/**
 * Binding service — links EvidenceItems to structured targets.
 *
 * Implements `wiki/ArchitectureOverview.md` §4.6 + SharedContracts §2.4
 * (status enum), §2.5 (relation enum). Emits §4 events:
 * `EvidenceLinkCreated`, `EvidenceLinkUpdated`, `EvidenceItemActivated`.
 *
 * MVP semantics:
 *   - `linkEvidenceToTarget` defaults `relation="supports"`, `status="candidate"`.
 *   - `unlinkEvidence` is hard-delete; the rejected-status path is left to
 *     a later ADR.
 *   - `setActiveEvidence` emits an `EvidenceItemActivated` event with
 *     `source="form-field"` so the viewer/sidebar can react.
 */

import type {
  EvidenceLink,
  EvidenceLinkStoredStatus,
  EvidenceRelation,
  EvidenceTarget,
} from "@citation-evidence/engine/shared";
import type { EvidenceItemId, EvidenceLinkId } from "@citation-evidence/engine/shared";
import { newId } from "@citation-evidence/engine/shared";

import type { EventBus } from "@citation-evidence/engine";

import type { EvidenceLinkRepository } from "../repos/in-memory-links";

export interface LinkEvidenceToTargetInput {
  readonly evidenceItemId: EvidenceItemId;
  readonly target: EvidenceTarget;
  readonly relation?: EvidenceRelation;
  readonly status?: EvidenceLinkStoredStatus;
  readonly confidence?: number;
  readonly createdBy?: string;
}

export interface UpdateLinkStatusInput {
  readonly status?: EvidenceLinkStoredStatus;
  readonly relation?: EvidenceRelation;
  readonly confidence?: number;
}

export interface BindingService {
  linkEvidenceToTarget(input: LinkEvidenceToTargetInput): EvidenceLink;
  unlinkEvidence(id: EvidenceLinkId): boolean;
  updateLink(id: EvidenceLinkId, input: UpdateLinkStatusInput): EvidenceLink;
  getLink(id: EvidenceLinkId): EvidenceLink | null;
  listEvidenceForTarget(target: EvidenceTarget): readonly EvidenceLink[];
  listTargetsForEvidence(evidenceItemId: EvidenceItemId): readonly EvidenceLink[];
  setActiveEvidence(evidenceItemId: EvidenceItemId): void;
}

export function createBindingService(
  links: EvidenceLinkRepository,
  bus: EventBus,
  now: () => string = () => new Date().toISOString(),
): BindingService {
  return {
    linkEvidenceToTarget(input) {
      const ts = now();
      const link: EvidenceLink = {
        id: newId("evidence-link"),
        evidenceItemId: input.evidenceItemId,
        targetType: input.target.targetType,
        targetId: input.target.targetId,
        relation: input.relation ?? "supports",
        status: input.status ?? "candidate",
        ...(input.confidence !== undefined ? { confidence: input.confidence } : {}),
        ...(input.createdBy !== undefined ? { createdBy: input.createdBy } : {}),
        createdAt: ts,
        updatedAt: ts,
      };
      const stored = links.create(link);
      bus.emit({ type: "EvidenceLinkCreated", linkId: stored.id, link: stored });
      return stored;
    },
    unlinkEvidence(id) {
      const removed = links.delete(id);
      if (removed) {
        bus.emit({ type: "EvidenceLinkRemoved", linkId: id });
      }
      return removed;
    },
    updateLink(id, input) {
      const existing = links.get(id);
      if (!existing) {
        throw new Error(`BindingService.updateLink: unknown id ${id}`);
      }
      const next: EvidenceLink = {
        ...existing,
        ...(input.status !== undefined ? { status: input.status } : {}),
        ...(input.relation !== undefined ? { relation: input.relation } : {}),
        ...(input.confidence !== undefined ? { confidence: input.confidence } : {}),
        updatedAt: now(),
      };
      const stored = links.update(next);
      bus.emit({ type: "EvidenceLinkUpdated", linkId: stored.id, link: stored });
      return stored;
    },
    getLink(id) {
      return links.get(id);
    },
    listEvidenceForTarget(target) {
      return links.listForTarget(target);
    },
    listTargetsForEvidence(evidenceItemId) {
      return links.listForEvidenceItem(evidenceItemId);
    },
    setActiveEvidence(evidenceItemId) {
      bus.emit({
        type: "EvidenceItemActivated",
        evidenceItemId,
        source: "form-field",
      });
    },
  };
}