// The writer-claim record (#1507, CHAT-03 §2, D1).
//
// A claim holds two keys, the seat tuple (seat, project, workspace) and the
// native session identity. Each key is a directory under the claim root and
// each revision a numbered file in it (r0000000001.json, ...). A revision is
// published by writing a temporary file in the same directory, fsyncing it,
// link()ing it to the next revision name and fsyncing the directory. link()
// fails when the name exists, so publication is exclusive and a revision name
// only ever points at complete contents. Revisions are never rewritten.
//
// Keys are taken seat first, then session. Every step of the lifecycle
// publishes on the seat key and then on the session key. The pair's state is
// the more conservative of the two: uncertain > stopping > active > reserved
// > stopped. A key is held unless its highest revision is `stopped` with a
// proof reference. A highest revision that does not parse holds the key as
// `uncertain`; an older revision is never reused.
//
// The store is internal. It never crosses the wire, and it stores only the
// CHAT-01 binding fields it needs.

import { closeSync, fsyncSync, linkSync, mkdirSync, openSync, readdirSync, readFileSync, unlinkSync, writeSync } from "node:fs";
import { join } from "node:path";
import { createHash, randomBytes } from "node:crypto";
import { bootId as readBootId, identityOf, ownerState } from "../../discord/src/journal.mjs";
import { ControlRefusal } from "./safe-fs.mjs";
import { ID } from "./parts.mjs";

export const CLAIM_VERSION = 1;
export const STATES = Object.freeze(["uncertain", "stopping", "active", "reserved", "stopped"]);
export const PROOF_KINDS = Object.freeze(["cohortProof", "boot", "no-unit"]);
export const ALREADY_ACTIVE = "already-active";
export const UNSAFE_REPLACEMENT = "unsafe-replacement";
export const FOREIGN_HOST = "foreign-host";

const REVISION = /^r(\d{10})\.json$/;
const revName = (n) => `r${String(n).padStart(10, "0")}.json`;
const rank = (state) => STATES.indexOf(state);

export function machineId() {
  try {
    const id = readFileSync("/etc/machine-id", "utf8").trim();
    return /^[0-9a-f]{32}$/.test(id) ? id : null;
  } catch {
    return null;
  }
}

export const defaultHost = Object.freeze({ machineId, bootId: readBootId });

export function newClaimId() {
  return "c" + randomBytes(12).toString("hex");
}

export function unitNameFor(claimId) {
  return `mosaic-chat-${claimId}`;
}

// The more conservative of two states.
export function conservative(a, b) {
  return rank(a) <= rank(b) ? a : b;
}

const keyHash = (key) => createHash("sha256").update(JSON.stringify(key)).digest("hex").slice(0, 32);

export function seatKey({ seat, project, workspace }) {
  return { kind: "seat", seat, project, workspace };
}

export function sessionKey(session) {
  return { kind: "session", session };
}

function valid(rec, key, n) {
  return rec && typeof rec === "object" && rec.version === CLAIM_VERSION && rec.kind === "writer-claim" &&
    rec.revision === n && JSON.stringify(rec.key) === JSON.stringify(key) && typeof rec.claimId === "string" &&
    ID.test(rec.claimId) && STATES.includes(rec.state) && rec.host && typeof rec.host === "object" &&
    (rec.proof === null || (rec.proof && PROOF_KINDS.includes(rec.proof.kind)));
}

// A key's highest revision is free only when it is `stopped` with a proof.
export function held(head) {
  if (head.n === 0) return false;
  if (head.damaged) return true;
  return !(head.record.state === "stopped" && head.record.proof);
}

export function headState(head) {
  if (head.n === 0) return "stopped";
  if (head.damaged) return "uncertain";
  if (head.record.state === "stopped" && !head.record.proof) return "uncertain";
  return head.record.state;
}

export class ClaimStore {
  constructor({ root, host = defaultHost, identity = identityOf, barrier = null, now = () => new Date() }) {
    if (typeof root !== "string" || !root) throw new ControlRefusal("configuration", "a claim root is required; CHAT-03 has no default");
    this.root = root;
    this.host = host;
    this.identity = identity;
    this.barrier = barrier;
    this.now = now;
  }

