import { describe, expect, it } from "vitest";
import { classicRegions, type PuzzleDefinition } from "../../src/domain";
import type { LogicalStep } from "../../src/solver";
import {
  applyLogicalStepToSession,
  autoRemoveNotesAfterPlacements,
  fillLegalCenterCandidates,
  pruneInvalidNotes,
} from "../../src/state/candidateMaintenance";
import { createSession, maskValues } from "../../src/state/session";

function puzzle4(): PuzzleDefinition {
  return {
    version: 1,
    size: 4,
    givens: new Array<number>(16).fill(0),
    regions: classicRegions(4),
    constraints: [],
  };
}

describe("candidate maintenance", () => {
  it("fills legal center candidates without changing corner notes or metadata", () => {
    const session = createSession(new Array<number>(16).fill(0));
    session.values[0] = 1;
    session.cornerMarks[1] = 0b1111;
    session.centerMarks[10] = 0b0010;
    session.colors[3] = 4;
    session.elapsedSeconds = 73;
    session.paused = true;

    const result = fillLegalCenterCandidates(session, puzzle4());

    expect(result).not.toBe(session);
    expect(result.centerMarks).not.toBe(session.centerMarks);
    expect(result.centerMarks[0]).toBe(0);
    expect(maskValues(result.centerMarks[1]!, 4)).toEqual([2, 3, 4]);
    expect(maskValues(result.centerMarks[10]!, 4)).toEqual([1, 2, 3, 4]);
    expect(result.cornerMarks[1]).toBe(0b1111);
    expect(result.colors[3]).toBe(4);
    expect(result.elapsedSeconds).toBe(73);
    expect(result.paused).toBe(true);
    expect(session.centerMarks[10]).toBe(0b0010);
  });

  it("only removes illegal center and corner notes", () => {
    const session = createSession(new Array<number>(16).fill(0));
    session.values[0] = 1;
    session.centerMarks.fill(0b1111);
    session.cornerMarks.fill(0b1111 | (1 << 8));

    const result = pruneInvalidNotes(session, puzzle4());

    expect(result.centerMarks[0]).toBe(0);
    expect(result.cornerMarks[0]).toBe(0);
    expect(maskValues(result.centerMarks[1]!, 4)).toEqual([2, 3, 4]);
    expect(maskValues(result.cornerMarks[4]!, 4)).toEqual([2, 3, 4]);
    expect(maskValues(result.centerMarks[10]!, 4)).toEqual([1, 2, 3, 4]);
    expect(result.cornerMarks[10]).toBe(0b1111);
    expect(session.cornerMarks[1]).toBe(0b1111 | (1 << 8));
  });

  it("auto-removes notes after placements but does not invent notes on erase", () => {
    const previous = createSession(new Array<number>(16).fill(0));
    previous.centerMarks.fill(0b1111);
    previous.cornerMarks.fill(0b1111);
    const placed = createSession(new Array<number>(16).fill(0));
    placed.centerMarks.fill(0b1111);
    placed.cornerMarks.fill(0b1111);
    placed.values[0] = 1;

    const maintained = autoRemoveNotesAfterPlacements(
      previous,
      placed,
      puzzle4(),
    );
    expect(maskValues(maintained.centerMarks[1]!, 4)).toEqual([2, 3, 4]);
    expect(maskValues(maintained.cornerMarks[4]!, 4)).toEqual([2, 3, 4]);
    expect(maintained.centerMarks[10]).toBe(0b1111);

    const erased = createSession(new Array<number>(16).fill(0));
    erased.centerMarks[1] = 0b0001;
    const previousFilled = createSession(new Array<number>(16).fill(0));
    previousFilled.values[0] = 1;
    const afterErase = autoRemoveNotesAfterPlacements(
      previousFilled,
      erased,
      puzzle4(),
    );
    expect(afterErase.centerMarks[1]).toBe(0b0001);
    expect(afterErase).not.toBe(erased);
  });

  it("applies a logical step to tracked candidates as one immutable transition", () => {
    const base = createSession(new Array<number>(16).fill(0));
    base.cornerMarks.fill(0b1111);
    base.colors[10] = 3;
    base.elapsedSeconds = 99;
    const session = fillLegalCenterCandidates(base, puzzle4());
    const step: LogicalStep = {
      technique: "naked-single",
      placements: [{ cell: 0, value: 1 }],
      eliminations: [{ cell: 10, values: [2] }],
      focusCells: [0, 10],
      explanation: "Test step",
    };

    const result = applyLogicalStepToSession(session, step, puzzle4());

    expect(result.values[0]).toBe(1);
    expect(result.centerMarks[0]).toBe(0);
    expect(result.cornerMarks[0]).toBe(0);
    expect(maskValues(result.centerMarks[1]!, 4)).toEqual([2, 3, 4]);
    expect(maskValues(result.centerMarks[10]!, 4)).toEqual([1, 3, 4]);
    expect(result.cornerMarks[1]).toBe(0b1111);
    expect(result.colors[10]).toBe(3);
    expect(result.elapsedSeconds).toBe(99);
    expect(session.values[0]).toBe(0);
    expect(session.centerMarks[10]).toBe(0b1111);
  });

  it("leaves absent tracked candidates absent and rejects stale steps", () => {
    const session = createSession(new Array<number>(16).fill(0));
    const elimination: LogicalStep = {
      technique: "pointing",
      placements: [],
      eliminations: [{ cell: 1, values: [1] }],
      focusCells: [1],
      explanation: "Test elimination",
    };
    expect(
      applyLogicalStepToSession(session, elimination, puzzle4()).centerMarks[1],
    ).toBe(0);

    session.values[0] = 2;
    const placement: LogicalStep = {
      ...elimination,
      placements: [{ cell: 0, value: 1 }],
      eliminations: [],
    };
    expect(() =>
      applyLogicalStepToSession(session, placement, puzzle4()),
    ).toThrow(/filled cell/u);
  });
});