/* Copyright (C) 2001-2023 Artifex Software, Inc.
   All Rights Reserved.

   This software is provided AS-IS with no warranty, either express or
   implied.

   This software is distributed under license and may not be copied,
   modified or distributed except as expressly authorized under the terms
   of the license contained in the file LICENSE in this distribution.

   Refer to licensing information at http://www.artifex.com or contact
   Artifex Software, Inc.,  39 Mesa Street, Suite 108A, San Francisco,
   CA 94129, USA, for further information.
*/

/*
  memory-based simulated file system
 */

#include "unistd_.h"
#include "string_.h"
#include "gx.h"
#include "gserrors.h"
#include "gp.h"
#include "gscdefs.h"
#include "gsparam.h"
#include "gsstruct.h"
#include "ramfs.h"

#define MACROBLOCK_REALLOC_MAX 128

typedef struct _ramfs {
    struct _ramdirent * files;
    struct _ramfs_enum* active_enums;
    gs_memory_t *memory;
    int blocksfree;
    int last_error;
}__ramfs;

gs_private_st_simple(st_ramfs, struct _ramfs, "gsram_ramfs");

struct _ramdirent {
    char* filename;
    struct _ramfile* inode;
    struct _ramdirent* next;
};

gs_private_st_simple(st_ramdirent, struct _ramdirent, "gsram_ramdirent");

typedef struct _ramfile {
    ramfs* fs;
    int refcount;
    int size;
    int blocks;
    int blocklist_size;
    char** data;
} ramfile;

gs_private_st_simple(st_ramfile, struct _ramfile, "gsram_ramfile");

struct _ramhandle {
    ramfile * file;
    int last_error;
    int filepos;
    int mode;
};

gs_private_st_simple(st_ramhandle, struct _ramhandle, "gsram_ramhandle");

struct _ramfs_enum {
    ramfs* fs;
    ramdirent * current;
    struct _ramfs_enum* next;
};

gs_private_st_simple(st_ramfs_enum, struct _ramfs_enum, "gsram_ramfs_enum");

static void unlink_node(ramfile * inode);
static int ramfile_truncate(ramhandle * handle,int size);

ramfs * ramfs_new(gs_memory_t *mem, int size)
{
    ramfs * fs = gs_alloc_struct(mem->non_gc_memory, ramfs, &st_ramfs, "ramfs_new");

    if (fs == NULL) {
        return NULL;
    }
    size = size/(RAMFS_BLOCKSIZE/1024);
    fs->files = NULL;
    fs->active_enums = NULL;
    fs->blocksfree = size;
    fs->last_error = 0;
    fs->memory = mem->non_gc_memory;
    return fs;
}

/* This function makes no attempt to check that there are no open files or
   enums.  If there are any when this function is called, memory leakage will
   result and any attempt to access the open files or enums will probably
   cause a segfault.  Caveat emptor, or something.
*/
void ramfs_destroy(gs_memory_t *mem, ramfs * fs)
{
    ramdirent * ent;

    if(fs == NULL) return;

    ent = fs->files;
    while(ent) {
        ramdirent* prev;
        gs_free_object(fs->memory, ent->filename, "ramfs_destroy, filename");
        unlink_node(ent->inode);
        prev = ent;
        ent = ent->next;
        gs_free_object(fs->memory, prev, "ramfs_destroy, entry");
    }
    gs_free_object(fs->memory, fs, "ramfs_destroy");
}

int ramfs_error(const ramfs* fs) { return fs->last_error; }

static int resize(ramfile * file,int size)
{
    int newblocks = (size+RAMFS_BLOCKSIZE-1)/RAMFS_BLOCKSIZE;
    void *buf;

    if(newblocks > file->blocks) {
        /* allocate blocks for file as necessary */

        if(newblocks-file->blocks > file->fs->blocksfree) {
            return -RAMFS_NOSPACE;
        }
        if(file->blocklist_size < newblocks) {
            int newsize = file->blocklist_size;
            if (newsize > MACROBLOCK_REALLOC_MAX) {
                newsize = ((newblocks+MACROBLOCK_REALLOC_MAX-1)/
                    MACROBLOCK_REALLOC_MAX) * MACROBLOCK_REALLOC_MAX;
            } else {
                if(!newsize) newsize = 1;
                while(newsize < newblocks) newsize *= 2;
            }
            buf = gs_alloc_bytes(file->fs->memory, newsize * sizeof(char*), "ramfs resize");
            if (!buf)
                return gs_note_error(gs_error_VMerror);
            memcpy(buf, file->data, file->blocklist_size * sizeof(char *));
            gs_free_object(file->fs->memory, file->data, "ramfs resize, free buffer");
            file->data = buf;
            file->blocklist_size = newsize;
        }
        while(file->blocks<newblocks) {
            char * block = file->data[file->blocks] =
                (char *)gs_alloc_bytes_immovable(file->fs->memory, RAMFS_BLOCKSIZE, "ramfs resize");
            if(!block) {
                return -RAMFS_NOMEM;
            }
            file->blocks++;
            file->fs->blocksfree--;
        }
    } else if (newblocks < file->blocks) {
        /* don't bother shrinking the block array */
        file->fs->blocksfree += (file->blocks-newblocks);
        while(file->blocks > newblocks) {
            gs_free_object(file->fs->memory, file->data[--file->blocks], "ramfs resize");
        }
    }
    file->size = size;
    return 0;
}

