import { existsSync } from "node:fs";
import type { GoatCodeConfig } from "../types/config";
import { deepMerge } from "../shared/deep-merge";
import { log } from "../shared/logger";
import { validateConfig } from "./validator";
import {
  resolveLegacyProjectConfigPath,
  resolveProjectConfigPath,
  resolveUserConfigPath,
} from "./paths";

export async function loadConfigFile(configPath: string): Promise<GoatCodeConfig | null> {
  try {
    const module = await import(configPath);
    const raw = module.default ?? module;
    if (typeof raw === "function") {
      return await raw();
    }

    return raw as GoatCodeConfig;
  } catch (error) {
    log("[config/loader] Failed to load config file", { configPath, error });
    return null;
  }
}

async function loadValidatedConfigFile(configPath: string): Promise<GoatCodeConfig | null> {
  const raw = await loadConfigFile(configPath);
  if (raw === null) return null;

  const validation = validateConfig(raw);
  if (!validation.success) {
    log("[config/loader] Loaded config failed validation", {
      configPath,
      errors: validation.errors,
    });
    return null;
  }

  return validation.config;
}

export async function loadConfig(projectDir: string): Promise<GoatCodeConfig | null> {
  const userConfigPath = resolveUserConfigPath();
  const userConfig =
    userConfigPath && existsSync(userConfigPath)
      ? await loadValidatedConfigFile(userConfigPath)
      : null;

  const projectConfigPath = resolveProjectConfigPath(projectDir);
  const hasProjectConfig = existsSync(projectConfigPath);
  let projectConfig: GoatCodeConfig | null = null;
  let projectConfigInvalid = false;

  if (hasProjectConfig) {
    projectConfig = await loadValidatedConfigFile(projectConfigPath);
    projectConfigInvalid = projectConfig === null;
  }

  if (!hasProjectConfig) {
    const legacyConfigPath = resolveLegacyProjectConfigPath(projectDir);
    if (existsSync(legacyConfigPath)) {
      log(
        "[config/loader] Found legacy ochead.config.ts — please rename it to goatcode.config.ts",
        {
          legacyPath: legacyConfigPath,
        },
      );
      process.stderr.write(
        `[goatcode] DEPRECATION: ochead.config.ts is deprecated. Please rename it to goatcode.config.ts\n`,
      );
      projectConfig = await loadValidatedConfigFile(legacyConfigPath);
      projectConfigInvalid = projectConfig === null;
    }
  }

  if (projectConfigInvalid) {
    return null;
  }

  if (userConfig && projectConfig) {
    return deepMerge(
      userConfig as Record<string, unknown>,
      projectConfig as Record<string, unknown>,
    ) as GoatCodeConfig;
  }

  return projectConfig ?? userConfig;
}