a mini-console support with scroll up / down (#112)

* a mini-console support with scroll up / down

* fix compile error

libs/core/console.ts

@@ -0,0 +1,107 @@
+/// <reference no-default-lib="true"/>
+
+/**
+ * Reading and writing data to the console output.
+ */
+//% weight=12 color=#002050 icon="\uf120"
+//% advanced=true
+namespace console {
+    type Listener = (text: string) => void;
+
+    const listeners: Listener[] = [
+        (text: string) => serial.writeLine(text)
+    ];
+
+    /**
+     * Write a line of text to the console output.
+     * @param value to send
+     */
+    //% weight=90
+    //% help=console/log blockGap=8
+    //% blockId=console_log block="console|log %text"
+    export function log(text: string): void {
+        for (let i = 0; i < listeners.length; ++i)
+            listeners[i](text);
+    }
+
+    /**
+     * Write a name:value pair as a line of text to the console output.
+     * @param name name of the value stream, eg: "x"
+     * @param value to write
+     */
+    //% weight=88 blockGap=8
+    //% help=console/log-value
+    //% blockId=console_log_value block="console|log value %name|= %value"
+    export function logValue(name: string, value: number): void {
+        log(`${name}: ${value}`)
+    }
+
+    /**
+     * Adds a listener for the log messages
+     * @param listener 
+     */
+    //%
+    export function addListener(listener: (text: string) => void) {
+        if (!listener) return;
+        listeners.push(listener);
+    }
+
+    /**
+     * Sends the log messages to the brick screen and uses the brick up and down buttons to scroll.
+     */
+    //% blockId=logsendtostreen block="send console to screen"
+    //% weight=1
+    export function sendToScreen(): void {
+        console.screen.attach();
+    }
+}
+
+namespace console.screen {
+    const maxLines = 100;
+    const screenLines = 8;
+    const lineHeight = 12;
+    let lines: string[];
+    let scrollPosition = 0;
+
+    export function attach() {
+        if (!lines) {
+            lines = [];
+            console.addListener(log);
+            brick.buttonUp.onEvent(ButtonEvent.Click, () => scroll(1))
+            brick.buttonDown.onEvent(ButtonEvent.Click, () => scroll(-1))                
+        }
+    }
+
+    function printLog() {
+        brick.clearScreen()
+        if (!lines) return;
+        for (let i = 0; i < screenLines; ++i) {
+            const line = lines[i + scrollPosition];
+            if (line)
+                brick.print(line, 0, 4 + i * lineHeight)
+        }
+    }
+
+    function scroll(pos: number) {
+        if (!pos) return;
+
+        scrollPosition += pos >> 0;
+        if (scrollPosition >= lines.length) scrollPosition = lines.length - 1;
+        if (scrollPosition < 0) scrollPosition = 0;
+        printLog();
+    }
+
+    function log(msg: string): void {    
+        lines.push(msg);
+        if (lines.length + 5 > maxLines) {
+            lines.splice(0, maxLines - lines.length);
+            scrollPosition = Math.min(scrollPosition, lines.length - 1)
+        }
+        // move down scroll once it gets large than the screen
+        if (lines.length > screenLines
+            && lines.length >= scrollPosition + screenLines) {
+            scrollPosition++;
+        }
+        printLog();
+    }
+}