#========================================================================
# Copyright (c) 2007, Metaweb Technologies, Inc.
# All rights reserved.
# 
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#     * Redistributions of source code must retain the above copyright
#       notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above
#       copyright notice, this list of conditions and the following
#       disclaimer in the documentation and/or other materials provided
#       with the distribution.
# 
# THIS SOFTWARE IS PROVIDED BY METAWEB TECHNOLOGIES ``AS IS'' AND ANY
# EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
# PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL METAWEB TECHNOLOGIES BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
# BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
# WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
# OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
# IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
# ========================================================================
#
# This is the full "metaweb.py" module from the Metaweb API documentation
#
# In the documentation, each function is presented as a separate
# example.  This is the whole file.
#
# If you find any errors or have suggestions for improving this module,
# send them to the Freebase developers mailing list: developers@freebase.com
# You can subscribe to the mailing list at http://lists.freebase.com/
#

import httplib
import urllib        # URL encoding
import urllib2       # Higher-level URL content fetching
import simplejson    # JSON serialization and parsing
import cookielib     # Cookie handling
import os

#
# When experimenting, use the sandbox-freebase.com service.
# Every Monday, sandbox-freebase.com is erased and it is updated
# with a fresh copy of data from www.freebase.com.  This makes
# it an ideal place to experiment.
#
host = 'sandbox-freebase.com'              # The Metaweb host
readservice = '/api/service/mqlread'   # Path to mqlread service
loginservice = '/api/account/login'     # Path to login service
writeservice = '/api/service/mqlwrite'  # Path to mqlwrite service
uploadservice = '/api/service/upload'   # Path to upload service
searchservice = '/api/service/search'   # Path to search service
                 
credentials = None      # default credential from login()
escape = False          # default escape, set to 'html' for HTML escaping
permission = None       # default permission used when creating new objects
debug = False           # default debug setting

# Install a CookieProcessor
cookiefile = os.path.join(os.environ["HOME"], ".metaweb.cookies.txt")
cookiejar = cookielib.LWPCookieJar()
if os.path.isfile(cookiefile):
    cookiejar.load(cookiefile)

urllib2.install_opener(
    urllib2.build_opener(
        urllib2.HTTPCookieProcessor(cookiejar)))

# If anything goes wrong when talking to a Metaweb service, we raise MQLError.
class MQLError(Exception):
    def __init__(self, value):     # This is the exception constructor method
        self.value = value
    def __str__(self):             # Convert error object to a string
        return repr(self.value)

# Submit the MQL query q and return the result as a Python object.
# If authentication credentials are supplied, use them in a cookie.
# Raises MQLError if the query was invalid. Raises urllib2.HTTPError if
# mqlread returns an HTTP status code other than 200 (which should not happen).
def read(q, credentials=credentials, escape=escape):
    # Put the query in an envelope
    envelope = {'query':q}

    # Add escape if needed
    if escape != 'html':
        envelope['escape'] = False if not escape else escape

    # Encode the result
    encoded = urllib.urlencode({'query': simplejson.dumps(envelope)})

    # Build the URL and create a Request object for it
    url = 'http://%s%s' % (host, readservice)
    req = urllib2.Request(url)

    # The body of the POST request is encoded URL parameters
    req.add_header('Content-type', 'application/x-www-form-urlencoded')

    # Send our authentication credentials, if any, as a cookie.
    # The need for mqlread authentication is a temporary restriction.
    if credentials: req.add_header('Cookie', credentials)

    # Use the encoded envelope as the value of the q parameter in the body
    # of the request.  Specifying a body automatically makes this a POST.
    req.add_data(encoded)

    # Now upen the URL and and parse its JSON content
    f = urllib2.urlopen(req)        # Open the URL
    inner = simplejson.load(f)      # Parse JSON response to an object

    # If anything was wrong with the invocation, mqlread will return an HTTP
    # error, and the code above with raise urllib2.HTTPError.
    # If anything was wrong with the query, we won't get an HTTP error, but
    # will get an error status code in the response envelope.  In this case
    # we raise our own MQLError exception.
    if not inner['code'].startswith('/api/status/ok'):
        if debug: print q
        if debug: print inner
        if debug: print f.info()['X-Metaweb-Cost']
        if debug: print f.info()['X-Metaweb-TID']
        error = inner['messages'][0]
        raise MQLError('%s: %s' % (error['code'], error['message']))

