// Package textfile renders and writes the Prometheus textfile that
// node-exporter's textfile collector scrapes.
package textfile

import (
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"git.mial.net/mokhtar/x1208-exporter/internal/sensor"
)

// Render returns the exposition text for the last complete sample.
//
// The first four metrics are byte-identical to the pre-daemon exporter. Their
// names and value formatting are referenced by Grafana alerts and by the
// dashboard, so they must not change. The golden test locks this.
//
// healthy reports the outcome of the most recent read attempt; failures counts
// failed attempts since process start. Both are additive and safe to scrape.
//
// When a read fails the caller re-renders the PREVIOUS sample with healthy=0.
// rpi_ups_last_update_seconds therefore stops advancing, which is what the
// RpiUpsExporterStale alert measures, while the failure stays visible instead
// of being hidden behind a frozen file.
func Render(s sensor.Reading, healthy bool, failures uint64) string {
	ac := 0
	if s.ACPresent {
		ac = 1
	}
	health := 0
	if healthy {
		health = 1
	}

	var b strings.Builder
	b.WriteString("# HELP rpi_ups_last_update_seconds Unix timestamp of last successful exporter run.\n")
	b.WriteString("# TYPE rpi_ups_last_update_seconds gauge\n")
	fmt.Fprintf(&b, "rpi_ups_last_update_seconds %d\n", s.At.Unix())
	b.WriteString("# HELP rpi_ups_ac_power AC adapter present (1=plugged in, 0=on battery).\n")
	b.WriteString("# TYPE rpi_ups_ac_power gauge\n")
	fmt.Fprintf(&b, "rpi_ups_ac_power %d\n", ac)
	b.WriteString("# HELP rpi_ups_voltage_volts Battery cell voltage from MAX17040 fuel gauge.\n")
	b.WriteString("# TYPE rpi_ups_voltage_volts gauge\n")
	fmt.Fprintf(&b, "rpi_ups_voltage_volts %.3f\n", s.Volts)
	b.WriteString("# HELP rpi_ups_battery_percent Battery state of charge from MAX17040 fuel gauge.\n")
	b.WriteString("# TYPE rpi_ups_battery_percent gauge\n")
	fmt.Fprintf(&b, "rpi_ups_battery_percent %.2f\n", s.SOC)
	b.WriteString("# HELP rpi_ups_sensor_healthy Whether the most recent UPS read succeeded (1=yes, 0=no).\n")
	b.WriteString("# TYPE rpi_ups_sensor_healthy gauge\n")
	fmt.Fprintf(&b, "rpi_ups_sensor_healthy %d\n", health)
	b.WriteString("# HELP rpi_ups_read_failures_total Cumulative failed UPS reads since exporter start.\n")
	b.WriteString("# TYPE rpi_ups_read_failures_total counter\n")
	fmt.Fprintf(&b, "rpi_ups_read_failures_total %d\n", failures)
	return b.String()
}

// WriteAtomic writes content to path via a temporary file and a rename, so a
// scrape never observes a half-written file.
func WriteAtomic(path, 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)
}