#!/usr/bin/env bash
# Test: high latency slows first read; cached second read is much faster
#
# Injects 500 ms of latency via tc netem, reads a 100 KB file (cold cache),
# then removes the latency and reads the same file again (warm cache).
# The second read should be significantly faster because it hits the VFS
# cache and skips the network round-trip.
set -euo pipefail
SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
source "$SCRIPT_DIR/../harness/helpers.sh"
source "$SCRIPT_DIR/../harness/mock-nas.sh"

require_root
setup_test_env
trap teardown_test_env EXIT

# --- Arrange ---
start_mock_nas
nas_create_file "file.dat" 100              # 100 KB

gen_config

start_warpgate
wait_for_mount
wait_for_rc_api

# --- Act ---
# Inject 500 ms latency on the host-side veth
inject_latency 500

# Time the first read (cold cache, over high-latency link)
time1_start=$(date +%s%N)
cat "$TEST_MOUNT/file.dat" > /dev/null
time1_end=$(date +%s%N)

first_read_ns=$(( time1_end - time1_start ))

# Remove latency injection
clear_network_injection

# Time the second read (should come from local VFS cache)
time2_start=$(date +%s%N)
cat "$TEST_MOUNT/file.dat" > /dev/null
time2_end=$(date +%s%N)

second_read_ns=$(( time2_end - time2_start ))

# --- Assert ---
first_read_ms=$(( first_read_ns / 1000000 ))
second_read_ms=$(( second_read_ns / 1000000 ))

echo "  first read:  ${first_read_ms} ms (cold cache, 500 ms netem delay)"
echo "  second read: ${second_read_ms} ms (warm cache, no injection)"

# The cached read should be at least 5x faster than the latency-impacted read.
# With 500 ms netem the first read is typically > 500 ms; a cached read is < 50 ms.
if [[ "$first_read_ms" -gt 0 ]] && [[ $(( second_read_ms * 5 )) -lt "$first_read_ms" ]]; then
    echo "  cache speedup confirmed (>5x)"
else
    echo "FAIL: cached read was not significantly faster than the high-latency read" >&2
    echo "  first_read_ms=$first_read_ms  second_read_ms=$second_read_ms" >&2
    exit 1
fi

echo "PASS: $(basename "$0" .sh)"