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

/**
 * Extensions known to also rewrite compaction results or filter model
 * context. If one of these is installed alongside pi-context-epochs, the
 * last-registered session_before_compact handler wins, which can silently
 * replace our epoch boundary. We warn at startup and fail closed at
 * session_compact verification time (no continuation is sent for a boundary
 * we do not own).
 */
export const KNOWN_CONFLICTING_PACKAGES = [
  "pi-agenticoding",
  "pi-context",
  "pi-context-prune",
  "billion-context-pi",
  "pi-codex-compaction",
  "pi-codex-compact",
  "pi-session-continuity",
  "pi-continue",
];

function settingsPackageSources(settings: unknown): string[] {
  if (!settings || typeof settings !== "object" || Array.isArray(settings)) return [];
  const packages = (settings as { packages?: unknown }).packages;
  if (!Array.isArray(packages)) return [];
  const sources: string[] = [];
  for (const entry of packages) {
    if (typeof entry === "string") sources.push(entry);
    else if (entry && typeof entry === "object" && typeof (entry as { source?: unknown }).source === "string") {
      sources.push((entry as { source: string }).source);
    }
  }
  return sources;
}

function sourceMatches(source: string): string | null {
  const lower = source.toLowerCase();
  for (const name of KNOWN_CONFLICTING_PACKAGES) {
    // npm:<name>, git:<...>/<name>, bare path ending in <name>
    if (lower === name || lower.endsWith(`/${name}`) || lower.includes(`:${name}`) || lower.includes(`npm:${name}@`) || lower.startsWith(name)) {
      return name;
    }
    const base = lower.split("/").pop()?.replace(/\.jsonl$/, "") ?? lower;
    if (base === name) return name;
  }
  return null;
}

export interface ConflictScanResult {
  conflicts: string[];
  scanned: string[];
}

/** Best-effort scan of global and project settings for competing extensions. */
export function scanForConflictingPackages(projectCwd: string | undefined): ConflictScanResult {
  const candidates = [join(homedidSafe(), ".pi", "agent", "settings.json")];
  if (projectCwd) candidates.push(join(projectCwd, ".pi", "settings.json"));
  const conflicts = new Set<string>();
  const scanned: string[] = [];
  for (const path of candidates) {
    if (!existsSync(path)) continue;
    scanned.push(path);
    try {
      const settings = JSON.parse(readFileSync(path, "utf8"));
      for (const source of settingsPackageSources(settings)) {
        const match = sourceMatches(source);
        if (match) conflicts.add(match);
      }
    } catch {
      // unreadable settings: not fatal
    }
  }
  return { conflicts: [...conflicts], scanned };
}

function homedidSafe(): string {
  try {
    return homedir();
  } catch {
    return "";
  }
}