##  \package seal.nlp.rom
#   Romanizers.
#
#   Romanized text can always contain the following escapes:
# 
#       \\(xxx xxx)  Unicode characters
#       \\\          Literal backslash
#       \\c=aaa      Define c as a code for romanization aaa.  c must be UNDEFINED.
#       \\c          Set romanization to the one with code c.  c must be defined.
#       \\!          Unset romanization.
#       \\:          Silently ignored, can be used to terminate aaa
#       \\<EOF>      Silently ignored
#       \\Z          Silently ignored
#      
#    - c   - any single lowercase character.
#    - aaa - any characters except backslash, space, or newline.
#    - xxx - any number of hexadecimal digits.
#    - Z   - any single character other than lowercase letter, left paren, backslash, or colon.
#
#   N.b., \\c=aaa is interpreted as \\c followed by literal =aaa if c is defined.
#
#   DECODING
#
#   A romanization consists of a list of key-value pairs.  Keys may not
#   contain backslash, but may contain any other ASCII characters.
#   At each point in the input:
#
#     - If the next character is \\, it is interpreted as an escape.  It
#       is silently discarded if the following characters do not yield
#       a valid escape sequence.
#
#     - If a key matches, the longest matching key is replaced with its
#       value.
#
#     - Otherwise, a single character is passed unchanged to the output.
#
#   ENCODING
#
#   The input potentially contains non-ASCII characters, and the ouput
#   should contain only ASCII characters, such that decoding will yield
#   the input.  At each point in the input:
#
#     - If a value matches, the longest matching value is replaced with
#       the corresponding key.  However, if some prefix of the key when
#       combined with the suffix of the previous output would give an
#       overlapping key, then \\: is output before outputting the key.
#      
#     - If the next character is backslash, it is replaced with \\\\.
#
#     - If the next character is not ASCII, it is replaced with a numeric
#       code.
#
#     - Otherwise the next character is passed through unchanged.  However,
#       if combining the character with the suffix of the previous output
#       completes a key, \\: is output first.
#
#   ROMANIZATION
#
#   A romanization is internalized as a state sequence.  States are
#   accessed using single ASCII characters, and the return value is
#   a new state or None.  A state may also be associated with an output
#   value.
#

import os, codecs
from os.path import exists
from io import StringIO
from codecs import CodecInfo
from .io import ispathlike, Format
from .com import shift
from .data import path as datapath
from . import config

default_registry = None


#--  Romanization file  --------------------------------------------------------

def load_romfile (fn):
    with open(fn, 'rb') as f:
        return read_romfile(f)

# Since this is returned from inside 'with open', it should not be a generator
# that requires the file to be open

def read_romfile (f):
    return list(_read_romfile_1(f))

def _read_romfile_1 (f):
    for line in f:
        line = line.rstrip(b'\r\n')
        if line.startswith(b'#') or not line:
            continue
        (key, value) = line.split(b'\t')
        yield (key, value)


#--  Romanization  -------------------------------------------------------------

##  State in the romanization dictionary.

class State (dict):

    ##  Constructor.

    def __init__ (self):
        dict.__init__(self)

        ##  Non-null if this state corresponds to a valid code.
        self.value = None


##  A romanization.

class Romanization (object):

    ##  Constructor.

    def __init__ (self, name=None, fn=None):

        ##  Its name.
        self.name = name

        ##  Filename.
        self.filename = fn

        ##  Start state.
        self.start = None

        if fn: self.load(fn)

    ##  Load from file.  Called by the constructor.

    def load (self, fn):
        decode = Decoder()
        for (key, value) in load_romfile(fn):
            self[key] = decode(value)

    ##  Store an association.

    def __setitem__ (self, key, value):
        if not key: raise Exception('Empty key')
        if value is None: raise Exception('Null value')
        if self.start is None: self.start = State()
        q = self.start
        i = 0
        for c in key:
            if c < 0x20 or c > 0x7f:
                raise Exception('Control or non-ASCII character in key: %s' % key)
            if c == 0x5c:
                raise Exception('Backslash in key: %s' % key)
            if c in q:
                q = q[c]
            else:
                next = State()
                q[c] = next
                q = next
        if q.value is None:
            q.value = value
        else:
            raise Exception('Duplicate key: %s' % key)

    def items (self):
        return load_romfile(self.filename)

    def __str__ (self):
        with open(self.filename) as f:
            return f.read()

