/**
 * claude-sdk-sessionstore #9 (Part 2) — ClaudeSdkBackend.
 *
 * A warm, resumable backend for the `claude` agent built on the Claude Agent SDK
 * (`@anthropic-ai/claude-agent-sdk`), implementing the Phase-0 `AgentBackend`
 * contract (same shape as `WarmAcpBackend` / `OpenCodeServerBackend`). One
 * persistent `query()` per (chat, agent) session, driven in STREAMING-INPUT mode:
 * the `prompt` is a pushable `AsyncIterable<SDKUserMessage>` that stays open across
 * turns, so the SDK subprocess + conversation stay warm between `prompt()` calls
 * until `closeSession`/`dispose`.
 *
 * ⚠ LIVE PUMP IS HOST-ONLY. The actual streaming turn needs the real `claude`
 * binary + ANTHROPIC auth on a host — it CANNOT run in the dev container. This file
 * is written against the REAL SDK types so it TYPECHECKS, and the PURE pieces (the
 * `mapSdkMessage` mapper + the `createPushable` queue) are unit-tested. Routing to
 * this backend is gated behind `CLAUDE_SDK_BACKEND` (default OFF) so production
 * claude stays on the working PTY path until a host smoke validates the pump +
 * cross-turn resume.
 *
 * Lifecycle (mirrors warm-acp.ts / opencode-server.ts):
 *   - `ensureSession`: resolve the resume id from `agent_sessions(chat_id,'claude')`
 *     and (re)build the single `query()` if not already live. The SDK's own
 *     `sessionStore` (Part 1 PostgresSessionStore) materializes the transcript on
 *     resume; `options.resume` carries the provider session id.
 *   - `prompt`: push ONE user message onto the open queue, iterate the generator,
 *     map each `SDKMessage` → `AgentEvent`s via `mapSdkMessage`, forward to
 *     `ctx.onEvent`, and resolve when the turn's `result` message lands. Capture the
 *     `session_id` from the `init` message and persist it to `agent_sessions`;
 *     accumulate `result.usage` / `total_cost_usd` onto the row (mirrors opencode U.6).
 *   - `closeSession` / `dispose`: close the queue + dispose the query generator.
 *   - A thrown error or `result.subtype==='error*'` marks `agent_sessions.status='crashed'`.
 *
 * Turn serialization: like warm-acp, exactly one turn is in flight at a time on a
 * given backend (the dispatcher's per-session `inflight` map enforces this upstream;
 * `isBusy()` reports it so the pool never evicts mid-turn).
 */
import { query, type Query, type SDKMessage, type SDKUserMessage, type Options } from '@anthropic-ai/claude-agent-sdk';
import type { FastifyBaseLogger } from 'fastify';
import type { Sql } from '../../db.js';
import { PostgresSessionStore } from './claude-session-store.js';
import { createPushable, type Pushable } from './pushable-iterable.js';
import { mapSdkMessage, createClaudeSdkMapState, type ClaudeSdkMapState } from './claude-sdk-map.js';
import type {
  AgentBackend,
  AgentSessionHandle,
  EnsureSessionOpts,
  PromptCtx,
  TurnResult,
} from '../agent-backend.js';

export interface ClaudeSdkBackendDeps {
  sql: Sql;
  log: FastifyBaseLogger;
  /** The (chat, agent) this backend serves — its pool identity + DB key. */
  chatId: string;
  /** Always 'claude' today; kept explicit so the pool key + DB writes stay honest. */
  agent: string;
  /** Resolved `claude` binary path (available_agents.install_path); null → SDK default. */
  installPath: string | null;
}

export class ClaudeSdkBackend implements AgentBackend {
  readonly backend = 'claude_sdk' as const;

  private readonly sql: Sql;
  private readonly log: FastifyBaseLogger;
  private readonly chatId: string;
  private readonly agent: string;
  private readonly installPath: string | null;
  private readonly sessionStore: PostgresSessionStore;

