From 2672029a3c87b21b051c89990f51710cf0254f29 Mon Sep 17 00:00:00 2001
From: Will Hopkins <willothyh@gmail.com>
Date: Wed, 27 Dec 2023 01:09:51 -0800
Subject: [PATCH] feat: basic hinting behavior with ^ and $ motions

---
 lua/precognition/init.lua | 80 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 76 insertions(+), 4 deletions(-)

diff --git a/lua/precognition/init.lua b/lua/precognition/init.lua
index 1b8267b..8e61116 100644
--- a/lua/precognition/init.lua
+++ b/lua/precognition/init.lua
@@ -20,7 +20,7 @@ local default = {
 }
 
 ---@type Precognition.Config
-local config = {}
+local config = default
 
 --- Show the hints until the next keypress or CursorMoved event
 function M.peek()
@@ -46,14 +46,86 @@ end
 function M.setup(opts)
 	config = vim.tbl_deep_extend("force", default, opts or {})
 
-	vim.api.nvim_create_autocmd("CursorMoved", {
+	local ns = vim.api.nvim_create_namespace("precognition")
+	local au = vim.api.nvim_create_augroup("precognition", { clear = true })
+
+	-- This is a test with basic functionality, definitely should be moved out of the setup function and into
+	-- functions that the public methods can call.
+
+	local re_line_start = vim.regex("^\\s*[^\\s]") --[[@as vim.regex]]
+
+	---@type integer?
+	local extmark -- the active extmark in the current buffer
+
+	-- clear the extmark entirely when leaving a buffer (hints should only show in current buffer)
+	vim.api.nvim_create_autocmd("BufLeave", {
+		group = au,
+		callback = function(ev)
+			vim.api.nvim_buf_clear_namespace(ev.buf, ns, 0, -1)
+			extmark = nil
+		end,
+	})
+
+	-- clear the extmark when the cursor moves, or when insert mode is entered
+	vim.api.nvim_create_autocmd({ "CursorMoved", "InsertEnter" }, {
+		group = au,
 		callback = function()
-			-- todo: hide the hints
+			if extmark then
+				vim.api.nvim_buf_del_extmark(0, ns, extmark)
+				extmark = nil
+			end
 		end,
 	})
+
 	vim.api.nvim_create_autocmd("CursorHold", {
+		group = au,
+		-- TODO: add debounce / delay before showing hints to reduce flickering
+		-- during fast movements
 		callback = function()
-			-- todo: show the hints if they're hidden
+			if extmark then
+				return
+			end
+
+			local cursorline, _cursorcol = unpack(vim.api.nvim_win_get_cursor(0))
+			local cur_line = vim.api.nvim_get_current_line()
+
+			-- vim.fn.col("^") doesn't work :(
+			local line_end = vim.fn.col("$") - 1
+
+			-- FIXME: does not play nice with utf-8, we need a better way to
+			-- get char offsets.
+			--
+			-- Notice that on a line with a string containing utf-8 symbols, the marks to not
+			-- appear in the correct place. We need to treat this as a char array, it seems that vim regex
+			-- treats it like a byte array.
+			local line_start = select(2, re_line_start:match_str(cur_line))
+
+			local virt_line = {}
+
+			-- create the list of hints to show in { hint, column } format
+			-- TODO: extract this into a function, add hints for other motions
+			local marks = {}
+			table.insert(marks, { "^", math.max(0, line_start - 1) })
+			table.insert(marks, { "$", line_end - 1 })
+
+			-- build the virtual line out of virt text chunks
+			local last_col = 0
+			for _, mark in ipairs(marks) do
+				local hint = config.hints[mark[1]] or mark[1]
+				local col = mark[2]
+				if col > last_col then
+					-- add padding between hints
+					table.insert(virt_line, { string.rep(" ", (col - last_col)) })
+					last_col = col + 1
+				end
+				table.insert(virt_line, { hint, "Comment" })
+			end
+
+			-- create (or overwrite) the extmark
+			extmark = vim.api.nvim_buf_set_extmark(0, ns, cursorline - 1, line_start, {
+				id = extmark, -- reuse the same extmark if it exists
+				virt_lines = { virt_line },
+			})
 		end,
 	})
 end