// Package config defines the configuration types and defaults for ExploreDNS,
// along with validation helpers and the CLI usage text.
package config

import (
	"errors"
	"fmt"
	"net"
	"os"
	"strings"

	"github.com/miekg/dns"
)

var (
	ErrInvalidQueryType     = errors.New("invalid query type")
	ErrInvalidUDPSize       = errors.New("UDP size must be between 512 and 4096")
	ErrInvalidMaxDepth      = errors.New("max depth must be between 1 and 100")
	ErrInvalidRetries       = errors.New("retries must be between 0 and 10")
	ErrMissingDomain        = errors.New("domain is required")
	ErrAlwaysTCPRequiresTCP = errors.New("--always-tcp requires --allow-tcp")
)

type Config struct {
	QueryType      string
	RootServer     string
	AllRootServers bool
	RootAAAA       bool
	FollowAAAA     bool
	// DNSUpstream is the upstream resolver used for root server discovery.
	// Format: "host:port" (e.g. "8.8.8.8:53"). Empty means use the system resolver.
	DNSUpstream string
	UDPSize     int
	AllowTCP    bool
	AlwaysTCP   bool
	MaxDepth    int
	Retries     int
	Fast        bool
	Verbose     bool
	Debug       int
	Quiet       bool

	ShowProgress       bool
	ShowResolves       bool
	ShowServers        bool
	ShowVersions       bool
	ShowAllStats       bool
	ShowResults        bool
	ShowSummaryResults bool
}

func ParseQueryType(s string) (uint16, error) {
	s = strings.ToUpper(s)
	switch s {
	case "A":
		return dns.TypeA, nil
	case "AAAA":
		return dns.TypeAAAA, nil
	case "NS":
		return dns.TypeNS, nil
	case "CNAME":
		return dns.TypeCNAME, nil
	case "MX":
		return dns.TypeMX, nil
	case "TXT":
		return dns.TypeTXT, nil
	case "SOA":
		return dns.TypeSOA, nil
	case "PTR":
		return dns.TypePTR, nil
	case "ANY":
		return dns.TypeANY, nil
	default:
		return 0, fmt.Errorf("%w: %s", ErrInvalidQueryType, s)
	}
}

func (c *Config) Validate() error {
	if _, err := ParseQueryType(c.QueryType); err != nil {
		return err
	}

	if c.UDPSize < 512 || c.UDPSize > 4096 {
		return fmt.Errorf("%w: %d", ErrInvalidUDPSize, c.UDPSize)
	}

	if c.MaxDepth < 1 || c.MaxDepth > 100 {
		return fmt.Errorf("%w: %d", ErrInvalidMaxDepth, c.MaxDepth)
	}

	if c.Retries < 0 || c.Retries > 10 {
		return fmt.Errorf("%w: %d", ErrInvalidRetries, c.Retries)
	}

	if c.AlwaysTCP && !c.AllowTCP {
		return ErrAlwaysTCPRequiresTCP
	}

	if c.DNSUpstream != "" {
		if _, _, err := net.SplitHostPort(c.DNSUpstream); err != nil {
			return fmt.Errorf("--dns-upstream %q is not a valid host:port address", c.DNSUpstream)
		}
	}

	return nil
}

func (c *Config) GetDomain(args []string) (string, error) {
	if len(args) == 0 {
		return "", ErrMissingDomain
	}
	return args[0], nil
}

// ParseDebugLevel returns the debug verbosity level from the -d and -dd flag values.
// dd=true → 2 (library debug), d=true → 1 (application debug), neither → 0.
func ParseDebugLevel(d, dd bool) int {
	if dd {
		return 2
	}
	if d {
		return 1
	}
	return 0
}

func PrintUsage() {
	fmt.Fprintf(os.Stderr, "ExploreDNS - DNS reconnaissance and exploration tool\n\n")
	fmt.Fprintf(os.Stderr, "Usage:\n")
	fmt.Fprintf(os.Stderr, "  exploredns [flags] <domain>\n\n")
	fmt.Fprintf(os.Stderr, "Flags:\n")

	// Ordered slice, not a map: --help output must be stable.
	flagGroups := []struct {
		name  string
		flags [][2]string
	}{
		{"Query Options", [][2]string{
			{"--type", "Record type (default a)"},
			{"--root-server", "Initial root server, hostname or IP (default: ask upstream)"},
			{"--all-root-servers", "Traverse from all root servers (default false)"},
			{"--root-aaaa", "Include IPv6 root addresses (not implemented yet)"},
			{"--follow-aaaa", "Only follow AAAA for referrals (not implemented yet)"},
			{"--dns-upstream", "Upstream resolver for root discovery (default: system)"},
		}},
		{"Transport Options", [][2]string{
			{"--udp-size", "EDNS0 buffer size; 512 turns EDNS0 off (default 2048)"},
			{"--allow-tcp", "TCP fallback on truncation (default true)"},
			{"--always-tcp", "Always use TCP (default false)"},
			{"--retries", "Number of 2s retries before timing out (default 2)"},
		}},
		{"Traversal Options", [][2]string{
			{"--max-depth", "Max traversal depth (default 20)"},
			{"--fast", "Fast mode; turn off to be more accurate (default true)"},
		}},
		{"Output Options", [][2]string{
			{"--json", "Emit a single JSON document instead of text"},
			{"--verbose, -v", "Verbose progress ([qname] and <bailiwick> shown)"},
			{"-d, --debug", "Print debug diagnostics to stderr"},
			{"-dd", "Like -d plus library-level debug"},
			{"--quiet, -q", "Suppress the header block"},
			{"--show-progress", "Show traversal progress (default true)"},
			{"--show-resolves", "Show glue resolution progress (default false)"},
			{"--show-servers", "Show servers encountered (default false)"},
			{"--show-versions", "Show server version fingerprints (default true)"},
			{"--show-all-stats", "Show statistics after every node (default false)"},
			{"--show-results", "Show the results (default true)"},
			{"--show-summary-results", "Show the summary results (default true)"},
		}},
		{"General Options", [][2]string{
			{"--version, -V", "Print version and exit"},
		}},
	}

	for _, group := range flagGroups {
		fmt.Fprintf(os.Stderr, "\n%s:\n", group.name)
		for _, f := range group.flags {
			fmt.Fprintf(os.Stderr, "  %-25s %s\n", f[0], f[1])
		}
	}
	fmt.Fprintf(os.Stderr, "\nEvery --show-X flag can be negated with --show-X=false or --no-show-X.\n")
}

func DefaultConfig() *Config {
	return &Config{
		// Lowercase like the reference default (:a); explicit --type values
		// keep the user's case in the "Running query" line.
		QueryType:          "a",
		RootServer:         "",
		AllRootServers:     false,
		RootAAAA:           false,
		FollowAAAA:         false,
		DNSUpstream:        "",
		UDPSize:            2048,
		AllowTCP:           true,
		AlwaysTCP:          false,
		MaxDepth:           20,
		Retries:            2,
		Fast:               true,
		Verbose:            false,
		Debug:              0,
		Quiet:              false,
		ShowProgress:       true,
		ShowResolves:       false,
		ShowServers:        false,
		ShowVersions:       true,
		ShowAllStats:       false,
		ShowResults:        true,
		ShowSummaryResults: true,
	}
}