commit aae6cee886427fef8be9587100a0259bc7564c20
Author: m5r <mokhtar@mial.net>
Date:   Fri Apr 17 20:30:34 2026 +0200

    initial commit: geekworm x1208 ups prometheus exporter

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..f83240a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/build/
+/monitoring-overlay/*.original
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..62b3c65
--- /dev/null
+++ b/README.md
@@ -0,0 +1,49 @@
+# x1208-exporter
+
+One-shot Prometheus textfile exporter for the Geekworm X1208 UPS HAT on Raspberry Pi 5.
+
+Reads:
+
+- GPIO 6 (PLD) — `1` = AC plugged in, `0` = on battery.
+- I2C `0x36` (MAX17040 fuel gauge) — battery voltage and state of charge.
+
+Writes `/var/lib/node-exporter/textfiles/x1208.prom` atomically. node-exporter's
+textfile collector serves it at scrape time.
+
+## Metrics
+
+| Name                            | Type  | Description                                  |
+| ------------------------------- | ----- | -------------------------------------------- |
+| `rpi_ups_ac_power`              | gauge | `1` = AC present, `0` = on battery           |
+| `rpi_ups_voltage_volts`         | gauge | Battery cell voltage                         |
+| `rpi_ups_battery_percent`       | gauge | State of charge (0–100)                      |
+| `rpi_ups_last_update_seconds`   | gauge | Unix timestamp of last exporter run         |
+
+## Deploy
+
+```bash
+just deploy
+```
+
+Builds the arm64 binary, scps to `rpi`, installs systemd units, starts the timer.
+
+## Verify
+
+```bash
+just run-once   # forces one read, prints the prom file
+just logs       # journalctl tail
+```
+
+## How node-exporter picks it up
+
+The `monitoring` compose stack on the Pi must mount the textfile dir and pass
+the flag to node-exporter:
+
+```yaml
+node-exporter:
+  volumes:
+    - /var/lib/node-exporter/textfiles:/textfiles:ro
+  command:
+    - '--collector.textfile.directory=/textfiles'
+    # ...existing flags
+```
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..3d08c17
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,8 @@
+module github.com/mokhtar/x1208-exporter
+
+go 1.23
+
+require (
+	github.com/warthog618/go-gpiocdev v0.9.1
+	golang.org/x/sys v0.27.0
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..431bb30
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,16 @@
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/testify v1.9.0 h1:HtqpIVDClZ4nwg75+f6Lvsy/wHu+3BoSGCbBAcpTsTg=
+github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+github.com/warthog618/go-gpiocdev v0.9.1 h1:pwHPaqjJfhCipIQl78V+O3l9OKHivdRDdmgXYbmhuCI=
+github.com/warthog618/go-gpiocdev v0.9.1/go.mod h1:dN3e3t/S2aSNC+hgigGE/dBW8jE1ONk9bDSEYfoPyl8=
+github.com/warthog618/go-gpiosim v0.1.1 h1:MRAEv+T+itmw+3GeIGpQJBfanUVyg0l3JCTwHtwdre4=
+github.com/warthog618/go-gpiosim v0.1.1/go.mod h1:YXsnB+I9jdCMY4YAlMSRrlts25ltjmuIsrnoUrBLdqU=
+golang.org/x/sys v0.27.0 h1:wBqf8DvsY9Y/2P8gAfPDEYNuS30J4lPHJxXSb/nJZ+s=
+golang.org/x/sys v0.27.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
diff --git a/justfile b/justfile
new file mode 100644
index 0000000..edb700b
--- /dev/null
+++ b/justfile
@@ -0,0 +1,23 @@
+default:
+    @just --list
+
+build:
+    GOOS=linux GOARCH=arm64 go build -ldflags="-s -w" -o build/x1208-exporter ./...
