package applog

import (
	"bytes"
	"context"
	"encoding/json"
	"log/slog"
	"strings"
	"testing"
)

func TestNewLogger_FiltersBelowConfiguredLevel(t *testing.T) {
	var buf bytes.Buffer
	logger := NewLogger("warn", &buf)

	logger.Info("should be dropped")
	if buf.Len() != 0 {
		t.Fatalf("expected no output for an Info message under a warn-level logger, got %q", buf.String())
	}

	logger.Warn("should appear")
	if !strings.Contains(buf.String(), "should appear") {
		t.Fatalf("expected the Warn message in output, got %q", buf.String())
	}
}

func TestNewLogger_WritesValidJSON(t *testing.T) {
	var buf bytes.Buffer
	logger := NewLogger("info", &buf)
	logger.Info("hello", "key", "value")

	var decoded map[string]any
	if err := json.Unmarshal(buf.Bytes(), &decoded); err != nil {
		t.Fatalf("output is not valid JSON: %v (%q)", err, buf.String())
	}
	if decoded["msg"] != "hello" || decoded["key"] != "value" {
		t.Errorf("decoded = %+v, want msg=hello key=value", decoded)
	}
}

func TestWithLogger_FromContext_RoundTrip(t *testing.T) {
	logger := slog.New(slog.NewJSONHandler(&bytes.Buffer{}, nil))
	ctx := WithLogger(context.Background(), logger)

	if got := FromContext(ctx); got != logger {
		t.Errorf("FromContext returned a different logger than what was stashed")
	}
}

func TestFromContext_DefaultsWhenNoneSet(t *testing.T) {
	if got := FromContext(context.Background()); got == nil {
		t.Fatal("FromContext on a bare context returned nil, want slog.Default()")
	}
}