import {Inject, Singleton} from '../../di'
import {CanonicalInstantiable} from '../../service/CanonicalInstantiable'
import {Migration} from '../migrations/Migration'
import {CanonicalDefinition, CanonicalResolver} from '../../service/Canonical'
import {UniversalPath} from '../../util'
import {lib} from '../../lib'
import {CommandLine} from '../../cli'

/**
 * Service unit that loads and instantiates migration classes.
 */
@Singleton()
export class Migrations extends CanonicalInstantiable<Migration> {
    @Inject()
    protected readonly cli!: CommandLine

    protected appPath = ['migrations']

    protected canonicalItem = 'migration'

    protected suffix = '.migration'

    async up(): Promise<void> {
        if ( await this.path.exists() ) {
            await super.up()
        } else {
            this.logging.debug(`Base migration path does not exist, or has no files: ${this.path}`)
        }

        // Register the migrations for @extollo/lib
        const basePath = lib().concat('migrations')
        const resolver = await this.buildMigrationNamespaceResolver('@extollo', basePath)
        this.registerNamespace('@extollo', resolver)
    }

    async initCanonicalItem(definition: CanonicalDefinition): Promise<Migration> {
        const instance = await super.initCanonicalItem(definition)

        if ( !(instance instanceof Migration) ) {
            throw new TypeError(`Invalid migration: ${definition.originalName}. Migrations must extend from @extollo/lib.Migration.`)
        }

        instance.setMigrationIdentifier(definition.canonicalName)

        return instance
    }

    /**
     * Creates a CanonicalResolver for a directory that contains migration files.
     *
     * @example
     * ```ts
     * const path = universalPath('path', 'to', 'migrations', 'folder')
     * const namespace = '@mypackage'
     *
     * const resolver = await migrations.buildMigrationNamespaceResolver(namespace, path)
     * migrations.registerNamespace(namespace, resolver)
     * ```
     * @param name
     * @param basePath
     */
    public async buildMigrationNamespaceResolver(name: string, basePath: UniversalPath): Promise<CanonicalResolver<Migration>> {
        if ( !name.startsWith('@') ) {
            name = `@${name}`
        }

        const namespace: {[key: string]: Migration} = {}

        for await ( const entry of basePath.walk() ) {
            if ( !this.isValidSuffix(entry) ) {
                this.logging.debug(`buildMigrationNamespaceResolver - Skipping file with invalid suffix: ${entry}`)
                continue
            }

            const definition = await this.buildCanonicalDefinition(entry, basePath)
            this.logging.verbose(`buildMigrationNamespaceResolver - Discovered canonical ${this.canonicalItem} "${definition.canonicalName}" from ${entry}`)
            namespace[definition.canonicalName] = await this.initCanonicalItem(definition)
            namespace[definition.canonicalName].setMigrationIdentifier(`${name}:${namespace[definition.canonicalName].identifier}`)
        }

        return {
            get: (key: string) => namespace[key],
            all: () => Object.keys(namespace),
        }
    }
}