/**
 * Internal dependencies
 */
import Op from './Op';

export default class Iterator {
	ops: Op[];
	index: number;
	offset: number;

	constructor( ops: Op[] ) {
		this.ops = ops;
		this.index = 0;
		this.offset = 0;
	}

	hasNext(): boolean {
		return this.peekLength() < Infinity;
	}

	next( length?: number ): Op {
		if ( ! length ) {
			length = Infinity;
		}
		const nextOp = this.ops[ this.index ];
		if ( nextOp ) {
			const offset = this.offset;
			const opLength = Op.length( nextOp );
			if ( length >= opLength - offset ) {
				length = opLength - offset;
				this.index += 1;
				this.offset = 0;
			} else {
				this.offset += length;
			}
			if ( typeof nextOp.delete === 'number' ) {
				return { delete: length };
			}
			const retOp: Op = {};
			if ( nextOp.attributes ) {
				retOp.attributes = nextOp.attributes;
			}
			if ( typeof nextOp.retain === 'number' ) {
				retOp.retain = length;
			} else if (
				typeof nextOp.retain === 'object' &&
				nextOp.retain !== null
			) {
				// offset should === 0, length should === 1
				retOp.retain = nextOp.retain;
			} else if ( typeof nextOp.insert === 'string' ) {
				retOp.insert = nextOp.insert.substr( offset, length );
			} else {
				// offset should === 0, length should === 1
				retOp.insert = nextOp.insert;
			}
			return retOp;
		}
		return { retain: Infinity };
	}

	peek(): Op {
		return this.ops[ this.index ];
	}

	peekLength(): number {
		if ( this.ops[ this.index ] ) {
			// Should never return 0 if our index is being managed correctly
			return Op.length( this.ops[ this.index ] ) - this.offset;
		}
		return Infinity;
	}

	peekType(): string {
		const op = this.ops[ this.index ];
		if ( op ) {
			if ( typeof op.delete === 'number' ) {
				return 'delete';
			} else if (
				typeof op.retain === 'number' ||
				( typeof op.retain === 'object' && op.retain !== null )
			) {
				return 'retain';
			}
			return 'insert';
		}
		return 'retain';
	}

	rest(): Op[] {
		if ( ! this.hasNext() ) {
			return [];
		} else if ( this.offset === 0 ) {
			return this.ops.slice( this.index );
		}
		const offset = this.offset;
		const index = this.index;
		const next = this.next();
		const rest = this.ops.slice( this.index );
		this.offset = offset;
		this.index = index;
		return [ next ].concat( rest );
	}
}