import binascii
import struct

HDRMGC = b"TlvInfo"
HDRVER = 1
HDRFMT = ">7sxBH"
HDRLEN = struct.calcsize(HDRFMT)

CRCFMT = ">BBL"
CRCLEN = struct.calcsize(CRCFMT)

def pack_varstr(s, maxlen=0xff):
    b = bytes(s, "ascii")
    assert(len(b) <= maxlen)
    return b

def unpack_varstr(b):
    return b.decode("ascii")


def pack_u8(num):
    return struct.pack("B", num)

def unpack_u8(b):
    return struct.unpack("B", b)[0]


def pack_u16(num):
    return struct.pack(">H", num)

def unpack_u16(b):
    return struct.unpack(">H", b)[0]


def pack_u32(num):
    return struct.pack(">L", num)

def unpack_u32(b):
    return struct.unpack(">L", b)[0]


def pack_date(datestr):
    assert(len(datestr) == 19)
    return pack_varstr(datestr, 19)

def pack_country(cstr):
    assert(len(cstr) == 2)
    return pack_varstr(cstr, 2)

def pack_mac(macstr):
    return struct.pack("6B", *[int(o, 16) for o in macstr.split(":")])

def unpack_mac(b):
    o = struct.unpack("6B", b)
    return f"{o[0]:02x}:{o[1]:02x}:{o[2]:02x}:{o[3]:02x}:{o[4]:02x}:{o[5]:02x}"

OPS = {
    "varstr":   (pack_varstr, unpack_varstr),
    "u8":       (pack_u8, unpack_u8),
    "u16":      (pack_u16, unpack_u16),
    "u32":      (pack_u32, unpack_u32),

    "date":     (pack_date, unpack_varstr),
    "country":  (pack_country, unpack_varstr),
    "mac":      (pack_mac, unpack_mac),
}

TLV = (
    { "type": 0x21, "name": "product-name",     "ops": "varstr"  },
    { "type": 0x22, "name": "part-number",      "ops": "varstr"  },
    { "type": 0x23, "name": "serial-number",    "ops": "varstr"  },
    { "type": 0x24, "name": "mac-address",      "ops": "mac"     },
    { "type": 0x25, "name": "manufacture-date", "ops": "date"    },
    { "type": 0x26, "name": "device-version",   "ops": "u8"      },
    { "type": 0x27, "name": "label-revision",   "ops": "varstr"  },
    { "type": 0x28, "name": "platform-name",    "ops": "varstr"  },
    { "type": 0x29, "name": "onie-version",     "ops": "varstr"  },
    { "type": 0x2a, "name": "num-macs",         "ops": "u16"     },
    { "type": 0x2b, "name": "manufacturer",     "ops": "varstr"  },
    { "type": 0x2c, "name": "country-code",     "ops": "country" },
    { "type": 0x2d, "name": "vendor",           "ops": "varstr"  },
    { "type": 0x2e, "name": "diag-version",     "ops": "varstr"  },
    { "type": 0x2f, "name": "service-tag",      "ops": "varstr"  },
)

TLV_VENDOR_EXTENSION = 0xfd
TLV_CRC32 = 0xfe

def _tlv_by_lambda(fn):
    info = next(filter(fn, TLV))
    if "ops" in info:
        return info, OPS[info["ops"]]
    else:
        return info

def tlv_by_name(name):
    try:
        return _tlv_by_lambda(lambda info: info["name"] == name)
    except StopIteration:
        raise ValueError(f"Unknown type name \"{name}\"")

def tlv_by_type(t):
    try:
        return _tlv_by_lambda(lambda info: info["type"] == t)
    except StopIteration:
        raise ValueError(f"Unknown type id {t}")

def into_tlv(d):
    def pack_vendor(exts):
        out = b""
        for (iana_pen, val) in exts:
            b = bytes(val, "utf-8")
            l = len(b) + struct.calcsize(">L")
            assert(l <= 0xff)
            out += struct.pack(">BBL", TLV_VENDOR_EXTENSION, l, iana_pen) + b

        return out

    out = b""

    # Generate all optional data
    for (k, v) in sorted(d.items()):
        if k == "vendor-extension":
            out += pack_vendor(v)
        else:
            info, (pack, _) = tlv_by_name(k)
            val = pack(v)
            out += struct.pack("BB", info["type"], len(val)) + val

    # Prepend the header now that we know the total length of the
    # optional fields - make sure sure to include the CRC TLV length,
    # which is appended in the last step
    out  = struct.pack(HDRFMT, HDRMGC, HDRVER, len(out) + CRCLEN) + out

    out += struct.pack("BB", TLV_CRC32, struct.calcsize(">L"))
    out += struct.pack(">L", binascii.crc32(out))
    return out

def from_tlv(f):
    d = {}

    def unpack_vendor(ext):
        head, tail = ext[:4], ext[4:]
        iana_pen = struct.unpack(">L", head)[0]
        val = tail.decode("utf-8")

        if "vendor-extension" not in d:
            d["vendor-extension"] = []

        d["vendor-extension"].append([iana_pen, val])

    head = f.read(HDRLEN)
    magic, ver, l = struct.unpack(HDRFMT, head)
    assert(magic == HDRMGC)
    assert(ver == 1)

    tail = f.read(l)
    b = head + tail
    assert(len(b) >= HDRLEN + l)

    crcoffs = HDRLEN + l - CRCLEN
    t, l, v = struct.unpack(CRCFMT, b[crcoffs:crcoffs+CRCLEN])
    assert(t == TLV_CRC32)
    assert(v == binascii.crc32(b[:crcoffs + struct.calcsize("BB")]))

    while len(tail) >= 2:
        t, l = struct.unpack("BB", tail[:2])
        v = tail[2:l+2]
        tail = tail[l+2:]

        if t == TLV_VENDOR_EXTENSION:
            unpack_vendor(v)
            continue
        elif t == TLV_CRC32:
            break

        info, (_, unpack) = tlv_by_type(t)
        d[info["name"]] = unpack(v)

    return d
