#include "Parser.h"

#include <fstream>
#include <sstream>

#include <iostream>

#include <regex>

#include <utility>
#include <stdexcept>

#include "Environment.h"
#include <locale>
#include <codecvt>

namespace {
	using namespace NVL;

	struct ParseGroup {
		String accept;

		operator String() const {
			return accept;
		}
		bool operator== (const String& other) const {
			return accept == other;
		}
	};

	struct Match {
		String accept;
		
		operator wchar_t() const {
			if (accept.length() == 1)
				return accept[0];
			else {
				std::wcerr << "Cannot demote Match " << accept << " to char" << std::endl;
				return '\0';
			}
		}
		bool operator== (const String& other) const {
			return accept == other;
		}
	};

	const ParseGroup NUMERIC = { L"1234567890" };
	const Match DECIMAL_DOT = { L"." };
	const Match NEGATIVE = { L"-" };
	const ParseGroup ALPHA = { L"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" };
	const Match ARRAY_OPEN = { L"[" };
	const Match ARRAY_CLOSE = { L"]" };
	const Match ARRAY_DELIM = { L"," };
	const Match GROUP_OPEN = { L"(" };
	const Match GROUP_CLOSE = { L")" };
	const Match QUOTE = { L"\"" };
	const Match COMMENT_BEGIN = { L"//" };
	const Match DIALOGUE_OPEN = { L"<<-" };
	const Match DIALOGUE_CLOSE = { L"->>" };
	const Match BEGIN = { L"BEGIN" };
	const Match END = { L"END" };
	const ParseGroup SYMBOL = { ALPHA.accept + NUMERIC.accept + L"_"};
	const Match SPECIAL_SYMBOLS[] = {
		{ L"+" },
		{ L"-" },
		{ L"*" },
		{ L"/" },
		{ L"=?" },
		{ L">?" },
		{ L"<?" },
		{ L"<=?" },
		{ L">=?" }
	};
	const ParseGroup WS = { L" \t\v\f\r\n" };
	const ParseGroup SEPARATOR = {
		WS.accept + 
		wchar_t(ARRAY_OPEN) + 
		wchar_t(ARRAY_CLOSE) + 
		wchar_t(GROUP_OPEN) + 
		wchar_t(GROUP_CLOSE) + 
		wchar_t(ARRAY_DELIM) + 
		COMMENT_BEGIN.accept[0]
	};
	const Match NEWLINE = { L"\n" };
	const ParseGroup ESCAPED = { L"\\\"" };

	const Match ESCAPE = { L"\\" };

	// Dialogue mode matches
	const Match MARKUP_OPEN = { L"[" };
	const Match MARKUP_CLOSE = { L"]" };
	const Match SPEAKER_OPEN = { L"[" };
	const Match SPEAKER_CLOSE = { L"]" };
	const Match MARKUP_TEXT_OPEN = { L"{" };
	const Match MARKUP_TEXT_CLOSE = { L"}" };
	const Match TEMPLATE_IND = { L"$" };
	const Match TEMPLATE_OPEN = { L"{" };
	const Match TEMPLATE_CLOSE = { L"}" };
	
	const Match COMMAND_ESCAPE = { L"*!" };
	const ParseGroup DIALOGUE_ESCAPED_SINGLE = { 
		ESCAPE.accept +
		wchar_t(MARKUP_OPEN) + 
		wchar_t(MARKUP_CLOSE) + 
		wchar_t(MARKUP_TEXT_OPEN) + 
		wchar_t(MARKUP_TEXT_CLOSE) +
		// char(SPEAKER_OPEN) +
		// char(SPEAKER_CLOSE) +
		wchar_t(TEMPLATE_IND)
		// char(TEMPLATE_OPEN) + 
		// char(TEMPLATE_CLOSE) 
	};

	std::wstring read_file_to_string(const std::string& path) {
		std::ifstream f(path);
		{	// Some apps on Windows adds this signature in front of UTF-8 files when saving
			char a, b, c;
			a = f.get(); b = f.get(); c = f.get();
			if (a != (char)0xEF || b != (char)0xBB || c != (char)0xBF)
				f.seekg(0);
			else
				std::cerr << "Warning: Windows UTF-8 BOM skipped" << std::endl;
		}
		std::stringstream buffer;
		buffer << f.rdbuf();
		std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> converter;
		return converter.from_bytes(buffer.str());
	}

