my-pi/pi-compaction/src/config.ts

import { readFile } from "node:fs/promises";
import { fileURLToPath } from "node:url";
import type { PiCompactionConfig } from "./types.js";

// Bundle-level `config/` is the single source of truth: the extension reads
// `config/pi-compaction.json` from inside the installed bundle (resolved
// relative to this source file). It never reads `settings.json` and never
// writes config at runtime.
export const CONFIG_PATH = fileURLToPath(
  new URL("../../config/pi-compaction.json", import.meta.url),
);

export const DEFAULT_CONFIG: PiCompactionConfig = {
  enabled: true,
  softRatio: 0.72,
  hardRatio: 0.9,
  targetRatio: 0.55,
  deterministic: {
    enabled: true,
    maxStubTokens: 1_024,
  },
  semantic: {
    enabled: true,
    model: "default",
    thinking: "low",
    concurrency: 1,
    minInputChars: 4_000,
    maxInputChars: 24_000,
    maxRetries: 2,
  },
  native: {
    enabled: true,
  },
};

function ratio(value: unknown, fallback: number): number {
  return typeof value === "number" && Number.isFinite(value) && value > 0 && value < 1 ? value : fallback;
}

function integer(value: unknown, fallback: number, min = 0, max = Number.MAX_SAFE_INTEGER): number {
  return typeof value === "number" && Number.isInteger(value) && value >= min && value <= max ? value : fallback;
}

function object(value: unknown): Record<string, unknown> {
  return value !== null && typeof value === "object" && !Array.isArray(value)
    ? value as Record<string, unknown>
    : {};
}

export function normalizeConfig(value: unknown): PiCompactionConfig {
  const input = object(value);
  const deterministic = object(input.deterministic);
  const semantic = object(input.semantic);
  const native = object(input.native);
  const softRatio = ratio(input.softRatio, DEFAULT_CONFIG.softRatio);
  const hardRatio = Math.max(softRatio + 0.01, ratio(input.hardRatio, DEFAULT_CONFIG.hardRatio));
  const targetRatio = Math.min(softRatio - 0.01, ratio(input.targetRatio, DEFAULT_CONFIG.targetRatio));
  const thinking = ["off", "minimal", "low", "medium", "high", "xhigh"].includes(String(semantic.thinking))
    ? semantic.thinking as PiCompactionConfig["semantic"]["thinking"]
    : DEFAULT_CONFIG.semantic.thinking;

  return {
    enabled: typeof input.enabled === "boolean" ? input.enabled : DEFAULT_CONFIG.enabled,
    softRatio,
    hardRatio: Math.min(0.99, hardRatio),
    targetRatio: Math.max(0.1, targetRatio),
    deterministic: {
      enabled: typeof deterministic.enabled === "boolean" ? deterministic.enabled : DEFAULT_CONFIG.deterministic.enabled,
      maxStubTokens: integer(deterministic.maxStubTokens, DEFAULT_CONFIG.deterministic.maxStubTokens, 32, 4_096),
    },
    semantic: {
      enabled: typeof semantic.enabled === "boolean" ? semantic.enabled : DEFAULT_CONFIG.semantic.enabled,
      model: typeof semantic.model === "string" && semantic.model.trim() ? semantic.model.trim() : DEFAULT_CONFIG.semantic.model,
      thinking,
      concurrency: integer(semantic.concurrency, DEFAULT_CONFIG.semantic.concurrency, 1, 4),
      minInputChars: integer(semantic.minInputChars, DEFAULT_CONFIG.semantic.minInputChars, 0, 1_000_000),
      maxInputChars: integer(semantic.maxInputChars, DEFAULT_CONFIG.semantic.maxInputChars, 1_000, 1_000_000),
      maxRetries: integer(semantic.maxRetries, DEFAULT_CONFIG.semantic.maxRetries, 0, 5),
    },
    native: {
      enabled: typeof native.enabled === "boolean" ? native.enabled : DEFAULT_CONFIG.native.enabled,
    },
  };
}

export async function loadConfig(
  configPath: string = CONFIG_PATH,
): Promise<PiCompactionConfig> {
  try {
    const parsed = JSON.parse(await readFile(configPath, "utf8"));
    return normalizeConfig(parsed);
  } catch {
    return structuredClone(DEFAULT_CONFIG);
  }
}