    # If there was no error, then just return the result from the envelope
    return inner['result']

# Submit the MQL query q and return the result as a Python object
# This function behaves like read() above, but uses cursors so that
# it works even for very large result sets. See also the cursor class below.
def readall(q, credentials=credentials, escape=escape):
    # This is the start of the mqlread URL.
    # We just need to append the envelope to it
    url = 'http://%s%s' % (host, readservice)

    # The query and most of the envelope are constant. We just need to append
    # the encoded cursor value and some closing braces to this prefix string
    jsonq = simplejson.dumps(q)

    # Add escape if needed
    if escape != 'html':
        jsonq += ',"escape":' + ('false' if not escape else escape)
 
    cursor = 'true'   # This is the initial value of the cursor
    results = []      # We accumulate results in this array

    # Loop until mqlread tells us there are no more results
    while cursor:
        # append the cursor and the closing braces to the envelope
        envelope = urllib.urlencode({'query': '{"query":' + jsonq + ',"cursor":' + cursor + '}'})

        # Begin an HTTP request for the URL
        req = urllib2.Request(url)

        # The body of the POST request is encoded URL parameters
        req.add_header('Content-type', 'application/x-www-form-urlencoded')

        # Send our authentication credentials, if any, as a cookie.
        # The need for mqlread authentication is a temporary restriction.
        if credentials: 
            req.add_header('Cookie', credentials)

        # Use the encoded envelope as the value of the q parameter in the body
        # of the request.  Specifying a body automatically makes this a POST.
        req.add_data(envelope)

        # Read and parse the URL contents
        f = urllib2.urlopen(req)          # Open URL
        inner = simplejson.load(f)        # Parse JSON response

        # Raise a MQLError if there were errors
        if not inner['code'].startswith('/api/status/ok'):
            if debug: print q
            if debug: print inner
            if debug: print f.info()['X-Metaweb-Cost']
            if debug: print f.info()['X-Metaweb-TID']
            error = inner['messages'][0]
            raise MQLError('%s: %s' % (error['code'], error['message']))

        # Append this batch of results to the main array of results.
        results.extend(inner['result'])

        # Finally, get the new value of the cursor for the next iteration
        cursor = inner['cursor']
        if cursor:                        # If it is not false, put it
            cursor = '"' + cursor + '"'   #  in quotes as a JSON string

    # Now that we're done with the loop, return the results array
    return results

# Submit multiple MQL queries and return the result as a Python array.
# If authentication credentials are supplied, use them in a cookie.
# Raises MQLError if the query was invalid. Raises urllib2.HTTPError if
# mqlread returns an HTTP status code other than 200 (which should not happen).
def readmulti(queries, credentials=credentials, escape=escape):
    encoded = ""
    for i in range(0, len(queries)):
        # Put the query in an envelope
        envelope = {'query':queries[i]}
        # Add escape if needed
        if escape != 'html':
            envelope['escape'] = False if not escape else escape
        if i > 0:
            encoded += ","
        encoded += '"q%d":%s' % (i, simplejson.dumps(envelope))

    # URL encode the outer envelope
    encoded = urllib.urlencode({'queries': "{" + encoded + "}"})

    # Build the URL and create a Request object for it
    url = 'http://%s%s' % (host, readservice)
    req = urllib2.Request(url)

    # The body of the POST request is encoded URL parameters
    req.add_header('Content-type', 'application/x-www-form-urlencoded')

    # Send our authentication credentials, if any, as a cookie.
    # The need for mqlread authentication is a temporary restriction.
    if credentials: req.add_header('Cookie', credentials)

    # Use the encoded envelope as the value of the q parameter in the body
    # of the request.  Specifying a body automatically makes this a POST.
    req.add_data(encoded)

    # Now upen the URL and and parse its JSON content
    f = urllib2.urlopen(req)        # Open the URL
    inner = simplejson.load(f)      # Parse JSON response to an object

    # If anything was wrong with the invocation, mqlread will return an HTTP
    # error, and the code above with raise urllib2.HTTPError.
    # If anything was wrong with the query, we won't get an HTTP error, but
    # will get an error status code in the response envelope.  In this case
    # we raise our own MQLError exception.
    if not inner['code'].startswith('/api/status/ok'):
        if debug: print queries
        if debug: print inner
        if debug: print f.info()['X-Metaweb-Cost']
        if debug: print f.info()['X-Metaweb-TID']
        error = inner['messages'][0]
        raise MQLError('%s: %s' % (error['code'], error['message']))

