import sys
from dataclasses import dataclass
from functools import lru_cache
import re
from typing import Iterator, List, Optional, Union

if sys.version_info >= (3, 8):
    from typing import Final
else:
    from typing_extensions import Final

from blib2to3.pytree import Node, Leaf
from blib2to3.pgen2 import token

from black.nodes import first_leaf_column, preceding_leaf, container_of
from black.nodes import STANDALONE_COMMENT, WHITESPACE

# types
LN = Union[Leaf, Node]

FMT_OFF: Final = {"# fmt: off", "# fmt:off", "# yapf: disable"}
FMT_SKIP: Final = {"# fmt: skip", "# fmt:skip"}
FMT_PASS: Final = {*FMT_OFF, *FMT_SKIP}
FMT_ON: Final = {"# fmt: on", "# fmt:on", "# yapf: enable"}

COMMENT_EXCEPTIONS = {True: " !:#'", False: " !:#'%"}


@dataclass
class ProtoComment:
    """Describes a piece of syntax that is a comment.

    It's not a :class:`blib2to3.pytree.Leaf` so that:

    * it can be cached (`Leaf` objects should not be reused more than once as
      they store their lineno, column, prefix, and parent information);
    * `newlines` and `consumed` fields are kept separate from the `value`. This
      simplifies handling of special marker comments like ``# fmt: off/on``.
    """

    type: int  # token.COMMENT or STANDALONE_COMMENT
    value: str  # content of the comment
    newlines: int  # how many newlines before the comment
    consumed: int  # how many characters of the original leaf's prefix did we consume


def generate_comments(leaf: LN, *, preview: bool) -> Iterator[Leaf]:
    """Clean the prefix of the `leaf` and generate comments from it, if any.

    Comments in lib2to3 are shoved into the whitespace prefix.  This happens
    in `pgen2/driver.py:Driver.parse_tokens()`.  This was a brilliant implementation
    move because it does away with modifying the grammar to include all the
    possible places in which comments can be placed.

    The sad consequence for us though is that comments don't "belong" anywhere.
    This is why this function generates simple parentless Leaf objects for
    comments.  We simply don't know what the correct parent should be.

    No matter though, we can live without this.  We really only need to
    differentiate between inline and standalone comments.  The latter don't
    share the line with any code.

    Inline comments are emitted as regular token.COMMENT leaves.  Standalone
    are emitted with a fake STANDALONE_COMMENT token identifier.
    """
    for pc in list_comments(
        leaf.prefix, is_endmarker=leaf.type == token.ENDMARKER, preview=preview
    ):
        yield Leaf(pc.type, pc.value, prefix="\n" * pc.newlines)


@lru_cache(maxsize=4096)
def list_comments(
    prefix: str, *, is_endmarker: bool, preview: bool
) -> List[ProtoComment]:
    """Return a list of :class:`ProtoComment` objects parsed from the given `prefix`."""
    result: List[ProtoComment] = []
    if not prefix or "#" not in prefix:
        return result

    consumed = 0
    nlines = 0
    ignored_lines = 0
    for index, line in enumerate(re.split("\r?\n", prefix)):
        consumed += len(line) + 1  # adding the length of the split '\n'
        line = line.lstrip()
        if not line:
            nlines += 1
        if not line.startswith("#"):
            # Escaped newlines outside of a comment are not really newlines at
            # all. We treat a single-line comment following an escaped newline
            # as a simple trailing comment.
            if line.endswith("\\"):
                ignored_lines += 1
            continue

        if index == ignored_lines and not is_endmarker:
            comment_type = token.COMMENT  # simple trailing comment
        else:
            comment_type = STANDALONE_COMMENT
        comment = make_comment(line, preview=preview)
        result.append(
            ProtoComment(
                type=comment_type, value=comment, newlines=nlines, consumed=consumed
            )
        )
        nlines = 0
    return result


def make_comment(content: str, *, preview: bool) -> str:
    """Return a consistently formatted comment from the given `content` string.

    All comments (except for "##", "#!", "#:", '#'") should have a single
    space between the hash sign and the content.

    If `content` didn't start with a hash sign, one is provided.
    """
    content = content.rstrip()
    if not content:
        return "#"

    if content[0] == "#":
        content = content[1:]
    NON_BREAKING_SPACE = " "
    if (
        content
        and content[0] == NON_BREAKING_SPACE
        and not content.lstrip().startswith("type:")
    ):
        content = " " + content[1:]  # Replace NBSP by a simple space
    if content and content[0] not in COMMENT_EXCEPTIONS[preview]:
        content = " " + content
    return "#" + content


def normalize_fmt_off(node: Node, *, preview: bool) -> None:
    """Convert content between `# fmt: off`/`# fmt: on` into standalone comments."""
    try_again = True
    while try_again:
        try_again = convert_one_fmt_off_pair(node, preview=preview)


def convert_one_fmt_off_pair(node: Node, *, preview: bool) -> bool:
    """Convert content of a single `# fmt: off`/`# fmt: on` into a standalone comment.