+
+deploy: build
+    scp build/x1208-exporter rpi:/tmp/x1208-exporter
+    scp systemd/x1208-exporter.service systemd/x1208-exporter.timer rpi:/tmp/
+    ssh rpi 'sudo install -m 0755 /tmp/x1208-exporter /usr/local/bin/x1208-exporter && \
+        sudo install -m 0644 /tmp/x1208-exporter.service /etc/systemd/system/ && \
+        sudo install -m 0644 /tmp/x1208-exporter.timer /etc/systemd/system/ && \
+        sudo install -d -m 0755 -o root /var/lib/node-exporter/textfiles && \
+        sudo systemctl daemon-reload && \
+        sudo systemctl enable --now x1208-exporter.timer && \
+        sudo systemctl start x1208-exporter.service && \
+        cat /var/lib/node-exporter/textfiles/x1208.prom'
+
+logs:
+    ssh rpi 'journalctl -u x1208-exporter.service -n 30 --no-pager'
+
+run-once:
+    ssh rpi 'sudo systemctl start x1208-exporter.service && cat /var/lib/node-exporter/textfiles/x1208.prom'
diff --git a/main.go b/main.go
new file mode 100644
index 0000000..93693a8
--- /dev/null
+++ b/main.go
@@ -0,0 +1,181 @@
+package main
+
+import (
+	"encoding/binary"
+	"flag"
+	"fmt"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/warthog618/go-gpiocdev"
+	"golang.org/x/sys/unix"
+)
+
+const (
+	i2cDev      = "/dev/i2c-1"
+	gpioChip    = "gpiochip0"
+	gpioPLDPin  = 6
+	maxAddr     = 0x36
+	regVoltage  = 0x02
+	regCapacity = 0x04
+	i2cSlave    = 0x0703 // I2C_SLAVE
+	maxRetries  = 3
+)
+
+func readI2CWord(fd int, reg byte) (uint16, error) {
+	if _, err := unix.Write(fd, []byte{reg}); err != nil {
+		return 0, fmt.Errorf("write reg: %w", err)
+	}
+	buf := make([]byte, 2)
+	n, err := unix.Read(fd, buf)
+	if err != nil {
+		return 0, fmt.Errorf("read: %w", err)
+	}
+	if n != 2 {
+		return 0, fmt.Errorf("short read: %d bytes", n)
+	}
+	return binary.BigEndian.Uint16(buf), nil
+}
+
+func readI2CWordRetry(fd int, reg byte, validate func(uint16) bool) (uint16, error) {
+	var lastErr error
+	for i := 0; i < maxRetries; i++ {
+		v, err := readI2CWord(fd, reg)
+		if err == nil && validate(v) {
+			return v, nil
+		}
+		if err != nil {
+			lastErr = err
+		} else {
+			lastErr = fmt.Errorf("read out of range: 0x%04x", v)
+		}
+		time.Sleep(20 * time.Millisecond)
+	}
+	return 0, lastErr
+}
+
+func readBattery() (voltage float64, percent float64, err error) {
+	fd, err := unix.Open(i2cDev, unix.O_RDWR, 0)
+	if err != nil {
+		return 0, 0, fmt.Errorf("open %s: %w", i2cDev, err)
+	}
+	defer unix.Close(fd)
+
+	if err := unix.IoctlSetInt(fd, i2cSlave, maxAddr); err != nil {
+		return 0, 0, fmt.Errorf("ioctl I2C_SLAVE: %w", err)
+	}
+
+	rawV, err := readI2CWordRetry(fd, regVoltage, func(v uint16) bool {
+		f := float64(v) * 1.25 / 1000 / 16
+		return f > 2.0 && f < 5.0
+	})
+	if err != nil {
+		return 0, 0, fmt.Errorf("voltage: %w", err)
+	}
+	voltage = float64(rawV) * 1.25 / 1000 / 16
+
+	rawC, err := readI2CWordRetry(fd, regCapacity, func(v uint16) bool {
+		return float64(v)/256 <= 110
+	})
+	if err != nil {
+		return 0, 0, fmt.Errorf("capacity: %w", err)
+	}
+	percent = float64(rawC) / 256
+	return voltage, percent, nil
+}
+
+func readACPower() (int, error) {
+	line, err := gpiocdev.RequestLine(gpioChip, gpioPLDPin,
+		gpiocdev.AsInput,
+		gpiocdev.WithConsumer("x1208-exporter"))
+	if err != nil {
