3 files changed, 120 insertions, 2 deletions
diff --git a/plugin/src/extension.js b/plugin/src/extension.js
index 1101ed6..a7b4834 100644
--- a/plugin/src/extension.js
+++ b/plugin/src/extension.js
@@ -1,6 +1,33 @@
 'use strict';
 
-// Language registration and TextMate highlighting are declarative.
-function activate() {}
+const vscode = require('vscode');
+const { indentationEdits } = require('./indentation');
+const { codeOnly } = require('./lexical');
+const languageId = 'cie-pseudocode';
+
+function formatLines(document, startLine, endLine, keepBlankIndent = false) {
+	const lines = document.getText().split(/\r?\n/);
+	return indentationEdits(lines, startLine, endLine, keepBlankIndent).map(edit =>
+		vscode.TextEdit.replace(new vscode.Range(edit.line, 0, edit.line, edit.length), edit.text));
+}
+
+function activate(context) {
+	context.subscriptions.push(
+		vscode.languages.registerDocumentRangeFormattingEditProvider(languageId, {
+			provideDocumentRangeFormattingEdits(document, range) {
+				const endLine = range.end.character === 0 && range.end.line > range.start.line
+					? range.end.line - 1 : range.end.line;
+				return formatLines(document, range.start.line, endLine);
+			}
+		}),
+		vscode.languages.registerOnTypeFormattingEditProvider(languageId, {
+			provideOnTypeFormattingEdits(document, position, char) {
+				if (char !== '\n' && !/^\s*(?:ELSE|ENDIF|ENDWHILE|UNTIL|NEXT|ENDFUNCTION|ENDPROCEDURE|ENDTYPE)\b/.test(
+					codeOnly(document.lineAt(position.line).text))) return [];
+				return formatLines(document, position.line, position.line, char === '\n');
+			}
+		}, '\n', 'E', 'F', 'L', 'T', 'N')
+	);
+}
 
 module.exports = { activate };
diff --git a/plugin/src/indentation.js b/plugin/src/indentation.js
new file mode 100644
index 0000000..c8af770
--- /dev/null
+++ b/plugin/src/indentation.js
@@ -0,0 +1,58 @@
+'use strict';
+
+const { codeOnly } = require('./lexical');
+const closers = {
+	ENDIF: 'IF', ENDWHILE: 'WHILE', UNTIL: 'REPEAT', NEXT: 'FOR',
+	ENDFUNCTION: 'FUNCTION', ENDPROCEDURE: 'PROCEDURE', ENDTYPE: 'TYPE'
+};
+
+function lineDepths(lines) {
+	const stack = [];
+	const depth = () => stack.filter(block => block.active).length;
+	return lines.map(line => {
+		const code = codeOnly(line).trim();
+		const keyword = /^([A-Za-z][A-Za-z0-9_]*)\b/.exec(code)?.[1];
+		if (closers[keyword] || keyword === 'ELSE') {
+			const kind = keyword === 'ELSE' ? 'IF' : closers[keyword];
+			const index = stack.findLastIndex(block => block.kind === kind);
+			if (index >= 0) {
+				stack.length = index;
+				const current = depth();
+				if (keyword === 'ELSE') stack.push({ kind: 'IF', active: true });
+				return current;
+			}
+			// Incomplete code should still format without negative indentation.
+			return depth();
+		}
+
+		const current = depth();
+		if (keyword === 'THEN' || keyword === 'DO') {
+			const top = stack[stack.length - 1];
+			if (top?.kind === (keyword === 'THEN' ? 'IF' : 'WHILE')) top.active = true;
+		} else if (keyword === 'IF' || keyword === 'WHILE') {
+			stack.push({ kind: keyword, active: new RegExp(
+				keyword === 'IF' ? '\\bTHEN\\b' : '\\bDO\\b').test(code) });
+		} else if (['FOR', 'REPEAT', 'FUNCTION', 'PROCEDURE'].includes(keyword)) {
+			stack.push({ kind: keyword, active: true });
+		} else if (/^TYPE\s+[A-Za-z][A-Za-z0-9_]*$/.test(code)) {
+			stack.push({ kind: 'TYPE', active: true });
+		}
+		return current;
+	});
+}
+
+function indentationEdits(lines, startLine, endLine, keepBlankIndent = false) {
+	const depths = lineDepths(lines.slice(0, endLine + 1));
+	const edits = [];
+	for (let line = startLine; line <= endLine; line++) {
+		const oldIndent = /^[\t ]*/.exec(lines[line])[0];
+		const blank = lines[line].trim() === '';
+		const newIndent = blank && !keepBlankIndent ? '' : '\t'.repeat(depths[line]);
+		if (oldIndent !== newIndent) {
+			edits.push({ line, length: oldIndent.length, text: newIndent });
+		}
+	}
+	return edits;
+}
+
+module.exports = { lineDepths, indentationEdits };
diff --git a/plugin/src/lexical.js b/plugin/src/lexical.js
new file mode 100644
index 0000000..3fc856a
--- /dev/null
+++ b/plugin/src/lexical.js
@@ -0,0 +1,33 @@
+'use strict';
+
+// Preserve UTF-16 offsets and newlines, masking CIE quotes and // comments.
+// Unlike C++, CIE has no escapes or multiline literals.
+function codeOnly(text) {
+	let quote = null;
+	let comment = false;
+	const result = [];
+	for (let i = 0; i < text.length; i++) {
+		const char = text[i];
+		if (char === '\n' || char === '\r') {
+			quote = null;
+			comment = false;
+			result.push(char);
+		} else if (comment) {
+			result.push(' ');
+		} else if (quote) {
+			if (char === quote) quote = null;
+			result.push(' ');
+		} else if (char === '"' || char === "'") {
+			quote = char;
+			result.push(' ');
+		} else if (char === '/' && text[i + 1] === '/') {
+			comment = true;
+			result.push(' ');
+		} else {
+			result.push(char);
+		}
+	}
+	return result.join('');
+}
+
+module.exports = { codeOnly };