static ramdirent * ramfs_findfile(const ramfs* fs,const char *filename)
{
    ramdirent * thisdirent = fs->files;
    while(thisdirent) {
        if(strcmp(thisdirent->filename,filename) == 0) break;
        thisdirent = thisdirent->next;
    }
    return thisdirent;
}

ramhandle * ramfs_open(gs_memory_t *mem, ramfs* fs,const char * filename,int mode)
{
    ramdirent * thisdirent;
    ramfile* file;
    ramhandle* handle;

    if(mode & (RAMFS_CREATE|RAMFS_APPEND)) mode |= RAMFS_WRITE;

    thisdirent = ramfs_findfile(fs,filename);

    if(!thisdirent) {
        /* create file? */
        char * dirent_filename;

        if(!(mode & RAMFS_CREATE)) {
            fs->last_error = RAMFS_NOTFOUND;
            return NULL;
        }

        thisdirent = gs_alloc_struct(fs->memory, ramdirent, &st_ramdirent, "new ram directory entry");
        file = gs_alloc_struct(fs->memory, ramfile, &st_ramfile, "new ram file");
        dirent_filename = (char *)gs_alloc_bytes(fs->memory, strlen(filename) + 1, "ramfs filename");
        if(!(thisdirent && file && dirent_filename)) {
            gs_free_object(fs->memory, thisdirent, "error, cleanup directory entry");
            gs_free_object(fs->memory, file, "error, cleanup ram file");
            gs_free_object(fs->memory, dirent_filename, "error, cleanup ram filename");
            fs->last_error = RAMFS_NOMEM;
            return NULL;
        }
        strcpy(dirent_filename,filename);
        thisdirent->filename = dirent_filename;
        file->refcount = 1;
        file->size = 0;
        file->blocks = 0;
        file->blocklist_size = 0;
        file->data = NULL;
        file->fs = fs;
        thisdirent->inode = file;
        thisdirent->next = fs->files;
        fs->files = thisdirent;
    }
    file = thisdirent->inode;
    file->refcount++;

    handle = gs_alloc_struct(fs->memory, ramhandle, &st_ramhandle, "new ram directory entry");
    if(!handle) {
        fs->last_error = RAMFS_NOMEM;
        return NULL;
    }
    handle->file = file;
    handle->last_error = 0;
    handle->filepos = 0;
    handle->mode = mode;

    if(mode & RAMFS_TRUNC) {
        resize(file,0);
    }
    return handle;
}

int ramfs_blocksize(ramfs * fs) { return RAMFS_BLOCKSIZE; }
int ramfs_blocksfree(ramfs * fs) { return fs->blocksfree; }
int ramfile_error(ramhandle * handle) { return handle->last_error; }

static void unlink_node(ramfile * inode)
{
    int c;

    --inode->refcount;
    if(inode->refcount) return;

    /* remove the file and its data */
    for(c=0;c<inode->blocks;c++) {
        gs_free_object(inode->fs->memory, inode->data[c], "unlink node");
    }
    inode->fs->blocksfree += c;
    gs_free_object(inode->fs->memory, inode->data, "unlink node");
    gs_free_object(inode->fs->memory, inode, "unlink node");
}

int ramfs_unlink(ramfs * fs,const char *filename)
{
    ramdirent ** last;
    ramdirent * thisdirent;
    ramfs_enum* e;

    last = &fs->files;
    while(1) {
        if(!(thisdirent = *last)) {
            fs->last_error = RAMFS_NOTFOUND;
            return -1;
        }
        if(strcmp(thisdirent->filename,filename) == 0) break;
        last = &(thisdirent->next);
    }

    unlink_node(thisdirent->inode);
    gs_free_object(fs->memory, thisdirent->filename, "unlink");
    (*last) = thisdirent->next;

    e = fs->active_enums;
    /* advance enums that are pointing to the just-deleted file */
    while(e) {
        if(e->current == thisdirent) e->current = thisdirent->next;
        e = e->next;
    }
    gs_free_object(fs->memory, thisdirent, "unlink");
    return 0;
}

int ramfs_rename(ramfs * fs,const char* oldname,const char* newname)
{
    ramdirent * thisdirent;
    char * newnamebuf;

    thisdirent = ramfs_findfile(fs,oldname);

    if(!thisdirent) {
        fs->last_error = RAMFS_NOTFOUND;
        return -1;
    }

    /* just in case */
    if(strcmp(oldname,newname) == 0) return 0;

    newnamebuf = (char *)gs_alloc_bytes(fs->memory, strlen(newname)+1, "ramfs rename");
    if(!newnamebuf) {
        fs->last_error = RAMFS_NOMEM;
        return -1;
    }

