: bad length")

        match fmt:
            case b'commit' : c=GitCommit
            case b'tree'   : c=GitTree
            case b'tag'    : c=GitTag
            case b'blob'   : c=GitBlob
            case _:
                raise Exception(f"Unknown type {fmt.decode('ascii')} for object {sha}")

        return c(raw[y+1:])

def object_write(obj, repo=None):
    data = obj.serialize()
    # Add header
    result = obj.fmt + b' ' + str(len(data)).encode() + b'\x00' + data
    # Compute hash
    sha = hashlib.sha1(result).hexdigest()

    if repo:
        # Compute path
        path=GitRepository.repo_file(repo, "objects", sha[0:2], sha[2:], mkdir=True)

        if not os.path.exists(path):
            with open(path, 'wb') as f:
                f.write(zlib.compress(result))
    return sha

class GitBlob(GitObject):
    fmt=b'blob'

    def serialize(self):
        return self.blobdata

    def deserialize(self, data):
        self.blobdata = data

argsp = argsubparsers.add_parser("cat-file",
                                 help="Provide content of repository objects")

argsp.add_argument("type",
                   metavar="type",
                   choices=["blob", "commit", "tag", "tree"],
                   help="Specify the type")

argsp.add_argument("object",
                   metavar="object",
                   help="The object to display")

def cmd_cat_file(args):
    repo = repo_find()
    cat_file(repo, args.object, fmt=args.type.encode())

def cat_file(repo, obj, fmt=None):
    obj = object_read(repo, object_find(repo, obj, fmt=fmt))
    sys.stdout.buffer.write(obj.serialize())

def object_find(repo, name, fmt=None, follow=True):
    return name

argsp = argsubparsers.add_parser(
    "hash-object",
    help="Compute object ID an optionally creates a blob from a file")

argsp.add_argument("-t",
                   metavar="type",
                   dest="type",
                   choices=["blob", "commit", "tag", "tree"],
                   default="blob",
                   help="Specify the type")

argsp.add_argument("-w",
                   dest="write",
                   action="store_true",
                   help="Actually write the object into the database")

argsp.add_argument("path",
                   help="Read object from <file>")

def cmd_hash_object(args):
    if args.write:
        repo = repo_find()
    else:
        repo = None

    with open(args.path, "rb") as fd:
        sha = object_hash(fd, args.type.encode(), repo)
        print(sha)

def object_hash(fd, fmt, repo=None):
    """Hash object, writing it to repo if provided"""
    data = fd.read()

    match fmt:
        case b'commit' : obj=GitCommit(data)
        case b'tree'   : obj=GitTree(data)
        case b'tag'    : obj=GitTag(data)
        case b'blob'   : obj=GitBlob(data)
        case _         : raise Exception(f"Unknown type {fmt}")

    return object_write(obj, repo)