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machine.js

const assessmentMachine = Machine(
  {
    id: "assessment",
    initial: "phq9_1",
    context: {
      phq9: 0,
      gad7: 0,
      mhq: false,
      answers: []
    },
    on: {
      PHQ9: {
        actions: ["addPHQ9", raise("NEXT")]
      },
      GAD7: {
        actions: ["addGAD7", raise("NEXT")]
      },
      MHQ: {
        actions: ["addMHQ", raise("NEXT")]
      }
    },
    states: {
      phq9_1: {
        on: {
          NEXT: "phq9_2"
        }
      },
      phq9_2: {
        on: {
          NEXT: [
            {
              target: "phq9_3",
              cond: "isPHQ2High"
            },
            { target: "gad7_1" }
          ]
        }
      },
      phq9_3: {
        on: {
          NEXT: "therapy"
        }
      },
      gad7_1: {
        on: {
          NEXT: "gad7_2"
        }
      },
      gad7_2: {
        on: {
          NEXT: [
            {
              cond: "isGAD2High",
              target: "gad7_3"
            },
            { target: "mhq_1" }
          ]
        }
      },
      gad7_3: {
        on: {
          NEXT: "therapy"
        }
      },
      mhq_1: {
        on: {
          NEXT: [
            {
              cond: "isMHQ",
              target: "exclusion"
            },
            {
              target: "coaching"
            }
          ]
        }
      },
      exclusion: { type: "final" },
      coaching: { type: "final" },
      therapy: { type: "final" }
    }
  },
  {
    actions: {
      addPHQ9: assign({
        phq9: (ctx, e) => ctx.phq9 + e.answer,
        answers: (ctx, e) => [
          ...ctx.answers,
          { question: e.question, answer: e.answer }
        ]
      }),
      addGAD7: assign({
        gad7: (ctx, e) => ctx.gad7 + e.answer,
        answers: (ctx, e) => [
          ...ctx.answers,
          { question: e.question, answer: e.answer }
        ]
      }),
      addMHQ: assign({
        mhq: (ctx, e) => Boolean(ctx.mhq || e.answer === "yes"),
        answers: (ctx, e) => [
          ...ctx.answers,
          { question: e.question, answer: e.answer }
        ]
      })
    },
    guards: {
      isPHQ2High: (ctx) => ctx.phq9 > 2,
      isGAD2High: (ctx) => ctx.gad7 > 2,
      isMHQ: (ctx) => ctx.mhq
    }
  }
);