#!/bin/bash
# explode - Move a directory's contents up one level, then remove the empty directory
#
# Usage:
#   explode [options] <directory>
#
# Options:
#   -f, --force    Overwrite existing files at the destination
#   -n, --dry-run  Show what would happen without making changes
#   -v, --verbose  List each item as it is moved
#   -h, --help     Display this help message

_explode() (
    local SCRIPT_NAME; SCRIPT_NAME="$(basename "${BASH_SOURCE[0]}")"
    case "${BASH_SOURCE[0]}" in /dev/*|/proc/*) SCRIPT_NAME="" ;; esac
    case "$SCRIPT_NAME" in ""|bash|sh|zsh|dash) SCRIPT_NAME="explode" ;; esac

    _show_help() {
        local s; [ -t 1 ] && s=$'\033[4m'
        local r; [ -t 1 ] && r=$'\033[24m'
        echo "NAME"
        echo "  $SCRIPT_NAME - move a directory's contents up one level, then remove it"
        echo "SYNOPSIS"
        echo "  $SCRIPT_NAME [${s}options${r}] <${s}directory${r}>"
        echo "  $SCRIPT_NAME -h"
        echo "DESCRIPTION"
        echo "  Moves every item in ${s}directory${r} into its parent, then removes the"
        echo "  now-empty ${s}directory${r}. Aborts without changes if any items would"
        echo "  collide with existing files, unless --force is given."
        echo "OPTIONS"
        echo "  -f, --force    Overwrite existing files at the destination"
        echo "  -n, --dry-run  Show what would happen without making changes"
        echo "  -v, --verbose  List each item as it is moved"
        echo "  -h, --help     Display this help message"
        echo "EXIT STATUS"
        echo "  0   Success (or help/dry-run completed)"
        echo "  1   Usage error, collision without --force, or a move failed"
        echo "  2   Directory removal failed (items remain after attempted moves)"
    }
    _error() { echo "[ERR][$SCRIPT_NAME] $*" >&2; }

    _expand_short_opts() {
        # $1 = string of short-opt letters that take a value (e.g. "nXHd"); "" for flag-only scripts
        # $2..$N = "$@"
        # Populates _EXPANDED; caller does: set -- "${_EXPANDED[@]}"; unset _EXPANDED
        local value_opts="$1"; shift
        _EXPANDED=()
        local passthru=""
        local arg
        local rest
        local c
        for arg in "$@"; do
            if [ -n "$passthru" ]; then _EXPANDED+=("$arg"); continue; fi
            case "$arg" in
                --)          passthru=1; _EXPANDED+=("$arg") ;;
                --*|-|"")    _EXPANDED+=("$arg") ;;
                -[a-zA-Z]?*)
                    rest="${arg#-}"
                    while [ -n "$rest" ]; do
                        c="${rest%"${rest#?}"}"; rest="${rest#?}"
                        _EXPANDED+=("-$c")
                        case "$value_opts" in *"$c"*)
                            [ -n "$rest" ] && _EXPANDED+=("$rest")
                            rest="" ;;
                        esac
                    done ;;
                *)        _EXPANDED+=("$arg") ;;
            esac
        done
    }

    local force=false
    local dryrun=false
    local verbose=false
    local dir

    _expand_short_opts "" "$@"
    set -- "${_EXPANDED[@]}"; unset _EXPANDED

    while [ $# -gt 0 ]; do
        case "$1" in
            -f|--force)
                force=true
                shift
                ;;
            -n|--dry-run)
                dryrun=true
                shift
                ;;
            -v|--verbose)
                verbose=true
                shift
                ;;
            -h|--help)
                _show_help
                return 0
                ;;
            --)
                shift
                [ $# -gt 0 ] && dir="$1"
                break
                ;;
            -*)
                _error "Unknown argument '$1'. Run \`$SCRIPT_NAME -h\` for usage"
                return 1
                ;;
            *)
                if [ -n "$dir" ]; then
                    _error "Multiple directories specified. Run \`$SCRIPT_NAME -h\` for usage"
                    return 1
                fi
                dir="$1"
                shift
                ;;
        esac
    done

    if [ -z "$dir" ]; then
        _error "No directory specified. Run \`$SCRIPT_NAME -h\` for usage"
        return 1
    fi
    if [ ! -e "$dir" ]; then
        _error "$dir does not exist"
        return 1
    fi
    if [ ! -d "$dir" ]; then
        _error "$dir is not a directory"
        return 1
    fi

    local dest; dest="$(dirname "$dir")"

    # Check for collisions
    # -d '' delimits on null byte, pairing with find -print0 for safe filename handling
    local collisions=()
    local item
    while IFS= read -r -d '' item; do
        local base; base="$(basename "$item")"
        if [ -e "$dest/$base" ]; then
            collisions+=("$base")
        fi
    done < <(find "$dir" -mindepth 1 -maxdepth 1 -print0)

    if [ ${#collisions[@]} -gt 0 ] && ! $force; then
        _error "Aborting -- the following items already exist in $dest:"
        local c
        for c in "${collisions[@]}"; do
            echo "  $c" >&2
        done
        return 1
    fi

    if $dryrun; then
        if [ ${#collisions[@]} -gt 0 ]; then
            echo "Would overwrite (--force):"
            local c
            for c in "${collisions[@]}"; do
                echo "  $c"
            done
        fi
        echo "Would move to $dest:"
        find "$dir" -mindepth 1 -maxdepth 1 -exec basename {} \; | sort
        echo "Would remove: $dir"
        return 0
    fi

    # Move contents
    local mv_flags="-n"
    $force && mv_flags="-f"
    local failed=false
    while IFS= read -r -d '' item; do
        if $verbose; then
            echo "$(basename "$item") -> $dest/"
        fi
        if ! mv "$mv_flags" "$item" "$dest/"; then
            _error "Failed to move $item"
            failed=true
        fi
    done < <(find "$dir" -mindepth 1 -maxdepth 1 -print0)

    if $failed; then
        _error "Some items failed to move. Directory not removed"
        return 1
    fi

    # Remove the now-empty directory
    if ! rmdir "$dir"; then
        local num_remaining
        num_remaining="$(find "$dir" -mindepth 1 -maxdepth 1 -print0 | tr -cd '\0' | wc -c | tr -d ' ')"
        _error "Failed to remove $dir ($num_remaining items remaining)"
        return 2
    fi
)

_explode "$@"
__explode_rc=$?
unset -f _explode
if [ -n "${BASH_SOURCE[0]}" ] && [ "${BASH_SOURCE[0]}" != "$0" ]; then
    eval "unset __explode_rc; return $__explode_rc"
fi
eval "unset __explode_rc; exit $__explode_rc"