  dir(key) {
    return join(this.root, key.kind, keyHash(key));
  }

  async pause(name, detail) {
    if (this.barrier) await this.barrier(name, detail);
  }

  head(key) {
    const dir = this.dir(key);
    let names;
    try {
      names = readdirSync(dir);
    } catch (err) {
      if (err.code === "ENOENT") return { key, n: 0, record: null, damaged: false };
      throw err;
    }
    let n = 0;
    for (const name of names) {
      const m = REVISION.exec(name);
      if (m) n = Math.max(n, Number(m[1]));
    }
    if (n === 0) return { key, n: 0, record: null, damaged: false };
    let record = null;
    try {
      record = JSON.parse(readFileSync(join(dir, revName(n)), "utf8"));
    } catch {
      record = null;
    }
    if (!valid(record, key, n)) return { key, n, record: null, damaged: true };
    return { key, n, record, damaged: false };
  }

  revisions(key) {
    const dir = this.dir(key);
    let names;
    try {
      names = readdirSync(dir);
    } catch {
      return [];
    }
    return names.filter((x) => REVISION.test(x)).sort().map((name) => ({ name, text: readFileSync(join(dir, name), "utf8") }));
  }

  // Publishes revision `n` on `key`. Returns null when another writer
  // published that revision first.
  async publish(key, n, body) {
    const dir = this.dir(key);
    mkdirSync(dir, { recursive: true, mode: 0o700 });
    const record = { ...body, key, revision: n, writtenAt: this.now().toISOString() };
    const tmp = join(dir, `.tmp-${randomBytes(8).toString("hex")}`);
    const fd = openSync(tmp, "wx", 0o400);
    try {
      writeSync(fd, JSON.stringify(record) + "\n");
      await this.pause("temp-written", { key, n });
      fsyncSync(fd);
    } finally {
      closeSync(fd);
    }
    await this.pause("temp-synced", { key, n });
    let won = true;
    try {
      linkSync(tmp, join(dir, revName(n)));
    } catch (err) {
      if (err.code !== "EEXIST") throw err;
      won = false;
    }
    unlinkSync(tmp);
    if (!won) return null;
    await this.pause("linked", { key, n });
    const dfd = openSync(dir, "r");
    try {
      fsyncSync(dfd);
    } finally {
      closeSync(dfd);
    }
    await this.pause("dir-synced", { key, n });
    return record;
  }

  owner(incarnation) {
    const id = this.identity(process.pid);
    return { pid: process.pid, start: id.start, boot: id.boot, incarnation };
  }

  // Why a held pair refuses a new claim.
  refusal(seat, session) {
    const heads = [seat, session].filter(held);
    const mine = this.host.machineId();
    if (heads.some((h) => !h.damaged && h.record.host.machineId !== mine)) return FOREIGN_HOST;
    if (heads.some((h) => h.damaged)) return UNSAFE_REPLACEMENT;
    if (heads.length === 2 && heads[0].record.claimId !== heads[1].record.claimId) return UNSAFE_REPLACEMENT;
    const state = heads.map(headState).reduce(conservative, "stopped");
    return state === "reserved" || state === "active" ? ALREADY_ACTIVE : UNSAFE_REPLACEMENT;
  }

  refuse(seat, session) {
    const code = this.refusal(seat, session);
    return new ControlRefusal(code, `the writer claim for this seat or session is held (${code})`);
  }

