/**
 * Base type for a canonical definition.
 */
import {Canon} from './Canon'
import {universalPath, UniversalPath, ErrorWithContext, Safe} from '../util'
import {Logging} from './Logging'
import {Inject} from '../di'
import * as nodePath from 'path'
import {Unit} from '../lifecycle/Unit'
import {isCanonicalReceiver} from '../support/CanonicalReceiver'

/**
 * Interface describing a definition of a single canonical item loaded from the app.
 */
export interface CanonicalDefinition {
    canonicalName: string,
    originalName: string,
    imported: any,
}

/**
 * Type alias for a function that resolves a canonical name to a canonical item, if one exists.
 */
export type CanonicalResolverFunction<T> = (key: string) => T | undefined

/**
 * Interface for a canonical resolver that provides additional information.
 */
export interface ComplexCanonicalResolver<T> {
    get: CanonicalResolverFunction<T>,
    all: () => string[],
}

export type CanonicalResolver<T> = CanonicalResolverFunction<T> | ComplexCanonicalResolver<T>

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

/**
 * Abstract unit type that loads items recursively from a directory structure, assigning
 * them normalized names ("canonical names"), and providing a way to fetch the resources
 * by name.
 *
 * @example
 * The Config service is a Canonical derivative that loads files ending with `.config.js`
 * from the `app/config` directory.
 *
 * If, for example, there is a config file `app/config/auth/Forms.config.js` (in the
 * generated code), it can be loaded by the canonical name `auth:Forms`.
 *
 */
export abstract class Canonical<T> extends Unit {
    @Inject()
    protected readonly logging!: Logging

    @Inject()
    protected readonly canon!: Canon

    /**
     * The base path directory where the canonical definitions reside.
     * @type string
     */
    protected appPath: string[] = []

    /**
     * The file suffix of files in the base path that should be loaded.
     * This should EXCLUDE `.js` or `.ts`. These file extensions are determined
     * by the framework depending on the Node runtime.
     * @example `.service`
     * @example `.middleware`
     * @type string
     */
    protected suffix = ''

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

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

    /**
     * Object mapping canonical namespaces to resolver functions.
     * @protected
     */
    protected loadedNamespaces: { [key: string]: CanonicalResolver<T> } = {}

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

        return {
            resource,
            item,
            particular,
        }
    }

    /**
     * Returns true if the given file path has the correct suffix to be loaded by this unit.
     */
    public isValidSuffix(path: string): boolean {
        const jsSuffix = `${this.suffix}.js`
        const tsSuffix = `${this.suffix}.ts`
        return path.endsWith(jsSuffix) || path.endsWith(tsSuffix)
    }

    /**
     * Return an array of all loaded canonical names.
     */
    public all(namespace?: string): string[] {
        if ( namespace ) {
            const resolver = this.loadedNamespaces[namespace]
            if ( !resolver ) {
                throw new ErrorWithContext(`Unable to find namespace for ${this.canonicalItem}: ${namespace}`, {
                    canonicalItem: this.canonicalItem,
                    namespace,
                })
            }

            if ( typeof resolver === 'function' ) {
                return []
            } else {
                return resolver.all()
            }
        }

        return Object.keys(this.loadedItems)
    }

    /**
     * Return an array of all loaded canonical namespaces.
     */
    public namespaces(): string[] {
        return Object.keys(this.loadedNamespaces)
    }

    /**
     * Get a Universal path to the base directory where this unit loads its canonical files from.
     */
    public get path(): UniversalPath {
        return this.app().appPath(...this.appPath)
    }

    /** Get the plural name of the canonical items provided by this unit. */
    public get canonicalItems(): string {
        return `${this.canonicalItem}s`
    }