    ##  Print out the state graph.

    def print_graph (self):
        todo = [self.start]
        stateno = {id(self.start): 1}
        while todo:
            q = todo[0]
            del todo[0]
            print(stateno[id(q)])
            for c in sorted(q):
                next = q[c]
                j = id(next)
                if j not in stateno:
                    stateno[j] = len(stateno)+1
                    todo.append(next)
                print("   %d ('%s')" % (c, chr(c)), stateno[j])
            if q.value:
                print('    value=', repr(q.value))

    ##  Match an input.  Returns a pair (j, value).

    def match (self, input, i=0):
        q = self.start
        value = None
        j = None

        while i < len(input) and q is not None and input[i] in q:
            q = q[input[i]]
            i += 1
            if q.value is not None:
                value = q.value
                j = i

        return (j, value)
    
    ##  Decode an input.

    def decode (self, input, output=None, errors='strict', registry=None):
        try:
            decoder = Decoder(rom=self, registry=registry)
            return decoder(input, output)
        except Exception as e:
            if errors == 'strict':
                raise UnicodeDecodeError(str(e))
            elif errors == 'ignore':
                pass
            else:
                raise Exception('Bad value for errors: %s' % errors)

    ##  Decode in the form expected by CodecInfo.

    def std_decoder (self, input, errors='strict'):
        s = self.decode(input, errors=errors)
        return (s, len(input))


#--  as_bytes  -----------------------------------------------------------------

##  If the input is a string,
#   convert it to bytes using the ASCII codec.
#   Otherwise, assume it is bytes and leave it alone.
#   (Python sometimes passes memory objects that are not instances of
#   bytes or bytesarray; no easy way to distinguish that from a bad argument.)

def as_bytes (s):
    if isinstance(s, str):
        return s.encode('ascii')
    else:
        return s

##  Return the i-th character, or -1 if i is beyond the end of the string.

def peek (s, i):
    if i < len(s): return s[i]
    else: return -1


#--  Decoder  ------------------------------------------------------------------

##  A decoder.  The main entry points are __call__() and match_escape().

class Decoder (object):

    ##  Constructor.

    def __init__ (self, rom=None, registry=None):
        global default_registry
        if registry is None:
            registry = default_registry
        if isinstance(rom, str):
            rom = registry[rom]
        assert rom is None or isinstance(rom, Romanization)

        ##  The registry, needed if the romanization is given by name,
        #   and for romanization changes in the input.
        self.registry = registry

        ##  The current romanization, may be None.
        self.rom = rom

        ##  Table of romanizations.  Keys are single-character codes.
        self.roms = {}

        ##  1 if inside \( ... ), 0 otherwise.
        self.state = 0

    ##  Main entry point.
    #   \arg input:  a byte-like object or an ASCII string.  Non-ascii characters
    #         will cause an encoding error to be raised.
    #   \arg rom:    a romanization or a string naming a romanization.
    #   \arg output: an output stream or None.  If None, a string will be returned.

    def __call__ (self, input, output=None):
        input = as_bytes(input)
        if output is None:
            with StringIO() as output:
                self.transduce(input, output)
                return output.getvalue()
        else:
            self.transduce(input, output)

    ##  Transduce input to output.

    def transduce (self, input, output):
        i = 0
        while i < len(input):
            (j, s) = self.match(input, i)
            i = j
            output.write(s)

    ##  Parse the input.  Returns two values: a list of points marking the beginnings of
    #   matched tokens, and the output string.

    def parse (self, input):
        input = as_bytes(input)
        i = 0
        t = 0
        points = [(0,0)]
        with StringIO() as output:
            while i < len(input):
                (i, s) = self.match(input, i)
                output.write(s)
                t += len(s)
                points.append((i,t))
            if self.state != 0: self.error(input, i, 'Incomplete input')
            return (points, output.getvalue())

    ##  Get the longest match at position i.

    def match (self, input, i):
        c = input[i]

