"""

File-like objects that read from or write to a bsddb record.

This implements (nearly) all stdio methods.

f = DBRecIO(db, key, txn=None)

f.close()           # explicitly release resources held

flag = f.isatty()   # always false

pos = f.tell()      # get current position

f.seek(pos)         # set current position

f.seek(pos, mode)   # mode 0: absolute; 1: relative; 2: relative to EOF

buf = f.read()      # read until EOF

buf = f.read(n)     # read up to n bytes

f.truncate([size])  # truncate file at to at most size (default: current pos)

f.write(buf)        # write at current position

f.writelines(list)  # for line in list: f.write(line)

Notes:

- fileno() is left unimplemented so that code which uses it triggers

  an exception early.

- There's a simple test set (see end of this file) - not yet updated

  for DBRecIO.

- readline() is not implemented yet.

From:

    Itamar Shtull-Trauring <itamar@maxnm.com>

"""

import errno

import string

class DBRecIO:

    def __init__(self, db, key, txn=None):

        self.db = db

        self.key = key

        self.txn = txn

        self.len = None

        self.pos = 0

        self.closed = 0

        self.softspace = 0

    def close(self):

        if not self.closed:

            self.closed = 1

            del self.db, self.txn

    def isatty(self):

        if self.closed:

            raise ValueError, "I/O operation on closed file"

        return 0

    def seek(self, pos, mode = 0):

        if self.closed:

            raise ValueError, "I/O operation on closed file"

        if mode == 1:

            pos = pos + self.pos

        elif mode == 2:

            pos = pos + self.len

        self.pos = max(0, pos)

    def tell(self):

        if self.closed:

            raise ValueError, "I/O operation on closed file"

        return self.pos

    def read(self, n = -1):

        if self.closed:

            raise ValueError, "I/O operation on closed file"

        if n < 0:

            newpos = self.len

        else:

            newpos = min(self.pos+n, self.len)

        dlen = newpos - self.pos

        r = self.db.get(self.key, txn=self.txn, dlen=dlen, doff=self.pos)

        self.pos = newpos

        return r

    __fixme = """

    def readline(self, length=None):

        if self.closed:

            raise ValueError, "I/O operation on closed file"

        if self.buflist:

            self.buf = self.buf + string.joinfields(self.buflist, '')

            self.buflist = []

        i = string.find(self.buf, '\n', self.pos)

        if i < 0:

            newpos = self.len

        else:

            newpos = i+1

        if length is not None:

            if self.pos + length < newpos:

                newpos = self.pos + length

        r = self.buf[self.pos:newpos]

        self.pos = newpos

        return r

    def readlines(self, sizehint = 0):

        total = 0

        lines = []

        line = self.readline()

        while line:

            lines.append(line)

            total += len(line)

            if 0 < sizehint <= total:

                break

            line = self.readline()

        return lines

    """

    def truncate(self, size=None):

        if self.closed:

            raise ValueError, "I/O operation on closed file"

        if size is None:

            size = self.pos

        elif size < 0:

            raise IOError(errno.EINVAL,

                                      "Negative size not allowed")

        elif size < self.pos:

            self.pos = size

        self.db.put(self.key, "", txn=self.txn, dlen=self.len-size, doff=size)

    def write(self, s):

        if self.closed:

            raise ValueError, "I/O operation on closed file"

        if not s: return

        if self.pos > self.len:

            self.buflist.append('\0'*(self.pos - self.len))

            self.len = self.pos

        newpos = self.pos + len(s)

        self.db.put(self.key, s, txn=self.txn, dlen=len(s), doff=self.pos)

        self.pos = newpos

    def writelines(self, list):

        self.write(string.joinfields(list, ''))

    def flush(self):

        if self.closed:

            raise ValueError, "I/O operation on closed file"

"""

# A little test suite

def _test():

    import sys

    if sys.argv[1:]:

        file = sys.argv[1]

    else:

        file = '/etc/passwd'

    lines = open(file, 'r').readlines()

    text = open(file, 'r').read()

    f = StringIO()

    for line in lines[:-2]:

        f.write(line)

    f.writelines(lines[-2:])

    if f.getvalue() != text:

        raise RuntimeError, 'write failed'

    length = f.tell()

    print 'File length =', length

    f.seek(len(lines[0]))

    f.write(lines[1])

    f.seek(0)

    print 'First line =', repr(f.readline())

    here = f.tell()

    line = f.readline()

    print 'Second line =', repr(line)

    f.seek(-len(line), 1)

    line2 = f.read(len(line))

    if line != line2:

        raise RuntimeError, 'bad result after seek back'

    f.seek(len(line2), 1)

    list = f.readlines()

    line = list[-1]

    f.seek(f.tell() - len(line))

    line2 = f.read()

    if line != line2:

        raise RuntimeError, 'bad result after seek back from EOF'

    print 'Read', len(list), 'more lines'

    print 'File length =', f.tell()

    if f.tell() != length:

        raise RuntimeError, 'bad length'

    f.close()

if __name__ == '__main__':

    _test()

"""