init.lua

-- fettle — prototype
-- The loop: hotkey -> Cmd+A, Cmd+C -> correct(text) -> paste back -> restore clipboard.
--
-- Correction engine: your own Anthropic API key + a model you pick from the
-- menu-bar dropdown. No bundled model, so the whole thing stays tiny.

local HOTKEY_MODS = { "alt" } -- Option
local HOTKEY_KEY = "space" -- Option+Space

local API_URL = "https://api.anthropic.com/v1/messages"
local API_VERSION = "2023-06-01"
local MAX_TOKENS = 2048

-- Key lives in Hammerspoon's config dir, OUTSIDE this repo, so a secret can
-- never be committed and the path works for anyone who installs the tool.
local KEY_FILE = hs.configdir .. "/fettle-key.txt"

-- Models you can pick between from the menu bar. Add/remove freely.
local MODELS = {
	{ label = "Haiku 4.5  —  fast & cheap", id = "claude-haiku-4-5-20251001" },
	{ label = "Sonnet 5  —  balanced", id = "claude-sonnet-5" },
	{ label = "Opus 5  —  best, slower", id = "claude-opus-5" },
}
local DEFAULT_MODEL = MODELS[1].id
local SETTING_MODEL = "fettle.model" -- persisted across reloads/restarts

-- British English, and a tight instruction to *only* return the corrected text.
local SYSTEM_PROMPT = table.concat({
	"You fix text. Correct spelling, typos, grammar, and verb tense.",
	"Preserve the original meaning, tone, punctuation style, and line breaks.",
	"Use British English spelling (colour, organise, favour).",
	"Do not rephrase or add anything; make the smallest changes needed to make it correct.",
	"Return ONLY the corrected text — no quotes, no commentary, no explanation.",
	"If the text is already correct, return it unchanged.",
}, " ")

-- Poll settings for waiting on the async clipboard copy to land.
local POLL_INTERVAL = 0.02 -- seconds between checks
local POLL_MAX_TRIES = 25 -- ~0.5s total timeout
local RESTORE_DELAY = 0.35 -- seconds to wait before restoring the old clipboard

local function trim(s)
	return (s:gsub("^%s+", ""):gsub("%s+$", ""))
end

local function currentModel()
	return hs.settings.get(SETTING_MODEL) or DEFAULT_MODEL
end

local function modelLabel(id)
	for _, m in ipairs(MODELS) do
		if m.id == id then
			return m.label
		end
	end
	return id
end

local function getApiKey()
	local envKey = os.getenv("ANTHROPIC_API_KEY")
	if envKey and envKey ~= "" then
		return trim(envKey)
	end
	local f = io.open(KEY_FILE, "r")
	if not f then
		return nil
	end
	local contents = f:read("*a")
	f:close()
	local key = trim(contents or "")
	return key ~= "" and key or nil
end

-- === the correction engine ==================================================
-- Async so the network round-trip never blocks the UI. Calls done(fixedText).
-- On any error we fall back to the original text (no destructive change).
local function correctAsync(text, done)
	local key = getApiKey()
	if not key then
		hs.alert.show("fettle: no API key (add " .. KEY_FILE .. ")")
		done(text)
		return
	end

	local body = hs.json.encode({
		model = currentModel(),
		max_tokens = MAX_TOKENS,
		system = SYSTEM_PROMPT,
		messages = { { role = "user", content = text } },
	})
	local headers = {
		["x-api-key"] = key,
		["anthropic-version"] = API_VERSION,
		["content-type"] = "application/json",
	}

	hs.http.asyncPost(API_URL, body, headers, function(status, respBody, _)
		if status ~= 200 or not respBody then
			local detail = respBody and trim(respBody):sub(1, 120) or "no response"
			hs.alert.show("fettle: API error " .. tostring(status) .. " — " .. detail)
			done(text)
			return
		end

		local ok, parsed = pcall(hs.json.decode, respBody)
		if not ok or type(parsed) ~= "table" or type(parsed.content) ~= "table" or not parsed.content[1] then
			hs.alert.show("fettle: unexpected response")
			done(text)
			return
		end

		local fixed = trim(parsed.content[1].text or "")
		if fixed == "" then
			done(text)
		else
			done(fixed)
		end
	end)
end
-- =============================================================================

-- Wait for the pasteboard changeCount to move (i.e. our Cmd+C landed), with a
-- timeout so an empty/unsupported field can't hang us forever.
local function waitForCopy(startCount, onReady, triesLeft)
	triesLeft = triesLeft or POLL_MAX_TRIES
	if hs.pasteboard.changeCount() ~= startCount then
		onReady(true)
	elseif triesLeft <= 0 then
		onReady(false)
	else
		hs.timer.doAfter(POLL_INTERVAL, function()
			waitForCopy(startCount, onReady, triesLeft - 1)
		end)
	end
end

local function fixSelection()
	local original = hs.pasteboard.getContents()
	local startCount = hs.pasteboard.changeCount()

	-- Grab whatever's in the focused field.
	hs.eventtap.keyStroke({ "cmd" }, "a", 0)
	hs.eventtap.keyStroke({ "cmd" }, "c", 0)

	waitForCopy(startCount, function(copied)
		if not copied then
			hs.alert.show("fettle: nothing to grab")
			return
		end

		local text = hs.pasteboard.getContents()
		if not text or text == "" then
			hs.alert.show("fettle: empty selection")
			return
		end

		-- Immediate feedback so the network wait feels intentional, not laggy.
		local fixingId = hs.alert.show("✍️  fettling…", hs.alert.defaultStyle, hs.screen.mainScreen(), 10)

		correctAsync(text, function(fixed)
			hs.alert.closeSpecific(fixingId)
			hs.pasteboard.setContents(fixed)
			hs.eventtap.keyStroke({ "cmd" }, "v", 0)

			-- Give the paste a moment to consume the clipboard, then restore
			-- whatever was there before so we don't clobber it.
			hs.timer.doAfter(RESTORE_DELAY, function()
				if original then
					hs.pasteboard.setContents(original)
				end
			end)
		end)
	end)
end

-- === menu bar ===============================================================
local menubar = hs.menubar.new()

local function ensureKeyFileExists()
	local f = io.open(KEY_FILE, "r")
	if f then
		f:close()
	else
		local w = io.open(KEY_FILE, "a")
		if w then
			w:close()
		end
	end
end

local function buildMenu()
	local items = {
		{ title = "fettle", disabled = true },
		{ title = "-" },
		{ title = "Model", disabled = true },
	}
	for _, m in ipairs(MODELS) do
		table.insert(items, {
			title = "   " .. m.label,
			checked = (m.id == currentModel()),
			fn = function()
				hs.settings.set(SETTING_MODEL, m.id)
				hs.alert.show("fettle: model → " .. m.label)
			end,
		})
	end
	table.insert(items, { title = "-" })
	table.insert(items, {
		title = "Edit API key…",
		fn = function()
			ensureKeyFileExists()
			hs.execute("open -e '" .. KEY_FILE .. "'")
		end,
	})
	table.insert(items, { title = "Reload config", fn = function() hs.reload() end })
	return items
end

if menubar then
	menubar:setTitle("✍️")
	menubar:setMenu(buildMenu)
end
-- =============================================================================

hs.hotkey.bind(HOTKEY_MODS, HOTKEY_KEY, fixSelection)
hs.alert.show("fettle loaded — Option+Space (" .. modelLabel(currentModel()) .. ")")