import {Connection} from "mysql";

import {ServerError} from "../HttpError.js";
import Model, {ModelType} from "./Model.js";
import ModelQuery, {WhereTest} from "./ModelQuery.js";

export const EMAIL_REGEX = /^[a-zA-Z0-9.!#$%&'*+\\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)+$/;

export default class Validator<V> {
    public static async validate(
        validationMap: { [p: string]: Validator<unknown> },
        body: { [p: string]: unknown },
    ): Promise<void> {
        const bag = new ValidationBag();

        for (const p of Object.keys(validationMap)) {
            try {
                await validationMap[p].execute(p, body[p], false);
            } catch (e) {
                if (e instanceof ValidationBag) {
                    bag.addBag(e);
                } else throw e;
            }
        }

        if (bag.hasMessages()) throw bag;
    }


    private readonly steps: ValidationStep<V>[] = [];
    private readonly validationAttributes: string[] = [];

    private readonly rawValueToHuman?: (val: V) => string;
    private _min?: number;
    private _max?: number;

    public constructor(rawValueToHuman?: (val: V) => string) {
        this.rawValueToHuman = rawValueToHuman;
    }

    /**
     * @param thingName The name of the thing to validate.
     * @param value The value to verify.
     * @param onlyFormat {@code true} to only validate format properties, {@code false} otherwise.
     * @param connection A connection to use in case of wrapped transactions.
     */
    public async execute(
        thingName: string,
        value: V | undefined,
        onlyFormat: boolean,
        connection?: Connection,
    ): Promise<void> {
        const bag = new ValidationBag<V>();

        for (const step of this.steps) {
            if (onlyFormat && !step.isFormat) continue;

            let result;
            try {
                result = step.verifyStep(value, thingName, connection);
                if (result instanceof Promise) {
                    result = await result;
                }
            } catch (e) {
                if (e instanceof Error) {
                    throw new ServerError(`An error occurred while validating ${thingName} with value "${value}".`, e);
                } else {
                    throw e;
                }
            }

            if (result === false && step.throw) {
                const error: ValidationError<V> = step.throw();
                error.rawValueToHuman = this.rawValueToHuman;
                error.thingName = thingName;
                error.value = value;
                bag.addMessage(error);
                break;
            } else if (step.interrupt !== undefined && step.interrupt(value)) {
                break;
            }
        }

        if (bag.hasMessages()) {
            throw bag;
        }
    }

    public defined(): Validator<V> {
        this.validationAttributes.push('required');

        this.addStep({
            verifyStep: val => val !== undefined,
            throw: () => new UndefinedValueValidationError(),
            isFormat: true,
        });
        return this;
    }

    public acceptUndefined(alsoAcceptEmptyString: boolean = false): Validator<V> {
        this.addStep({
            verifyStep: () => true,
            throw: null,
            interrupt: val => {
                return val === undefined ||
                    val === null ||
                    alsoAcceptEmptyString && typeof val === 'string' && val.length === 0;
            },
            isFormat: true,
        });
        return this;
    }

    public equals(other?: V): Validator<V> {
        this.addStep({
            verifyStep: val => val === other,
            throw: () => new BadValueValidationError(other),
            isFormat: true,
        });
        return this;
    }

    public sameAs(otherName?: string, other?: V): Validator<V> {
        this.addStep({
            verifyStep: val => val === other,
            throw: () => new DifferentThanError(otherName),
            isFormat: true,
        });
        return this;
    }

    public regexp(regexp: RegExp): Validator<V> {
        this.validationAttributes.push(`pattern="${regexp}"`);
        this.addStep({
            verifyStep: val => regexp.test(<string><unknown>val),
            throw: () => new InvalidFormatValidationError(),
            isFormat: true,
        });
        return this;
    }

    public length(length: number): Validator<V> {
        this.addStep({
            verifyStep: val => isLenghtable(val) && val.length === length,
            throw: () => new BadLengthValidationError(length),
            isFormat: true,
        });
        return this;
    }

    /**
     * @param minLength included
     */
    public minLength(minLength: number): Validator<V> {
        this.addStep({
            verifyStep: val => isLenghtable(val) && val.length >= minLength,
            throw: () => new TooShortError(minLength),
            isFormat: true,
        });
        return this;
    }

