// Package logging configures the structured JSON logger used across the service.
package logging

import (
	"context"
	"log/slog"
	"os"
)

type ctxKey int

const requestIDKey ctxKey = iota

// New returns a slog.Logger that writes JSON to stdout at the given level.
// Valid levels: "debug", "info", "warn", "error". Unknown levels default to info.
func New(level string) *slog.Logger {
	var lvl slog.Level
	switch level {
	case "debug":
		lvl = slog.LevelDebug
	case "warn":
		lvl = slog.LevelWarn
	case "error":
		lvl = slog.LevelError
	default:
		lvl = slog.LevelInfo
	}

	handler := slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
		Level: lvl,
		ReplaceAttr: func(_ []string, a slog.Attr) slog.Attr {
			if a.Key == slog.TimeKey {
				return slog.Attr{Key: "time", Value: a.Value}
			}
			if a.Key == slog.MessageKey {
				return slog.Attr{Key: "event", Value: a.Value}
			}
			return a
		},
	})
	return slog.New(handler)
}

// WithRequestID stores the request ID in the context for downstream loggers.
func WithRequestID(ctx context.Context, id string) context.Context {
	return context.WithValue(ctx, requestIDKey, id)
}

// RequestIDFrom returns the request ID stored in ctx, or empty string if absent.
func RequestIDFrom(ctx context.Context) string {
	if v, ok := ctx.Value(requestIDKey).(string); ok {
		return v
	}
	return ""
}

// FromContext returns a logger pre-bound with the request_id from ctx (if any).
func FromContext(ctx context.Context, base *slog.Logger) *slog.Logger {
	if id := RequestIDFrom(ctx); id != "" {
		return base.With("request_id", id)
	}
	return base
}