package config

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

type Config struct {
	BackendURL        string `json:"backendUrl"`
	Identifier        string `json:"identifier"`
	APIKey            string `json:"apiKey"`
	ReportIntervalSec int    `json:"reportIntervalSec"`
	LogLevel          string `json:"logLevel"`
	RootFS            string `json:"rootFs"`
	MonitorPort       int    `json:"monitorPort"`
}

type Overrides struct {
	BackendURL        string
	Identifier        string
	APIKey            string
	ReportIntervalSec int
	LogLevel          string
	RootFS            string
	MonitorPort       int
}

func Load(path string) (Config, error) {
	return LoadWithOverrides(path, Overrides{})
}

func LoadWithOverrides(path string, overrides Overrides) (Config, error) {
	// If running inside a container with the host FS bind-mounted, prefer
	// the host's /etc/hostname for the default identifier. The container's
	// own os.Hostname() is a docker-assigned random string under
	// network_mode: host (UTS namespace is not shared).
	rootFSEarly := getenvAny([]string{"HF_MONITER_ROOTFS", "HF_MONITOR_ROOTFS"}, "")
	defaultIdentifier := hostHostname(rootFSEarly)
	if defaultIdentifier == "" {
		defaultIdentifier = hostnameOr("unknown-host")
	}

	cfg := Config{
		BackendURL:        getenvAny([]string{"HF_MONITER_BACKEND_URL", "HF_MONITOR_BACKEND_URL"}, "https://monitor.hangman-lab.top"),
		Identifier:        getenvAny([]string{"HF_MONITER_IDENTIFIER", "HF_MONITOR_IDENTIFIER"}, defaultIdentifier),
		APIKey:            getenvAny([]string{"HF_MONITER_API_KEY", "HF_MONITOR_API_KEY"}, ""),
		ReportIntervalSec: getenvIntAny([]string{"HF_MONITER_REPORT_INTERVAL", "HF_MONITOR_REPORT_INTERVAL"}, 30),
		LogLevel:          getenvAny([]string{"HF_MONITER_LOG_LEVEL", "HF_MONITOR_LOG_LEVEL"}, "info"),
		RootFS:            getenvAny([]string{"HF_MONITER_ROOTFS", "HF_MONITOR_ROOTFS"}, ""),
	}

	if path != "" {
		if fileCfg, err := loadFile(path); err == nil {
			merge(&cfg, fileCfg)
		} else if !os.IsNotExist(err) {
			return cfg, fmt.Errorf("load config file: %w", err)
		}
	}

	// env always wins over file
	cfg.BackendURL = getenvAny([]string{"HF_MONITER_BACKEND_URL", "HF_MONITOR_BACKEND_URL"}, cfg.BackendURL)
	cfg.Identifier = getenvAny([]string{"HF_MONITER_IDENTIFIER", "HF_MONITOR_IDENTIFIER"}, cfg.Identifier)
	if v := getenvAny([]string{"HF_MONITER_API_KEY", "HF_MONITOR_API_KEY"}, ""); v != "" {
		cfg.APIKey = v
	}
	cfg.ReportIntervalSec = getenvIntAny([]string{"HF_MONITER_REPORT_INTERVAL", "HF_MONITOR_REPORT_INTERVAL"}, cfg.ReportIntervalSec)
	cfg.LogLevel = getenvAny([]string{"HF_MONITER_LOG_LEVEL", "HF_MONITOR_LOG_LEVEL"}, cfg.LogLevel)
	cfg.RootFS = getenvAny([]string{"HF_MONITER_ROOTFS", "HF_MONITOR_ROOTFS"}, cfg.RootFS)
	cfg.MonitorPort = getenvIntAny([]string{"MONITOR_PORT", "HF_MONITOR_PORT"}, cfg.MonitorPort)

	if overrides.BackendURL != "" {
		cfg.BackendURL = overrides.BackendURL
	}
	if overrides.Identifier != "" {
		cfg.Identifier = overrides.Identifier
	}
	if overrides.APIKey != "" {
		cfg.APIKey = overrides.APIKey
	}
	if overrides.ReportIntervalSec > 0 {
		cfg.ReportIntervalSec = overrides.ReportIntervalSec
	}
	if overrides.LogLevel != "" {
		cfg.LogLevel = overrides.LogLevel
	}
	if overrides.RootFS != "" {
		cfg.RootFS = overrides.RootFS
	}
	if overrides.MonitorPort > 0 {
		cfg.MonitorPort = overrides.MonitorPort
	}

	if cfg.BackendURL == "" {
		return cfg, fmt.Errorf("backendUrl is required")
	}
	if cfg.Identifier == "" {
		return cfg, fmt.Errorf("identifier is required")
	}
	if cfg.ReportIntervalSec <= 0 {
		cfg.ReportIntervalSec = 30
	}
	applyHostFSEnv(cfg.RootFS)
	return cfg, nil
}

func loadFile(path string) (Config, error) {
	var cfg Config
	buf, err := os.ReadFile(path)
	if err != nil {
		return cfg, err
	}
	if err := json.Unmarshal(buf, &cfg); err != nil {
		return cfg, err
	}
	return cfg, nil
}

func merge(dst *Config, src Config) {
	if src.BackendURL != "" {
		dst.BackendURL = src.BackendURL
	}
	if src.Identifier != "" {
		dst.Identifier = src.Identifier
	}
	if src.APIKey != "" {
		dst.APIKey = src.APIKey
	}
	if src.ReportIntervalSec > 0 {
		dst.ReportIntervalSec = src.ReportIntervalSec
	}
	if src.LogLevel != "" {
		dst.LogLevel = src.LogLevel
	}
	if src.RootFS != "" {
		dst.RootFS = src.RootFS
	}
	if src.MonitorPort > 0 {
		dst.MonitorPort = src.MonitorPort
	}
}

func getenvAny(keys []string, fallback string) string {
	for _, key := range keys {
		if v := os.Getenv(key); v != "" {
			return v
		}
	}
	return fallback
}

func getenvIntAny(keys []string, fallback int) int {
	for _, key := range keys {
		if v := os.Getenv(key); v != "" {
			var out int
			if _, err := fmt.Sscanf(v, "%d", &out); err == nil && out > 0 {
				return out
			}
		}
	}
	return fallback
}

func hostnameOr(fallback string) string {
	if name, err := os.Hostname(); err == nil && name != "" {
		return name
	}
	return fallback
}

// hostHostname reads the hostname from <rootFS>/etc/hostname. Used when
// Monitor runs inside a container and wants the host's hostname rather
// than the container's UTS namespace hostname (which docker randomizes
// unless hostname: is set).
func hostHostname(rootFS string) string {
	if rootFS == "" {
		return ""
	}
	buf, err := os.ReadFile(filepath.Join(rootFS, "etc", "hostname"))
	if err != nil {
		return ""
	}
	return strings.TrimSpace(string(buf))
}

func applyHostFSEnv(rootFS string) {
	if rootFS == "" {
		return
	}
	setIfEmpty("HOST_PROC", filepath.Join(rootFS, "proc"))
	setIfEmpty("HOST_SYS", filepath.Join(rootFS, "sys"))
	setIfEmpty("HOST_ETC", filepath.Join(rootFS, "etc"))
	setIfEmpty("HOST_VAR", filepath.Join(rootFS, "var"))
	setIfEmpty("HOST_RUN", filepath.Join(rootFS, "run"))
}

func setIfEmpty(key, value string) {
	if os.Getenv(key) == "" {
		_ = os.Setenv(key, value)
	}
}