#!/usr/bin/env bash
set -euo pipefail

AGENT_NAME=${1:-${MOSAIC_AGENT_NAME:-}}
MOSAIC_TMUX_SOCKET=${MOSAIC_TMUX_SOCKET:-mosaic-factory}
MOSAIC_AGENT_RUNTIME=${MOSAIC_AGENT_RUNTIME:-pi}
MOSAIC_AGENT_WORKDIR=${MOSAIC_AGENT_WORKDIR:-$HOME}
MOSAIC_AGENT_COMMAND=${MOSAIC_AGENT_COMMAND:-}
MOSAIC_HEARTBEAT_RUN_DIR=${MOSAIC_HEARTBEAT_RUN_DIR:-${MOSAIC_HOME:-$HOME/.config/mosaic}/fleet/run}
MOSAIC_HEARTBEAT_INTERVAL=${MOSAIC_HEARTBEAT_INTERVAL:-15}

if [ -z "$AGENT_NAME" ]; then
  echo "ERROR: agent name argument or MOSAIC_AGENT_NAME is required" >&2
  exit 64
fi

if ! command -v tmux >/dev/null 2>&1; then
  echo "ERROR: tmux is required" >&2
  exit 69
fi

if tmux -L "$MOSAIC_TMUX_SOCKET" has-session -t "=${AGENT_NAME}:0.0" 2>/dev/null; then
  echo "Mosaic agent session already running: $AGENT_NAME on socket $MOSAIC_TMUX_SOCKET"
  exit 0
fi

if [ -z "$MOSAIC_AGENT_COMMAND" ]; then
  MOSAIC_AGENT_COMMAND="mosaic yolo $MOSAIC_AGENT_RUNTIME"
fi

# ── Derive a runtime-bin PATH prefix ─────────────────────────────────────────
# Precedence:
#   1. $MOSAIC_RUNTIME_BIN (explicit override)
#   2. $(npm config get prefix)/bin  (if npm is on PATH)
#   3. Fallbacks: $HOME/.npm-global/bin and $HOME/.local/bin
#
# Only directories that already exist are included.  The prefix is baked into
# the pane command regardless of what the LAUNCHER process's $PATH contains,
# because the tmux pane inherits the tmux SERVER environment (not this script's
# environment).  A dir on the launcher's PATH may be absent from the server PATH,
# so every existing candidate must always be included.  Dedup within the
# constructed prefix avoids listing the same dir twice.
_build_runtime_bin_prefix() {
  local candidates=()

  if [ -n "${MOSAIC_RUNTIME_BIN:-}" ]; then
    candidates+=("$MOSAIC_RUNTIME_BIN")
  fi

  if command -v npm >/dev/null 2>&1; then
    local npm_prefix
    npm_prefix=$(npm config get prefix 2>/dev/null) || true
    if [ -n "$npm_prefix" ]; then
      candidates+=("${npm_prefix}/bin")
    fi
  fi

  candidates+=("$HOME/.npm-global/bin")
  candidates+=("$HOME/.local/bin")

  local prefix=""
  for dir in "${candidates[@]}"; do
    [ -d "$dir" ] || continue
    if [ -z "$prefix" ]; then
      prefix="$dir"
    else
      case ":${prefix}:" in
        *":${dir}:"*) ;;  # already in our prefix — skip
        *) prefix="${prefix}:${dir}" ;;
      esac
    fi
  done

  printf '%s' "$prefix"
}

MOSAIC_RUNTIME_BIN_PREFIX=$(_build_runtime_bin_prefix)