    /**
     * @param maxLength included
     */
    public maxLength(maxLength: number): Validator<V> {
        this.addStep({
            verifyStep: val => isLenghtable(val) && val.length <= maxLength,
            throw: () => new TooLongError(maxLength),
            isFormat: true,
        });
        return this;
    }

    /**
     * @param minLength included
     * @param maxLength included
     */
    public between(minLength: number, maxLength: number): Validator<V> {
        this.addStep({
            verifyStep: val => {
                return isLenghtable(val) &&
                    val.length >= minLength && val.length <= maxLength;
            },
            throw: () => new BadLengthValidationError(minLength, maxLength),
            isFormat: true,
        });
        return this;
    }

    /**
     * @param min included
     */
    public min(min: number): Validator<V> {
        this.validationAttributes.push(`min="${min}"`);
        this._min = min;
        this.addStep({
            verifyStep: val => {
                return typeof val === 'number' && val >= min;
            },
            throw: () => new OutOfRangeValidationError(this._min, this._max),
            isFormat: true,
        });
        return this;
    }

    /**
     * @param max included
     */
    public max(max: number): Validator<V> {
        this.validationAttributes.push(`max="${max}"`);
        this._max = max;
        this.addStep({
            verifyStep: val => {
                return typeof val === 'number' && val <= max;
            },
            throw: () => new OutOfRangeValidationError(this._min, this._max),
            isFormat: true,
        });
        return this;
    }

    public unique<M extends Model>(
        model: M | ModelType<M>,
        foreignKey?: string,
        querySupplier?: () => ModelQuery<M>,
    ): Validator<V> {
        this.addStep({
            verifyStep: async (val, thingName, c) => {
                if (!foreignKey) foreignKey = thingName;
                let query: ModelQuery<M>;
                if (querySupplier) {
                    query = querySupplier();
                } else {
                    query = (model instanceof Model ? <ModelType<M>>model.constructor : model).select('');
                }
                query.where(foreignKey, val);
                if (model instanceof Model && typeof model.id === 'number')
                    query = query.where('id', model.id, WhereTest.NE);
                return (await query.execute(c)).results.length === 0;
            },
            throw: () => new AlreadyExistsValidationError(model.table),
            isFormat: false,
        });
        return this;
    }

    public exists(modelType: ModelType<Model>, foreignKey?: string): Validator<V> {
        this.addStep({
            verifyStep: async (val, thingName, c) => {
                const results = await modelType.select('')
                    .where(foreignKey !== undefined ? foreignKey : thingName, val)
                    .execute(c);
                return results.results.length >= 1;
            },
            throw: () => new UnknownRelationValidationError(modelType.table, foreignKey),
            isFormat: false,
        });
        return this;
    }

    private addStep(step: ValidationStep<V>) {
        this.steps.push(step);
    }

    public getValidationAttributes(): string[] {
        return this.validationAttributes;
    }

    public step(step: number): Validator<V> {
        this.validationAttributes.push(`step="${step}"`);
        return this;
    }
}

interface ValidationStep<V> {
    interrupt?: (val?: V) => boolean;

    verifyStep(val: V | undefined, thingName: string, connection?: Connection): boolean | Promise<boolean>;

    throw: ((val?: V) => ValidationError<V>) | null;

    readonly isFormat: boolean;
}

export class ValidationBag<V> extends Error {
    private readonly errors: ValidationError<V>[] = [];

    public addMessage(err: ValidationError<V>): void {
        if (!err.thingName) throw new Error('Null thing name');
        this.errors.push(err);
    }

    public addBag(otherBag: ValidationBag<V>): void {
        for (const error of otherBag.errors) {
            this.errors.push(error);
        }
    }

    public hasMessages(): boolean {
        return this.errors.length > 0;
    }

    public getMessages(): { [p: string]: ValidationError<V> } {
        const messages: { [p: string]: ValidationError<V> } = {};
        for (const err of this.errors) {
            messages[err.thingName || 'unknown'] = {
                name: err.name,
                message: err.message,
                value: err.value,
            };
        }
        return messages;
    }

    public getErrors(): ValidationError<V>[] {
        return this.errors;
    }
}

export class ValidationError<V> extends Error {
    public rawValueToHuman?: (val: V) => string;
    public thingName?: string;
    public value?: V;

