jj.nvim/lua/jj/diff/native.lua

local utils = require("jj.utils")
local buffer = require("jj.core.buffer")

local diff = require("jj.diff")

--- Get the content of a file at a specific revision
--- @param rev string The revision
--- @param path string The file path
--- @return table lines The file content
local function get_file_content(rev, path)
	local cmd = string.format("jj file show -r %s %s", vim.fn.shellescape(rev), vim.fn.shellescape(path))
	local content = vim.fn.system(cmd)
	local success = vim.v.shell_error == 0
	if success then
		return vim.split(content, "\n", { trimempty = true })
	else
		return {}
	end
end

--- Open a read-only buffer for a specific revision of a file
--- @param rev string The revision
--- @param path string The file path
local function open_revision(rev, path)
	local lines = get_file_content(rev, path)

	local buf = vim.api.nvim_create_buf(false, true)

	local buf_name = string.format("jj://%s/%s", rev, path)
	vim.api.nvim_buf_set_name(buf, buf_name)
	vim.api.nvim_buf_set_lines(buf, 0, -1, false, lines)

	local ft = vim.filetype.match({ filename = path })
	if ft then
		vim.bo[buf].filetype = ft
	end

	vim.bo[buf].buftype = "nofile"
	vim.bo[buf].bufhidden = "wipe"
	vim.bo[buf].readonly = true
	vim.bo[buf].swapfile = false
	vim.bo[buf].modifiable = true

	vim.api.nvim_win_set_buf(0, buf)
end

-----------------------------------------------------------------------
-- Native Backend
-----------------------------------------------------------------------

diff.register_backend("native", {
	--- Opens a side-by-side diff of the current buffer against a revision.
	--- Creates a split with the revision content on the left and the current buffer on the right.
	--- Closing either side will clean up both and restore the original cursor position.
	diff_current = function(opts)
		if not utils.ensure_jj() then
			return
		end

		-- Save current state to restore after diff is closed
		local prev_buf = vim.api.nvim_get_current_buf()
		local prev_cur_pos = buffer.get_cursor(prev_buf) or { 1, 0 }

		local rev = opts.rev or "@-"
		local path = opts.path or vim.api.nvim_buf_get_name(0)
		local layout = opts.layout or "vertical"

		local split_fun = layout == "horizontal" and vim.cmd.split or vim.cmd.vsplit
		local orig_win = vim.api.nvim_get_current_win()

		-- Use better diff algorithm for code moves and indentation
		local saved_diffopt = vim.o.diffopt
		vim.opt.diffopt:append("algorithm:patience,indent-heuristic")

		-- Set up diff: current buffer on right, revision on left
		vim.cmd.diffthis()
		split_fun({ mods = { split = "aboveleft" } })
		open_revision(rev, path)
		vim.cmd.diffthis()

		local rev_buf = vim.api.nvim_get_current_buf()
		local augroup = vim.api.nvim_create_augroup("JJDiffCleanup" .. rev_buf, { clear = true })

		-- Cleanup closes both sides, exits diff mode, and restores cursor.
		local function cleanup()
			vim.api.nvim_del_augroup_by_id(augroup)
			vim.schedule(function()
				if vim.api.nvim_buf_is_valid(rev_buf) then
					vim.api.nvim_buf_delete(rev_buf, { force = true })
				end
				if vim.api.nvim_win_is_valid(orig_win) then
					vim.api.nvim_set_current_win(orig_win)
					vim.cmd.diffoff()
				end
				buffer.set_cursor(prev_buf, prev_cur_pos)
				vim.o.diffopt = saved_diffopt
			end)
		end

		-- Trigger cleanup when either the revision buffer or original window is closed
		vim.api.nvim_create_autocmd({ "BufWipeout", "BufHidden" }, {
			group = augroup,
			buffer = rev_buf,
			once = true,
			callback = cleanup,
		})

		vim.api.nvim_create_autocmd("WinClosed", {
			group = augroup,
			pattern = tostring(orig_win),
			once = true,
			callback = cleanup,
		})
	end,
	show_revision = function(opts)
		local terminal = require("jj.ui.terminal")

		local cmd = string.format("jj show -r %s --quiet --no-pager", opts.rev)
		terminal.run_floating(cmd)
	end,
	diff_revisions = function(opts)
		local terminal = require("jj.ui.terminal")

		local cmd = string.format("jj diff -f %s -t %s --quiet --no-pager", opts.left, opts.right)
		terminal.run_floating(cmd)
	end,
	diff_history_revisions = function(_)
		utils.notify(
			"Diffing revisions with history mode is not supported on the `native` backend.",
			vim.log.levels.WARN
		)
	end,
})