Fix Windows mpv logging and add log export (#88)

src/shared/mpv-logging-args.ts

@@ -0,0 +1,27 @@
+export type SharedLogLevel = 'debug' | 'info' | 'warn' | 'error';
+
+function hasOption(args: readonly string[], option: string): boolean {
+  return args.some((arg) => arg === option || arg.startsWith(`${option}=`));
+}
+
+export function buildMpvMsgLevel(logLevel: SharedLogLevel): string {
+  return `all=warn,subminer=${logLevel}`;
+}
+
+export function buildMpvLoggingArgs(
+  logLevel: SharedLogLevel,
+  logPath: string,
+  existingArgs: readonly string[] = [],
+): string[] {
+  if (!logPath.trim()) {
+    return [];
+  }
+  const args: string[] = [];
+  if (!hasOption(existingArgs, '--log-file')) {
+    args.push(`--log-file=${logPath}`);
+  }
+  if (!hasOption(existingArgs, '--msg-level')) {
+    args.push(`--msg-level=${buildMpvMsgLevel(logLevel)}`);
+  }
+  return args;
+}