// lib/journal.ts — per-incarnation append-only JSONL journal (PRD R6, NG-3).
//
// One file per incarnation identity (the NG-1 process-launch identity —
// NEVER PI_SESSION_ID) under the XDG state home:
//   ${XDG_STATE_HOME:-~/.local/state}/mosaic-core/<incarnationId>.jsonl
//
// Append-only is structural: the only write primitive is appendFileSync of a
// newline-terminated JSON line. No read-modify-write, no truncation, no
// rewrite — a journal that can be edited is a journal that cannot prove
// anything. Event payloads are pre-sanitized by their producers (the denial
// event carries tool+reason only; proposals pass the proposal sanitizer).

import { appendFileSync, mkdirSync } from "node:fs";
import { homedir } from "node:os";
import { join } from "node:path";

export type JournalKind = "reconciliation" | "denial" | "improvement-proposal";

export interface JournalEvent {
  ts: string;
  incarnationId: string;
  kind: JournalKind;
  [field: string]: unknown;
}

export interface JournalIO {
  mkdirSync(path: string, opts: { recursive: boolean }): void;
  appendFileSync(path: string, data: string): void;
}

function defaultIO(): JournalIO {
  return { mkdirSync, appendFileSync };
}

export function journalDir(stateHome: string | undefined, home: string = homedir()): string {
  return join(stateHome ?? join(home, ".local", "state"), "mosaic-core");
}

export interface Journal {
  path: string;
  append(event: Omit<JournalEvent, "ts" | "incarnationId">): void;
}

export function createJournal(opts: {
  incarnationId: string;
  stateHome?: string;
  io?: JournalIO;
  now?: () => string;
}): Journal {
  const io = opts.io ?? defaultIO();
  const now = opts.now ?? (() => new Date().toISOString());
  const dir = journalDir(opts.stateHome);
  const path = join(dir, `${opts.incarnationId}.jsonl`);
  io.mkdirSync(dir, { recursive: true });
  return {
    path,
    append(event) {
      const line = `${JSON.stringify({ ts: now(), incarnationId: opts.incarnationId, ...event })}\n`;
      io.appendFileSync(path, line);
    },
  };
}