	std::vector<String> split_string_by_lines(const String& str) {
		std::vector<String> lines;
		size_t pos = 0;
		size_t prev = 0;
		while ((pos = str.find(NEWLINE, prev)) != String::npos) {
			lines.push_back(str.substr(prev, pos - prev));
			prev = pos + 1;
		}

		lines.push_back(str.substr(prev));
		return lines;
	}

	inline bool IsNumeric(const String& str) {
		bool negative = str[0] == NEGATIVE;
		bool had_dot = false;
			
		for (auto& c : negative ? str.substr(1) : str) {
			if (NUMERIC.accept.find(c) == String::npos) {
				if (c == DECIMAL_DOT.accept[0]) {
					if (had_dot)
						return false;
					else
						had_dot = true;
				}
				else
					return false;
			}
		}

		if (had_dot + negative == str.length())
			return false;

		return true;
	}

	inline bool ContainsOnlyWS(const String& s) {
		for (auto& c : s) {
			if (WS.accept.find(c) == String::npos)
				return false;
		}
		return true;
	}

	void SkipWS(const String& f, size_t& pos) {
		while (WS.accept.find(f[pos]) != String::npos)
			pos++;
	}

	void SkipToNextLine(const String& f, size_t& pos) {
		while (f[pos] != NEWLINE.accept[0])
			pos++;
		pos++;
	}

	void SkipComments(const String& f, size_t& pos) {
		SkipWS(f, pos);
		while (f.substr(pos, 2) == COMMENT_BEGIN.accept) {
			SkipToNextLine(f, pos);
			SkipWS(f, pos);
		}
	}

	void SkipOverFirstChar(const String& f, size_t& pos) {
		SkipWS(f, pos);
		pos++;
	}

	String GetToken(const String& f, size_t& pos) {
		SkipWS(f, pos);
		auto start = pos;
		while (++pos) {
			if (SEPARATOR.accept.find(f[pos]) != String::npos)
				break;
		}
		return f.substr(start, pos - start);
	}	
	
	String PeekToken(const String& f, size_t pos) {
		SkipWS(f, pos);
		auto start = pos;
		while (++pos) {
			if (SEPARATOR.accept.find(f[pos]) != String::npos)
				break;
		}
		return f.substr(start, pos - start);
	}

	bool IsLegalSymbolName(const String& token) {
		for (const auto& x: SPECIAL_SYMBOLS) {
			if (token == x.accept)
				return true;
		}
		if (ALPHA.accept.find(token[0]) == String::npos)
			return false;
		for (auto& i : token)
			if (SYMBOL.accept.find(i) == String::npos)
				return false;
		return true;
	}

	Parse::Object ParseExpression(const String& f, size_t& pos);
	Parse::Object ParseArray(const String& f, size_t& pos, u32 layer) {
		SkipComments(f, pos);

		std::vector<Parse::Object> array{};
		
		array.push_back(ParseExpression(f, pos));
		while (PeekToken(f, pos)[0] != ARRAY_CLOSE) {
			if (PeekToken(f, pos)[0] == ARRAY_DELIM)
				SkipOverFirstChar(f, pos);
			else
				throw std::runtime_error("Invalid array member");
			array.push_back(ParseExpression(f, pos));
		}

		return { Parse::Type::Array, array };
	}

	String ParseString(const String& f, size_t& pos) {
		SkipComments(f, pos);
		std::vector<size_t> discards{};
		auto start = ++pos; // skip opening quote
		do {
			if (f[pos] == QUOTE) {
				break;
			}
			else if (f[pos] == ESCAPE)	{
				if (ESCAPED.accept.find(f[pos]) != String::npos) {
					discards.push_back(pos++);
				}
				else
					throw std::runtime_error("Unrecognized escape sequence");
			}
			else if (f[pos] == NEWLINE) {
				throw std::runtime_error("Unclosed String");
			}
		} while (pos++);
		auto str = f.substr(start, pos++ - start);
		for (size_t i = 0; i < discards.size(); i++) {
			str.erase(discards[i] - start - i, 1);
		}
		return str;
	}
	u32 GetProcedureArity(const String& key) {
		return Environment::ENVIRONMENT.get(key).length;
	}

	Parse::Command ParseCommand(const String& f, size_t& pos) {
		SkipComments(f, pos);

		auto proc = GetToken(f, pos);

		if (!IsLegalSymbolName(proc)) throw std::runtime_error("Illegal Procedure name");
		Parse::Command c{ Parse::Object{ Parse::Type::Symbol, proc } };
		for (u32 i = 0; i < GetProcedureArity(proc); i++) {
			c.push_back(ParseExpression(f, pos));
		}

