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// 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"
        "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)
}