import { ChildProcess } from 'child_process'
import { GitProgressParser, IGitProgress, IGitOutput } from './git'
import { IGitExecutionOptions } from '../core/git';

const byline = require('byline')

/**
 * Merges an instance of IGitExecutionOptions with a process callback provided
 * by progressProcessCallback.
 *
 * If the given options object already has a processCallback specified it will
 * be overwritten.
 */
export function executionOptionsWithProgress(
    options: IGitExecutionOptions,
    parser: GitProgressParser,
    progressCallback: (progress: IGitProgress | IGitOutput) => void): IGitExecutionOptions {

    return merge(options, {
        processCallback: progressProcessCallback(parser, progressCallback),
    })
}

/**
 * Returns a callback which can be passed along to the processCallback option
 * in IGitExecution. The callback then takes care of reading stderr of the
 * process and parsing its contents using the provided parser.
 */
export function progressProcessCallback(
    parser: GitProgressParser,
    progressCallback: (progress: IGitProgress | IGitOutput) => void): (process: ChildProcess) => void {

    return (process) => {
        byline(process.stderr).on('data', (line: string) => {
            progressCallback(parser.parse(line))
        })
    }
}

function merge<T, K extends keyof T>(obj: T, subset: Pick<T, K>): T {
    const copy = Object.assign({}, obj)
    for (const k in subset) {
        if (subset.hasOwnProperty(k)) {
            copy[k] = subset[k]
        }
    }
    return copy
}