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package dev.jbang.util;

import java.io.File;
import java.util.Properties;

/**
 * Parses a string and replaces any references recursively to system properties
 * or environment variables in the string ${[env.]some.name:}
 *
 * @author David M. Lloyd
 */
public class PropertiesValueResolver {

	private static final int INITIAL = 0;
	private static final int GOT_DOLLAR = 1;
	private static final int GOT_OPEN_BRACE = 2;
	private static final int RESOLVED = 3;
	private static final int DEFAULT = 4;

	/**
	 * Replace properties of the form:
	 * ${<[env.]name>[,<[env.]name2>[,<[env.]name3>...]][:<default>]}
	 *
	 * @param value - either a system property or environment variable reference
	 * @return the value of the system property or environment variable referenced
	 *         if it exists
	 */
	public static String replaceProperties(final String value) {
		return replaceProperties(value, System.getProperties());
	}

	/**
	 * Replace properties of the form:
	 * ${<[env.]name>[,<[env.]name2>[,<[env.]name3>...]][:<default>]}
	 *
	 * @param value - either a system property or environment variable reference
	 * @return the value of the system property or environment variable referenced
	 *         if it exists
	 */
	public static String replaceProperties(final String value, final Properties properties) {
		final StringBuilder builder = new StringBuilder();
		final int len = value.length();
		int state = INITIAL;
		int start = -1;
		int nameStart = -1;
		String resolvedValue = null;
		for (int i = 0; i < len; i = value.offsetByCodePoints(i, 1)) {
			final int ch = value.codePointAt(i);
			switch (state) {
			case INITIAL: {
				switch (ch) {
				case '$': {
					state = GOT_DOLLAR;
					continue;
				}
				default: {
					builder.appendCodePoint(ch);
					continue;
				}
				}
				// not reachable
			}
			case GOT_DOLLAR: {
				switch (ch) {
				case '$': {
					builder.appendCodePoint(ch);
					state = INITIAL;
					continue;
				}
				case '{': {
					start = i + 1;
					nameStart = start;
					state = GOT_OPEN_BRACE;
					continue;
				}
				default: {
					// invalid; emit and resume
					builder.append('$').appendCodePoint(ch);
					state = INITIAL;
					continue;
				}
				}
				// not reachable
			}
			case GOT_OPEN_BRACE: {
				switch (ch) {
				case ':':
				case '}':
				case ',': {
					final String name = value.substring(nameStart, i).trim();
					if ("/".equals(name)) {
						builder.append(File.separator);
						state = ch == '}' ? INITIAL : RESOLVED;
						continue;
					} else if (":".equals(name)) {
						builder.append(File.pathSeparator);
						state = ch == '}' ? INITIAL : RESOLVED;
						continue;
					}
					// First check for system property, then env variable
					String val = properties.getProperty(name);
					if (val == null && name.startsWith("env."))
						val = System.getenv(name.substring(4));

					if (val != null) {
						builder.append(val);
						resolvedValue = val;
						state = ch == '}' ? INITIAL : RESOLVED;
						continue;
					} else if (ch == ',') {
						nameStart = i + 1;
						continue;
					} else if (ch == ':') {
						start = i + 1;
						state = DEFAULT;
						continue;
					} else {
						throw new IllegalStateException(
								"Failed to resolve expression: " + value.substring(start - 2, i + 1));
					}
				}
				default: {
					continue;
				}
				}
				// not reachable
			}
			case RESOLVED: {
				if (ch == '}') {
					state = INITIAL;
				}
				continue;
			}
			case DEFAULT: {
				if (ch == '}') {
					state = INITIAL;
					builder.append(value, start, i);
				}
				continue;
			}
			default:
				throw new IllegalStateException("Unexpected char seen: " + ch);
			}
		}
		switch (state) {
		case GOT_DOLLAR: {
			builder.append('$');
			break;
		}
		case DEFAULT: {
			builder.append(value.substring(start - 2));
			break;
		}
		case GOT_OPEN_BRACE: {
			// We had a reference that was not resolved, throw ISE
			if (resolvedValue == null)
				throw new IllegalStateException("Incomplete expression: " + builder.toString());
			break;
		}
		}
		return builder.toString();
	}

}