#include "request.h"

#include <ctype.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <lauxlib.h>
#include <lua.h>

#include "http.h"

static const int REQUEST_DATA_SIZE = 4096;
static const int MAX_HEADERS = 30;

/// Allocates and initializes request structure.
/// \return Pointer to initialized request or NULL in case of an error
/// \see /free_request
struct request * new_request(lua_State * L)
{
	struct request * request = malloc(sizeof(struct request));

	if (NULL == request)
	{
		return NULL;
	}

	memset(request, 0, sizeof(struct request));
	request->step = parse_step_method;

	request->data = malloc(REQUEST_DATA_SIZE);

	if (NULL == request->data)
	{
		free(request);
		return NULL;
	}

	request->lua = lua_newthread(L);
	request->reference = luaL_ref(L, LUA_REGISTRYINDEX);

	return request;
}

/// Releases memory used by the request and the request itself.
/// \param request Request to free
/// \see /new_request
void free_request(lua_State * L, struct request * request)
{
	if (NULL != request->data)
	{
		free(request->data);
	}

	if (NULL != request->headerv)
	{
		free(request->headerv);
	}

	luaL_unref(L, LUA_REGISTRYINDEX, request->reference);

	free(request);
}

/// Collects request between calls to `poll`.
/// \param fd Client socket
/// \param request Pointer to current request context of handled client
/// \return Number of bytes parsed, -1 if an error occured or 0 if expects more data
int parse_request(lua_State * L, const int fd, struct request ** request)
{
	if (NULL == *request)
	{
		*request = new_request(L);
		if (NULL == *request)
		{
			return -1;
		}
	}

	// TODO: Expand buffer until EAGAIN or arbitrary limit
	int length = read(fd, (*request)->data, REQUEST_DATA_SIZE - 1);

	if (0 == length || (-1 == length && EWOULDBLOCK != errno && EAGAIN != errno))
	{
		return -1; // TODO: Handle errors properly
	}

	(*request)->data[length] = 0;
	(*request)->length = length;

	return (*request)->step(*request);
}


/// Progresses the readout of the request until delimiter is found.
/// \param request Request to process
/// \param delimiter Character that marks the end of the readout
/// \return Position of the delimiter or 0 if the deliminter could not be found
static int read_until_char(struct request * request, const char delimiter)
{
	char character;
	while (request->position < request->length)
	{
		character = request->data[request->position];
		if (delimiter == character)
		{
			return request->position;
		}
		request->position++;
	}
	return 0;
}

/// Progresses the readout of the request until non-whitespace character is found.
/// \param request Request to process
/// \return Position of the first non-whitespace character or 0 if it could not be found
/// \see isalpha(3)
static int read_until_word(struct request * request)
{
	char character;
	while (request->position < request->length)
	{
		character = request->data[request->position];
		if (!isspace(character))
		{
			return request->position;
		}
		request->position++;
	}
	return 0;
}

/// Progresses the readout of the request until line separator is found.
/// \param request Request to process
/// \return Position of the first byte of the separator or 0 if line separator could not be found
static int read_rest_of_line(struct request * request)
{
	while (request->position < request->length - 1)
	{
		if ('\r' == request->data[request->position] && '\n' == request->data[request->position + 1])
		{
			return request->position;
		}
		else if ('\r' == request->data[request->position + 1])
		{
			request->position += 1;
		}
		else
		{
			request->position += 2;
		}
	}
	return 0;
}

#define PROCEED_TO(_x) \
	request->temp.start = 0; \
	request->temp.length = 0; \
	request->step = _x; \
	return _x(request)

/// Parses method field of the request.
/// \param request Request to process
/// \return -1 if an error has occured, 0 if too little data available or total number of bytes processed
int parse_step_method(struct request * request)
{
	// TODO: Consider reworking read_* functions to be more aware of word boundaries.
	request->temp.length = read_until_char(request, ' ');

	if (0 == request->temp.length)
	{
		return 0;
	}

	lua_pushlstring(request->lua, request->data + request->temp.start, request->temp.length);

