from __future__ import annotations

import binascii
import email.parser
import email.policy
import os.path
import re
import shutil
import subprocess
import typing as t

import dulwich.refs
import mercurial.error as hgerr
from mercurial import extensions
from mercurial import registrar
from mercurial import wireprotoserver

if t.TYPE_CHECKING:
    import hggit.git_handler
    import mercurial.hgweb.hgweb_mod_inner as web_inner
    import mercurial.hgweb.request as hgreq
    import mercurial.interfaces.repository as hgrepo
    import mercurial.ui as hgui

    class GittyRepo(hgrepo.IRepo, t.Protocol):
        githandler: hggit.git_handler.GitHandler

    PermissionCheck = t.Callable[
        [web_inner.requestcontext, hgreq.parsedrequest, bytes],
        None,
    ]
    GitPrelude = t.Sequence[bytes | str | os.PathLike]


def _is_gitty(repo: hgrepo.IRepo) -> t.TypeGuard[GittyRepo]:
    """Ensures that we have hg-git installed and active."""
    return hasattr(repo, 'githandler')


_CGI_VAR = re.compile(rb'[A-Z0-9_]+$')
"""Environment variables that we need to pass to git-as-cgi."""


def _build_git_environ(
    req_ctx: web_inner.requestcontext,
    request: hgreq.parsedrequest,
) -> dict[bytes, bytes]:
    """Builds the environment to be sent to Git to serve HTTP."""
    fixed = {
        k: v
        for (k, v) in request.rawenv.items()
        if isinstance(v, bytes) and _CGI_VAR.match(k)
    }
    fixed[b'GIT_HTTP_EXPORT_ALL'] = b'yes'
    fixed[b'GIT_PROJECT_ROOT'] = req_ctx.repo.path
    fixed[b'PATH_INFO'] = b'/git/' + request.dispatchpath
    return fixed


def _parse_cgi_response(
    output: t.IO[bytes],
) -> tuple[bytes, dict[bytes, bytes], t.IO[bytes]]:
    """Parses a CGI response into a status, headers, and everyhting else."""
    parser = email.parser.BytesFeedParser(policy=email.policy.HTTP)
    while line := output.readline():
        if not line.rstrip(b'\r\n'):
            # We've reached the end of the headers.
            # Leave the rest in the output for later.
            break
        parser.feed(line)
    msg = parser.close()
    status = msg.get('Status', '200 OK I guess').encode('utf-8')
    del msg['Status']  # this won't raise an exception
    byte_headers = {
        k.encode('utf-8'): v.encode('utf-8') for (k, v) in msg.items()
    }
    return status, byte_headers, output


def _handle_git_protocol(
    original: t.Callable[..., bool],
    req_ctx: web_inner.requestcontext,
    request: hgreq.parsedrequest,
    response: hgreq.wsgiresponse,
    check_permission: PermissionCheck,
) -> bool:
    """Intercepts requests from Git, if needed."""
    repo = req_ctx.repo
    if not _is_gitty(repo) or b'git-protocol' not in request.headers:
        # We only handle Git requests; everything else is normal.
        return original(req_ctx, request, response, check_permission)
    check_permission(req_ctx, request, b'pull')
    # If a request is git, we assume we should be the one handling it.
    cgi_env = _build_git_environ(req_ctx, request)
    content_length_hdr = request.headers.get(b'content-length', b'0')
    try:
        content_length = int(content_length_hdr)
    except ValueError as ve:
        raise hgerr.InputError(
            f'Invalid content-length {content_length!r}'.encode()
        ) from ve
    http_backend = req_ctx.repo.ui.configlist(
        b'git-serve', b'http-backend', default=(b'git', b'http-backend')
    )
    call = subprocess.Popen(
        http_backend,
        close_fds=True,
        stdin=subprocess.PIPE,
        stdout=subprocess.PIPE,
        stderr=subprocess.DEVNULL,
        env=cgi_env,
        text=False,
    )
    assert call.stdout
    assert call.stdin
    # Git will not start writing output until stdin is fully closed.
    with call.stdin:
        if content_length:
            shutil.copyfileobj(
                request.bodyfh, call.stdin, length=content_length
            )