        # in the middle of \( ... )?
        if self.state == 1:

            # if space, there's another code point
            if c == 0x20:
                i += 1
                return self.scan_code_point(input, i)

            # if right paren, we're done
            elif c == 0x29: # right paren
                self.state = 0
                return (i+1, '')

            else:
                self.error(input, i, 'Expected space or right paren')

        # if c is a backslash, decode an escape sequence
        elif c == 0x5c:
            return self.match_escape(input, i)

        else:
            j = None
            if self.rom: (j, s) = self.rom.match(input, i)

            # the rom matched
            if j is not None: return (j, s)

            # no rom, or no match; pass through the input character
            else: return (i+1, chr(c))

    ##  Print an error message, including input position, and raise an exception.

    def error (self, input, i, msg):
        print('**', msg)
        print('Input:', repr(input[0:i]), repr(input[i:]))
        print('i=', i)
        raise Exception(msg)

    ##  Scan a backslash escape.  Advance i, write to out.
    #   May change rom.

    def match_escape (self, input, i):
        i += 1 # the triggering backslash

        # will be -1 at EOF
        c = peek(input, i)

        # \<EOF>
        if c < 0:
            return (i, '')

        # escaped backslash
        elif c == 0x5c:
            return (i+1, '\\')

        # \:
        elif c == 0x3a: # colon
            return (i+1, '')

        # \(
        elif c == 0x28: # left paren
            i += 1
            self.state = 1
            return self.scan_code_point(input, i)

        # \0
        elif c == 0x30:
            self.rom = self.registry.get('default') or Romanization()
            return (i+1, '')

        # \c or \c=aaa.
        elif c >= 0x61 and c <= 0x7a: # in range a-z
            code = c
            i += 1

            # \c is defined, use it.
            if code in self.roms:
                self.rom = self.roms[code]
                return (i, '')

            # \c is not defined, define it.
            else:
                c = peek(input, i)
                if c != 0x3d: self.error('Expecting =')
                i += 1
                # terminated by backslash, space, or nl
                (i, name) = self.scan_name(input, i)
                # consume the space or newline
                if peek(input, i) != 0x5c: i += 1
                rom = self.registry.get(name)
                if rom is None: self.error(input, i, 'No such romanization: %s' % name)
                self.roms[code] = rom
                return (i, '')
    
        # anything else is silently ignored
        else:
            return (i+1, '')

    ##  Called following \\(.
    #   Reads a block of hex digits, translates to character.

    def scan_code_point (self, input, i):
        j = i
        c = peek(input, j)
        # digit, A-F, a-f
        while ((c >= 0x30 and c <= 0x39) or
               (c >= 0x41 and c <= 0x46) or
               (c >= 0x61 and c <= 0x66)):
            j += 1
            c = peek(input, j)
        if j == i: self.error(input, i, 'Empty code point')
        return (j, chr(int(input[i:j], base=16)))

    ##  Scan the aaa following c=aaa.
    #   Returns a string.

    def scan_name (self, input, i):
        # name terminated by backslash, space, newline
        j = i
        while (j < len(input) and
               input[j] not in [0x20, 0x5c, 0x0a]):
            j += 1
        if i == j: self.error(input, i, 'Empty name')
        return (j, input[i:j].decode('ascii'))


##  Decode input.  Instantiates Decoder and calls it.

def decode (input, rom=None, output=None, registry=None):
    d = Decoder(rom, registry)
    return d(input, output)


#--  To Html  ------------------------------------------------------------------

##  Convert to a bytes object.  Printable ASCII characters, tab, newline, and
#   carriage return are passed through.  All other characters are replaced with
#   HTML character entities of form &#...;
#   Returns a pair: the bytes object and the length of the input string.

def to_html_1 (s):
    out = bytearray()
    for c in s:
        n = ord(c)
        # 0x09 = tab, 0x0a = newline, 0x0d = cr
        if (n >= 0x20 and n <= 0x7e) or n in [0x09, 0x0a, 0x0d]:
            out.append(n)
        else:
            out.extend(ord(c) for c in ('&#%d;' % n))
    return (bytes(out), len(s))