		SkipComments(f, pos);
		return c;
	}

	Parse::Object ParseExpression(const String& f, size_t& pos) {
		SkipComments(f, pos);

		auto t = PeekToken(f, pos);
		if (t[0] == ARRAY_OPEN) {
			SkipOverFirstChar(f, pos);
			auto c = ParseArray(f, pos, 0);
			if (PeekToken(f, pos)[0] != ARRAY_CLOSE)
				throw std::runtime_error("Cannot match closing Array");
			else
				SkipOverFirstChar(f, pos);
			return c;
		}
		else if (t[0] == GROUP_OPEN) {
			SkipOverFirstChar(f, pos);
			auto c = ParseCommand(f, pos);
			if (PeekToken(f, pos)[0] != GROUP_CLOSE)
				throw std::runtime_error("Cannot match closing subexpression");
			else
				SkipOverFirstChar(f, pos);
			return Parse::Object{ Parse::Type::Subexpression, c };
		}
		else if (t[0] == GROUP_CLOSE)
			throw std::runtime_error("Cannot match closing subexpression, likely too few arguments");
		else if (t[0] == QUOTE)
			return { Parse::Type::String, ParseString(f, pos) };
		else if (t[0] == ARRAY_CLOSE)
			throw std::runtime_error("Cannot match closing array");
		else {
			auto token = GetToken(f, pos);
			if (IsNumeric(token))
				return { std::stof(token) };
			else if (IsLegalSymbolName(token))
				return { Parse::Type::Symbol, token };
			else
				throw std::runtime_error("Illegal symbol");
		}
	
	}

	/*
	*	NVL Markup Parsetree
	* 
	*	*	- Vec:2	- Num: Markup begin
	*		|		|
	*		|		- Num: Markup end
	*		|
	*		- Vec:N	- Str: T of Markup 
	*				|
	*				OR
	*				|
	*				- Vec:2	- Str: T of Markup
	*						|
	*						- Vec: Params
	*/
	Parse::Object MatchMarkup(String& s) {
		static const std::regex typer(R"((?:^|[^\\])\[([^\]]+)\]\s*\{([^\}]+)\})"); // G1 -> Specifiers, G2 -> Contents
		static const std::regex effect(R"(\s*(?:([^,\(\)]+?)\s*\(\s*([^\(\)]+?)\s*\)|([^,\(\)]+?))\s*(?:,\s*|$))"); // G1 & G2 -> Func, G3 -> Attr
		static const std::regex param(R"(([^,]+?)\s*(?:,\s*|$))"); // Comma split of func args

		std::vector<Parse::Object> tags;

		std::wsmatch tags_match;
		std::wsmatch effects_match;
		std::wsmatch params_match;

		String reconstruction{};

		size_t running_offset = 0; // to account for characters removed

		bool has_markup{};

		// Match tags
		String::const_iterator tags_start(s.cbegin());
		while (std::regex_search(tags_start, s.cend(), tags_match, typer)) {
			has_markup = true;
			Parse::Object m{ Parse::Type::Array, std::vector<Parse::Object>{} };
			reconstruction.append(tags_match.prefix().first, std::next(tags_match[0].first, 1)); // match will overmatch behind by 1
			reconstruction.append(tags_match[2].first, tags_match[2].second);
			running_offset += tags_match[2].first - std::next(tags_match[0].first, 1);

			size_t begin = tags_match[2].first - s.cbegin() - running_offset;

			Parse::Object range{ Parse::Type::Array, { std::vector<Parse::Object>{
					{ static_cast<Number>(begin) },
					{ static_cast<Number>(begin + (tags_match[2].second - tags_match[2].first)) }
				}
			} };

			std::vector<Parse::Object> effects{};

			// Match markup options
			String::const_iterator effects_start(tags_match[1].first);
			while (std::regex_search(effects_start, tags_match[1].second, effects_match, effect)) {
				if (effects_match[3].matched) {
					effects.push_back({ Parse::Type::String, effects_match[3].str() });
				}
				else {
					std::vector<Parse::Object> args;
					String::const_iterator params_start(effects_match[2].first);
					while (std::regex_search(params_start, effects_match[2].second, params_match, param)) {
						size_t temp = 0;
						args.push_back(ParseExpression(params_match[1].str() + SEPARATOR.accept[0], temp)); // PeekToken will freak out if I don't do this
						params_start = params_match.suffix().first;
					}
					effects.push_back({ Parse::Type::Array, std::vector<Parse::Object>{ { Parse::Type::String, effects_match[1].str() }, { Parse::Type::Array, args } } });
				}
				effects_start = effects_match.suffix().first;
			}
			running_offset += tags_match[0].second - tags_match[2].second;
			tags_start = tags_match.suffix().first;
			tags.push_back({ Parse::Type::Array, std::vector<Parse::Object>{ range, { Parse::Type::Array, effects } } });
		}

		if (has_markup) {
			reconstruction.append(tags_match.suffix().first, tags_match.suffix().second);

			s = reconstruction;

			return { Parse::Type::Array, tags };
		}
		else {
			return { Parse::Type::Array, std::vector<Parse::Object>{} };
		}
	}


