simple.go

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"net/http"
	"sync"
	"syscall/js"
)

func main() {
	// Use a channel to keep the program alive
	keepAlive := make(chan struct{})

	// Register the function
	// The first argument "getTarkovPrices" MUST match window.getTarkovPrices()
	js.Global().Set("getTarkovPrices", js.FuncOf(func(this js.Value, args []js.Value) any {
		return runAsPromise(func() (any, error) {
			res, err := getPrices()
			return res.Data.Items, err
		})
	}))
	js.Global().Set("getTarkovRecipes", js.FuncOf(func(this js.Value, args []js.Value) any {
		return runAsPromise(func() (any, error) {
			res, err := getRecipes()
			return res.Data.Items, err
		})
	}))

	fmt.Println("Go functions registered!")
	<-keepAlive
}

// sendQuery loads an unmarshalled json into target. Returns an error if there is one.
//
// * This function assumes query is a valid one that has been pre-tested before it is called. *
func sendQuery(query string, target any) error {
	payload := graphqlRequest{Query: query}
	body, _ := json.Marshal(payload)

	req, err := http.NewRequest("POST", "https://api.tarkov.dev/graphql", bytes.NewBuffer(body))
	if err != nil {
		return err
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Accept", "application/json")

	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	return json.NewDecoder(resp.Body).Decode(target)
}

// runAsPromise wraps a Go-data-fetching function into a JS Promise, allowing asynchronus execution across the WASM boundary.
func runAsPromise(fetchFunc func() (any, error)) js.Value {
	handler := js.FuncOf(func(this js.Value, args []js.Value) any {
		resolve := args[0]
		reject := args[1]

		go func() {
			data, err := fetchFunc()
			if err != nil {
				reject.Invoke(js.ValueOf(err.Error()))
				return
			}

			jsonBytes, _ := json.Marshal(data)
			resolve.Invoke(js.ValueOf(string(jsonBytes)))
		}()
		return nil
	})
	return js.Global().Get("Promise").New(handler)
}

// TODO: handle error if the api is down
func getPrices() (itemPrices, error) {
	var result itemPrices
	err := sendQuery(pricesString, &result)
	if err != nil {
		return result, err
	}

	for i := range result.Data.Items {
		maxPrice := 0
		for _, vendorPrices := range result.Data.Items[i].SellFor {
			if vendorPrices.PricesRUB > maxPrice {
				maxPrice = vendorPrices.PricesRUB
			}
		}
		if result.Data.Items[i].LastLowPrice > maxPrice {
			maxPrice = result.Data.Items[i].LastLowPrice
		}
		// FIXME: calculate recipe items that are part of another recipe's barter item
		result.Data.Items[i].BestPrice = maxPrice
	}

	return result, nil
}

func getRecipes() (itemRecipes, error) {
	var recipeResult itemRecipes
	var priceResult itemPrices
	var wg sync.WaitGroup
	var recipeErr, priceErr error

	// Concurrent data fetch
	wg.Add(2)
	go func() {
		defer wg.Done()
		recipeErr = sendQuery(recipesString, &recipeResult)
	}()
	go func() {
		defer wg.Done()
		priceResult, priceErr = getPrices()
	}()
	wg.Wait()
	if recipeErr != nil {
		return recipeResult, recipeErr
	}
	if priceErr != nil {
		return recipeResult, priceErr
	}

	// Map best price for each item
	priceMap := make(map[string]int)
	for _, item := range priceResult.Data.Items {
		priceMap[item.Id] = item.BestPrice
	}

	// TODO: see if it's possible to merge the logic
	// Calculate recipe cost
	for i := range recipeResult.Data.Items {
		for j := range recipeResult.Data.Items[i].BartersFor {
			recipe := &recipeResult.Data.Items[i].BartersFor[j]
			cost := &recipe.TotalCost

			for k := range recipe.RequiredItems {
				item := &recipe.RequiredItems[k]
				*cost += item.Quantity * priceMap[item.Item.Id]
			}
		}
	}

	// Determine cheapest recipe
	for i := range recipeResult.Data.Items {
		recipe := recipeResult.Data.Items[i].BartersFor

		cheapestIndex := 0
		for j := 1; j < len(recipe); j++ {
			if recipe[j].TotalCost > 0 && recipe[j].TotalCost < recipe[cheapestIndex].TotalCost {
				cheapestIndex = j
			}
		}
		recipeResult.Data.Items[i].BartersFor[cheapestIndex].IsBestOption = true
	}

	return recipeResult, nil
}

type graphqlRequest struct {
	Query string `json:"query"`
}

type itemPrices struct {
	Data struct {
		Items []struct {
			ShortName    string `json:"shortName"`
			IconLink     string `json:"iconLink"`
			Id           string `json:"id"`
			BestPrice    int    `json:"bestPrice"` // Best selling price
			LastLowPrice int    `json:"lastLowPrice"`
			SellFor      []struct {
				PricesRUB int `json:"priceRUB"`
			} `json:"sellFor"`
		} `json:"items"`
	} `json:"data"`
}

const pricesString = `
{
	items(
		lang: en
		ids: [
			"5d1b376e86f774252519444e"
			"5d40407c86f774318526545a"
			"5d403f9186f7743cac3f229b"
			"5c052e6986f7746b207bc3c9"
			"5c0530ee86f774697952d952"
			"5af0548586f7743a532b7e99"
			"57347c93245977448d35f6e3"
			"6389c8c5dbfd5e4b95197e6b"
			"61bf7c024770ee6f9c6b8b53"
			"590c621186f774138d11ea29"
			"59faff1d86f7746c51718c9c"
			"5d235a5986f77443f6329bc6"
			"59fb023c86f7746d0d4b423c"
			"5aafbde786f774389d0cbc0f"
			"61bf7b6302b3924be92fa8c3"
			"544fb6cc4bdc2d34748b456e"
			"567143bf4bdc2d1a0f8b4567"
			"5d1b371186f774253763a656"
			"5d1b2fa286f77425227d1674"
			"5c06779c86f77426e00dd782"
			"5d1b309586f77425227d1676"
			"5d03775b86f774203e7e0c4b"
		]
		gameMode: pve
	) {
		shortName
		iconLink
		id
		lastLowPrice
		sellFor {
			priceRUB
		}
	}
}
`

type itemRecipes struct {
	Data struct {
		Items []struct {
			Name       string `json:"name"`
			ShortName  string `json:"shortName"`
			IconLink   string `json:"iconLink"`
			BartersFor []struct {
				RequiredItems []struct {
					Quantity int `json:"quantity"`
					Item     struct {
						ShortName string `json:"shortName"`
						IconLink  string `json:"iconLink"`
						Id        string `json:"id"`
					} `json:"item"`
				} `json:"requiredItems"`
				TotalCost    int  `json:"totalCost"`    // Sum of all required items' cost
				IsBestOption bool `json:"isBestOption"` // true, if this recipe is the cheapest
			} `json:"bartersFor"`
		} `json:"items"`
	} `json:"data"`
}

const recipesString = `	
{
	items(
		lang: en
		ids: [
			"5b6d9ce188a4501afc1b2b25"
			"5c0a840b86f7742ffa4f2482"
			"59fb023c86f7746d0d4b423c"
		]
		gameMode: pve
	) {
		name
		shortName
		iconLink
		bartersFor {
			requiredItems {
				item {
					shortName
					iconLink
					id
				}
				quantity
			}
		}
	}
}
`