package webapp

import (
	"os"
	"path/filepath"
	"testing"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
)

// makeFakeMetricsProc writes a minimal /proc tree with stat, meminfo,
// loadavg, uptime, and net/dev files so CollectSnapshot can parse
// it without a real /proc.
func makeFakeMetricsProc(t *testing.T) string {
	t.Helper()
	root := t.TempDir()
	require.NoError(t, os.WriteFile(filepath.Join(root, "stat"), []byte(statFixture), 0o644))
	require.NoError(t, os.WriteFile(filepath.Join(root, "meminfo"), []byte(meminfoFixture), 0o644))
	require.NoError(t, os.WriteFile(filepath.Join(root, "loadavg"), []byte(loadavgFixture), 0o644))
	require.NoError(t, os.WriteFile(filepath.Join(root, "uptime"), []byte(uptimeFixture), 0o644))
	require.NoError(t, os.MkdirAll(filepath.Join(root, "net"), 0o755))
	require.NoError(t, os.WriteFile(filepath.Join(root, "net", "dev"), []byte(netdevFixture), 0o644))
	require.NoError(t, os.WriteFile(filepath.Join(root, "mounts"), []byte(mountsFixture), 0o644))
	return root
}

const statFixture = `cpu  100 0 50 800 20 0 0 0 0 0
cpu0 25 0 12 200 5 0 0 0 0 0
intr 12345 0 0 0
ctxt 78910
btime 1700000000
`

const meminfoFixture = `MemTotal:       16384000 kB
MemFree:         4096000 kB
MemAvailable:    8192000 kB
Buffers:          512000 kB
Cached:          2048000 kB
SwapCached:            0 kB
SwapTotal:       2048000 kB
SwapFree:        2048000 kB
`

const loadavgFixture = "0.42 0.85 1.23 1/123 4567\n"

const uptimeFixture = "12345.67\n"

const netdevFixture = `Inter-|   Receive                                                |  Transmit
 face |bytes    packets errs drop fifo frame compressed multicast|bytes    packets errs drop fifo colls carrier compressed
    lo: 1000000    1000    0    0    0     0          0         0  1000000    1000    0    0    0     0       0          0
  eth0: 9999999    5000    1    2    0     0          0         0  8888888    4500    0    0    0     0       0          0
`

const mountsFixture = `/dev/sda1 / ext4 rw,relatime 0 0
tmpfs /run tmpfs rw,nosuid 0 0
`

func TestReadProcStatPercentages(t *testing.T) {
	root := t.TempDir()
	require.NoError(t, os.WriteFile(filepath.Join(root, "stat"), []byte(statFixture), 0o644))
	cpu, err := readProcStat(filepath.Join(root, "stat"))
	require.NoError(t, err)
	// Fixture: user=100, nice=0, system=50, idle=800, iowait=20, steal=0
	// Total = 970, idle+iowait = 820, busy = 150.
	assert.InDelta(t, 10.31, cpu.UserPct, 0.01)
	assert.InDelta(t, 5.15, cpu.SystemPct, 0.01)
	assert.InDelta(t, 82.47, cpu.IdlePct, 0.01)
	assert.InDelta(t, 15.46, cpu.TotalPct, 0.01)
}

func TestReadMemInfoBytes(t *testing.T) {
	root := t.TempDir()
	require.NoError(t, os.WriteFile(filepath.Join(root, "meminfo"), []byte(meminfoFixture), 0o644))
	mem, err := readMemInfo(filepath.Join(root, "meminfo"))
	require.NoError(t, err)
	assert.Equal(t, uint64(16384000*1024), mem.Total)
	assert.Equal(t, uint64(8192000*1024), mem.Available)
	assert.Equal(t, uint64(2048000*1024), mem.SwapTotal)
	// used = total - available = 8192 MiB
	// pct = 8192 / 16384 * 100 = 50.00
	assert.InDelta(t, 50.0, mem.UsedPct, 0.01)
}

func TestReadLoadAvg(t *testing.T) {
	root := t.TempDir()
	require.NoError(t, os.WriteFile(filepath.Join(root, "loadavg"), []byte(loadavgFixture), 0o644))
	load, err := readLoadAvg(filepath.Join(root, "loadavg"))
	require.NoError(t, err)
	assert.InDelta(t, 0.42, load.One, 0.001)
	assert.InDelta(t, 0.85, load.Five, 0.001)
	assert.InDelta(t, 1.23, load.Fifteen, 0.001)
}

func TestReadUptime(t *testing.T) {
	root := t.TempDir()
	require.NoError(t, os.WriteFile(filepath.Join(root, "uptime"), []byte(uptimeFixture), 0o644))
	d, err := readUptime(filepath.Join(root, "uptime"))
	require.NoError(t, err)
	assert.InDelta(t, 12345.67, d.Seconds(), 0.01)
}

func TestReadNetDev(t *testing.T) {
	root := t.TempDir()
	require.NoError(t, os.MkdirAll(filepath.Join(root, "net"), 0o755))
	require.NoError(t, os.WriteFile(filepath.Join(root, "net", "dev"), []byte(netdevFixture), 0o644))
	ifaces, err := readNetDev(filepath.Join(root, "net", "dev"))
	require.NoError(t, err)
	require.Len(t, ifaces, 2)
	eth := ifaces[1]
	assert.Equal(t, "eth0", eth.Name)
	assert.Equal(t, uint64(9999999), eth.RxBytes)
	assert.Equal(t, uint64(8888888), eth.TxBytes)
	assert.Equal(t, uint64(5000), eth.RxPkt)
	assert.Equal(t, uint64(1), eth.RxErr)
}

func TestReadMounts(t *testing.T) {
	root := t.TempDir()
	require.NoError(t, os.WriteFile(filepath.Join(root, "mounts"), []byte(mountsFixture), 0o644))
	mounts, err := readMounts(filepath.Join(root, "mounts"))
	require.NoError(t, err)
	require.Len(t, mounts, 2)
	assert.Equal(t, "/", mounts[0].Mount)
	assert.Equal(t, "ext4", mounts[0].FSType)
}

func TestCollectSnapshotEndToEnd(t *testing.T) {
	root := makeFakeMetricsProc(t)
	snap, err := CollectSnapshot(root)
	require.NoError(t, err)
	assert.InDelta(t, 15.46, snap.CPU.TotalPct, 0.5,
		"CPU busy should be in the expected range")
	assert.InDelta(t, 50.0, snap.Memory.UsedPct, 0.5,
		"memory used should be ~50% from the fixture")
	assert.InDelta(t, 12345.67, snap.Uptime.Seconds(), 0.5)
	require.Len(t, snap.Networks, 2)
	require.Len(t, snap.Disks, 2)
	assert.False(t, snap.BootAt.IsZero(), "boot time must be derivable")
}