d20-charsheet/src/main/lombok/org/leumasjaffe/format/StringFormatter.java

package org.leumasjaffe.format;

import java.util.HashMap;
import java.util.Objects;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import lombok.AccessLevel;
import lombok.experimental.FieldDefaults;

@FieldDefaults(level=AccessLevel.PRIVATE, makeFinal=true)
public class StringFormatter {
	private static final class NameMap extends HashMap<String, Object> {
		/**
		 * 
		 */
		private static final long serialVersionUID = -2243574068000774442L;

		NameMap(Object... args) {
			for (Object arg : args) {
				Objects.requireNonNull(arg);
				if (arg instanceof Named) {
					put(((Named) arg).getName(), arg);
				}
			}
		}
	}
	
	private static final class FmtStateMachine {
		final StringBuilder str;
		
		String fmt;
		Object[] args;
		int currentIdx;
		final NameMap named;
		int lastCh, endPos = 0;

		FmtStateMachine(String fmt, Object... args) {
			this(fmt, 0, args, new NameMap(args), '\0');
		}
		
		FmtStateMachine(String fmt, int idx, Object[] args, NameMap named, int lastCh) {
			this.str = new StringBuilder(fmt.length());
			this.fmt = fmt;
			this.currentIdx = idx;
			this.args = args;
			this.named = named;
			this.lastCh = lastCh;
		}
		
		FmtStateMachine formatMain() {
			int lpos = 0;
			for (int pos = fmt.indexOf('{'); pos != -1 && hasMore(pos); lpos = pos+1, pos = fmt.indexOf('{', lpos)) {
				str.append(fmt.substring(lpos, pos).replaceAll("}}", "}"));
				int epos = fmt.indexOf('}', pos);

				if (fmt.charAt(pos+1) == '{') { 
					// Literal '{'
					str.append('{');
					epos = pos + 1;
				} else if (epos == pos+1) {
					// Unmarked '{}' -> get the next argument
					str.append(getToken(null));
				} else {
					epos = formatToken(pos, epos);
				}
				pos = epos;
			}
			str.append(remaining(lpos).replaceAll("}}", "}"));
			return this;
		}

		private String remaining(int lpos) {
			this.endPos = fmt.indexOf(lastCh, lpos);
			return lastCh == '\0' ? fmt.substring(lpos) : fmt.substring(lpos, endPos++);
		}

		private boolean hasMore(int pos) {
			return lastCh == '\0' || pos < fmt.indexOf(lastCh);
		}
		
		private int formatToken(int pos, int epos) {
			final String token = fmt.substring(++pos, epos);
			// If token contains a '.', use reflection?
			// If token starts with '%', make it a c-format expression
			if (token.indexOf('?') != -1) {
				final int b1 = fmt.indexOf('?', pos)+1;
				boolean _if = getConditionToken(token, b1-pos-1);
				FmtStateMachine then = new FmtStateMachine(fmt.substring(b1), currentIdx, args, named, ':').formatMain();
				FmtStateMachine els = new FmtStateMachine(fmt.substring(then.endPos+b1), then.currentIdx, args, named, '}').formatMain();
				currentIdx = els.currentIdx;
				epos = els.endPos+then.endPos+b1-1;
				str.append(_if ? then : els);
			} else {
				str.append(getToken(token));
			}
			return epos;
		}

		private boolean getConditionToken(final String token, final int end) {
			final String cond = token.substring(0, end);
			Matcher matcher = Pattern.compile("^(\\d*|[a-zA-Z_]+)(>=?|<=?|!=|==?)(\\d+)$").matcher(cond);
			if (matcher.matches()) {
				final int cmp = ((Integer) getToken(matcher.group(1))).compareTo(Integer.valueOf(matcher.group(3)));
				switch (matcher.group(2)) {
				case "=" : return cmp == 0;
				case "==": return cmp == 0;
				case "!=": return cmp != 0;
				case "<" : return cmp <  0;
				case "<=": return cmp <= 0;
				case ">" : return cmp >  0;
				case ">=": return cmp >= 0;
				default: throw new IllegalStateException();
				}
			} else {
				return (Boolean) getToken(cond);
			}
		}

		private Object getToken(final String token) {
			if (token == null || token.isEmpty()) {
				return args[currentIdx++];
			} else if (Character.isDigit(token.charAt(0))) {
				return args[Integer.parseInt(token)];
			} else {
				return named.get(token);
			}
		}
		
		public String toString() {
			return str.toString();
		}
	}
	
	String fmt;
	
	public StringFormatter(String logFmtString) {
		Objects.requireNonNull(logFmtString);
		this.fmt = logFmtString;
	}
	
	public String format(Object... args) {
		return new FmtStateMachine(fmt, args).formatMain().toString();
	}
}