module SampleImages

using Colors

using Base64

struct BeadsImageSVG <: Main.SVG

buf::IOBuffer

end

# The following code is ad-hoc and highly depends on "beads.svg".

# Be careful when modifying the svg file or its code.

function BeadsImageSVG(caption::String; filter=nothing, width="64mm", height="36mm")

io = IOBuffer()

id = string(hash(caption), base=16)

open(joinpath("assets", "figures", "beads.svg"), "r") do file

for line in eachline(file, keep=true)

occursin("<?xml", line) && continue

if occursin("<svg", line)

line = replace(line, ">"=>

""" width="$width" height="$height" style="display:inline; margin-left:1em; margin-bottom:1em">""")

elseif occursin("filter_beads_g", line)

line = replace(line, "filter_beads_g"=>"filter_"*id)

elseif occursin("</svg>", line)

text = """

<text x="16" y="1000" style="fill:black;opacity:0.9;font-size:80px;">$caption</text>

</svg>"""

line = replace(line, "</svg>"=>text)

end

m = match(r"data:image/png;base64,([^\"] )", line)

if filter === nothing || m === nothing

write(io, line)

continue

end

head = m.offsets[1]

write(io, SubString(line, 1, head - 1))

src = IOBuffer(m.captures[1])

b64dec = Base64DecodePipe(src) # decode all for simplicity

b64enc = Base64EncodePipe(io)

write(b64enc, read(b64dec, 33)) # before the length of "PLTE"

replace_palette(b64enc, b64dec, filter)

n = write(b64enc, read(b64dec))

close(b64enc)

close(b64dec)

write(io, SubString(line, head length(m.captures[1]), length(line)))

end

end

BeadsImageSVG(io)

end

function replace_palette(dest::IO, src::IO, filter)

buf = IOBuffer() # to calculate chunk CRCs

u8(x) = write(buf, UInt8(x & 0xFF))

u16(x) = (u8((x & 0xFFFF)>>8); u8(x))

u32(x) = (u16((x & 0xFFFFFFFF)>>16); u16(x))

function read_palette()

uint32 = (UInt32(read(src, UInt8)) << 16) |

(UInt32(read(src, UInt8)) << 8) | read(src, UInt8)

reinterpret(RGB24, uint32)

end

function write_palette(c::Color)

rgb24 = convert(RGB24,c)

u8(rgb24.color>>16); u8(rgb24.color>>8); u8(rgb24.color)

end

crct(x) = (for i = 1:8; x = x & 1==1 ? 0xEDB88320 ⊻ (x>>1) : x>>1 end; x)

table = UInt32[crct(i) for i = 0x00:0xFF]

function crc32()

seekstart(buf)

crc = 0xFFFFFFFF

while !eof(buf)

crc = (crc>>8) ⊻ table[(crc&0xFF) ⊻ read(buf, UInt8) 1]

end

u32(crc ⊻ 0xFFFFFFFF)

end

lenbytes = read(src, 4)

len = (UInt32(lenbytes[3]) << 8) | lenbytes[4]

write(dest, lenbytes)

write(buf, read(src, 4)) # "PLTE"

for i = 1:(len÷3)

write_palette(filter(read_palette()))

end

read(src, 4) # CRC

crc32()

write(dest, take!(seekstart(buf)))

end

end