import { defineProperty, isNullable } from 'cosmokit'
import type { Dict } from 'cosmokit'
import { Context } from './context.ts'
import { getTraceable, symbols, withProps } from './utils.ts'
import { Fiber, FiberState } from './fiber.ts'

declare module './context.ts' {
  interface Context {
    /**
     * Read a service from the store without the inject requirement.
     *
     * @param name — the service name.
     * @param strict — when `true` (default), only return implementations
     * whose providing fiber is currently active.
     * @returns the service value, or `undefined` when not (yet) provided.
     */
    get<K extends string & keyof this>(name: K, strict?: boolean): undefined | this[K]
    /** Same as above for service names outside the typed `Context` surface. */
    get(name: string, strict?: boolean): any
    /**
     * Overwrite a provided service's value.
     *
     * Only the fiber that provided the service may set it; setting an
     * unprovided name throws.
     *
     * @param name — the service name.
     * @param value — the new service value.
     */
    set<K extends string & keyof this>(name: K, value: undefined | this[K]): void
    /** Same as above for service names outside the typed `Context` surface. */
    set(name: string, value: any): void
    /**
     * Register a service implementation owned by the current fiber.
     *
     * The service becomes visible to dependents in the same isolation scope
     * once the fiber is active; it is unregistered (waking dependents) when
     * the returned disposer runs or the fiber unloads. Throws if the name is
     * already provided in this scope or declared as an accessor.
     *
     * @param name — the service name.
     * @param value — the service value.
     * @returns a disposer that unregisters the service.
     */
    provide<K extends string & keyof this>(name: K, value: undefined | this[K]): () => void
    /** Same as above for service names outside the typed `Context` surface. */
    provide(name: string, value?: any): () => void
    /**
     * Define a computed context property backed by get/set hooks.
     *
     * The accessor is removed when the current fiber unloads. Throws if the
     * name is already declared.
     *
     * @param name — the context property name.
     * @param options — the `get` hook and optional `set` hook.
     */
    accessor(name: string, options: Omit<Property.Accessor, 'type'>): void
    /**
     * Expose selected members of a service directly on `ctx`.
     *
     * Each mixed-in key becomes an accessor that forwards to the service
     * (binding methods to it), so e.g. `ctx.on` forwards to `ctx.events.on`.
     * Mixins are removed when the current fiber unloads.
     *
     * @param name — the context property holding the source service.
     * @param mixins — keys to forward, or a source-key → ctx-key map.
     */
    mixin<K extends string & keyof this>(name: K, mixins: (keyof this & keyof this[K])[] | Dict<string>): void
    /** Same as above with a source object instead of a context property name. */
    mixin<T extends {}>(source: T, mixins: (keyof this & keyof T)[] | Dict<string>): void
  }
}

function enhanceError(error: Error) {
  const lines = error.stack!.split('\n')
  lines.splice(0, 2, `Error: ${error.message}`)
  error.stack = lines.join('\n')
  return error
}

const RESERVED_WORDS = ['prototype', 'then']

// - is a symbol
// - is a reserved word (prototype, then)
// - is a number string (0, 1, 2, ...)
// - starts with `_`
function isSpecialProperty(prop: string | symbol): prop is symbol {
  return typeof prop === 'symbol'
    || RESERVED_WORDS.includes(prop)
    || parseInt(prop).toString() === prop
    || prop.startsWith('_')
}

/** Context property definition known by the reflection service. */
export type Property = Property.Service | Property.Accessor

/** Property definition variants understood by `ReflectService`. */
export namespace Property {
  /** Service property backed by a provided implementation. */
  export interface Service {
    /** Discriminator. */
    type: 'service'
  }

  /** Computed context property backed by custom get/set hooks. */
  export interface Accessor {
    /** Discriminator. */
    type: 'accessor'
    /** Compute the property value; `error` carries the caller stack for diagnostics. */
    get: (this: Context, receiver: any, error: Error) => any
    /** Optional setter; return `false` to reject the write. */
    set?: (this: Context, value: any, receiver: any, error: Error) => boolean
  }
}

/** Concrete service implementation record stored in the root reflect service. */
export interface Impl {
  /** The service name. */
  name: string
  /** The fiber that provided the service (owns its lifetime). */
  fiber: Fiber
  /** The current service value. */
  value?: any
  /** Optional availability predicate consulted before dependents may load. */
  check?: () => boolean
}

