package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"os"

	"github.com/aws/aws-lambda-go/events"
	"github.com/aws/aws-lambda-go/lambda"

	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/feature/dynamodb/attributevalue"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
)

// Reading represents a single IoT measurement item returned to clients
type Reading struct {
	DeviceID    string  `json:"deviceId" dynamodbav:"deviceId"`
	Timestamp   string  `json:"timestamp" dynamodbav:"timestamp"`
	Temperature float64 `json:"temperature" dynamodbav:"temperature"`
	Humidity    float64 `json:"humidity" dynamodbav:"humidity"`
}

type ResponseBody struct {
	Data []Reading `json:"data"`
}

func handler(ctx context.Context, req events.APIGatewayV2HTTPRequest) (events.APIGatewayV2HTTPResponse, error) {
	tableName := os.Getenv("TABLE_NAME")
	if tableName == "" {
		log.Print("TABLE_NAME environment variable not set")
		return events.APIGatewayV2HTTPResponse{StatusCode: http.StatusInternalServerError}, nil
	}

	cfg, err := config.LoadDefaultConfig(ctx)
	if err != nil {
		log.Printf("failed to load AWS config: %v", err)
		return events.APIGatewayV2HTTPResponse{StatusCode: http.StatusInternalServerError}, nil
	}

	db := dynamodb.NewFromConfig(cfg)

	// Simple Scan as requested for the initial version
	scanInput := &dynamodb.ScanInput{
		TableName: &tableName,
	}

	scanOutput, err := db.Scan(ctx, scanInput)
	if err != nil {
		log.Printf("dynamodb scan error: %v", err)
		return events.APIGatewayV2HTTPResponse{StatusCode: http.StatusInternalServerError}, nil
	}

	readings := make([]Reading, 0, len(scanOutput.Items))
	for _, item := range scanOutput.Items {
		var r Reading
		err := attributevalue.UnmarshalMap(item, &r)
		if err != nil {
			// skip items that fail to unmarshal but log them
			log.Printf("failed to unmarshal item: %v", err)
			continue
		}
		readings = append(readings, r)
	}

	body := ResponseBody{Data: readings}
	b, err := json.Marshal(body)
	if err != nil {
		log.Printf("failed to marshal response: %v", err)
		return events.APIGatewayV2HTTPResponse{StatusCode: http.StatusInternalServerError}, nil
	}

	return events.APIGatewayV2HTTPResponse{
		StatusCode: http.StatusOK,
		Headers: map[string]string{
			"Content-Type": "application/json",
		},
		Body: string(b),
	}, nil
}

func main() {
	lambda.Start(handler)
}