import { readFileSync } from "node:fs";
import { homedir } from "node:os";
import { join, resolve } from "node:path";

export interface PiEnabledModelsResult {
  ids: string[];
  warnings: string[];
  source?: string;
}

interface LoadOptions {
  harnessDir: string;
  agentDir?: string;
  read?: (path: string) => string;
}

type Settings = Record<string, unknown>;
const INVALID = Symbol("invalid-settings");

function readSettings(
  path: string,
  optional: boolean,
  read: (path: string) => string,
  warnings: string[],
): Settings | undefined | typeof INVALID {
  try {
    const value = JSON.parse(read(path));
    if (!value || typeof value !== "object" || Array.isArray(value)) throw new Error();
    return value as Settings;
  } catch (error) {
    if (optional && (error as NodeJS.ErrnoException)?.code === "ENOENT") return undefined;
    warnings.push(`Pi settings are unreadable or invalid: ${path}`);
    return INVALID;
  }
}

function isExactCompositeId(value: unknown): value is string {
  if (typeof value !== "string" || /[\s*?:]/.test(value)) return false;
  const parts = value.split("/");
  return parts.length === 2 && parts.every((part) => part.length > 0);
}

export function loadPiEnabledModels(opts: LoadOptions): PiEnabledModelsResult {
  const warnings: string[] = [];
  const read = opts.read ?? ((path: string) => readFileSync(path, "utf8"));
  const agentDir = opts.agentDir
    ?? resolve(process.env.PI_CODING_AGENT_DIR ?? join(homedir(), ".pi", "agent"));
  const globalPath = join(agentDir, "settings.json");
  const projectPath = join(opts.harnessDir, ".pi", "settings.json");
  const globalSettings = readSettings(globalPath, false, read, warnings);
  const projectSettings = readSettings(projectPath, true, read, warnings);
  if (globalSettings === INVALID || projectSettings === INVALID) return { ids: [], warnings };

  const projectDefinesScope = projectSettings
    ? Object.prototype.hasOwnProperty.call(projectSettings, "enabledModels")
    : false;
  const settings = projectDefinesScope ? projectSettings : globalSettings;
  const source = projectDefinesScope ? projectPath : globalPath;
  const raw = settings?.enabledModels;
  if (!Array.isArray(raw) || raw.length === 0) {
    warnings.push(`Pi enabledModels is missing or empty: ${source}`);
    return { ids: [], warnings, source };
  }

  const ids: string[] = [];
  const seen = new Set<string>();
  raw.forEach((value, index) => {
    if (!isExactCompositeId(value)) {
      warnings.push(`Ignoring non-exact enabledModels entry at index ${index}: ${source}`);
      return;
    }
    if (!seen.has(value)) {
      seen.add(value);
      ids.push(value);
    }
  });
  if (ids.length === 0) warnings.push(`Pi enabledModels contains no exact model IDs: ${source}`);
  return { ids, warnings, source };
}