#!/usr/bin/env python3
"""
Fuzzy-find a file and edit it.

Dependencies
============
* fd
* fzf
"""

import argparse
import os
import shutil
import subprocess

from sys import platform

# ========== Constants ==========
# ----- Paths -----
BOOT_DIR = "/boot"
ETC_DIR = "/etc"

# ----- Exit Codes -----
E_INTERRUPT = 1
E_NOEDITORFOUND = 2
E_NOFILESELECTED = 3

# ----- Commands -----

# Options: show hidden files, null terminator, files only
# Optional arguments: show vcs files, show every file
FIND_CMD = shutil.which("fd")
FIND_OPTS = ["--hidden", "--print0", "--type", "f"]
EXTRA_FIND_OPTS = {"no_ignore_vcs": "--no-ignore", "no_ignore": "--no-ignore-vcs"}

# Options: null terminator, ignore case, print names matching all non-option arguments
LOCATE_CMD = shutil.which("locate")

# Options: read null terminator, auto-select if one option, exit if no options, print null terminator
FZF_CMD = shutil.which("fzf")
FZF_OPTS = ["--read0", "--select-1", "--exit-0", "--print0"]

# Platform-specific options
# macOS doesn't support GNU-style long options
if platform == "linux":
    LOCATE_OPTS = ["--all", "--ignore-case", "--null"]
elif platform == "darwin":
    LOCATE_OPTS = ["-0", "-i"]

# ----- Misc. -----
LOCALE = "utf-8"


# ========== Functions ==========
def select_editor(override=None):
    """Return a possible canonical path to an editor.
    Select an editor from one of:
    * -e, --editor
    * $EDITOR
    * Default of vim

    In this order

    If an editor cannot be resolved, then an Error is raised instead.

    :param override: argument to override an editor
    :returns: path to one of these editors
    :rtype: str
    :raises: FileNotFoundError if an editor could not be resolved
    """
    editor = None

    if override is not None:
        editor = shutil.which(override)
    elif "EDITOR" in os.environ:
        editor = shutil.which(os.environ.get("EDITOR"))
    elif shutil.which("vim") is not None:
        editor = shutil.which("vim")

    if editor is None:
        raise FileNotFoundError("An editor could not be resolved")

    return editor


def gen_editor_cmd(filename):
    """Generate a command line to run for editing a file based on
    permissions.

    This command does not pass extra options to the editor, hence
    there are no arguments to pass for options.

    :param filename: name of file to edit
    :type filename: str or path-like object
    :returns: command to execute to edit file
    :rtype: list
    """
    # Possible for a race condition to occur here
    # What happens if the file or its metadata changes?
    if os.access(filename, os.W_OK):
        return [editor, filename]
    else:
        return ["sudo", "--edit", filename]


def run_fzf(files):
    """Run fzf on a stream of searched files for the user to select.

    :param files: stream of null-terminated files to read
    :type files: bytes stream (stdout of a completed process)
    :returns: selected file
    :rtype: str
    """
    selected_file = subprocess.run(
        [FZF_CMD, *FZF_OPTS], input=files, stdout=subprocess.PIPE
    ).stdout

    return selected_file.decode(LOCALE).strip("\x00")


def find_files(opts, directory=None):
    """Use a find-based program to locate files, then pass to fzf.

    :param opts: options to pass to the find program
    :type opts: list of str
    :param directory: directory to search for files
    :type directory: str
    :returns: path of user-selected file
    :rtype: bytes
    """
    cmd = [FIND_CMD, *opts]

    if directory is not None:
        cmd.extend(["--", ".", directory])

    return subprocess.run(cmd, capture_output=True).stdout


def locate_files(patterns):
    """Use a locate-based program to locate files, then pass to fzf.

    :param patterns: patterns to pass to locate
    :type patterns: list
    :returns: path of user-selected file
    :rtype: bytes
    """
    cmd = [LOCATE_CMD] + LOCATE_OPTS
    cmd.extend(patterns)

    return subprocess.run(cmd, capture_output=True).stdout


# ========== Main Script ==========
if __name__ == "__main__":
    # This script doesn't support Windows
    if platform == "windows":
        sys.exit(E_INTERRUPT)

    parser = argparse.ArgumentParser()
    parser.add_argument(
        "-b",
        "--boot",
        action="store_const",
        const=BOOT_DIR,
        dest="dir",
        help="edit a file in /boot",
    )
    parser.add_argument(
        "-d", "--dir", dest="dir", type=str, help="edit a file in a given directory"
    )
    parser.add_argument(
        "-E",
        "--etc",
        action="store_const",
        const=ETC_DIR,
        dest="dir",
        help="edit a file in /etc",
    )
    parser.add_argument(
        "-I",
        "--no-ignore",
        action="append_const",
        const="--no-ignore",
        dest="extra_find_opts",
        help="do not respect .(git|fd)ignore files",
    )
    parser.add_argument(
        "-i",
        "--no-ignore-vcs",
        action="append_const",
        const="--no-ignore-vcs",
        dest="extra_find_opts",
        help="do not respect .gitignore files",
    )
    parser.add_argument("-e", "--editor", help="use a given editor")
    parser.add_argument(
        "patterns", type=str, nargs="*", help="patterns to pass to locate"
    )

    args = parser.parse_args()

    user_opts = [] if args.extra_find_opts is None else args.extra_find_opts
    user_opts.extend(FIND_OPTS)

    editor = ""

    try:
        editor = select_editor(args.editor)
    except FileNotFoundError as e:
        print(e)
        exit(E_NOEDITORFOUND)

    # If patterns were passed, use locate
    # Otherwise check for -d and use fd
    files = (
        find_files(user_opts, args.dir)
        if not args.patterns
        else locate_files(args.patterns)
    )

    try:
        selected_file = run_fzf(files)
    except KeyboardInterrupt:
        exit(E_INTERRUPT)

    if selected_file != "":
        cmd = gen_editor_cmd(selected_file)
        subprocess.run(cmd)
    else:
        exit(E_NOFILESELECTED)