  /** The single persistent query() generator; null until the first turn builds it. */
  private query: Query | null = null;
  /** The open input queue feeding the generator one SDKUserMessage per turn. */
  private input: Pushable<SDKUserMessage> | null = null;
  /** The provider's own session id (resume token), captured from the init message. */
  private agentSessionId: string | null = null;
  /** Resolved model the live query() was built with; a change forces a rebuild. */
  private builtModel: string | null = null;
  /** True between prompt() start and settle. */
  private busy = false;
  private up = false;

  constructor(deps: ClaudeSdkBackendDeps) {
    this.sql = deps.sql;
    this.log = deps.log;
    this.chatId = deps.chatId;
    this.agent = deps.agent;
    this.installPath = deps.installPath;
    this.sessionStore = new PostgresSessionStore(deps.sql);
  }

  /** §2: liveness for the health endpoint + dispatcher fallback decision. */
  health(): 'up' | 'down' {
    return this.up ? 'up' : 'down';
  }

  /** Phase 3: busy iff a turn is in flight (pool never evicts a busy backend). */
  isBusy(): boolean {
    return this.busy;
  }

  // ─── ensureSession: resolve resume id + (re)build the warm query ──────────────

  async ensureSession(sessionId: string, opts: EnsureSessionOpts): Promise<AgentSessionHandle> {
    // Resolve the resume token from the (chat_id, agent) row. A crashed row is not
    // resumed (the SDK would fail to load a dead session); we create fresh.
    const [row] = await this.sql<{ agent_session_id: string | null; status: string }[]>`
      SELECT agent_session_id, status FROM agent_sessions
      WHERE chat_id = ${opts.chatId} AND agent = ${opts.agent}
    `;
    const resumeId = row && row.status !== 'crashed' ? row.agent_session_id : null;

    // (Re)build the warm query if there is none, or the model changed (the SDK can
    // change model mid-session via setModel, but a fresh build is simplest + matches
    // opencode's config-drift → fresh-session rule). The query stays alive across
    // turns; only closeSession/dispose tears it down.
    if (!this.query || this.builtModel !== opts.model) {
      await this.teardownQuery();
      this.buildQuery(opts.worktreePath, opts.model, resumeId);
    }

    // Seed the in-memory resume id from the DB so a handle built before the first
    // turn's init message still carries the last-known token. The init message
    // overwrites it with the authoritative current id during the turn.
    if (this.agentSessionId == null) this.agentSessionId = resumeId;

    // Upsert the agent_sessions row (backend='claude_sdk'). agent_session_id may be
    // null until the first turn captures it from the init message; prompt() updates it.
    await this.sql`
      INSERT INTO agent_sessions
        (chat_id, session_id, worktree_id, agent, backend, agent_session_id, server_port, status, last_active_at)
      VALUES
        (${opts.chatId}, ${sessionId}, ${opts.worktreeId}, ${opts.agent}, 'claude_sdk', ${this.agentSessionId}, NULL, 'active', clock_timestamp())
      ON CONFLICT (chat_id, agent) DO UPDATE SET
        session_id = EXCLUDED.session_id,
        worktree_id = EXCLUDED.worktree_id,
        backend = 'claude_sdk',
        agent_session_id = COALESCE(EXCLUDED.agent_session_id, agent_sessions.agent_session_id),
        server_port = NULL,
        status = 'active',
        last_active_at = clock_timestamp()
    `.catch((err) => {
      this.log.warn({ err: errMsg(err), chatId: opts.chatId, agent: opts.agent }, 'claude-sdk: agent_sessions upsert failed (non-fatal)');
    });

    return {
      sessionId,
      agent: opts.agent,
      backend: 'claude_sdk',
      chatId: opts.chatId,
      worktreeId: opts.worktreeId,
      agentSessionId: this.agentSessionId,
      serverPort: null,
    };
  }

