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"""General logging facility

This module attempts to provide a simple programming API for logging
with a pluggable API for defining where log messages should go.

Programmers call the LOG function to log information.

The LOG function, in turn, calls the write_log method to actually write
logging information somewhere.  This module provides a very simple
write_log implementation.  It is intended that applications main
programs will replace this method with a method more suited to their needs.

The module provides a register_subsystem method that does nothing, but
provides a hook that logging management systems could use to collect information about subsystems being used.

The module defines several standard severities:

  TRACE=-300   -- Trace messages

  DEBUG=-200   -- Debugging messages

  BLATHER=-100 -- Somebody shut this app up.

  INFO=0       -- For things like startup and shutdown.

  PROBLEM=100  -- This isn't causing any immediate problems, but deserves
                  attention.

  WARNING=100  -- A wishy-washy alias for PROBLEM.

  ERROR=200    -- This is going to have adverse effects.

  PANIC=300    -- We're dead!

Also, looging facilities will normally ignore negative severities.

To plug in a log handler, simply replace the log_write function
with a callable object that takes 5 arguments:


      subsystem -- The subsystem generating the message (e.g. ZODB)

      severity -- The "severity" of the event.  This may be an integer or
                  a floating point number.  Logging back ends may
                  consider the int() of this valua to be significant.
                  For example, a backend may consider any severity
                  whos integer value is WARNING to be a warning.

      summary -- A short summary of the event

      detail -- A detailed description

      error -- A three-element tuple consisting of an error type, value, and
               traceback.  If provided, then a summary of the error
               is added to the detail.

There is a default stupid logging facility that:

  - swallows logging information by default,

  - outputs to sys.stderr if the environment variable
    STUPID_LOG_FILE is set to an empty string, and

  - outputs to file if the environment variable
    STUPID_LOG_FILE is set to a file name.

  - Ignores errors that have a severity < 0 by default. This
    can be overridden with the environment variable STUPID_LOG_SEVERITY

"""
import time, sys, string

# Standard severities
TRACE   = -300
DEBUG   = -200
BLATHER = -100
INFO    =    0      
PROBLEM =  100
WARNING =  100             
ERROR   =  200   
PANIC   =  300

def severity_string(severity, mapping={
    -300: 'TRACE',
    -200: 'DEBUG',
    -100: 'BLATHER',
       0: 'INFO',       
     100: 'PROBLEM', 
     200: 'ERROR',    
     300: 'PANIC', 
    }):
    """Convert a severity code to a string
    """
    s=int(severity)
    if mapping.has_key(s): s=mapping[s]
    else: s=''
    return "%s(%s)" % (s, severity)

def LOG(subsystem, severity, summary, detail='', error=None, reraise=None):
    """Log some information

    The required arguments are:

      subsystem -- The subsystem generating the message (e.g. ZODB)

      severity -- The "severity" of the event.  This may be an integer or
                  a floating point number.  Logging back ends may
                  consider the int() of this valua to be significant.
                  For example, a backend may consider any severity
                  whos integer value is WARNING to be a warning.

      summary -- A short summary of the event

      detail -- A detailed description

      error -- A three-element tuple consisting of an error type, value, and
               traceback.  If provided, then a summary of the error
               is added to the detail.

      reraise -- If provided with a true value, then the error given by
                 error is reraised.

    """
    log_write(subsystem, severity, summary, detail, error)
    if reraise and error:
        raise error[0], error[1], error[2]

_subsystems=[]
def register_subsystem(subsystem):
    """Register a subsystem name

    A logging facility might replace this function to collect information about
    subsystems used in an application.
    """
    _subsystems.append(subsystem)

def log_time():
    """Return a simple time string without spaces suitable for logging
    """
    return ("%4.4d-%2.2d-%2.2dT%2.2d:%2.2d:%2.2d"
            % time.gmtime(time.time())[:6])
    
_stupid_dest=None
_stupid_severity=None
_no_stupid_log=[]
def stupid_log_write(subsystem, severity, summary, detail, error):
    
    global _stupid_dest
    if _stupid_dest is None:
        import os
        if os.environ.has_key('STUPID_LOG_FILE'):
            f=os.environ['STUPID_LOG_FILE']
            if f: _stupid_dest=open(f,'a')
            else:
                import sys
                _stupid_dest=sys.stderr
        else:
            _stupid_dest=_no_stupid_log
            
    if _stupid_dest is _no_stupid_log: return

    global _stupid_severity
    if _stupid_severity is None:
        try: _stupid_severity=string.atoi(os.environ['STUPID_LOG_SEVERITY'])
        except: _stupid_severity=0
        
    if severity < _stupid_severity: return
               
    _stupid_dest.write(
        "------\n"
        "%s %s %s %s\n%s"
        %
        (log_time(),
         severity_string(severity),
         subsystem,
         summary,
         detail,
         )
        )
    _stupid_dest.flush()

    if error:
        try:
            _stupid_dest.write(format_exception(
                error[0], error[1], error[2],
                trailer='\n', limit=100))
        except:
            _stupid_dest.write("%s: %s\n" % error[:2])
            


log_write=stupid_log_write

format_exception_only=None
def format_exception(etype,value,tb,limit=None, delimiter='\n',
                     header='', trailer=''):
    global format_exception_only
    if format_exception_only is None:
        import traceback
        format_exception_only=traceback.format_exception_only
        
    result=['Traceback (innermost last):']
    if header: result.insert(0,header)
    if limit is None:
        if hasattr(sys, 'tracebacklimit'):
            limit = sys.tracebacklimit
    n = 0
    while tb is not None and (limit is None or n < limit):
        f = tb.tb_frame
        lineno = tb.tb_lineno
        co = f.f_code
        filename = co.co_filename
        name = co.co_name
        locals=f.f_locals
        result.append('  File %s, line %d, in %s'
                      % (filename,lineno,name))
        try: result.append('    (Object: %s)' %
                           locals[co.co_varnames[0]].__name__)
        except: pass
        try: result.append('    (Info: %s)' %
                           str(locals['__traceback_info__']))
        except: pass
        tb = tb.tb_next
        n = n+1
    result.append(string.join(format_exception_only(etype, value),
                       ' '))
    if trailer: result.append(trailer)
    
    return string.join(result, delimiter)