    public get name(): string {
        return this.constructor.name;
    }
}

export class BadLengthValidationError<V> extends ValidationError<V> {
    private readonly expectedLength: number;
    private readonly maxLength?: number;

    public constructor(expectedLength: number, maxLength?: number) {
        super();
        this.expectedLength = expectedLength;
        this.maxLength = maxLength;
    }

    public get message(): string {
        return `${this.thingName} expected length: ${this.expectedLength}${this.maxLength !== undefined ? ` to ${this.maxLength}` : ''}; ` +
            `actual length: ${isLenghtable(this.value) && this.value.length}.`;
    }
}

export class TooShortError<V> extends ValidationError<V> {
    private readonly minLength: number;

    public constructor(minLength: number) {
        super();
        this.minLength = minLength;
    }

    public get message(): string {
        return `${this.thingName} must be at least ${this.minLength} characters.`;
    }
}

export class TooLongError<V> extends ValidationError<V> {
    private readonly maxLength: number;

    public constructor(maxLength: number) {
        super();
        this.maxLength = maxLength;
    }

    public get message(): string {
        return `${this.thingName} must be at most ${this.maxLength} characters.`;
    }
}

export class BadValueValidationError<V> extends ValidationError<V> {
    private readonly expectedValue: V;

    public constructor(expectedValue: V) {
        super();
        this.expectedValue = expectedValue;
    }

    public get message(): string {
        let expectedValue: string = String(this.expectedValue);
        let actualValue: string = String(this.value);
        if (this.rawValueToHuman && this.value) {
            expectedValue = this.rawValueToHuman(this.expectedValue);
            actualValue = this.rawValueToHuman(this.value);
        }
        return `Expected: ${expectedValue}; got: ${actualValue}.`;
    }
}

export class DifferentThanError<V> extends ValidationError<V> {
    private readonly otherName?: string;

    public constructor(otherName?: string) {
        super();
        this.otherName = otherName;
    }

    public get message(): string {
        return `This should be the same as ${this.otherName}.`;
    }
}

export class OutOfRangeValidationError<V> extends ValidationError<V> {
    private readonly min?: number;
    private readonly max?: number;

    public constructor(min?: number, max?: number) {
        super();
        this.min = min;
        this.max = max;
    }

    public get message(): string {
        if (this.min === undefined) {
            return `${this.thingName} must be at most ${this.max}`;
        } else if (this.max === undefined) {
            return `${this.thingName} must be at least ${this.min}`;
        }
        let min: string = String(this.min);
        let max: string = String(this.max);
        if (this.rawValueToHuman) {
            min = this.rawValueToHuman(this.min as unknown as V);
            max = this.rawValueToHuman(this.max as unknown as V);
        }
        return `${this.thingName} must be between ${min} and ${max}.`;
    }
}

export class InvalidFormatValidationError<V> extends ValidationError<V> {
    public get message(): string {
        return `"${this.value}" is not a valid ${this.thingName}.`;
    }
}

export class UndefinedValueValidationError<V> extends ValidationError<V> {
    public get message(): string {
        return `${this.thingName} is required.`;
    }
}

export class AlreadyExistsValidationError<V> extends ValidationError<V> {
    private readonly table: string;

    public constructor(table: string) {
        super();
        this.table = table;
    }

    public get message(): string {
        return `${this.thingName} already exists in ${this.table}.`;
    }
}

export class UnknownRelationValidationError<V> extends ValidationError<V> {
    private readonly table: string;
    private readonly foreignKey?: string;

    public constructor(table: string, foreignKey?: string) {
        super();
        this.table = table;
        this.foreignKey = foreignKey;
    }

    public get message(): string {
        return `${this.thingName}=${this.value} relation was not found in ${this.table}${this.foreignKey !== undefined ? `.${this.foreignKey}` : ''}.`;
    }
}

export class FileError<V> extends ValidationError<V> {
    private readonly _message: string;

    public constructor(message: string) {
        super();
        this._message = message;
    }

    public get message(): string {
        return `${this._message}`;
    }
}

export type Lengthable = {
    length: number,
};

export function isLenghtable(value: unknown): value is Lengthable {
    return value !== undefined && value !== null &&
        typeof (value as Lengthable).length === 'number';
}