/* $Id$ */

#include "stdafx.h"
#include "openttd.h"
#include "fileio.h"
#include "functions.h"
#include "string.h"
#include "macros.h"
#include "variables.h"
#include "debug.h"

/*************************************************/
/* FILE IO ROUTINES ******************************/
/*************************************************/

#define FIO_BUFFER_SIZE 512
#define MAX_HANDLES 64

typedef struct {
	byte *buffer, *buffer_end;          ///< position pointer in local buffer and last valid byte of buffer
	uint32 pos;                         ///< current (system) position in file
	FILE *cur_fh;                       ///< current file handle
	FILE *handles[MAX_HANDLES];         ///< array of file handles we can have open
	byte buffer_start[FIO_BUFFER_SIZE]; ///< local buffer when read from file
#if defined(LIMITED_FDS)
	uint open_handles;                  ///< current amount of open handles
	const char *filename[MAX_HANDLES];  ///< array of filenames we (should) have open
	uint usage_count[MAX_HANDLES];      ///< count how many times this file has been opened
#endif /* LIMITED_FDS */
} Fio;

static Fio _fio;

// Get current position in file
uint32 FioGetPos(void)
{
	return _fio.pos + (_fio.buffer - _fio.buffer_start) - FIO_BUFFER_SIZE;
}

void FioSeekTo(uint32 pos, int mode)
{
	if (mode == SEEK_CUR) pos += FioGetPos();
	_fio.buffer = _fio.buffer_end = _fio.buffer_start + FIO_BUFFER_SIZE;
	_fio.pos = pos;
	fseek(_fio.cur_fh, _fio.pos, SEEK_SET);
}

#if defined(LIMITED_FDS)
static void FioRestoreFile(int slot)
{
	/* Do we still have the file open, or should we reopen it? */
	if (_fio.handles[slot] == NULL) {
		DEBUG(misc, 6, "Restoring file '%s' in slot '%d' from disk", _fio.filename[slot], slot);
		FioOpenFile(slot, _fio.filename[slot]);
	}
	_fio.usage_count[slot]++;
}
#endif /* LIMITED_FDS */

// Seek to a file and a position
void FioSeekToFile(uint32 pos)
{
	FILE *f;
#if defined(LIMITED_FDS)
	/* Make sure we have this file open */
	FioRestoreFile(pos >> 24);
#endif /* LIMITED_FDS */
	f = _fio.handles[pos >> 24];
	assert(f != NULL);
	_fio.cur_fh = f;
	FioSeekTo(GB(pos, 0, 24), SEEK_SET);
}

byte FioReadByte(void)
{
	if (_fio.buffer == _fio.buffer_end) {
		_fio.pos += FIO_BUFFER_SIZE;
		fread(_fio.buffer = _fio.buffer_start, 1, FIO_BUFFER_SIZE, _fio.cur_fh);
	}
	return *_fio.buffer++;
}

void FioSkipBytes(int n)
{
	for (;;) {
		int m = min(_fio.buffer_end - _fio.buffer, n);
		_fio.buffer += m;
		n -= m;
		if (n == 0) break;
		FioReadByte();
		n--;
	}
}

uint16 FioReadWord(void)
{
	byte b = FioReadByte();
	return (FioReadByte() << 8) | b;
}

uint32 FioReadDword(void)
{
	uint b = FioReadWord();
	return (FioReadWord() << 16) | b;
}

void FioReadBlock(void *ptr, uint size)
{
	FioSeekTo(FioGetPos(), SEEK_SET);
	_fio.pos += size;
	fread(ptr, 1, size, _fio.cur_fh);
}

static inline void FioCloseFile(int slot)
{
	if (_fio.handles[slot] != NULL) {
		fclose(_fio.handles[slot]);
		_fio.handles[slot] = NULL;
#if defined(LIMITED_FDS)
		_fio.open_handles--;
#endif /* LIMITED_FDS */
	}
}

void FioCloseAll(void)
{
	int i;

	for (i = 0; i != lengthof(_fio.handles); i++)
		FioCloseFile(i);
}

bool FioCheckFileExists(const char *filename)
{
	FILE *f = FioFOpenFile(filename);
	if (f == NULL) return false;

	fclose(f);
	return true;
}

#if defined(LIMITED_FDS)
static void FioFreeHandle()
{
	/* If we are about to open a file that will exceed the limit, close a file */
	if (_fio.open_handles + 1 == LIMITED_FDS) {
		uint i, count;
		int slot;

		count = UINT_MAX;
		slot = -1;
		/* Find the file that is used the least */
		for (i = 0; i < lengthof(_fio.handles); i++) {
			if (_fio.handles[i] != NULL && _fio.usage_count[i] < count) {
				count = _fio.usage_count[i];
				slot  = i;
			}
		}
		assert(slot != -1);
		DEBUG(misc, 6, "Closing filehandler '%s' in slot '%d' because of fd-limit", _fio.filename[slot], slot);
		FioCloseFile(slot);
	}
}
#endif /* LIMITED_FDS */

FILE *FioFOpenFile(const char *filename)
{
	FILE *f;
	char buf[MAX_PATH];

	snprintf(buf, lengthof(buf), "%s%s", _paths.data_dir, filename);

	f = fopen(buf, "rb");
#if !defined(WIN32)
	if (f == NULL) {
		strtolower(buf + strlen(_paths.data_dir) - 1);
		f = fopen(buf, "rb");

#if defined SECOND_DATA_DIR
		// tries in the 2nd data directory
		if (f == NULL) {
			snprintf(buf, lengthof(buf), "%s%s", _paths.second_data_dir, filename);
			strtolower(buf + strlen(_paths.second_data_dir) - 1);
			f = fopen(buf, "rb");
		}
#endif
	}
#endif

	return f;
}

void FioOpenFile(int slot, const char *filename)
{
	FILE *f;

#if defined(LIMITED_FDS)
	FioFreeHandle();
#endif /* LIMITED_FDS */
	f = FioFOpenFile(filename);
	if (f == NULL) error("Cannot open file '%s%s'", _paths.data_dir, filename);

	FioCloseFile(slot); // if file was opened before, close it
	_fio.handles[slot] = f;
#if defined(LIMITED_FDS)
	_fio.filename[slot] = filename;
	_fio.usage_count[slot] = 0;
	_fio.open_handles++;
#endif /* LIMITED_FDS */
	FioSeekToFile(slot << 24);
}