json.nula

// Nulang standard library — JSON encoding and decoding.
// Import: `import stdlib::json`
// NOTE: JsonNumber stores a Float. String.to_float and Float.to_string
// primitives are now available in the VM, enabling numeric conversion
// while preserving reasonable fidelity for round-tripping.

/// Represents a parsed JSON value.
pub type JsonValue =
    | JsonNull
    | JsonBool(Bool)
    | JsonNumber(Float)   // Numeric value parsed via String.to_float
    | JsonString(String)
    | JsonArray([JsonValue])
    | JsonObject([(String, JsonValue)])

/// Parse a JSON string into a JsonValue.
///
/// Pure-Nulang recursive-descent parser. Handles all JSON value types:
/// null, true, false, numbers (int/float/scientific), strings (with
/// \", \\, \/, \b, \f, \n, \r, \t, \uXXXX escapes), arrays, and
/// nested objects.
///
/// Trailing whitespace and extra content after the first value are
/// ignored. Empty or whitespace-only input returns JsonNull.
///
/// Example (verified by `scripts/verify_doc_examples.sh`):
/// ```nulang
/// // Round-trip a JSON object through parse + stringify.
/// import stdlib::json
///
/// fn main() {
///     let v = parse("{\"a\": 1, \"b\": [true, null]}")
///     let s = stringify(v)
///     perform IO.print("round-trip: " + s)
/// }
/// ```
pub fn parse(json: String) -> JsonValue {
    let len = perform String.length(json);

    // ── whitespace ────────────────────────────────────────────────────

    let skip_ws = fn(p) {
        var cp = p;
        while cp < len {
            let c = perform String.charAt(json, cp);
            if c == 32 || c == 9 || c == 10 || c == 13 then { cp = cp + 1 }
            else { return cp }
        };
        cp
    };

    // ── string ────────────────────────────────────────────────────────

    let parse_string = fn(p) {
        var cp = p + 1;  // skip opening "
        var result = "";
        var done = false;
        while !done && cp < len {
            let c = perform String.charAt(json, cp);
            if c == 34 then {  // closing "
                cp = cp + 1;
                done = true
            }
            else if c == 92 then {  // backslash
                cp = cp + 1;  // advance past backslash
                if cp < len then {
                    let esc = perform String.charAt(json, cp);
                    if esc == 34 then { result = perform String.concat(result, "\"") }
                    else if esc == 92 then { result = perform String.concat(result, "\\") }
                    else if esc == 47 then { result = perform String.concat(result, "/") }
                    else if esc == 98 then { result = perform String.concat(result, perform String.from_char(8)) }
                    else if esc == 102 then { result = perform String.concat(result, perform String.from_char(12)) }
                    else if esc == 110 then { result = perform String.concat(result, "\n") }
                    else if esc == 114 then { result = perform String.concat(result, "\r") }
                    else if esc == 116 then { result = perform String.concat(result, "\t") }
                    else if esc == 117 then {
                        cp = cp + 1;
                        var hex_val = 0;
                        var hi = 0;
                        while hi < 4 && cp < len {
                            let hc = perform String.charAt(json, cp);
                            var d = 0;
                            if hc >= 48 && hc <= 57 then { d = hc - 48 }
                            else if hc >= 65 && hc <= 70 then { d = hc - 55 }
                            else if hc >= 97 && hc <= 102 then { d = hc - 87 }
                            else {};
                            hex_val = hex_val * 16 + d;
                            cp = cp + 1;
                            hi = hi + 1
                        };
                        result = perform String.concat(result, perform String.from_char(hex_val))
                    }
                    else {
                        // unknown escape — emit the raw char after backslash
                        result = perform String.concat(result, perform String.substring(json, cp, 1))
                    };
                    cp = cp + 1  // advance past the escaped char
                } else {}
            }
            else {
                result = perform String.concat(result, perform String.substring(json, cp, 1));
                cp = cp + 1
            }
        };
        {value: result, pos: cp}
    };

