suaveplan/packages/foundation/bitpacker/bitpacker-strategies/src/strategies/string/string.ts

import type {
    BitPackerSchema,
    PackingContext,
    PackingStrategy,
} from "@suaveplan/bitpacker";
import {
    BITPACKER_CODES,
    BitpackerError,
    isFixedFloatSchema,
    isFloatSchema,
    isUuidSchema,
} from "@suaveplan/bitpacker";

function bitsRequired(maxValue: number): number {
    if (maxValue <= 0) return 0;
    return Math.floor(Math.log2(maxValue)) + 1;
}

/**
 * Strategy for string schemas.
 *
 * Handles:
 *  - Fixed strings:   `"20"`   → exactly 20 bytes
 *  - Variable strings:`"-20"`  → up to 20 bytes with length prefix
 *  - UUID:            `"uuid"` → 16 bytes
 *  - Float:           `"f32"`, `"f64"` → IEEE-754 floats
 *  - Fixed float:     `"4.2"`, `"-4.2"` → fixed-point numbers encoded as strings
 */
export class StringPackingStrategy implements PackingStrategy {
    canHandle(schema: BitPackerSchema): boolean {
        return typeof schema === "string";
    }

    pack(
        data: unknown,
        schema: BitPackerSchema,
        context: PackingContext
    ): void {
        const s = schema as string;

        if (isUuidSchema(s)) {
            this.#packUuid(data, context);
        } else if (isFloatSchema(s)) {
            this.#packFloat(data as number, s, context);
        } else if (isFixedFloatSchema(s)) {
            this.#packFixedFloat(data as number | string, s, context);
        } else {
            this.#packString(data as string, s, context);
        }
    }

    unpack(schema: BitPackerSchema, context: PackingContext): unknown {
        const s = schema as string;

        if (isUuidSchema(s)) {
            return this.#unpackUuid(context);
        }
        if (isFloatSchema(s)) {
            return this.#unpackFloat(s, context);
        }
        if (isFixedFloatSchema(s)) {
            return this.#unpackFixedFloat(s, context);
        }
        return this.#unpackString(s, context);
    }

    #packString(value: string, schema: string, context: PackingContext): void {
        const isFixed = !schema.startsWith("-");
        const maxLength = Number(isFixed ? schema : schema.slice(1));

        if (typeof value !== "string") {
            throw new BitpackerError(
                BITPACKER_CODES.INVALID_SCHEMA,
                `Expected string for schema "${schema}", got ${typeof value}`,
                { context: { schema, value } }
            );
        }

        const bytes = new TextEncoder().encode(value);
        const length = Math.min(bytes.length, maxLength);

        if (isFixed && bytes.length > maxLength) {
            throw new BitpackerError(
                BITPACKER_CODES.VALUE_OUT_OF_RANGE,
                `String length ${bytes.length} exceeds fixed schema length ${maxLength}`,
                { context: { schema, length: bytes.length, maxLength } }
            );
        }

        if (!isFixed) {
            context.writer.writeUint(length, bitsRequired(maxLength));
        }

        const writeCount = isFixed ? maxLength : length;
        for (let i = 0; i < writeCount; i++) {
            context.writer.writeUint(i < bytes.length ? bytes[i]! : 0, 8);
        }
    }

    #unpackString(schema: string, context: PackingContext): string {
        const isFixed = !schema.startsWith("-");
        const maxLength = Number(isFixed ? schema : schema.slice(1));

        let length = maxLength;
        if (!isFixed) {
            length = context.reader.readUint(bitsRequired(maxLength));
        }

        const bytes = new Uint8Array(length);
        for (let i = 0; i < length; i++) {
            bytes[i] = context.reader.readUint(8);
        }

        let actualLength = length;
        while (actualLength > 0 && bytes[actualLength - 1] === 0) {
            actualLength--;
        }

        return new TextDecoder().decode(bytes.subarray(0, actualLength));
    }

    #packUuid(value: unknown, context: PackingContext): void {
        let bytes: Uint8Array;
        if (typeof value === "string" && value.includes("-")) {
            const hex = value.replace(/-/g, "");
            if (hex.length !== 32) {
                throw new BitpackerError(
                    BITPACKER_CODES.VALUE_OUT_OF_RANGE,
                    `Invalid UUID string: ${value}`,
                    { context: { value } }
                );
            }
            bytes = new Uint8Array(16);
            for (let i = 0; i < 16; i++) {
                bytes[i] = Number.parseInt(hex.substring(i * 2, i * 2 + 2), 16);
            }
        } else if (value instanceof Uint8Array && value.length === 16) {
            bytes = value;
        } else {
            throw new BitpackerError(
                BITPACKER_CODES.INVALID_SCHEMA,
                "UUID must be a 36-char string or 16-byte Uint8Array",
                { context: { value } }
            );
        }
        context.writer.writeBytes(bytes);
    }

    #unpackUuid(context: PackingContext): string {
        const bytes = context.reader.readBytes(16);
        const hex = Array.from(bytes)
            .map((b) => b.toString(16).padStart(2, "0"))
            .join("");
        return `${hex.slice(0, 8)}-${hex.slice(8, 12)}-${hex.slice(12, 16)}-${hex.slice(16, 20)}-${hex.slice(20, 32)}`;
    }

    #packFloat(value: number, schema: string, context: PackingContext): void {
        if (typeof value !== "number") {
            throw new BitpackerError(
                BITPACKER_CODES.INVALID_SCHEMA,
                `Expected number for float schema "${schema}", got ${typeof value}`,
                { context: { schema, value } }
            );
        }
        if (schema === "f32") {
            const buf = new ArrayBuffer(4);
            new DataView(buf).setFloat32(0, value, false);
            context.writer.writeBytes(new Uint8Array(buf));
        } else {
            const buf = new ArrayBuffer(8);
            new DataView(buf).setFloat64(0, value, false);
            context.writer.writeBytes(new Uint8Array(buf));
        }
    }

    #unpackFloat(schema: string, context: PackingContext): number {
        const bytes = context.reader.readBytes(schema === "f32" ? 4 : 8);
        const view = new DataView(
            bytes.buffer,
            bytes.byteOffset,
            bytes.byteLength
        );
        if (schema === "f32") {
            return view.getFloat32(0, false);
        }
        return view.getFloat64(0, false);
    }

    #packFixedFloat(
        value: number | string,
        schema: string,
        context: PackingContext
    ): void {
        const [wholeStr, fracStr] = schema.split(".");
        const wholeBits = Math.abs(Number(wholeStr));
        const fracBits = Number(fracStr);
        const totalBits = wholeBits + fracBits;
        const isSigned = Number(wholeStr) < 0;

        const numValue = typeof value === "string" ? Number(value) : value;
        const factor = 1 << fracBits;
        const scaled = Math.round(numValue * factor);

        if (isSigned) {
            context.writer.writeInt(scaled, totalBits);
        } else {
            context.writer.writeUint(scaled, totalBits);
        }
    }

    #unpackFixedFloat(schema: string, context: PackingContext): number {
        const [wholeStr, fracStr] = schema.split(".");
        const wholeBits = Math.abs(Number(wholeStr));
        const fracBits = Number(fracStr);
        const totalBits = wholeBits + fracBits;
        const isSigned = Number(wholeStr) < 0;

        const scaled = isSigned
            ? context.reader.readInt(totalBits)
            : context.reader.readUint(totalBits);

        return scaled / (1 << fracBits);
    }
}