Part of a snippet emulator

vweb/src/snippet_emulator.css

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+body {
+    display: grid;
+    grid-template-columns: 1fr auto 1fr;
+    grid-template-rows: 2em auto;
+    background: #777777;
+}
+.react-root {
+    grid-area: 2 / 2 / 3 / 3;
+}
+
+.snippetEmulator {
+    display: grid;
+    grid-template-rows: 10em 1em 1em 2em;
+    grid-template-columns: 20em;
+    background: #333333;
+    font-family: monospace;
+    padding: 0.5em;
+}
+
+.snippetEmulator textarea { grid-area: 1 / 1 / 2 / 2 }
+.snippetEmulator .src { grid-area: 1 / 1 / 2 / 2 }
+.snippetEmulator .message { grid-area: 2 / 1 / 3 / 2 }
+.snippetEmulator .buttons { grid-area: 3 / 1 / 4 / 2 }
+.snippetEmulator .stacks { grid-area: 4 / 1 / 5 / 2 }
+.snippetEmulator textarea {
+    background: #0f0f0f;
+    color: #dddddd;
+    min-height: 10em;
+    border: none;
+    resize: vertical;
+    padding: 0;
+    border: none;
+}
+.snippetEmulator textarea:focus { outline: none; }
+.snippetEmulator .buttons a {
+    margin-right: 0.5em;
+    cursor: pointer;
+}
+.snippetEmulator .step, .snippetEmulator .run { color: lightgreen }
+.snippetEmulator .reset { color: lightcoral }
+.snippetEmulator .build, .snippetEmulator .edit { color: dodgerblue }

vweb/src/snippet_emulator.jsx

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+import './snippet_emulator.css'
+import React, {useState, useCallback, useEffect} from 'react'
+import { WasmCPU, assemble_snippet, source_map } from '../pkg/vweb.js'
+
+export default function({ snippet }) {
+    const [editing, setEditing] = useState(false) // Whether we're editing the snippet or running it
+    const [src, setSrc] = useState(snippet) // The source code currently set
+    const [message, setMessage] = useState('') // A status / error message
+    const onChangeSrc = useCallback((e) => setSrc(e.target.value), []) // Callback for the textarea
+    const [binary, setBinary] = useState(null) // The assembled binary
+    const [sourceMap, setSourceMap] = useState({}) // A map from byte address to line number
+
+    // A callback to build the binary from source
+    const rebuild = useCallback((code) => {
+        try {
+            const bin = assemble_snippet(code)
+            const sm = source_map(code)
+            setBinary(bin)
+            setSourceMap(sm)
+            setMessage(`Assembled ${bin.length} bytes`)
+            console.log(sm.Ok)
+            return true
+        } catch(e) {
+            setMessage(e.message)
+        }
+    }, [])
+
+    // On load, build the stuff
+    useEffect(() => { rebuild(snippet) }, [snippet])
+
+    if (editing) {
+        return (
+            <div className='snippetEmulator'>
+                <textarea value={src} onChange={onChangeSrc}></textarea>
+                <div className='message'>{message}</div>
+                <div className='buttons'>
+                    <a className='build' onClick={() => { rebuild(src) && setEditing(false) }}>[Build]</a>
+                </div>
+            </div>
+        )
+    } else {
+        return (
+            <div className='snippetEmulator'>
+                <SourceDisplay src={src}/>
+                <div className='message'>{message}</div>
+                <div className='buttons'>
+                    <a className='step'>[Step]</a>
+                    <a className='step'>[Run]</a>
+                    <a className='reset'>[Reset]</a>
+                    <a className='edit' onClick={() => { setEditing(true); setMessage('') }}>[Edit]</a>
+                </div>
+            </div>
+        )
+    }
+}
+
+function SourceDisplay({ src }) {
+    const lines = src.split('\n')
+    const lineDivs = lines.map((line, i) => {
+        return (<div key={`line_${i}`}>{line || <>&nbsp;</>}</div>)
+    })
+    return (
+        <div className='src'>{lineDivs}</div>
+    )
+}
+
+function StackDisplay({ data, call }) {
+
+}