// Copyright 2022 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 slog

import (
	"encoding"
	"fmt"
	"io"
	"strconv"
	"time"
	"unicode"
	"unicode/utf8"

	"golang.org/x/exp/slog/internal/buffer"
)

// TextHandler is a Handler that writes Records to an io.Writer as a
// sequence of key=value pairs separated by spaces and followed by a newline.
type TextHandler struct {
	*commonHandler
}

// NewTextHandler creates a TextHandler that writes to w,
// using the default options.
func NewTextHandler(w io.Writer) *TextHandler {
	return (HandlerOptions{}).NewTextHandler(w)
}

// NewTextHandler creates a TextHandler with the given options that writes to w.
func (opts HandlerOptions) NewTextHandler(w io.Writer) *TextHandler {
	return &TextHandler{
		&commonHandler{
			app:     textAppender{},
			attrSep: ' ',
			w:       w,
			opts:    opts,
		},
	}
}

// With returns a new TextHandler whose attributes consists
// of h's attributes followed by attrs.
func (h *TextHandler) With(attrs []Attr) Handler {
	return &TextHandler{commonHandler: h.commonHandler.with(attrs)}
}

// Handle formats its argument Record as a single line of space-separated
// key=value items.
//
// If the Record's time is zero, the time is omitted.
// Otherwise, the key is "time"
// and the value is output in RFC3339 format with millisecond precision.
//
// If the Record's level is zero, the level is omitted.
// Otherwise, the key is "level"
// and the value of [Level.String] is output.
//
// If the AddSource option is set and source information is available,
// the key is "source" and the value is output as FILE:LINE.
//
// The message's key "msg".
//
// To modify these or other attributes, or remove them from the output, use
// [HandlerOptions.ReplaceAttr].
//
// If a value implements [encoding.TextMarshaler], the result of MarshalText is
// written. Otherwise, the result of fmt.Sprint is written.
//
// Keys and values are quoted if they contain Unicode space characters,
// non-printing characters, '"' or '='.
//
// Each call to Handle results in a single serialized call to
// io.Writer.Write.
func (h *TextHandler) Handle(r Record) error {
	return h.commonHandler.handle(r)
}

type textAppender struct{}

func (textAppender) appendStart(*buffer.Buffer) {}

func (textAppender) appendEnd(*buffer.Buffer) {}

func (a textAppender) appendKey(buf *buffer.Buffer, key string) {
	a.appendString(buf, key)
	buf.WriteByte('=')
}

func (textAppender) appendString(buf *buffer.Buffer, s string) {
	if needsQuoting(s) {
		*buf = strconv.AppendQuote(*buf, s)
	} else {
		buf.WriteString(s)
	}
}

func (textAppender) appendTime(buf *buffer.Buffer, t time.Time) error {
	*buf = appendTimeRFC3339Millis(*buf, t)
	return nil
}

func (a textAppender) appendSource(buf *buffer.Buffer, file string, line int) {
	if needsQuoting(file) {
		a.appendString(buf, file+":"+strconv.Itoa(line))
	} else {
		// common case: no quoting needed.
		a.appendString(buf, file)
		buf.WriteByte(':')
		itoa((*[]byte)(buf), line, -1)
	}
}
func (app textAppender) appendAttrValue(buf *buffer.Buffer, a Attr) error {
	switch a.Kind() {
	case StringKind:
		app.appendString(buf, a.str())
	case TimeKind:
		_ = app.appendTime(buf, a.Time())
	case AnyKind:
		if tm, ok := a.any.(encoding.TextMarshaler); ok {
			data, err := tm.MarshalText()
			if err != nil {
				return err
			}
			// TODO: avoid the conversion to string.
			app.appendString(buf, string(data))
			return nil
		}
		app.appendString(buf, fmt.Sprint(a.Value()))
	default:
		*buf = a.appendValue(*buf)
	}
	return nil
}

func needsQuoting(s string) bool {
	for i := 0; i < len(s); {
		b := s[i]
		if b < utf8.RuneSelf {
			if needsQuotingSet[b] {
				return true
			}
			i++
			continue
		}
		r, size := utf8.DecodeRuneInString(s[i:])
		if r == utf8.RuneError || unicode.IsSpace(r) || !unicode.IsPrint(r) {
			return true
		}
		i += size
	}
	return false
}

var needsQuotingSet = [utf8.RuneSelf]bool{
	'"': true,
	'=': true,
}

func init() {
	for i := 0; i < utf8.RuneSelf; i++ {
		r := rune(i)
		if unicode.IsSpace(r) || !unicode.IsPrint(r) {
			needsQuotingSet[i] = true
		}
	}
}