improve default logging

I use to have logging enabled to be able to debug weird vis-lspc
behavior right away. But I got annoyed by vis-lspc cluttering all my
directories with vis-lspc.log files.
So vis-lspc will no write its log files to
$XDG_DATA_HOME/vis-lspc/<iso-date>-<cwd-basename>.log if
lspc.log_file is not set by the user.

This patch also introduces a helper to run a program and capture
its output.

2 files changed, 46 insertions, 4 deletions

diff --git a/README.md b/README.md
index ed990ff..a882907 100644
--- a/README.md
+++ b/README.md
@@ -104,7 +104,8 @@ Available fields are:
 
 * `name = 'vis-lspc'` - the name vis-lspc introduces itself to a language server
 * `logging = false` - enable logging only useful for debugging vis-lspc
-* `log_file = 'vis-lspc.log'` - file vis-lspc writes all log messages to
+* `log_file = nil` - nil, filename or function returning a filename
+  * If `log_file` is `nil` vis-lspc will create a new file in `$XDG_DATA_HOME/vis-lspc`
 * `autostart = true` - try to start a language server in WIN_OPEN
 * `menu_cmd = 'fzf' or 'vis-menu'` - program to prompt for user choices
 * `confirm_cmd = 'vis-menu'` - program to prompt for user confirmation
diff --git a/init.lua b/init.lua
index 0521a6c..12e6cf6 100644
--- a/init.lua
+++ b/init.lua
@@ -51,7 +51,7 @@ local lspc = {
   version = '0.1.3',
   -- write log messages to lspc.log_file
   logging = false,
-  log_file = 'vis-lspc.log',
+  log_file = nil,
   -- automatically start a language server when a new window is opened
   autostart = true,
   -- program used to let the user make choices
@@ -69,6 +69,25 @@ local lspc = {
   diagnostic_style = 'back:#e3514f',
 }
 
+-- Forward declaration of lspc_err to use it in capture_cmd
+local lspc_err
+
+-- Helper to execute a command and capture its output
+local function capture_cmd(cmd)
+  local p = assert(io.popen(cmd, 'r'))
+  local s = assert(p:read('*a'))
+  local success, _, status = p:close()
+  if not success then
+    local err = cmd .. ' failed with exit code: ' .. status
+    if lspc_err then
+      lspc_err(err)
+    else
+      vis:info('LSPC Error: ' .. err)
+    end
+  end
+  return s
+end
+
 -- logging system
 -- if lspc.logging is set to true the first call to lspc.log
 -- will open the log file and replace lspc.log with the actual log function
@@ -86,7 +105,29 @@ do
       return
     end
 
-    log_fd = assert(io.open(lspc.log_file, 'w'))
+    local log_file = lspc.log_file
+
+    -- open the default log file in $XDG_DATA_HOME/vis-lspc
+    if not log_file then
+      local xdg_data = os.getenv('XDG_DATA_HOME') or os.getenv('HOME') ..
+                           '/.local/share'
+      local log_dir = xdg_data .. '/vis-lspc'
+
+      -- ensure the direcoty exists
+      os.execute('mkdir -p ' .. log_dir)
+
+      -- log file format: {time-stamp}-{basename-cwd}.log
+      local log_file_fmt = log_dir .. '/%s-%s.log'
+      local timestamp = os.date('%Y-%m-%dT%H:%M:%S')
+      local cwd = capture_cmd('pwd')
+      local basename_cwd = capture_cmd('basename ' .. cwd):match('^%s*(.-)%s*$')
+      log_file = log_file_fmt:format(timestamp, basename_cwd)
+
+    elseif type(log_file) == 'function' then
+      log_file = log_file()
+    end
+
+    log_fd = assert(io.open(log_file, 'w'))
     lspc.log = log
 
     log(msg)
@@ -100,7 +141,7 @@ local function lspc_warn(msg)
   vis:info(warning)
 end
 
-local function lspc_err(msg)
+lspc_err = function(msg)
   local err = 'LSPC Error: ' .. msg
   lspc.log(err)
   vis:info(err)