package bjc.rgens.parser;

import static bjc.rgens.parser.RGrammarLogging.warn;

import java.io.Reader;
import java.io.StringReader;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import bjc.rgens.parser.RGrammarBuilder.AffixType;
import bjc.rgens.parser.elements.CaseElement;
import bjc.rgens.parser.elements.ChanceCaseElement;
import bjc.rgens.parser.elements.SerialCaseElement;
import bjc.rgens.parser.elements.VariableDefCaseElement;
import bjc.utils.data.Pair;
import bjc.utils.funcdata.FunctionalList;
import bjc.utils.funcdata.IList;
import bjc.utils.funcutils.TriConsumer;
import bjc.utils.ioutils.LevelSplitter;
import bjc.utils.ioutils.blocks.Block;
import bjc.utils.ioutils.blocks.BlockReader;
import bjc.utils.ioutils.blocks.SimpleBlockReader;
/**
 * Reads {@link RGrammar} from a input stream.
 *
 * @author student
 */
public class RGrammarParser {
	/**
	 *  Whether we are in debug mode or not.
	 */
	public static final boolean DEBUG = false;
	/**
	 * Whether or not to log endline numbers
	 */
	public static final boolean LINES = true;

	/*
	 * Templates for level-dependent delimiters.
	 */
	/* Pragma block delimiter. */
	private static final String TMPL_PRAGMA_BLOCK_DELIM   = "\\R\\t{%d}(?!\\t)";
	/* Rule declaration block delimiter. */
	private static final String TMPL_RULEDECL_BLOCK_DELIM = "\\R\\t\\t{%d}";
	/* Where block delimiter. */
	private static final String TMPL_WHERE_BLOCK_DELIM    = "\\R\\t{%d}(?:in|end)\\R";
	/* Top-level block delimiter. */
	private static final String TMPL_TOPLEVEL_BLOCK_DELIM = "\\R\\t{%d}\\.?\\R";

	/* Pragma impls. */
	private static Map<String, TriConsumer<String, RGrammarBuilder, Integer>> pragmas;

	/* Initialize pragmas. */
	static {
		pragmas = new HashMap<>();

		pragmas.put("initial-rule", (body, build, level) -> {
			List<String> bits = LevelSplitter.def.levelSplit(body, " ");

			if (bits.size() != 1) {
				String msg = "Must specify initial rule";
				throw new GrammarException(msg);
			}

			build.setInitialRule(bits.get(0));
		});

		pragmas.put("grammar-name", (body, build, level) -> {
			List<String> bits = LevelSplitter.def.levelSplit(body, " ");

			if (bits.size() != 1) {
				String msg = "Must specify grammar name";
				throw new GrammarException(msg);
			}

			build.name = bits.get(0);
		});

		pragmas.put("despace-rule", (body, build, level) -> {
			List<String> bits = LevelSplitter.def.levelSplit(body, " ");

			if (bits.size() < 1) {
				throw new GrammarException("Must specify rules to despace");
			}

			for(String bit : bits) {
				build.despaceRule(bit);
			}
		});

		pragmas.put("export-rule", (body, build, level) -> {
			List<String> exports = LevelSplitter.def.levelSplit(body, " ");

			if(exports.size() < 1) {
				throw new GrammarException("Must specify rules to export");
			}

			for (String export : exports) {
				build.addExport(export);
			}
		});

		pragmas.put("recur-limit", (body, build, level) -> {
			List<String> parts = LevelSplitter.def.levelSplit(body, " ");

			if(parts.size() != 2) {
				throw new GrammarException("Recur-limit pragma takes two arguments: the name of the rule to set the limit for, and the new value of the limit");
			}

			if(!parts.get(1).matches("\\A\\d+\\Z")) {
				throw new GrammarException("Limit value must be an integer");
			}

			build.setRuleRecur(parts.get(0), Integer.parseInt(parts.get(1)));
		});

		pragmas.put("enable-weight", (body, build, level) -> {
			List<String> parts = LevelSplitter.def.levelSplit(body, " ");

