#!/usr/bin/python

import sys,os,struct,string

site_base = "/var/lib/pgsql/base"
db_name = "betest"
table_name = "test"

db_path = os.path.join(site_base,db_name)
table_path = os.path.join(db_path,table_name)

page_size = 8*1024

def strbits(s,len):
    bits = []
    while s:
        c = s[0]
        s = s[1:]
        b = struct.unpack('B',c)[0]
        for i in range(8):
            if b & (1<<i): bits.append(1)
            else: bits.append(0)
    return string.join(map(str,bits),'')[:len]


class table_page:
    "class to represent a database table page"
    def __init__(self,fd,page_nr):
        fd.seek(page_nr*page_size)
        self.rawdata = fd.read(page_size)
        self.lower,\
        self.upper,\
        self.special,\
        self.opaque = struct.unpack('HHHH',self.rawdata[:8])
        self.item_pointers=[]
        self.items=[]
        for i in range(8,self.lower,4):
            rawItemIdData = self.rawdata[i:i+4]
            ItemIdData_I32 = struct.unpack('L',rawItemIdData)[0]
            if not ItemIdData_I32: break
            lp_len = int(ItemIdData_I32 >> 17)
            lp_flags = int((ItemIdData_I32 >> 15) & 3)
            lp_off = int(ItemIdData_I32 & 0x7fff)

            self.item_pointers.append(hex(ItemIdData_I32),lp_off,lp_flags,lp_len)
            rawItemData = self.rawdata[lp_off:lp_off+lp_len]
            t_oid  = struct.unpack('L', rawItemData[ 0: 4])[0]
            t_001  = struct.unpack('L', rawItemData[ 4: 8])[0]
            t_002  = struct.unpack('L', rawItemData[ 8:12])[0]
            t_xmin = struct.unpack('L', rawItemData[12:16])[0]
            t_xmax = struct.unpack('L', rawItemData[16:20])[0]
            t_ctid = struct.unpack('LH', rawItemData[20:26])  
            t_fcnt = struct.unpack('H', rawItemData[26:28])[0]
            t_xxx  = struct.unpack('2B', rawItemData[28:30])  
            t_doff = struct.unpack('B', rawItemData[30:31])[0]
            t_mask = strbits(rawItemData[31:t_doff],t_fcnt)   
#            t_mask = rawItemData[31:t_doff]
            t_data = rawItemData[t_doff:]   
            self.items.append(t_oid,t_001,t_002,t_xmin,t_xmax,t_ctid,t_fcnt,t_xxx,t_doff,t_mask,t_data)
    def __str__(self):
        strval = [str((self.lower, self.upper, self.special, self.opaque))]
        strval.append(string.join(map(str,self.item_pointers),'\n'))
        strval.append(string.join(map(repr,self.items),'\n'))
        return string.join(strval,'\n------------------\n')  


if __name__=="__main__":
    print '# dumping %s' % table_path
    fd = open(table_name)
    page = table_page(fd,0)
    print page