package credhelper

import (
	"fmt"
	"io"
	"net/http"
	"os"
	"os/exec"
	"path"
	"path/filepath"
	"regexp"
	"runtime"
	"strconv"
	"strings"
	"time"

	"github.com/spf13/cobra"
)

func newUpdateCmd() *cobra.Command {
	cmd := &cobra.Command{
		Use:   "update",
		Short: "Update to the latest version",
		RunE:  runUpdate,
	}
	cmd.Flags().Bool("check", false, "Only check for updates, don't install")
	return cmd
}

func runUpdate(cmd *cobra.Command, args []string) error {
	checkOnly, _ := cmd.Flags().GetBool("check")

	latest, err := fetchLatestVersion()
	if err != nil {
		return fmt.Errorf("checking for updates: %w", err)
	}

	if !isNewerVersion(latest, cfg.Version) {
		fmt.Printf("You're already running the latest version (%s)\n", cfg.Version)
		return nil
	}

	fmt.Printf("New version available: %s (current: %s)\n", latest, cfg.Version)

	if checkOnly {
		return nil
	}

	if err := performUpdate(latest); err != nil {
		return fmt.Errorf("update failed: %w", err)
	}

	fmt.Println("Update completed successfully!")
	return nil
}

// fetchLatestVersion resolves the latest released version by following the
// {ReleasesBaseURL}/tags/latest redirect chain. Tangled redirects
// DID→handle first, then handle/tags/latest→handle/tags/vX.Y.Z, so we follow
// the chain and read the tag from the final effective URL.
func fetchLatestVersion() (string, error) {
	client := httpClientWithTimeout(10*time.Second, nil)

	resp, err := client.Get(cfg.ReleasesBaseURL + "/tags/latest")
	if err != nil {
		return "", fmt.Errorf("fetching latest tag: %w", err)
	}
	defer resp.Body.Close()

	finalURL := resp.Request.URL
	tag := path.Base(finalURL.Path)
	if !strings.HasPrefix(tag, "v") {
		return "", fmt.Errorf("unexpected tag in final URL %q", finalURL.String())
	}

	return tag, nil
}

// isNewerVersion compares two version strings (simple semver comparison)
// describeSuffix matches the "-<commits>-g<sha>" tail `git describe` appends to
// the most recent tag, as in v0.1.4-18-g8f70cce.
var describeSuffix = regexp.MustCompile(`^(.*)-(\d+)-g[0-9a-f]+$`)

// parsedVersion is a version split into its numeric components plus, for a
// git-describe build, how many commits it sits past its tag.
type parsedVersion struct {
	nums  []int
	ahead int
}

// parseVersion reads "v0.1.4" and "v0.1.4-18-g8f70cce". It reports ok=false for
// anything it cannot read in full, so an unparseable version is never mistaken
// for an upgrade — the previous code swallowed strconv errors and substituted
// 0, which made every release look newer than any git-describe build.
func parseVersion(s string) (parsedVersion, bool) {
	s = strings.TrimPrefix(strings.TrimSpace(s), "v")
	if s == "" {
		return parsedVersion{}, false
	}

	var ahead int
	if m := describeSuffix.FindStringSubmatch(s); m != nil {
		n, err := strconv.Atoi(m[2])
		if err != nil {
			return parsedVersion{}, false
		}
		s, ahead = m[1], n
	}

	parts := strings.Split(s, ".")
	nums := make([]int, 0, len(parts))
	for _, p := range parts {
		n, err := strconv.Atoi(p)
		if err != nil {
			return parsedVersion{}, false
		}
		nums = append(nums, n)
	}
	return parsedVersion{nums: nums, ahead: ahead}, true
}

// versionComponent reads the i'th numeric component, treating absent trailing
// components as 0 so "0.1" and "0.1.0" compare equal.
func versionComponent(nums []int, i int) int {
	if i < len(nums) {
		return nums[i]
	}
	return 0
}

func isNewerVersion(newVersion, currentVersion string) bool {
	if currentVersion == "dev" {
		return true
	}

	newV, okNew := parseVersion(newVersion)
	curV, okCur := parseVersion(currentVersion)
	if !okNew || !okCur {
		return false
	}

	for i := range max(len(newV.nums), len(curV.nums)) {
		a, b := versionComponent(newV.nums, i), versionComponent(curV.nums, i)
		if a != b {
			return a > b
		}
	}

