Add diff split (#13)

lua/jj/diff.lua

@@ -0,0 +1,68 @@
+---@class jj.diff
+local M = {}
+
+local utils = require("jj.utils")
+
+--- 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", 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
+		-- File does not exist at revision
+		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
+function M.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)
+
+	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
+
+--- Open a diff split for a specific revision of the current file
+--- @param split_fun function Split function for the diff
+--- @param args table Any passed arguments
+function M.open_diff(split_fun, args)
+	if not utils.ensure_jj() then
+		return
+	end
+
+	local rev = args[1] or "@-"
+	local path = vim.api.nvim_buf_get_name(0)
+
+	vim.cmd.diffthis()
+	split_fun({ mods = { split = "aboveleft" } })
+	M.open_revision(rev, path)
+	vim.cmd.diffthis()
+end
+
+function M.open_vdiff(opts)
+	M.open_diff(vim.cmd.vsplit, opts.fargs)
+end
+
+function M.open_hdiff(opts)
+	M.open_diff(vim.cmd.split, opts.fargs)
+end
+
+return M