import { Satisfies, Unreachable } from "../type";
import { Parts } from "./_parts";
import { Append, Concat, ElementOf, IsEmpty, List, Prepend } from ".";
/**
 * constructs the pairs of finite, nonvariadic tuple `L`.
 */
type __Pairs<L extends List, Acc extends List<[unknown, unknown]> = []> = L extends readonly [infer H, infer HH, ...infer T] ? __Pairs<[HH, ...T], Append<Acc, [H, HH]>> : Acc;
/**
 * given lists `I`, `S`, and `T` corresponding to the init/spread/tail produced from `_Parts`,
 *  builds the pairs of the list from those three components.
 *
 * As it assumes the lists are produced from `_Parts`, it assumes that:
 * - if `S` is empty, then so too is `T` and thus only `I` needs to be handled
 * - `I` and `T` are both finite and nonvariadic
 * - `S`, if not empty, is a plain array (i.e. consists of a single spread element and nothing else)
 */
type _Pairs<I extends List, S extends List, T extends List> = IsEmpty<S> extends true ? __Pairs<I> : __Pairs<Concat<I, T>> | [
    ...__Pairs<Append<Required<I>, ElementOf<S>>>,
    ...[ElementOf<S>, ElementOf<S>][],
    ...__Pairs<Prepend<T, ElementOf<S>>>
];
/**
 * constructs a list of pairs of the adjacent elements of list `L`.
 *
 * properly works with variadic tuples.
 * optional elements are assumed to be required and included in the pairs.
 *
 * @since 0.0.2
 *
 * @example
 * ```ts
 * type e0 = Pairs<never>                           // [] | [any, any][] // DANGEROUS - might need to explicitly handle `never`...
 * type e1 = Pairs<[]>                              // []
 * type e2 = Pairs<[string]>                        // []
 * type e3 = Pairs<string[]>                        // [] | [string, string][]
 * type e4 = Pairs<[...string[], number]>           // [] | [...[string, string][], [string, number]]
 * type e5 = Pairs<[string, ...number[]]>           // [] | [[string, number], ...[number, number][]]
 * type e6 = Pairs<[string, ...number[], boolean]>  // [string, boolean] | [[string, number], ...[number, number][], [number, boolean]]
 * type e7 = Pairs<[string?]>                       // []
 * type e8 = Pairs<[string?, ...number[]]>          // [] | [[string, number], ...[number, number][]]
 *
 * // very large tuple [0..256, ...number[], 256..512]
 * type t9 = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211,212,213,214,215,216,217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255,...number[],256,257,258,259,260,261,262,263,264,265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,284,285,286,287,288,289,290,291,292,293,294,295,296,297,298,299,300,301,302,303,304,305,306,307,308,309,310,311,312,313,314,315,316,317,318,319,320,321,322,323,324,325,326,327,328,329,330,331,332,333,334,335,336,337,338,339,340,341,342,343,344,345,346,347,348,349,350,351,352,353,354,355,356,357,358,359,360,361,362,363,364,365,366,367,368,369,370,371,372,373,374,375,376,377,378,379,380,381,382,383,384,385,386,387,388,389,390,391,392,393,394,395,396,397,398,399,400,401,402,403,404,405,406,407,408,409,410,411,412,413,414,415,416,417,418,419,420,421,422,423,424,425,426,427,428,429,430,431,432,433,434,435,436,437,438,439,440,441,442,443,444,445,446,447,448,449,450,451,452,453,454,455,456,457,458,459,460,461,462,463,464,465,466,467,468,469,470,471,472,473,474,475,476,477,478,479,480,481,482,483,484,485,486,487,488,489,490,491,492,493,494,495,496,497,498,499,500,501,502,503,504,505,506,507,508,509,510,511]
 * type e9 = Pairs<t9>    // not gonna write it out, but it works fine with no error
 * ```
 */
export type Pairs<L extends List> = Parts<L> extends readonly [infer I, infer S, infer T] ? _Pairs<Satisfies<I, List>, Satisfies<S, List>, Satisfies<T, List>> : Unreachable;
export {};
//# sourceMappingURL=pairs.d.ts.map