# All bytes that are not hex digits are 0x0000FFFF
const _HEX_LUT = UInt32[
    b in UInt8('0'):UInt8('9') ? UInt32(b - UInt8('0')) :
        b in UInt8('a'):UInt8('f') ? UInt32(b - UInt8('a') + 0x0a) :
        b in UInt8('A'):UInt8('F') ? UInt32(b - UInt8('A') + 0x0a) :
        0xFFFF
    for b
    in UInt8(0):UInt8(255)
]

const _HEX_LUT_INV = UInt8.((
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f',
))

### SHA1 ###

struct SHA1
    h::NTuple{5,UInt32}
end

function Base.string(s::SHA1)
    out = Base.StringVector(40)
    i = 40
    @inbounds for j in 5:-1:1
        h = s.h[j]
        for _ in 1:8
            out[i] = _HEX_LUT_INV[0x01 + (h & 0x0f)]
            h >>= 4
            i -= 1
        end
    end
    return String(out)
end

# give SHA1 scalar behavior in broadcasting
Base.broadcastable(x::SHA1) = Ref(x)

supportedtype(::Type{SHA1}) = true

_set_tup5_at(t::NTuple{5,UInt32}, i, x::UInt32) = ntuple(j -> j == i ? x : t[j], 5)

function typeparser(::AbstractConf{SHA1}, source, pos, len, b, code, pl, options)
    if len - pos + 1 < 40
        @inbounds while pos <= len && _HEX_LUT[peekbyte(source, pos) + 0x01] != 0xFFFF
            pos += 1
            incr!(source)
        end
        eof(source, pos, len) && (code |= EOF)
        return (pos, code | INVALID, poslen(pl.pos, pos - pl.pos), SHA1((0,0,0,0,0)))
    end

    check = UInt32(0)
    out = ntuple(j -> UInt32(0), 5)
    @inbounds for i in 1:5
        h = UInt32(0)
        for _ in 0:7 # Maybe unroll?
            b = peekbyte(source, pos)
            c = _HEX_LUT[b + 0x01]
            check |= c
            h = ((h << 4) | c)
            pos += 1
            incr!(source)
        end
        # Only check validity every 8 bytes to hopefully enable some vectorization
        if check == 0xFFFF
            pos -= 8 # Backtrack to the start of the invalid hex
            fastseek!(source, pos - 1)
            while _HEX_LUT[peekbyte(source, pos) + 0x01] != 0xFFFF
                pos += 1
                incr!(source)
            end
            return pos, code | INVALID, poslen(pl.pos, pos - pl.pos), SHA1(out)
        end
        out = _set_tup5_at(out, i, h)
    end
    eof(source, pos, len) && (code |= EOF)
    return (pos, code | OK, poslen(pl.pos, pos - pl.pos), SHA1(out))
end

### UUID ###

supportedtype(::Type{UUID}) = true

function typeparser(::AbstractConf{UUID}, source, pos, len, b, code, pl, options)
    check = UInt32(0)
    hi = UInt64(0)
    lo = UInt64(0)

    @inbounds begin
        if len - pos + 1 < 36
            while (_HEX_LUT[b + 0x01] != 0xFFFF || b == UInt8('-'))
                pos += 1
                incr!(source)
                pos <= len || break
                b = peekbyte(source, pos)
            end
            eof(source, pos, len) && (code |= EOF)
            return (pos, code | INVALID, poslen(pl.pos, pos - pl.pos), UUID((hi, lo)))
        end

        segment_len = 8
        for _ in 1:segment_len
            b = peekbyte(source, pos)
            c = _HEX_LUT[b + 0x01]
            check |= c
            hi = ((hi << 4) | c)
            pos += 1
            incr!(source)
        end
        check != 0xFFFF || (return _backtrack_error(source, pos, len, code, segment_len, hi, lo, pl))
        peekbyte(source, pos) == UInt8('-') || @goto error

        pos += 1
        incr!(source)
        segment_len = 4
        for _ in 1:segment_len
            b = peekbyte(source, pos)
            c = _HEX_LUT[b + 0x01]
            check |= c
            hi = ((hi << 4) | c)
            pos += 1
            incr!(source)
        end
        check != 0xFFFF || (return _backtrack_error(source, pos, len, code, segment_len, hi, lo, pl))
        peekbyte(source, pos) == UInt8('-') || @goto error

        pos += 1
        incr!(source)
        segment_len = 4
        for _ in 1:segment_len
            b = peekbyte(source, pos)
            c = _HEX_LUT[b + 0x01]
            check |= c
            hi = ((hi << 4) | c)
            pos += 1
            incr!(source)
        end
        check != 0xFFFF || (return _backtrack_error(source, pos, len, code, segment_len, hi, lo, pl))
        peekbyte(source, pos) == UInt8('-') || @goto error

        pos += 1
        incr!(source)
        segment_len = 4
        for _ in 1:segment_len
            b = peekbyte(source, pos)
            c = _HEX_LUT[b + 0x01]
            check |= c
            lo = ((lo << 4) | c)
            pos += 1
            incr!(source)
        end
        check != 0xFFFF || (return _backtrack_error(source, pos, len, code, segment_len, hi, lo, pl))
        peekbyte(source, pos) == UInt8('-') || @goto error

        pos += 1
        incr!(source)
        segment_len = 12
        for _ in 1:segment_len
            b = peekbyte(source, pos)
            c = _HEX_LUT[b + 0x01]
            check |= c
            lo = ((lo << 4) | c)
            pos += 1
            incr!(source)
        end
        check != 0xFFFF || (return _backtrack_error(source, pos, len, code, segment_len, hi, lo, pl))
    end # @inbounds

    eof(source, pos, len) && (code |= EOF)
    return (pos, code | OK, poslen(pl.pos, pos - pl.pos), UUID((hi, lo)))

    @label error
    eof(source, pos, len) && (code |= EOF)
    return (pos, code | INVALID, poslen(pl.pos, pos - pl.pos), UUID((hi, lo)))
end

@noinline function _backtrack_error(source, pos, len, code, segment_len, hi, lo, pl)
    pos -= segment_len # Backtrack to the start of the invalid hex
    fastseek!(source, pos - 1)
    b = peekbyte(source, pos)
    while (_HEX_LUT[b + 0x01] != 0xFFFF || b == UInt8('-'))
        pos += 1
        incr!(source)
        pos <= len || break
        b = peekbyte(source, pos)
    end
    eof(source, pos, len) && (code |= EOF)
    return (pos, code | INVALID, poslen(pl.pos, pos - pl.pos), UUID((hi, lo)))
end