  // Reserves both keys under a new claim ID. `fields` holds the binding
  // fields the record stores. Refuses when either key is held.
  async acquire(seatK, sessionK, fields) {
    for (let attempt = 0; attempt < 4; attempt++) {
      const seat = this.head(seatK), session = this.head(sessionK);
      if (held(seat) || held(session)) throw this.refuse(seat, session);
      const claimId = fields.claimId ?? newClaimId();
      const body = {
        version: CLAIM_VERSION, kind: "writer-claim", claimId,
        bindingId: fields.bindingId, harness: fields.harness, conversation: fields.conversation,
        branch: fields.branch, leaf: fields.leaf, pins: fields.pins,
        host: { machineId: this.host.machineId(), bootId: this.host.bootId() },
        owner: fields.owner, unitName: unitNameFor(claimId), spawnMarker: false,
        invocationId: null, engine: null, shim: null, generation: fields.generation,
        state: "reserved", proof: null, stop: null, prior: fields.prior ?? null,
        execution: fields.execution ?? null, cohortRef: fields.cohortRef ?? null,
      };
      const first = await this.publish(seatK, seat.n + 1, body);
      if (!first) continue; // lost the seat key: re-read and re-decide
      await this.pause("between-keys", { claimId });
      const now = this.head(sessionK);
      const second = held(now) ? null : await this.publish(sessionK, now.n + 1, body);
      if (!second) {
        // The session key is held by someone else: close our seat revision
        // with a no-unit proof. Nothing was spawned.
        await this.publish(seatK, seat.n + 2, { ...body, state: "stopped", proof: { kind: "no-unit", ref: null } });
        throw this.refuse(this.head(seatK), this.head(sessionK));
      }
      return { claimId, seatKey: seatK, sessionKey: sessionK, n: { seat: first.revision, session: second.revision }, record: body };
    }
    throw new ControlRefusal(UNSAFE_REPLACEMENT, "the writer claim changed during every attempt");
  }

  // Publishes `patch` on both keys, seat first. Both heads must still be this
  // claim's own last revisions.
  async advance(claim, patch) {
    const next = { ...claim.record, ...patch };
    const n = { ...claim.n };
    for (const kind of ["seat", "session"]) {
      const key = kind === "seat" ? claim.seatKey : claim.sessionKey;
      const head = this.head(key);
      if (head.damaged || head.n !== n[kind] || head.record.claimId !== claim.claimId) {
        throw new ControlRefusal(UNSAFE_REPLACEMENT, `the ${kind} key changed under claim ${claim.claimId}`);
      }
      const rec = await this.publish(key, head.n + 1, next);
      if (!rec) throw new ControlRefusal(UNSAFE_REPLACEMENT, `another writer published on the ${kind} key of claim ${claim.claimId}`);
      n[kind] = rec.revision;
      if (kind === "seat") await this.pause("between-keys", { claimId: claim.claimId, patch });
    }
    claim.record = next;
    claim.n = n;
    return claim;
  }

  // Restart classification for a pair whose recorded owner may be gone. Acts
  // only when the owner is proven gone: a different boot, or no process with
  // the recorded pid and start time. `units.lookup(record)` reports the
  // intended unit as { state: "absent" | "alive" | "unknown" }. `bootProof`
  // issues the boot proof: it returns { proof, effects } once the verifier
  // accepted both, or null, which leaves the pair `uncertain`. `adopt` is the
  // owner record a recovery controller publishes when it takes over an
  // orphan; without it nothing is adopted. `stoppedPatch` adds fields (the
  // leaf at proof) to a `stopped` revision this classification publishes.
  async classify(seatK, sessionK, { units, bootProof = null, adopt = null, stoppedPatch = {} } = {}) {
    const seat = this.head(seatK), session = this.head(sessionK);
    if (!held(seat) && !held(session)) return { state: "free" };
    const code = this.refusal(seat, session);
    if (code === FOREIGN_HOST) return { state: "uncertain", refusal: FOREIGN_HOST };
    if (seat.damaged || session.damaged) return { state: "uncertain", refusal: UNSAFE_REPLACEMENT, damaged: true };
    const heads = [seat, session].filter(held);
    if (heads.length === 2 && heads[0].record.claimId !== heads[1].record.claimId) return { state: "uncertain", refusal: UNSAFE_REPLACEMENT };
    const claimId = heads[0].record.claimId;
    const ours = [seat, session].filter((h) => h.n > 0 && !h.damaged && h.record.claimId === claimId);
    const latest = ours.reduce((a, b) => (a.record.writtenAt >= b.record.writtenAt ? a : b)).record;
    const owner = latest.owner;
    if (adopt && owner?.incarnation === adopt.incarnation && owner?.pid === adopt.pid) return { state: "owned", claimId, record: latest };
    const status = ownerState(owner ? { pid: owner.pid, start: owner.start ?? null, boot: owner.boot ?? null } : { invalid: true }, { identity: this.identity });
    if (status === "live" || status === "unknown" || status === "invalid") return { state: headState(heads[0]), refusal: ALREADY_ACTIVE, claimId, record: latest };

    const pair = heads.map(headState).reduce(conservative, "stopped");
    const marker = ours.some((h) => h.record.spawnMarker);
    const claim = this.claimFrom(seatK, sessionK, claimId, seat, session, latest);

