ast_generator/ast_generator.ts

import {
    Grammar,
    Parser,
} from "https://deno.land/x/nearley@2.19.7-deno/mod.ts";

import compiledParserGrammar from "./parser.out.ts";
import {
    Enum,
    Name,
    Node,
    Param,
    Param_Named,
    Statement,
    Type,
} from "./ast.out.ts";

class TypescriptGenerator {
    private result = "";

    public generate(ast: Statement[]): string {
        this.result += "// Generated file by ast_generator\n";
        for (const statement of ast) {
            switch (statement.kind) {
                case "Enum":
                    this.generateEnum(statement[0]);
                    break;
                case "Node":
                    this.generateNode(statement[0]);
                    break;
            }
            this.result += "\n";
        }
        return this.result;
    }

    private generateEnum(enum_: Enum) {
        if (this.isShallowEnum(enum_)) {
            return this.generateShallowEnumBody(enum_);
        } else {
            return this.generateEnumBody(enum_);
        }
    }

    private isShallowEnum(enum_: Enum): boolean {
        return !enum_.nodes.some((node) => node.params.length > 0);
    }

    private generateShallowEnumBody(enum_: Enum) {
        const name = this.makeName(enum_.name);
        const fields = enum_.nodes.map((node) => this.makeName(node.name)).map(
            (name) => `${name}: "${name}"`,
        ).join(", ");
        this.result += `export const ${name} = { ${fields} } as const;\n`;
        this.result += `export type ${name} = keyof typeof ${name};\n`;
    }

    private generateEnumBody(enum_: Enum) {
        const enumName = this.makeName(enum_.name);
        const nodeNames: [string, string][] = [];
        for (const node of enum_.nodes) {
            const name = this.makeName(node.name);
            const fullName = `${enumName}_${name}`;
            nodeNames.push([name, fullName]);
            this.result += `export type ${fullName} = {\n`;
            this.result += `    kind: "${name}",\n`;
            this.result += node.params.map((p, i) => this.makeParamField(p, i))
                .map((field) => `    ${field},\n`).join("");
            this.result += `};\n`;
            const fnParams = this.makeFnParams(node.params);
            const fields = this.makeFnFields(node.params);
            this.result += `export const ${fullName}` +
                ` = (${fnParams}): ${fullName}` +
                ` => ({ kind: "${name}", ${fields} });\n`;
        }
        const typeList = nodeNames
            .map(([_, fullName]) => fullName)
            .join(" | ");
        this.result += `export type ${enumName} = ${typeList};\n`;
        const enumFieldFns = nodeNames
            .map(([name, fullName]) => `${name}: ${fullName}`)
            .join(", ");
        this.result +=
            `export const ${enumName} = { ${enumFieldFns} } as const;\n`;
    }

    private makeParamField(param: Param, index: number): string {
        switch (param.kind) {
            case "Named":
                return this.makeNamedParam(param);
            case "Unnamed":
                return `[${index}]: ${this.makeType(param[0])}`;
        }
    }

    private generateNode(
        node: Node,
    ) {
        const name = this.makeName(node.name);
        this.result += `export type ${name} = {\n`;
        for (
            const [param, index] of node.params
                .map((v, i) => [v, i] as const)
        ) {
            switch (param.kind) {
                case "Named":
                    this.result += `    ${this.makeNamedParam(param)};\n`;
                    break;
                case "Unnamed": {
                    const type_ = this.makeType(param[0]);
                    this.result += `    [${index}]: ${type_};\n`;
                    break;
                }
            }
        }
        this.result += "};\n";
        const fnParams = this.makeFnParams(node.params);
        const fields = this.makeFnFields(node.params);
        this.result += `export const ${name}` +
            ` = (${fnParams}): ${name}` +
            ` => ({ ${fields} });\n`;
    }

    private makeFnParams(params: Param[]): string {
        return params
            .map((param, index) => {
                switch (param.kind) {
                    case "Named":
                        return this.makeNamedParam(param);
                    case "Unnamed":
                        return `v${index}: ${this.makeType(param[0])}`;
                }
            })
            .join(", ");
    }

    private makeFnFields(params: Param[]): string {
        return params.map((param, index) => {
            switch (param.kind) {
                case "Named":
                    return this.makeName(param.name);
                case "Unnamed":
                    return `[${index}]: v${index}`;
            }
        })
            .join(", ");
    }

    private makeNamedParam(param: Param_Named): string {
        const name = this.makeName(param.name);
        const type_ = this.makeType(param.type_);
        return `${name}: ${type_}`;
    }

    private makeType(type_: Type): string {
        switch (type_.kind) {
            case "Name":
                return this.makeName(type_[0]);
            case "Optional":
                return `${this.makeType(type_[0])} | null`;
            case "Multiple":
                return `${this.makeType(type_[0])}[]`;
        }
    }

    private makeName(name: Name): string {
        return name[0];
    }
}

const parser = new Parser(Grammar.fromCompiled(compiledParserGrammar));

if (Deno.args.length < 1) {
    console.log("generate_ast <file>");
    throw new Error("not enough args");
}
if (["-h", "--help"].includes(Deno.args[0])) {
    console.log("generate_ast <file>");
    Deno.exit(0);
}
const text = await Deno.readTextFile(Deno.args[0]);
parser.feed(text);
const ast = parser.results[0];
// console.log(JSON.stringify(ast, null, "│   "));
const ts = new TypescriptGenerator().generate(ast);
console.log(ts);