#include "http.h"

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

static const int REQUEST_DATA_SIZE = 4096;

const char * status_str[] = {
	[STATUS_OK] = "200 OK",
	[STATUS_BAD_REQUEST] = "400 Bad Request",
	[STATUS_METHOD_NOT_ALLOWED] = "405 Method Not Allowed",
	[STATUS_REQUEST_TIMEOUT] = "408 Request Timeout",
	[STATUS_INTERNAL_SERVER_ERROR] = "500 Internal Server Error",
	[STATUS_NOT_IMPLEMENTED] = "501 Not Implemented",
	[STATUS_VERSION_NOT_SUPPORTED] = "505 Version Not Supported",
};

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

	return request;
}

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

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

	free(request);
}

/// Sends a simple response only with a status to the client.
/// \param fd File descriptor of the client socket
/// \param status HTTP response status code
/// \return Negative value if an error was encountered; numbers of bytes written otherwise
int respond_only_status(const int fd, const enum status status)
{
	static const char * pattern =
		"HTTP/1.1 %s\r\n"
		"Connection: close\r\n"
		"\r\n";

	return dprintf(fd, pattern, status_str[status]);
}

/// Sends a response with a status and a body to the client.
/// \param fd File descriptor of the client socket
/// \param status HTTP response status code
/// \param body Content that will be sent
/// \param size Size of the content in bytes
/// \return Negative value if an error was encountered; numbers of bytes written otherwise
int respond_with_body(const int fd, const enum status status, const char * body, const int size)
{
	static const char * pattern =
		"HTTP/1.1 %s\r\n"
		"Connection: close\r\n"
		"Content-Type: application/json\r\n"
		"Content-Size: %d\r\n"
		"\r\n";

	if (0 > dprintf(fd, pattern, status_str[status], size))
	{
		return -1; // TODO: Handle errors properly
	}

	return write(fd, body, size);
}

/// 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(const int fd, struct request ** request)
{
	if (NULL == *request)
	{
		*request = new_request();
		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;
}

/// 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)
{
	request->method.length = read_until_char(request, ' ');

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

	request->step = parse_step_path;

	return parse_step_path(request);
}

/// 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)
{
	if (0 >= request->path.start)
	{
		request->path.start = read_until_word(request);

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

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

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

	request->path.length = request->position - request->path.start;
	request->step = parse_step_version;

	return parse_step_version(request);
}

/// 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->version.start)
	{
		request->version.start = read_until_word(request);

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

	const int result = read_rest_of_line(request);

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

	request->version.length = request->position - request->version.start;
	request->step = NULL; // TODO: Parse headers

	return request->position;
}