feat: support zooming images with a default parameter

Closes https://github.com/sxyazi/yazi/issues/3000

zoom.yazi/README.md

@@ -37,6 +37,16 @@ run  = "plugin zoom -1"
 desc = "Zoom out hovered file"
 ```
 
+## Advanced
+
+If you want to apply a default zoom parameter to image previews, you can specify it while setting this plugin up as a custom previewer, for example:
+
+```toml
+[[plugin.prepend_previewers]]
+mime = "image/{jpeg,png,webp}"
+run  = "zoom 5"
+```
+
 ## TODO
 
 - [ ] Support more file types (e.g., videos, PDFs), PRs welcome!

zoom.yazi/main.lua

@@ -1,68 +1,85 @@
 --- @since 25.6.11
 
-local get = ya.sync(function(st)
+local get = ya.sync(function(st, url) return st.last == url and st.level end)
+
+local save = ya.sync(function(st, url, new)
+	local h = cx.active.current.hovered
+	if h and h.url == url then
+		st.last, st.level = url, new
+		return true
+	end
+end)
+
+local lock = ya.sync(function(st, url, old, new)
+	if st.last == url and st.level == old then
+		st.level = new
+		return true
+	end
+end)
+
+local move = ya.sync(function(st)
 	local h = cx.active.current.hovered
 	if not h then
 		return
 	end
 
-	if st.last ~= h:hash() then
-		st.level, st.last = 0, h:hash()
+	if st.last ~= h.url then
+		st.last, st.level = Url(h.url), 0
 	end
 
-	return {
-		url = h.url,
-		mime = h:mime() or "",
-		level = st.level,
-	}
+	return { url = h.url, level = st.level }
 end)
 
-local save = ya.sync(function(st, before, after)
-	if st.level == before then
-		st.level = after
-		return true
+local function end_(job, err)
+	if not job.old_level then
+		ya.preview_widget(job, err and ui.Text(err):area(job.area):wrap(ui.Wrap.YES))
+	elseif err then
+		ya.notify { title = "Zoom", content = tostring(err), timeout = 5, level = "error" }
 	end
-end)
+end
 
-local function fail(...) return ya.notify { title = "Zoom", content = string.format(...), timeout = 5, level = "error" } end
-
-local function canvas()
+local function canvas(area)
 	local cw, ch = rt.term.cell_size()
 	if not cw then
 		return rt.preview.max_width, rt.preview.max_height
 	end
 
-	local area = ui.area("preview")
 	return math.min(rt.preview.max_width, math.floor(area.w * cw)),
 		math.min(rt.preview.max_height, math.floor(area.h * ch))
 end
 
-local function entry(_, job)
-	local st = get(job.args[1])
-	if not st then
-		return
-	end
-
-	local info, err = ya.image_info(st.url)
+local function peek(_, job)
+	local url = job.file.url
+	local info, err = ya.image_info(url)
 	if not info then
-		return fail("Failed to get image info: %s", err)
+		return end_(job, Err("Failed to get image info: %s", err))
 	end
 
-	local motion = tonumber(job.args[1]) or 0
-	local level = ya.clamp(-10, st.level + motion, 10)
+	local level = ya.clamp(-10, job.new_level or get(Url(url)) or tonumber(job.args[1]) or 0, 10)
+	local sync = function()
+		if job.old_level then
+			return lock(url, job.old_level, level)
+		else
+			return save(url, level)
+		end
+	end
 
-	local max_w, max_h = canvas()
+	local max_w, max_h = canvas(job.area)
 	local min_w, min_h = math.min(max_w, info.w), math.min(max_h, info.h)
 	local new_w = min_w + math.floor(min_w * level * 0.1)
 	local new_h = min_h + math.floor(min_h * level * 0.1)
 	if new_w > max_w or new_h > max_h then
-		return -- Image larger than available preview area after zooming
+		if job.old_level then
+			return sync() -- Image larger than available preview area after zooming
+		else
+			new_w, new_h = max_w, max_h -- Run as a previewer, render the image anyway
+		end
 	end
 
 	local tmp = os.tmpname()
 	-- stylua: ignore
 	local status, err = Command("magick"):arg {
-		tostring(st.url),
+		tostring(url),
 		"-auto-orient", "-strip",
 		"-sample", string.format("%dx%d", new_w, new_h),
 		"-quality", rt.preview.image_quality,
@@ -70,12 +87,33 @@ local function entry(_, job)
 	}:status()
 
 	if not status then
-		fail("Failed to run `magick` command: %s", err)
+		end_(job, Err("Failed to run `magick` command: %s", err))
 	elseif not status.success then
-		fail("`magick` command exited with error code %d", status.code)
-	elseif save(st.level, level) then
-		ya.image_show(Url(tmp), ui.area("preview"))
+		end_(job, Err("`magick` command exited with error code %d", status.code))
+	elseif sync() then
+		ya.image_show(Url(tmp), job.area)
+	end
+	end_(job)
+end
+
+local function entry(self, job)
+	local st = move()
+	if not st then
+		return
+	end
+
+	local motion = tonumber(job.args[1]) or 0
+	local new = ya.clamp(-10, st.level + motion, 10)
+	if new ~= st.level then
+		peek(self, {
+			area = ui.area("preview"),
+			args = {},
+			file = { url = st.url }, -- FIXME: use `File` instead of a dummy file
+			skip = 0,
+			new_level = new,
+			old_level = st.level,
+		})
 	end
 end
 
-return { entry = entry }
+return { peek = peek, entry = entry }