import fs from 'fs/promises';
import { EventEmitter } from 'events';
import { v4 as uuidv4 } from 'uuid';

class GreenBean extends EventEmitter {
    constructor(dbPath = 'data.json', { autoSave = false } = {}) {
        super();
        this.dbPath = dbPath;
        this.data = null;
        this.initialized = false;
        this.frozen = false;
        this.autoSave = autoSave;
        this._initPromise = null;
        this._transactionLock = false;
        this._relationCache = new WeakMap();
    }

    async dispense(type, props = {}) {
        await this.init();
        const bean = {
            id: uuidv4(),
            __type: type,
            __meta: {
                created: new Date().toISOString(),
                modified: new Date().toISOString()
            },
            ...props
        };
        return this.createProxy(bean);
    }

    async load(type, id) {
        await this.init();
        const item = this.data[type]?.find(i => i.id === id);
        if (!item) return null;
        return this.createProxy({...item});
    }

    async store(bean) {
        if (this.frozen) throw new Error('Frozen database');
        await this.init();

        const type = bean.__type;
        bean.__meta.modified = new Date().toISOString();

        if (!this.data[type]) this.data[type] = [];

        const index = this.data[type].findIndex(i => i.id === bean.id);
        if (index >= 0) {
            this.data[type][index] = {...bean};
        } else {
            this.data[type].push({...bean});
        }

        await this.autoSave && this.save();
        return bean;
    }

    async trash(bean) {
        if (this.frozen) throw new Error('Frozen database');
        await this.init();

        const type = bean.__type;
        if (!this.data[type]) return;

        this.data[type] = this.data[type].filter(i => i.id !== bean.id);
        await this.handleCascadeDelete(bean);
        await this.autoSave && this.save();
    }

    async find(type, criteria = {}) {
        await this.init();
        if (!this.data[type]) return [];

        return this.data[type]
            .filter(item => this.matchCriteria(item, criteria))
            .map(item => this.createProxy({...item}));
    }

    async findOne(type, criteria) {
        const results = await this.find(type, criteria);
        return results[0] || null;
    }

    async transaction(callback) {
        if (this._transactionLock) throw new Error('Transaction in progress');
        this._transactionLock = true;

        const snapshot = JSON.stringify(this.data);
        try {
            const result = await callback();
            await this.save();
            return result;
        } catch (error) {
            this.data = JSON.parse(snapshot);
            throw error;
        } finally {
            this._transactionLock = false;
        }
    }

    createProxy(bean) {
        const handler = {
            get: (target, prop) => {
                if (prop === 'then') return; // Для async/await
                if (prop in target) return target[prop];

                return new Proxy({}, {
                    get: async (_, propName) => {
                        const relations = await this.resolveRelations(target);
                        return relations[prop];
                    },
                    apply: async () => {
                        return this.handleRelationAccess(target, prop);
                    }
                });
            },

            set: async (target, prop, value) => {
                if (prop === '__type' || prop === '__meta') {
                    throw new Error(`Cannot modify ${prop}`);
                }

                const relationType = await this.detectRelationship(target.__type, prop);
                if (relationType) {
                    await this.handleRelationUpdate(target, prop, value, relationType);
                    return true;
                }

                if (prop.endsWith('List') && Array.isArray(value)) {
                    target[prop] = value.map(i => ({
                        id: i.id,
                        __type: i.__type || this.guessType(i)
                    }));
                } else {
                    target[prop] = value;
                }

                target.__meta.modified = new Date().toISOString();
                await this.autoSave && this.store(target);
                return true;
            }
        };

        return new Proxy(bean, handler);
    }

    // ========== Relationship Handling ==========
    async resolveRelations(target) {
        if (!this._relationCache.has(target)) {
            this._relationCache.set(target, {});
        }
        const cache = this._relationCache.get(target);

        return new Proxy({}, {
            get: (_, prop) => {
                if (!cache[prop]) {
                    cache[prop] = this.handleRelationAccess(target, prop);
                }
                return cache[prop];
            }
        });
    }

    async handleRelationAccess(target, prop) {
        const relation = await this.detectRelationship(target.__type, prop);

        switch (relation.type) {
            case 'manyToMany':
                return this.getShared(target, prop);
            case 'oneToMany':
                return this.getOwn(target, prop);
            case 'oneToOne':
                return this.getXOwn(target, prop);
            default:
                return undefined;
        }
    }

    async handleRelationUpdate(target, prop, value, relation) {
        switch (relation.type) {
            case 'manyToMany':
                await this.shared(target, prop, value);
                break;
            case 'oneToMany':
                await this.own(target, prop, value);
                break;
            case 'oneToOne':
                await this.xownOne(target, prop, value);
                break;
        }
        this._relationCache.delete(target);
    }

    async detectRelationship(parentType, property) {
        // Many-to-Many detection
        const linkTable = `${parentType}_${property}`;
        if (this.data[linkTable]) {
            return { type: 'manyToMany', linkTable };
        }