/**
 * Reflection and service-resolution layer installed as `ctx.reflect`.
 *
 * This service powers the context proxy, service registration, accessors, and
 * the mixins that expose core service methods directly on `ctx`.
 */
export class ReflectService {
  /** Proxy traps implementing service resolution for every context object. */
  static handler: ProxyHandler<Context> = {
    get: (target, prop, ctx: Context) => {
      if (isSpecialProperty(prop)) {
        return Reflect.get(target, prop, ctx)
      }
      if (Reflect.has(target, prop)) {
        return getTraceable(ctx, Reflect.get(target, prop, ctx))
      }

      const error = new Error(`cannot get property "${prop}" without inject`)

      try {
        const def = target.reflect.props[prop]
        if (def?.type === 'accessor') {
          return def.get.call(ctx, ctx[symbols.receiver], error)
        }

        if (!ctx.fiber.runtime) return ctx.reflect.get(prop, false)
        return ctx.events.waterfall('internal/get', ctx, prop, error, () => {
          const key = target[symbols.isolate][prop]
          let fiber = (ctx[symbols.shadow] as Context ?? ctx).fiber
          while (true) {
            const impl = fiber.store?.[prop]
            if (impl) return getTraceable(ctx, impl.value)
            if (prop in fiber.inject) {
              error.message = `cannot get required service "${prop}" in inactive context`
              throw error
            }
            if (!fiber.runtime) throw error
            if (fiber.parent[symbols.isolate][prop] !== key) throw error
            fiber = fiber.parent.fiber
          }
        })
      } catch (e: any) {
        throw e === error ? enhanceError(e) : e
      }
    },

    set: (target, prop, value, ctx: Context) => {
      if (isSpecialProperty(prop)) {
        return Reflect.set(target, prop, value, ctx)
      }

      const error = new Error(`cannot set property "${prop}" without provide`)
      const def = target.reflect.props[prop]
      if (!def) {
        if (!ctx.fiber.runtime) return Reflect.set(target, prop, value, ctx)
        throw enhanceError(error)
      }

      try {
        if (def.type === 'accessor') {
          if (!def.set) return false
          return def.set.call(ctx, value, ctx[symbols.receiver], error)
        }

        return ctx.events.waterfall('internal/set', ctx, prop, value, error, () => {
          return ctx.reflect.set(prop, value, error)
        })
      } catch (e: any) {
        throw e === error ? enhanceError(e) : e
      }
    },

    has: (target, prop) => {
      if (isSpecialProperty(prop)) {
        return Reflect.has(target, prop)
      }
      if (Reflect.has(target, prop)) return true
      return !!target.reflect.props[prop]
    },
  }

  /** Service implementations, keyed by isolation label. */
  public store: Dict<Impl, symbol> = Object.create(null)
  /** Declared context properties (services and accessors), by name. */
  public props: Dict<Property> = Object.create(null)

  constructor(public ctx: Context) {
    defineProperty(this, symbols.tracker, {
      property: 'ctx',
      noShadow: true,
    })

    this.mixin('reflect', ['get', 'set', 'provide', 'accessor', 'mixin'])
    this.mixin('fiber', ['runtime', 'effect'])
    this.mixin('registry', ['inject', 'plugin'])
    this.mixin('events', ['on', 'once', 'parallel', 'emit', 'serial', 'bail', 'waterfall'])
  }

  /**
   * Read a service from the store without the inject requirement.
   *
   * @param name — the service name.
   * @param strict — when `true`, only return implementations whose providing
   * fiber is currently active.
   * @returns the service value, or `undefined` when not (yet) provided.
   */
  get(name: string, strict = true) {
    return getTraceable(this.ctx, this._getImpl(name, strict)?.value)
  }

  _getImpl(name: string, strict = true) {
    const key = this.ctx[symbols.isolate][name]
    const impl = key && this.store[key]
    if (!impl) return
    if (strict && impl.fiber.state !== FiberState.ACTIVE) return
    return impl
  }

  /**
   * Overwrite a provided service's value.
   *
   * @param name — the service name.
   * @param value — the new service value.
   * @param error — carrier for the caller stack in diagnostics.
   * @returns `true` on success.
   * @throws when `name` was never provided, or was provided by another fiber.
   */
  set(name: string, value: any, error?: Error) {
    const key = this.ctx[symbols.isolate][name]
    const impl = this.store[key]
    if (!impl) {
      throw new Error(`cannot set property "${name}" without provide`)
    }
    if (impl.fiber !== this.ctx.fiber) {
      throw new Error(`cannot set property "${name}" in multiple fibers`)
    }
    impl.value = value
    return true
  }