    # extract the results
    results = []
    for i in range(0, len(queries)):
        result = inner["q%d" % i]
        if not result['code'].startswith('/api/status/ok'):
            if debug: print queries[i]
            if debug: print result
            if debug: print f.info()['X-Metaweb-Cost']
            if debug: print f.info()['X-Metaweb-TID']
            error = result['messages'][0]
            raise MQLError('%s: %s' % (error['code'], error['message']))
        results.append(result['result'])
    
    # If there was no error, then just return the result from the envelope
    return results

# Submit the specified username and password to the Metaweb login service.
# Return opaque authentication credentials on success. 
# Raise MQLError on failure.
def login(username, password):
    # Establish a connection to the server and make a request.
    # Note that we use the low-level httplib library instead of urllib2.
    # This allows us to manage cookies explicitly.
    conn = httplib.HTTPConnection(host)
    conn.request('POST',                   # POST the request
                 loginservice,             # The URL path /api/account/login
                 # The body of the request: encoded username/password
                 urllib.urlencode({'username':username, 'password':password}),
                 # This header specifies how the body of the post is encoded.
                 {'Content-type': 'application/x-www-form-urlencoded'})

    # Get the response from the server
    response = conn.getresponse()

    if response.status == 200:  # We get HTTP 200 OK even if login fails
        # Parse response body and raise a MQLError if login failed
        body = simplejson.loads(response.read())
        if not body['code'].startswith('/api/status/ok'):
            if debug: print inner
            if debug: print f.info()['X-Metaweb-Cost']
            if debug: print f.info()['X-Metaweb-TID']
            error = body['messages'][0]
            raise MQLError('%s: %s' % (error['code'], error['message']))

        # Otherwise return cookies to serve as authentication credentials.
        # The set-cookie header holds one or more cookie specifications,
        # separated by commas. Each specification is a name, an equal
        # sign, a value, and one or more trailing clauses that consist
        # of a semicolon and some metadata.  We don't care about the
        # metadata. We just want to return a comma-separated list of
        # name=value pairs.
        cookies = response.getheader('set-cookie').split(',')
        return ';'.join([c[0:c.index(';')] for c in cookies])
    else:                      # This should never happen
        raise MQLError('HTTP Error: %d %s' % (response.status,response.reason))


# Submit the MQL write q and return the result as a Python object.
# Authentication credentials are required, obtained from login()
# Raises MQLError if the query was invalid. Raises urllib2.HTTPError if
# mqlwrite returns an HTTP status code other than 200
def write(query, credentials=credentials, escape=escape, permission=permission):
    # We're requesting this URL
    req = urllib2.Request('http://%s%s' % (host, writeservice))
    # Send our authentication credentials as a cookie
    if credentials:
        req.add_header('Cookie', credentials)
    # This custom header is required and guards against XSS attacks
    req.add_header('X-Metaweb-Request', 'True')
    # The body of the POST request is encoded URL parameters
    req.add_header('Content-type', 'application/x-www-form-urlencoded')
    # Wrap the query object in a query envelope
    envelope = {'qname': {'query': query}}
    # Add escape if needed
    if escape != 'html':
        envelope['qname']['escape'] = (False if not escape else escape)
    # Add permissions if needed
    if permission:
        envelope['qname']['use_permission_of'] = permission
    # JSON encode the envelope
    encoded = simplejson.dumps(envelope)
    # Use the encoded envelope as the value of the q parameter in the body
    # of the request.  Specifying a body automatically makes this a POST.
    req.add_data(urllib.urlencode({'queries':encoded}))

    # Now do the POST
    f = urllib2.urlopen(req)
    response = simplejson.load(f)   # Parse HTTP response as JSON
    inner = response['qname']       # Open outer envelope; get inner envelope

    # If anything was wrong with the invocation, mqlwrite will return an HTTP
    # error, and the code above with raise urllib2.HTTPError.
    # If anything was wrong with the query, we will get an error status code
    # in the response envelope.
    # we raise our own MQLError exception.
    if not inner['code'].startswith('/api/status/ok'):
        if debug: print query
        if debug: print inner
        if debug: print f.info()['X-Metaweb-Cost']
        if debug: print f.info()['X-Metaweb-TID']
        error = inner['messages'][0]
        raise MQLError('%s: %s' % (error['code'], error['message']))

