// COMSOL 6.4 Java API method body
// Continue 3D parallel-plate capacitor model.
// Existing model variable is provided.

// 1. Identify existing component.
String cp = "comp1";
String[] existingComps = model.component().tags();
if (existingComps.length > 0) {
    cp = existingComps[0];
} else {
    model.component().create(cp, true);
}

model.component(cp).label("3D Parallel Plate Capacitor");

// 2. Global parameters.
model.param().set("capL", "100[mm]");
model.param().set("capW", "100[mm]");
model.param().set("capGap", "10[mm]");
model.param().set("capVolt", "100[V]");
model.param().set("capEpsR", "1");

// 3. Reuse or create 3D geometry.
String gt = "geom1";
String[] geoms = model.component(cp).geom().tags();

if (geoms.length > 0) {
    gt = geoms[0];
} else {
    model.component(cp).geom().create(gt, 3);
}

if (model.component(cp).geom(gt).getSDim() != 3) {
    throw new RuntimeException(
        "Existing geometry is not 3D; no changes made to it."
    );
}

model.component(cp).geom(gt).lengthUnit("mm");

String blk = "capAir";
if (!java.util.Arrays.asList(
    model.component(cp).geom(gt).feature().tags()
).contains(blk)) {
    model.component(cp).geom(gt).create(blk, "Block");
}

model.component(cp).geom(gt).feature(blk)
    .label("Air dielectric volume");

model.component(cp).geom(gt).feature(blk)
    .set("size", new String[]{
        "capL", "capW", "capGap"
    });

model.component(cp).geom(gt).feature(blk)
    .set("base", "center");

model.component(cp).geom(gt).feature(blk)
    .set("pos", new String[]{
        "0[mm]", "0[mm]", "capGap/2"
    });

model.component(cp).geom(gt).run();

// 4. Apply air material.
String mt = "capAirMat";
if (!java.util.Arrays.asList(
    model.component(cp).material().tags()
).contains(mt)) {
    model.component(cp).material().create(mt, "Common");
}

model.component(cp).material(mt).label("Air dielectric");
model.component(cp).material(mt).selection().all();

model.component(cp).material(mt).propertyGroup("def")
    .set("relpermittivity", new String[]{
        "capEpsR", "0", "0",
        "0", "capEpsR", "0",
        "0", "0", "capEpsR"
    });

// 5. Electrode boundary selections.
String sTop = "capTop";
String sBot = "capBottom";

String[] selectionTags =
    model.component(cp).selection().tags();

if (!java.util.Arrays.asList(selectionTags).contains(sTop)) {
    model.component(cp).selection().create(sTop, "Box");
}

if (!java.util.Arrays.asList(
    model.component(cp).selection().tags()
).contains(sBot)) {
    model.component(cp).selection().create(sBot, "Box");
}

model.component(cp).selection(sTop).label("Upper plate");
model.component(cp).selection(sBot).label("Lower plate");

model.component(cp).selection(sTop).geom(gt, 2);
model.component(cp).selection(sBot).geom(gt, 2);

for (String tag : new String[]{sTop, sBot}) {
    model.component(cp).selection(tag)
        .set("entitydim", 2);
    model.component(cp).selection(tag)
        .set("condition", "inside");
    model.component(cp).selection(tag)
        .set("xmin", -51);
    model.component(cp).selection(tag)
        .set("xmax", 51);
    model.component(cp).selection(tag)
        .set("ymin", -51);
    model.component(cp).selection(tag)
        .set("ymax", 51);
}

model.component(cp).selection(sTop)
    .set("zmin", 9.99);
model.component(cp).selection(sTop)
    .set("zmax", 10.01);

model.component(cp).selection(sBot)
    .set("zmin", -0.01);
model.component(cp).selection(sBot)
    .set("zmax", 0.01);

