package bjc.rgens.newparser;

import bjc.utils.funcdata.FunctionalList;
import bjc.utils.funcdata.IList;
import bjc.utils.funcutils.TriConsumer;
import bjc.utils.ioutils.blocks.Block;
import bjc.utils.ioutils.blocks.BlockReader;
import bjc.utils.ioutils.blocks.SimpleBlockReader;

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

/**
 * 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;

	/*
	 * 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) -> {
			int sep = body.indexOf(' ');

			if (sep != -1) {
				String msg = "Initial-rule pragma takes only one argument, the name of the initial rule";
				throw new GrammarException(msg);
			}

			build.setInitialRule(body);
		});

		pragmas.put("despace-rule", (body, build, level) -> {
			int sep = body.indexOf(' ');

			if (sep != -1) {
				String msg = "despace-rule pragma takes only one argument, the name of the rule to despace";
				throw new GrammarException(msg);
			}

			build.despaceRule(body);
		});

		pragmas.put("export-rule", (body, build, level) -> {
			String[] exports = body.split(" ");

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

		pragmas.put("regex-rule", (body, build, level) -> {
			int nameIndex = body.indexOf(" ");

			if(nameIndex == -1) {
				throw new GrammarException("Regex-rule pragma takes two arguments: the name of the rule to process, then the regex to apply after the rule has been generated.");
			}

			String name = body.substring(0, nameIndex).trim();
			String patt = body.substring(nameIndex + 1).trim();

			build.regexizeRule(name, patt);
		});

		pragmas.put("suffix-with", (body, build, level) -> {
			String[] parts = body.trim().split(" ");

			if (parts.length != 2) {
				String msg = "Suffix-with pragma takes two arguments, the name of the rule to suffix, then what to suffix it with";

				throw new GrammarException(msg);
			}

			build.suffixWith(parts[0], parts[1]);
		});

		pragmas.put("prefix-with", (body, build, level) -> {
			String[] parts = body.trim().split(" ");

			if (parts.length != 2) {
				String msg = "Prefix-with pragma takes two arguments, the name of the rule to prefix, then what to prefix it with";

				throw new GrammarException(msg);
			}

			build.prefixWith(parts[0], parts[1]);
		});
	}

	/**
	 * 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();

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

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

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

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

	/* Handles an arbitrary block. */
	private static void handleBlock(RGrammarBuilder build, String block, 
			int level) 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);
		} else if (blockType.startsWith("[")) {
			handleRuleBlock(block, build, level);
		} else if (blockType.equalsIgnoreCase("where")) {
			handleWhereBlock(block, build, level);
		} else if (blockType.equalsIgnoreCase("#")) {
			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) throws GrammarException {
		String dlm = String.format(TMPL_PRAGMA_BLOCK_DELIM, level);
		try (BlockReader pragmaReader = new SimpleBlockReader(dlm, new StringReader(block))) {
			try {
				pragmaReader.forEachBlock((pragma) -> {
					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);
				});
			} catch (GrammarException gex) {
				Block pragma = pragmaReader.getBlock();
				String msg   = String.format("Error in pragma: (%s)", pragma);

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

	/* Handle an individual pragma in a block. */
	private static void handlePragma(String pragma, RGrammarBuilder build,
	                                 int level) 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) 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();

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

					ruleReader.forEachBlock((block) -> {
						/* Ignore comment lines. */
						if(block.contents.trim().startsWith("#")) return;

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

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

	/* Handle a rule declaration and its initial case. */
	private static Rule handleRuleDecl(RGrammarBuilder build, String declContents) {
		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";

				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);

		return rul;
	}

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

		for (String csepart : cse.split(" ")) {
			String partToAdd = csepart.trim();

			/* Ignore empty parts */
			if (partToAdd.equals(""))
				continue;

			caseParts.add(CaseElement.createElement(partToAdd));
		}

		rul.addCase(new RuleCase(RuleCase.CaseType.NORMAL, caseParts));
	}

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

		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();

				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();

				/**
				 * @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);
			}
		} catch (Exception ex) {
			throw new GrammarException("Unknown error in where block", ex);
		}
	}
}