import { createReadStream, mkdirSync, readFileSync, renameSync, writeFileSync } from "node:fs";
import path from "node:path";
import { fileURLToPath } from "node:url";
import { createBalanceLabJobService } from "./balance-lab-jobs.mjs";
import { cloneDefaultCompanionCooldownPolicy } from "./companion-cooldown-policy.mjs";
import {
  cloneDefaultCompanionSpecReadinessPolicy,
  normalizeCompanionSpecReadinessPolicy,
} from "./companion-spec-readiness.mjs";
import { GameDatabaseError } from "./database.mjs";

const API_ROOT = "/api/local/balance-lab";

function json(response, status, body) {
  const content = Buffer.from(JSON.stringify(body));
  response.writeHead(status, {
    "Content-Type": "application/json; charset=utf-8",
    "Content-Length": content.length,
    "Cache-Control": "no-store",
  });
  response.end(content);
}

async function readJson(request, limit) {
  const chunks = [];
  let size = 0;
  for await (const chunk of request) {
    size += chunk.length;
    if (size > limit) throw new GameDatabaseError("Request body is too large.", 413, "body_too_large");
    chunks.push(chunk);
  }
  if (size === 0) return {};
  try {
    return JSON.parse(Buffer.concat(chunks).toString("utf8"));
  } catch {
    throw new GameDatabaseError("Request body must be valid JSON.", 400, "invalid_json");
  }
}

function isLoopback(address) {
  return address === "127.0.0.1" || address === "::1" || address === "::ffff:127.0.0.1";
}

export function createLocalBalanceLabApi(options = {}) {
  const projectRoot = path.resolve(options.projectRoot ?? fileURLToPath(new URL("..", import.meta.url)));
  const dataDir = path.resolve(options.dataDir ?? path.join(projectRoot, "artifacts", "balance-lab-gui-runtime"));
  const readinessPath = path.join(dataDir, "companion-spec-readiness.json");
  mkdirSync(dataDir, { recursive: true });
  let readiness = { revision: 0, updatedAt: null, updatedBy: null, config: cloneDefaultCompanionSpecReadinessPolicy() };
  try {
    const stored = JSON.parse(readFileSync(readinessPath, "utf8"));
    readiness = {
      revision: Number.isInteger(stored.revision) ? stored.revision : 0,
      updatedAt: Number.isFinite(stored.updatedAt) ? stored.updatedAt : null,
      updatedBy: typeof stored.updatedBy === "string" ? stored.updatedBy : null,
      config: normalizeCompanionSpecReadinessPolicy(stored.config),
    };
  } catch { /* missing or corrupt local policy falls back to shipped defaults */ }
  const persistReadiness = () => {
    const temporaryPath = `${readinessPath}.tmp`;
    writeFileSync(temporaryPath, `${JSON.stringify(readiness, null, 2)}\n`, "utf8");
    renameSync(temporaryPath, readinessPath);
  };
  const service = createBalanceLabJobService({
    dataDir,
    projectRoot,
    pythonExecutable: options.pythonExecutable,
    spawnProcess: options.spawnProcess,
    runtimeProbe: options.runtimeProbe,
    maxConcurrent: options.maxConcurrent,
    maxQueued: options.maxQueued,
    cooldownPolicyProvider: () => ({ config: cloneDefaultCompanionCooldownPolicy() }),
    readinessPolicyProvider: () => readiness,
  });
  const account = Object.freeze({ username: "Local GUI" });

  return {
    service,
    async handle(request, response) {
      const url = new URL(request.url ?? "/", "http://127.0.0.1");
      if (url.pathname !== API_ROOT && !url.pathname.startsWith(`${API_ROOT}/`)) return false;
      if (!isLoopback(request.socket?.remoteAddress)) {
        json(response, 403, { error: "The local Balance Lab API accepts loopback requests only.", code: "loopback_required" });
        return true;
      }
      try {
        if (url.pathname === `${API_ROOT}/companion-spec-readiness` && request.method === "GET") {
          json(response, 200, readiness);
          return true;
        }
        if (url.pathname === `${API_ROOT}/companion-spec-readiness` && request.method === "PUT") {
          const body = await readJson(request, 256 * 1024);
          if (!Number.isInteger(body.expectedRevision) || body.expectedRevision !== readiness.revision) {
            throw new GameDatabaseError("The companion readiness policy changed. Reload and try again.", 409, "revision_conflict");
          }
          let config;
          try {
            config = normalizeCompanionSpecReadinessPolicy(body.config);
          } catch (error) {
            throw new GameDatabaseError(
              error instanceof Error ? error.message : "Invalid companion readiness policy.",
              400,
              "invalid_companion_spec_readiness",
            );
          }
          readiness = {
            revision: readiness.revision + 1,
            updatedAt: Date.now(),
            updatedBy: "Local GUI",
            config,
          };
          persistReadiness();
          json(response, 200, readiness);
          return true;
        }
        if (url.pathname === `${API_ROOT}/jobs` && request.method === "GET") {
          json(response, 200, { jobs: service.list() });
          return true;
        }
        if (url.pathname === `${API_ROOT}/runtime` && request.method === "GET") {
          json(response, 200, { runtime: service.runtime() });
          return true;
        }
        if (url.pathname === `${API_ROOT}/jobs/batch` && request.method === "POST") {
          json(response, 202, { jobs: service.startMany(await readJson(request, 4 * 1024 * 1024), account) });
          return true;
        }
        if (url.pathname === `${API_ROOT}/jobs` && request.method === "POST") {
          json(response, 202, { job: service.start(await readJson(request, 32 * 1024), account) });
          return true;
        }
        const artifactMatch = new RegExp(`^${API_ROOT}/jobs/([0-9a-f-]{36})/artifacts/([A-Za-z0-9._-]+)$`).exec(url.pathname);
        if (artifactMatch && request.method === "GET") {
          const artifact = service.artifact(artifactMatch[1], artifactMatch[2]);
          response.writeHead(200, {
            "Content-Type": artifact.contentType,
            "Content-Length": artifact.size,
            "Cache-Control": "no-store",
            "Content-Disposition": `inline; filename="${artifactMatch[2]}"`,
            "X-Content-Type-Options": "nosniff",
          });
          createReadStream(artifact.filePath).pipe(response);
          return true;
        }
        const jobMatch = new RegExp(`^${API_ROOT}/jobs/([0-9a-f-]{36})$`).exec(url.pathname);
        if (jobMatch && request.method === "GET") {
          json(response, 200, { job: service.get(jobMatch[1]) });
          return true;
        }
        json(response, 404, { error: "Local Balance Lab route not found.", code: "not_found" });
      } catch (error) {
        const known = error instanceof GameDatabaseError;
        json(response, known ? error.status : 500, {
          error: known ? error.message : "The local Balance Lab request failed.",
          code: known ? error.code : "internal_error",
        });
      }
      return true;
    },
    close() {
      service.close();
    },
  };
}