-- mini.diff source backed by jj.

local M = {}

local function resolve(buf_id)
	local name = vim.api.nvim_buf_get_name(buf_id)
	if name == "" then
		return nil
	end

	local change_id, rel = name:match("^jj://([^/]+)/(.+)$")
	if change_id then
		-- The path in the uri is repo-relative; jj resolves it from anywhere in
		-- the repo, so run from the current working directory.
		return { rev = change_id .. "-", from = change_id, file = rel, rel = rel, cwd = vim.fn.getcwd() }
	end

	local path = vim.uv.fs_realpath(name)
	if path == nil then
		return nil
	end
	local root = vim.fs.root(path, ".jj")
	return {
		rev = "@-",
		from = "@",
		file = path,
		rel = root and path:sub(#root + 2),
		cwd = vim.fs.dirname(path),
	}
end

local function set_ref_text(buf_id)
	if not vim.api.nvim_buf_is_valid(buf_id) then
		return
	end
	local target = resolve(buf_id)
	if target == nil then
		return
	end
	vim.system(
		{ "jj", "file", "show", "--ignore-working-copy", "-r", target.rev, target.file },
		{ cwd = target.cwd, text = true },
		vim.schedule_wrap(function(obj)
			if not vim.api.nvim_buf_is_valid(buf_id) then
				return
			end
			local text = obj.code == 0 and obj.stdout or ""
			pcall(MiniDiff.set_ref_text, buf_id, text)
		end)
	)
end

local function group_name(buf_id)
	return "MiniDiffSourceJj" .. buf_id
end

-- One filesystem watcher per repo root, tracking the buffers attached to it.
-- jj rewrites `.jj/repo/op_heads/heads/` on every operation (edit, squash, …),
-- so watching it lets us refresh signs when jj state changes out from under us.
local watchers = {}

local function refresh_watcher(root)
	local watcher = watchers[root]
	if watcher == nil then
		return
	end
	for buf_id in pairs(watcher.buffers) do
		if vim.api.nvim_buf_is_valid(buf_id) then
			set_ref_text(buf_id)
		else
			watcher.buffers[buf_id] = nil
		end
	end
end

local function start_watcher(root)
	local watcher = { buffers = {} }
	local heads = root .. "/.jj/repo/op_heads/heads"
	local handle = vim.uv.new_fs_event()
	if handle ~= nil then
		local ok = handle:start(heads, {}, function(err)
			if err then
				return
			end
			-- Debounce: an operation removes the old head and adds the new one,
			-- firing several events; coalesce them into a single refresh.
			if watcher.timer == nil then
				watcher.timer = vim.uv.new_timer()
				watcher.timer:start(
					50,
					0,
					vim.schedule_wrap(function()
						if watcher.timer ~= nil then
							watcher.timer:close()
							watcher.timer = nil
						end
						refresh_watcher(root)
					end)
				)
			end
		end)
		if ok then
			watcher.handle = handle
		else
			handle:close()
		end
	end
	watchers[root] = watcher
	return watcher
end

local function stop_watcher(root)
	local watcher = watchers[root]
	if watcher == nil then
		return
	end
	if watcher.timer ~= nil then
		watcher.timer:close()
		watcher.timer = nil
	end
	if watcher.handle ~= nil then
		watcher.handle:stop()
		watcher.handle:close()
	end
	watchers[root] = nil
end

local buf_roots = {}

local function attach(buf_id)
	local target = resolve(buf_id)
	if target == nil then
		return false
	end

	local root = vim.fs.root(target.cwd, ".jj")
	if root == nil then
		return false
	end

	local group = vim.api.nvim_create_augroup(group_name(buf_id), { clear = true })
	vim.api.nvim_create_autocmd({ "BufWritePost", "BufReadPost", "BufEnter", "FocusGained", "FileChangedShellPost" }, {
		group = group,
		buffer = buf_id,
		desc = "Refresh jj diff reference",
		callback = function()
			set_ref_text(buf_id)
		end,
	})

	local watcher = watchers[root] or start_watcher(root)
	watcher.buffers[buf_id] = true
	buf_roots[buf_id] = root

	set_ref_text(buf_id)
end

local function detach(buf_id)
	pcall(vim.api.nvim_del_augroup_by_name, group_name(buf_id))

	local root = buf_roots[buf_id]
	buf_roots[buf_id] = nil
	local watcher = root and watchers[root]
	if watcher ~= nil then
		watcher.buffers[buf_id] = nil
		if next(watcher.buffers) == nil then
			stop_watcher(root)
		end
	end
end

-- Squash the given hunks into the revision we diff against. jj has no index to
-- stage into, so instead we rebuild what the parent should look like (the
-- reference text with only those hunks applied) and hand it to `jj squash -i`
-- through a diff editor that just copies our file over jj's right side.
local function apply_hunks(buf_id, hunks)
	local target = resolve(buf_id)
	if target == nil or target.rel == nil then
		return
	end

	local ref = vim.split(MiniDiff.get_buf_data(buf_id).ref_text, "\n")
	-- mini.diff always terminates the reference text with a newline
	if ref[#ref] == "" then
		table.remove(ref)
	end
	local buf = vim.api.nvim_buf_get_lines(buf_id, 0, -1, false)

	-- Bottom-up so earlier hunks keep their reference line numbers.
	local sorted = vim.deepcopy(hunks)
	table.sort(sorted, function(a, b) return a.ref_start > b.ref_start end)
	for _, hunk in ipairs(sorted) do
		-- "add" hunks have no reference line, `ref_start` is the one above them
		local from = hunk.ref_start + (hunk.ref_count == 0 and 1 or 0)
		local to = from + hunk.ref_count - 1
		local out = vim.list_slice(ref, 1, from - 1)
		vim.list_extend(out, buf, hunk.buf_start, hunk.buf_start + hunk.buf_count - 1)
		vim.list_extend(out, ref, to + 1, #ref)
		ref = out
	end

	local tmp = vim.fn.tempname()
	vim.fn.writefile(ref, tmp)
	vim.system({
		"jj",
		"squash",
		"--from",
		target.from,
		"--into",
		target.rev,
		"--use-destination-message",
		"--tool",
		"minidiff",
		"--config",
		'merge-tools.minidiff.program="cp"',
		"--config",
		string.format(
			"merge-tools.minidiff.edit-args=[%s, %s]",
			vim.json.encode(tmp),
			vim.json.encode("$right/" .. target.rel)
		),
		"--",
		target.rel,
	}, { cwd = target.cwd, text = true }, vim.schedule_wrap(function(obj)
		vim.fn.delete(tmp)
		if obj.code ~= 0 then
			vim.notify(obj.stderr, vim.log.levels.ERROR)
		end
	end))
end

M.source = {
	name = "jj",
	attach = attach,
	detach = detach,
	apply_hunks = apply_hunks,
}

-- support jj:// buffers
function M.setup()
	local group = vim.api.nvim_create_augroup("MiniDiffJjRevisionBuffers", { clear = true })
	vim.api.nvim_create_autocmd({ "BufWinEnter", "BufReadPost" }, {
		group = group,
		desc = "Enable mini.diff on jj revision buffers",
		callback = function(ev)
			vim.schedule(function()
				if not vim.api.nvim_buf_is_valid(ev.buf) then
					return
				end
				if vim.api.nvim_buf_get_name(ev.buf):match("^jj://") then
					pcall(require("mini.diff").enable, ev.buf)
				end
			end)
		end,
	})
end

return M