interface FlagT<T, Z> {
    default?: T,
    aliases?: string[],
    /** Shorthands, AKA only work with singular minus signs like -f; Multiple characters are allowed; Will not count as a full (like --f) flag alias; */
    shorthands?: string|string[],
    type?: Z
    /** If enabled, sends/throws an error if the flag is present but no value is set, either with an assigned value (ie: ["--flag=value"]), or natural value (ie: ["--flag", "value"]) @default false */
    requiredValue?: boolean
    /** If disabled, only accepts assigned values (ie: ["--flag=value"]) for flag values (ie: the would-have-been value will instead become input) @default true*/
    acceptsNaturalValue?: boolean
};

export type FlagTypes = "string" | "boolean" | "bigint" | "number" | "any";

export type FlagAny = FlagT<string, "string"> | FlagT<boolean, "boolean"> | FlagT<number, "number"> | FlagT<bigint, "bigint"> | FlagT<string | number | bigint | boolean, "any">

export interface FlagsI { [key: readonly string]: FlagAny }

export type DefaultParserOptsType = ParserOpts<FlagsI>

/** This object will be modified by parser */
export interface ParserOpts<Flags extends FlagsI> {
    flags?: Flags, 
    /** Wether to allow versions of `-flag` as a singular and valid flag. @default false */
    allowSingularDashLongFlags?: boolean = false 
    /** Wether to allow flags not denoted in the flag property. @default true */
    allowUnknownFlags?: boolean = true
    /** Wether to lowercase all flags key. Incompatible with camelCaseFlags option. @default true */
    lowerCaseFlags?: boolean = true
    /** Wether to automatically resolve flag number values into numbers and boolean flags into booleans if flag type is explicitly set. @default true */
    resolveFlagValueTypes?: boolean = true
    /**
     * Setting according flag to the inversed provided boolean value (defaulting to false if none is provided) with their '--no' variants unless a defined flag exists with that
     * name already; Additional informations in sub-properties.
     * @default 
     * ```js
     *  = { enabled: true, allowUnspacedNegatedFlags: true, shorthandNegation: true }
     * ```
     */
   automaticBooleanFlagNegation?: {
       /** Wether to automatically resolve boolean flags that are negated to the inverse boolean value. Requires resolveFlagValueTypes. @default true */
       enabled?: boolean;
       /** Allows flags negated without a space (eg: "--noflag") to still be automatically resolved @default true */
       allowUnspacedNegatedFlags?: boolean;
       /** Wether to negate shorthand flags with if an n is present before hand (eg: '-nf'). Providing a shorthand of 'n' will disable this feature. @default true */
       shorthandNegation?: boolean;
    }
    /** Enable this option to silence any warnings about potentially unexpected behavior (eg: a flag's unset type being set to the default). @default false */
    silenceWarnings?: boolean;
    /** Override to change how warnings are emitted @default console.warn */
    warningLogger?(log: string): void;
    /** Default type for either unknown flags or flags without an explicit type being set @default "any" */
    defaultFlagType?: FlagTypes;
    /** 
     * Behavior when input does not follow the provided flags constraints (eg: flag assigned value (--flag=value) not being the correct type). 
     * 
     * Setting it to 'ignore' or 'log' is highly not recommended and will lead to undefined behavior. (eg: flags not meeting the configuration not being present 
     * in the final returned object)
     * Setting this to 'ignore' will give the same undefined behavior as setting it to 'log', but without emitting any logs to `warningLogger`.
     * @default 'throw'
     */
    behaviorOnInputError?: 'throw' | 'log' | 'log&exit' | 'ignore';
    /** Wether to allow default flag values set to null being valid @default true */
    allowNullDefaultFlagValues?: boolean;
    /** 
     * If enabled, makes all input values lowercase after flag processing. It does not apply to 'values' that get naturally assigned to flags 
     * (eg: `['--flag', 'VALUE']` -> `{ 'flag': 'VALUE' }`)
     * @default false
     */
    lowerCaseInputValues?: boolean
    /** 
     * If enabled, makes all string flag values lowercase. It applies to any string flag values, either naturally assigned (eg: `['--flag', 'VALUE']` -> `{ flags: { 'flag': 'value' } }`)
     * or directly assigned (eg: `['--flag=VALUE']` -> `{ flags: { 'flag': 'value' } }`)
     * @default false
     */
    lowerCaseFlagValues?: boolean
    /** 
     * If disabled, does not acknowledge or consume backslashes, making flag assignments (=) and designated flag characters (--) inescapable within flags
     * 
     * 
     * #### It needs to be noted that backslashes are only ever handled/consumed in flags AND if they impact special flag characters (ie: minus signs (-) and equal signs (=));
     * The only exception is a backslash escaping a flag character (-) at the very beginning of a value (ie: '\--not_a_flag'), which will be consumed with this option
     * enabled but not counted as a flag (ie: `['\--not_a_flag']` -> `{ input: ['--not_a_flag'], flags: {} }`), and not consumed but also not counted as a flag with it 
     * disabled (ie: `['\--not_a_flag']` -> `{ input: ['\--not_a_flag'], flags: {} }`).
     * @default true
     */
    handleBackslashesForSpecialFlagChars?: boolean
    /** If enabled, automatically adds shorthands as valid flag aliases (eg: -f &-> --f) @default true */
    addFlagShorthandsAsAliases?: boolean
    /** 
     * If a function is provided, stops parsing when that function returns a truthy value. 
     * 
     * Adds any following args (including the matching arg) into the returned unparsed array.
     * 
     * **Overrides shouldStopParsingStr**
     * @param arg - to-be parsed arg
     * @param index - index of the arg within the argv array
     * @param argv - argv array
     * @param argMeta - meta object containing informations about the arg (*properties subject to change)
     * @param input - input array, containing the currently parsed input values
     * @default null 
     */
    shouldStopParsingFunc?(arg: string, index: number, argv: string[], argMeta: argMeta, input: string[]): boolean
    /**
     * If a string is provided, stops parsing if the to-be parsed arg matches the string provided exactly.
     * The to-be parsed arg is not yet lowercased by any lowerCase* options, it is therefore recommended to use shouldStopParsingFunc instead if that is a requirement.
     * 
     * Adds any following args (including the matching arg) into the returned unparsed array.
     * 
     * **Overridden by shouldStopParsingFunc**
     * @default null
     */
    shouldStopParsingStr?: null | string
    /**
     * If a function is provided, will only parse the provided arg if the provided function returns a truthy value. 
     * 
     * Runs after shouldStopParsingFunc
     * 
     * Does not add filtered out args into the returned unparsed array.
     * 
     * @param arg - to-be parsed arg
     * @param index - index of the arg within the argv array
     * @param argv - argv array
     * @param argMeta - meta object containing informations about the arg (*properties subject to change)
     * @param input - input array, containing the currently parsed input values
     * @default null
     */
    parseFilterFunc?(arg: string, index: number, argv: string[], argMeta: argMeta, input: string[]): boolean
    /** 
     * Allows multiple flag values & changes the returned flags to always be arrays, with the default being the first value if the flag was not set, or an
     * empty array if the flag does not have a default but was not present.
     * @example
     * ```js
     * const { flags } = parser(["--flag=hello", "--flag=world"], {
     *     flags: {
     *         defaultedFlag: { default: "missing", type: "string" },
     *         missingFlag:   { type: "string" },
     *     },
     *     allowMultipleFlagValues: true,
     *     allowUnknownFlags: true,
     * });
     * flags === { flag: ["hello", "world"], defaultedFlag: ["missing"], missingFlag: [] }
     * ```
     * @default false
     */
    allowMultipleFlagValues?: boolean
}

