import LifecycleUnit from '../lifecycle/Unit.ts'
import {fs, path} from '../external/std.ts'
import {Canon} from './Canon.ts'
import {Logging} from '../service/logging/Logging.ts'

/**
 * Base type for a canonical definition.
 */
export interface CanonicalDefinition {
    canonical_name: string,
    original_name: string,
    imported: any,
}

/**
 * Base type for a canonical name reference.
 */
export interface CanonicalReference {
    resource?: string,
    item: string,
    particular?: string,
}

/**
 * Base class for all canonical units. Provides helpers for reading and standardizing
 * the names of classes defined in the filesystem structure.
 * @extends LifecycleUnit
 */
export class Canonical<T> extends LifecycleUnit {
    /**
     * The base path directory where the canonical definitions reside.
     * @type string
     */
    protected base_path: string = '.'

    /**
     * The file suffix of files in the base path that should be loaded.
     * @type string
     */
    protected suffix: string = '.ts'

    /**
     * The singular, programmatic name of one of these canonical items.
     * @example middleware
     * @type string
     */
    protected canonical_item: string = ''

    /**
     * Object mapping canonical names to loaded file references.
     * @type object
     */
    protected _items: { [key: string]: T } = {}

    /**
     * Resolve a canonical reference from its string form to a CanonicalReference.
     * @param {string} reference
     * @return CanonicalReference
     */
    public static resolve(reference: string): CanonicalReference {
        const rsc_parts = reference.split('::')
        const resource = rsc_parts.length > 1 ? rsc_parts[0] + 's' : undefined
        const rsc_less = rsc_parts.length > 1 ? rsc_parts[1] : rsc_parts[0]
        const prt_parts = rsc_less.split('.')
        const item = prt_parts[0]
        const particular = prt_parts.length > 1 ? prt_parts.slice(1).join('.') : undefined

        return {
            resource, item, particular
        }
    }

    /**
     * Get an array of all canonical reference names.
     * @return Array<string>
     */
    public all(): string[] {
        return Object.keys(this._items)
    }

    /**
     * Get the fully-qualified path to the base directory for this unit.
     * @type string
     */
    public get path(): string {
        return path.resolve(this.base_path)
    }

    /**
     * Get the plural, programmatic name of the canonical items provide by this unit.
     * @type string
     */
    public get canonical_items() {
        return `${this.canonical_item}s`
    }

    public async up() {
        const logger = this.make(Logging)
        for await ( const entry of fs.walk(this.path) ) {
            if ( !entry.isFile || !entry.path.endsWith(this.suffix) ) {
                if ( entry.isFile ) logger.debug(`Skipping file in canonical path with invalid suffix: ${entry.path}`)
                continue
            }
            const def = await this._get_canonical_definition(entry.path)
            logger.verbose(`Registering canonical ${this.canonical_item} "${def.canonical_name}" from ${entry.path}.`)
            this._items[def.canonical_name] = await this.init_canonical_item(def)
        }
        this.make(Canon).register_canonical(this)
    }

    /**
     * Given a single canonical definition loaded from a file in the base path,
     * initialize the item and return the result that should be mapped to the reference name.
     * @param {CanonicalDefinition} definition
     * @return Promise<any>
     */
    public async init_canonical_item(definition: CanonicalDefinition): Promise<T> {
        return definition.imported.default
    }

    /**
     * Given a file path, build the canonical definition represented by that path.
     * @param {string} file_path
     * @private
     * @return Promise<CanonicalDefinition>
     */
    private async _get_canonical_definition(file_path: string): Promise<CanonicalDefinition> {
        const original_name = file_path.replace(this.path, '').substr(1)
        const path_regex = new RegExp(path.SEP, 'g')
        const canonical_name = original_name.replace(path_regex, ':')
            .split('').reverse().join('')
            .substr(this.suffix.length)
            .split('').reverse().join('')

        if ( file_path.startsWith('/') ) {
            file_path = `file://${file_path}`
        }

        this.make(Logging).debug(`Importing from: ${file_path}`)
        const imported = await import(file_path)
        return { canonical_name, original_name, imported }
    }

    /**
     * Given a canonical reference string, get the corresponding item, if it exists.
     * @param {string} key
     * @return any | undefined
     */
    public get(key: string): T | undefined {
        return this._items[key]
    }
}