import io
import ecdsa
import hashlib
import yaml
import base64
import sys

def render_path(path):
    if path:
        return "'" + ", ".join(path) + "'"
    else:
        return "the top level"

class ErrorHandlingDict(dict):
    def __init__(self, filename, path):
        self._filename = filename
        self._path = path
        dict.__init__({})
    def __missing__(self, key):
        path = render_path(self._path)
        print >>sys.stderr, "error: could not find configuration key '%s' at %s in %s" % (key, path, self._filename)
        sys.exit(1)

def errorhandlify(term, filename, path=[]):
    if isinstance(term, basestring):
        return term
    elif isinstance(term, int):
        return term
    elif isinstance(term, dict):
        result = ErrorHandlingDict(filename, path)
        for k, v in term.items():
            result[k] = errorhandlify(v, filename, path + [k])
        return result
    elif isinstance(term, list):
        return [errorhandlify(e, filename, path + ["item %d" % i]) for i, e in enumerate(term, start=1)]
    else:
        print "unknown type", type(term)
        sys.exit(1)

def verify_config(rawconfig, signature, publickey_base64, filename):
    publickey = base64.decodestring(publickey_base64)

    try:
        vk = ecdsa.VerifyingKey.from_der(publickey)
        vk.verify(signature, rawconfig, hashfunc=hashlib.sha256,
                sigdecode=ecdsa.util.sigdecode_der)
    except ecdsa.keys.BadSignatureError:
        print >>sys.stderr, "error: configuration file %s did not have a correct signature" % (filename,)
        sys.exit(1)

    return errorhandlify(yaml.load(io.BytesIO(rawconfig), yaml.SafeLoader), filename)

def verify_and_read_config(filename, publickey_base64, schema=None):
    rawconfig = open(filename).read()
    signature = open(filename + ".sig").read()

    verify_config(rawconfig, signature, publickey_base64, filename)
    config = yaml.load(io.BytesIO(rawconfig), yaml.SafeLoader)
    if schema:
        check_config_schema(config, schema)
    return errorhandlify(config, filename)

def insert_schema_path(schema, path, datatype, highleveldatatype):
    if len(path) == 1:
        schema[path[0]] = (datatype, highleveldatatype)
    else:
        if path[0] not in schema:
            schema[path[0]] = {}
        insert_schema_path(schema[path[0]], path[1:], datatype, highleveldatatype)

def transform_schema(in_schema):
    schema = {}
    for (rawpath, datatype, highleveldatatype) in in_schema:
        path = rawpath.split("/")
        insert_schema_path(schema, path, datatype, highleveldatatype)
    return schema

def check_config_schema(config, schema):
    transformed_schema = transform_schema(schema)
    error = check_config_schema_part(config, transformed_schema)
    if error:
        print >>sys.stderr, "error:", error
        sys.exit(1)

def check_config_schema_part(term, schema, path=[]):
    joined_path = render_path(path)
    if isinstance(term, basestring):
        (schema_lowlevel, schema_highlevel) = schema
        if schema_lowlevel != "string":
            return "expected %s at %s, not a string" % (schema_lowlevel, joined_path,)
        return None
    elif isinstance(term, int):
        (schema_lowlevel, schema_highlevel) = schema
        if schema_lowlevel != "integer":
            return "expected %s at %s, not an integer" % (schema_lowlevel, joined_path,)
        return None
    elif isinstance(term, dict):
        if not isinstance(schema, dict):
            return "expected %s at %s, not a key" % (schema, joined_path,)
        for k, v in term.items():
            schema_part = schema.get(k)
            if schema_part == None and len(schema.keys()) == 1 and schema.keys()[0].startswith("*"):
                schema_part = schema[schema.keys()[0]]
            if schema_part == None:
                return "configuration key '%s' at %s unknown" % (k, joined_path)
            result = check_config_schema_part(v, schema_part, path + [k])
            if result:
                return result
        return None
    elif isinstance(term, list):
        if not isinstance(schema, dict):
            return "expected %s at %s, not a list" % (schema, joined_path,)
        schema_part = schema.get("[]")
        if schema_part == None:
            return "expected dict at %s, not a list" % (joined_path,)
        for i, e in enumerate(term, start=1):
            result = check_config_schema_part(e, schema_part, path + ["item %d" % i])
            if result:
                return result
        return None
    else:
        print >>sys.stderr, "unknown type", type(term)
        sys.exit(1)


def read_config(filename, schema=None):
    config = yaml.load(open(filename), yaml.SafeLoader)
    if schema:
        check_config_schema(config, schema)
    return errorhandlify(config, filename)