export type argMeta = {
    /** Is set to true if the arg will be parsed as a flag */
    isFlag: boolean;
    /** Is isFlag is true, the flag will be parsed as a shorthand */
    isShorthand: boolean;
    /** Is isFlag is true, is set to the flag key without any leading flag characters (eg: `"--flag" -> "flag"`) */
    flagKey: string;
    /** Is true if isFlag is true and the flag has an assigned value (ie: `arg === "--flag=value"`) */
    hasFlagAssignedValue: boolean;
    /** Is hasFlagAssignedValue is true, is set to the flag's assigned value (eg: `"--flag=value" -> "value"`) */
    flagAssignedValue: string;
    /** Is set to true if the arg will be treated as an input string, ie: if isFlag and isFlagNaturalValue are false */
    isInput: boolean;
    /** Is set to true if this arg would be treated as the value to the most recently parsed flag (ie: `["--flag", "value"][1].argMeta.isFlagNaturalValue === true` ) */
    isFlagNaturalValue: boolean;
}

function __type__getType(e: any) { return typeof e };

export type JSTypes = ReturnType<typeof __type__getType>;

export type FlagReturnType<FlagType extends FlagTypes> = 
    FlagType extends 'boolean' ? boolean
        : FlagType extends 'number' ? number
        : FlagType extends 'bigint' ? bigint
        : FlagType extends 'string' ? string
        : string | boolean | number | bigint;

type ValueOf<T> = T[keyof T];
type OptionalKeys<T, K extends keyof T> = Pick<T, K> & Partial<Omit<T, K>>;

type _OptionalIfFlagDefaultNotPresent<T> = OptionalKeys<T, ValueOf<{ [V in keyof T]: 'default' extends keyof T[V] ? never : V }>>;
type _ResolveFlagTypes<Flags extends FlagsI, allowMultipleFlagValues extends boolean> = {
    [K in keyof Flags]: allowMultipleFlagValues extends true 
        ? FlagReturnType<Flags[K]['type']>[] 
        : FlagReturnType<Flags[K]['type']>
}

export type FlagsReturn<Opts extends ParserOpts> = _ResolveFlagTypes<
    Opts['allowMultipleFlagValues'] extends true ? Opts['flags'] : _OptionalIfFlagDefaultNotPresent<Opts['flags']>, 
    Opts['allowMultipleFlagValues'] extends true ? true : false
>;