			if(parts.size() != 1) {
				throw new GrammarException("Enable-weight pragma takes one argument: the name of the rule to set the weight factor for");
			}

			build.setWeight(parts.get(0));
		});

		pragmas.put("enable-descent", (body, build, level) -> {
			List<String> parts = LevelSplitter.def.levelSplit(body, " ");

			if(parts.size() != 2) {
				throw new GrammarException("Enable-descent pragma takes two arguments: the name of the rule to set the descent factor for, and the new value of the factor");
			}

			if(!parts.get(1).matches("\\A\\d+\\Z")) {
				throw new GrammarException("Factor value must be an integer");
			}

			build.setDescent(parts.get(0), Integer.parseInt(parts.get(1)));
		});

		pragmas.put("enable-binomial", (body, build, level) -> {
			// @NOTE 9/4/18
			//
			// This can be kind of hard to read right off. Is there
			// a format to put stuff in that looks better and is
			// more readable?
			List<String> parts = LevelSplitter.def.levelSplit(body, " ");

			if(parts.size() != 4) {
				throw new GrammarException("Enable-descent pragma takes four arguments: the name of the rule to set the binomial factors for, and the three binomial parameters (target, bound trials)");
			}

			if(!parts.get(1).matches("\\A\\d+\\Z")) {
				throw new GrammarException("Target value must be an integer");
			}
			if(!parts.get(2).matches("\\A\\d+\\Z")) {
				throw new GrammarException("Bound value must be an integer");
			}
			if(!parts.get(3).matches("\\A\\d+\\Z")) {
				throw new GrammarException("Trials value must be an integer");
			}

			build.setBinomial(parts.get(0), Integer.parseInt(parts.get(1)), Integer.parseInt(parts.get(2)), Integer.parseInt(parts.get(3)));
		});

		/*
		 * @NOTE 4/9/18
		 *
		 * Consider if we want to replace this with something more akin
		 * to the `definer` feature from DiceLang. This will work fine
		 * in most cases, but there are some cases where you'd want the
		 * extra power. No examples are apparent at the moment.
		 */
		pragmas.put("find-replace-rule", (body, build, level) -> {
			List<String> bits = LevelSplitter.def.levelSplit(body, " ");

			if(bits.size() != 3) {
				throw new GrammarException("Regex-rule pragma takes three arguments: the name of the rule to process, then the find/replace pair to apply after the rule has been generated.");
			}

			build.findReplaceRule(bits.get(0), bits.get(1), bits.get(2));
		});

		pragmas.put("reject-rule", (body, build, level) -> {
			List<String> bits = LevelSplitter.def.levelSplit(body, " ");

			if(bits.size() != 3) {
				throw new GrammarException("Reject-rule pragma takes two arguments: the name of the rule to process, then the rejection pattern to apply after the rule has been generated.");
			}

			build.rejectRule(bits.get(0), bits.get(1));
		});

		pragmas.put("prefix-with", (body, build, level) -> {
			doAffixWith(body, build, level, AffixType.PREFIX);
		});

		pragmas.put("suffix-with", (body, build, level) -> {
			doAffixWith(body, build, level, AffixType.SUFFIX);
		});

		pragmas.put("circumfix-with", (body, build, level) -> {
			doAffixWith(body, build, level, AffixType.CIRCUMFIX);
		});
		/*
		 * @NOTE 9/4/18
		 *
		 * Right now, we ignore additional elements to autovivify. Not
		 * sure yet if this is the desired behavior.
		 *
		 * As I see it, there are a couple of alternatives:
		 * 
		 * 1) Continue what we're doing. This is simple, but seems
		 *                  somewhat inelegant.
		 *
		 * 2) Error if more than one is provided. Even simpler, but also
		 *                  seems inelegant.
		 *
		 * 3) Parse them independantly. Each element is treated as a
		 *                  seperate autovar. Seems simple, but may
		 *                  cause issues with mixing rule & nonrule
		 *                  variables, as well as naming.
		 *
		 * 4) Parse them together. Autovars are stored as cases instead
		 *                  of case elements. Also simple, but may have
		 *                  some odd corner cases, and I can't think of
		 *                  any cases where the additional power would
		 *                  be useful.
		 *
		 *
		 *
		 *
		 *
		 *
		 * As an additional aside, we currently error if we provide
		 * something that isn't a variable definition. This is because
		 * we pull the name for the auto-vivify variable from the
		 * element. If we go with option 4 above, the user will have to
		 * specify a name for the variable, and we should likely add
		 * some check when the variable is made live that it actually
		 * created the variable it said it would.
		 *
		 */
		pragmas.put("autovivify", (body, build, level) -> {
			doAutoVar(body, build, level, false);
		});

