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+#!/bin/sh
+## twerk: a twtxt client
+# by Case Duckworth
+
+### Entry point
+
+usage() {
+        cat >&2 <<EOF
+TWERK: a twtxt client
+usage: twerk [options] [file]
+
+twerk can be fed a list of URLs from standard input or from a FILE.
+Each line is expected to contain a URL of a twtxt feed and (optionally) the
+display name to use for that feed.
+
+options (default):
+ -h          Show this help and exit.
+ -t          Include the time in each post date.
+ -f          Force redownload of twt data.
+ -n LIMIT    Only show LIMIT posts (25).  0 means no limit.
+ -w WIDTH    Limit the output's width to WIDTH characters (72).
+ -W WIDTH    Limit the username's width to WIDTH characters (12).
+ -i INDENT   Use INDENT spaces as a hanging indent for too-long lines
+             ([calculated]).
+ -p COMMAND  Use COMMAND to post twts ([not set]).
+             This command will be fed a twtxt-formatted string via stdin.
+             Recommended: \`ssh <host> tee -a <file>\`.
+
+parameters:
+ FILE        List of twtxt feeds to fetch, one feed per line.
+             Optionally, a string after the feed URL will be its
+             display name.
+EOF
+        exit "${1:-0}"
+}
+
+configure() {
+        # defaults
+        TWERK_WIDTH="${TWERK_WIDTH:-72}"
+        TWERK_LIMIT="${TWERK_LIMIT:-25}"
+        TWERK_INCLUDE_TIME="${TWERK_INCLUDE_TIME:-0}"
+        TWERK_USER_WIDTH="${TWERK_USER_WIDTH:-12}"
+        TWERK_HANG="${TWERK_HANG:-}" # empty to calculate off other variables
+        TWERK_FORCE="${TWERK_FORCE:-false}"
+        TWERK_POST_COMMAND="${TWERK_POST_COMMAND:-:}" # no-op
+
+        while getopts htfn:w:W:i:p:c: opt
+        do
+                case "$opt" in
+                        h) usage ;;
+                        t) TWERK_INCLUDE_TIME=1 ;;
+                        f) TWERK_FORCE=true ;;
+                        n) TWERK_LIMIT="$OPTARG" ;;
+                        w) TWERK_WIDTH="$OPTARG" ;;
+                        W) TWERK_USER_WIDTH="$OPTARG" ;;
+                        i) TWERK_HANG="$OPTARG" ;;
+                        p) TWERK_POST_COMMAND="$OPTARG" ;;
+                        c) TWERK_FEEDS="$OPTARG" ;;
+                        *) usage 1 ;;
+                esac
+        done
+
+        if test -z "$TWERK_HANG"
+        then
+                TWERK_HANG=$((TWERK_USER_WIDTH+(TWERK_INCLUDE_TIME*6)+10+3))
+                echo >&2 "$TWERK_HANG"
+        fi
+}
+
+main() {
+        TWERK_CACHE="${XDG_CACHE_HOME:-$HOME/.cache}/twerk"
+        mkdir -p "$TWERK_CACHE"
+        TWERK_FILE="$TWERK_CACHE/:file:"
+
+        TWERK_LESSKEY="$TWERK_CACHE/:lesskey:"
+        lesskey_setup
+
+        if "$_TWERK_INITIAL"
+        then
+                configure "$@"
+                shift "$((OPTIND - 1))"
+                TWERK_FEEDS="$1"
+        fi
+
+        cat "$TWERK_FEEDS" |
+                fetch_posts |
+                sort_posts |
+                limit_posts "$TWERK_LIMIT" |
+                format_posts > "$TWERK_FILE"
+
+        read_posts "$TWERK_FILE"
+}
+
+### Library
+
+fetch_posts() {
+        while read -r url name
+        do
+                if test -z "$name"
+                then
+                        file="$TWERK_CACHE/$(url_normalize "$name")"
+                else
+                        file="$TWERK_CACHE/$name"
+                fi
+
+                if "$TWERK_FORCE" || test -z "$(find "$file" -prune -mtime -1 2>/dev/null)"
+                then
+                        printf >&2 'Downloading %s...\n' "$url"
+                        curl -sf "$url" |
+                                filter_lines |
+                                while read -r date post
+                                do
+                                        printf '%s\t%s\t%s\t%s\n' \
+                                               "$date" "$name" "$url" "$post"
+                                done |
+                                tee "$file"
+                else
+                        cat "$file"
+                fi
+        done
+}
+
+url_normalize() {
+        printf '%s\n' "$1" | tr -d ':/~'
+}
+
+filter_lines() {
+        while read -r line
+        do
+                case "$line" in
+                        \#*) ;;
+                        '') ;;
+                        *) printf '%s\n' "$line" ;;
+                esac
+        done
+}
+
+limit_posts() {
+        ln=0
+        while read -r line
+        do
+                if test "$1" -ne 0 && test "$ln" -gt "$1"
+                then
+                        break
+                fi
+                printf '%s\n' "$line"
+                ln=$((ln+1))
+        done
+}
+
+sort_posts() {
+        sort -r
+}
+
+format_posts() {
+        while IFS='     ' read -r date name url post
+        do
+                if test 0 -eq "$TWERK_INCLUDE_TIME"
+                then
+                        TWERK_DATE_WIDTH=10
+                        date="${date%T*}"
+                else
+                        TWERK_DATE_WIDTH=16
+                fi
+
+                printf "%${TWERK_DATE_WIDTH}s | %${TWERK_USER_WIDTH}s | " \
+                       "$(echo "$date" | head -c$TWERK_DATE_WIDTH)" \
+                       "$(echo "$name" | head -c$TWERK_USER_WIDTH)"
+
+                export url name date post TWERK_WIDTH TWERK_HANG
+                export linewidth="$TWERK_HANG"
+
+                printf '%s\n' "$post" |
+                        tr ' ' '\n' |
+                        while IFS= read word
+                        do
+                                if test $(( linewidth + ${#word} )) -ge "$TWERK_WIDTH"
+                                then
+                                        echo
+                                        linewidth=0
+                                        printf "%${TWERK_HANG}s \` " ""
+                                        linewidth=$((linewidth+TWERK_HANG+2))
+                                fi
+                                printf '%s ' "$word"
+                                linewidth=$((linewidth + ${#word}))
+                        done
+                echo
+        done
+}
+
+
+lesskey_setup() {
+        # t will exit with code 48
+        if ! test -r "$TWERK_LESSKEY"
+        then
+                lesskey -o "$TWERK_LESSKEY" - <<EOF
+#command
+t quit 0
+g quit 1
+#line-edit
+#env
+EOF
+        fi
+}
+
+read_posts() {
+        less \
+                -k "$TWERK_LESSKEY" \
+                -Pm'twerk! t\: twt, g\: refresh' -m \
+                "$1"
+
+        case "$?" in
+                0) exit ;;
+                48) post ;;
+                49) refresh ;;
+        esac
+}
+
+post() {
+        printf 'Twt: ' >&2
+        read -r post
+        echo >&2
+
+        post="$(printf '%s\t%s\n' "$(date +'%FT%T%z')" "$post")"
+
+        eval "printf '%s\n' \"\$post\" | $TWERK_POST_COMMAND"
+        _TWERK_INITIAL=false main "$TWERK_FEEDS"
+}
+
+refresh() {
+        TWERK_FORCE=true main "$TWERK_FEEDS"
+}
+
+###################################
+_TWERK_INITIAL=true
+test -z "$DEBUG" || set -x
+test -z "$SOURCE" && main "$@"