	Parse::Command ParseDialogue(const String& s) {
		if (s.substr(0, 2) == COMMAND_ESCAPE.accept) {
			size_t dummy = 0;
			// Pad a space towards the end, the helpers do not expect strings to immediately terminate
			return ParseCommand(s.substr(2) + L" ", dummy);
		}

		// assume arity for SwitchSpeaker and Say

		if (s.back() == SPEAKER_CLOSE) {
			if (s.front() == SPEAKER_OPEN) {
				auto name = s.substr(1, s.length() - 2);
				// if (IsLegalSymbolName(name))
				return { { Parse::Type::Symbol, L"SwitchSpeaker" }, { Parse::Type::String, name } };
			}
			else
				throw std::runtime_error("Malformed speaker command");
		}

		String copy{ s };
		Parse::Object tags = MatchMarkup(copy); // THIS WILL MODIFY COPY

		return { { Parse::Type::Symbol, L"Say" }, { Parse::Type::String, copy },  tags };
	}

	Parse::Scene ParseScene(const String& f, size_t& pos) {
		SkipComments(f, pos);

		if (!(GetToken(f, pos) == BEGIN.accept))
			throw std::runtime_error("Could not match accept at root");

		auto scene_name = GetToken(f, pos);
		if (!IsLegalSymbolName(scene_name)) throw std::runtime_error("Illegal Scene name");
		Parse::Scene s{ scene_name };

		bool dialogue_mode = false;

		while (PeekToken(f, pos) != END.accept) {
			if (!dialogue_mode)
				if (PeekToken(f, pos) == DIALOGUE_OPEN.accept) {
					dialogue_mode = true;
					GetToken(f, pos); // skip DIALOGUE_OPEN
					SkipComments(f, pos);
				}
				else
					s.append(ParseCommand(f, pos));
			else {
				auto end = f.find(NEWLINE.accept + DIALOGUE_CLOSE.accept, pos);
				if (end == String::npos)
					throw std::runtime_error("Dialogue does not terminate");
				auto lines = split_string_by_lines(f.substr(pos, end - pos));
				for (auto& l : lines) {
					if (!l.empty() && !ContainsOnlyWS(l))
						s.append(ParseDialogue(l));
				}
				dialogue_mode = false;
				pos = end;
				GetToken(f, pos); // skip DIALOGUE_CLOSE
				SkipComments(f, pos);
			}
		}

		if (dialogue_mode)
			throw std::runtime_error("Illegal Scene end");

		GetToken(f, pos); // skip END

		SkipComments(f, pos);
		return s;
	}
}

namespace NVL::Parse {

	Object::Object(const Number& v) : type(Type::Number), value(v) { }

	Object::Object(Type t, const String& v) : type(t), value(v) {
		if (t != Type::String && t != Type::Symbol) throw std::runtime_error("Bad type when constructing object!");
	}

	Object::Object(Type t, const std::vector<Object>& v) : type(t), value(v) {
		if (t != Type::Array && t != Type::Subexpression) throw std::runtime_error("Bad type when constructing object!");
	}

	Object::Object(Number&& v) : type(Type::Number), value(std::move(v)) {
	}

	Object::Object(Type t, String&& v) : type(t), value(std::move(v)) {
		if (t != Type::String && t != Type::Symbol) throw std::runtime_error("Bad type when constructing object!");
	}

	Object::Object(Type t, std::vector<Object>&& v) : type(t), value(std::move(v)) {
		if (t != Type::Array && t != Type::Subexpression) throw std::runtime_error("Bad type when constructing object!");
	}

	std::vector<Scene> ParseFile(const std::string& path) {
		std::wstring f = read_file_to_string(path);

		std::vector<Scene> list {}; // Vector of scenes which each contain a vector of Parses
		for (size_t i = 0; i < f.length(); i++) {
			list.push_back(ParseScene(f, i));
		}

		return list;
	}
}