    status, headers, rest = _parse_cgi_response(call.stdout)
    response.status = status
    for k, v in headers.items():
        response.headers[k] = v

    def write_the_rest():
        with call, rest:
            while more := rest.read(1024 * 1024):
                yield more

    response.setbodygen(write_the_rest())
    response.sendresponse()
    return True


def _clean_all_refs(refs: dulwich.refs.RefsContainer) -> None:
    """Removes all refs from the Git repository."""
    for ref in refs.allkeys():
        refs.remove_if_equals(ref, None)


def _set_head(ui: hgui.ui, repo: GittyRepo, at_name: bytes) -> None:
    """Creates a HEAD reference in Git referring to the current HEAD."""
    # By default, we use '@', since that's what will be auto checked out.
    current = b'@'
    if current not in repo._bookmarks:
        current = repo._bookmarks.active or current

    # We'll be moving this (possibly fake) bookmark into Git.
    git_current = current
    if current == b'@':
        # @ is a special keyword in Git, so we can't use it as a bookmark.
        git_current = at_name
    git_branch = dulwich.refs.LOCAL_BRANCH_PREFIX + git_current
    if not dulwich.refs.check_ref_format(git_branch):
        # We can't export this ref to Git. Give up.
        ui.warn(f'{git_branch!r} is not a valid branch name for Git.'.encode())
        return
    try:
        # Maybe this is a real bookmark?
        hgsha = repo._bookmarks[current]
    except KeyError:
        # Not a real bookmark. Assume we want the tip of the current branch.
        branch = repo.dirstate.branch()
        try:
            tip = repo.branchtip(branch)
        except hgerr.RepoLookupError:
            # This branch somehow doesn't exist???
            ui.warn(f"{branch} doesn't seem to exist?".encode())
            return
        hgsha = binascii.hexlify(tip)
    gitsha = repo.githandler.map_git_get(hgsha)
    if not gitsha:
        # No Git SHA to match this Hg sha. Give up.
        ui.warn(f'revision {hgsha} was not exported to Git'.encode())
        return
    refs = repo.githandler.git.refs
    refs.add_packed_refs({git_branch: gitsha})
    refs.set_symbolic_ref(b'HEAD', git_branch)


def fix_refs_hook(ui: hgui.ui, repo: hgrepo.IRepo, **__: object) -> None:
    """Exports to Git and sets up for serving."""
    if not _is_gitty(repo):
        return
    _fix_refs(ui, repo)


def _fix_refs(ui: hgui.ui, repo: GittyRepo) -> None:
    """After a git export, fix up the refs."""
    _clean_all_refs(repo.githandler.git.refs)
    repo.githandler.export_hg_tags()
    repo.githandler.update_references()
    default_branch_name = ui.config(
        b'hggit-serve', b'default-branch', b'default'
    )
    _set_head(ui, repo, default_branch_name)


def export_hook(ui: hgui.ui, repo: hgrepo.IRepo, **__: object) -> None:
    if not _is_gitty(repo):
        return
    auto_export = ui.config(b'hggit-serve', b'auto-export')
    if auto_export == b'never':
        return
    if auto_export == b'always' or os.path.isdir(repo.githandler.gitdir):
        repo.githandler.export_commits()
        _fix_refs(ui, repo)


# Interfacing with Mercurial

__version__ = '0.1.4'
testedwith = b'7.1 7.2'

cmdtable: dict[bytes, object] = {}

command = registrar.command(cmdtable)


def uisetup(_: hgui.ui) -> None:
    extensions.wrapfunction(
        wireprotoserver, 'handlewsgirequest', _handle_git_protocol
    )


def uipopulate(ui: hgui.ui) -> None:
    ui.setconfig(
        b'hooks', b'post-git-export.__gitserve_add_tag__', fix_refs_hook
    )
    ui.setconfig(b'hooks', b'txnclose.__gitserve_export__', export_hook)


__all__ = (
    '__version__',
    'cmdtable',
    'command',
    'testedwith',
    'uipopulate',
    'uisetup',
)