#!/usr/bin/env bash
#
# qdb-watch.sh --- the IRC capture side of qdb.
#
# Tails an `ii` channel `out` file, keeps a ring buffer of the last
# MAXLINES lines, and on a `.qdb [N]` command from the channel writes
# the preceding N lines to quotes/<id>.txt (the format qdbviewer.lhs
# reads) and announces the gopher permalink back to the channel.
#
# On simulacra the IRC server (ngircd) runs on the same host, so `ii`
# connects to it over loopback; for a remote server an optional
# stunnel sits in front (see README.txt). Either way this script only
# ever touches ii's filesystem interface.
#
# Config via environment (defaults suit the simulacra deployment):
#
#   QDB_IRC_BASE    base dir ii writes into        ($HOME/irc)
#   QDB_IRC_NETDIR  ii's on-disk subdir: the host  (= QDB_IRC_NET)
#                   ii dialled. With the stunnel
#                   setup ii dials 127.0.0.1, so
#                   this is "127.0.0.1".
#   QDB_IRC_NET     network *display* name, written (irc.someodd.zip)
#                   into the snapshot header
#   QDB_IRC_CHAN    channel dir / announce target  (#main)
#   QDB_QUOTES_DIR  where <id>.txt files are kept  (/var/gopher/applets/qdb/quotes)
#   GOPHER_HOST     host used in announced URLs    (gopher.someodd.zip)
#
# Run under systemd, after the qdb-ii service. On restart it starts
# from the end of `out` (tail -n 0), so old `.qdb` lines are never
# re-processed; the ring buffer refills as the channel talks.

set -u

IRC_BASE="${QDB_IRC_BASE:-$HOME/irc}"
IRC_NET="${QDB_IRC_NET:-irc.someodd.zip}"        # display name, recorded in snapshots
IRC_NETDIR="${QDB_IRC_NETDIR:-$IRC_NET}"         # ii's on-disk subdir (the host it dialled)
IRC_CHAN="${QDB_IRC_CHAN:-#main}"
QUOTES_DIR="${QDB_QUOTES_DIR:-/var/gopher/applets/qdb/quotes}"
GOPHER_HOST="${GOPHER_HOST:-gopher.someodd.zip}"

OUT="$IRC_BASE/$IRC_NETDIR/$IRC_CHAN/out"
IN="$IRC_BASE/$IRC_NETDIR/$IRC_CHAN/in"
COUNTER="$QUOTES_DIR/.counter"

MAXLINES=50      # ring-buffer size and the hard cap on N
DEFLINES=10      # N used for a bare `.qdb` with no number

mkdir -p "$QUOTES_DIR"

# announce <text> --- send a line to the channel. Backgrounded and
# timeout-bounded so a dead ii (nobody draining the FIFO) can never
# block or wedge the capture loop.
announce() {
  [ -p "$IN" ] || return 0
  ( timeout 5 sh -c 'printf "%s\n" "$0" > "$1"' "$1" "$IN" ) 2>/dev/null &
}

# fmt_line <ii-out-line> --- rewrite ii's leading `<epoch>` timestamp
# as a readable `YYYY-MM-DD HH:MM` (UTC), leaving the rest untouched.
# Non-timestamped lines pass through verbatim. This is what makes a
# snapshot's transcript human-readable instead of epoch soup.
fmt_line() {
  local line="$1"
  if [[ "$line" =~ ^([0-9]+)\ (.*)$ ]]; then
    local epoch="${BASH_REMATCH[1]}" rest="${BASH_REMATCH[2]}" when
    when=$(date -u -d "@$epoch" +'%Y-%m-%d %H:%M' 2>/dev/null) || when="$epoch"
    printf '%s %s\n' "$when" "$rest"
  else
    printf '%s\n' "$line"
  fi
}

# save_quote <nick> <n> --- snapshot the last <n> buffered lines.
# `buf` is the ring buffer; it does NOT include the `.qdb` command
# line itself (we snapshot before appending each line).
save_quote() {
  local nick="$1" n="$2"
  local count=${#buf[@]}
  (( n > count )) && n=$count
  if (( n < 1 )); then
    announce "qdb: nothing buffered yet --- try again once the channel's been talking"
    return
  fi

  local last next id now tmp
  last=$(cat "$COUNTER" 2>/dev/null || echo 0)
  case "$last" in ''|*[!0-9]*) last=0 ;; esac
  next=$(( last + 1 ))
  id=$(printf '%04d' "$next")
  now=$(date -u +%Y-%m-%dT%H:%M:%SZ)

  # Write to a dotfile tmp then rename, so qdbviewer.lhs never reads a
  # half-written snapshot (rename is atomic within a filesystem).
  tmp="$QUOTES_DIR/.$id.tmp"
  {
    echo "qdb #$id"
    echo "========="
    echo "saved-by: $nick"
    echo "channel:  $IRC_CHAN"
    echo "network:  $IRC_NET"
    echo "date:     $now"
    echo "lines:    $n"
    echo
    for l in "${buf[@]: -n}"; do fmt_line "$l"; done
  } > "$tmp"
  mv "$tmp" "$QUOTES_DIR/$id.txt"
  echo "$next" > "$COUNTER"

  announce "qdb #$id saved ($n lines) -> gopher://$GOPHER_HOST/1/applets/qdb/qdbviewer.lhs/q/$id"
}

buf=()

# tail -n 0 -F: emit only lines appended after we start, and survive
# `out` being rotated/recreated (ii reconnects, log pruning, etc).
while IFS= read -r line; do
  # ii out lines are `<epoch> <nick> message` for channel messages
  # (and `<epoch> -!- ...` for joins/parts/notices). A `.qdb` command:
  # `<epoch> <nick> .qdb` optionally followed by a line count.
  # Anything else after `.qdb` is ignored as not-a-command.
  is_cmd=0
  if [[ "$line" =~ ^[0-9]+\ \<([^>]+)\>\ \.qdb([[:space:]]+([0-9]+))?[[:space:]]*$ ]]; then
    nick="${BASH_REMATCH[1]}"
    n="${BASH_REMATCH[3]:-$DEFLINES}"
    (( n < 1 )) && n=1
    (( n > MAXLINES )) && n=$MAXLINES
    save_quote "$nick" "$n"
    is_cmd=1
  fi

  # Buffer only chat lines --- `<epoch> <nick> message`. Skip ii's
  # `<epoch> -!- ...` meta lines (joins/parts/quits/nick changes/
  # topics) and the `.qdb` command lines themselves, so a snapshot is
  # conversation, not channel noise. Keep the most recent MAXLINES.
  chat_re='^[0-9]+ <[^>]+> '
  if (( ! is_cmd )) && [[ "$line" =~ $chat_re ]]; then
    buf+=("$line")
    (( ${#buf[@]} > MAXLINES )) && buf=("${buf[@]: -MAXLINES}")
  fi
done < <(tail -n 0 -F "$OUT")