#include "Parser.h"

#include <fstream>
#include <sstream>

#include <iostream>

#include <stdexcept>

#include "Environment.h"

namespace {
	struct ParseGroup {
		std::string accept;

		operator std::string() const {
			return accept;
		}
		bool operator== (const std::string& other) const {
			return accept == other;
		}
	};

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

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

	const Match ESCAPE = { "\\" };

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

	std::string 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();
		return buffer.str();
	}

	std::vector<std::string> split_string_by_lines(const std::string& str) {
		std::vector<std::string> lines;
		int pos = 0;
		int prev = 0;
		while ((pos = str.find(NEWLINE, prev)) != std::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 std::string& str) {
		bool negative = str[0] == NEGATIVE;
		bool had_dot = false;
			
		for (auto& c : negative ? str.substr(1) : str) {
			if (NUMERIC.accept.find(c) == std::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 std::string& s) {
		for (auto& c : s) {
			if (WS.accept.find(c) == std::string::npos)
				return false;
		}
		return true;
	}

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

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

	void SkipComments(const std::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 std::string& f, size_t& pos) {
		SkipWS(f, pos);
		pos++;
	}

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

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

	NVL::Parse::Object ParseExpression(const std::string& f, size_t& pos);
	NVL::Parse::Object ParseArray(const std::string& f, size_t& pos, int layer) {
		SkipComments(f, pos);

		std::vector<NVL::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 { NVL::Parse::Type::Array, array };
	}

	std::string ParseString(const std::string& f, size_t& pos) {
		SkipComments(f, pos);
		std::vector<int> discards{};
		auto start = ++pos; // skip opening quote
		do {
			if (f[pos] == QUOTE) {
				break;
			}
			else if (f[pos] == ESCAPE)	{
				if (ESCAPED.accept.find(f[pos]) != std::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 (int i = 0; i < discards.size(); i++) {
			str.erase(discards[i] - start - i, 1);
		}
		return str;
	}
	unsigned GetProcedureArity(const std::string& key) {
		return NVL::Environment::ENVIRONMENT.get(key).length;
	}

	NVL::Parse::Command ParseCommand(const std::string& f, size_t& pos) {
		SkipComments(f, pos);

		auto proc = GetToken(f, pos);

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

		SkipComments(f, pos);
		return c;
	}

	NVL::Parse::Object ParseExpression(const std::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 NVL::Parse::Object{ NVL::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 { NVL::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 { NVL::Parse::Type::Number, std::stof(token) };
			else if (IsLegalSymbolName(token))
				return { NVL::Parse::Type::Symbol, token };
			else
				throw std::runtime_error("Illegal symbol");
		}
	
	}

	NVL::Parse::Command ParseDialogue(const std::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) + " ", dummy);
		}

		// assume SwitchSpeaker and Say are unary for now

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

		return { { NVL::Parse::Type::Symbol, "Say" }, { NVL::Parse::Type::String, s } };
	}

	NVL::Parse::Scene ParseScene(const std::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");
		NVL::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 == std::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 {
	std::vector<Scene> ParseFile(const std::string& path) {
		std::string 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;
	}
}