import {
    ValueType,
    NumberType,
    StringType,
    array,
    typeToString,
    isValidType,
    isValidNativeType
} from '../types';
import {RuntimeError} from '../runtime_error';
import {typeOf} from '../values';

import type {Expression} from '../expression';
import type {ParsingContext} from '../parsing_context';
import type {EvaluationContext} from '../evaluation_context';
import type {Type} from '../types';

export class Slice implements Expression {
    type: Type;
    input: Expression;
    beginIndex: Expression;
    endIndex: Expression;

    constructor(type: Type, input: Expression, beginIndex: Expression, endIndex?: Expression) {
        this.type = type;
        this.input = input;
        this.beginIndex = beginIndex;
        this.endIndex = endIndex;
    }

    static parse(args: ReadonlyArray<unknown>, context: ParsingContext): Expression {
        if (args.length <= 2 || args.length >= 5) {
            return context.error(
                `Expected 2 or 3 arguments, but found ${args.length - 1} instead.`
            ) as null;
        }

        const input = context.parse(args[1], 1, ValueType);
        const beginIndex = context.parse(args[2], 2, NumberType);

        if (!input || !beginIndex) return null;

        if (!isValidType(input.type, [array(ValueType), StringType, ValueType])) {
            return context.error(
                `Expected first argument to be of type array or string, but found ${typeToString(input.type)} instead`
            ) as null;
        }

        if (args.length === 4) {
            const endIndex = context.parse(args[3], 3, NumberType);
            if (!endIndex) return null;
            return new Slice(input.type, input, beginIndex, endIndex);
        } else {
            return new Slice(input.type, input, beginIndex);
        }
    }

    evaluate(ctx: EvaluationContext) {
        const input = this.input.evaluate(ctx) as any;
        const beginIndex = this.beginIndex.evaluate(ctx) as number;

        let endIndex;
        if (this.endIndex) {
            endIndex = this.endIndex.evaluate(ctx) as number;
        }

        if (isValidNativeType(input, ['string'])) {
            // Indices may be affected by surrogate pairs.
            return [...input].slice(beginIndex, endIndex).join('');
        } else if (isValidNativeType(input, ['array'])) {
            return input.slice(beginIndex, endIndex);
        } else {
            throw new RuntimeError(
                `Expected first argument to be of type array or string, but found ${typeToString(typeOf(input))} instead.`
            );
        }
    }

    eachChild(fn: (_: Expression) => void) {
        fn(this.input);
        fn(this.beginIndex);
        if (this.endIndex) {
            fn(this.endIndex);
        }
    }

    outputDefined() {
        return false;
    }
}