+		return 0, fmt.Errorf("request gpio: %w", err)
+	}
+	defer line.Close()
+
+	v, err := line.Value()
+	if err != nil {
+		return 0, fmt.Errorf("read gpio: %w", err)
+	}
+	return v, nil
+}
+
+func writeAtomic(path string, content string) error {
+	dir := filepath.Dir(path)
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return err
+	}
+	tmp, err := os.CreateTemp(dir, ".x1208.*.tmp")
+	if err != nil {
+		return err
+	}
+	tmpPath := tmp.Name()
+	defer os.Remove(tmpPath)
+	if _, err := tmp.WriteString(content); err != nil {
+		tmp.Close()
+		return err
+	}
+	if err := tmp.Chmod(0o644); err != nil {
+		tmp.Close()
+		return err
+	}
+	if err := tmp.Close(); err != nil {
+		return err
+	}
+	return os.Rename(tmpPath, path)
+}
+
+func main() {
+	out := flag.String("out", "/var/lib/node-exporter/textfiles/x1208.prom", "output prom file")
+	flag.Parse()
+
+	var (
+		ac           int
+		voltage      float64
+		percent      float64
+		acErr, batErr error
+	)
+
+	ac, acErr = readACPower()
+	voltage, percent, batErr = readBattery()
+
+	if acErr != nil && batErr != nil {
+		fmt.Fprintf(os.Stderr, "all reads failed: ac=%v bat=%v\n", acErr, batErr)
+		os.Exit(1)
+	}
+
+	now := time.Now().Unix()
+	var content string
+	content += "# HELP rpi_ups_last_update_seconds Unix timestamp of last successful exporter run.\n"
+	content += "# TYPE rpi_ups_last_update_seconds gauge\n"
+	content += fmt.Sprintf("rpi_ups_last_update_seconds %d\n", now)
+
+	if acErr == nil {
+		content += "# HELP rpi_ups_ac_power AC adapter present (1=plugged in, 0=on battery).\n"
+		content += "# TYPE rpi_ups_ac_power gauge\n"
+		content += fmt.Sprintf("rpi_ups_ac_power %d\n", ac)
+	} else {
+		fmt.Fprintf(os.Stderr, "ac read failed: %v\n", acErr)
+	}
+
+	if batErr == nil {
+		content += "# HELP rpi_ups_voltage_volts Battery cell voltage from MAX17040 fuel gauge.\n"
+		content += "# TYPE rpi_ups_voltage_volts gauge\n"
+		content += fmt.Sprintf("rpi_ups_voltage_volts %.3f\n", voltage)
+		content += "# HELP rpi_ups_battery_percent Battery state of charge from MAX17040 fuel gauge.\n"
+		content += "# TYPE rpi_ups_battery_percent gauge\n"
+		content += fmt.Sprintf("rpi_ups_battery_percent %.2f\n", percent)
+	} else {
+		fmt.Fprintf(os.Stderr, "battery read failed: %v\n", batErr)
+	}
+
+	if err := writeAtomic(*out, content); err != nil {
+		fmt.Fprintf(os.Stderr, "write %s: %v\n", *out, err)
+		os.Exit(1)
+	}
+
+	if acErr != nil || batErr != nil {
+		os.Exit(1)
+	}
+}
diff --git a/monitoring-overlay/README.md b/monitoring-overlay/README.md
new file mode 100644
index 0000000..91aff57
--- /dev/null
+++ b/monitoring-overlay/README.md
@@ -0,0 +1,26 @@
+# Monitoring overlay for the Pi
+
+These two files are the desired state of `/home/mokhtar/app/monitoring/` on the Pi
+after the X1208 exporter is in place. The `.original` siblings are snapshots of
+what's there right now (pulled with `ssh rpi cat ...`).
+
+## Diff summary
+
+**`compose.yaml`** — node-exporter service:
+
+- Add volume `/var/lib/node-exporter/textfiles:/textfiles:ro`
+- Add command flag `--collector.textfile.directory=/textfiles`
+
+**`prometheus.yaml`** — global block:
+
+- Add `external_labels: { host: rpi }` so metrics are tagged in Grafana Cloud
+  (instead of relying on the Docker service name as `instance`).
