// The MIT License (MIT)
//
// Copyright (c) 2015 Yusuke Inuzuka
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

package server

import (
	"fmt"
	"time"
)

type flagScanner struct {
	flag       byte
	start      string
	end        string
	buf        []byte
	str        string
	Length     int
	Pos        int
	HasFlag    bool
	ChangeFlag bool
}

func newFlagScanner(flag byte, start, end, str string) *flagScanner {
	return &flagScanner{flag, start, end, make([]byte, 0, len(str)), str, len(str), 0, false, false}
}

func (fs *flagScanner) AppendString(str string) { fs.buf = append(fs.buf, str...) }

func (fs *flagScanner) AppendChar(ch byte) { fs.buf = append(fs.buf, ch) }

func (fs *flagScanner) String() string { return string(fs.buf) }

func (fs *flagScanner) Next() (byte, bool) {
	c := byte('\000')
	fs.ChangeFlag = false
	if fs.Pos == fs.Length {
		if fs.HasFlag {
			fs.AppendString(fs.end)
		}
		return c, true
	}
	c = fs.str[fs.Pos]
	if c == fs.flag {
		if fs.Pos < (fs.Length-1) && fs.str[fs.Pos+1] == fs.flag {
			fs.HasFlag = false
			fs.AppendChar(fs.flag)
			fs.Pos += 2
			return fs.Next()
		} else if fs.Pos != fs.Length-1 {
			if fs.HasFlag {
				fs.AppendString(fs.end)
			}
			fs.AppendString(fs.start)
			fs.ChangeFlag = true
			fs.HasFlag = true
		}
	}
	fs.Pos++
	return c, false
}

var cDateFlagToGo = map[byte]string{
	'a': "mon", 'A': "Monday", 'b': "Jan", 'B': "January", 'c': "02 Jan 06 15:04 MST", 'd': "02",
	'F': "2006-01-02", 'H': "15", 'I': "03", 'm': "01", 'M': "04", 'p': "PM", 'P': "pm", 'S': "05",
	'x': "15/04/05", 'X': "15:04:05", 'y': "06", 'Y': "2006", 'z': "-0700", 'Z': "MST"}

func strftime(t time.Time, cfmt string) string {
	sc := newFlagScanner('%', "", "", cfmt)
	for c, eos := sc.Next(); !eos; c, eos = sc.Next() {
		if !sc.ChangeFlag {
			if sc.HasFlag {
				if v, ok := cDateFlagToGo[c]; ok {
					sc.AppendString(t.Format(v))
				} else {
					switch c {
					case 'w':
						sc.AppendString(fmt.Sprint(int(t.Weekday())))
					default:
						sc.AppendChar('%')
						sc.AppendChar(c)
					}
				}
				sc.HasFlag = false
			} else {
				sc.AppendChar(c)
			}
		}
	}

	return sc.String()
}
