// Package applog provides geniusrun's structured JSON logging: a
// log/slog-based logger writing to stdout, plus context helpers so a
// logger enriched in one layer (e.g. internal/api's HTTP middleware,
// attaching a request_id) is picked up by another (e.g. internal/garmin's
// wrapper-call logging) without either package depending on the other.
package applog

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

// NewLogger builds a JSON-handler *slog.Logger writing to w at the given
// level ("debug"|"info"|"warn"|"error", case-insensitive; anything else
// defaults to info).
func NewLogger(level string, w io.Writer) *slog.Logger {
	return slog.New(slog.NewJSONHandler(w, &slog.HandlerOptions{Level: parseLevel(level)}))
}

func parseLevel(level string) slog.Level {
	switch strings.ToLower(level) {
	case "debug":
		return slog.LevelDebug
	case "warn":
		return slog.LevelWarn
	case "error":
		return slog.LevelError
	default:
		return slog.LevelInfo
	}
}

type ctxKey struct{}

// WithLogger returns a context carrying logger, retrievable via FromContext.
func WithLogger(ctx context.Context, logger *slog.Logger) context.Context {
	return context.WithValue(ctx, ctxKey{}, logger)
}

// FromContext returns the logger stashed by WithLogger, or slog.Default()
// if none was -- callers (e.g. the background incremental-sync loop, or
// tests that don't bother injecting one) always get a working logger,
// never nil.
func FromContext(ctx context.Context) *slog.Logger {
	if logger, ok := ctx.Value(ctxKey{}).(*slog.Logger); ok {
		return logger
	}
	return slog.Default()
}