	PROCEED_TO(parse_step_path);
}

/// Parses path field of the request.
/// \param request Request to process
/// \return -1 if an error has occured, 0 if too little data available or total number of bytes processed
// TODO: Consider spliting path into an actual path and arguments in this stage
int parse_step_path(struct request * request)
{
	// TODO: Rethink interface of parse_step_* and read_* functions. After a break it looks like mess; it's a bad sign.
	if (0 >= request->temp.start)
	{
		request->temp.start = read_until_word(request);

		if (0 == request->temp.start)
		{
			return 0;
		}
	}

	const int result = read_until_char(request, ' ');

	if (0 == result)
	{
		return 0;
	}

	request->temp.length = request->position - request->temp.start;

	// TODO: Use macro for pushing temporary span. Also clear the span in that macro instead of PROCEED_TO.
	lua_pushlstring(request->lua, request->data + request->temp.start, request->temp.length);

	PROCEED_TO(parse_step_version);
}

/// Parses and verifies http version field of the request.
/// \param request Request to process
/// \return -1 if an error has occured, 0 if too little data available or total number of bytes processed
// TODO: Return -1 if version is unsupported, meaning other than HTTP/1.1
int parse_step_version(struct request * request)
{
	if (0 >= request->temp.start)
	{
		request->temp.start = read_until_word(request);

		if (0 == request->temp.start)
		{
			return 0;
		}
	}

	const int result = read_rest_of_line(request);

	if (0 == result)
	{
		return 0;
	}

	request->temp.length = request->position - request->temp.start;

	lua_pushlstring(request->lua, request->data + request->temp.start, request->temp.length);

	PROCEED_TO(parse_step_header_name);
}

/// Parses and verifies name of a single header from the request.
/// \param request Request to process
/// \return -1 if an error has occured, 0 if too little data available or total number of bytes processed
int parse_step_header_name(struct request * request)
{
	if (NULL == request->headerv)
	{
		request->headerv = malloc(sizeof(struct header) * MAX_HEADERS);
		request->headerc = 0;
		memset(request->headerv, 0, sizeof(struct header) * MAX_HEADERS);

		if (NULL == request->headerv)
		{
			return -1;
		}
	}

	// TODO: Check for the header section end without backtracking.
	const int position = request->position;
	int result = read_rest_of_line(request);

	if (0 == result)
	{
		return 0;
	}

	if (2 == result - position)
	{
		// Header section ended, nothing left to parse.
		return request->position + 2;
	}

	request->position = position;

	if (0 >= request->headerv[request->headerc].name.start)
	{
		request->headerv[request->headerc].name.start = read_until_word(request);

		if (0 == request->headerv[request->headerc].name.start)
		{
			return 0;
		}
	}

	result = read_until_char(request, ':');

	if (0 == result)
	{
		return 0;
	}

	request->headerv[request->headerc].name.length = request->position - request->headerv[request->headerc].name.start;
	request->step = parse_step_header_value;

	// Skip ':'
	request->position++;

	return parse_step_header_value(request);
}

/// Parses and verifies value of a single header from the request.
/// \param request Request to process
/// \return -1 if an error has occured, 0 if too little data available or total number of bytes processed
int parse_step_header_value(struct request * request)
{
	if (0 >= request->headerv[request->headerc].value.start)
	{
		request->headerv[request->headerc].value.start = read_until_word(request);

		if (0 == request->headerv[request->headerc].value.start)
		{
			return 0;
		}
	}

	const int result = read_rest_of_line(request);

	if (0 == result)
	{
		return 0;
	}

	request->headerv[request->headerc].value.length = request->position - request->headerv[request->headerc].value.start;
	request->step = parse_step_header_name;
	request->headerc++;

	if (MAX_HEADERS == request->headerc)
	{
		return -1;
	}

	return parse_step_header_name(request);
}