  /**
   * Register a service implementation owned by the current fiber.
   *
   * See the `ctx.provide()` overload above for the full contract.
   *
   * @param name — the service name.
   * @param value — the service value.
   * @param check — optional availability predicate for dependents.
   * @returns a disposer that unregisters the service.
   */
  provide(name: string, value?: any, check?: () => boolean) {
    return this.ctx.fiber.effect(() => {
      if (!this.props[name]) {
        this.props[name] ??= { type: 'service' }
      } else if (this.props[name].type !== 'service') {
        throw new Error(`property "${name}" is already declared as ${this.props[name].type}`)
      }
      this.props[name] = { type: 'service' }

      this.ctx.root[symbols.isolate][name] ??= Symbol(name)
      const key = this.ctx[symbols.isolate][name]
      const impl: Impl = { name, value, fiber: this.ctx.fiber, check }
      if (this.store[key]) {
        throw new Error(`service "${name}" has been registered at <${this.store[key].fiber.name}>`)
      }
      this.store[key] = impl
      this.ctx.fiber.store![name] = impl
      if (this.ctx.fiber.state === FiberState.ACTIVE) {
        this.notify([name])
      }
      return async () => {
        delete this.store[key]
        const fibers = this.notify([name])
        await Promise.allSettled(fibers.map(fiber => fiber.await()))
        // ensure self access before dependencies cleanup
        delete this.ctx.fiber.store![name]
      }
    }, `ctx.provide(${JSON.stringify(name)})`)
  }

  /**
   * Re-evaluate every fiber that requires one of the given services.
   *
   * @param names — the service names that changed.
   * @param filter — restricts notification to matching isolation scopes.
   * @returns the fibers whose dependency state was refreshed.
   */
  notify(names: string[], filter = (ctx: Context, name: string) => ctx[symbols.isolate][name] === this.ctx[symbols.isolate][name]) {
    const fibers: Fiber[] = []
    for (const runtime of this.ctx.registry.values()) {
      for (const fiber of runtime.fibers) {
        let hasUpdate = false
        for (const name of names) {
          if (!(name in fiber.inject)) continue
          if (!filter(fiber.ctx, name)) continue
          hasUpdate = true
          fiber._checkImpl(name)
        }
        if (!hasUpdate) continue
        fiber._refresh()
        fibers.push(fiber)
      }
    }
    for (const name of names) {
      const self: Context = Object.create(this.ctx)
      self[symbols.filter] = (target: Context) => filter(target, name)
      this.ctx.events.emit(self, 'internal/service', name, this._getImpl(name, false)?.value)
    }
    return fibers
  }

  /**
   * Define a computed context property backed by get/set hooks.
   *
   * @param name — the context property name.
   * @param options — the `get` hook and optional `set` hook.
   * @returns a disposer that removes the accessor.
   */
  accessor(name: string, options: Omit<Property.Accessor, 'type'>) {
    return this.ctx.fiber.effect(() => {
      if (name in this.props) {
        throw new Error(`property "${name}" is already declared as ${this.props[name].type}`)
      }
      this.props[name] = { type: 'accessor', ...options }
      return () => delete this.props[name]
    }, `ctx.accessor(${JSON.stringify(name)})`)
  }

  /**
   * Expose selected members of a service directly on `ctx`.
   *
   * See the `ctx.mixin()` overload above for the full contract.
   *
   * @param source — a context property name or a source object.
   * @param mixins — keys to forward, or a source-key → ctx-key map.
   * @returns a disposer that removes all created accessors.
   */
  mixin(source: any, mixins: string[] | Dict<string>) {
    const self = this
    return this.ctx.fiber.effect(function* () {
      const entries = Array.isArray(mixins) ? mixins.map(key => [key, key]) : Object.entries(mixins)
      const getTarget = (ctx: Context, error: Error) => {
        // TODO enhance error message
        return ctx[source]
      }
      for (const [key, value] of entries) {
        yield self.accessor(value, {
          get(receiver, error) {
            const service = getTarget(this, error)
            if (isNullable(service)) return service
            const mixin = receiver ? withProps(receiver, service) : service
            const value = Reflect.get(service, key, mixin)
            if (typeof value !== 'function') return value
            return value.bind(mixin ?? service)
          },
          set(value, receiver, error) {
            const service = getTarget(this, error)
            const mixin = receiver ? withProps(receiver, service) : service
            return Reflect.set(service, key, value, mixin)
          },
        })
      }
    }, `ctx.mixin(${JSON.stringify(source)})`)
  }

  /**
   * Attach this context's tracing wrapper to a value.
   *
   * @param value — the value to wrap.
   * @returns the traceable wrapper (or the value itself when not applicable).
   */
  trace<T>(value: T) {
    return getTraceable(this.ctx, value)
  }

  /**
   * Wrap a callback so calls trace `this` and arguments to this context.
   *
   * @param callback — the function to wrap.
   * @returns a proxy delegating to `callback` with traced values.
   */
  bind<T extends Function>(callback: T) {
    return new Proxy(callback, {
      apply: (target, thisArg, args) => {
        return Reflect.apply(target, this.trace(thisArg), args.map(arg => this.trace(arg)))
      },
      construct: (target, args, newTarget) => {
        return Reflect.construct(target, args.map(arg => this.trace(arg)), newTarget)
      },
    })
  }
}