# ── Build the pane command ────────────────────────────────────────────────────
# The pane command must:
#   - Export the augmented PATH so the runtime binary is found.
#   - exec the agent command so the runtime is the pane's foreground process
#     (makes `fleet ps` pane_current_command check reliable; no DRIFT false-positive).
#
# Quoting strategy: single-quote the inner shell snippet so that variable
# references in MOSAIC_AGENT_COMMAND are NOT expanded here — they expand inside
# the pane shell.  However, MOSAIC_RUNTIME_BIN_PREFIX and PATH must be expanded
# NOW (in this script) because the pane shell inherits the tmux server
# environment, not this script's env.
#
# We build the snippet as a double-quoted here-string embedded in a printf call
# to avoid nested quoting problems.

if [ -n "$MOSAIC_RUNTIME_BIN_PREFIX" ]; then
  PANE_SHELL_SNIPPET="export PATH=\"${MOSAIC_RUNTIME_BIN_PREFIX}:\${PATH}\"; exec ${MOSAIC_AGENT_COMMAND}"
else
  PANE_SHELL_SNIPPET="exec ${MOSAIC_AGENT_COMMAND}"
fi

mkdir -p "$MOSAIC_AGENT_WORKDIR"

# ── Launch the tmux session (no exec — we continue to wire the heartbeat) ────
tmux -L "$MOSAIC_TMUX_SOCKET" new-session -d -s "$AGENT_NAME" -c "$MOSAIC_AGENT_WORKDIR" \
  bash -c "$PANE_SHELL_SNIPPET"

# ── Resolve the pane PID (retry briefly to let the session initialise) ────────
PANE_PID=""
for _retry in 1 2 3 4 5; do
  PANE_PID=$(tmux -L "$MOSAIC_TMUX_SOCKET" list-panes \
    -t "=${AGENT_NAME}:0.0" -F '#{pane_pid}' 2>/dev/null || true)
  [ -n "$PANE_PID" ] && break
  sleep 0.2
done

# ── Spawn the heartbeat sidecar (detached, best-effort) ──────────────────────
# The sidecar writes ~/.config/mosaic/fleet/run/<AGENT>.hb atomically while the
# pane process is alive, then exits so the file goes stale (fleet ps shows stale
# then PANE=dead).  It is runtime-agnostic: it only cares about the pane PID.
_start_heartbeat_sidecar() {
  local agent="$1"
  local pane_pid="$2"
  local run_dir="$3"
  local interval="$4"
  local hb_file="${run_dir}/${agent}.hb"

  mkdir -p "$run_dir"

  # Write the sidecar as a self-contained bash one-liner so it carries no
  # references to any variables from this script's environment.
  local sidecar_script
  sidecar_script=$(printf \
    'hb=%s; pid=%s; iv=%s; mkdir -p "$(dirname "$hb")"; while kill -0 "$pid" 2>/dev/null; do tmp="$hb.tmp.$$"; printf "ts=%%s\npid=%%s\nstatus=ok\n" "$(date +%%Y-%%m-%%dT%%H:%%M:%%S%%z)" "$pid" > "$tmp" && mv "$tmp" "$hb"; sleep "$iv"; done' \
    "$hb_file" "$pane_pid" "$interval")

  # setsid + disown ensures the sidecar survives this script exiting.
  # stderr/stdout go to /dev/null; failures are non-fatal.
  if command -v setsid >/dev/null 2>&1; then
    setsid bash -c "$sidecar_script" </dev/null >/dev/null 2>&1 &
  else
    bash -c "$sidecar_script" </dev/null >/dev/null 2>&1 &
  fi
  disown $! 2>/dev/null || true
}

if [ -n "$PANE_PID" ]; then
  # Guard: do not let sidecar startup failures abort the launcher (set -e).
  _start_heartbeat_sidecar "$AGENT_NAME" "$PANE_PID" \
    "$MOSAIC_HEARTBEAT_RUN_DIR" "$MOSAIC_HEARTBEAT_INTERVAL" || \
    echo "WARNING: heartbeat sidecar could not be started for $AGENT_NAME" >&2
else
  echo "WARNING: could not resolve pane PID for $AGENT_NAME — heartbeat sidecar not started" >&2
fi