		pragmas.put("autovivify-rule", (body, build, level) -> {
			doAutoVar(body, build, level, true);
		});
	}

	private static void doAffixWith(String body, RGrammarBuilder build, int level, AffixType afxType) {
		int idx = body.indexOf(" ");

		if (idx == -1) {
			String msg = "Affixing pragma %s-with takes at least two arguments, the name of the rule to affix, then what to affix it with\n\tThis can be more than one token, to get them affixed as a group";

			throw new GrammarException(String.format(msg, afxType.toString().toLowerCase()));
		}

		String rName = body.substring(0, idx);

		IList<CaseElement> elms = parseElementString(body.substring(idx + 1)).getLeft();

		build.affixWith(rName, elms, afxType);
	}

	private static void doAutoVar(String body, RGrammarBuilder build, int level, boolean isRule) {
		List<String> bits = LevelSplitter.def.levelSplit(body, " ");

		if (bits.size() < 1) {
			String msg = "Must specify name of variable and definition to autovivify";
			throw new GrammarException(msg);
		}

		String[] bitArr = bits.toArray(new String[0]);

		IList<CaseElement> elmList = parseElementString(bitArr).getLeft();
		CaseElement elm = elmList.first();

		if (elmList.getSize() > 1) {
			warn("Ignoring %d additional elements for autovivify: %s", elmList.getSize(), elmList.tail());
		}

		if (!(elm instanceof VariableDefCaseElement)) {
			throw new GrammarException(String.format("Autovivify expression must be a variable defn. (expr. %s)", elm));
		}

		{
			String name = ((VariableDefCaseElement)elm).varName;

			if (isRule) build.addAutoRlVar(name, elm);
			else        build.addAutoVar(name, elm);
		}
	}

	/**
	 * Read a {@link RGrammar} from an input stream.
	 *
	 * @param is
	 * 	The input stream to read from.
	 *
	 * @return 
	 * 	The grammar represented by the stream.
	 *
	 * @throws GrammarException
	 * 	Thrown if the grammar has a syntax error.
	 */
	public static RGrammar readGrammar(Reader is) throws GrammarException {
		String dlm = String.format(TMPL_TOPLEVEL_BLOCK_DELIM, 0);

		try (BlockReader reader = new SimpleBlockReader(dlm, is)) {
			if (!reader.hasNextBlock()) {
				throw new GrammarException("At least one top-level block must be present");
			}

			try {
				RGrammarBuilder build = new RGrammarBuilder();

				for(Block block : reader) {
					if(DEBUG)
						System.err.printf("Handling top-level block (%s)\n", block);

					handleBlock(build, block.contents, 0, block.startLine);
				}

				if(LINES)
					System.err.printf("%d ", reader.getBlock().endLine);

				return build.toRGrammar();
			} catch (GrammarException gex) {
				String msg = String.format("Error in block (%s)", reader.getBlock());
				throw new GrammarException(msg, gex, gex.getRootMessage());
			}
		} catch (Exception ex) {
			throw new GrammarException("Unknown error handling block", ex, ex.getMessage());
		}
	}

	/* Throughout these, level indicates the nesting level of that construct. */

	/* Handles an arbitrary block. */
	private static void handleBlock(RGrammarBuilder build, String block, 
			int level, int lineOffset) throws GrammarException {
		/* Discard empty blocks. */
		if (block.equals("") || block.matches("\\R"))
			return;

		int typeSep = block.indexOf(' ');

		if (typeSep == -1) {
			throw new GrammarException(
			        "A block must start with a introducer, followed by a space, then the rest of the block");
		}