    // ── number ────────────────────────────────────────────────────────

    let parse_number = fn(p) {
        var cp = p;
        let start = cp;
        // optional minus
        if cp < len then {
            let fc = perform String.charAt(json, cp);
            if fc == 45 then { cp = cp + 1 } else {}
        } else {};
        // integer digits
        while cp < len {
            let c = perform String.charAt(json, cp);
            if c >= 48 && c <= 57 then { cp = cp + 1 } else { break }
        };
        // optional fractional part
        if cp < len then {
            let c = perform String.charAt(json, cp);
            if c == 46 then {
                cp = cp + 1;
                while cp < len {
                    let fc = perform String.charAt(json, cp);
                    if fc >= 48 && fc <= 57 then { cp = cp + 1 } else { break }
                }
            } else {}
        } else {};
        // optional exponent (e/E [+-]? digits)
        if cp < len then {
            let c = perform String.charAt(json, cp);
            if c == 101 || c == 69 then {
                cp = cp + 1;
                if cp < len then {
                    let sc = perform String.charAt(json, cp);
                    if sc == 43 || sc == 45 then { cp = cp + 1 } else {}
                } else {};
                while cp < len {
                    let dc = perform String.charAt(json, cp);
                    if dc >= 48 && dc <= 57 then { cp = cp + 1 } else { break }
                }
            } else {}
        } else {};
        {value: perform String.substring(json, start, cp - start), pos: cp}
    };

    // ── value ─────────────────────────────────────────────────────────

    let rec parse_value = fn(p) {
        var cp = skip_ws(p);
        if cp >= len then { {value: JsonNull, pos: cp} }
        else {
            let c = perform String.charAt(json, cp);
            if c == 34 then {  // string
                let sr = parse_string(cp);
                {value: JsonString(sr.value), pos: sr.pos}
            }
            else if c == 116 then {  // true
                {value: JsonBool(true), pos: cp + 4}
            }
            else if c == 102 then {  // false
                {value: JsonBool(false), pos: cp + 5}
            }
            else if c == 110 then {  // null
                {value: JsonNull, pos: cp + 4}
            }
            else if c == 91 then {  // array
                cp = skip_ws(cp + 1);
                var items = [];
                if cp < len then {
                    let nc = perform String.charAt(json, cp);
                    if nc == 93 then { {value: JsonArray(items), pos: cp + 1} }
                    else {
                        var done = false;
                        var arr_pos = cp;
                        var arr_items = items;
                        while !done {
                            let vr = parse_value(arr_pos);
                            arr_items = perform Array.push(arr_items, vr.value);
                            arr_pos = skip_ws(vr.pos);
                            if arr_pos < len then {
                                let sep = perform String.charAt(json, arr_pos);
                                if sep == 44 then { arr_pos = skip_ws(arr_pos + 1) }
                                else if sep == 93 then { arr_pos = arr_pos + 1; done = true }
                                else { done = true }
                            } else { done = true }
                        };
                        {value: JsonArray(arr_items), pos: arr_pos}
                    }
                } else { {value: JsonArray(items), pos: cp} }
            }
            else if c == 123 then {  // object
                cp = skip_ws(cp + 1);
                var fields = [];
                if cp < len then {
                    let nc = perform String.charAt(json, cp);
                    if nc == 125 then { {value: JsonObject(fields), pos: cp + 1} }
                    else {
                        var done = false;
                        var obj_pos = cp;
                        var obj_fields = fields;
                        while !done {
                            let kr = parse_string(obj_pos);
                            obj_pos = skip_ws(kr.pos);
                            if obj_pos < len then {
                                let colon = perform String.charAt(json, obj_pos);
                                if colon == 58 then { obj_pos = obj_pos + 1 } else {}
                            } else {};
                            let vr = parse_value(obj_pos);
                            obj_fields = perform Array.push(obj_fields, (kr.value, vr.value));
                            obj_pos = skip_ws(vr.pos);
                            if obj_pos < len then {
                                let sep = perform String.charAt(json, obj_pos);
                                if sep == 44 then { obj_pos = skip_ws(obj_pos + 1) }
                                else if sep == 125 then { obj_pos = obj_pos + 1; done = true }
                                else { done = true }
                            } else { done = true }
                        };
                        {value: JsonObject(obj_fields), pos: obj_pos}
                    }
                } else { {value: JsonObject(fields), pos: cp} }
            }
            else {  // number
                let nr = parse_number(cp);
                {value: JsonNumber(perform String.to_float(nr.value)), pos: nr.pos}
            }
        }
    };

    let r = parse_value(0);
    r.value
}

/// Convert a JsonValue back to a JSON string.
///
/// Full fidelity for all types including nested arrays and objects.
/// Numbers are emitted exactly as parsed (raw text).
/// Strings are escaped for valid JSON output: \", \\, \n, \r, \t,
/// \b, \f, and control characters (0x00–0x1F) as \u00XX.
pub fn stringify(value: JsonValue) -> String {
    // ── hex digit helper ──────────────────────────────────────────────

    let hex_char = fn(d) {
        if d < 10 then { perform String.from_char(d + 48) }
        else { perform String.from_char(d + 87) }
    };

