import { randomUUID } from "node:crypto";

export const DEFAULT_CODE_AGENT_SESSION_IDLE_TIMEOUT_MS = 30 * 60 * 1000;
export const DEFAULT_CODE_AGENT_MAX_SESSIONS = 200;
export const CODE_AGENT_SESSION_STATUSES = Object.freeze([
  "creating",
  "ready",
  "busy",
  "idle",
  "interrupted",
  "expired",
  "failed"
]);

export function createCodeAgentSessionRegistry(options = {}) {
  const idleTimeoutMs = positiveInteger(options.idleTimeoutMs, DEFAULT_CODE_AGENT_SESSION_IDLE_TIMEOUT_MS);
  const maxSessions = positiveInteger(options.maxSessions, DEFAULT_CODE_AGENT_MAX_SESSIONS);
  const idFactory = typeof options.idFactory === "function" ? options.idFactory : () => `ses_${randomUUID()}`;
  const defaultNow = options.now;
  const sessions = new Map();
  const conversations = new Map();

  function acquire(params = {}) {
    const timestamp = timestampFor(params.now ?? defaultNow);
    const timestampMs = Date.parse(timestamp);
    const conversationId = requiredId(params.conversationId, "cnv");
    const requestedSessionId = optionalId(params.sessionId);
    const mappedSessionId = conversations.get(conversationId) ?? null;

    if (mappedSessionId && requestedSessionId && mappedSessionId !== requestedSessionId) {
      const mappedSession = sessions.get(mappedSessionId) ?? null;
      return blockedAcquire({
        code: "session_reuse_conflict",
        summary: `conversationId ${conversationId} is already bound to sessionId ${mappedSessionId}; requested ${requestedSessionId}.`,
        session: mappedSession,
        timestamp,
        traceId: params.traceId
      });
    }

    const effectiveSessionId = mappedSessionId || requestedSessionId || requiredId(idFactory(), "ses");
    let session = sessions.get(effectiveSessionId) ?? null;
    const reused = Boolean(session);

    if (session && sessionExpired(session, timestampMs)) {
      session.status = "expired";
      session.updatedAt = timestamp;
      session.lastTraceId = optionalId(params.traceId);
      return blockedAcquire({
        code: "session_expired",
        summary: `Code Agent runner session ${effectiveSessionId} expired after ${session.idleTimeoutMs}ms idle timeout.`,
        session,
        timestamp,
        traceId: params.traceId
      });
    }

    if (session?.status === "busy") {
      session.updatedAt = timestamp;
      session.lastTraceId = optionalId(params.traceId) ?? session.lastTraceId;
      return blockedAcquire({
        code: "session_busy",
        summary: `Code Agent runner session ${effectiveSessionId} is already busy with traceId ${session.currentTraceId ?? "unknown"}.`,
        session,
        timestamp,
        traceId: params.traceId
      });
    }

    if (!session) {
      session = {
        sessionId: effectiveSessionId,
        conversationIds: new Set(),
        status: "creating",
        workspace: params.workspace ?? null,
        sandbox: params.sandbox ?? "read-only",
        runnerKind: params.runnerKind ?? "hwlab-readonly-runner",
        capabilityLevel: params.capabilityLevel ?? "read-only-session-tools",
        implementationType: params.implementationType ?? "controlled-readonly-session-registry",
        createdAt: timestamp,
        updatedAt: timestamp,
        idleTimeoutMs,
        expiresAt: plusMs(timestampMs, idleTimeoutMs),
        lastTraceId: optionalId(params.traceId),
        currentTraceId: null,
        turn: 0,
        durable: false,
        longLivedSession: false,
        codexStdio: false,
        secretMaterialStored: false
      };
      sessions.set(effectiveSessionId, session);
    }

    session.conversationIds.add(conversationId);
    session.workspace = params.workspace ?? session.workspace;
    session.sandbox = params.sandbox ?? session.sandbox;
    session.runnerKind = params.runnerKind ?? session.runnerKind;
    session.capabilityLevel = params.capabilityLevel ?? session.capabilityLevel;
    session.implementationType = params.implementationType ?? session.implementationType;
    session.status = "busy";
    session.updatedAt = timestamp;
    session.expiresAt = plusMs(timestampMs, idleTimeoutMs);
    session.lastTraceId = optionalId(params.traceId);
    session.currentTraceId = optionalId(params.traceId);
    session.turn += 1;
    conversations.set(conversationId, effectiveSessionId);
    prune();

    return {
      ok: true,
      reused,
      session: publicSession(session, { conversationId, reused, timestamp })
    };
  }

  function release(sessionId, params = {}) {
    const session = sessions.get(requiredId(sessionId, "ses")) ?? null;
    if (!session) return null;
    const timestamp = timestampFor(params.now ?? defaultNow);
    const timestampMs = Date.parse(timestamp);
    session.status = CODE_AGENT_SESSION_STATUSES.includes(params.status) ? params.status : "idle";
    session.updatedAt = timestamp;
    session.expiresAt = plusMs(timestampMs, session.idleTimeoutMs);
    session.lastTraceId = optionalId(params.traceId) ?? session.lastTraceId;
    session.currentTraceId = null;
    session.statusReason = params.statusReason ?? null;
    return publicSession(session, {
      conversationId: params.conversationId,
      reused: params.reused,
      timestamp
    });
  }

