// Package cli implements the command line interface.
//
// `serve` is the default when no subcommand is given, so running the binary
// with no arguments starts the server, which is the overwhelmingly common case.
package cli

import (
	"context"
	"errors"
	"flag"
	"fmt"
	"io"
	"log/slog"
	"os"
	"strings"

	"github.com/owen/vibedns/internal/config"
	"github.com/owen/vibedns/internal/version"
)

// Command is one subcommand.
type Command struct {
	Name    string
	Summary string
	Usage   string
	Run     func(ctx context.Context, env *Env, args []string) error
}

// Env carries what every command needs.
type Env struct {
	Boot   config.Bootstrap
	Stdout io.Writer
	Stderr io.Writer
	Log    *slog.Logger
}

// ExitError carries a specific process exit status.
type ExitError struct {
	Code int
	Err  error
}

func (e *ExitError) Error() string { return e.Err.Error() }
func (e *ExitError) Unwrap() error { return e.Err }

// Exit wraps an error with an exit code.
func Exit(code int, format string, args ...any) error {
	return &ExitError{Code: code, Err: fmt.Errorf(format, args...)}
}

// commands is the full command table.
func commands() []*Command {
	return []*Command{
		serveCommand(),
		versionCommand(),
		configCommand(),
		adminCommand(),
		databaseCommand(),
	}
}

// Main parses arguments and runs the selected command.
func Main(ctx context.Context, args []string, stdout, stderr io.Writer) int {
	env := &Env{Boot: config.DefaultBootstrap(), Stdout: stdout, Stderr: stderr}

	// Find the subcommand: the first argument that is not a flag. This lets
	// both `vibedns --db x serve` and `vibedns serve --db x` work.
	name := ""
	rest := args
	for i, a := range args {
		if !strings.HasPrefix(a, "-") {
			name = a
			rest = append(append([]string{}, args[:i]...), args[i+1:]...)
			break
		}
	}

	switch name {
	case "help", "-h", "--help", "":
		if name == "" && !wantsHelp(args) {
			// No subcommand: serve.
			return run(ctx, env, serveCommand(), args)
		}
		usage(stdout)
		return 0
	}

	for _, c := range commands() {
		if c.Name == name {
			return run(ctx, env, c, rest)
		}
	}

	fmt.Fprintf(stderr, "unknown command %q\n\n", name)
	usage(stderr)
	return 2
}

func wantsHelp(args []string) bool {
	for _, a := range args {
		if a == "-h" || a == "--help" || a == "help" {
			return true
		}
	}
	return false
}

func run(ctx context.Context, env *Env, c *Command, args []string) int {
	err := c.Run(ctx, env, args)
	if err == nil {
		return 0
	}
	if errors.Is(err, flag.ErrHelp) {
		return 0
	}
	var ee *ExitError
	if errors.As(err, &ee) {
		fmt.Fprintf(env.Stderr, "%s: %v\n", c.Name, ee.Err)
		return ee.Code
	}
	fmt.Fprintf(env.Stderr, "%s: %v\n", c.Name, err)
	return 1
}

func usage(w io.Writer) {
	fmt.Fprintf(w, `%s %s — authoritative DNS server, recursive resolver and filtering appliance

Usage:
  vibedns [command] [flags]

Commands:
`, version.Name, version.Version)

	for _, c := range commands() {
		fmt.Fprintf(w, "  %-20s %s\n", c.Name, c.Summary)
	}

	fmt.Fprintf(w, `
Running with no command starts the server.

Common flags:
  --db PATH             SQLite database file (default %s)
  --http ADDR           management interface address (default %s)
  --dns ADDR            DNS listen address for UDP and TCP (default %s)
  --log-level LEVEL     debug, info, warn or error
  --log-format FORMAT   text or json

Environment variables:
  %-22s database file
  %-22s management interface address
  %-22s DNS listen address
  %-22s initial administrator username
  %-22s initial administrator password
  %-22s log level
  %-22s log format

Examples:
  vibedns
  vibedns serve --db /var/lib/vibedns/dns.db --http 127.0.0.1:8080
  vibedns config check
  vibedns admin reset-password
  vibedns database backup --output /var/backups
  vibedns version

`,
		config.DefaultDBPath, config.DefaultHTTPAddr, config.DefaultDNSAddr,
		config.EnvDBPath, config.EnvHTTPAddr, config.EnvDNSAddr,
		config.EnvAdminUsername, config.EnvAdminPassword,
		config.EnvLogLevel, config.EnvLogFormat)
}

// newFlagSet builds a flag set that prints its own usage on error.
func newFlagSet(env *Env, c *Command) *flag.FlagSet {
	fs := flag.NewFlagSet(c.Name, flag.ContinueOnError)
	fs.SetOutput(env.Stderr)
	fs.Usage = func() {
		fmt.Fprintf(env.Stderr, "%s\n\n", c.Usage)
		fs.PrintDefaults()
	}
	return fs
}

// versionCommand prints build information.
func versionCommand() *Command {
	return &Command{
		Name:    "version",
		Summary: "print version and build information",
		Usage:   "Usage: vibedns version",
		Run: func(ctx context.Context, env *Env, args []string) error {
			fmt.Fprint(env.Stdout, version.Long())
			return nil
		},
	}
}

// confirm asks for an interactive yes/no answer. It returns false when stdin
// is not a terminal, so a piped invocation can never be silently destructive.
func confirm(env *Env, prompt string) bool {
	fi, err := os.Stdin.Stat()
	if err != nil || (fi.Mode()&os.ModeCharDevice) == 0 {
		fmt.Fprintf(env.Stderr,
			"%s\nRefusing to continue without an interactive confirmation; pass --yes to proceed.\n", prompt)
		return false
	}
	fmt.Fprintf(env.Stdout, "%s [y/N]: ", prompt)
	var answer string
	_, _ = fmt.Fscanln(os.Stdin, &answer)
	answer = strings.ToLower(strings.TrimSpace(answer))
	return answer == "y" || answer == "yes"
}