// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package log implements a simple logging package. It defines a type, Logger,
// with methods for formatting output. It also has a predefined 'standard'
// Logger accessible through helper functions Print[f|ln], Fatal[f|ln], and
// Panic[f|ln], which are easier to use than creating a Logger manually.
// That logger writes to standard error and prints the date and time
// of each logged message.
// The Fatal functions call os.Exit(1) after writing the log message.
// The Panic functions call panic after writing the log message.
package log

import (
	"bytes"
	_ "debug/elf"
	"fmt"
	"io"
	"os"
	"runtime"
	"sync"
	"time"
)

// These flags define which text to prefix to each log entry generated by the Logger.
const (
	// Bits or'ed together to control what's printed. There is no control over the
	// order they appear (the order listed here) or the format they present (as
	// described in the comments).  A colon appears after these items:
	//	2009/0123 01:23:23.123123 /a/b/c/d.go:23: message
	Ldate         = 1 << iota     // the date: 2009/0123
	Ltime                         // the time: 01:23:23
	Lmicroseconds                 // microsecond resolution: 01:23:23.123123.  assumes Ltime.
	Llongfile                     // full file name and line number: /a/b/c/d.go:23
	Lshortfile                    // final file name element and line number: d.go:23. overrides Llongfile
	LstdFlags     = Ldate | Ltime // initial values for the standard logger
)

// A Logger represents an active logging object that generates lines of
// output to an io.Writer.  Each logging operation makes a single call to
// the Writer's Write method.  A Logger can be used simultaneously from
// multiple goroutines; it guarantees to serialize access to the Writer.
type Logger struct {
	mu     sync.Mutex   // ensures atomic writes; protects the following fields
	prefix string       // prefix to write at beginning of each line
	flag   int          // properties
	out    io.Writer    // destination for output
	buf    bytes.Buffer // for accumulating text to write
}

// New creates a new Logger.   The out variable sets the
// destination to which log data will be written.
// The prefix appears at the beginning of each generated log line.
// The flag argument defines the logging properties.
func New(out io.Writer, prefix string, flag int) *Logger {
	return &Logger{out: out, prefix: prefix, flag: flag}
}

var std = New(os.Stderr, "", LstdFlags)

// Cheap integer to fixed-width decimal ASCII.  Give a negative width to avoid zero-padding.
// Knows the buffer has capacity.
func itoa(buf *bytes.Buffer, i int, wid int) {
	var u uint = uint(i)
	if u == 0 && wid <= 1 {
		buf.WriteByte('0')
		return
	}

	// Assemble decimal in reverse order.
	var b [32]byte
	bp := len(b)
	for ; u > 0 || wid > 0; u /= 10 {
		bp--
		wid--
		b[bp] = byte(u%10) + '0'
	}

	// avoid slicing b to avoid an allocation.
	for bp < len(b) {
		buf.WriteByte(b[bp])
		bp++
	}
}

func (l *Logger) formatHeader(buf *bytes.Buffer, t time.Time, file string, line int) {
	buf.WriteString(l.prefix)
	if l.flag&(Ldate|Ltime|Lmicroseconds) != 0 {
		if l.flag&Ldate != 0 {
			year, month, day := t.Date()
			itoa(buf, year, 4)
			buf.WriteByte('/')
			itoa(buf, int(month), 2)
			buf.WriteByte('/')
			itoa(buf, day, 2)
			buf.WriteByte(' ')
		}
		if l.flag&(Ltime|Lmicroseconds) != 0 {
			hour, min, sec := t.Clock()
			itoa(buf, hour, 2)
			buf.WriteByte(':')
			itoa(buf, min, 2)
			buf.WriteByte(':')
			itoa(buf, sec, 2)
			if l.flag&Lmicroseconds != 0 {
				buf.WriteByte('.')
				itoa(buf, t.Nanosecond()/1e3, 6)
			}
			buf.WriteByte(' ')
		}
	}
	if l.flag&(Lshortfile|Llongfile) != 0 {
		if l.flag&Lshortfile != 0 {
			short := file
			for i := len(file) - 1; i > 0; i-- {
				if file[i] == '/' {
					short = file[i+1:]
					break
				}
			}
			file = short
		}
		buf.WriteString(file)
		buf.WriteByte(':')
		itoa(buf, line, -1)
		buf.WriteString(": ")
	}
}

// Output writes the output for a logging event.  The string s contains
// the text to print after the prefix specified by the flags of the
// Logger.  A newline is appended if the last character of s is not
// already a newline.  Calldepth is used to recover the PC and is
// provided for generality, although at the moment on all pre-defined
// paths it will be 2.
func (l *Logger) Output(calldepth int, s string) error {
	now := time.Now() // get this early.
	var file string
	var line int
	l.mu.Lock()
	defer l.mu.Unlock()
	if l.flag&(Lshortfile|Llongfile) != 0 {
		// release lock while getting caller info - it's expensive.
		l.mu.Unlock()
		var ok bool
		_, file, line, ok = runtime.Caller(calldepth)
		if !ok {
			file = "???"
			line = 0
		}
		l.mu.Lock()
	}
	l.buf.Reset()
	l.formatHeader(&l.buf, now, file, line)
	l.buf.WriteString(s)
	if len(s) > 0 && s[len(s)-1] != '\n' {
		l.buf.WriteByte('\n')
	}
	_, err := l.out.Write(l.buf.Bytes())
	return err
}

