import { homedir } from "node:os";
import { join } from "node:path";
import type { ConfigError, ConfigPaths, LoadOptions, LoadResult, Scope, ValidatedSource } from "./types";
import { CONFIG_DIR_NAME } from "./types";
import { ConfigValidationError, freezeConfig, mergeSources, validateSource } from "./schema";

export function configPaths(cwd: string, homeDir = homedir()): ConfigPaths {
  return { global: join(homeDir, CONFIG_DIR_NAME, "agent", "fallback-models.json"), project: join(cwd, CONFIG_DIR_NAME, "fallback-models.json") };
}
export interface ReadSource { scope: Scope; path: string; raw?: Record<string, unknown>; value?: ValidatedSource; error?: ConfigError; }
const readSource = async (fs: LoadOptions["fs"], scope: Scope, path: string): Promise<ReadSource> => {
  try {
    const text = await fs.read(path);
    if (text === undefined) return { scope, path };
    const raw = JSON.parse(text);
    return { scope, path, raw, value: validateSource(raw, path) };
  } catch (error) {
    const message = error instanceof ConfigValidationError ? error.message : `${path}: invalid JSON`;
    return { scope, path, error: { scope, path, message } };
  }
};
export async function readSources(options: LoadOptions): Promise<[ReadSource, ReadSource]> {
  const paths = configPaths(options.cwd, options.homeDir);
  return Promise.all([readSource(options.fs, "global", paths.global), readSource(options.fs, "project", paths.project)]);
}
export async function loadConfig(options: LoadOptions): Promise<LoadResult> {
  const paths = configPaths(options.cwd, options.homeDir);
  const [global, project] = await readSources(options);
  const errors: ConfigError[] = [global.error, project.error].filter((error): error is ConfigError => !!error);
  // mergeSources is total for already validated sources (AD-3): the project-over-global overlay cannot
  // synthesize a local violation, so an unexpected merge exception is a programming failure, not
  // evidence that the project source is invalid — it must surface rather than silently drop the
  // project source the way the old merged-cycle catch did.
  const config = mergeSources(global.value, project.value);
  for (const error of errors) options.ui?.notify(error.message);
  return { config, errors: Object.freeze(errors), paths };
}