package windsurf

import (
	"fmt"
	"os"
	"path/filepath"
	"runtime"
	"strings"
)

// ErrBinaryNotFound is returned when no Windsurf LS binary can be located
// via any configured source (env, explicit config, or platform candidates).
var ErrBinaryNotFound = fmt.Errorf("windsurf: language server binary not found")

// binaryStatFn reports whether the given path exists and is executable for
// the current platform. It is a package variable so tests can replace it
// with a map-backed implementation that does not touch the filesystem.
var binaryStatFn = defaultBinaryStat

// userHomeFn returns the user's home directory. Replaced in tests.
var userHomeFn = defaultUserHome

func defaultBinaryStat(path string) bool {
	info, err := os.Stat(path)
	if err != nil || info.IsDir() {
		return false
	}
	if runtime.GOOS == "windows" {
		// Windows ignores the Unix execute bit — rely on the .exe suffix.
		return strings.HasSuffix(strings.ToLower(path), ".exe")
	}
	return info.Mode()&0o111 != 0
}

func defaultUserHome() string {
	if dir, err := os.UserHomeDir(); err == nil {
		return dir
	}
	return ""
}

// DiscoverBinary resolves the Windsurf LS binary path for the current
// platform. Resolution order:
//
//  1. LS_BINARY_PATH environment variable (explicit override — user intent
//     wins even if the path doesn't exist, so we can surface a clear error)
//  2. cfg.Binary (explicit config override)
//  3. Platform-specific candidate list (official install locations)
//
// Returns ErrBinaryNotFound when none of the sources yield an executable
// file; the error message directs the user to LS_BINARY_PATH or ls_mode=docker.
func DiscoverBinary(cfg LSPoolConfig) (string, error) {
	return discoverBinaryFor(DetectPlatform(), os.Getenv("LS_BINARY_PATH"), cfg.Binary)
}

func discoverBinaryFor(p Platform, envPath, cfgPath string) (string, error) {
	if envPath != "" {
		return validateBinaryPath(envPath, p, "LS_BINARY_PATH")
	}
	if cfgPath != "" {
		return validateBinaryPath(cfgPath, p, "cfg.Binary")
	}

	candidates, err := platformCandidates(p)
	if err != nil {
		return "", err
	}
	for _, path := range candidates {
		if binaryStatFn(path) {
			return path, nil
		}
	}

	return "", fmt.Errorf("%w for %s; searched %d paths (%s); set LS_BINARY_PATH or use ls_mode=docker",
		ErrBinaryNotFound, p, len(candidates), strings.Join(candidates, ", "))
}

func validateBinaryPath(path string, p Platform, source string) (string, error) {
	if binaryStatFn(path) {
		return path, nil
	}
	hint := "file does not exist or is not executable"
	if p.OS == "windows" && !strings.HasSuffix(strings.ToLower(path), ".exe") {
		hint = "Windows LS binaries must end in .exe"
	} else if p.OS != "windows" {
		hint += " (try chmod +x)"
	}
	return "", fmt.Errorf("%w: %s=%q — %s; set LS_BINARY_PATH to a valid path or use ls_mode=docker",
		ErrBinaryNotFound, source, path, hint)
}

// platformCandidates returns the ordered list of paths where the official
// Windsurf LS binary may be installed on the given platform. Paths are
// ordered by preference — the first existing+executable path wins.
func platformCandidates(p Platform) ([]string, error) {
	filename, err := BinaryFilename(p)
	if err != nil {
		return nil, err
	}

	switch p.OS {
	case "darwin":
		return darwinCandidates(filename), nil
	case "linux":
		return linuxCandidates(filename), nil
	case "windows":
		return windowsCandidates(filename), nil
	}
	// BinaryFilename would have errored first, so this is defensive.
	return nil, fmt.Errorf("%w: %s (no candidate list)", ErrUnsupportedPlatform, p)
}

func darwinCandidates(filename string) []string {
	const bundleSubpath = "Contents/Resources/app/extensions/windsurf/bin"
	candidates := []string{
		filepath.Join("/Applications/Windsurf.app", bundleSubpath, filename),
	}
	if home := userHomeFn(); home != "" {
		candidates = append(candidates,
			filepath.Join(home, "Applications/Windsurf.app", bundleSubpath, filename),
		)
	}
	// Legacy sub2api install (pre-cross-platform).
	candidates = append(candidates, filepath.Join("/opt/windsurf", filename))
	return candidates
}

func linuxCandidates(filename string) []string {
	candidates := []string{
		// Legacy sub2api install (pre-cross-platform) — matches existing deployments.
		filepath.Join("/opt/windsurf", filename),
		// Official Debian/RPM install locations.
		filepath.Join("/usr/share/windsurf/resources/app/extensions/windsurf/bin", filename),
		filepath.Join("/usr/lib/windsurf/resources/app/extensions/windsurf/bin", filename),
	}
	// User-local install (Flatpak/AppImage unpacked).
	if home := userHomeFn(); home != "" {
		candidates = append(candidates,
			filepath.Join(home, ".local/share/windsurf/resources/app/extensions/windsurf/bin", filename),
		)
	}
	return candidates
}

func windowsCandidates(filename string) []string {
	// Split the install subpath into its components so filepath.Join produces
	// a platform-native path on whichever OS this runs (Windows '\\', Unix '/').
	// This matters for tests running on non-Windows builders.
	installSubpath := []string{"resources", "app", "extensions", "windsurf", "bin", filename}
	var candidates []string
	if localAppData := os.Getenv("LOCALAPPDATA"); localAppData != "" {
		candidates = append(candidates,
			filepath.Join(append([]string{localAppData, "Programs", "Windsurf"}, installSubpath...)...),
		)
	}
	if programFiles := os.Getenv("PROGRAMFILES"); programFiles != "" {
		candidates = append(candidates,
			filepath.Join(append([]string{programFiles, "Windsurf"}, installSubpath...)...),
		)
	}
	return candidates
}