/**
 * Turns the API's OpenAPI document into MCP tools, one per operation.
 *
 * The tools are derived rather than written by hand for the same reason the
 * TypeScript types are: `openapi.yaml` is held to the truth by the contract
 * tests, and nothing would hold a second, hand-written description of the API
 * to anything. A new endpoint documented there is a new tool here with no
 * change to this file.
 */

// Endpoints that exist for someone other than an operator. Telemetry is the
// frontend reporting back with its own secret; the submissions are a visitor's
// forms, and a call to one puts a row in the inbox and notifies real people.
const EXCLUDED_TAGS = new Set(['Telemetry', 'Submissions']);

// Obtaining a token is the client's job, not the model's.
const EXCLUDED_OPERATIONS = new Set(['POST /v1/auth/token']);

const METHODS = ['get', 'post', 'put', 'patch', 'delete'];

// OpenAPI keywords that either mean nothing to JSON Schema or only describe
// responses. `nullable` is translated rather than dropped.
const DROPPED_KEYWORDS = new Set([
  'nullable', 'example', 'readOnly', 'writeOnly', 'discriminator', 'xml', 'externalDocs',
]);

/**
 * @typedef {object} Operation
 * @property {string} method        Upper-case HTTP method.
 * @property {string} path          Path as documented, e.g. /v1/pages/{page}.
 * @property {{name: string, in: string}[]} params
 * @property {boolean} hasBody
 * @property {string[]} files       Multipart fields filled from a local file, read from `<name>_path`.
 * @property {boolean} requiresAuth
 *
 * @typedef {object} Tool
 * @property {string} name
 * @property {string} description
 * @property {object} inputSchema
 * @property {object} annotations
 * @property {Operation} operation  Kept server-side; never sent to the client.
 */

/**
 * @param {object} spec  The parsed OpenAPI document.
 * @param {object} [options]
 * @param {boolean} [options.localFiles] Offer uploads from a path on this
 *   machine. Only true over stdio, where this machine is the caller's own; a
 *   deployed server would be reading its own disk on a stranger's say-so.
 * @returns {Tool[]}
 */
export function buildTools(spec, { localFiles = false } = {}) {
  const paths = Object.keys(spec.paths ?? {});
  const tools = [];

  for (const path of paths) {
    const item = spec.paths[path];

    for (const method of METHODS) {
      const op = item[method];

      if (!op) continue;
      if (EXCLUDED_OPERATIONS.has(`${method.toUpperCase()} ${path}`)) continue;
      if ((op.tags ?? []).some((tag) => EXCLUDED_TAGS.has(tag))) continue;

      const tool = buildTool(spec, paths, path, method, item, op, localFiles);

      if (tool) tools.push(tool);
    }
  }

  // A clash would silently shadow one endpoint behind another, so it is a
  // startup failure rather than something to discover by calling the wrong one.
  const seen = new Map();

  for (const tool of tools) {
    const { method, path } = tool.operation;

    if (seen.has(tool.name)) {
      throw new Error(`Tool name "${tool.name}" is derived from both ${seen.get(tool.name)} and ${method} ${path}`);
    }

    seen.set(tool.name, `${method} ${path}`);
  }

  return tools;
}

function buildTool(spec, paths, path, method, item, op, localFiles) {
  const params = mergeParameters(spec, item.parameters, op.parameters)
    // Headers are credentials here (preview and ingest secrets), which come
    // from the server's configuration, never from the model.
    .filter((param) => param.in === 'path' || param.in === 'query');

  const properties = {};
  const required = [];

  for (const param of params) {
    const schema = toJsonSchema(spec, param.schema ?? { type: 'string' });

    properties[param.name] = param.description
      ? { ...schema, description: param.description.trim() }
      : schema;

    if (param.required || param.in === 'path') required.push(param.name);
  }

  const bodySchema = op.requestBody?.content?.['application/json']?.schema;
  const multipartSchema = op.requestBody?.content?.['multipart/form-data']?.schema;

