package logging

import (
	"context"
	"log/slog"
)

type contextKey string

// RequestIDKey is the context key for the request ID value.
const RequestIDKey contextKey = "req_id"

// contextHandler wraps a slog.Handler, extracting req_id from the
// context.Context and appending it to every log record.
type contextHandler struct {
	underlying slog.Handler
}

// NewContextHandler wraps an slog.Handler so that records get a req_id
// attribute extracted from context.Context (if present).
func NewContextHandler(h slog.Handler) slog.Handler {
	return &contextHandler{underlying: h}
}

func (h *contextHandler) Enabled(ctx context.Context, level slog.Level) bool {
	return h.underlying.Enabled(ctx, level)
}

func (h *contextHandler) Handle(ctx context.Context, r slog.Record) error {
	if reqID, ok := ctx.Value(RequestIDKey).(string); ok && reqID != "" {
		r.AddAttrs(slog.String("req_id", reqID))
	}
	return h.underlying.Handle(ctx, r)
}

func (h *contextHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
	return &contextHandler{underlying: h.underlying.WithAttrs(attrs)}
}

func (h *contextHandler) WithGroup(name string) slog.Handler {
	return &contextHandler{underlying: h.underlying.WithGroup(name)}
}

// WithRequestID returns a child context carrying a request ID.
func WithRequestID(ctx context.Context, id string) context.Context {
	return context.WithValue(ctx, RequestIDKey, id)
}