		String blockType = block.substring(0, typeSep).trim();

		if (blockType.equalsIgnoreCase("pragma")) {
			handlePragmaBlock(block, build, level, lineOffset);
		} else if (blockType.startsWith("[")) {
			handleRuleBlock(block, build, level, lineOffset);
		} else if (blockType.equalsIgnoreCase("where")) {
			handleWhereBlock(block, build, level, lineOffset);
		} else if (blockType.startsWith("#")) {
			if(DEBUG)
				System.err.printf("Handled comment block (%s)\n", block);
			/*
			 * Comment block.
			 *
			 * @TODO 10/11/17 Ben Culkin :GrammarComment
			 *
			 * 	Attach these to the grammar somehow so that they
			 * 	can be re-output during formatting.
			 */
			return;
		} else {
			String msg = String.format("Unknown block type: '%s'", blockType);
			throw new GrammarException(msg);
		}
	}

	/* Handle reading a block of pragmas. */
	private static void handlePragmaBlock(String block, RGrammarBuilder build,
	                                      int level, int lineOffset) throws GrammarException {
		String dlm = String.format(TMPL_PRAGMA_BLOCK_DELIM, level);
		try (BlockReader pragmaReader = new SimpleBlockReader(dlm, new StringReader(block))) {
			try {
				for(Block pragma : pragmaReader) {
					pragma.lineOffset = lineOffset;

					if(DEBUG)
						System.err.printf("Handled pragma block (%s)\n", pragma);

					String pragmaContents = pragma.contents;

					int pragmaSep = pragmaContents.indexOf(' ');

					if (pragmaSep == -1) {
						String msg = "A pragma invocation must consist of the word pragma, followed by a space, then the body of the pragma";

						throw new GrammarException(msg);
					}

					String pragmaLeader = pragmaContents.substring(0, pragmaSep);
					String pragmaBody   = pragmaContents.substring(pragmaSep + 1);

					if (!pragmaLeader.equalsIgnoreCase("pragma")) {
						String msg = String.format("Illegal line leader in pragma block: '%s'", pragmaLeader);

						throw new GrammarException(msg);
					}

					handlePragma(pragmaBody, build, level, pragma.startLine + lineOffset);
				}
			} catch (GrammarException gex) {
				Block pragma = pragmaReader.getBlock();
				String msg   = String.format("Error in pragma: (%s)", pragma);

				throw new GrammarException(msg, gex, gex.getRootMessage());
			}
		} catch (Exception ex) {
			throw new GrammarException("Unknown error handling pragma block", ex, ex.getMessage());
		}
	}

	/* Handle an individual pragma in a block. */
	private static void handlePragma(String pragma, RGrammarBuilder build,
	                                 int level, int lineOffset) throws GrammarException {
		int bodySep = pragma.indexOf(' ');

		if (bodySep == -1)
			bodySep = pragma.length();

		String pragmaName = pragma.substring(0, bodySep);
		String pragmaBody = pragma.substring(bodySep + 1);

		if (pragmas.containsKey(pragmaName)) {
			try {
				if(DEBUG)
					System.err.printf("Handled pragma '%s'\n", pragmaName);

				pragmas.get(pragmaName).accept(pragmaBody, build, level);
			} catch (GrammarException gex) {
				String msg = String.format("Error in pragma '%s'", pragmaName);

				throw new GrammarException(msg, gex);
			}
		} else {
			String msg = String.format("Unknown pragma '%s'", pragmaName);

			throw new GrammarException(msg);
		}
	}

	/* Handle a block of a rule declaration and one or more cases. */
	private static void handleRuleBlock(String ruleBlock, RGrammarBuilder build,
	                                    int level, int lineOffset) throws GrammarException {
		String dlm = String.format(TMPL_RULEDECL_BLOCK_DELIM, level);
		try (BlockReader ruleReader = new SimpleBlockReader(dlm, new StringReader(ruleBlock))) {
			try {
				if (ruleReader.hasNextBlock()) {
					/* Rule with a declaration followed by multiple cases. */
					ruleReader.nextBlock();
					Block declBlock = ruleReader.getBlock();
					declBlock.lineOffset = lineOffset;