  function fail(sessionId, params = {}) {
    return release(sessionId, { ...params, status: "failed" });
  }

  function interrupt(sessionId, params = {}) {
    return release(sessionId, { ...params, status: "interrupted" });
  }

  function get(sessionId, params = {}) {
    const session = sessions.get(requiredId(sessionId, "ses")) ?? null;
    return session ? publicSession(session, params) : null;
  }

  function getByConversation(conversationId, params = {}) {
    const sessionId = conversations.get(requiredId(conversationId, "cnv"));
    return sessionId ? get(sessionId, { ...params, conversationId }) : null;
  }

  function expireIdle(params = {}) {
    const timestamp = timestampFor(params.now ?? defaultNow);
    const timestampMs = Date.parse(timestamp);
    let expired = 0;
    for (const session of sessions.values()) {
      if (!sessionExpired(session, timestampMs)) continue;
      session.status = "expired";
      session.updatedAt = timestamp;
      session.currentTraceId = null;
      expired += 1;
    }
    return expired;
  }

  function describe() {
    return {
      kind: "code-agent-session-registry",
      implementationType: "controlled-readonly-session-registry",
      status: "available",
      sessionCount: sessions.size,
      maxSessions,
      idleTimeoutMs,
      statuses: [...CODE_AGENT_SESSION_STATUSES],
      longLivedCodexStdio: false,
      durable: false,
      secretMaterialStored: false,
      valuesRedacted: true
    };
  }

  function clear() {
    sessions.clear();
    conversations.clear();
  }

  function prune() {
    if (sessions.size <= maxSessions) return;
    const sorted = [...sessions.entries()]
      .sort((a, b) => String(a[1].updatedAt).localeCompare(String(b[1].updatedAt)));
    for (const [sessionId, session] of sorted.slice(0, sessions.size - maxSessions)) {
      sessions.delete(sessionId);
      for (const conversationId of session.conversationIds) {
        if (conversations.get(conversationId) === sessionId) {
          conversations.delete(conversationId);
        }
      }
    }
  }

  return {
    acquire,
    release,
    fail,
    interrupt,
    get,
    getByConversation,
    expireIdle,
    describe,
    clear
  };
}

function blockedAcquire({ code, summary, session, timestamp, traceId }) {
  const publicEvidence = session
    ? publicSession(session, { timestamp, reused: true })
    : {
        status: "failed",
        updatedAt: timestamp,
        lastTraceId: optionalId(traceId),
        secretMaterialStored: false,
        valuesRedacted: true
      };
  return {
    ok: false,
    code,
    message: summary,
    session: publicEvidence,
    blocker: {
      code,
      sourceIssue: "pikasTech/HWLAB#317",
      summary
    }
  };
}

function publicSession(session, { conversationId = null, reused = null } = {}) {
  const conversationIds = [...session.conversationIds];
  return {
    sessionId: session.sessionId,
    conversationId: conversationId ?? conversationIds[0] ?? null,
    conversationIds,
    status: session.status,
    workspace: session.workspace,
    sandbox: session.sandbox,
    runnerKind: session.runnerKind,
    capabilityLevel: session.capabilityLevel,
    implementationType: session.implementationType,
    createdAt: session.createdAt,
    updatedAt: session.updatedAt,
    idleTimeoutMs: session.idleTimeoutMs,
    expiresAt: session.expiresAt,
    lastTraceId: session.lastTraceId,
    currentTraceId: session.currentTraceId,
    turn: session.turn,
    reused: reused === null ? undefined : Boolean(reused),
    durable: session.durable === true,
    longLivedSession: session.longLivedSession === true,
    codexStdio: session.codexStdio === true,
    secretMaterialStored: false,
    valuesRedacted: true,
    ...(session.statusReason ? { statusReason: session.statusReason } : {})
  };
}

function sessionExpired(session, timestampMs) {
  if (!Number.isFinite(timestampMs) || session.status === "expired") return session.status === "expired";
  return Date.parse(session.expiresAt) <= timestampMs;
}

function timestampFor(now) {
  const value = typeof now === "function" ? now() : now;
  if (typeof value === "string" && !Number.isNaN(Date.parse(value))) return value;
  if (value instanceof Date && !Number.isNaN(value.valueOf())) return value.toISOString();
  return new Date().toISOString();
}

function plusMs(timestampMs, offsetMs) {
  return new Date(timestampMs + offsetMs).toISOString();
}

function requiredId(value, fallbackPrefix) {
  const id = optionalId(value);
  if (id) return id;
  return `${fallbackPrefix}_${randomUUID()}`;
}

function optionalId(value) {
  return typeof value === "string" && value.trim() ? value.trim() : null;
}

function positiveInteger(value, fallback) {
  return Number.isInteger(value) && value > 0 ? value : fallback;
}