handler.go

package yadu

import (
	"bytes"
	"context"
	"fmt"
	"io"
	"log/slog"
	"regexp"
	"runtime"
	"slices"
	"strings"
	"sync"

	"gopkg.in/yaml.v3"

	"github.com/fatih/color"
)

const VERSION = "0.1.3"

// We use RFC datestring by default
const DefaultTimeFormat = "2006-01-02T03:04.05 MST"

// Default log level is INFO:
const defaultLevel = slog.LevelInfo

// holds attributes added with logger.With()
type attributes map[string]interface{}

type Handler struct {
	writer      io.Writer
	mu          *sync.Mutex
	level       slog.Leveler
	groups      []string
	attrs       attributes
	timeFormat  string
	replaceAttr func(groups []string, a slog.Attr) slog.Attr
	addSource   bool
	indenter    *regexp.Regexp

	/*
		This is being used in Postprocess() to fix
		https://github.com/go-yaml/yaml/issues/1020 and
		https://github.com/TLINDEN/yadu/issues/12 respectively.

		yaml.v3 follows the YAML standard and quotes all keys and values
		matching this regex (see https://yaml.org/type/bool.html):
		`y|Y|yes|Yes|YES|n|N|no|No|NO|true|True|TRUE|false|False|FALSE|on|On|ON|off|Off|OFF`

		The problem is,  that the YAML "standard" does  not state wether
		this  applies  to  values  or   keys  or  values&keys  and  most
		implementors, as gopkg.in/yaml.v3, do it just for keys and values.

		Therefore if  we dump a struct  containing a key "Y"  it ends up
		being quoted, while any other  keys remain unquoted, which looks
		pretty ugly, makes evaluating  the output harder,  especially in
		game development where you have to dump coordinates, points etc,
		all containing X,Y with X unquoted and Y quoted.

		To fix  this utter nonsence,  I just  replace all quotes  in all
		keys. Period. This is just a logging module, nobody will and can
		use its output to postprocess  it with some yaml parser, because
		we not only dump the structs as  yaml, we also write a one liner
		in front of it with the  timestamp and the message. So, we don't
		output  valid  YAML  anyway  and  we don't  give  a  shit  about
		compliance because of this. AND because this rule is bullshit.
	*/
	yamlcleaner *regexp.Regexp
}

// Options are options for the Yadu [log/slog.Handler].
//
// Level sets the minimum log level.
//
// ReplaceAttr is a function you  can define to customize how supplied
// attrs are being handled. It is empty by default, so nothing will be
// altered.
//
// Loglevel and message cannot be altered using ReplaceAttr. Timestamp
// can only be removed, see example. Keep in mind that everything will
// be passed to yaml.Marshal() in the end.
type Options struct {
	Level       slog.Leveler
	ReplaceAttr func(groups []string, a slog.Attr) slog.Attr
	TimeFormat  string
	AddSource   bool
	NoColor     bool
}

func (h *Handler) Handle(ctx context.Context, r slog.Record) error {
	level := r.Level.String() + ":"

	switch r.Level {
	case slog.LevelDebug:
		level = color.MagentaString(level)
	case slog.LevelInfo:
		level = color.BlueString(level)
	case slog.LevelWarn:
		level = color.YellowString(level)
	case slog.LevelError:
		level = color.RedString(level)
	}

	fields := make(map[string]interface{}, r.NumAttrs())
	r.Attrs(func(a slog.Attr) bool {
		//fields[a.Key] = a.Value.Any()
		a.Value = a.Value.Resolve()
		wa := make(map[string]interface{})
		h.appendAttr(wa, a)
		fields[a.Key] = wa[a.Key]
		return true
	})

	tree := ""
	source := ""

	if h.addSource && r.PC != 0 {
		source = h.getSource(r.PC)
	}

	if len(h.attrs) > 0 {
		bytetree, err := yaml.Marshal(h.attrs)
		if err != nil {
			return err
		}
		tree = h.Postprocess(bytetree)
	}

	if len(fields) > 0 {
		bytetree, err := yaml.Marshal(&fields)
		if err != nil {
			return err
		}

		tree += h.Postprocess(bytetree)
	}

	timeStr := ""
	timeAttr := slog.Time(slog.TimeKey, r.Time)