    // A different boot on the same host: every process of that boot is gone.
    if (latest.host.bootId !== this.host.bootId()) {
      if (!bootProof) return { state: "uncertain", refusal: UNSAFE_REPLACEMENT, claimId, record: latest, needs: "boot-proof" };
      const issued = await bootProof(latest);
      if (!issued) return { state: "uncertain", refusal: UNSAFE_REPLACEMENT, claimId, record: latest, needs: "boot-proof" };
      const { proof, effects = null } = issued;
      await this.finish(claim, { ...stoppedPatch, state: "stopped", proof: { kind: "boot", ref: proof.id, effects: effects?.id ?? null }, spawnMarker: marker });
      return { state: "stopped", proofKind: "boot", proof, effects, claimId, record: claim.record };
    }

    // Keys disagree because a release stopped between them: finish it under
    // the same claim ID and proof.
    const stoppedHead = ours.find((h) => h.record.state === "stopped" && h.record.proof);
    if (stoppedHead) {
      await this.finish(claim, { state: "stopped", proof: stoppedHead.record.proof, spawnMarker: marker || latest.spawnMarker, leafAtProof: stoppedHead.record.leafAtProof ?? null, branchAtProof: stoppedHead.record.branchAtProof ?? null });
      return { state: "stopped", proofKind: stoppedHead.record.proof.kind, claimId, record: claim.record, completed: true };
    }

    const unit = await units.lookup(latest);
    if (pair === "reserved" && !marker && unit.state === "absent") {
      await this.finish(claim, { ...stoppedPatch, state: "stopped", proof: { kind: "no-unit", ref: null } });
      return { state: "stopped", proofKind: "no-unit", claimId, record: claim.record };
    }

    // A marker with no unit, a unit that exists, or an engine that may run:
    // the pair is uncertain. A collected scope is an absent observation, not
    // proof that every process ended. The marker is copied, never dropped.
    const patch = { state: latest.state === "stopping" && latest.stop ? "stopping" : "uncertain", spawnMarker: marker };
    if (adopt) patch.owner = adopt;
    await this.finish(claim, patch);
    return { state: patch.state, claimId, record: claim.record, unit, adopted: Boolean(adopt), claim, resumeStop: latest.stop && latest.state === "stopping" ? latest.stop : null };
  }

  claimFrom(seatK, sessionK, claimId, seat, session, latest) {
    return {
      claimId, seatKey: seatK, sessionKey: sessionK,
      n: { seat: seat.n, session: session.n },
      heads: { seat, session },
      record: { ...latest },
    };
  }

  // Brings both keys of a claim to `patch`, seat first. A key whose head
  // belongs to an older claim (a half-done acquire) gains the revision too.
  async finish(claim, patch) {
    const next = { ...claim.record, ...patch };
    for (const kind of ["seat", "session"]) {
      const key = kind === "seat" ? claim.seatKey : claim.sessionKey;
      const head = this.head(key);
      if (head.damaged) throw new ControlRefusal(UNSAFE_REPLACEMENT, `the ${kind} key is unreadable`);
      if (head.n > 0 && head.record.claimId !== claim.claimId && held(head)) throw new ControlRefusal(UNSAFE_REPLACEMENT, `the ${kind} key belongs to another claim`);
      const same = head.n > 0 && head.record.claimId === claim.claimId && head.record.state === next.state &&
        JSON.stringify(head.record.proof) === JSON.stringify(next.proof) && head.record.spawnMarker === next.spawnMarker &&
        JSON.stringify(head.record.owner) === JSON.stringify(next.owner);
      if (same) {
        claim.n[kind] = head.n;
        continue;
      }
      const rec = await this.publish(key, head.n + 1, next);
      if (!rec) throw new ControlRefusal(UNSAFE_REPLACEMENT, `another writer published on the ${kind} key of claim ${claim.claimId}`);
      claim.n[kind] = rec.revision;
      if (kind === "seat") await this.pause("between-keys", { claimId: claim.claimId, patch });
    }
    claim.record = next;
    return claim;
  }
}