package boot

import (
	"context"
	"io"
	"log/slog"

	"atlas9.dev/c/demo/lib"
)

// LogHandler builds the process-wide slog handler. The app always logs JSON,
// in dev and production alike; pretty output and trace grouping are the
// consumer's job (cmd/dev, cmd/traces). Records logged with a context
// (slog.InfoContext etc.) carry a "request" attribute from the request ID
// stored in the context, which is what groups lines into traces.
func LogHandler(w io.Writer) slog.Handler {

	return requestIDHandler{slog.NewJSONHandler(w, &slog.HandlerOptions{Level: slog.LevelDebug})}
}

// requestIDHandler adds the request ID from the context, if any, to each
// log record. DEBUG records are request-scoped detail (db statements, access
// checks, request shapes); outside a request they are dropped, which keeps
// background polling (task workers) from flooding the logs.
type requestIDHandler struct {
	slog.Handler
}

func (h requestIDHandler) Enabled(ctx context.Context, level slog.Level) bool {

	if level == slog.LevelDebug && lib.GetRequestID(ctx) == "" {
		return false
	}
	return h.Handler.Enabled(ctx, level)
}

func (h requestIDHandler) Handle(ctx context.Context, r slog.Record) error {

	if id := lib.GetRequestID(ctx); id != "" {
		r.AddAttrs(slog.String("request", id))
	}
	return h.Handler.Handle(ctx, r)
}

func (h requestIDHandler) WithAttrs(attrs []slog.Attr) slog.Handler {

	return requestIDHandler{h.Handler.WithAttrs(attrs)}
}

func (h requestIDHandler) WithGroup(name string) slog.Handler {

	return requestIDHandler{h.Handler.WithGroup(name)}
}