    // ── string escape helper ──────────────────────────────────────────

    let esc_string = fn(s) {
        var result = "\"";
        var i = 0;
        let slen = perform String.length(s);
        while i < slen {
            let c = perform String.charAt(s, i);
            if c == 34 then {  // "
                result = perform String.concat(result, "\\\"")
            }
            else if c == 92 then {  // \
                result = perform String.concat(result, "\\\\")
            }
            else if c == 10 then {  // \n
                result = perform String.concat(result, "\\n")
            }
            else if c == 13 then {  // \r
                result = perform String.concat(result, "\\r")
            }
            else if c == 9 then {  // \t
                result = perform String.concat(result, "\\t")
            }
            else if c == 8 then {  // \b
                result = perform String.concat(result, "\\b")
            }
            else if c == 12 then {  // \f
                result = perform String.concat(result, "\\f")
            }
            else if c < 32 then {  // other control char → \u00XX
                let hi = c / 16;
                let lo = c % 16;
                result = perform String.concat(result, "\\u00");
                result = perform String.concat(result, hex_char(hi));
                result = perform String.concat(result, hex_char(lo))
            }
            else {
                result = perform String.concat(result, perform String.substring(s, i, 1))
            };
            i = i + 1
        };
        perform String.concat(result, "\"")
    };

    // ── recursive value stringify ─────────────────────────────────────

    let rec go = fn(v) {
        match v {
            JsonNull => "null",
            JsonBool(b) => if b then "true" else "false",
            JsonNumber(f) => perform Float.to_string(f),
            JsonString(s) => esc_string(s),
            JsonArray(items) => {
                var result = "[";
                var i = 0;
                let alen = perform Array.length(items);
                while i < alen {
                    if i > 0 then { result = perform String.concat(result, ",") } else {};
                    result = perform String.concat(result, go(items[i]));
                    i = i + 1
                };
                perform String.concat(result, "]")
            },
            JsonObject(fields) => {
                var result = "{";
                var i = 0;
                let olen = perform Array.length(fields);
                while i < olen {
                    if i > 0 then { result = perform String.concat(result, ",") } else {};
                    let pair = fields[i];
                    result = perform String.concat(result, esc_string(pair.0));
                    result = perform String.concat(result, ":");
                    result = perform String.concat(result, go(pair.1));
                    i = i + 1
                };
                perform String.concat(result, "}")
            }
        }
    };

    go(value)
}


/// Get a string field from a JSON object, or return a default.
pub fn get_string(obj: JsonValue, key: String, default: String) -> String {
    match obj {
        JsonObject(fields) => {
            var i = 0;
            var len = perform Array.length(fields);
            while i < len {
                let pair = fields[i];
                if pair.0 == key then {
                    match pair.1 {
                        JsonString(s) => return s,
                        _ => return default,
                    }
                } else { };
                i = i + 1
            };
            default
        },
        _ => default,
    }
}

/// Get a number field from a JSON object, or return a default.
/// Returns the parsed Float value.
pub fn get_number(obj: JsonValue, key: String, default: Float) -> Float {
    match obj {
        JsonObject(fields) => {
            var i = 0;
            var len = perform Array.length(fields);
            while i < len {
                let pair = fields[i];
                if pair.0 == key then {
                    match pair.1 {
                        JsonNumber(n) => return n,
                        _ => return default,
                    }
                } else { };
                i = i + 1
            };
            default
        },
        _ => default,
    }
}

/// Get a bool field from a JSON object, or return a default.
pub fn get_bool(obj: JsonValue, key: String, default: Bool) -> Bool {
    match obj {
        JsonObject(fields) => {
            var i = 0;
            var len = perform Array.length(fields);
            while i < len {
                let pair = fields[i];
                if pair.0 == key then {
                    match pair.1 {
                        JsonBool(b) => return b,
                        _ => return default,
                    }
                } else { };
                i = i + 1
            };
            default
        },
        _ => default,
    }
}