import { Injectable, computed, inject, signal } from '@angular/core';
import type { FileEntry, TransferSnapshot } from '@shared/types';
import { DialogsService } from './dialogs.service';
import { PanelsService, type Side } from './panels.service';
import { RpcService } from './rpc.service';
import { SettingsService } from './settings.service';
import { ToastService } from './toast.service';

const AUTO_DISMISS_COMPLETED_MS = 5000;
const ACTIVE_STATES = ['queued', 'scanning', 'running'];
// EMA smoothing for the displayed transfer speed
const SPEED_SMOOTHING = 0.7;

@Injectable({ providedIn: 'root' })
export class TransfersService {
  private readonly rpc = inject(RpcService);
  private readonly panels = inject(PanelsService);
  private readonly toast = inject(ToastService);
  private readonly dialogs = inject(DialogsService);
  private readonly settings = inject(SettingsService);

  private readonly jobMap = signal<ReadonlyMap<string, TransferSnapshot>>(new Map());
  /** Smoothed bytes/sec per running job (UI-computed from progress deltas). */
  readonly speeds = signal<ReadonlyMap<string, number>>(new Map());
  private speedTrack = new Map<string, { bytes: number; time: number; speed: number }>();
  readonly jobs = computed(() => [...this.jobMap().values()]);
  readonly hasJobs = computed(() => this.jobMap().size > 0);
  readonly activeJobs = computed(() => this.jobs().filter((j) => ACTIVE_STATES.includes(j.state)));
  readonly currentJob = computed(
    () => this.jobs().find((j) => j.state === 'running' || j.state === 'scanning') ?? null,
  );
  readonly queuedCount = computed(() => this.jobs().filter((j) => j.state === 'queued').length);
  readonly failedJobs = computed(() => this.jobs().filter((j) => j.state === 'failed'));
  readonly finishedJobs = computed(() => this.jobs().filter((j) => !ACTIVE_STATES.includes(j.state)));

  /** Whether the detailed per-job list is shown (toggled from the status bar). */
  readonly expanded = signal(false);

  constructor() {
    if (this.rpc.available) {
      this.rpc.onTransferUpdate((snapshot) => this.apply(snapshot));
    }
  }

  /** Copy the given panel's targets into the other panel's cwd (F5 / toolbar). */
  async copyToOtherPanel(fromSide: Side): Promise<void> {
    const src = this.panels.get(fromSide);
    const dst = this.panels.other(fromSide);

    const selected = src.selectedEntries();
    const atCursor = src.sorted()[src.cursor()];
    const targets = (selected.length ? selected : atCursor ? [atCursor] : []).filter(
      (e) => e.type !== 'symlink' && e.name !== '..',
    );
    if (!targets.length) {
      this.toast.info('Nothing to copy (symlinks are skipped)');
      return;
    }
    const sameFs = src.fsKey() === dst.fsKey();
    if (sameFs && src.cwd() === dst.cwd()) {
      this.toast.info('Both panels show the same folder');
      return;
    }

    const finalTargets = await this.resolveCollisions(targets, dst.entries(), sameFs);
    if (finalTargets === null) return; // user cancelled
    if (!finalTargets.length) {
      this.toast.info('Nothing to copy — all conflicting items were skipped');
      return;
    }

    const res = await this.rpc.request.enqueueTransfers({
      srcSessionId: src.sessionId(),
      items: finalTargets.map(({ path, type }) => ({ path, type })),
      dstSessionId: dst.sessionId(),
      dstDir: dst.cwd(),
    });
    if (!res.ok) this.toast.error(res.error);
  }