  /** Build the persistent query() in streaming-input mode. Lazy — no subprocess
   *  work happens until the generator is first iterated in prompt(). */
  private buildQuery(worktreePath: string, model: string, resumeId: string | null): void {
    const input = createPushable<SDKUserMessage>();
    const options: Options = {
      sessionStore: this.sessionStore,
      cwd: worktreePath,
      // Stream partial assistant messages so text/thinking/tool deltas arrive live
      // (the mapper reads them; without this only terminal messages land).
      includePartialMessages: true,
      ...(model ? { model } : {}),
      ...(resumeId ? { resume: resumeId } : {}),
      ...(this.installPath ? { pathToClaudeCodeExecutable: this.installPath } : {}),
      // ANTHROPIC auth/env must reach the child; inherit the process env (host concern).
      env: process.env as Record<string, string>,
    };
    this.input = input;
    this.query = query({ prompt: input.iterable, options });
    this.builtModel = model;
    this.up = true;
    this.log.info({ chatId: this.chatId, agent: this.agent, model, resume: resumeId ?? null }, 'claude-sdk: warm query built');
  }

  // ─── prompt: push one user message + drain the generator until result ─────────

  async prompt(handle: AgentSessionHandle, input: string, ctx: PromptCtx): Promise<TurnResult> {
    if (!this.query || !this.input) {
      // ensureSession should have built it; rebuild defensively (e.g. evicted/raced).
      this.buildQuery(ctx.worktreePath, ctx.model, handle.agentSessionId);
    }
    const gen = this.query!;
    const queue = this.input!;

    if (ctx.signal.aborted) return { ok: false, error: 'aborted' };

    this.busy = true;
    const state: ClaudeSdkMapState = createClaudeSdkMapState();
    // Per-turn abort: interrupt the in-flight query on the SAME generator (never
    // tear down the warm query — that's the pool's lifetime). The generator then
    // emits its terminal result and the drain loop exits.
    let aborted = false;
    const onAbort = () => {
      if (aborted) return;
      aborted = true;
      void gen.interrupt().catch(() => {});
    };
    ctx.signal.addEventListener('abort', onAbort, { once: true });

    // Push the turn's user message onto the open queue. session_id is optional on
    // the wire; the SDK manages it via resume + the init message.
    const userMsg: SDKUserMessage = {
      type: 'user',
      message: { role: 'user', content: input },
      parent_tool_use_id: null,
      ...(handle.agentSessionId ? { session_id: handle.agentSessionId } : {}),
    };
    queue.push(userMsg);

    try {
      for await (const msg of gen) {
        // Capture the provider session id from the init message (authoritative).
        if (msg.type === 'system' && msg.subtype === 'init' && msg.session_id) {
          if (this.agentSessionId !== msg.session_id) {
            this.agentSessionId = msg.session_id;
            await this.persistAgentSessionId(msg.session_id);
          }
        }
        // The result message ends THIS turn (it does not close the generator —
        // streaming-input keeps it alive for the next pushed message).
        if (msg.type === 'result') {
          await this.accumulateUsage(msg);
          const ok = msg.subtype === 'success' && !aborted;
          if (!ok) {
            // error_during_execution / error_max_turns / aborted → crashed row.
            await this.markCrashed();
          } else {
            await this.markIdle();
          }
          if (aborted) return { ok: false, error: 'aborted' };
          return ok
            ? { ok: true }
            : { ok: false, error: resultErrorMessage(msg) };
        }
        // Map renderable content → AgentEvents for the dispatcher's onEvent.
        for (const ev of mapSdkMessage(msg, state)) {
          ctx.onEvent(ev);
        }
      }
      // Generator ended without a result message (e.g. it was disposed) — treat as
      // a non-fatal incomplete turn so the dispatcher still finalizes the row.
      if (aborted) return { ok: false, error: 'aborted' };
      return { ok: false, error: 'claude-sdk: query ended before result' };
    } catch (err) {
      if (aborted) return { ok: false, error: 'aborted' };
      await this.markCrashed();
      return { ok: false, error: errMsg(err) };
    } finally {
      ctx.signal.removeEventListener('abort', onAbort);
      this.busy = false;
    }
  }