    # save cookie
    cookiejar.save(cookiefile)

    # If there was no error, then just return the result from the envelope
    return inner['result']

# Upload the specified content (and give it the specified type).
# Return the guid of the /type/content object that represents it.
# The returned guid can be used to retrieve the content with /api/trans/raw.
def upload(content, type, credentials=credentials):
    # This is the URL we POST content to
    url = 'http://%s%s'%(host,uploadservice)
    # Build the HTTP request
    req = urllib2.Request(url, content)         # URL and content to POST
    req.add_header('Content-Type', type)        # Content type header
    if credentials:
        req.add_header('Cookie', credentials)       # Authentication header
    req.add_header('X-Metaweb-Request', 'True') # Guard against XSS attacks
    f = urllib2.urlopen(req)                # POST the request
    response = simplejson.load(f)           # Parse the response
    if not response['code'].startswith('/api/status/ok'):
        if debug: print inner
        if debug: print f.info()['X-Metaweb-Cost']
        if debug: print f.info()['X-Metaweb-TID']
        error = response['messages'][0]
        raise MQLError('%s: %s' % (error['code'], error['message']))
    return response['result']['id']         # Extract and return content id

# Search for topics
def search(query, type=None, start=0, limit=0):
    args = {"query": query}
    if type:
        args["type"] = type
    if start > 0:
        args["start"] = start
    if limit > 0:
        args["limit"] = limit
    url = 'http://%s%s?%s'%(host, searchservice, urllib.urlencode(args))
    f = urllib2.urlopen(url)
    response = simplejson.load(f)           # Parse the response
    if not response['code'].startswith('/api/status/ok'):
        if debug: print query
        if debug: print inner
        if debug: print f.info()['X-Metaweb-Cost']
        if debug: print f.info()['X-Metaweb-TID']
        error = response['messages'][0]
        raise MQLError('%s: %s' % (error['code'], error['message']))
    return response['result']

# Cursor for iterating over large data sets
# For example:
#    query = {"name": None, "type":"/type/media_type"}
#    for row in metaweb.cursor([query]):
#        print row
class cursor:
    def __init__(self, query, credentials=credentials, escape=escape):
        self.query = query
        self.credentials = credentials
        self.index = 0
        self.results = []
        self.cursor = 'true'
        self.url = 'http://%s%s' % (host, readservice)
        self.jsonq = simplejson.dumps(self.query)
        if escape != 'html':
            self.jsonq += ',"escape":' + ('false' if not escape else escape)
 
    def __iter__(self):
        return self

    def next(self):
        # return the next value
        if self.index < len(self.results):
            result = self.results[self.index]
            self.index = self.index + 1
            return result

        # check if there is more
        if not self.cursor:
            raise StopIteration
        
        # append the cursor and the closing braces to the envelope
        envelope = urllib.urlencode({'query': '{"query":' + self.jsonq + ',"cursor":' + self.cursor + '}'})

        # Begin an HTTP request for the URL
        req = urllib2.Request(self.url)

        # The body of the POST request is encoded URL parameters
        req.add_header('Content-type', 'application/x-www-form-urlencoded')

        # Send our authentication credentials, if any, as a cookie.
        # The need for mqlread authentication is a temporary restriction.
        if self.credentials: req.add_header('Cookie', self.credentials)

        # Use the encoded envelope as the value of the q parameter in the body
        # of the request.  Specifying a body automatically makes this a POST.
        req.add_data(envelope)

        # Read and parse the URL contents
        f = urllib2.urlopen(req)          # Open URL
        inner = simplejson.load(f)        # Parse JSON response

        # Raise a MQLError if there were errors
        if not inner['code'].startswith('/api/status/ok'):
            if debug: print self.query
            if debug: print inner
            if debug: print f.info()['X-Metaweb-Cost']
            if debug: print f.info()['X-Metaweb-TID']
            error = inner['messages'][0]
            raise MQLError('%s: %s' % (error['code'], error['message']))

        # Remember the next cursor
        self.cursor = inner['cursor']
        if self.cursor:                             # If it is not false, put it
            self.cursor = '"' + self.cursor + '"'   #  in quotes as a JSON string

        # Append this batch of results to the main array of results.
        self.results = inner['result']
        if len(self.results) == 0:
            raise StopIteration

        # Return the first result
        self.index = 1
        return self.results[0]