#!/usr/bin/env python3

"""
flacinfo

A script analoguous to `mp3info`, allowing one to easily tag their music
collection, but for flac files.
"""

import argparse
import subprocess
import os
import sys


VORBIS_ARG_NAME = {
    "title": "TITLE",
    "track": "TRACKNUMBER",
    "artist": "ARTIST",
    "album": "ALBUM",
    "albumartist": "ALBUMARTIST",
    "albumnumber": "DISCNUMBER",
    "genre": "GENRE",
    "year": "DATE",
    "comment": "COMMENT",
}


class NoSuchTag(Exception):
    """Raised when trying to reverse the `VORBIS_ARG_NAME` dict on an invalid tag name"""

    def __init__(self, tag):
        super().__init__()
        self.tag = tag

    def __str__(self):
        return "No such Vorbis tag {}".format(self.tag)


class MetaflacError(Exception):
    """Raised when an invocation of metaflac failed."""


def argparser():
    """Parses the arguments from sys.argv"""
    parser = argparse.ArgumentParser(
        description="Edit flac files' metadata",
        epilog=(
            "When no option modifying the tags is passed, the currently "
            "set tags are shown."
        ),
    )
    parser.add_argument("-a", "--artist", help="Specify artist name")
    parser.add_argument("-c", "--comment", help="Specify an arbitrary comment")
    parser.add_argument("-g", "--genre", help="Specify genre (in plain text)")
    parser.add_argument("-l", "--album", help="Specify album name")
    parser.add_argument("-m", "--albumnumber", help="Specify album number")
    parser.add_argument("-n", "--track", help="Specify track number")
    parser.add_argument("-t", "--title", help="Specify track title")
    parser.add_argument("-y", "--year", help="Specify album year")
    parser.add_argument("-A", "--albumartist", help="Specify album artist")
    parser.add_argument(
        "file", nargs="+", metavar="FILE", help="The file(s) to work on"
    )
    return parser.parse_args()


def is_flac_file(path):
    """Checks whether `path` refers to an existing, writeable flac file"""
    if not os.path.isfile(path) or not os.access(path, os.W_OK):
        return False
    try:
        subprocess.run(
            ["metaflac", "--list", path],
            stdout=subprocess.DEVNULL,
            stderr=subprocess.DEVNULL,
            check=True,
        )
    except subprocess.CalledProcessError:
        return False  # Metaflac failed to list the files' metadata

    return True


def make_metaflac_args(in_args):
    out_args = []

    for arg in in_args:
        arg_val = in_args[arg]
        if arg not in VORBIS_ARG_NAME or arg_val is None:
            continue
        arg_name = VORBIS_ARG_NAME[arg]

        out_args.append("--remove-tag={}".format(arg_name))
        if arg_val:
            out_args.append("--set-tag={}={}".format(arg_name, arg_val))

    return out_args


def edit_flac(args):
    """Perfoms the requested edition operations"""
    metaflac_args = make_metaflac_args(args)
    metaflac_args += args["file"]
    metaflac_args.insert(0, "metaflac")
    try:
        subprocess.run(metaflac_args, check=True)
    except subprocess.CalledProcessError as exn:
        raise MetaflacError(
            "Failed to edit tags: metaflac exited with error {}. Output:\n{}".format(
                exn.returncode, exn.stderr
            )
        ) from exn


def reverse_tag(vorbis_tag):
    """Reverses a Vorbis tag to an argument name"""
    for tag in VORBIS_ARG_NAME:
        if VORBIS_ARG_NAME[tag].upper() == vorbis_tag.upper():
            return tag
    raise NoSuchTag(vorbis_tag)


def get_tags(path):
    """Retrieves the relevant tags for a single file"""
    metaflac_args = ["metaflac"]
    for tag in VORBIS_ARG_NAME:
        metaflac_args += ["--show-tag", VORBIS_ARG_NAME[tag]]
    metaflac_args.append(path)

    try:
        metaflac_run = subprocess.run(metaflac_args, check=True, stdout=subprocess.PIPE)
    except subprocess.CalledProcessError as exn:
        raise MetaflacError(
            (
                "Failed to get tags for {}: metaflac exited with error {}."
                "Output:\n{}"
            ).format(path, exn.returncode, exn.stderr)
        ) from exn
    meta_out = metaflac_run.stdout.decode("utf-8")
    output = {}

    for line in meta_out.split("\n"):
        split = line.split("=")
        tag, value = split[0], "=".join(split[1:])
        if not tag:
            continue
        tag = reverse_tag(tag)
        output[tag] = value
    return output


def show_tags(path):
    """Shows the relevant tags already present in the given flac file"""
    tags = get_tags(path)
    print("File: {}".format(path))

    tag_len = max([len(tag) for tag in tags]) + 1
    for tag in tags:
        print((" {:<" + str(tag_len) + "} {}").format(tag + ":", tags[tag]))
    print("")


def main():
    """Entrypoint function"""
    args = vars(argparser())

    has_errors = False
    for cur_file in args["file"]:
        if not is_flac_file(cur_file):
            print(
                (
                    "Error: file {} does not exist, or is not writeable by " "metaflac"
                ).format(cur_file),
                file=sys.stderr,
            )
            has_errors = True
    if has_errors:
        print("One or more file cannot be manipulated. Aborting.", file=sys.stderr)
        sys.exit(1)

    edit_mode = False
    for tag in VORBIS_ARG_NAME:
        if args[tag] is not None:
            edit_mode = True
            break

    if edit_mode:
        edit_flac(args)
    else:
        for path in args["file"]:
            show_tags(path)


if __name__ == "__main__":
    main()