//
//  StringArrayOperators.swift
//
//  Created by Antonio Pallares.
//

import Foundation

extension RulesEngine {

    /// String + array operators: `in`, `cat`, `substr`, `merge`.
    ///
    /// Behavior follows the JSON Logic JS reference (`json-logic-js`).
    /// `substr` slices by Unicode code points, not UTF-16 code units —
    /// matches Swift's `String.Character` semantics; differs from JS only
    /// for surrogate-pair characters.
    enum StringArrayOperators {

        /// `{"in": [needle, haystack]}` — substring or array-membership
        /// test. For a `.string` haystack, the needle is stringified and
        /// the test is substring containment (mirrors JS
        /// `String.prototype.indexOf`); when the haystack is falsy,
        /// json-logic-js returns false immediately
        /// (`if (!haystack) return false`), so an empty string never matches.
        /// For an `.array` haystack, the test is strict element equality
        /// (mirrors JS `Array.prototype.indexOf`, which uses `===`). Any
        /// other haystack type returns `false`. `json-logic-js` implements
        /// `in` as `function(a, b)` (needle, haystack); missing or extra
        /// operands short-circuit to `false`.
        static func opIn(args: Value, vars: Scope) throws -> Value {
            let evaluated = try Operators.evalArgs(args, vars: vars)
            let needle = evaluated.first ?? .null
            let haystack = evaluated.indices.contains(1) ? evaluated[1] : .null
            switch haystack {
            case .string(let haystackString):
                // json-logic-js: `if (!haystack || …) return false` — empty
                // string is falsy, so `in` never matches regardless of needle.
                if haystackString.isEmpty { return .bool(false) }
                return .bool(haystackString.contains(jsString(needle)))
            case .array(let items):
                return .bool(items.contains { strictEq(needle, $0) })
            default:
                return .bool(false)
            }
        }

        /// `{"cat": [a, b, ...]}` — variadic string concatenation. Each
        /// operand is rendered via [`jsArrayElementString`] (mirrors
        /// `Array.prototype.join` on the argument list: `null` → `""`).
        /// 0 args returns `""`.
        static func opCat(args: Value, vars: Scope) throws -> Value {
            let evaluated = try Operators.evalArgs(args, vars: vars)
            let joined = evaluated.map(jsArrayElementString).joined()
            return .string(joined)
        }

        /// `{"substr": [source, start]}` or
        /// `{"substr": [source, start, length]}`. `source` is stringified.
        /// Negative `start` counts from the end. A negative `length` drops
        /// that many characters from the right of the substring that starts
        /// at `start`. Code-point-based, not byte-based — see type docs.
        /// `json-logic-js` declares `substr` as
        /// `function(source, start, end)`, so a missing `start` defaults
        /// to `0` and arguments past the third are silently ignored. A
        /// missing `source` is `undefined`, which stringifies to
        /// `"undefined"` (not `"null"`).
        static func opSubstr(args: Value, vars: Scope) throws -> Value {
            let evaluated = try Operators.evalArgs(args, vars: vars)
            let source = evaluated.first ?? .undefined
            let start = evaluated.indices.contains(1) ? evaluated[1] : .null
            let length: Value? = evaluated.indices.contains(2) ? evaluated[2] : nil

            let chars = Array(jsString(source))
            let total = chars.count

            // Non-numeric start coerces to 0 (matches JS `ToInteger`).
            let startN = Operators.clampedInt(start.asNumber ?? 0)
            let begin: Int
            if startN < 0 {
                begin = max(total + startN, 0)
            } else {
                begin = min(startN, total)
            }

            let afterStart = Array(chars[begin...])

            let result: String
            if let length = length {
                let lenN = Operators.clampedInt(length.asNumber ?? 0)
                let count: Int
                if lenN < 0 {
                    count = max(afterStart.count + lenN, 0)
                } else {
                    count = min(lenN, afterStart.count)
                }
                result = String(afterStart[..<count])
            } else {
                result = String(afterStart)
            }
            return .string(result)
        }

        /// `{"merge": [a, b, ...]}` — variadic, flattens one level. Array
        /// operands are spliced in; non-array operands are appended as
        /// single elements.
        static func opMerge(args: Value, vars: Scope) throws -> Value {
            let evaluated = try Operators.evalArgs(args, vars: vars)
            var merged: [Value] = []
            for item in evaluated {
                if case .array(let inner) = item {
                    merged.append(contentsOf: inner)
                } else {
                    merged.append(item)
                }
            }
            return .array(merged)
        }
    }
}