import os
import re
import shutil
import subprocess
import tempfile


def clone_repo(url, treeish):
    """Clones a git repo at the given URL into a temp folder and checks out the
    given tree-ish (either branch or tag).

    The current working directory will be set to the repository folder.

    Keyword argument:
    url -- The URL of the git repo
    treeish -- The tree-ish to check out (branch or tag)
    """
    os.chdir(tempfile.gettempdir())

    repo = os.path.basename(url)
    dest = os.path.join(os.getcwd(), repo).rstrip(".git")

    # Clone Git repository into current directory or update it
    if not os.path.exists(dest):
        subprocess.run(["git", "clone", url, dest])
        os.chdir(dest)
    else:
        os.chdir(dest)
        subprocess.run(["git", "fetch", "origin", treeish])

    # Get list of heads
    # Example output of "git ls-remote --heads":
    #   From https://gitlab.com/libeigen/eigen.git
    #   77c66e368c7e355f8be299659f57b0ffcaedb505  refs/heads/3.4
    #   3e006bfd31e4389e8c5718c30409cddb65a73b04  refs/heads/master
    ls_out = subprocess.check_output(["git", "ls-remote",
                                      "--heads"]).decode().rstrip()
    heads = [x.split()[1] for x in ls_out.split("\n")[1:]]

    if f"refs/heads/{treeish}" in heads:
        # Checking out the remote branch avoids needing to handle syncing a
        # preexisting local one
        subprocess.run(["git", "checkout", f"origin/{treeish}"])
    else:
        subprocess.run(["git", "checkout", treeish])


def walk_if(top, pred):
    """Walks the current directory, then returns a list of files for which the
    given predicate is true.

    Keyword arguments:
    top -- the top directory to walk
    pred -- a function that takes a directory path and a filename, then returns
            True if the file should be included in the output list
    """
    return [
        os.path.join(dp, f)
        for dp, dn, fn in os.walk(top)
        for f in fn
        if pred(dp, f)
    ]


def copy_to(files, root):
    if os.path.exists(root):
        # Delete old install
        for filename in os.listdir(root):
            filepath = os.path.join(root, filename)
            if os.path.isfile(filepath) or os.path.islink(filepath):
                os.unlink(filepath)
            elif os.path.isdir(filepath):
                shutil.rmtree(filepath)
    else:
        os.makedirs(root)

    for f in files:
        dest_file = os.path.join(root, f)

        # Rename .cc file to .cpp
        if dest_file.endswith(".cc"):
            dest_file = os.path.splitext(dest_file)[0] + ".cpp"

        # Make leading directory
        dest_dir = os.path.dirname(dest_file)
        if not os.path.exists(dest_dir):
            os.makedirs(dest_dir)

        shutil.copyfile(f, dest_file)


def comment_out_invalid_includes(filename, include_roots):
    """Comment out #include directives that include a nonexistent file

    Keyword arguments:
    filename -- file to search for includes
    include_roots -- list of search paths for includes
    """
    # Read header
    with open(filename) as f:
        old_contents = f.read()

    new_contents = ""
    pos = 0
    for match in re.finditer(r"#include \"([^\"]+)\"", old_contents):
        include = match.group(1)

        # Write contents from before this match
        new_contents += old_contents[pos:match.span()[0]]

        # Comment out #include if the file doesn't exist in current directory or
        # include root
        if not os.path.exists(os.path.join(
                os.path.dirname(filename), include)) and not any(
                    os.path.exists(os.path.join(include_root, include))
                    for include_root in include_roots):
            new_contents += "// "

        new_contents += match.group()
        pos = match.span()[1]

    # Write rest of file if it wasn't all processed
    if pos < len(old_contents):
        new_contents += old_contents[pos:]

    # Write modified file back out
    if old_contents != new_contents:
        with open(filename, "w") as f:
            f.write(new_contents)