1 files changed, 112 insertions, 0 deletions
diff --git a/examples/server/public/json-schema-to-grammar.mjs b/examples/server/public/json-schema-to-grammar.mjs
new file mode 100644
index 00000000..3f1b255c
--- /dev/null
+++ b/examples/server/public/json-schema-to-grammar.mjs
@@ -0,0 +1,112 @@
+const SPACE_RULE = '" "?';
+
+const PRIMITIVE_RULES = {
+  boolean: '("true" | "false") space',
+  number: '("-"? ([0-9] | [1-9] [0-9]*)) ("." [0-9]+)? ([eE] [-+]? [0-9]+)? space',
+  integer: '("-"? ([0-9] | [1-9] [0-9]*)) space',
+  string: ` "\\"" (
+        [^"\\\\] |
+        "\\\\" (["\\\\/bfnrt] | "u" [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F] [0-9a-fA-F])
+      )* "\\"" space`,
+  null: '"null" space',
+};
+
+const INVALID_RULE_CHARS_RE = /[^\dA-Za-z-]+/g;
+const GRAMMAR_LITERAL_ESCAPE_RE = /[\n\r"]/g;
+const GRAMMAR_LITERAL_ESCAPES = {'\r': '\\r', '\n': '\\n', '"': '\\"'};
+
+export class SchemaConverter {
+  constructor(propOrder) {
+    this._propOrder = propOrder || {};
+    this._rules = new Map();
+    this._rules.set('space', SPACE_RULE);
+  }
+
+  _formatLiteral(literal) {
+    const escaped = JSON.stringify(literal).replace(
+      GRAMMAR_LITERAL_ESCAPE_RE,
+      m => GRAMMAR_LITERAL_ESCAPES[m]
+    );
+    return `"${escaped}"`;
+  }
+
+  _addRule(name, rule) {
+    let escName = name.replace(INVALID_RULE_CHARS_RE, '-');
+    let key = escName;
+
+    if (this._rules.has(escName)) {
+      if (this._rules.get(escName) === rule) {
+        return key;
+      }
+
+      let i = 0;
+      while (this._rules.has(`${escName}${i}`)) {
+        i += 1;
+      }
+      key = `${escName}${i}`;
+    }
+
+    this._rules.set(key, rule);
+    return key;
+  }
+
+  visit(schema, name) {
+    const schemaType = schema.type;
+    const ruleName = name || 'root';
+
+    if (schema.oneOf || schema.anyOf) {
+      const rule = (schema.oneOf || schema.anyOf).map((altSchema, i) =>
+        this.visit(altSchema, `${name}${name ? "-" : ""}${i}`)
+      ).join(' | ');
+
+      return this._addRule(ruleName, rule);
+    } else if ('const' in schema) {
+      return this._addRule(ruleName, this._formatLiteral(schema.const));
+    } else if ('enum' in schema) {
+      const rule = schema.enum.map(v => this._formatLiteral(v)).join(' | ');
+      return this._addRule(ruleName, rule);
+    } else if (schemaType === 'object' && 'properties' in schema) {
+      // TODO: `required` keyword (from python implementation)
+      const propOrder = this._propOrder;
+      const propPairs = Object.entries(schema.properties).sort((a, b) => {
+        // sort by position in prop_order (if specified) then by key
+        const orderA = typeof propOrder[a[0]] === 'number' ? propOrder[a[0]] : Infinity;
+        const orderB = typeof propOrder[b[0]] === 'number' ? propOrder[b[0]] : Infinity;
+        return orderA - orderB || a[0].localeCompare(b[0]);
+      });
+
+      let rule = '"{" space';
+      propPairs.forEach(([propName, propSchema], i) => {
+        const propRuleName = this.visit(propSchema, `${name}${name ? "-" : ""}${propName}`);
+        if (i > 0) {
+          rule += ' "," space';
+        }
+        rule += ` ${this._formatLiteral(propName)} space ":" space ${propRuleName}`;
+      });
+      rule += ' "}" space';
+
+      return this._addRule(ruleName, rule);
+    } else if (schemaType === 'array' && 'items' in schema) {
+      // TODO `prefixItems` keyword (from python implementation)
+      const itemRuleName = this.visit(schema.items, `${name}${name ? "-" : ""}item`);
+      const rule = `"[" space (${itemRuleName} ("," space ${itemRuleName})*)? "]" space`;
+      return this._addRule(ruleName, rule);
+    } else {
+      if (!PRIMITIVE_RULES[schemaType]) {
+        throw new Error(`Unrecognized schema: ${JSON.stringify(schema)}`);
+      }
+      return this._addRule(
+        ruleName === 'root' ? 'root' : schemaType,
+        PRIMITIVE_RULES[schemaType]
+      );
+    }
+  }
+
+  formatGrammar() {
+    let grammar = '';
+    this._rules.forEach((rule, name) => {
+      grammar += `${name} ::= ${rule}\n`;
+    });
+    return grammar;
+  }
+}