package config

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

// Config contains all runtime, reporting, collection, and service settings.
type Config struct {
	HostID  string        `json:"host_id"`
	HTTP    HTTPConfig    `json:"http"`
	Collect CollectConfig `json:"collect"`
	Report  ReportConfig  `json:"report"`
	Service ServiceConfig `json:"service"`
}

// HTTPConfig controls the local HTTP API listener.
type HTTPConfig struct {
	ListenAddress string `json:"listen_address"`
}

// CollectConfig controls periodic host status collection.
type CollectConfig struct {
	Interval Duration `json:"interval"`
	Timeout  Duration `json:"timeout"`
}

// ReportConfig controls optional periodic status POST reporting.
type ReportConfig struct {
	Enabled  bool     `json:"enabled"`
	Endpoint string   `json:"endpoint"`
	Interval Duration `json:"interval"`
	Timeout  Duration `json:"timeout"`
}

// ServiceConfig controls operating system service registration metadata.
type ServiceConfig struct {
	Name        string `json:"name"`
	DisplayName string `json:"display_name"`
	Description string `json:"description"`
}

// Duration wraps time.Duration so JSON config can use Go duration strings.
type Duration time.Duration

// Duration returns the standard library duration value.
func (d Duration) Duration() time.Duration {
	return time.Duration(d)
}

// MarshalJSON writes the duration as a Go duration string such as "30s".
func (d Duration) MarshalJSON() ([]byte, error) {
	return json.Marshal(time.Duration(d).String())
}

// UnmarshalJSON parses a Go duration string from JSON.
func (d *Duration) UnmarshalJSON(data []byte) error {
	var raw string
	if err := json.Unmarshal(data, &raw); err != nil {
		return err
	}
	parsed, err := time.ParseDuration(raw)
	if err != nil {
		return err
	}
	*d = Duration(parsed)
	return nil
}

// Default returns safe local defaults for running the agent.
func Default() Config {
	return Config{
		HTTP: HTTPConfig{ListenAddress: "127.0.0.1:8080"},
		Collect: CollectConfig{
			Interval: Duration(30 * time.Second),
			Timeout:  Duration(10 * time.Second),
		},
		Report: ReportConfig{
			Enabled:  false,
			Interval: Duration(60 * time.Second),
			Timeout:  Duration(5 * time.Second),
		},
		Service: ServiceConfig{
			Name:        "mfd-monitor-agent",
			DisplayName: "MFD Monitor Agent",
			Description: "Collects host status and exposes it over HTTP.",
		},
	}
}

// Load reads optional JSON config, applies environment overrides, and validates required settings.
func Load(path string) (Config, error) {
	cfg := Default()
	if path != "" {
		data, err := os.ReadFile(path)
		if err != nil {
			return cfg, err
		}
		if err := json.Unmarshal(data, &cfg); err != nil {
			return cfg, err
		}
	}
	applyEnv(&cfg)
	if cfg.Report.Enabled && cfg.Report.Endpoint == "" {
		return cfg, errors.New("report endpoint is required when reporting is enabled")
	}
	return cfg, nil
}

// applyEnv overlays supported MFD_AGENT_* environment variables onto cfg.
func applyEnv(cfg *Config) {
	if value := os.Getenv("MFD_AGENT_HOST_ID"); value != "" {
		cfg.HostID = value
	}
	if value := os.Getenv("MFD_AGENT_LISTEN"); value != "" {
		cfg.HTTP.ListenAddress = value
	}
	if value := os.Getenv("MFD_AGENT_REPORT_ENABLED"); value != "" {
		if parsed, err := strconv.ParseBool(value); err == nil {
			cfg.Report.Enabled = parsed
		}
	}
	if value := os.Getenv("MFD_AGENT_REPORT_ENDPOINT"); value != "" {
		cfg.Report.Endpoint = value
	}
	if value := os.Getenv("MFD_AGENT_REPORT_INTERVAL"); value != "" {
		if parsed, err := time.ParseDuration(value); err == nil {
			cfg.Report.Interval = Duration(parsed)
		}
	}
	if value := os.Getenv("MFD_AGENT_REPORT_TIMEOUT"); value != "" {
		if parsed, err := time.ParseDuration(value); err == nil {
			cfg.Report.Timeout = Duration(parsed)
		}
	}
	if value := os.Getenv("MFD_AGENT_COLLECT_INTERVAL"); value != "" {
		if parsed, err := time.ParseDuration(value); err == nil {
			cfg.Collect.Interval = Duration(parsed)
		}
	}
	if value := os.Getenv("MFD_AGENT_COLLECT_TIMEOUT"); value != "" {
		if parsed, err := time.ParseDuration(value); err == nil {
			cfg.Collect.Timeout = Duration(parsed)
		}
	}
}