package main

import (
	"encoding/json"
	"os"
	"strconv"
)

// Config holds the agent runtime configuration. It is read from an optional
// JSON file and can be overridden by environment variables, which is handy for
// systemd drop-ins and for deploying the same binary to many nodes.
type Config struct {
	Node        string `json:"node"`         // value of the "instance" label attached to every series
	HubURL      string `json:"hub_url"`      // full metrics ingest URL, e.g. https://metrics-…/api/v1/import/prometheus
	LokiURL     string `json:"loki_url"`     // full Loki push URL, e.g. https://logs-…/loki/api/v1/push (empty disables log shipping)
	User        string `json:"user"`         // basic-auth user, shared by metrics and logs (empty disables auth)
	Pass        string `json:"pass"`         // basic-auth password
	IntervalSec int    `json:"interval_sec"` // metrics push period in seconds (default 15)
	// Extra labels attached to every metric series and log stream of this node,
	// e.g. {"role": "vps"}. Enables filtering in Grafana (per-role dashboards).
	Labels map[string]string `json:"labels"`
	// Android/Termux exec workaround: the standard Go binary cannot exec
	// subprocesses there (seccomp blocks pidfd_open with SIGSYS). When set, the
	// agent reads battery JSON from this file (written by a shell helper) instead
	// of running termux-battery-status itself.
	BatteryFile string `json:"battery_file"`
	// When set, the agent tails this log file (written by a shell `logcat`
	// helper) and ships it to Loki, instead of exec-ing journald/logcat.
	LogFile string `json:"log_file"`
}

// defaultConfig returns the baseline configuration: the machine hostname as the
// node name and a 15-second push interval.
func defaultConfig() Config {
	host, _ := os.Hostname()
	return Config{Node: host, IntervalSec: 15}
}

// loadConfig reads the JSON file at path (when non-empty) and then applies
// environment overrides. Recognised env vars: FLEET_NODE, FLEET_HUB_URL,
// FLEET_USER, FLEET_PASS, FLEET_INTERVAL.
func loadConfig(path string) (Config, error) {
	cfg := defaultConfig()
	if path != "" {
		b, err := os.ReadFile(path)
		if err != nil {
			return cfg, err
		}
		if err := json.Unmarshal(b, &cfg); err != nil {
			return cfg, err
		}
	}
	if v := os.Getenv("FLEET_NODE"); v != "" {
		cfg.Node = v
	}
	if v := os.Getenv("FLEET_HUB_URL"); v != "" {
		cfg.HubURL = v
	}
	if v := os.Getenv("FLEET_LOKI_URL"); v != "" {
		cfg.LokiURL = v
	}
	if v := os.Getenv("FLEET_BATTERY_FILE"); v != "" {
		cfg.BatteryFile = v
	}
	if v := os.Getenv("FLEET_LOG_FILE"); v != "" {
		cfg.LogFile = v
	}
	if v := os.Getenv("FLEET_USER"); v != "" {
		cfg.User = v
	}
	if v := os.Getenv("FLEET_PASS"); v != "" {
		cfg.Pass = v
	}
	if v := os.Getenv("FLEET_INTERVAL"); v != "" {
		if n, err := strconv.Atoi(v); err == nil && n > 0 {
			cfg.IntervalSec = n
		}
	}
	if cfg.IntervalSec <= 0 {
		cfg.IntervalSec = 15
	}
	if cfg.Node == "" {
		cfg.Node, _ = os.Hostname()
	}
	return cfg, nil
}

// extraLabels returns the labels attached to every series/stream: the node's
// instance plus any custom labels (e.g. role). The optional extra map is merged
// last (used to add per-stream labels like job/unit for logs).
func (cfg Config) extraLabels(extra map[string]string) map[string]string {
	m := map[string]string{"instance": cfg.Node}
	for k, v := range cfg.Labels {
		m[k] = v
	}
	for k, v := range extra {
		m[k] = v
	}
	return m
}