    /* this may return RAMFS_NOTFOUND, which can be ignored. */
    ramfs_unlink(fs,newname);

    strcpy(newnamebuf,newname);
    gs_free_object(fs->memory, thisdirent->filename, "ramfs rename");
    thisdirent->filename = newnamebuf;
    return 0;
}

ramfs_enum * ramfs_enum_new(ramfs * fs)
{
    ramfs_enum * e;

    e = gs_alloc_struct(fs->memory, ramfs_enum, &st_ramfs_enum, "new ramfs enumerator");
    if(!e) {
        fs->last_error = RAMFS_NOMEM;
        return NULL;
    }
    e->current = fs->files;
    e->next = fs->active_enums;
    e->fs = fs;
    fs->active_enums = e;
    return e;
}

char* ramfs_enum_next(ramfs_enum * e)
{
    char * filename = NULL;
    if(e->current) {
        filename = e->current->filename;
        e->current = e->current->next;
    }
    return filename;
}

void ramfs_enum_end(ramfs_enum * e)
{
    ramfs_enum** last = &e->fs->active_enums;
    while(*last) {
        if(*last == e) {
            *last = e->next;
            break;
        }
        last = &(e->next);
    }
    gs_free_object(e->fs->memory, e, "free ramfs enumerator");
}

int ramfile_read(ramhandle * handle,void * buf,int len)
{
    ramfile * file = handle->file;
    int left;
    char *t = (char *)buf;

    if(len>file->size - handle->filepos) len = file->size-handle->filepos;
    if(len<0) return 0;

    left = len;
    while(left) {
        char * p = file->data[handle->filepos/RAMFS_BLOCKSIZE]+handle->filepos%RAMFS_BLOCKSIZE;
        int x = RAMFS_BLOCKSIZE-handle->filepos%RAMFS_BLOCKSIZE;
        if(x>left) x = left;

        memcpy(t,p,x);
        handle->filepos += x;
        left -= x;
        t += x;
    }
    return len;
}

int ramfile_write(ramhandle * handle,const void * buf,int len)
{
    ramfile * file = handle->file;
    int left;
    char *t = (char *)buf;

    if(!(handle->mode & RAMFS_WRITE)) {
        handle->last_error = RAMFS_NOACCESS;
        return -1;
    }

    if(handle->mode & RAMFS_APPEND) {
        handle->filepos = file->size;
    }

    if(file->size < handle->filepos) {
        /* if this fails then pass the error on */
        if(ramfile_truncate(handle,handle->filepos) == -1) return -1;
    }

    if(file->size < handle->filepos+len) {
        int x = resize(file,handle->filepos+len);
        if(x) {
            handle->last_error = -x;
            return -1;
        }
    }

    /* This is exactly the same as for reading, cept the copy is in the
       other direction. */
    left = len;
    while(left) {
        char * p = file->data[handle->filepos/RAMFS_BLOCKSIZE] +
            handle->filepos%RAMFS_BLOCKSIZE;
        int x = RAMFS_BLOCKSIZE-handle->filepos%RAMFS_BLOCKSIZE;
        if(x>left) x = left;

        memcpy(p,t,x);
        handle->filepos += x;
        left -= x;
        t += x;
    }
    return len;
}

int ramfile_seek(ramhandle * handle,int pos,int whence)
{
    /* Just set the handle's file position.  The effects become noticeable
       at the next read or write.
    */
    if(whence == RAMFS_SEEK_CUR) {
        handle->filepos += pos;
    } else if(whence == RAMFS_SEEK_END) {
        handle->filepos = handle->file->size+pos;
    } else {
        handle->filepos = pos;
    }
    return 0;
}

int ramfile_size(ramhandle * handle)
{
    return handle->file->size;
}

static int ramfile_truncate(ramhandle * handle,int size)
{
    ramfile * file = handle->file;
    int oldsize = file->size;
    int x = resize(file,size);

    if(x) {
        handle->last_error = -x;
        return -1;
    }
    if(oldsize >= size) return 0;

    /* file was expanded. fill the new space with zeros. */
    while(oldsize < file->size) {
        char * p = file->data[oldsize/RAMFS_BLOCKSIZE]+oldsize%RAMFS_BLOCKSIZE;
        int len = RAMFS_BLOCKSIZE - oldsize%RAMFS_BLOCKSIZE;
        if(len>file->size-oldsize) len = file->size-oldsize;
        oldsize += len;
        memset(p,0,len);
    }
    return 0;
}

void ramfile_close(ramhandle * handle)
{
    ramfile * file = handle->file;
    unlink_node(file);
    gs_free_object(handle->file->fs->memory, handle, "ramfs close");
}

int ramfile_tell(ramhandle* handle)
{
    return handle->filepos;
}

int ramfile_eof(ramhandle* handle)
{
    return (handle->filepos >= handle->file->size);
}