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

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

export type BitPackerArrayConfig = {
    type: "array";
    maxLength: number;
} & (
    | { elementType: "integer"; elementMax?: number }
    | { elementType: "float"; elementMax?: number }
    | { elementType: "string"; elementMax?: number }
    | { elementType: "boolean" }
    | { elementType: "schema"; elementSchema: BitPackerSchema }
);

export function isArrayConfig(schema: unknown): schema is BitPackerArrayConfig {
    if (
        typeof schema !== "object" ||
        schema === null ||
        Array.isArray(schema)
    ) {
        return false;
    }
    const obj = schema as Record<string, unknown>;
    if (obj["type"] !== "array") return false;
    if (typeof obj["maxLength"] !== "number") return false;
    if (
        !["integer", "float", "string", "boolean", "schema"].includes(
            obj["elementType"] as string
        )
    )
        return false;
    if (obj["elementType"] === "schema" && !("elementSchema" in obj))
        return false;
    return true;
}

export function validateArrayData(
    data: unknown[],
    config: BitPackerArrayConfig
): boolean {
    if (!Array.isArray(data)) return false;
    if (data.length > config.maxLength) return false;

    return data.every((item) => {
        switch (config.elementType) {
            case "integer":
                return (
                    typeof item === "number" &&
                    Number.isInteger(item) &&
                    item >= 0 &&
                    item <= (config.elementMax || 255)
                );
            case "float":
                return (
                    typeof item === "number" &&
                    item >= 0 &&
                    item <= (config.elementMax || 100)
                );
            case "string":
                return (
                    typeof item === "string" &&
                    item.length <= (config.elementMax || 100)
                );
            case "boolean":
                return typeof item === "boolean";
            case "schema":
                return true;
            default:
                return false;
        }
    });
}

/**
 * Strategy for packing array configurations.
 *
 * Schema shape: `{ type: "array", maxLength: number, elementType: "integer"|"float"|"string"|"boolean"|"schema", ... }`
 */
export class ArrayConfigPackingStrategy implements PackingStrategy {
    canHandle(schema: BitPackerSchema): boolean {
        return isArrayConfig(schema);
    }

    pack(
        data: unknown,
        schema: BitPackerSchema,
        context: PackingContext
    ): void {
        const arrayConfig = schema as BitPackerArrayConfig;
        if (!Array.isArray(data)) {
            throw new BitpackerError(
                BITPACKER_CODES.INVALID_SCHEMA,
                `Expected array data for array configuration but received ${typeof data}`,
                { context: { data } }
            );
        }

        if (!validateArrayData(data, arrayConfig)) {
            throw new BitpackerError(
                BITPACKER_CODES.INVALID_SCHEMA,
                `Invalid array data for array configuration with elementType "${arrayConfig.elementType}"`,
                { context: { data, elementType: arrayConfig.elementType } }
            );
        }

        // Pack array length
        const lengthBits = bitsRequired(arrayConfig.maxLength);
        context.writer.writeUint(data.length, lengthBits);

        // Pack elements
        for (const item of data) {
            switch (arrayConfig.elementType) {
                case "integer": {
                    const max = arrayConfig.elementMax || 255;
                    context.writer.writeUint(item as number, bitsRequired(max));
                    break;
                }
                case "float": {
                    const max = arrayConfig.elementMax || 100;
                    context.writer.writeUint(item as number, bitsRequired(max));
                    break;
                }
                case "string": {
                    const maxLen = arrayConfig.elementMax || 100;
                    const bytes = new TextEncoder().encode(item as string);
                    const len = Math.min(bytes.length, maxLen);
                    for (let i = 0; i < maxLen; i++) {
                        context.writer.writeUint(i < len ? bytes[i]! : 0, 8);
                    }
                    break;
                }
                case "boolean":
                    context.writer.writeBool(item as boolean);
                    break;
                case "schema":
                    context.packValue(item, arrayConfig.elementSchema);
                    break;
            }
        }
    }

    unpack(schema: BitPackerSchema, context: PackingContext): unknown {
        const arrayConfig = schema as BitPackerArrayConfig;
        const lengthBits = bitsRequired(arrayConfig.maxLength);
        const length = context.reader.readUint(lengthBits);
        const result: unknown[] = [];

        for (let i = 0; i < length; i++) {
            switch (arrayConfig.elementType) {
                case "integer": {
                    const max = arrayConfig.elementMax || 255;
                    result.push(context.reader.readUint(bitsRequired(max)));
                    break;
                }
                case "float": {
                    const max = arrayConfig.elementMax || 100;
                    result.push(context.reader.readUint(bitsRequired(max)));
                    break;
                }
                case "string": {
                    const maxLen = arrayConfig.elementMax || 100;
                    let str = "";
                    for (let j = 0; j < maxLen; j++) {
                        const byte = context.reader.readUint(8);
                        if (byte !== 0) str += String.fromCharCode(byte);
                    }
                    result.push(str);
                    break;
                }
                case "boolean":
                    result.push(context.reader.readBool());
                    break;
                case "schema":
                    result.push(context.unpackValue(arrayConfig.elementSchema));
                    break;
            }
        }

        return result;
    }
}