"""
Implementation of a custom transfer agent for the transfer type "multipart" for git-lfs.

Inspired by: github.com/cbartz/git-lfs-swift-transfer-agent/blob/master/git_lfs_swift_transfer.py

Spec is: github.com/git-lfs/git-lfs/blob/master/docs/custom-transfers.md


To launch debugger while developing:

``` [lfs "customtransfer.multipart"]

path = /path/to/transformers/.env/bin/python

args = -m debugpy --listen 5678 --wait-for-client /path/to/transformers/src/transformers/commands/transformers_cli.py
lfs-multipart-upload ```
"""

import json
import os
import subprocess
import sys
from argparse import ArgumentParser
from contextlib import AbstractContextManager
from typing import Dict, List, Optional

import requests
from transformers.commands import BaseTransformersCLICommand

from ..utils import logging


logger = logging.get_logger(__name__)  # pylint: disable=invalid-name


LFS_MULTIPART_UPLOAD_COMMAND = "lfs-multipart-upload"


class LfsCommands(BaseTransformersCLICommand):
    """
    Implementation of a custom transfer agent for the transfer type "multipart" for git-lfs. This lets users upload
    large files >5GB 🔥. Spec for LFS custom transfer agent is:
    https://github.com/git-lfs/git-lfs/blob/master/docs/custom-transfers.md

    This introduces two commands to the CLI:

    1. $ transformers-cli lfs-enable-largefiles

    This should be executed once for each model repo that contains a model file >5GB. It's documented in the error
    message you get if you just try to git push a 5GB file without having enabled it before.

    2. $ transformers-cli lfs-multipart-upload

    This command is called by lfs directly and is not meant to be called by the user.
    """

    @staticmethod
    def register_subcommand(parser: ArgumentParser):
        enable_parser = parser.add_parser(
            "lfs-enable-largefiles", help="Configure your repository to enable upload of files > 5GB."
        )
        enable_parser.add_argument("path", type=str, help="Local path to repository you want to configure.")
        enable_parser.set_defaults(func=lambda args: LfsEnableCommand(args))

        upload_parser = parser.add_parser(
            LFS_MULTIPART_UPLOAD_COMMAND, help="Command will get called by git-lfs, do not call it directly."
        )
        upload_parser.set_defaults(func=lambda args: LfsUploadCommand(args))


class LfsEnableCommand:
    def __init__(self, args):
        self.args = args

    def run(self):
        local_path = os.path.abspath(self.args.path)
        if not os.path.isdir(local_path):
            print("This does not look like a valid git repo.")
            exit(1)
        subprocess.run(
            "git config lfs.customtransfer.multipart.path transformers-cli".split(), check=True, cwd=local_path
        )
        subprocess.run(
            f"git config lfs.customtransfer.multipart.args {LFS_MULTIPART_UPLOAD_COMMAND}".split(),
            check=True,
            cwd=local_path,
        )
        print("Local repo set up for largefiles")


def write_msg(msg: Dict):
    """Write out the message in Line delimited JSON."""
    msg = json.dumps(msg) + "\n"
    sys.stdout.write(msg)
    sys.stdout.flush()


def read_msg() -> Optional[Dict]:
    """Read Line delimited JSON from stdin. """
    msg = json.loads(sys.stdin.readline().strip())

    if "terminate" in (msg.get("type"), msg.get("event")):
        # terminate message received
        return None

    if msg.get("event") not in ("download", "upload"):
        logger.critical("Received unexpected message")
        sys.exit(1)

    return msg


class FileSlice(AbstractContextManager):
    """
    File-like object that only reads a slice of a file

    Inspired by stackoverflow.com/a/29838711/593036
    """

    def __init__(self, filepath: str, seek_from: int, read_limit: int):
        self.filepath = filepath
        self.seek_from = seek_from
        self.read_limit = read_limit
        self.n_seen = 0

    def __enter__(self):
        self.f = open(self.filepath, "rb")
        self.f.seek(self.seek_from)
        return self

    def __len__(self):
        total_length = os.fstat(self.f.fileno()).st_size
        return min(self.read_limit, total_length - self.seek_from)

    def read(self, n=-1):
        if self.n_seen >= self.read_limit:
            return b""
        remaining_amount = self.read_limit - self.n_seen
        data = self.f.read(remaining_amount if n < 0 else min(n, remaining_amount))
        self.n_seen += len(data)
        return data

    def __iter__(self):
        yield self.read(n=4 * 1024 * 1024)

    def __exit__(self, *args):
        self.f.close()


class LfsUploadCommand:
    def __init__(self, args):
        self.args = args

    def run(self):
        # Immediately after invoking a custom transfer process, git-lfs
        # sends initiation data to the process over stdin.
        # This tells the process useful information about the configuration.
        init_msg = json.loads(sys.stdin.readline().strip())
        if not (init_msg.get("event") == "init" and init_msg.get("operation") == "upload"):
            write_msg({"error": {"code": 32, "message": "Wrong lfs init operation"}})
            sys.exit(1)

        # The transfer process should use the information it needs from the
        # initiation structure, and also perform any one-off setup tasks it
        # needs to do. It should then respond on stdout with a simple empty
        # confirmation structure, as follows:
        write_msg({})

        # After the initiation exchange, git-lfs will send any number of
        # transfer requests to the stdin of the transfer process, in a serial sequence.
        while True:
            msg = read_msg()
            if msg is None:
                # When all transfers have been processed, git-lfs will send
                # a terminate event to the stdin of the transfer process.
                # On receiving this message the transfer process should
                # clean up and terminate. No response is expected.
                sys.exit(0)

            oid = msg["oid"]
            filepath = msg["path"]
            completion_url = msg["action"]["href"]
            header = msg["action"]["header"]
            chunk_size = int(header.pop("chunk_size"))
            presigned_urls: List[str] = list(header.values())

            parts = []
            for i, presigned_url in enumerate(presigned_urls):
                with FileSlice(filepath, seek_from=i * chunk_size, read_limit=chunk_size) as data:
                    r = requests.put(presigned_url, data=data)
                    r.raise_for_status()
                    parts.append(
                        {
                            "etag": r.headers.get("etag"),
                            "partNumber": i + 1,
                        }
                    )
                    # In order to support progress reporting while data is uploading / downloading,
                    # the transfer process should post messages to stdout
                    write_msg(
                        {
                            "event": "progress",
                            "oid": oid,
                            "bytesSoFar": (i + 1) * chunk_size,
                            "bytesSinceLast": chunk_size,
                        }
                    )
                    # Not precise but that's ok.

            r = requests.post(
                completion_url,
                json={
                    "oid": oid,
                    "parts": parts,
                },
            )
            r.raise_for_status()

            write_msg({"event": "complete", "oid": oid})
