/**
 * Emits TypeScript declarations for the RPC wire bundle.
 *
 * The output describes the wire shape: a field with a decoder default may be
 * absent, so it is optional here. `test/rpc-wire/conformance.types.ts` checks
 * the output against the server's hand-written `rpc-types.ts` and the internal
 * types behind it.
 */
import type { WireDef, WireModel, WireType } from "./model";

const IDENTIFIER = /^[A-Za-z_$][A-Za-z0-9_$]*$/;

function render(type: WireType): string {
	switch (type.kind) {
		case "string":
		case "boolean":
		case "null":
		case "unknown":
			return type.kind;
		case "integer":
		case "number":
			return "number";
		case "literal":
			return JSON.stringify(type.value);
		case "enum":
			return type.values.map(value => JSON.stringify(value)).join(" | ");
		case "ref":
			return type.name;
		case "array": {
			const items = render(type.items);
			return type.items.kind === "union" || type.items.kind === "enum" ? `(${items})[]` : `${items}[]`;
		}
		case "record":
			return `Record<string, ${render(type.values)}>`;
		case "union":
			return type.members.map(render).join(" | ");
	}
}

function docComment(text: string | undefined, indent: string): string {
	if (!text) return "";
	const lines = text.split("\n");
	if (lines.length === 1) return `${indent}/** ${text} */\n`;
	return `${indent}/**\n${lines.map(line => `${indent} * ${line}`).join("\n")}\n${indent} */\n`;
}

function renderDef(def: WireDef): string {
	const head = docComment(def.doc, "");
	if (def.kind === "alias") return `${head}export type ${def.name} = ${render(def.type)};\n`;
	const fields = def.fields
		.map(field => {
			const key = IDENTIFIER.test(field.key) ? field.key : JSON.stringify(field.key);
			const optional = field.required ? "" : "?";
			return `${docComment(field.doc, "\t")}\t${key}${optional}: ${render(field.type)};\n`;
		})
		.join("");
	return `${head}export interface ${def.name} {\n${fields}}\n`;
}

/** Renders the generated TypeScript module. */
export function emitTypeScript(model: WireModel): string {
	const parts = [
		"// Generated by `bun run gen:rpc` from src/modes/rpc/wire. Do not edit.\n",
		...[...model.defs.values()].map(renderDef),
	];
	const commands = model.commands
		.map(command => {
			const params = command.params ?? "undefined";
			const result =
				command.result === null ? "undefined" : command.nullable ? `${command.result} | null` : command.result;
			return `\t${command.name}: { params: ${params}; result: ${result} };\n`;
		})
		.join("");
	parts.push(
		`/** Every RPC command's parameters and successful response \`data\`. */\nexport interface RpcWireCommands {\n${commands}}\n`,
	);
	return parts.join("\n");
}