rc/sh/decently

#!/usr/bin/env sh
# YES_ZSH
# YES_BASH
# YES_DASH
# YES_ASH

# TODO: check if this is compatible with busybox.

decently() ( ### @-
    ### given a list of directories, update the last-modified timestamp
    ### of each argument to that of the most recent file that it contains.
    ###
    ### note that *files* are found recursively, but only the
    ### *outermost directory* (the one specified by argument)
    ### has its timestamp updated. symlinks are followed.
    ### `.git` subdirectories are skipped over.
    ### the timestamps of subdirectories are ignored.
    [ -n "$1" ] || { printf '%s: missing directory argument\n' decently >&2; return 1; }

    local arg= dir= latest= prev= ts= fails= succs=0

    finder() {
        find "$dir" -type f "$@" \
        '!' \
        '(' -path '*/.git/*' \
        -or -path '*/CVS/*' \
        -or -path '*/CVSROOT/*' \
        -or -path '*/__pycache__/*' \
        -or -path '*/[Dd]esktop.ini' \
        -or -path '*/Thumbs.db' \
        -or -path '*/.DS_Store' \
        ')' \
        -exec ls -t1 '{}' + \
          2>/dev/null \
          | while read -r f; do
            printf '%s\n' "$f"
            break
        done
    }

    for arg; do
        dir="$(readlink -f -- "$arg")" || continue
        [ -d "$dir" ] || { printf '%s: not a directory: %s\n' decently "$dir" >&2; continue; }

        prev=
        latest="$(finder)" || continue
        while [ -n "$latest" ]; do
            prev="$latest"
            latest="$(finder -newer "$latest")" || break
        done
        [ -e "$prev" ] || { printf '%s: no valid files found: %s\n' decently "$dir" >&2; continue; }

        ts="$(date -u '+%s' -r "$prev")"
        dir="${dir%/}/" # ensure dir has a trailing slash
        printf '%s\t%s\n' "$ts" "${arg%/}/${prev#$dir}"
        touch -c -r "$prev" "$dir" || continue
        : $(( succs+=1 ))
    done

    fails=$(( $# - succs ))
    [ $fails -le 255 ] || fails=255
    return $fails
)

[ -n "${preload+-}" ] || decently "$@"