// 6. Electrostatics physics.
String pt = "es";

if (!java.util.Arrays.asList(
    model.component(cp).physics().tags()
).contains(pt)) {
    model.component(cp).physics()
        .create(pt, "Electrostatics", gt);
}

model.component(cp).physics(pt)
    .label("Electrostatics");

if (!java.util.Arrays.asList(
    model.component(cp).physics(pt).feature().tags()
).contains("capPot")) {
    model.component(cp).physics(pt)
        .create("capPot", "ElectricPotential", 2);
}

model.component(cp).physics(pt).feature("capPot")
    .label("Positive electrode 100 V");

model.component(cp).physics(pt).feature("capPot")
    .selection().named(sTop);

model.component(cp).physics(pt).feature("capPot")
    .set("V0", "capVolt");

if (!java.util.Arrays.asList(
    model.component(cp).physics(pt).feature().tags()
).contains("capGnd")) {
    model.component(cp).physics(pt)
        .create("capGnd", "Ground", 2);
}

model.component(cp).physics(pt).feature("capGnd")
    .label("Ground electrode 0 V");

model.component(cp).physics(pt).feature("capGnd")
    .selection().named(sBot);

// 7. Generate three-dimensional mesh.
String meshTag = "mesh1";

if (!java.util.Arrays.asList(
    model.component(cp).mesh().tags()
).contains(meshTag)) {
    model.component(cp).mesh().create(meshTag);
}

model.component(cp).mesh(meshTag)
    .label("Capacitor 3D mesh");

model.component(cp).mesh(meshTag).autoMeshSize(4);
model.component(cp).mesh(meshTag).run();

// 8. Stationary study.
String studyTag = "std1";

if (!java.util.Arrays.asList(
    model.study().tags()
).contains(studyTag)) {
    model.study().create(studyTag);
}

model.study(studyTag)
    .label("Stationary Electrostatics");

if (!java.util.Arrays.asList(
    model.study(studyTag).feature().tags()
).contains("stat")) {
    model.study(studyTag)
        .create("stat", "Stationary");
}

model.study(studyTag).feature("stat")
    .activate(pt, true);

// 9. Electric field magnitude visualization.
String pgE = "capField3D";

if (!java.util.Arrays.asList(
    model.result().tags()
).contains(pgE)) {
    model.result().create(pgE, "PlotGroup3D");
}

model.result(pgE)
    .label("Electric Field Magnitude (V/m)");

if (!java.util.Arrays.asList(
    model.result(pgE).feature().tags()
).contains("slc1")) {
    model.result(pgE).feature()
        .create("slc1", "Slice");
}

model.result(pgE).feature("slc1")
    .set("expr", pt + ".normE");

// 10. Electric potential visualization.
String pgV = "capPotential3D";

if (!java.util.Arrays.asList(
    model.result().tags()
).contains(pgV)) {
    model.result().create(pgV, "PlotGroup3D");
}

model.result(pgV)
    .label("Electric Potential (V)");

if (!java.util.Arrays.asList(
    model.result(pgV).feature().tags()
).contains("slc1")) {
    model.result(pgV).feature()
        .create("slc1", "Slice");
}

model.result(pgV).feature("slc1")
    .set("expr", "V");

// 11. Analytical verification reference.
model.param().set(
    "capEReference",
    "capVolt/capGap"
);

model.param().set(
    "capCReference",
    "epsilon0_const*capL*capW/capGap"
);

// 12. Completion diagnostics.
System.out.println("COMSOL capacitor setup completed.");
System.out.println("Component: " + cp);
System.out.println("Geometry: " + gt);
System.out.println("Physics: " + pt);
System.out.println("Study: " + studyTag);
System.out.println("3D geometry and mesh built.");
System.out.println("Upper electrode: 100 V");
System.out.println("Lower electrode: 0 V");
System.out.println("Expected electric field: 10000 V/m");
System.out.println("Expected capacitance: 8.854 pF");
System.out.println("No solver run was requested.");