  // A file in a multipart body cannot travel as JSON — as base64 an ordinary
  // photo costs hundreds of thousands of tokens — so the model names a path
  // and the server reads it. Only where that path is on the caller's machine.
  const files = localFiles && multipartSchema
    ? Object.entries(toJsonSchema(spec, multipartSchema).properties ?? {})
      .filter(([, property]) => property.format === 'binary')
      .map(([name]) => name)
    : [];

  // Multipart only, and no way to send a file from here: nothing to offer.
  if (!bodySchema && multipartSchema && files.length === 0) return null;

  for (const field of files) {
    const name = `${field}_path`;

    if (name in properties) {
      throw new Error(`${method.toUpperCase()} ${path} has a parameter named "${name}", which the file upload needs`);
    }

    properties[name] = {
      type: 'string',
      description: `Absolute path to a file on this machine, uploaded as \`${field}\`. Read by the MCP server; use instead of \`body\`.`,
    };
  }

  if (bodySchema) {
    if ('body' in properties) {
      throw new Error(`${method.toUpperCase()} ${path} has a parameter named "body", which the request body needs`);
    }

    const body = toJsonSchema(spec, bodySchema);

    // Create and update share one write schema, so its `required` describes
    // creation. On a partial update it would force the model to resend fields
    // it has no reason to touch.
    if (method === 'patch') delete body.required;

    // Beside a file, the body carries the upload's other fields (`for`, say)
    // rather than the JSON alternative, whose own requirements — a `url` —
    // would then be wrong.
    if (files.length > 0) delete body.required;

    properties.body = {
      ...body,
      description: files.length > 0
        ? 'JSON request body; with a file, its other fields go here too.'
        : 'JSON request body.',
    };

    // With a file to send instead, the JSON body is the other way in rather
    // than a requirement; the API says which one it missed if neither comes.
    if (op.requestBody.required && files.length === 0) required.push('body');
  }

  const security = op.security ?? spec.security ?? [];

  return {
    name: toolName(paths, path, method),
    description: describe(path, method, op, security.length > 0),
    inputSchema: {
      type: 'object',
      properties,
      ...(required.length ? { required } : {}),
      additionalProperties: false,
    },
    annotations: {
      title: op.summary,
      readOnlyHint: method === 'get',
      destructiveHint: method === 'delete',
      idempotentHint: method === 'get' || method === 'put' || method === 'delete',
    },
    operation: {
      method: method.toUpperCase(),
      path,
      params: params.map(({ name, in: location }) => ({ name, in: location })),
      hasBody: Boolean(bodySchema),
      files,
      requiresAuth: security.length > 0,
    },
  };
}

/**
 * Named after the Laravel route the operation lands on, so a tool reads the
 * same as `routes/api.php`: /v1/pages/{page} under PATCH is admin_pages_update,
 * /public/v1/projects/{slug} under GET is public_projects_show.
 */
export function toolName(paths, path, method) {
  const segments = path.split('/').filter(Boolean).filter((s) => s !== 'v1');
  const scope = segments[0] === 'public' ? 'public' : 'admin';

  if (segments[0] === 'public') segments.shift();

  const isParam = (segment) => segment.startsWith('{');
  const endsInParam = isParam(segments.at(-1));
  const base = segments.filter((s) => !isParam(s)).map((s) => s.replaceAll('-', '_'));

  let action = null;

  if (endsInParam) {
    action = { get: 'show', put: 'update', patch: 'update', delete: 'destroy' }[method];
  } else if (method === 'get') {
    // A collection has an item route next to it; /site or /radar does not,
    // and is named after itself alone.
    const hasItemRoute = paths.some((p) => p.startsWith(`${path}/{`));
    action = hasItemRoute ? 'index' : null;
  } else if (method === 'post') {
    // /pages/{page}/restore is an action named by its last segment already.
    action = segments.length > 1 && isParam(segments.at(-2)) ? null : 'store';
  } else {
    action = method;
  }

  return [scope, ...base, ...(action ? [action] : [])].join('_');
}

function describe(path, method, op, requiresAuth) {
  const parts = [op.summary, op.description].filter(Boolean).map((s) => s.trim());

