import {LexInput} from '../lexer.js'
import {ExpectedEndOfInputError, InvalidVariableNameError, UnexpectedEndOfInputError} from "../parse.js";

export type StrLVal = { term: 'variable', name: string }

export type StrTerm =
    { term: 'string', value: string }
    | StrLVal

export class ParseContext {
    constructor(
        private inputs: LexInput[],
    ) {}

    assertEmpty() {
        if ( this.inputs.length ) {
            throw new ExpectedEndOfInputError(`Expected end of input. Found: ${this.inputs[0].value}`)
        }
    }

    popOptionalTerm(): StrTerm|undefined {
        if ( this.inputs.length ) return this.popTerm()
        return undefined
    }

    popTerm(): StrTerm {
        if ( !this.inputs.length ) {
            throw new UnexpectedEndOfInputError('Unexpected end of input. Expected term.');
        }

        const input = this.inputs.shift()!

        // Check if the token is a literal variable name:
        if ( !input.literal && input.value.startsWith('$') ) {
            if ( !input.value.match(/^\$[a-zA-Z0-9_]+$/) ) {
                throw new InvalidVariableNameError(`Invalid variable name: ${input.value}`)
            }

            return { term: 'variable', name: input.value }
        }

        // Otherwise, parse it as a string literal:
        return { term: 'string', value: input.value }
    }

    popLVal(): StrLVal {
        if ( !this.inputs.length ) {
            throw new UnexpectedEndOfInputError('Unexpected end of input. Expected lval.');
        }

        const input = this.inputs.shift()!

        if ( input.literal || !input.value.match(/^\$[a-zA-Z0-9_]+$/) ) {
            throw new InvalidVariableNameError(`Expected variable name. Found: ${input.value}`)
        }

        return { term: 'variable', name: input.value }
    }
}

export type CommandData = Record<string, unknown>

export abstract class Command<TData extends CommandData> {
    abstract isParseCandidate(token: LexInput): boolean

    abstract attemptParse(context: ParseContext): TData

    abstract getDisplayName(): string

    protected isKeyword(token: LexInput, keyword: string): boolean {
        return !token.literal && token.value === keyword
    }
}