from collections import defaultdict, deque
from os.path import join as pjoin

from snakeoil.osutils import listdir_files
from snakeoil.sequences import iflatten_instance

from ..log import logger
from .atom import atom


def _scan_directory(path, eapi):
    files = []
    for filename in listdir_files(path):
        match = eapi.options.update_regex.match(filename)
        if match is not None:
            files.append(filename)
        else:
            logger.error(f"incorrectly named update file: {filename!r}")
    return sorted(files)


def read_updates(path, eapi):
    def f():
        d = deque()
        return [d, d]

    # mods tracks the start point [0], and the tail, [1].
    # via this, pkg moves into a specific pkg can pick up
    # changes past that point, while ignoring changes prior
    # to that point.
    # Afterwards, we flatten it to get a per cp chain of commands.
    # no need to do lookups basically, although we do need to
    # watch for cycles.
    mods = defaultdict(f)
    moved = {}

    try:
        for fp in _scan_directory(path, eapi):
            with open(pjoin(path, fp)) as f:
                data = (line.rstrip("\n") for line in f)
                _process_updates(data, fp, mods, moved)
    except FileNotFoundError:
        pass

    # force a walk of the tree, flattening it
    commands = {k: list(iflatten_instance(v[0], tuple)) for k, v in mods.items()}
    # filter out empty nodes.
    commands = {k: v for k, v in commands.items() if v}

    return commands


def _process_updates(sequence, filename, mods, moved):
    for lineno, raw_line in enumerate(sequence, 1):
        line = raw_line.strip()
        if not line:
            logger.error(f"file {filename!r}: empty line {lineno}")
            continue
        elif line != raw_line:
            logger.error(
                f"file {filename!r}: extra whitespace in {raw_line!r} on line {lineno}"
            )

        line = line.split()
        if line[0] == "move":
            if len(line) != 3:
                logger.error(
                    f"file {filename!r}: {raw_line!r} on line {lineno}: bad move form"
                )
                continue
            src, trg = atom(line[1]), atom(line[2])
            if src.fullver is not None:
                logger.error(
                    f"file {filename!r}: {raw_line!r} on line {lineno}: "
                    f"atom {src} must be versionless"
                )
                continue
            elif trg.fullver is not None:
                logger.error(
                    f"file {filename!r}: {raw_line!r} on line {lineno}: "
                    f"atom {trg} must be versionless"
                )
                continue

            if src.key in moved:
                logger.warning(
                    f"file {filename!r}: {raw_line!r} on line {lineno}: "
                    f"{src} was already moved to {moved[src.key]}, "
                    "this line is redundant"
                )
                continue

            d = deque()
            mods[src.key][1].extend([("move", src, trg), d])
            # start essentially a new checkpoint in the trg
            mods[trg.key][1].append(d)
            mods[trg.key][1] = d
            moved[src.key] = trg

        elif line[0] == "slotmove":
            if len(line) != 4:
                logger.error(
                    f"file {filename!r}: {raw_line!r} on line {lineno}: "
                    "bad slotmove form"
                )
                continue
            src = atom(line[1])

            if src.key in moved:
                logger.warning(
                    f"file {filename!r}: {raw_line!r} on line {lineno}: "
                    f"{src} was already moved to {moved[src.key]}, "
                    "this line is redundant"
                )
                continue
            elif src.slot is not None:
                logger.error(
                    f"file {filename!r}: {raw_line!r} on line {lineno}: "
                    "slotted atom makes no sense for slotmoves"
                )
                continue

            src_slot = atom(f"{src}:{line[2]}")
            _ = atom(f"{src.key}:{line[3]}")

            mods[src.key][1].append(("slotmove", src_slot, line[3]))
        else:
            logger.error(
                f"file {filename!r}: {raw_line!r} on line {lineno}: unknown command"
            )