  parts.push(`${method.toUpperCase()} /api${path} · ${requiresAuth ? 'authenticated' : 'public, no token'}`);

  return parts.join('\n\n');
}

/**
 * Path-level parameters apply to every operation under the path; an operation
 * may redeclare one, and its own declaration wins.
 */
function mergeParameters(spec, pathLevel = [], operationLevel = []) {
  const merged = new Map();

  for (const raw of [...pathLevel, ...operationLevel]) {
    const param = resolve(spec, raw);
    merged.set(`${param.in}:${param.name}`, param);
  }

  return [...merged.values()];
}

function resolve(spec, node) {
  let current = node;
  const visited = new Set();

  while (current && typeof current.$ref === 'string') {
    if (visited.has(current.$ref)) throw new Error(`Circular $ref ${current.$ref}`);

    visited.add(current.$ref);
    current = lookup(spec, current.$ref);
  }

  return current;
}

function lookup(spec, ref) {
  if (!ref.startsWith('#/')) throw new Error(`Only local $refs are supported, got ${ref}`);

  const target = ref
    .slice(2)
    .split('/')
    .map((part) => part.replaceAll('~1', '/').replaceAll('~0', '~'))
    .reduce((node, key) => node?.[key], spec);

  if (target === undefined) throw new Error(`Unresolvable $ref ${ref}`);

  return target;
}

/**
 * OpenAPI 3.0 schema → self-contained JSON Schema: references inlined (MCP
 * clients receive each tool's schema on its own, with no `components` to point
 * into) and `nullable` spelled the way JSON Schema spells it.
 */
export function toJsonSchema(spec, schema, stack = []) {
  if (schema === null || typeof schema !== 'object') return schema;

  if (typeof schema.$ref === 'string') {
    // A recursive schema cannot be inlined forever; past the first repeat the
    // model gets "anything" and the server's validation has the last word.
    if (stack.includes(schema.$ref)) return {};

    const { $ref, nullable: isNullable, ...siblings } = schema;

    return nullable(isNullable, {
      ...toJsonSchema(spec, lookup(spec, $ref), [...stack, $ref]),
      ...toJsonSchema(spec, siblings, stack),
    });
  }

  // `allOf: [{$ref}]` next to a description is how this document annotates a
  // shared schema in place. Flattened, the model reads one schema, not a
  // composition of one.
  if (Array.isArray(schema.allOf) && schema.allOf.length === 1) {
    const { allOf, nullable: isNullable, ...siblings } = schema;

    return nullable(isNullable, {
      ...toJsonSchema(spec, allOf[0], stack),
      ...toJsonSchema(spec, siblings, stack),
    });
  }

  const out = {};

  for (const [key, value] of Object.entries(schema)) {
    if (DROPPED_KEYWORDS.has(key)) continue;

    if (key === 'properties') {
      out.properties = Object.fromEntries(
        Object.entries(value)
          // Response-only fields have no business in something the model writes.
          .filter(([, property]) => !resolve(spec, property)?.readOnly)
          .map(([name, property]) => [name, toJsonSchema(spec, property, stack)]),
      );
    } else if (['allOf', 'oneOf', 'anyOf'].includes(key)) {
      out[key] = value.map((member) => toJsonSchema(spec, member, stack));
    } else if (['items', 'additionalProperties', 'not'].includes(key) && typeof value === 'object') {
      out[key] = toJsonSchema(spec, value, stack);
    } else {
      out[key] = value;
    }
  }

  return nullable(schema.nullable, out);
}

function nullable(isNullable, schema) {
  if (!isNullable) return schema;

  if (typeof schema.type === 'string') {
    const out = { ...schema, type: [schema.type, 'null'] };

    if (Array.isArray(out.enum) && !out.enum.includes(null)) out.enum = [...out.enum, null];

    return out;
  }

  const { description, ...rest } = schema;

  return { ...(description ? { description } : {}), anyOf: [rest, { type: 'null' }] };
}