	// Same tag: whichever build sits further past it is the newer one. This is
	// deliberately not semver ordering, where a prerelease sorts below its
	// release — a git-describe build is commits AHEAD of its tag, not behind.
	return newV.ahead > curV.ahead
}

// goreleaserArchiveName returns the archive filename goreleaser publishes for
// the given version and the current platform. The naming template lives in
// .goreleaser.yaml: <UpdateAssetName>_{Version}_{Title(OS)}_{Arch} with
// amd64→x86_64 and 386→i386.
func goreleaserArchiveName(version string) string {
	versionNoV := strings.TrimPrefix(version, "v")

	os := strings.ToUpper(runtime.GOOS[:1]) + runtime.GOOS[1:]

	arch := runtime.GOARCH
	switch arch {
	case "amd64":
		arch = "x86_64"
	case "386":
		arch = "i386"
	}

	return fmt.Sprintf("%s_%s_%s_%s.tar.gz", cfg.UpdateAssetName, versionNoV, os, arch)
}

// performUpdate downloads and installs the new version
func performUpdate(latest string) error {
	filename := goreleaserArchiveName(latest)
	downloadURL := fmt.Sprintf("%s/tags/%s/download/%s", cfg.ReleasesBaseURL, latest, filename)

	fmt.Printf("Downloading update from %s...\n", downloadURL)

	tmpDir, err := os.MkdirTemp("", cfg.BinaryName+"-update-")
	if err != nil {
		return fmt.Errorf("creating temp directory: %w", err)
	}
	defer os.RemoveAll(tmpDir)

	archivePath := filepath.Join(tmpDir, "archive.tar.gz")
	if err := downloadFile(downloadURL, archivePath); err != nil {
		return fmt.Errorf("downloading: %w", err)
	}

	binaryPath := filepath.Join(tmpDir, cfg.BinaryName)
	if runtime.GOOS == "windows" {
		binaryPath += ".exe"
	}

	if err := extractTarGz(archivePath, tmpDir); err != nil {
		return fmt.Errorf("extracting archive: %w", err)
	}

	currentPath, err := os.Executable()
	if err != nil {
		return fmt.Errorf("getting current executable path: %w", err)
	}
	currentPath, err = filepath.EvalSymlinks(currentPath)
	if err != nil {
		return fmt.Errorf("resolving symlinks: %w", err)
	}

	fmt.Println("Verifying new binary...")
	verifyCmd := exec.Command(binaryPath, "--version")
	if output, err := verifyCmd.Output(); err != nil {
		return fmt.Errorf("new binary verification failed: %w", err)
	} else {
		fmt.Printf("New binary version: %s", string(output))
	}

	backupPath := currentPath + ".bak"
	if err := os.Rename(currentPath, backupPath); err != nil {
		return fmt.Errorf("backing up current binary: %w", err)
	}

	if err := copyFile(binaryPath, currentPath); err != nil {
		os.Rename(backupPath, currentPath) //nolint:errcheck
		return fmt.Errorf("installing new binary: %w", err)
	}

	if err := os.Chmod(currentPath, 0755); err != nil {
		os.Remove(currentPath)             //nolint:errcheck
		os.Rename(backupPath, currentPath) //nolint:errcheck
		return fmt.Errorf("setting permissions: %w", err)
	}

	os.Remove(backupPath) //nolint:errcheck
	return nil
}

// downloadFile downloads a file from a URL to a local path
func downloadFile(url, destPath string) error {
	resp, err := httpClient().Get(url) //nolint:gosec
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("download returned status %d", resp.StatusCode)
	}

	out, err := os.Create(destPath)
	if err != nil {
		return err
	}
	defer out.Close()

	_, err = io.Copy(out, resp.Body)
	return err
}

// extractTarGz extracts a .tar.gz archive
func extractTarGz(archivePath, destDir string) error {
	cmd := exec.Command("tar", "-xzf", archivePath, "-C", destDir)
	if output, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("tar failed: %s: %w", string(output), err)
	}
	return nil
}

// copyFile copies a file from src to dst
func copyFile(src, dst string) error {
	input, err := os.ReadFile(src)
	if err != nil {
		return err
	}
	return os.WriteFile(dst, input, 0755)
}