examples: add poll_coindesk_bitcoin_vs_usd_rate.v

examples/poll_coindesk_bitcoin_vs_usd_rate.v

@@ -0,0 +1,66 @@
+import log
+import term
+import time
+import x.json2
+import net.http
+
+const url = 'https://api.coindesk.com/v1/bpi/currentprice.json'
+
+fn main() {
+	mut old_rate := f64(0)
+	for i := u64(1); true; i++ {
+		data := http.get(url) or {
+			log.error('polling ${url} failed')
+			time.sleep(10 * time.second)
+			continue
+		}
+		if data.status_code == 200 {
+			res := json2.decode[PriceResult](data.body) or {
+				log.error('can not decode data: ${data.body}')
+				time.sleep(10 * time.second)
+				continue
+			}
+			new_rate := res.bpi['USD'].rate_float
+			show_result(i, res, new_rate - old_rate)
+			old_rate = new_rate
+		}
+		time.sleep(3 * time.second)
+	}
+}
+
+fn show_result(i u64, res PriceResult, delta f64) {
+	if delta == 0 {
+		return
+	}
+	mut sdelta := '${delta:10.3f}'
+	color := if delta > 0 {
+		term.green
+	} else if delta == 0 {
+		term.white
+	} else {
+		term.red
+	}
+	cdelta := term.colorize(color, sdelta)
+	log.info('cycle: ${i:5} | ${res.chart_name} | updated_iso: ${res.time.updated_iso} | USD rate: ${res.bpi['USD'].rate_float:10.3f} | delta: ${cdelta}')
+}
+
+struct PriceTime {
+	updated_iso time.Time @[json: 'updatedISO']
+	updated     string
+	updateduk   string
+}
+
+struct CurrencyResult {
+	code        string
+	symbol      string
+	rate        string
+	description string
+	rate_float  f64
+}
+
+struct PriceResult {
+	time       PriceTime
+	disclaimer string
+	chart_name string @[json: 'chartName']
+	bpi        map[string]CurrencyResult
+}