        // One-to-Many detection
        const childType = property;
        if (this.data[childType]?.some(i => i[`${parentType}_id`])) {
            return { type: 'oneToMany', childType };
        }

        // One-to-One detection
        if (this.data[property]?.some(i =>
            i[`${parentType}_id`] && this.isFieldUnique(property, `${parentType}_id`)
        )) {
            return { type: 'oneToOne', childType: property };
        }

        return { type: 'none' };
    }

    async getShared(target, prop) {
        const linkTable = `${target.__type}_${prop}`;
        const links = await this.find(linkTable, {
            [`${target.__type}_id`]: target.id
        });

        return Promise.all(
            links.map(link =>
                this.load(link[`${prop}_type`], link[`${prop}_id`])
            )
        );
    }

    async getOwn(target, prop) {
        return this.find(prop, {
            [`${target.__type}_id`]: target.id
        });
    }

    async getXOwn(target, prop) {
        return this.findOne(prop, {
            [`${target.__type}_id`]: target.id
        });
    }

    async shared(target, prop, values) {
        const linkTable = `${target.__type}_${prop}`;
        await this.trashRelations(linkTable, target.id);

        for (const value of [values].flat()) {
            const link = await this.dispense(linkTable, {
                [`${target.__type}_id`]: target.id,
                [`${prop}_id`]: value.id,
                [`${prop}_type`]: value.__type
            });
            await this.store(link);
        }
    }

    async own(target, prop, values) {
        const children = [values].flat();
        for (const child of children) {
            child[`${target.__type}_id`] = target.id;
            await this.store(child);
        }
    }

    async xownOne(target, prop, value) {
        const current = await this.getXOwn(target, prop);
        if (current) {
            delete current[`${target.__type}_id`];
            await this.store(current);
        }
        if (value) {
            value[`${target.__type}_id`] = target.id;
            await this.store(value);
        }
    }

    // ========== Helpers ==========
    async init() {
        if (this._initPromise) return this._initPromise;
        this._initPromise = (async () => {
            try {
                const exists = await fs.access(this.dbPath).then(() => true).catch(() => false);
                this.data = exists ?
                    JSON.parse(await fs.readFile(this.dbPath, 'utf-8')) :
                    {};
                this.initialized = true;
            } catch (error) {
                throw new Error(`Init failed: ${error.message}`);
            }
        })();
        return this._initPromise;
    }

    async save() {
        await fs.writeFile(this.dbPath, JSON.stringify(this.data, null, 2));
        this.emit('save');
    }

    async handleCascadeDelete(bean) {
        const relations = await this.detectAllRelationships(bean.__type);
        for (const rel of relations) {
            switch (rel.type) {
                case 'oneToMany':
                    const children = await this.find(rel.childType, {
                        [`${bean.__type}_id`]: bean.id
                    });
                    for (const child of children) {
                        await this.trash(child);
                    }
                    break;
                case 'oneToOne':
                    const linked = await this.findOne(rel.childType, {
                        [`${bean.__type}_id`]: bean.id
                    });
                    if (linked) await this.trash(linked);
                    break;
                case 'manyToMany':
                    await this.trashRelations(rel.linkTable, bean.id);
                    break;
            }
        }
    }

    async trashRelations(linkTable, sourceId) {
        if (!this.data[linkTable]) return;
        this.data[linkTable] = this.data[linkTable].filter(
            i => i[`${linkTable.split('_')[0]}_id`] !== sourceId
        );
    }

    matchCriteria(item, criteria) {
        return Object.entries(criteria).every(([key, condition]) => {
            if (typeof condition === 'object' && condition !== null) {
                return Object.entries(condition).every(([op, value]) => {
                    switch(op) {
                        case 'gt': return item[key] > value;
                        case 'lt': return item[key] < value;
                        case 'like': return new RegExp(value).test(item[key]);
                        default: return item[key] === condition;
                    }
                });
            }
            return item[key] === condition;
        });
    }

    isFieldUnique(type, field) {
        const values = this.data[type]?.map(i => i[field]);
        return new Set(values).size === values?.length;
    }

    guessType(obj) {
        return obj.__type || Object.getPrototypeOf(obj)?.constructor?.name.toLowerCase();
    }

    freeze(frozen = true) {
        this.frozen = frozen;
    }

    async nuke() {
        if (this.frozen) throw new Error('Cannot nuke frozen DB');
        this.data = {};
        await this.save();
    }
}

export default GreenBean;