	if h.replaceAttr != nil {
		timeAttr = h.replaceAttr(nil, timeAttr)
	}

	if !r.Time.IsZero() && !timeAttr.Equal(slog.Attr{}) {
		timeStr = r.Time.Format(h.timeFormat)
	}

	msg := color.CyanString(r.Message)

	buf := bytes.Buffer{}

	if len(timeStr) > 0 {
		buf.WriteString(timeStr)
		buf.WriteString(" ")
	}
	buf.WriteString(level)
	buf.WriteString(" ")
	buf.WriteString(msg)
	buf.WriteString(" ")
	buf.WriteString(source)
	buf.WriteString(" ")
	buf.WriteString(color.WhiteString(tree))
	buf.WriteString("\n")

	h.mu.Lock()
	defer h.mu.Unlock()
	_, err := h.writer.Write(buf.Bytes())

	return err
}

// report caller source+line as yaml string
func (h *Handler) getSource(pc uintptr) string {
	fs := runtime.CallersFrames([]uintptr{pc})
	source, _ := fs.Next()
	return fmt.Sprintf("%s: %d", source.File, source.Line)
}

func (h *Handler) Postprocess(yamlstr []byte) string {
	tree := string(yamlstr)
	clean := h.yamlcleaner.ReplaceAllString(tree, "$1$2:")
	return "\n    " + strings.TrimSpace(h.indenter.ReplaceAllString(clean, "    "))
}

// NewHandler returns a [log/slog.Handler] using the receiver's options.
// Default options are used if opts is nil.
func NewHandler(out io.Writer, opts *Options) *Handler {
	if opts == nil {
		opts = &Options{}
	}

	h := &Handler{
		writer:      out,
		mu:          &sync.Mutex{},
		level:       opts.Level,
		timeFormat:  opts.TimeFormat,
		replaceAttr: opts.ReplaceAttr,
		addSource:   opts.AddSource,
		indenter:    regexp.MustCompile(`(?m)^`),
		yamlcleaner: regexp.MustCompile("(?m)^( *)\"([^\"]*)\":"),
	}

	if opts.Level == nil {
		h.level = defaultLevel
	}

	if h.timeFormat == "" {
		h.timeFormat = DefaultTimeFormat
	}

	if opts.NoColor {
		color.NoColor = true
	}

	return h
}

// Enabled indicates whether the receiver logs at the given level.
func (h *Handler) Enabled(_ context.Context, l slog.Level) bool {
	return l >= h.level.Level()
}

// attributes plus attrs.
func (h *Handler) appendAttr(wa map[string]interface{}, a slog.Attr) {
	a.Value = a.Value.Resolve()

	if a.Value.Kind() == slog.KindGroup {
		attrs := a.Value.Group()
		name := ""
		if len(attrs) == 0 {
			return
		}

		if a.Key != "" {
			name = a.Key
			h.groups = append(h.groups, a.Key)
		}

		innerwa := make(map[string]interface{})
		for _, a := range attrs {
			h.appendAttr(innerwa, a)
		}
		wa[name] = innerwa

		if a.Key != "" && len(h.groups) > 0 {
			h.groups = h.groups[:len(h.groups)-1]
		}

		return
	}

	if h.replaceAttr != nil {
		a = h.replaceAttr(h.groups, a)
	}

	if !a.Equal(slog.Attr{}) {
		wa[a.Key] = a.Value.Any()
	}
}

// sub logger is to be created, possibly with attrs, add them to h.attrs
func (h *Handler) WithAttrs(attrs []slog.Attr) slog.Handler {
	if len(attrs) == 0 {
		return h
	}

	h2 := h.clone()

	wa := make(map[string]interface{})

	for _, a := range attrs {
		h2.appendAttr(wa, a)
	}

	h2.attrs = wa

	return h2
}

// WithGroup returns a new [log/slog.Handler] with name appended to the
// receiver's groups.
func (h *Handler) WithGroup(name string) slog.Handler {
	if name == "" {
		return h
	}
	h2 := h.clone()
	h2.groups = append(h2.groups, name)
	return h2
}

func (h *Handler) clone() *Handler {
	return &Handler{
		writer:      h.writer,
		mu:          h.mu,
		level:       h.level,
		groups:      slices.Clip(h.groups),
		attrs:       h.attrs,
		timeFormat:  h.timeFormat,
		replaceAttr: h.replaceAttr,
		addSource:   h.addSource,
		indenter:    h.indenter,
		yamlcleaner: h.yamlcleaner,
	}
}