// Printf calls l.Output to print to the logger.
// Arguments are handled in the manner of fmt.Printf.
func (l *Logger) Printf(format string, v ...interface{}) {
	l.Output(2, fmt.Sprintf(format, v...))
}

// Print calls l.Output to print to the logger.
// Arguments are handled in the manner of fmt.Print.
func (l *Logger) Print(v ...interface{}) { l.Output(2, fmt.Sprint(v...)) }

// Println calls l.Output to print to the logger.
// Arguments are handled in the manner of fmt.Println.
func (l *Logger) Println(v ...interface{}) { l.Output(2, fmt.Sprintln(v...)) }

// Fatal is equivalent to l.Print() followed by a call to os.Exit(1).
func (l *Logger) Fatal(v ...interface{}) {
	l.Output(2, fmt.Sprint(v...))
	os.Exit(1)
}

// Fatalf is equivalent to l.Printf() followed by a call to os.Exit(1).
func (l *Logger) Fatalf(format string, v ...interface{}) {
	l.Output(2, fmt.Sprintf(format, v...))
	os.Exit(1)
}

// Fatalln is equivalent to l.Println() followed by a call to os.Exit(1).
func (l *Logger) Fatalln(v ...interface{}) {
	l.Output(2, fmt.Sprintln(v...))
	os.Exit(1)
}

// Panic is equivalent to l.Print() followed by a call to panic().
func (l *Logger) Panic(v ...interface{}) {
	s := fmt.Sprint(v...)
	l.Output(2, s)
	panic(s)
}

// Panicf is equivalent to l.Printf() followed by a call to panic().
func (l *Logger) Panicf(format string, v ...interface{}) {
	s := fmt.Sprintf(format, v...)
	l.Output(2, s)
	panic(s)
}

// Panicln is equivalent to l.Println() followed by a call to panic().
func (l *Logger) Panicln(v ...interface{}) {
	s := fmt.Sprintln(v...)
	l.Output(2, s)
	panic(s)
}

// Flags returns the output flags for the logger.
func (l *Logger) Flags() int {
	l.mu.Lock()
	defer l.mu.Unlock()
	return l.flag
}

// SetFlags sets the output flags for the logger.
func (l *Logger) SetFlags(flag int) {
	l.mu.Lock()
	defer l.mu.Unlock()
	l.flag = flag
}

// Prefix returns the output prefix for the logger.
func (l *Logger) Prefix() string {
	l.mu.Lock()
	defer l.mu.Unlock()
	return l.prefix
}

// SetPrefix sets the output prefix for the logger.
func (l *Logger) SetPrefix(prefix string) {
	l.mu.Lock()
	defer l.mu.Unlock()
	l.prefix = prefix
}

// SetOutput sets the output destination for the standard logger.
func SetOutput(w io.Writer) {
	std.mu.Lock()
	defer std.mu.Unlock()
	std.out = w
}

// Flags returns the output flags for the standard logger.
func Flags() int {
	return std.Flags()
}

// SetFlags sets the output flags for the standard logger.
func SetFlags(flag int) {
	std.SetFlags(flag)
}

// Prefix returns the output prefix for the standard logger.
func Prefix() string {
	return std.Prefix()
}

// SetPrefix sets the output prefix for the standard logger.
func SetPrefix(prefix string) {
	std.SetPrefix(prefix)
}

// These functions write to the standard logger.

// Print calls Output to print to the standard logger.
// Arguments are handled in the manner of fmt.Print.
func Print(v ...interface{}) {
	std.Output(2, fmt.Sprint(v...))
}

// Printf calls Output to print to the standard logger.
// Arguments are handled in the manner of fmt.Printf.
func Printf(format string, v ...interface{}) {
	std.Output(2, fmt.Sprintf(format, v...))
}

// Println calls Output to print to the standard logger.
// Arguments are handled in the manner of fmt.Println.
func Println(v ...interface{}) {
	std.Output(2, fmt.Sprintln(v...))
}

// Fatal is equivalent to Print() followed by a call to os.Exit(1).
func Fatal(v ...interface{}) {
	std.Output(2, fmt.Sprint(v...))
	os.Exit(1)
}

// Fatalf is equivalent to Printf() followed by a call to os.Exit(1).
func Fatalf(format string, v ...interface{}) {
	std.Output(2, fmt.Sprintf(format, v...))
	os.Exit(1)
}

// Fatalln is equivalent to Println() followed by a call to os.Exit(1).
func Fatalln(v ...interface{}) {
	std.Output(2, fmt.Sprintln(v...))
	os.Exit(1)
}

// Panic is equivalent to Print() followed by a call to panic().
func Panic(v ...interface{}) {
	s := fmt.Sprint(v...)
	std.Output(2, s)
	panic(s)
}

// Panicf is equivalent to Printf() followed by a call to panic().
func Panicf(format string, v ...interface{}) {
	s := fmt.Sprintf(format, v...)
	std.Output(2, s)
	panic(s)
}

// Panicln is equivalent to Println() followed by a call to panic().
func Panicln(v ...interface{}) {
	s := fmt.Sprintln(v...)
	std.Output(2, s)
	panic(s)
}