import { eraseFunctionTypes, type PageAst, type RuntimeFunctionDecl } from "@wrnexus/syntax";

const RESERVED_BINDINGS = new Set([
  "await",
  "break",
  "case",
  "catch",
  "class",
  "const",
  "continue",
  "debugger",
  "default",
  "delete",
  "do",
  "else",
  "enum",
  "export",
  "extends",
  "false",
  "finally",
  "for",
  "function",
  "if",
  "implements",
  "import",
  "in",
  "instanceof",
  "interface",
  "let",
  "new",
  "null",
  "package",
  "private",
  "protected",
  "public",
  "return",
  "static",
  "super",
  "switch",
  "this",
  "throw",
  "true",
  "try",
  "typeof",
  "var",
  "void",
  "while",
  "with",
  "yield",
]);
const RUNTIME_BINDINGS = new Set([
  "context",
  "state",
  "output",
  "server",
  "props",
  "refs",
  "event",
  "payload",
]);

function safeIdentifier(name: string): boolean {
  return /^[A-Za-z_$][A-Za-z0-9_$]*$/.test(name) && !RESERVED_BINDINGS.has(name);
}

function functionEntry(
  ast: PageAst,
  fn: RuntimeFunctionDecl,
  availableFunctions: string[],
): string {
  const parameterNames = new Set(fn.parameters.map((parameter) => parameter.name));
  const stateNames = ast.states
    .filter(
      (state) =>
        state.runtime !== "server" &&
        safeIdentifier(state.name) &&
        !RUNTIME_BINDINGS.has(state.name) &&
        !parameterNames.has(state.name),
    )
    .map((state) => state.name);
  const stateSet = new Set(stateNames);
  const propNames = ast.props
    .filter(
      (prop) =>
        safeIdentifier(prop.name) &&
        !RUNTIME_BINDINGS.has(prop.name) &&
        !parameterNames.has(prop.name) &&
        !stateSet.has(prop.name),
    )
    .map((prop) => prop.name);
  const functionAliases = availableFunctions.filter(
    (name) =>
      safeIdentifier(name) &&
      !RUNTIME_BINDINGS.has(name) &&
      !parameterNames.has(name) &&
      !stateSet.has(name) &&
      !propNames.includes(name),
  );
  const parameters = fn.parameters.map((parameter) => parameter.name).join(", ");
  const initialStateSnapshot = stateNames.length
    ? `const __wrnexusInitialState = { ${stateNames.map((name) => `${JSON.stringify(name)}: context.state.${name}`).join(", ")} };`
    : "";
  const stateAliases = stateNames.length ? `let { ${stateNames.join(", ")} } = context.state;` : "";
  const propAliases = propNames.length ? `const { ${propNames.join(", ")} } = context.props;` : "";
  const syncStateToContext = stateNames.map((name) => `context.state.${name} = ${name};`).join(" ");
  const syncStateFromContext = stateNames
    .map((name) => `${name} = context.state.${name};`)
    .join(" ");
  const peerAliases = functionAliases
    .map((name) => {
      const call = `context.functions[${JSON.stringify(name)}](...__wrnexusPeerArgs)`;
      if (!stateNames.length) {
        return `const ${name} = (...__wrnexusPeerArgs) => ${call};`;
      }
      return `const ${name} = (...__wrnexusPeerArgs) => {
      ${syncStateToContext}
      let __wrnexusPeerResult;
      try {
        __wrnexusPeerResult = ${call};
      } catch (__wrnexusPeerError) {
        ${syncStateFromContext}
        throw __wrnexusPeerError;
      }
      if (__wrnexusPeerResult && typeof __wrnexusPeerResult.then === "function") {
        return Promise.resolve(__wrnexusPeerResult).finally(() => { ${syncStateFromContext} });
      }
      ${syncStateFromContext}
      return __wrnexusPeerResult;
    };`;
    })
    .join("\n");
  const copyBack = stateNames
    .map(
      (name) =>
        `if (!Object.is(${name}, __wrnexusInitialState[${JSON.stringify(name)}])) context.state.${name} = ${name};`,
    )
    .join("\n");
  const body = eraseFunctionTypes(fn.body);
  const runtimeBindings = [
    !parameterNames.has("output") ? "const output = context.output;" : "",
    !parameterNames.has("server") ? "const server = context.server;" : "",
    !parameterNames.has("props") ? "const props = context.props;" : "",
    !parameterNames.has("refs") ? "const refs = context.refs;" : "",
  ]
    .filter(Boolean)
    .join("\n    ");
  return `${JSON.stringify(fn.name)}: ${fn.async ? "async " : ""}function(context${parameters ? `, ${parameters}` : ""}) {
    ${initialStateSnapshot}
    ${stateAliases}
    ${propAliases}
    ${peerAliases}
    ${runtimeBindings}
    try {
      ${body}
    } finally {
      ${copyBack}
    }
  }`;
}

export function generateBrowserModule(ast: PageAst): string {
  const functions = ast.runtimeFunctions.filter((fn) =>
    ["legacy", "client", "shared"].includes(fn.runtime),
  );
  const functionNames = functions.map((fn) => fn.name);
  const state = ast.states.filter((entry) => entry.runtime !== "server").map((entry) => entry.name);
  const storeImports = ast.structuredImports.filter(
    (entry) =>
      !entry.typeOnly && entry.source.endsWith(".wrn") && /(?:^|\/)stores?\//.test(entry.source),
  );
  const imports = ast.structuredImports
    .filter((entry) => !entry.typeOnly)
    .filter((entry) => !entry.source.endsWith(".wrn") || /(?:^|\/)stores?\//.test(entry.source))
    .map((entry) => entry.raw)
    .join("\n");
  const importedBindings = storeImports
    .flatMap((entry) => [
      ...(entry.defaultImport ? [entry.defaultImport] : []),
      ...(entry.namespaceImport ? [entry.namespaceImport] : []),
      ...entry.namedImports.map((item) => item.local),
    ])
    .filter(safeIdentifier);
  return `// generated WRNexusJS browser module for ${ast.name}
${imports}
export const __wrnexusClientFunctions = {
${functions.map((fn) => `  ${functionEntry(ast, fn, functionNames)}`).join(",\n")}
};
export const __wrnexusClientState = ${JSON.stringify(state)};
export const __wrnexusOutputs = ${JSON.stringify(ast.outputs)};
export const __wrnexusImportedBindings = { ${importedBindings.join(", ")} };
export function bindClientScope(context) {
  const functions = {};
  const scopedContext = { ...context, functions };
  for (const [name, handler] of Object.entries(__wrnexusClientFunctions)) {
    functions[name] = (...args) => handler(scopedContext, ...args);
  }
  return functions;
}
`;
}