"""Definitions and lookup tables for MIDI messages.

Todo:

    * add lookup functions for messages definitions by type and status
      byte.
"""
# Todo: these include undefined messages.
CHANNEL_MESSAGES = set(range(0x80, 0xf0))
COMMON_MESSAGES = set(range(0xf0, 0xf8))
REALTIME_MESSAGES = set(range(0xf8, 0x100))

SYSEX_START = 0xf0
SYSEX_END = 0xf7

# Pitchwheel is a 14 bit signed integer
MIN_PITCHWHEEL = -8192
MAX_PITCHWHEEL = 8191

# Song pos is a 14 bit unsigned integer
MIN_SONGPOS = 0
MAX_SONGPOS = 16383


def _defmsg(status_byte, type_, value_names, length):
    return {
        'status_byte': status_byte,
        'type': type_,
        'value_names': value_names,
        'attribute_names': set(value_names) | {'type', 'time'},
        'length': length,
    }


SPECS = [
    _defmsg(0x80, 'note_off', ('channel', 'note', 'velocity'), 3),
    _defmsg(0x90, 'note_on', ('channel', 'note', 'velocity'), 3),
    _defmsg(0xa0, 'polytouch', ('channel', 'note', 'value'), 3),
    _defmsg(0xb0, 'control_change', ('channel', 'control', 'value'), 3),
    _defmsg(0xc0, 'program_change', ('channel', 'program',), 2),
    _defmsg(0xd0, 'aftertouch', ('channel', 'value',), 2),
    _defmsg(0xe0, 'pitchwheel', ('channel', 'pitch',), 3),
    
    # System common messages.
    # 0xf4 and 0xf5 are undefined.
    _defmsg(0xf0, 'sysex', ('data',), float('inf')),
    _defmsg(0xf1, 'quarter_frame', ('frame_type', 'frame_value'), 2),
    _defmsg(0xf2, 'songpos', ('pos',), 3),
    _defmsg(0xf3, 'song_select', ('song',), 2),
    _defmsg(0xf6, 'tune_request', (), 1),
    
    # System real time messages.
    # 0xf9 and 0xfd are undefined.
    _defmsg(0xf8, 'clock', (), 1),
    _defmsg(0xfa, 'start', (), 1),
    _defmsg(0xfb, 'continue', (), 1),
    _defmsg(0xfc, 'stop', (), 1),
    _defmsg(0xfe, 'active_sensing', (), 1),
    _defmsg(0xff, 'reset', (), 1),
]


def _make_spec_lookups(specs):
    lookup = {}
    by_status = {}
    by_type = {}

    for spec in specs:
        type_ = spec['type']
        status_byte = spec['status_byte']

        by_type[type_] = spec

        if status_byte in CHANNEL_MESSAGES:
            for channel in range(16):
                by_status[status_byte | channel] = spec
        else:
            by_status[status_byte] = spec
                
    lookup.update(by_status)
    lookup.update(by_type)

    return lookup, by_status, by_type


SPEC_LOOKUP, SPEC_BY_STATUS, SPEC_BY_TYPE = _make_spec_lookups(SPECS)

REALTIME_TYPES = {'tune_request', 'clock', 'start', 'continue', 'stop'}

DEFAULT_VALUES = {
    'channel': 0,
    'control': 0,
    'data': (),
    'frame_type': 0,
    'frame_value': 0,
    'note': 0,
    'pitch': 0,
    'pos': 0,
    'program': 0,
    'song': 0,
    'value': 0,
    'velocity': 64,

    'time': 0,
}


# Todo: should this be in decode.py?

def make_msgdict(type_, overrides):
    """Return a new message.

    Returns a dictionary representing a message.

    Message values can be overriden.

    No type or value checking is done.  The caller is responsible for
    calling check_msgdict().
    """
    if type_ in SPEC_BY_TYPE:
        spec = SPEC_BY_TYPE[type_]
    else:
        raise LookupError('Unknown message type {!r}'.format(type_))

    msg = {'type': type_, 'time': DEFAULT_VALUES['time']}

    for name in spec['value_names']:
        msg[name] = DEFAULT_VALUES[name]

    msg.update(overrides)

    return msg