    /** Get a canonical item by key, throwing an error if it could not be found. */
    public getOrFail(key: string): T {
        const result = this.get(key)
        if ( !result ) {
            throw new ErrorWithContext(`Unable to resolve Canonical key: ${key}`, {
                key,
            })
        }

        return result
    }

    /** Get a canonical item by key. */
    public get(key: string): T | undefined {
        if ( key.startsWith('@') ) {
            const [namespace, ...rest] = key.split(':')
            key = rest.join(':')

            const resolver = this.loadedNamespaces[namespace]
            if ( !resolver ) {
                throw new ErrorWithContext(`Unable to find namespace for ${this.canonicalItem}: ${namespace}`, {
                    canonicalItem: this.canonicalItem,
                    namespace,
                    key,
                })
            }

            if ( typeof resolver === 'function' ) {
                return resolver(key)
            } else {
                return resolver.get(key)
            }
        }

        return this.loadedItems[key]
    }

    /** Get a canonical item by key as a Safe value. */
    public safe(key: string): Safe {
        return (new Safe(this.get(key))).onError((message, value) => {
            throw new ErrorWithContext(`Invalid canonical value: ${message}`, {
                canonicalKey: key,
                canonicalItems: this.canonicalItems,
                value,
                message,
            })
        })
    }

    /**
     * Register a namespace resolver with the canonical unit.
     *
     * Namespaces are canonical names that start with a particular key, beginning with the `@` character,
     * which resolve their resources using a resolver function.
     *
     * @example
     * ```typescript
     * const items = {
     *     'foo:bar': 123,
     *     'bob': 456,
     * }
     *
     * const resolver = (key: string) => items[key]
     *
     * canonical.registerNamespace('@mynamespace', resolver)
     * ```
     *
     * Now, the items in the `@mynamespace` namespace can be accessed like so:
     *
     * ```typescript
     * canonical.get('@mynamespace:foo:bar')  // => 123
     * canonical.get('@mynamespace:bob')  // => 456
     * ```
     *
     * @param name
     * @param resolver
     */
    public registerNamespace(name: string, resolver: CanonicalResolver<T>): void {
        if ( !name.startsWith('@') ) {
            throw new ErrorWithContext(`Canonical namespaces must start with @.`, { name })
        }

        if ( this.loadedNamespaces[name] ) {
            this.logging.warn(`Replacing canonical namespace resolver for: ${name}`)
        }

        this.loadedNamespaces[name] = resolver
    }

    public async up(): Promise<void> {
        if ( await this.path.exists() ) {
            for await ( const entry of this.path.walk() ) {
                if ( !this.isValidSuffix(entry) ) {
                    this.logging.debug(`Skipping file with invalid suffix: ${entry}`)
                    continue
                }

                const definition = await this.buildCanonicalDefinition(entry)
                this.logging.verbose(`Registering canonical ${this.canonicalItem} "${definition.canonicalName}" from ${entry}`)
                const resolvedItem = await this.initCanonicalItem(definition)

                if ( isCanonicalReceiver(resolvedItem) ) {
                    resolvedItem.setCanonicalResolver(
                        `${this.canonicalItems}::${definition.canonicalName}`,
                        definition.canonicalName,
                    )
                }

                this.loadedItems[definition.canonicalName] = resolvedItem
            }
        }

        this.canon.registerCanonical(this)
    }

    /**
     * Called for each canonical item loaded from a file. This function should do any setup necessary and return the item
     * that should be associated with the canonical name.
     * @param definition
     */
    public async initCanonicalItem(definition: CanonicalDefinition): Promise<T> {
        return definition.imported.default ?? definition.imported[definition.canonicalName.split(':').reverse()[0]]
    }

    /**
     * Given the path to a file in the canonical items directory, create a CanonicalDefinition record from that file.
     * @param filePath
     * @param basePath
     * @protected
     */
    protected async buildCanonicalDefinition(filePath: string, basePath?: UniversalPath): Promise<CanonicalDefinition> {
        const originalName = filePath.replace((basePath || this.path).toLocal, '').substr(1)
        const pathRegex = new RegExp(nodePath.sep, 'g')
        const canonicalName = originalName.replace(pathRegex, ':')
            .split('')
            .reverse()
            .join('')
            .substr(this.suffix.length + 3)  // +3 to account for `.js` or `.ts` ending
            .split('')
            .reverse()
            .join('')

        const fullUniversalPath = universalPath(filePath)
        this.logging.verbose(`Importing from: ${fullUniversalPath}`)

        const imported = await import(fullUniversalPath.toLocal)
        return { canonicalName,
            originalName,
            imported }
    }
}