					String declContents = declBlock.contents;
					Rule rl = handleRuleDecl(build, declContents, lineOffset + declBlock.startLine);

					for(Block block : ruleReader) {
						/* Ignore comment lines. */
						if(block.contents.trim().startsWith("#")) return;

						handleRuleCase(block.contents, build, rl, block.startLine + lineOffset);
					}
				} else {
					/* Rule with a declaration followed by a single case. */
					handleRuleDecl(build, ruleBlock, lineOffset);
				}
			} catch (GrammarException gex) {
				String msg = String.format("Error in rule case (%s)", ruleReader.getBlock());

				throw new GrammarException(msg, gex, gex.getRootMessage());
			}
		} catch (Exception ex) {
			throw new GrammarException("Unknown error handling rule block", ex, ex.getMessage());
		}
	}

	/* Handle a rule declaration and its initial case. */
	private static Rule handleRuleDecl(RGrammarBuilder build, String declContents, int lineOffset) {
		int declSep = declContents.indexOf("\u2192");

		if (declSep == -1) {
			/*
			 * @NOTE
			 * 	We should maybe remove support for the old
			 * 	syntax at some point. However, maybe we don't
			 * 	want to do so so as to make inputting grammars
			 * 	easier.
			 */
			declSep = declContents.indexOf(' ');

			if (declSep == -1) {
				String msg = "A rule must be given at least one case in its declaration, and seperated from that case by \u2192 or ' '";

				throw new GrammarException(msg);
			}
		}

		String ruleName = declContents.substring(0, declSep).trim();
		String ruleBody = declContents.substring(declSep + 1).trim();

		if (ruleName.equals("")) {
			throw new GrammarException("The empty string is not a valid rule name");
		}

		Rule rul = build.getOrCreateRule(ruleName);

		handleRuleCase(ruleBody, build, rul, lineOffset);

		return rul;
	}

	/* Handle a single case of a rule. */
	private static void handleRuleCase(String cse, RGrammarBuilder build, Rule rul, int lineOffset) {
		Pair<IList<CaseElement>, Integer> caseParts = parseElementString(cse);

		rul.addCase(new NormalRuleCase(caseParts.getLeft()), caseParts.getRight());
	}

	/* Handle a where block (a block with local rules). */
	private static void handleWhereBlock(String block, RGrammarBuilder build,
			int level, int lineOffset) throws GrammarException {
		int nlIndex = block.indexOf("\\nin");

		if (nlIndex == -1) {
			throw new GrammarException("Where block must be a context followed by a body");
		}

		String trimBlock = block.substring(nlIndex).trim();

		String whereDelim = String.format(TMPL_WHERE_BLOCK_DELIM, level);

		try (BlockReader whereReader = new SimpleBlockReader(whereDelim,
					new StringReader(trimBlock))) {
			try {
				Block whereCtx = whereReader.next();
				whereCtx.lineOffset = lineOffset;

				StringReader ctxReader = new StringReader(whereCtx.contents.trim());
				String ctxDelim = String.format(TMPL_TOPLEVEL_BLOCK_DELIM, level + 1);

				try (BlockReader bodyReader = new SimpleBlockReader(ctxDelim, ctxReader)) {
					Block whereBody = whereReader.next();
					whereBody.lineOffset = lineOffset + whereCtx.startLine;

