// Package config loads and validates the targets.yaml file.
package config

import (
	"fmt"
	"os"
	"time"

	"gopkg.in/yaml.v3"
)

// Duration wraps time.Duration so YAML values like "30s" parse naturally.
type Duration struct{ time.Duration }

func (d *Duration) UnmarshalYAML(value *yaml.Node) error {
	var s string
	if err := value.Decode(&s); err != nil {
		return err
	}
	dur, err := time.ParseDuration(s)
	if err != nil {
		return fmt.Errorf("invalid duration %q: %w", s, err)
	}
	d.Duration = dur
	return nil
}

// CheckType enumerates the supported probe kinds.
type CheckType string

const (
	CheckHTTP   CheckType = "http"
	CheckTCP    CheckType = "tcp"
	CheckTLS    CheckType = "tls"
	CheckICMP   CheckType = "icmp"
	CheckDocker CheckType = "docker"
)

// Target is one monitored endpoint.
type Target struct {
	ID   string    `yaml:"id"`
	Name string    `yaml:"name"`
	Type CheckType `yaml:"type"`

	// Type-specific endpoints.
	URL       string `yaml:"url"`       // http
	Address   string `yaml:"address"`   // tcp, tls (host:port)
	Host      string `yaml:"host"`      // icmp
	Container string `yaml:"container"` // docker
	Socket    string `yaml:"socket"`    // docker (default /var/run/docker.sock)

	Interval Duration `yaml:"interval"`
	Timeout  Duration `yaml:"timeout"`

	// Flap detection: N consecutive failures before "down",
	// M consecutive successes before "up" again.
	FailThreshold    int `yaml:"fail_threshold"`
	RecoverThreshold int `yaml:"recover_threshold"`

	ExpectStatus      int     `yaml:"expect_status"`       // http: exact status (0 = any < 400)
	WarnDays          int     `yaml:"warn_days"`           // tls: degraded when cert expires sooner
	DegradedLatencyMS float64 `yaml:"degraded_latency_ms"` // any: degraded above this latency
}

// Settings holds server-level options.
type Settings struct {
	Listen      string `yaml:"listen"`
	DB          string `yaml:"db"`
	HistoryDays int    `yaml:"history_days"`
}

// Config is the full parsed targets.yaml.
type Config struct {
	Settings Settings `yaml:"settings"`
	Targets  []Target `yaml:"targets"`
}

// Load reads, parses, validates and applies defaults to a config file.
func Load(path string) (*Config, error) {
	raw, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	var cfg Config
	if err := yaml.Unmarshal(raw, &cfg); err != nil {
		return nil, fmt.Errorf("parse %s: %w", path, err)
	}
	if err := cfg.validate(); err != nil {
		return nil, err
	}
	cfg.applyDefaults()
	return &cfg, nil
}

func (c *Config) validate() error {
	if len(c.Targets) == 0 {
		return fmt.Errorf("no targets defined")
	}
	seen := map[string]bool{}
	for i, t := range c.Targets {
		if t.ID == "" {
			return fmt.Errorf("target %d: missing id", i)
		}
		if seen[t.ID] {
			return fmt.Errorf("duplicate target id %q", t.ID)
		}
		seen[t.ID] = true
		switch t.Type {
		case CheckHTTP:
			if t.URL == "" {
				return fmt.Errorf("target %q: http check requires url", t.ID)
			}
		case CheckTCP, CheckTLS:
			if t.Address == "" {
				return fmt.Errorf("target %q: %s check requires address (host:port)", t.ID, t.Type)
			}
		case CheckICMP:
			if t.Host == "" {
				return fmt.Errorf("target %q: icmp check requires host", t.ID)
			}
		case CheckDocker:
			if t.Container == "" {
				return fmt.Errorf("target %q: docker check requires container", t.ID)
			}
		default:
			return fmt.Errorf("target %q: unknown check type %q", t.ID, t.Type)
		}
	}
	return nil
}

func (c *Config) applyDefaults() {
	if c.Settings.Listen == "" {
		c.Settings.Listen = ":8080"
	}
	if c.Settings.DB == "" {
		c.Settings.DB = "dash.db"
	}
	if c.Settings.HistoryDays <= 0 {
		c.Settings.HistoryDays = 30
	}
	for i := range c.Targets {
		t := &c.Targets[i]
		if t.Name == "" {
			t.Name = t.ID
		}
		if t.Interval.Duration <= 0 {
			t.Interval.Duration = 30 * time.Second
		}
		if t.Timeout.Duration <= 0 {
			t.Timeout.Duration = 5 * time.Second
		}
		if t.FailThreshold <= 0 {
			t.FailThreshold = 3
		}
		if t.RecoverThreshold <= 0 {
			t.RecoverThreshold = 2
		}
		if t.Type == CheckTLS && t.WarnDays <= 0 {
			t.WarnDays = 14
		}
		if t.Type == CheckDocker && t.Socket == "" {
			t.Socket = "/var/run/docker.sock"
		}
	}
}