log: allow file logging

examples/log.v

@@ -1,7 +1,7 @@
 import log
 
 fn main(){
-    mut l := log.Log{level:log.INFO}
+    mut l := log.Log{level:log.INFO, 'terminal'}
     l.info('info')
     l.warn('warn')
     l.error('error')

vlib/log/log.v

@@ -1,5 +1,7 @@
 module log
 
+import os
+import time
 import term
 
 const (
@@ -13,6 +15,7 @@ const (
 struct Log{
 mut:
     level int
+    output string
 }
 
 
@@ -20,34 +23,72 @@ pub fn (l mut Log) set_level(level int){
     l.level = level
 }
 
+pub fn (l mut Log) set_output(output string) {
+    l.output = output
+}
+
+fn (l Log) log_file(s string, e string) {
+    filename := l.output
+    f := os.open_append(l.output) or {
+        panic('error reading file $filename')
+        return
+    }
+    timestamp := time.now().format_ss()
+    f.writeln('$timestamp [$e] $s')
+}
+
 pub fn (l Log) fatal(s string){
     panic(s)
 }
 
 pub fn (l Log) error(s string){
     if l.level >= ERROR{
+        switch l.output {
+        case 'terminal':
             f := term.red('E')
             println('[$f]$s')
+
+        default:
+            l.log_file(s, 'E')
+        }
     }
 }
 
 pub fn (l Log) warn(s string){
     if l.level >= WARN{
+        switch l.output {
+        case 'terminal':
             f := term.yellow('W')
             println('[$f]$s')
+
+        default:
+            l.log_file(s, 'W')
+        }
     }  
 }
 
 pub fn (l Log) info(s string){
     if l.level >= INFO{
+        switch l.output {
+        case 'terminal':
             f := term.white('I')
             println('[$f]$s')
+
+        default:
+            l.log_file(s, 'I')
+        }
     }
 }
 
 pub fn (l Log) debug(s string){
     if l.level >= DEBUG{
+        switch l.output {
+        case 'terminal':
             f := term.blue('D')
             println('[$f]$s')
+
+        default:
+            l.log_file(s, 'D')
+        }
     }
 }