+
+## Apply
+
+```bash
+scp compose.yaml prometheus.yaml rpi:/home/mokhtar/app/monitoring/
+ssh rpi 'cd /home/mokhtar/app/monitoring && docker compose up -d'
+```
+
+This recreates the node-exporter container (~2s blip) and reloads Prometheus.
diff --git a/monitoring-overlay/compose.yaml b/monitoring-overlay/compose.yaml
new file mode 100644
index 0000000..656393d
--- /dev/null
+++ b/monitoring-overlay/compose.yaml
@@ -0,0 +1,42 @@
+services:
+  node-exporter:
+    image: prom/node-exporter:latest
+    hostname: node-exporter
+    restart: unless-stopped
+    volumes:
+      - /proc:/host/proc:ro
+      - /sys:/host/sys:ro
+      - /:/rootfs:ro
+      - /var/lib/node-exporter/textfiles:/textfiles:ro
+    command:
+      - '--path.procfs=/host/proc'
+      - '--path.rootfs=/rootfs'
+      - '--path.sysfs=/host/sys'
+      - '--collector.filesystem.mount-points-exclude=^/(sys|proc|dev|host|etc)($$|/)'
+      - '--collector.textfile.directory=/textfiles'
+      - '--web.telemetry-path=/_prom/metrics'
+    expose:
+      - 9100
+    networks:
+      - monitoring-network
+    logging:
+      driver: journald
+      options:
+        tag: "container-{{.Name}}"
+
+  prometheus:
+    image: prom/prometheus:latest
+    restart: unless-stopped
+    depends_on:
+      - node-exporter
+    volumes:
+      - "./prometheus.yaml:/etc/prometheus/prometheus.yml"
+    networks:
+      - monitoring-network
+    logging:
+      driver: journald
+      options:
+        tag: "container-{{.Name}}"
+
+networks:
+  monitoring-network:
diff --git a/monitoring-overlay/prometheus.yaml b/monitoring-overlay/prometheus.yaml
new file mode 100644
index 0000000..3d16e78
--- /dev/null
+++ b/monitoring-overlay/prometheus.yaml
@@ -0,0 +1,16 @@
+global:
+  scrape_interval: 60s
+  external_labels:
+    host: rpi
+
+scrape_configs:
+  - job_name: scrape_mokhtar-rpi
+    metrics_path: /_prom/metrics
+    static_configs:
+      - targets: ['node-exporter:9100']
+
+remote_write:
+  - url: 'https://prometheus-prod-39-prod-eu-north-0.grafana.net/api/prom/push'
+    basic_auth:
+      username: '1830601'
+      password: 'glc_eyJvIjoiNTM3NDYzIiwibiI6InN0YWNrLTEwNTY4MDYtaG0td3JpdGUtcHJvbWV0aGV1cy1ycGkiLCJrIjoidDlXblM2ME1EMTNNMEpKM2IycDBTMWt1IiwibSI6eyJyIjoicHJvZC1ldS1ub3J0aC0wIn19'
diff --git a/systemd/x1208-exporter.service b/systemd/x1208-exporter.service
new file mode 100644
index 0000000..45b0b6b
--- /dev/null
+++ b/systemd/x1208-exporter.service
@@ -0,0 +1,15 @@
+[Unit]
+Description=Geekworm X1208 UPS metrics exporter (one-shot)
+After=local-fs.target
+
+[Service]
+Type=oneshot
+ExecStart=/usr/local/bin/x1208-exporter
+Nice=10
+ProtectSystem=strict
+ReadWritePaths=/var/lib/node-exporter/textfiles
+ProtectHome=true
+PrivateTmp=true
+NoNewPrivileges=true
+DeviceAllow=/dev/i2c-1 rw
+DeviceAllow=/dev/gpiochip0 rw
diff --git a/systemd/x1208-exporter.timer b/systemd/x1208-exporter.timer
new file mode 100644
index 0000000..d40a168
--- /dev/null
+++ b/systemd/x1208-exporter.timer
@@ -0,0 +1,11 @@
+[Unit]
+Description=Run X1208 UPS metrics exporter every 30s
+
+[Timer]
+OnBootSec=30s
+OnUnitActiveSec=30s
+AccuracySec=1s
+Unit=x1208-exporter.service
+
+[Install]
+WantedBy=timers.target