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import {PENDING, REDO, RESOLVED, UNDO} from './constants';
import type {History} from '../history';
/**
* Offsets history by offset length
* @param {History} history
* @param {Integer} offsetValue
*/
export default function offset(history: History, offsetValue: number): Promise<History>
{
if (history.commandState === PENDING)
{
return Promise.resolve(history);
}
let position = history.position + offsetValue;
let {state} = history;
if (offsetValue < 0 && history.state !== UNDO)
{
position += 1;
state = UNDO;
}
if (offsetValue > 0 && history.state !== REDO)
{
position -= 1;
state = REDO;
}
if (position <= history.stack.length - 1 && position >= 0)
{
history.position = position;
history.state = state;
const entry = history.stack[position];
if (entry)
{
const command = history.commands[entry.command];
if (command)
{
history.commandState = PENDING;
return command[state](entry)
.then(() => {
history.commandState = RESOLVED;
return history;
})
.catch(() => {
history.commandState = RESOLVED;
return offset(history, offsetValue);
});
}
}
}
return Promise.resolve(history);
}