Version 2 rewrite

This is a redesign of the old library that splits the code internally
into three parts:

- The grammar. This uses Peggy now instead of PEG.js, but is pretty much
  unchanged.
- The AST types. These are plain objects with `type` properties. The
  compiled parser outputs data matching these types.
- The expander. This does the work that was previously combined into the
  expression classes.

The external API is compatible with version 1, but it's possible that
people were relying on internal details of library (e.g. instanceof
checks) so I'm bumping the major to version 2.

Because this version also returns the AST for the parsed expressions, it
should be much more suitable for constructing a separate "matcher" that
can extract variable values from a URL string.

Author: grncdr

Makefile

@@ -1,6 +1,6 @@
 .PHONY: check publish clean
 
-all: lib/grammar.js dist/index.js dist/classes.js
+all: lib/grammar.js dist/index.js
 
 dist/%.js: lib/%.ts
 	@npx tsc

lib/ast.ts

@@ -0,0 +1,59 @@
+import { abort } from "process";
+
+export interface Template {
+  type: "template";
+  parts: (Literal | Expression)[];
+}
+
+export interface Literal {
+  type: "literal";
+  value: string;
+}
+
+export interface Expression {
+  type: "expression";
+  operator: Operator;
+  variables: Variable[];
+}
+
+export type Operator = "/" | ";" | "." | "?" | "&" | "+" | "#" | "";
+
+export interface Variable {
+  type: "variable";
+  name: string;
+  modifier?: SubstrModifier | ExplodeModifier;
+  extension?: string;
+}
+
+export interface ExplodeModifier {
+  type: "explode";
+}
+
+export interface SubstrModifier {
+  type: "substr";
+  length: number;
+}
+
+export function toString(
+  node: Template | Literal | Expression | Variable
+): string {
+  switch (node.type) {
+    case "template":
+      return node.parts.map(toString).join("");
+    case "literal":
+      return node.value;
+    case "expression":
+      return `{${node.operator}${node.variables.map(toString).join(",")}}`;
+    case "variable":
+      let out = node.name;
+      if (node.modifier?.type == "explode") {
+        out += "*";
+      } else if (node.modifier?.type == "substr") {
+        out += `:${node.modifier.length}`;
+      }
+      if (node.extension) {
+        out += `(${node.extension})`;
+      }
+      return out;
+  }
+}