/**
 * KHAELOR
 * File: src/phases/state.ts
 * Description: Pure fold of phase events into the current phase-gate state (v2 design §1).
 *
 * Author: Simon-Pierre Boucher
 * Contact: contact@spboucher.ai
 */

import type { DesignArtifact, DurableEvent, Phase } from "../session/index.js";

export interface PhaseState {
  /** Current phase; sessions without any phase event are in "understand". */
  phase: Phase;
  /** Artifact submitted but not yet approved/rejected. */
  pendingArtifact: { artifactId: string; artifact: DesignArtifact } | null;
  /** The artifact id whose approval unlocked implement, when one exists. */
  approvedArtifactId: string | null;
  /** True once a phase.approved{phase:"design"} exists in the session. */
  designApproved: boolean;
}

/** Fold the durable stream into the phase-gate decision state. */
export function foldPhaseState(events: readonly DurableEvent[]): PhaseState {
  let phase: Phase = "understand";
  let pending: PhaseState["pendingArtifact"] = null;
  let approvedArtifactId: string | null = null;
  let designApproved = false;

  for (const event of events) {
    switch (event.type) {
      case "phase.entered":
        phase = event.payload.phase;
        break;
      case "phase.artifact":
        pending = { artifactId: event.payload.artifactId, artifact: event.payload.artifact };
        break;
      case "phase.approved":
        if (event.payload.phase === "design") {
          designApproved = true;
          approvedArtifactId = event.payload.artifactId ?? pending?.artifactId ?? null;
          pending = null;
        }
        break;
      case "phase.rejected":
        pending = null;
        break;
      default:
        break;
    }
  }

  return { phase, pendingArtifact: pending, approvedArtifactId, designApproved };
}