import {
    __rt_number_to_string,
    __rt_string_char_code_at,
    __rt_string_concat,
    __rt_string_from_char_code,
    __rt_string_slice,
} from "jsrt:native";

// Converts any value to a string, like the spec's ToString
export function String(x) {
    switch (typeof x) {
        case "string": return x;
        case "number": return __rt_number_to_string(x);
        case "boolean": return x ? "true" : "false";
        case "undefined": return "undefined";
        case "function": return "function () { [native code] }";
        case "object":
            if (x === null) return "null";
            if (typeof x.toString === "function") return x.toString();
            return "[object Object]";
    }
}

String.fromCharCode = function (code) {
    return __rt_string_from_char_code(code);
};

// In these methods `this` is the primitive string itself
String.prototype = {
    toString() { return this; },
    valueOf() { return this; },

    // ── Characters ──
    charAt(i) {
        if (i < 0 || i >= this.length) return "";
        return __rt_string_slice(this, i, i + 1);
    },
    charCodeAt(i) {
        if (i < 0 || i >= this.length) return NaN;
        return __rt_string_char_code_at(this, i);
    },
    at(i) {
        if (i < 0) i += this.length;
        if (i < 0 || i >= this.length) return undefined;
        return __rt_string_slice(this, i, i + 1);
    },

    // ── Search ──
    indexOf(search, from) {
        let start = from === undefined ? 0 : clampIndex(from, this.length);
        for (let i = start; i + search.length <= this.length; i++) {
            if (__rt_string_slice(this, i, i + search.length) === search) return i;
        }
        return -1;
    },
    lastIndexOf(search) {
        for (let i = this.length - search.length; i >= 0; i--) {
            if (__rt_string_slice(this, i, i + search.length) === search) return i;
        }
        return -1;
    },
    includes(search, from) { return this.indexOf(search, from) !== -1; },
    startsWith(search, from) {
        let start = from === undefined ? 0 : clampIndex(from, this.length);
        return __rt_string_slice(this, start, start + search.length) === search;
    },
    endsWith(search, end) {
        let stop = end === undefined ? this.length : clampIndex(end, this.length);
        let start = stop - search.length;
        return start >= 0 && __rt_string_slice(this, start, stop) === search;
    },

    // ── Substrings ──
    slice(start, end) {
        let len = this.length;
        let s = relativeIndex(start === undefined ? 0 : start, len);
        let e = relativeIndex(end === undefined ? len : end, len);
        return s < e ? __rt_string_slice(this, s, e) : "";
    },
    substring(start, end) {
        let len = this.length;
        let s = clampIndex(start === undefined ? 0 : start, len);
        let e = clampIndex(end === undefined ? len : end, len);
        return s < e ? __rt_string_slice(this, s, e) : __rt_string_slice(this, e, s);
    },

    // ── Case ──
    toUpperCase() { return mapCodes(this, 97, 122, -32); }, // a-z to A-Z
    toLowerCase() { return mapCodes(this, 65, 90, 32); },   // A-Z to a-z

    // ── Whitespace ──
    trim() { return this.trimStart().trimEnd(); },
    trimStart() {
        let i = 0;
        while (i < this.length && isSpace(__rt_string_char_code_at(this, i))) i++;
        return __rt_string_slice(this, i, this.length);
    },
    trimEnd() {
        let i = this.length;
        while (i > 0 && isSpace(__rt_string_char_code_at(this, i - 1))) i--;
        return __rt_string_slice(this, 0, i);
    },

    // ── Building ──
    repeat(count) {
        let s = "";
        for (let i = 0; i < count; i++) s = __rt_string_concat(s, this);
        return s;
    },
    padStart(length, fill) { return pad(this, length, fill, true); },
    padEnd(length, fill) { return pad(this, length, fill, false); },
};

// An index clamped to [0, len]
function clampIndex(i, len) {
    return i < 0 ? 0 : i > len ? len : i;
}

// An index where a negative value counts from the end, clamped to [0, len]
export function relativeIndex(i, len) {
    return clampIndex(i < 0 ? i + len : i, len);
}

// `s` with every char code in [lo, hi] moved by `shift`, for ASCII case mapping
function mapCodes(s, lo, hi, shift) {
    let out = "";
    for (let i = 0; i < s.length; i++) {
        let c = __rt_string_char_code_at(s, i);
        if (c >= lo && c <= hi) c += shift;
        out = __rt_string_concat(out, __rt_string_from_char_code(c));
    }
    return out;
}

function isSpace(c) {
    // tab, line feed, vertical tab, form feed, carriage return, space, nbsp
    return (c >= 9 && c <= 13) || c === 32 || c === 160;
}

function pad(s, length, fill, atStart) {
    let f = fill === undefined ? " " : String(fill);
    if (s.length >= length || f.length === 0) return s;

    let padding = "";
    while (padding.length < length - s.length) padding = __rt_string_concat(padding, f);
    padding = __rt_string_slice(padding, 0, length - s.length);

    return atStart ? __rt_string_concat(padding, s) : __rt_string_concat(s, padding);
}