  /**
   * Confirm name collisions with the destination listing one by one.
   * Returns the approved target list, or null if the user cancelled.
   */
  private async resolveCollisions(
    targets: FileEntry[],
    dstEntries: FileEntry[],
    sameFs: boolean,
  ): Promise<FileEntry[] | null> {
    const dstByName = new Map(dstEntries.map((e) => [e.name, e]));
    const collisions = targets.filter((t) => {
      const dst = dstByName.get(t.name);
      return dst && (dst.type === 'dir') === (t.type === 'dir');
    });

    let mode: 'ask' | 'all' | 'none' = 'ask';
    let asked = 0;
    const finalTargets: FileEntry[] = [];

    for (const target of targets) {
      const dstEntry = dstByName.get(target.name);
      if (!dstEntry) {
        finalTargets.push(target);
        continue;
      }
      if (sameFs && dstEntry.path === target.path) {
        // replacing a file with ITSELF would only destroy it — never offer that
        this.toast.info(`Skipped "${target.name}" — it is the same file`);
        continue;
      }
      if ((dstEntry.type === 'dir') !== (target.type === 'dir')) {
        this.toast.info(`Skipped "${target.name}" — a different kind of item is in the way`);
        continue;
      }
      if (mode === 'all') {
        finalTargets.push(target);
        continue;
      }
      if (mode === 'none') continue;

      const choice = await this.dialogs.askOverwrite({
        srcEntry: target,
        dstEntry,
        index: ++asked,
        total: collisions.length,
      });
      if (choice === 'cancel') return null;
      if (choice === 'overwriteAll') {
        mode = 'all';
        finalTargets.push(target);
      } else if (choice === 'skipAll') {
        mode = 'none';
      } else if (choice === 'overwrite') {
        finalTargets.push(target);
      }
    }
    return finalTargets;
  }

  async cancel(jobId: string): Promise<void> {
    await this.rpc.request.cancelTransfer({ jobId });
  }

  /** Remove every finished (completed/failed/cancelled) entry; running ones stay. */
  clearFinished(): void {
    for (const job of this.finishedJobs()) {
      void this.dismiss(job.id);
    }
  }

  async dismiss(jobId: string): Promise<void> {
    this.jobMap.update((prev) => {
      const next = new Map(prev);
      next.delete(jobId);
      return next;
    });
    this.speedTrack.delete(jobId);
    this.speeds.update((prev) => {
      const next = new Map(prev);
      next.delete(jobId);
      return next;
    });
    await this.rpc.request.dismissTransfer({ jobId });
  }

  private apply(snapshot: TransferSnapshot): void {
    const previous = this.jobMap().get(snapshot.id);
    this.jobMap.update((prev) => new Map(prev).set(snapshot.id, snapshot));
    this.trackSpeed(snapshot);

    const justFinished = previous?.state !== snapshot.state;
    if (!justFinished) return;

    if (snapshot.state === 'completed') {
      this.refreshPanelsOn(snapshot.dstSessionId);
      if (this.settings.autoClearCompleted()) {
        setTimeout(() => void this.dismiss(snapshot.id), AUTO_DISMISS_COMPLETED_MS);
      }
    } else if (snapshot.state === 'failed') {
      this.expanded.set(true);
      this.toast.error(`Transfer "${snapshot.name}" failed: ${snapshot.error ?? 'unknown error'}`);
      this.refreshPanelsOn(snapshot.dstSessionId);
    } else if (snapshot.state === 'cancelled') {
      this.refreshPanelsOn(snapshot.dstSessionId);
    }
  }

  private refreshPanelsOn(sessionId: string): void {
    for (const panel of this.panels.allPanels()) {
      if (panel.sessionId() === sessionId) void panel.refresh();
    }
  }

  private trackSpeed(snapshot: TransferSnapshot): void {
    if (snapshot.state !== 'running') {
      if (snapshot.state !== 'queued' && snapshot.state !== 'scanning') {
        this.speedTrack.delete(snapshot.id);
      }
      return;
    }
    const now = performance.now();
    const prev = this.speedTrack.get(snapshot.id);
    if (!prev) {
      this.speedTrack.set(snapshot.id, { bytes: snapshot.doneBytes, time: now, speed: 0 });
      return;
    }
    const dt = (now - prev.time) / 1000;
    if (dt < 0.2) return; // wait for a meaningful window
    const instant = Math.max(0, (snapshot.doneBytes - prev.bytes) / dt);
    const speed = prev.speed ? SPEED_SMOOTHING * prev.speed + (1 - SPEED_SMOOTHING) * instant : instant;
    this.speedTrack.set(snapshot.id, { bytes: snapshot.doneBytes, time: now, speed });
    this.speeds.update((map) => new Map(map).set(snapshot.id, speed));
  }
}