#!/usr/bin/env bash
# Portable, append-only git relay for deliberate cross-agent communication.
set -euo pipefail

CONFIG_PATH="${MOS_COMMS_CONFIG:-$HOME/.config/mos-comms/mos-comms.config}"
CONFIG_PRESENT=0
if [[ -f "$CONFIG_PATH" ]]; then
  # Configuration is local operator input. It must not be committed to the relay repo.
  # shellcheck source=/dev/null
  source "$CONFIG_PATH"
  CONFIG_PRESENT=1
fi

AGENT_NAME="${AGENT_NAME:-}"
COMMS_REMOTE="${COMMS_REMOTE:-}"
COMMS_REPO_DIR="${COMMS_REPO_DIR:-$HOME/.local/state/mos-comms/repo}"
COMMS_BRANCH="${COMMS_BRANCH:-mos-comms}"
TMUX_SOCKET="${TMUX_SOCKET:-}"
TMUX_SESSION="${TMUX_SESSION:-mos-claude}"
STATE_DIR="${STATE_DIR:-$HOME/.local/state/mos-comms}"
GIT_CRED_HELPER="${GIT_CRED_HELPER:-}"

usage() {
  cat <<'EOF'
Usage: mos-comms.sh setup | poll | read | send <text> | selftest

Messages are append-only files on the configured shared git branch. `poll` is
mechanical: it only checks git and emits a fixed tmux notification.
EOF
}

die() {
  printf 'mos-comms: %s\n' "$*" >&2
  exit 1
}

warn() {
  printf 'mos-comms: warning: %s\n' "$*" >&2
}

gitc() {
  if [[ -n "$GIT_CRED_HELPER" ]]; then
    git -c credential.helper="$GIT_CRED_HELPER" "$@"
  else
    git "$@"
  fi
}

require_identity() {
  [[ -n "$AGENT_NAME" ]] || die 'AGENT_NAME is required in the local config'
  [[ "$AGENT_NAME" =~ ^[A-Za-z0-9.-]+$ ]] || die 'AGENT_NAME may contain only letters, numbers, dots, and hyphens'
}

require_remote() {
  [[ -n "$COMMS_REMOTE" ]] || die 'COMMS_REMOTE is required in the local config'
}

ensure_state_dir() {
  mkdir -p "$STATE_DIR"
  chmod 700 "$STATE_DIR"
}

remote_branch_exists() {
  gitc -C "$COMMS_REPO_DIR" show-ref --verify --quiet "refs/remotes/origin/$COMMS_BRANCH"
}

setup() {
  require_remote
  require_identity
  mkdir -p "$(dirname "$COMMS_REPO_DIR")"

  if [[ ! -d "$COMMS_REPO_DIR/.git" ]]; then
    gitc clone "$COMMS_REMOTE" "$COMMS_REPO_DIR"
  fi

  gitc -C "$COMMS_REPO_DIR" remote set-url origin "$COMMS_REMOTE"
  gitc -C "$COMMS_REPO_DIR" fetch origin
  if remote_branch_exists; then
    # Preserve any local append-only commit that is awaiting a retry; do not
    # reset a checked-out branch to origin here.
    if gitc -C "$COMMS_REPO_DIR" show-ref --verify --quiet "refs/heads/$COMMS_BRANCH"; then
      gitc -C "$COMMS_REPO_DIR" checkout "$COMMS_BRANCH"
    else
      gitc -C "$COMMS_REPO_DIR" checkout --track -b "$COMMS_BRANCH" "origin/$COMMS_BRANCH"
    fi
    gitc -C "$COMMS_REPO_DIR" branch --set-upstream-to="origin/$COMMS_BRANCH" "$COMMS_BRANCH"
  else
    gitc -C "$COMMS_REPO_DIR" checkout -B "$COMMS_BRANCH"
  fi

  mkdir -p "$COMMS_REPO_DIR/comms"
  ensure_state_dir
}

ensure_remote_branch() {
  if ! remote_branch_exists; then
    warn "origin branch '$COMMS_BRANCH' does not exist yet"
    return 1
  fi
}

message_is_from_self() {
  local file="$1"
  [[ "$file" == *"__from-${AGENT_NAME}__"* ]]
}

changed_message_files() {
  local from_sha="$1"
  local to_sha="$2"
  if [[ -n "$from_sha" ]] && gitc -C "$COMMS_REPO_DIR" cat-file -e "$from_sha^{commit}" 2>/dev/null; then
    gitc -C "$COMMS_REPO_DIR" diff --name-only "$from_sha" "$to_sha" -- comms/
  else
    gitc -C "$COMMS_REPO_DIR" ls-tree -r --name-only "$to_sha" -- comms/
  fi
}

tmuxc() {
  if [[ -n "$TMUX_SOCKET" ]]; then
    tmux -L "$TMUX_SOCKET" "$@"
  else
    tmux "$@"
  fi
}

send() {
  require_identity
  require_remote
  [[ $# -ge 1 ]] || die 'send requires message text'
  setup

  local body="$*"
  local utc filename path
  utc="$(date -u +%Y%m%dT%H%M%SZ)"
  filename="${utc}__from-${AGENT_NAME}__${RANDOM}${RANDOM}.md"
  path="$COMMS_REPO_DIR/comms/$filename"
  umask 077
  {
    printf '%s\n' '---'
    printf 'from: %s\n' "$AGENT_NAME"
    printf '%s\n' 'to: all'
    printf 'utc: %s\n' "$utc"
    printf '%s\n\n' '---'
    printf '%s\n' "$body"
  } >"$path"

