import { SourceError } from "../core/errors.ts";
import type { Token } from "../core/tokenizer.ts";
import type { Environment, Plugin } from "../core/environment.ts";

export default function (): Plugin {
  return (env: Environment) => {
    env.tags.push(setTag);
  };
}

const VARNAME = /^[a-zA-Z_$][\w$]*$/;
const DETECTED_VARS = /([a-zA-Z_$][\w$]*)\b(?!\s*\:)/g;
const VALID_TAG = /^set\s+([\w{}[\]\s,:.$]+)\s*=\s*([\s\S]+)$/;

function setTag(
  env: Environment,
  token: Token,
  _output: string,
  tokens: Token[],
): string | undefined {
  const [, code, position] = token;

  if (!code.startsWith("set ")) {
    return;
  }

  const expression = code.replace(/^set\s+/, "");
  const { dataVarname } = env.options;

  // Value is set (e.g. {{ set foo = "bar" }})
  if (expression.includes("=")) {
    const match = code.match(VALID_TAG);

    if (!match) {
      throw new SourceError("Invalid set tag", position);
    }

    const variable = match[1].trim();
    const value = match[2].trim();
    const val = env.compileFilters(tokens, value);

    if (
      (variable.startsWith("{") && variable.endsWith("}")) ||
      (variable.startsWith("[") && variable.endsWith("]"))
    ) {
      const names = Array.from(variable.matchAll(DETECTED_VARS))
        .map((n) => n[1]);
      return `
        var ${variable} = ${val};
        Object.assign(${dataVarname}, { ${names.join(", ")} });
      `;
    }
    if (!VARNAME.test(variable)) {
      throw new SourceError("Invalid variable name", position);
    }

    return `var ${variable} = ${dataVarname}["${variable}"] = ${val};`;
  }

  // Value is captured (eg: {{ set foo }}bar{{ /set }})
  const compiled: string[] = [];
  const varName = expression.trim();
  const subvarName = `${dataVarname}["${varName}"]`;
  const compiledFilters = env.compileFilters(tokens, subvarName);

  compiled.push(`${subvarName} = "";`);
  compiled.push(...env.compileTokens(tokens, subvarName, "/set"));
  compiled.push(`var ${varName} = ${subvarName} = ${compiledFilters};`);
  return compiled.join("\n");
}