import { Context, Service } from '@deepseek-ai/cordis'
import { Entry, type EntryOptions } from './entry.ts'
import { EntryTree } from './tree.ts'

/** Runtime owner for a list of child loader entries. */
export class EntryGroup {
  static readonly key = Symbol.for('cordis.group')

  public data: EntryOptions[] = []

  constructor(public ctx: Context, public tree: EntryTree) {
    const entry = ctx.fiber.entry
    if (entry) entry.subgroup = this
  }

  get context(): Context {
    return this.ctx
  }

  async create(options: Omit<EntryOptions, 'id'>) {
    const id = this.tree.ensureId(options)
    const existing = this.tree.store[id]
    const entry: Entry = existing ?? (this.tree.store[id] = new Entry(this.ctx.loader))
    const previousParent = entry.parent
    // Entry may be moved from another group,
    // so we need to update the parent reference.
    entry.parent = this
    // Use `create: true` to replace existing entry.options.
    try {
      await entry.update(options, true, true)
    } catch (error) {
      if (existing) {
        entry.parent = previousParent
      } else {
        delete this.tree.store[id]
      }
      throw error
    }
    return entry.id
  }

  unlink(options: EntryOptions) {
    const config = this.data
    const index = config.indexOf(options)
    if (index >= 0) config.splice(index, 1)
  }

  async remove(id: string, isDispose = false) {
    const entry = this.tree.store[id]
    if (!entry) return
    await entry._dispose()
    if (!isDispose) {
      this.unlink(entry.options)
    }
    delete this.tree.store[id]
    this.context.emit('loader/partial-dispose', entry, entry.options, false)
  }

  async update(config: EntryOptions[]) {
    const oldConfig = this.data as EntryOptions[]
    const seen = new Set<string>()
    for (const options of config) {
      const id = this.tree.ensureId(options)
      if (seen.has(id)) throw new TypeError(`duplicate loader entry id: ${id}`)
      seen.add(id)
    }
    const oldMap = Object.fromEntries(oldConfig.map(options => [options.id, options]))
    const newMap = Object.fromEntries(config.map(options => [options.id, options]))

    try {
      const outcomes = await Promise.allSettled(config.map(options => this.create(options)))
      // Disposal owns termination: sibling starts can still be settling after
      // the containing tree has gone away, but their failures no longer
      // describe a live update to roll back.
      if (this.ctx.fiber.uid === null) return
      const failures = outcomes
        .filter((outcome): outcome is PromiseRejectedResult => outcome.status === 'rejected')
        .map(outcome => outcome.reason)
      if (failures.length === 1) throw failures[0]
      if (failures.length > 1) throw new AggregateError(failures, 'loader entries failed to apply')
      for (const id of Object.keys(oldMap)) {
        if (!newMap[id]) await this.remove(id, true)
      }
      this.data = config
    } catch (error) {
      const rollbackErrors: unknown[] = []
      for (const id of Object.keys(newMap).reverse()) {
        if (oldMap[id]) continue
        try {
          await this.remove(id, true)
        } catch (rollbackError) {
          rollbackErrors.push(rollbackError)
        }
      }
      for (const options of oldConfig) {
        try {
          await this.create(options)
        } catch (rollbackError) {
          rollbackErrors.push(rollbackError)
        }
      }
      this.data = oldConfig
      if (rollbackErrors.length) throw new AggregateError([error, ...rollbackErrors], 'loader entry rollback failed')
      throw error
    }
  }

  async stop() {
    for (const options of this.data) {
      await this.remove(options.id, true)
    }
  }
}

/** Plugin that mounts a nested loader entry group. */
export class Group extends EntryGroup {
  static initial: Omit<EntryOptions, 'id'>[] = []
  static readonly [EntryGroup.key] = true

  constructor(public ctx: Context, public config: EntryOptions[]) {
    super(ctx, ctx.fiber.entry!.parent.tree)
    ctx.on('internal/update', config => this.update(config))
  }

  async* [Service.init]() {
    yield () => this.stop()
    await this.update(this.config)
  }
}