import type { Simplify, ValueOf } from "type-fest";

type UnaryFn<T, R> = (shape: T) => R;

// ============================================================================
// ✔️ Exhaustive
// ❌ ReturnsStrict
// ============================================================================
type PatternPrimitiveUnion<R, T extends string | number> = {
    [K in T]: UnaryFn<K, R>;
};

type PatternReturns<
    P extends Record<string | number, UnaryFn<never, unknown>>,
> = ReturnType<ValueOf<P>>;

export const getPrimitiveUnionMatcherW: <T extends string | number>() => <
    P extends PatternPrimitiveUnion<unknown, T>,
>(
    pattern: Simplify<P>,
) => UnaryFn<T, PatternReturns<P>> = () => (pattern) => (shape) =>
    // Rewrite not to use any is possible, was evaluated and solutions were
    // more complex than the current solution.

    // oxlint-disable-next-line typescript/no-explicit-any typescript/no-unsafe-type-assertion
    (pattern[shape] as any)(shape);

// ============================================================================
// ✔️ Exhaustive
// ✔️ ReturnsStrict
// ============================================================================
export const getPrimitiveUnionMatcher: <T extends string | number>() => <R>(
    pattern: Simplify<PatternPrimitiveUnion<R, T>>,
) => UnaryFn<T, R> = getPrimitiveUnionMatcherW;

// ============================================================================
// ❌ Exhaustive
// ✔️ ReturnsStrict
// ============================================================================
type PatternPrimitiveUnionPartial<R, T extends string | number> =
    | PatternPrimitiveUnion<R, T>
    | (Partial<PatternPrimitiveUnion<R, T>> & {
          _: UnaryFn<T, R>;
      });

export const getPrimitiveUnionMatcherPartial: <T extends string | number>() => <
    R,
>(
    pattern: Simplify<PatternPrimitiveUnionPartial<R, T>>,
) => UnaryFn<T, R> = () => (pattern) => (shape) =>
    // Rewrite not to use any is possible, was evaluated and solutions were
    // more complex than the current solution.

    // oxlint-disable-next-line typescript/no-explicit-any typescript/no-unsafe-type-assertion
    (pattern[shape] ?? (pattern as any)["_"])(shape);

// ============================================================================
// ❌ Exhaustive
// ❌ ReturnsStrict
// ============================================================================
export const getPrimitiveUnionMatcherPartialW: <
    T extends string | number,
>() => <P extends PatternPrimitiveUnionPartial<unknown, T>>(
    // `Simplify<P>` is the inference hook: callers infer `P` from the argument.
    // the second half pins the impl parameter's `R` to `PatternReturns<P>`.
    // that makes the `= getPrimitiveUnionMatcherPartial` assignment type-check.
    // neither half works alone.
    // without the witness the union's `_` arm demands `_ ∈ keyof P`.
    // without `Simplify<P>` the parameter types do not compare.
    pattern: Simplify<P> & PatternPrimitiveUnionPartial<PatternReturns<P>, T>,
) => UnaryFn<T, PatternReturns<P>> = getPrimitiveUnionMatcherPartial;