package main

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

// Node is a single unibus cluster member to probe. Name is the logical node
// label ("magnus", "homer", "datardos"); URL is its full /healthz endpoint
// (e.g. https://135.125.201.30:8470/healthz).
type Node struct {
	Name string `json:"name"`
	URL  string `json:"url"`
}

// Config is the exporter runtime configuration, read from a JSON file. It holds
// the list of unibus nodes to probe, the cluster CA used to verify their TLS,
// the VictoriaMetrics ingest endpoint and its basic-auth credentials.
//
// Secrets (pass) live only in this file (chmod 600) or come from the environment
// — never in argv. The example config carries a placeholder, not the real one.
type Config struct {
	Nodes       []Node            `json:"nodes"`         // unibus members to probe
	CACertPath  string            `json:"ca_cert_path"`  // PEM CA of the unibus cluster, used to verify each node's TLS
	HubURL      string            `json:"hub_url"`       // VictoriaMetrics import endpoint (…/api/v1/import/prometheus)
	User        string            `json:"user"`          // basic-auth user for the hub (empty disables auth)
	Pass        string            `json:"pass"`          // basic-auth password for the hub
	IntervalSec int               `json:"interval_sec"`  // scrape+push period in seconds (default 15)
	TimeoutSec  int               `json:"timeout_sec"`   // per-node healthz GET timeout in seconds (default 8)
	Labels      map[string]string `json:"labels"`        // extra labels added to every series via extra_label (e.g. {"job":"unibus_exporter"})
}

// loadConfig reads and validates the JSON config at path. Environment overrides:
// UNIBUS_HUB_URL, UNIBUS_USER, UNIBUS_PASS, UNIBUS_CA_CERT, UNIBUS_INTERVAL.
func loadConfig(path string) (Config, error) {
	cfg := Config{IntervalSec: 15, TimeoutSec: 8}
	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("UNIBUS_HUB_URL"); v != "" {
		cfg.HubURL = v
	}
	if v := os.Getenv("UNIBUS_USER"); v != "" {
		cfg.User = v
	}
	if v := os.Getenv("UNIBUS_PASS"); v != "" {
		cfg.Pass = v
	}
	if v := os.Getenv("UNIBUS_CA_CERT"); v != "" {
		cfg.CACertPath = v
	}
	if v := os.Getenv("UNIBUS_INTERVAL"); v != "" {
		if n, err := parsePositiveInt(v); err == nil {
			cfg.IntervalSec = n
		}
	}
	if cfg.IntervalSec <= 0 {
		cfg.IntervalSec = 15
	}
	if cfg.TimeoutSec <= 0 {
		cfg.TimeoutSec = 8
	}
	if cfg.Labels == nil {
		cfg.Labels = map[string]string{"job": "unibus_exporter"}
	} else if _, ok := cfg.Labels["job"]; !ok {
		cfg.Labels["job"] = "unibus_exporter"
	}
	return cfg, validate(cfg)
}

func validate(cfg Config) error {
	if cfg.HubURL == "" {
		return fmt.Errorf("hub_url is required")
	}
	if len(cfg.Nodes) == 0 {
		return fmt.Errorf("at least one node is required")
	}
	if cfg.CACertPath == "" {
		return fmt.Errorf("ca_cert_path is required (PEM CA of the unibus cluster)")
	}
	for i, n := range cfg.Nodes {
		if n.Name == "" || n.URL == "" {
			return fmt.Errorf("node[%d]: name and url are required", i)
		}
	}
	return nil
}

func parsePositiveInt(s string) (int, error) {
	var n int
	_, err := fmt.Sscanf(s, "%d", &n)
	if err != nil {
		return 0, err
	}
	if n <= 0 {
		return 0, fmt.Errorf("not positive")
	}
	return n, nil
}