##  Calls to_html_1() and returns just the bytes object.

def to_html (s):
    (b,n) = to_html_1(s)
    return b


#--  Registry  -----------------------------------------------------------------

##  A table of romanizations.
#   Romanization and Decoder only use the methods get() and __getitem__().
#   They are expected to return Romanizations.

class Registry (object):

    ##  Constructor.

    def __init__ (self, path):
        # backwards compatibility
        if isinstance(path, str):
            path = [path]

        for d in path:
            assert ispathlike(d)

        ##  A list of directory filenames to search for rom files.
        self.path = path

        ##  Cache romanizations that have been loaded.
        #   A 'default' romanization is always available.
        self.cache = {'default': Romanization('default')}

    ##  Convert a name to a '.rom' filename that exists in one of the
    #   path directories.  Returns None if no existing rom file is found.

    def find_filename (self, name):
        for d in self.path:
            fn = os.path.join(d, name + '.rom')
            if exists(fn):
                return fn

    ##  Load a named romanization, ignoring the cache.

    def load (self, name):
        fn = self.find_filename(name)
        if fn:
            return Romanization(name, fn)
        else:
            raise Exception(f'No such rom file: {name}')

    ##  Get the romanization with the given name, loading it from file
    #   if it exists and is not already cached.

    def get (self, name):
        if name in self.cache:
            return self.cache[name]
        else:
            fn = self.find_filename(name)
            if fn:
                rom = Romanization(name, fn)
                self.cache[name] = rom
                return rom
    
    ##  Get the named romanization, signalling an error if it does not exist.

    def __getitem__ (self, name):
        if isinstance(name, Romanization): return name
        rom = self.get(name)
        if rom is None:
            raise KeyError('Romanization not found: %s' % repr(name))
        return rom

    ##  Whether the named romanization exists.

    def __contains__ (self, name):
        return name in self.cache or self.find_filename(name)

    ##  Iterate over all valid romanization names.  Does not load them.

    def __iter__ (self):
        for d in self.path:
            if os.path.exists(d):
                for name in os.listdir(d):
                    if name.endswith('.rom'):
                        yield name[:-4]


def _create_default_registry ():
    path = ['.']
    try:
        path = config['data']['rompath']
    except:
        pass
    path.append(datapath('roms'))
    return Registry(path)
    
##  The seal registry.
default_registry = _create_default_registry()

##  Backwards compatibility.

def require_rom (name):
    global default_registry
    return default_registry[name]

##  Backwards compatibility.

def rom_filename (name):
    global default_registry
    return default_registry.filename(name)

##  Backwards compatibility.

def load_rom (name):
    global default_registry
    return default_registry.load(name)

##  Backwards compatibility.

def find_rom (name):
    global default_registry
    return default_registry.get(name)

##  Find or create a codec from the named romanization.

def find_codec (name):
    global default_registry
    if name == 'html':
        return CodecInfo(to_html_1, None, name='html')
    else:
        rom = default_registry.get(name)
        if rom:
            return CodecInfo(None,
                             rom.std_decoder,
                             name=name)

codecs.register(find_codec)


#--  RomFormat  ----------------------------------------------------------------

RomFormat = Format(read_romfile, None)


#--  Main  ---------------------------------------------------------------------

##  Main function.
#   Argument: [INFILE].
#   Flags:
#
#       -d DIR - set the registry directory.
#       -h - set the output encoding to 'html'.
#       -o FN - specify the output filename.
#       -r ROM - specify a romanization.
#
#   Uses the named romanization to decode the input to the output.

def main ():
    global default_registry
    registry = default_registry
    rom = None
    outenc = 'utf8'
    infile = '-'
    outfile = '-'
    while shift.isflag():
        flag = shift()
        if flag == '-d':
            registry = Registry(shift())
        elif flag == '-h':
            outenc = 'html'
        elif flag == '-o':
            outfile = shift()
        elif flag == '-r':
            rom = shift()
        else:
            shift.error('Bad flag: %s' % flag)
    if not shift.isdone():
        infile = shift()
    shift.done()

    decoder = Decoder(rom=rom, registry=registry)
    f = File(infile, binary=True)
    with File(outfile, binary=True).writer() as write:
        for b in f:
            line = decoder(b)
            o = line.encode(outenc)
            write(o)

if __name__ == '__main__':
    main()
