local preset = (function()
local GROUP, MODE, INTENSITY, GLOW, RADIUS, RED, GREEN, BLUE, FADE_MS, FLAGS, RECORD_SIZE, PREFIX, PAGE_SIZE, create, presetCount, pageKeys, label, select, setMode, setIntensity, setFadeMs, setFullbright, save, selectedKey, currentMode, currentIntensity, currentGlow, currentRadius, currentFadeMs, isEnabled, isFullbright, currentColor

GROUP = 0 -- u8
MODE = 1 -- u8, zero-based mode ID
INTENSITY = 2 -- u8, whole percent
GLOW = 3 -- u8, whole percent
RADIUS = 4 -- u8, whole meters
RED = 5 -- u8, sRGB
GREEN = 6 -- u8, sRGB
BLUE = 7 -- u8, sRGB
FADE_MS = 8 -- u16, milliseconds
FLAGS = 10 -- enabled, fullbright, castLight, sync, ownerOnly
RECORD_SIZE = 11
PREFIX = "p:" -- one linkset data key per preset, e.g. p:Evening
PAGE_SIZE = 10 -- dialog labels per page, leaving two navigation buttons

local PATTERN = "^p:"
local MODES = {"steady", "fade", "pulse", "cycle"}
local ENABLED = bit32.lshift(1, 0)
local FULLBRIGHT = bit32.lshift(1, 1)

local key = ""
local record

--- Read once per selection and kept in variables for code that runs often.
local mode = "steady"
local intensity = 0
local glow = 0
local radius = 0
local fadeMs = 0
local flags = 0
local color = vector.create(0, 0, 0)

--- Save a new preset with default settings. Returns false if the name is taken or the write fails.
function create(name: string): boolean
    assert(#name >= 1 and #name <= 24, "names need 1 to 24 bytes")

    local presetKey = PREFIX .. name

    if ll.LinksetDataRead(presetKey) ~= "" then
        return false
    end

    local data = buffer.create(RECORD_SIZE)

    buffer.writeu8(data, GROUP, 1)
    buffer.writeu8(data, INTENSITY, 75)
    buffer.writeu8(data, GLOW, 5)
    buffer.writeu8(data, RADIUS, 10)
    buffer.writeu8(data, RED, 255)
    buffer.writeu8(data, GREEN, 200)
    buffer.writeu8(data, BLUE, 128)
    buffer.writeu16(data, FADE_MS, 250)
    buffer.writeu8(data, FLAGS, ENABLED)

    return ll.LinksetDataWrite(
        presetKey,
        llbase64.encode(data)
    ) == LINKSETDATA_OK
end

--- Counts saved presets without loading their keys.
function presetCount(): number
    return ll.LinksetDataCountFound(PATTERN)
end

--- Keys for one dialog page, in alphabetical order. SLua's `ll` counts `start` from 1.
function pageKeys(page: number)
    return ll.LinksetDataFindKeys(PATTERN, page * PAGE_SIZE + 1, PAGE_SIZE)
end

--- The button label for a key: its name without the prefix.
function label(presetKey: string): string
    return string.sub(presetKey, #PREFIX + 1)
end

--- Load one preset and read its values. Returns false if the key holds no preset.
function select(presetKey: string): boolean
    local saved = ll.LinksetDataRead(presetKey)

    if saved == "" then
        return false
    end

    key = presetKey
    record = llbase64.decode(saved, true)

    mode = MODES[buffer.readu8(record, MODE) + 1]
    intensity = buffer.readu8(record, INTENSITY) / 100
    glow = buffer.readu8(record, GLOW) / 100
    radius = buffer.readu8(record, RADIUS)
    fadeMs = buffer.readu16(record, FADE_MS)
    flags = buffer.readu8(record, FLAGS)
    color = ll.sRGB2Linear(vector.create(
        buffer.readu8(record, RED) / 255,
        buffer.readu8(record, GREEN) / 255,
        buffer.readu8(record, BLUE) / 255
    ))

    return true
end

function setMode(modeId: number)
    assert(
        modeId >= 0 and modeId < #MODES and modeId == math.floor(modeId),
        "invalid mode"
    )

    buffer.writeu8(record, MODE, modeId)
    mode = MODES[modeId + 1]
end

function setIntensity(value: number)
    assert(value >= 0 and value <= 1, "intensity must be between 0 and 1")

    local percent = math.floor(value * 100 + 0.5)
    buffer.writeu8(record, INTENSITY, percent)
    intensity = percent / 100
end

function setFadeMs(value: number)
    assert(
        value >= 0 and value <= 65535 and value == math.floor(value),
        "invalid fade duration"
    )

    buffer.writeu16(record, FADE_MS, value)
    fadeMs = value
end

function setFullbright(enabled: boolean)
    flags = enabled and bit32.bor(flags, FULLBRIGHT) or bit32.band(
        flags,
        bit32.bnot(FULLBRIGHT)
    )
    buffer.writeu8(record, FLAGS, flags)
end

--- Write the selected preset back to its own key. Keep the edit if this returns false.
function save(): boolean
    local status = ll.LinksetDataWrite(
        key,
        llbase64.encode(record)
    )

    return status == LINKSETDATA_OK or status == LINKSETDATA_NOUPDATE
end

function selectedKey(): string
    return key
end

function currentMode(): string
    return mode
end

function currentIntensity(): number
    return intensity
end

function currentGlow(): number
    return glow
end

function currentRadius(): number
    return radius
end

function currentFadeMs(): number
    return fadeMs
end

function isEnabled(): boolean
    return bit32.band(flags, ENABLED) ~= 0
end

function isFullbright(): boolean
    return bit32.band(flags, FULLBRIGHT) ~= 0
end

--- Linear color for `PRIM_POINT_LIGHT`, converted once per selection.
function currentColor()
    return color
end
return { GROUP = GROUP, MODE = MODE, INTENSITY = INTENSITY, GLOW = GLOW, RADIUS = RADIUS, RED = RED, GREEN = GREEN, BLUE = BLUE, FADE_MS = FADE_MS, FLAGS = FLAGS, RECORD_SIZE = RECORD_SIZE, PREFIX = PREFIX, PAGE_SIZE = PAGE_SIZE, create = create, presetCount = presetCount, pageKeys = pageKeys, label = label, select = select, setMode = setMode, setIntensity = setIntensity, setFadeMs = setFadeMs, setFullbright = setFullbright, save = save, selectedKey = selectedKey, currentMode = currentMode, currentIntensity = currentIntensity, currentGlow = currentGlow, currentRadius = currentRadius, currentFadeMs = currentFadeMs, isEnabled = isEnabled, isFullbright = isFullbright, currentColor = currentColor }
end)()

local first = preset.pageKeys(0)[1]
if first and preset.select(first) then
    print("Selected " .. preset.label(first) .. ": " .. preset.currentMode())
else
    print("No presets yet. Call preset.create(name) to add one.")
end