package browser

import (
	"context"
	"errors"
	"fmt"
	"io/fs"
	"net"
	"net/url"
	"os"
	"path/filepath"
	"strconv"
	"strings"

	"chub/internal/domain"
)

var (
	ErrExecutableNotFound = errors.New("browser executable was not found")
	ErrUnsafeArgument     = errors.New("browser argument is controlled or unsafe")
)

type Discoverer struct {
	getenv func(string) string
	stat   func(string) (fs.FileInfo, error)
}

func NewDiscoverer() *Discoverer { return &Discoverer{getenv: os.Getenv, stat: os.Stat} }

func (d *Discoverer) Resolve(ctx context.Context, kind domain.BrowserKind, configured string) (string, error) {
	if err := ctx.Err(); err != nil {
		return "", err
	}
	if d == nil || d.getenv == nil || d.stat == nil || !kind.Valid() {
		return "", ErrExecutableNotFound
	}
	if configured = strings.TrimSpace(configured); configured != "" {
		if path, ok := d.executable(configured); ok {
			return path, nil
		}
		return "", fmt.Errorf("%w: configured path is unavailable", ErrExecutableNotFound)
	}
	seen := make(map[string]struct{})
	for _, candidate := range d.candidates(kind) {
		cleaned := filepath.Clean(candidate)
		key := strings.ToLower(cleaned)
		if candidate == "" {
			continue
		}
		if _, exists := seen[key]; exists {
			continue
		}
		seen[key] = struct{}{}
		if path, ok := d.executable(cleaned); ok {
			return path, nil
		}
	}
	return "", ErrExecutableNotFound
}

func (d *Discoverer) candidates(kind domain.BrowserKind) []string {
	var suffixes []string
	switch kind {
	case domain.BrowserChrome:
		suffixes = []string{`Google\Chrome\Application\chrome.exe`}
	case domain.BrowserEdge:
		suffixes = []string{`Microsoft\Edge\Application\msedge.exe`}
	}
	var candidates []string
	for _, root := range []string{"PROGRAMFILES", "PROGRAMFILES(X86)", "LOCALAPPDATA"} {
		for _, suffix := range suffixes {
			candidates = append(candidates, filepath.Join(d.getenv(root), suffix))
		}
	}
	return candidates
}

func (d *Discoverer) executable(path string) (string, bool) {
	cleaned := filepath.Clean(strings.TrimSpace(path))
	if cleaned == "." || !filepath.IsAbs(cleaned) {
		return "", false
	}
	info, err := d.stat(cleaned)
	if err != nil || info.IsDir() || !info.Mode().IsRegular() {
		return "", false
	}
	return cleaned, true
}

func BuildArgs(spec domain.LaunchSpec) ([]string, error) {
	normalized, err := spec.Normalize()
	if err != nil {
		return nil, err
	}
	proxy, err := normalizeProxy(normalized.ProxyServer)
	if err != nil {
		return nil, err
	}
	args := []string{
		"--user-data-dir=" + normalized.UserDataDir,
		"--no-first-run",
		"--disable-default-apps",
	}
	if normalized.ProfileDirectory != "" {
		args = append(args, "--profile-directory="+normalized.ProfileDirectory)
	}
	if normalized.Headless {
		args = append(args, "--headless=new")
	}
	if proxy != "" {
		args = append(args, "--proxy-server="+proxy)
	}
	for _, extra := range normalized.ExtraArgs {
		if err := validateExtraArg(extra); err != nil {
			return nil, err
		}
		args = append(args, extra)
	}
	return append(args, normalized.TargetURL), nil
}

func normalizeProxy(value string) (string, error) {
	proxy := strings.TrimSpace(value)
	if proxy == "" {
		return "", nil
	}
	parsed, err := url.Parse(proxy)
	if err != nil || parsed.User != nil || parsed.Hostname() == "" || parsed.Port() == "" || parsed.Path != "" || parsed.RawQuery != "" || parsed.Fragment != "" {
		return "", fmt.Errorf("%w: proxy must be scheme://host:port without credentials", domain.ErrInvalidLaunchSpec)
	}
	scheme := strings.ToLower(parsed.Scheme)
	if scheme != "http" && scheme != "https" && scheme != "socks4" && scheme != "socks5" {
		return "", fmt.Errorf("%w: unsupported proxy scheme", domain.ErrInvalidLaunchSpec)
	}
	port, err := strconv.Atoi(parsed.Port())
	if err != nil || port < 1 || port > 65535 {
		return "", fmt.Errorf("%w: proxy port out of range", domain.ErrInvalidLaunchSpec)
	}
	return scheme + "://" + net.JoinHostPort(strings.ToLower(parsed.Hostname()), strconv.Itoa(port)), nil
}

func validateExtraArg(value string) error {
	arg := strings.TrimSpace(value)
	if arg == "" || !strings.HasPrefix(arg, "--") {
		return fmt.Errorf("%w: extra arguments must be non-empty flags", ErrUnsafeArgument)
	}
	name := strings.ToLower(strings.SplitN(arg[2:], "=", 2)[0])
	for _, controlled := range []string{"user-data-dir", "profile-directory", "proxy-server", "remote-debugging-address", "remote-debugging-port"} {
		if name == controlled {
			return fmt.Errorf("%w: --%s is controlled by LaunchSpec", ErrUnsafeArgument, controlled)
		}
	}
	return nil
}