    Returns True if a pair was converted.
    """
    for leaf in node.leaves():
        previous_consumed = 0
        for comment in list_comments(leaf.prefix, is_endmarker=False, preview=preview):
            if comment.value not in FMT_PASS:
                previous_consumed = comment.consumed
                continue
            # We only want standalone comments. If there's no previous leaf or
            # the previous leaf is indentation, it's a standalone comment in
            # disguise.
            if comment.value in FMT_PASS and comment.type != STANDALONE_COMMENT:
                prev = preceding_leaf(leaf)
                if prev:
                    if comment.value in FMT_OFF and prev.type not in WHITESPACE:
                        continue
                    if comment.value in FMT_SKIP and prev.type in WHITESPACE:
                        continue

            ignored_nodes = list(generate_ignored_nodes(leaf, comment, preview=preview))
            if not ignored_nodes:
                continue

            first = ignored_nodes[0]  # Can be a container node with the `leaf`.
            parent = first.parent
            prefix = first.prefix
            if comment.value in FMT_OFF:
                first.prefix = prefix[comment.consumed :]
            if comment.value in FMT_SKIP:
                first.prefix = ""
            hidden_value = "".join(str(n) for n in ignored_nodes)
            if comment.value in FMT_OFF:
                hidden_value = comment.value + "\n" + hidden_value
            if comment.value in FMT_SKIP:
                hidden_value += "  " + comment.value
            if hidden_value.endswith("\n"):
                # That happens when one of the `ignored_nodes` ended with a NEWLINE
                # leaf (possibly followed by a DEDENT).
                hidden_value = hidden_value[:-1]
            first_idx: Optional[int] = None
            for ignored in ignored_nodes:
                index = ignored.remove()
                if first_idx is None:
                    first_idx = index
            assert parent is not None, "INTERNAL ERROR: fmt: on/off handling (1)"
            assert first_idx is not None, "INTERNAL ERROR: fmt: on/off handling (2)"
            parent.insert_child(
                first_idx,
                Leaf(
                    STANDALONE_COMMENT,
                    hidden_value,
                    prefix=prefix[:previous_consumed] + "\n" * comment.newlines,
                ),
            )
            return True

    return False


def generate_ignored_nodes(
    leaf: Leaf, comment: ProtoComment, *, preview: bool
) -> Iterator[LN]:
    """Starting from the container of `leaf`, generate all leaves until `# fmt: on`.

    If comment is skip, returns leaf only.
    Stops at the end of the block.
    """
    container: Optional[LN] = container_of(leaf)
    if comment.value in FMT_SKIP:
        prev_sibling = leaf.prev_sibling
        if comment.value in leaf.prefix and prev_sibling is not None:
            leaf.prefix = leaf.prefix.replace(comment.value, "")
            siblings = [prev_sibling]
            while (
                "\n" not in prev_sibling.prefix
                and prev_sibling.prev_sibling is not None
            ):
                prev_sibling = prev_sibling.prev_sibling
                siblings.insert(0, prev_sibling)
            for sibling in siblings:
                yield sibling
        elif leaf.parent is not None:
            yield leaf.parent
        return
    while container is not None and container.type != token.ENDMARKER:
        if is_fmt_on(container, preview=preview):
            return

        # fix for fmt: on in children
        if contains_fmt_on_at_column(container, leaf.column, preview=preview):
            for child in container.children:
                if contains_fmt_on_at_column(child, leaf.column, preview=preview):
                    return
                yield child
        else:
            yield container
            container = container.next_sibling


def is_fmt_on(container: LN, preview: bool) -> bool:
    """Determine whether formatting is switched on within a container.
    Determined by whether the last `# fmt:` comment is `on` or `off`.
    """
    fmt_on = False
    for comment in list_comments(container.prefix, is_endmarker=False, preview=preview):
        if comment.value in FMT_ON:
            fmt_on = True
        elif comment.value in FMT_OFF:
            fmt_on = False
    return fmt_on


def contains_fmt_on_at_column(container: LN, column: int, *, preview: bool) -> bool:
    """Determine if children at a given column have formatting switched on."""
    for child in container.children:
        if (
            isinstance(child, Node)
            and first_leaf_column(child) == column
            or isinstance(child, Leaf)
            and child.column == column
        ):
            if is_fmt_on(child, preview=preview):
                return True

    return False


def contains_pragma_comment(comment_list: List[Leaf]) -> bool:
    """
    Returns:
        True iff one of the comments in @comment_list is a pragma used by one
        of the more common static analysis tools for python (e.g. mypy, flake8,
        pylint).
    """
    for comment in comment_list:
        if comment.value.startswith(("# type:", "# noqa", "# pylint:")):
            return True

    return False
