//---
// fxos-shell.parser: Command-line parser
//---

#ifndef FXOS_PARSER_H
#define FXOS_PARSER_H

#include <cstdint>
#include <string>
#include <stdexcept>
#include <initializer_list>
#include <vector>
#include <map>
#include <functional>
#include <variant>

#include <fxos/memory.h>
#include <fxos/vspace.h>

#include "session.h"

/* Token values; just integers, but with conversion to and from string */
class T
{
public:
	enum TokenName: int8_t {
		END        = 0,
		SPC        = 1,
		SEPARATOR  = 2,
		NUM        = 3,
		SYMBOL     = 4,
		SYSCALL    = 5,
		OPTION     = 6,
		STRING     = 7,
		/* Other tokens using character literals:
	       + - * / % ( ) $ :
	       '.' for "..", '<' for "<<", '>' for ">>" */
	};

	/* Construction with no value and explicit value */
	T() = default;
	constexpr T(int name): m_name((TokenName)name) {}
	constexpr T(TokenName name): m_name(name) {}

	/* Conversion to integer value, comparisons */
	constexpr operator TokenName() const noexcept { return m_name; }

	/* Conversion to string */
	std::string str() const;

private:
	TokenName m_name;
};

/* Range with start included and end excluded */
struct Range
{
	long start;
	long end;
};

/* Token with their data */
struct Token
{
	/* Lexer-style attribute */
	struct LexAttribute {
		long NUM;
		char *STRING;
	};

	/* Attribute once in the parser */
	struct Attribute {
		long NUM;
		std::string STRING; /* SYMBOL, OPTION, STRING */
	};

	/* Token type and value */
	T type;
	Attribute value;

	/* Conversion to string */
	std::string str() const;
};

//---
// Lexer interface
//---

/* Whether all files have finished executing */
bool lex_idle();
/* Path of file that provided the last token, "" if at top-level */
std::string lex_last_used_file();
/* Lex this input coming from the interactive command-line */
void lex_repl(std::string input);
/* Lex the input coming from these files, sequentially */
void lex_include(std::vector<std::string> files);

/* For the parser: get one token from the current source */
Token lex_read();

//---
// Parser interface for commands
//---

/* Parser class, used both for final command parsing and completion */
class Parser
{
public:
	Parser(bool complete);
	/* Start parsing, should be called just once after constructing */
	void start();

	/* Whether the end of a command has been reached */
	bool at_end() const;
	/* Lookahead token */
	Token lookahead() const;
	/* Require that command is finished */
	void end();
	/* Exhaust all input (usually after encountering an error) */
	void exhaust();
	/* Whether we are parsing for autocompletion. This is only available to
	   allow appropriate decisions about printing vs. ignoring error messages.
	   Do not change parsing rules based on this information! */
	bool completing() const;

	/* Expect a token of this type, or of any of the listed types */
	Token expect(T type, bool ignore_spaces=true);
	Token expect(std::initializer_list<T> types, bool ignore_spaces=true);

	using OptionHandler = std::function<void(std::string const &value)>;

	/* Specify an option to be accepted until the next SEPARATOR or END token
	   (basically for the current command). The function will be called when
	   the option is found during a call to accept_options(). */
	void option(std::string name, OptionHandler callback);

	/* Read a symbol from the specified category; the category name is used to
	   determine completion options on the command-line */
	std::string symbol(std::string category="");
	/* Literal string */
	std::string str();
	/* Read a numerical constant, or an expression. Expression uses the space
	   to access the program counter and query symbol values */
	long num();
	long expr(VirtualSpace *space);
	/* Read a range; again $ and symbols are interpreted. If (before) and
	   (after) are both specified, a single value will also be accepted, and
	   the range [value-before, value+after) will be returned. */
	Range range(VirtualSpace *space, long before=-1, long after=-1);
	/* Read an expression or a range */
	std::variant<long, Range> expr_or_range(VirtualSpace *space);
	/* Read a memory region (allows both ranges and symbolic names) */
	FxOS::MemoryRegion region(VirtualSpace *space, long before=-1,
		long after=-1);
	/* Read options, if any. Never fails */
	void accept_options();

	/* Skip separators, used when reading several commands at once */
	void skip_separators();
	/* Read everything until end of command (used when commands abort) */
	void exhaust_until_separator();
	/* Exhaust input until separators, used for debugging the lexer */
	void dump_command();

	//---
	// Completion system
	//---

	class SyntaxError: public std::invalid_argument
	{
	public:
		SyntaxError(char const *what): std::invalid_argument(what) {}
	};

	/* A completion request is thrown by the parser when in completion mode to
	   signal the expected next element */
	struct CompletionRequest
	{
		CompletionRequest(std::string const &c, std::string const &v,
			VirtualSpace *s=nullptr): category(c), value(v), space(s) {}
		std::string category;
		std::string value;
		VirtualSpace *space;
	};

	//---
	// Internal stuff
	//---

private:
	/* Read a token into the lookahead and return the former*/
	Token feed(bool ignore_spaces=true);

	/* Parsing rules for expressions */
	long term();
	long factor();
	long atom();

	/* true if we're completing a partial command, false if we're parsing a
	   finished one */
	bool m_complete;
	/* Lookahead token */
	Token m_la;

	/* Virtual space for evaluation of symbols, can only be non-null during
	   calls to expr() */
	VirtualSpace *m_expr_space;

	/* Options (retained until next SEPARATOR or END) */
	std::map<std::string, OptionHandler> m_options;
};

#endif /* FXOS_PARSER_H */