package log

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

const (
	obrimLogSoftwareName  = "softwarelower"
	obrimLogFileExtension = ".log"
)

// ObrimLog writes a structured log entry.
func ObrimLog(label string, message string) {
	softwareName := obrimLogSoftwareNameResolve()
	if softwareName == "" {
		return
	}

	entry := obrimLogEntryBuild(
		obrimLogTimestampGenerate(),
		label,
		message,
	)

	filePath := obrimLogFileResolve(softwareName)
	if filePath == "" {
		return
	}

	if err := obrimLogFileEnsure(filePath); err != nil {
		return
	}

	_ = obrimLogWrite(filePath, entry)
}

// obrimLogSoftwareNameResolve resolves the software name from a local variable.
func obrimLogSoftwareNameResolve() string {
	return strings.TrimSpace(obrimLogSoftwareName)
}

// obrimLogTimestampGenerate generates deterministic timestamps.
func obrimLogTimestampGenerate() string {
	return time.Now().UTC().Format(time.RFC3339)
}

// obrimLogEntryBuild constructs formatted log entries.
func obrimLogEntryBuild(
	timestamp string,
	label string,
	message string,
) string {
	return fmt.Sprintf(
		"[%s] [%s] %s\n",
		strings.TrimSpace(timestamp),
		strings.TrimSpace(label),
		strings.TrimSpace(message),
	)
}

// obrimLogDirectoryResolve resolves platform-specific log directory paths.
func obrimLogDirectoryResolve(
	softwareName string,
) string {
	switch runtime.GOOS {
	case "linux":
		return obrimLogDirectoryResolveLinux(softwareName)

	case "windows":
		return obrimLogDirectoryResolveWindows(softwareName)

	case "darwin":
		return obrimLogDirectoryResolveMacOS(softwareName)

	default:
		return ""
	}
}

// obrimLogFileResolve resolves platform-specific log file paths.
func obrimLogFileResolve(
	softwareName string,
) string {
	directoryPath := obrimLogDirectoryResolve(softwareName)
	if directoryPath == "" {
		return ""
	}

	return filepath.Join(
		directoryPath,
		softwareName+obrimLogFileExtension,
	)
}

// obrimLogFileEnsure creates and verifies required log directories and files.
func obrimLogFileEnsure(
	filePath string,
) error {
	directoryPath := filepath.Dir(filePath)

	if err := os.MkdirAll(directoryPath, 0o755); err != nil {
		return err
	}

	file, err := os.OpenFile(
		filePath,
		os.O_CREATE,
		0o644,
	)
	if err != nil {
		return err
	}

	return file.Close()
}

// obrimLogWrite persists log entries to the filesystem.
func obrimLogWrite(
	filePath string,
	entry string,
) error {
	file, err := os.OpenFile(
		filePath,
		os.O_APPEND|os.O_CREATE|os.O_WRONLY,
		0o644,
	)
	if err != nil {
		return err
	}

	defer file.Close()

	_, err = file.WriteString(entry)

	return err
}

// obrimLogDirectoryResolveLinux resolves Linux log directory paths.
func obrimLogDirectoryResolveLinux(
	softwareName string,
) string {
	// Mutable XDG state home environment variable.
	var xdgStateHome = strings.TrimSpace(
		os.Getenv("XDG_STATE_HOME"),
	)

	if xdgStateHome != "" {
		return filepath.Join(
			xdgStateHome,
			"."+softwareName,
			"logs",
		)
	}

	// Mutable user home directory.
	var homeDirectory string

	userHomeDirectory, err := os.UserHomeDir()
	if err != nil {
		return ""
	}

	homeDirectory = userHomeDirectory

	return filepath.Join(
		homeDirectory,
		".local",
		"state",
		"."+softwareName,
		"logs",
	)
}

// obrimLogDirectoryResolveWindows resolves Windows log directory paths.
func obrimLogDirectoryResolveWindows(
	softwareName string,
) string {
	// Mutable LOCALAPPDATA environment variable.
	var localAppData = strings.TrimSpace(
		os.Getenv("LOCALAPPDATA"),
	)

	if localAppData == "" {
		return ""
	}

	return filepath.Join(
		localAppData,
		softwareName,
		"Logs",
	)
}

// obrimLogDirectoryResolveMacOS resolves macOS log directory paths.
func obrimLogDirectoryResolveMacOS(
	softwareName string,
) string {
	// Mutable user home directory.
	var homeDirectory string

	userHomeDirectory, err := os.UserHomeDir()
	if err != nil {
		return ""
	}

	homeDirectory = userHomeDirectory

	return filepath.Join(
		homeDirectory,
		"Library",
		"Logs",
		"."+softwareName,
	)
}