import * as Context from "effect/Context";
import * as Clock from "effect/Clock";
import * as Duration from "effect/Duration";
import * as Effect from "effect/Effect";
import * as Layer from "effect/Layer";
import * as Option from "effect/Option";
import * as Schedule from "effect/Schedule";
import type * as Scope from "effect/Scope";

import * as ProjectionSnapshotQuery from "../orchestration/Services/ProjectionSnapshotQuery.ts";
import * as ProviderService from "./ProviderService.ts";
import * as ProviderSessionDirectory from "./ProviderSessionDirectory.ts";

export class ProviderSessionReaper extends Context.Service<
  ProviderSessionReaper,
  {
    /** Start the background provider session reaper within the provided scope. */
    readonly start: () => Effect.Effect<void, never, Scope.Scope>;
  }
>()("t3/provider/ProviderSessionReaper") {}

const DEFAULT_INACTIVITY_THRESHOLD_MS = 30 * 60 * 1000;
const DEFAULT_SWEEP_INTERVAL_MS = 5 * 60 * 1000;

export interface ProviderSessionReaperOptions {
  readonly inactivityThresholdMs?: number;
  readonly sweepIntervalMs?: number;
}

export const make = (options?: ProviderSessionReaperOptions) =>
  Effect.gen(function* () {
    const providerService = yield* ProviderService.ProviderService;
    const directory = yield* ProviderSessionDirectory.ProviderSessionDirectory;
    const projectionSnapshotQuery = yield* ProjectionSnapshotQuery.ProjectionSnapshotQuery;

    const inactivityThresholdMs = Math.max(
      1,
      options?.inactivityThresholdMs ?? DEFAULT_INACTIVITY_THRESHOLD_MS,
    );
    const sweepIntervalMs = Math.max(1, options?.sweepIntervalMs ?? DEFAULT_SWEEP_INTERVAL_MS);

    const sweep = Effect.gen(function* () {
      const bindings = yield* directory.listBindings();
      const now = yield* Clock.currentTimeMillis;
      let reapedCount = 0;

      for (const binding of bindings) {
        if (binding.status === "stopped") {
          continue;
        }

        const lastSeenMs = Date.parse(binding.lastSeenAt);
        if (Number.isNaN(lastSeenMs)) {
          yield* Effect.logWarning("provider.session.reaper.invalid-last-seen", {
            threadId: binding.threadId,
            provider: binding.provider,
            lastSeenAt: binding.lastSeenAt,
          });
          continue;
        }

        const idleDurationMs = now - lastSeenMs;
        if (idleDurationMs < inactivityThresholdMs) {
          continue;
        }

        const thread = yield* projectionSnapshotQuery
          .getThreadShellById(binding.threadId)
          .pipe(Effect.map(Option.getOrUndefined));
        if (thread?.session?.activeTurnId != null) {
          yield* Effect.logDebug("provider.session.reaper.skipped-active-turn", {
            threadId: binding.threadId,
            activeTurnId: thread.session.activeTurnId,
            idleDurationMs,
          });
          continue;
        }

        const reaped = yield* providerService.stopSession({ threadId: binding.threadId }).pipe(
          Effect.tap(() =>
            Effect.logInfo("provider.session.reaped", {
              threadId: binding.threadId,
              provider: binding.provider,
              idleDurationMs,
              reason: "inactivity_threshold",
            }),
          ),
          Effect.as(true),
          Effect.catchCause((cause) =>
            Effect.logWarning("provider.session.reaper.stop-failed", {
              threadId: binding.threadId,
              provider: binding.provider,
              idleDurationMs,
              cause,
            }).pipe(Effect.as(false)),
          ),
        );

        if (reaped) {
          reapedCount += 1;
        }
      }

      if (reapedCount > 0) {
        yield* Effect.logInfo("provider.session.reaper.sweep-complete", {
          reapedCount,
          totalBindings: bindings.length,
        });
      }
    });

    const start: ProviderSessionReaper["Service"]["start"] = () =>
      Effect.gen(function* () {
        yield* Effect.forkScoped(
          sweep.pipe(
            Effect.catch((error: unknown) =>
              Effect.logWarning("provider.session.reaper.sweep-failed", { error }),
            ),
            Effect.catchDefect((defect: unknown) =>
              Effect.logWarning("provider.session.reaper.sweep-defect", { defect }),
            ),
            Effect.repeat(Schedule.spaced(Duration.millis(sweepIntervalMs))),
          ),
        );

        yield* Effect.logInfo("provider.session.reaper.started", {
          inactivityThresholdMs,
          sweepIntervalMs,
        });
      });

    return ProviderSessionReaper.of({ start });
  });

export const layer = Layer.effect(ProviderSessionReaper, make());