  gitc -C "$COMMS_REPO_DIR" add -- "comms/$filename"
  if ! gitc -C "$COMMS_REPO_DIR" config user.name >/dev/null; then
    gitc -C "$COMMS_REPO_DIR" config user.name "$AGENT_NAME mos-comms"
  fi
  if ! gitc -C "$COMMS_REPO_DIR" config user.email >/dev/null; then
    gitc -C "$COMMS_REPO_DIR" config user.email "$AGENT_NAME@localhost"
  fi
  gitc -C "$COMMS_REPO_DIR" commit -m "comms: ${AGENT_NAME} ${utc}"

  local attempt
  for attempt in 1 2 3; do
    if remote_branch_exists; then
      gitc -C "$COMMS_REPO_DIR" pull --rebase origin "$COMMS_BRANCH"
    fi
    if gitc -C "$COMMS_REPO_DIR" push origin "HEAD:refs/heads/$COMMS_BRANCH"; then
      printf 'sent: %s\n' "$filename"
      return 0
    fi
    if [[ "$attempt" -lt 3 ]]; then
      warn "push rejected; retrying ($attempt/3)"
      gitc -C "$COMMS_REPO_DIR" fetch origin
    fi
  done
  die 'push was rejected after 3 attempts; local message commit remains available for retry'
}

poll() {
  require_identity
  require_remote
  setup
  gitc -C "$COMMS_REPO_DIR" fetch origin
  ensure_remote_branch || return 0

  local head marker last_notified
  head="$(gitc -C "$COMMS_REPO_DIR" rev-parse "origin/$COMMS_BRANCH")"
  marker="$STATE_DIR/last_notified_sha"
  if [[ ! -f "$marker" ]]; then
    printf '%s\n' "$head" >"$marker"
    printf 'poll: baseline recorded; existing history was not notified\n'
    return 0
  fi
  last_notified="$(<"$marker")"
  if [[ "$last_notified" == "$head" ]]; then
    return 0
  fi

  local file count=0
  while IFS= read -r file; do
    [[ -n "$file" ]] || continue
    if ! message_is_from_self "$file"; then
      ((count += 1))
    fi
  done < <(changed_message_files "$last_notified" "$head")

  if ((count > 0)); then
    # Intentionally static except for an integer: never inject peer data into tmux.
    tmuxc send-keys -t "$TMUX_SESSION" "[mos-comms] $count new peer message(s) — run: mos-comms.sh read"
    tmuxc send-keys -t "$TMUX_SESSION" Enter
  fi
  printf '%s\n' "$head" >"$marker"
}

read_messages() {
  require_identity
  require_remote
  setup
  gitc -C "$COMMS_REPO_DIR" fetch origin
  ensure_remote_branch || return 0

  local head marker last_read file found=0
  head="$(gitc -C "$COMMS_REPO_DIR" rev-parse "origin/$COMMS_BRANCH")"
  marker="$STATE_DIR/last_read_sha"
  last_read=""
  if [[ -f "$marker" ]]; then
    last_read="$(<"$marker")"
  fi

  while IFS= read -r file; do
    [[ -n "$file" ]] || continue
    if message_is_from_self "$file"; then
      continue
    fi
    found=1
    printf '%s\n' "===== $file ====="
    # Peer content is printed as data. It is never evaluated or sent to tmux.
    gitc -C "$COMMS_REPO_DIR" show "origin/$COMMS_BRANCH:$file"
    printf '\n'
  done < <(changed_message_files "$last_read" "$head")

  printf '%s\n' "$head" >"$marker"
  if ((found == 0)); then
    printf 'No new peer messages.\n'
  fi
}

selftest() {
  local remote_ok=0 branch_ok=0 tmux_ok=0 config_ok=0
  if ((CONFIG_PRESENT == 1)); then
    printf 'PASS config present: %s\n' "$CONFIG_PATH"
    config_ok=1
  else
    printf 'FAIL config present: %s\n' "$CONFIG_PATH"
  fi

  if [[ -z "$COMMS_REMOTE" ]]; then
    printf 'WARN remote reachable: COMMS_REMOTE is not configured\n'
  elif gitc ls-remote "$COMMS_REMOTE" >/dev/null 2>&1; then
    printf 'PASS remote reachable\n'
    remote_ok=1
  else
    printf 'FAIL remote reachable\n'
  fi

  if ((remote_ok == 1)) && gitc ls-remote --exit-code --heads "$COMMS_REMOTE" "$COMMS_BRANCH" >/dev/null 2>&1; then
    printf 'PASS branch resolves: %s\n' "$COMMS_BRANCH"
    branch_ok=1
  elif [[ -z "$COMMS_REMOTE" ]]; then
    printf 'WARN branch resolves: skipped without a remote\n'
  else
    printf 'FAIL branch resolves: %s\n' "$COMMS_BRANCH"
  fi

  if tmuxc has-session -t "$TMUX_SESSION" 2>/dev/null; then
    printf 'PASS tmux session exists: %s\n' "$TMUX_SESSION"
    tmux_ok=1
  else
    printf 'FAIL tmux session exists: %s\n' "$TMUX_SESSION"
  fi

  # Report all checks without making a no-remote first-run unusable.
  if ((config_ok == 1 && remote_ok == 1 && branch_ok == 1 && tmux_ok == 1)); then
    printf 'PASS selftest complete\n'
  else
    printf 'FAIL selftest incomplete (see checks above)\n'
  fi
}

case "${1:-}" in
  setup) [[ $# -eq 1 ]] || usage; setup ;;
  poll) [[ $# -eq 1 ]] || usage; poll ;;
  read) [[ $# -eq 1 ]] || usage; read_messages ;;
  send) shift; send "$@" ;;
  selftest) [[ $# -eq 1 ]] || usage; selftest ;;
  -h|--help|help) usage ;;
  *) usage; exit 2 ;;
esac