purchases-ios/Sources/RulesEngine/Operators/MinMaxOperators.swift

//
//  MinMaxOperators.swift
//
//  Created by Antonio Pallares.
//

import Foundation

extension RulesEngine {

    /// Numeric extrema: `min`, `max`.
    ///
    /// Variadic over a flat list of values (`{"max": [v1, v2, ...]}` /
    /// `{"min": [v1, v2, ...]}`), matching JS `Math.max` / `Math.min`. Each
    /// operand goes through `Value.asNumber` (JS `Number()`), so
    /// single-element arrays bridge to a number via `toString`
    /// (`Math.max(1, [2]) === 2`); multi-element arrays, objects, and
    /// unparseable strings become `Double.nan` and poison the result.
    ///
    /// Empty input mirrors `Math.max()` / `Math.min()`: `max` → `-∞`,
    /// `min` → `+∞`.
    enum MinMaxOperators {

        /// `{"max": [v1, v2, ...]}` — variadic numeric maximum.
        static func opMax(args: Value, vars: Scope) throws -> Value {
            try reduceExtremum(args, vars: vars, empty: -.infinity) { Swift.max($0, $1) }
        }

        /// `{"min": [v1, v2, ...]}` — variadic numeric minimum.
        static func opMin(args: Value, vars: Scope) throws -> Value {
            try reduceExtremum(args, vars: vars, empty: .infinity) { Swift.min($0, $1) }
        }

        /// Evaluate each operand to a `Double` (non-numeric → `nan`) and fold
        /// it into a single extremum in one pass. `empty` is the no-operand
        /// result (`Math.max()` → `-∞`, `Math.min()` → `+∞`); any `nan`
        /// operand poisons the accumulator, mirroring `Math.max` / `Math.min`.
        private static func reduceExtremum(
            _ args: Value,
            vars: Scope,
            empty: Double,
            combine: (Double, Double) -> Double
        ) throws -> Value {
            let result = try Operators.evalArgs(args, vars: vars).reduce(empty) { accumulator, value in
                let number = value.asNumber ?? .nan
                guard !accumulator.isNaN, !number.isNaN else { return .nan }
                return combine(accumulator, number)
            }
            return .float(result)
        }
    }
}