  // ─── persistence helpers ──────────────────────────────────────────────────────

  private async persistAgentSessionId(id: string): Promise<void> {
    await this.sql`
      UPDATE agent_sessions
      SET agent_session_id = ${id}, last_active_at = clock_timestamp()
      WHERE chat_id = ${this.chatId} AND agent = ${this.agent}
    `.catch((err) => {
      this.log.warn({ err: errMsg(err), chatId: this.chatId }, 'claude-sdk: failed to persist agent_session_id (non-fatal)');
    });
  }

  /**
   * Accumulate the turn's usage/cost onto the (chat_id, agent) row — mirrors the
   * opencode U.6 running-total pattern. The SDK reports usage once per turn on the
   * result message (not per step), so this fires once per prompt(). Cache read/write
   * input tokens fold into `input_tokens`; usage telemetry never fails a turn.
   */
  private async accumulateUsage(result: Extract<SDKMessage, { type: 'result' }>): Promise<void> {
    const u = result.usage;
    const input = num(u?.input_tokens) + num(u?.cache_read_input_tokens) + num(u?.cache_creation_input_tokens);
    const output = num(u?.output_tokens);
    const cost = numF(result.total_cost_usd);
    if (input === 0 && output === 0 && cost === 0) return;
    await this.sql`
      UPDATE agent_sessions SET
        input_tokens = input_tokens + ${input},
        output_tokens = output_tokens + ${output},
        cost = cost + ${cost}
      WHERE chat_id = ${this.chatId} AND agent = ${this.agent}
    `.catch((err) => {
      this.log.warn({ err: errMsg(err), chatId: this.chatId }, 'claude-sdk: failed to persist usage (non-fatal)');
    });
  }

  private async markIdle(): Promise<void> {
    await this.sql`
      UPDATE agent_sessions SET status = 'idle', last_active_at = clock_timestamp()
      WHERE chat_id = ${this.chatId} AND agent = ${this.agent}
    `.catch(() => {});
  }

  private async markCrashed(): Promise<void> {
    await this.sql`
      UPDATE agent_sessions SET status = 'crashed'
      WHERE chat_id = ${this.chatId} AND agent = ${this.agent}
    `.catch(() => {});
  }

  // ─── teardown ────────────────────────────────────────────────────────────────

  async closeSession(handle: AgentSessionHandle): Promise<void> {
    await this.teardownQuery();
    await this.sql`
      UPDATE agent_sessions SET status = 'closed'
      WHERE chat_id = ${handle.chatId} AND agent = ${handle.agent}
    `.catch(() => {});
  }

  async dispose(): Promise<void> {
    await this.teardownQuery();
  }

  /** Close the input queue + dispose the generator. Idempotent. */
  private async teardownQuery(): Promise<void> {
    this.up = false;
    this.busy = false;
    const q = this.query;
    const queue = this.input;
    this.query = null;
    this.input = null;
    this.builtModel = null;
    queue?.close();
    if (q) {
      // return() ends the AsyncGenerator and lets the SDK clean up its subprocess.
      await q.return(undefined).catch(() => {});
    }
  }
}

// ─── helpers ──────────────────────────────────────────────────────────────────

/** Coerce to a non-negative finite integer (tokens). */
function num(v: unknown): number {
  const x = typeof v === 'number' ? v : Number(v);
  return Number.isFinite(x) && x > 0 ? Math.round(x) : 0;
}

/** Coerce to a non-negative finite float (cost USD). */
function numF(v: unknown): number {
  const x = typeof v === 'number' ? v : Number(v);
  return Number.isFinite(x) && x > 0 ? x : 0;
}

/** Build a human-readable error from an SDK error-result message. */
function resultErrorMessage(result: Extract<SDKMessage, { type: 'result' }>): string {
  if (result.subtype === 'success') return 'ok';
  const errs = (result as { errors?: string[] }).errors;
  if (Array.isArray(errs) && errs.length > 0) return `${result.subtype}: ${errs.join('; ')}`;
  return result.subtype;
}

function errMsg(e: unknown): string {
  return e instanceof Error ? e.message : String(e);
}