/**
 * Filesystem-backed workflow store.
 *
 * Stores each run as `{basePath}/{runId}/run.json` and
 * `{basePath}/{runId}/events.jsonl`. Thread-safe writes use atomic
 * rename (write to temp file, then rename).
 */

import { mkdir, writeFile, readFile, readdir, rename, unlink } from 'node:fs/promises';
import { existsSync } from 'node:fs';
import { join } from 'node:path';
import { nanoid } from 'nanoid';

import type {
  IWorkflowStore,
  WorkflowRun,
  WorkflowEvent,
  WorkflowRunStatus,
  CreateWorkflowRunData,
} from '../engine/deps.js';

// ---------------------------------------------------------------------------
// Helpers
// ---------------------------------------------------------------------------

const ACTIVE_STATUSES: WorkflowRunStatus[] = ['pending', 'running'];

function parseRun(raw: string): WorkflowRun {
  const obj = JSON.parse(raw);
  return {
    ...obj,
    createdAt: new Date(obj.createdAt),
    updatedAt: new Date(obj.updatedAt),
  };
}

function serializeRun(run: WorkflowRun): string {
  return JSON.stringify(
    {
      ...run,
      createdAt: run.createdAt.toISOString(),
      updatedAt: run.updatedAt.toISOString(),
    },
    null,
    2,
  );
}

function parseEvent(line: string): WorkflowEvent {
  const obj = JSON.parse(line);
  return {
    ...obj,
    createdAt: new Date(obj.createdAt),
  };
}

function serializeEvent(event: WorkflowEvent): string {
  return JSON.stringify({
    ...event,
    createdAt: event.createdAt.toISOString(),
  });
}

// ---------------------------------------------------------------------------
// Atomic write helper
// ---------------------------------------------------------------------------

async function atomicWrite(filePath: string, data: string): Promise<void> {
  const tmp = `${filePath}.${nanoid(8)}.tmp`;
  await writeFile(tmp, data, 'utf-8');
  await rename(tmp, filePath);
}

// ---------------------------------------------------------------------------
// Factory
// ---------------------------------------------------------------------------

export function createFsStore(basePath: string): IWorkflowStore {
  // Ensure base directory exists on first write — no side effects at import.

  const store: IWorkflowStore = {
    // -- Run lifecycle -------------------------------------------------------

    async createWorkflowRun(data: CreateWorkflowRunData): Promise<WorkflowRun> {
      const id = nanoid();
      const now = new Date();
      const run: WorkflowRun = {
        id,
        workflowPath: data.workflowPath,
        workflowName: data.workflowName,
        status: 'pending',
        trigger: data.trigger,
        input: data.input,
        createdAt: now,
        updatedAt: now,
      };

      const runDir = join(basePath, id);
      await mkdir(runDir, { recursive: true });
      await atomicWrite(join(runDir, 'run.json'), serializeRun(run));
      // Create empty events file
      await atomicWrite(join(runDir, 'events.jsonl'), '');

      return run;
    },

    async getWorkflowRun(id: string): Promise<WorkflowRun | null> {
      const filePath = join(basePath, id, 'run.json');
      if (!existsSync(filePath)) return null;
      const raw = await readFile(filePath, 'utf-8');
      return parseRun(raw);
    },

    async updateWorkflowRun(
      id: string,
      data: Partial<WorkflowRun>,
    ): Promise<WorkflowRun> {
      const existing = await store.getWorkflowRun(id);
      if (!existing) throw new Error(`WorkflowRun not found: ${id}`);

      const updated: WorkflowRun = {
        ...existing,
        ...data,
        id: existing.id, // id is immutable
        updatedAt: new Date(),
      };

      await atomicWrite(
        join(basePath, id, 'run.json'),
        serializeRun(updated),
      );
      return updated;
    },

    async failWorkflowRun(id: string, error: string): Promise<WorkflowRun> {
      return store.updateWorkflowRun(id, {
        status: 'failed',
        error,
      } as Partial<WorkflowRun>);
    },

    async getWorkflowRunStatus(
      id: string,
    ): Promise<WorkflowRunStatus | null> {
      const run = await store.getWorkflowRun(id);
      return run?.status ?? null;
    },

    // -- Events --------------------------------------------------------------

    async createWorkflowEvent(
      event: Omit<WorkflowEvent, 'id' | 'createdAt'>,
    ): Promise<WorkflowEvent> {
      const full: WorkflowEvent = {
        ...event,
        id: nanoid(),
        createdAt: new Date(),
      };

      const eventsPath = join(basePath, event.runId, 'events.jsonl');
      // Ensure directory exists
      if (!existsSync(join(basePath, event.runId))) {
        await mkdir(join(basePath, event.runId), { recursive: true });
      }

      const line = serializeEvent(full) + '\n';
      // Append — not atomic for appends, but each line is self-contained
      const existing = existsSync(eventsPath)
        ? await readFile(eventsPath, 'utf-8').catch(() => '')
        : '';
      await atomicWrite(eventsPath, existing + line);

      return full;
    },

    async getCompletedDagNodeOutputs(
      runId: string,
    ): Promise<Record<string, Record<string, unknown>>> {
      const eventsPath = join(basePath, runId, 'events.jsonl');
      if (!existsSync(eventsPath)) return {};

      const raw = await readFile(eventsPath, 'utf-8');
      const lines = raw.split('\n').filter(Boolean);

      const outputs: Record<string, Record<string, unknown>> = {};
      for (const line of lines) {
        const event = parseEvent(line);
        if (event.type === 'node_complete' && event.nodeId && event.data?.output) {
          outputs[event.nodeId] = event.data.output as Record<string, unknown>;
        }
      }

      return outputs;
    },

    // -- Active runs ---------------------------------------------------------

    async getActiveWorkflowRunByPath(
      path: string,
      opts?: { excludeId?: string },
    ): Promise<WorkflowRun | null> {
      if (!existsSync(basePath)) return null;

      const entries = await readdir(basePath, { withFileTypes: true });
      for (const entry of entries) {
        if (!entry.isDirectory()) continue;
        const runPath = join(basePath, entry.name, 'run.json');
        if (!existsSync(runPath)) continue;

        const raw = await readFile(runPath, 'utf-8');
        const run = parseRun(raw);

        if (run.workflowPath !== path) continue;
        if (!ACTIVE_STATUSES.includes(run.status)) continue;
        if (opts?.excludeId && run.id === opts.excludeId) continue;

        return run;
      }

      return null;
    },

    // -- Codebase ------------------------------------------------------------

    async getCodebase(
      _id: string,
    ): Promise<Record<string, unknown> | null> {
      // Filesystem store does not persist codebase records
      return null;
    },

    async getCodebaseEnvVars(
      _id: string,
    ): Promise<Record<string, string>> {
      // Filesystem store does not persist codebase env vars
      return {};
    },

    // -- Resumption ----------------------------------------------------------

    async resumeWorkflowRun(id: string): Promise<WorkflowRun> {
      return store.updateWorkflowRun(id, {
        status: 'running',
      } as Partial<WorkflowRun>);
    },
  };

  return store;
}