					System.err.printf("\tUNIMPLEMENTED WHERE:\n%s\n", whereBody.contents);
					/**
					 * @TODO 10/11/17 Ben Culkin :WhereBlocks
					 * 	Implement where blocks. 
					 *
					 * 	A where block has the context evaluated
					 * 	in a new context, and the body executed
					 * 	in that context.
					 */
				}
			} catch (GrammarException gex) {
				throw new GrammarException(String.format("Error in where block (%s)",
							whereReader.getBlock()), gex, gex.getRootMessage());
			}
		} catch (Exception ex) {
			throw new GrammarException("Unknown error in where block", ex, ex.getMessage());
		}
	}

	public static Pair<IList<CaseElement>, Integer> parseElementString(String cses) {
		/*
		 * @NOTE
		 *
		 * This is done using String.split because using things like (
		 * as groupers breaks certain grammars. Maybe it can be used if
		 * some sort of way to set which groupers to use is added?
		 *
		 *  List<String> cseList = LevelSplitter.def.levelSplit(cses.trim(), " ");
		 *
		 *  return parseElementString(cseList.toArray(new String[0]));
		 */

		return parseElementString(cses.split(" "));
	}

	public static Pair<IList<CaseElement>, Integer> parseElementString(String... cses) {
		IList<CaseElement> caseParts = new FunctionalList<>();

		int weight = 1;

		int repCount = 1;

		int serialLower = -1;
		int serialUpper = -1;

		int chance = -1;
		boolean doSerial = false;
		boolean doChance = false;

		for (String csepart : cses) {
			String partToAdd = csepart.trim();

			if (partToAdd.equals("")) {
				/* Ignore empty parts */
				continue;
			} else if(partToAdd.matches("\\<\\^\\d+\\>")) {
				/* Set case weights */
				weight = Integer.parseInt(partToAdd.substring(2, partToAdd.length() - 1));
			} else if(partToAdd.matches("\\<&\\d+\\>")) {
				repCount = Integer.parseInt(partToAdd.substring(2, partToAdd.length() - 1));
			} else if(partToAdd.matches("\\<&\\d+\\.\\.\\d+\\>")) {
				serialLower = Integer.parseInt(partToAdd.substring(2, partToAdd.indexOf(".")));
				serialUpper = Integer.parseInt(partToAdd.substring(partToAdd.lastIndexOf(".") + 1, partToAdd.length() - 1));

				doSerial = true;
			} else if(partToAdd.matches("\\<\\?\\d+\\>")) {
				chance = Integer.parseInt(partToAdd.substring(2, partToAdd.length() - 1));

				doChance = true;
			} else if (partToAdd.matches("\\<\\<\\>")) {
				/*
				 * @NOTE
				 *
				 * One, am I even using this feature anywhere?
				 * As far as I can tell, this says to apply the
				 * current set of case part rules to the
				 * previous case part. This may be useful in
				 * certain cases, but none come to mind at the
				 * moment.
				 *
				 * @PERF
				 *
				 * For performance reasons, we may want to
				 * consider setting the chance/serial values as
				 * a setting on CaseElement, instead of having
				 * their own CaseElement type.
				 */
				CaseElement elm = caseParts.popLast();

				if(repCount == 0) {
					/* Skip no-reps */
				} else {
					if(doChance) {
						elm = new ChanceCaseElement(elm, chance);

						doChance = false;
					}

					if(doSerial) {
						elm = new SerialCaseElement(elm, serialLower, serialUpper);

						doSerial = false;
					}

					for(int i = 1; i <= repCount; i++) {
						caseParts.add(elm);
					}

					repCount = 1;
				}
			} else if(partToAdd.matches("\\<[^\\>]+\\>")) {
				throw new GrammarException("Unknown parser meta-rule " + partToAdd);
			} else {
				CaseElement elm = CaseElement.createElement(partToAdd);

				if(repCount == 0) {
					/* Skip no-reps */
				} else {
					if(doChance) {
						elm = new ChanceCaseElement(elm, chance);

						doChance = false;
					}

					if(doSerial) {
						elm = new SerialCaseElement(elm, serialLower, serialUpper);

						doSerial = false;
					}

					for(int i = 1; i <= repCount; i++) {
						caseParts.add(elm);
					}

				}

				repCount = 1;
			}
		}

		return new Pair<>(caseParts, weight);
	}
}