#!/usr/bin/env fish

# nixos-config - My current NixOS configuration
#
# Copyright (C) 2025 Benedikt Peetz <benedikt.peetz@b-peetz.de>
# SPDX-License-Identifier: GPL-3.0-or-later
#
# This file is part of my nixos-config.
#
# You should have received a copy of the License along with this program.
# If not, see <https://www.gnu.org/licenses/gpl-3.0.txt>.

# This was taken from the
# `${pkgs.nix-index}/etc/profile.d/command-not-found.sh` file on 2024-02-28

function _log
    printf $argv >&2
end

function _bail
    __fish_default_command_not_found_handler $argv
    return "$status"
end

function _common_prefix
    set --function prefix

    for str in $argv
        set position 1
        for c in (string split '' "$str")
            if test -z $prefix[$position]
                set prefix[$position] "$c"
            else if test $prefix[$position] != "$c"
                if test $position = 1
                    # The first letter of the prefix mis-matched.
                    # As such there is no shared prefix, and we can simple bail early.
                    echo ""
                    return
                else
                    set prefix $prefix[1..(math $position - 1)]
                end
                break
            end

            set position (math $position + 1)
        end
    end

    echo "$(string join "" $prefix)"
end

function fish_command_not_found
    # Only run if it's an interactive shell
    if not status is-interactive
        return (_bail $argv)
    end

    # The nixpkgs flake should always be available on NixOS
    set --local toplevel nixpkgs
    set --local cmd "$argv[1]"

    set --local attrs "$(nix-locate --minimal --no-group --type x --type s --whole-name --at-root "/bin/$cmd")"

    if test -n "$attrs"
        set --function len "$(echo "$attrs" | count)"
    else
        set --function len 0
    end

    switch "$len"
    case 0
    case 1 or '*'
        _log "The program '%s' is currently not installed.\n" "$cmd"
    end

    switch "$len"
    case 0
        return (_bail $argv)
    case 1
        # If only one package provides this, then we can invoke it
        # without asking the user.

        # These will not return 127 if they worked correctly.

        _log "A shell will be opened with it.\n"

        if nix build "$toplevel#$attrs" --no-link
            nix shell "$toplevel#$attrs"
            return "$status"
        else
            _log "Failed to build: '%s#%s'\n" "$toplevel" "$attrs"
            return (_bail $argv)
        end
    case '*'
        _log "It is provided by several packages. You can run it load it with:\n"

        set --local counter 0
        set --local attrs $(echo $attrs)
        for attr in $attrs
            _log "%3s)" "$counter"
            _log " nix shell %s#%s\n" "$toplevel" "$attr";

            set counter "$(math "$counter" + 1)"
        end

        commandline "nix shell $toplevel#$(_common_prefix $attrs)"
    end

    # command not found should always exit with 127
    return 127
end