/**
 * Agent presets: each session composes its model-facing plugin set from one
 * preset `cordis.yml`, mounted ONCE per preset under a standing scope and
 * joined by every agent that names it.
 *
 * The standing mount is what makes a preset one composition rather than one
 * per session: its plugin instances, tool registrations, prompt sections, and
 * projection units exist exactly once, keyed per session inside the plugins
 * themselves (they predate presets and were written for a shared world). An
 * agent joins by having its scope key parented to the mount's
 * ({@link setScopeParent}), which makes the mount's registrations visible to
 * that agent's views and the mount's listeners receive that agent's events —
 * and a host reader with no agent at all (a cold transcript read) resolves
 * the same standing registrations by preset id.
 *
 * This package owns the preset vocabulary, filesystem discovery, and the
 * guarded standing mount. It does not decide when an agent is created — the
 * agent factory's `setup(agentCtx)` hook is the one supported call site,
 * because only there is the join installed while the agent is still
 * unpublished, so a rejected composition rolls the whole creation back.
 * @module @deepseek-ai/dsh-agent-presets
 */

import { Context, Service } from 'cordis'
import z from 'schemastery'
import { createScope, scopeOf, setScopeParent, type Scope, type ScopeKey } from '@deepseek-ai/dsh-scope'
import { settingsNamespace, type SettingsScope } from '@deepseek-ai/dsh-settings'
import { discoverPresets } from './discovery.ts'
import { mountPreset, serviceForAgent } from './mount.ts'
import { UnknownPresetError, type AgentPreset, type Config } from './types.ts'

/** Settings namespace carrying the user's chosen default preset. */
export const SETTINGS_NAMESPACE = 'agent-presets'

/** The user-writable slice of this plugin's config. */
export interface AgentPresetSettings {
  /** Preset mounted when a session names none. */
  default?: string
}

/** Runtime schema for the user-writable slice. */
export const AgentPresetSettingsSchema: z<AgentPresetSettings> = z.object({
  default: z.string(),
})

export { COMPOSITION_FILE, discoverPresets, scanRoot } from './discovery.ts'
export {
  inactiveRows, leakedServices, livePresetMounts, mountPreset, serviceForAgent,
  type PresetMount,
} from './mount.ts'
export { resolveSessionPreset, type PresetBearingSession } from './session.ts'
export { PresetMountError, UnknownPresetError } from './types.ts'
export type { AgentPreset, Config, PresetRoot, PresetTrust } from './types.ts'

declare module 'cordis' {
  interface Context {
    agentPresets: AgentPresets
  }
}

/**
 * Registry over the deployment's agent presets.
 *
 * Discovery is unmemoized: `list()` and `resolve()` re-read the roots on every
 * call so a preset authored while the process runs is visible immediately,
 * and a preset deleted underneath a picker disappears from the next read.
 */
export class AgentPresets extends Service {
  static inject = ['loader']

  /** Runtime schema for the preset roster. */
  static Config = z.object({
    default: z.string().required(),
    roots: z.array(z.object({
      path: z.string().required(),
      trust: z.union(['system', 'user'] as const).default('user'),
    })).default([]),
  }) as z<Config>

  /**
   * The user layer over `config.default`, present only while a settings
   * provider is composed. Held rather than snapshotted so a hot-reloaded
   * document takes effect without a restart.
   */
  private settings: SettingsScope<AgentPresetSettings> | undefined

  /**
   * The service's own untraced context. Methods invoked through the traceable
   * proxy see `this.ctx` rebound to the CALLER's context, which carries a
   * shadow; a subtree minted from it resolves every service through that
   * shadow's fiber instead of each entry's own inject store, so preset rows
   * would fail on the very services they declare. Standing mounts must hang
   * off the untraced original (the `tasks-local` selfCtx precedent).
   */
  private readonly selfCtx: Context

  constructor(ctx: Context, public config: Config) {
    super(ctx, 'agentPresets')
    this.selfCtx = ctx
    // Deliberately not `installSettingsSection`: that helper exists to re-judge
    // what a consumer DERIVED from the source — memoized resolutions,
    // registration-level facts — across attach, detach, and change. Nothing
    // here is derived. `defaultId` reads through on every call, so both of its
    // hooks would be no-ops and the source thunk would restate this field.
    ctx.inject(['settings'], (settingsCtx) => {
      this.settings = settingsCtx.settings.register(
        settingsNamespace(SETTINGS_NAMESPACE),
        AgentPresetSettingsSchema,
        { base: { default: config.default } },
      )
      settingsCtx.effect(() => () => { this.settings = undefined }, 'agentPresets.settings()')
    })
  }

  /**
   * The preset id mounted when a caller names none.
   *
   * Read per call rather than cached: the settings document is hot-reloaded, so
   * changing the default takes effect on the next session created and leaves
   * every running session on the preset it was composed from.
   */
  get defaultId(): string {
    return this.settings?.get().default ?? this.config.default
  }

  /**
   * Every preset the configured roots currently supply.
   * @returns the presets, first-root-wins per id.
   */
  async list(): Promise<AgentPreset[]> {
    return await discoverPresets(this.config.roots)
  }

  /**
   * Resolve one preset by id.
   * @param id - the preset id, or `undefined` for {@link defaultId}.
   * @returns the resolved preset.
   * @throws when no configured root supplies that id.
   */
  async resolve(id?: string): Promise<AgentPreset> {
    const wanted = id ?? this.defaultId
    const presets = await this.list()
    const found = presets.find(preset => preset.id === wanted)
    if (found === undefined) {
      throw new UnknownPresetError(wanted, presets.map(preset => preset.id))
    }
    return found
  }

  /**
   * Standing mounts by preset id, single-flight so two agents racing the
   * first use of one preset share one composition. A settled failure is
   * removed so a later session retries a preset whose file has been fixed; a
   * settled success is permanent for the process — the composition a running
   * session joined must survive the file changing or disappearing underneath
   * it, so file edits reach only future generations (a later authoring layer
   * swaps this pointer; it never disposes a joined generation).
   */
  private readonly standing = new Map<string, Promise<StandingMount>>()

  /**
   * Compose one agent from a preset: ensure the preset's standing mount, then
   * parent the agent's scope key to it so the mount's registrations and
   * listeners cover this agent.
   *
   * Call from the agent factory's `setup(agentCtx)`; a rejection there rolls
   * the agent creation back, so a broken preset never yields a half-composed
   * session.
   * @param agentCtx - the agent's scope context.
   * @param id - the preset id, or `undefined` for {@link defaultId}.
   * @returns the preset that was composed, for the caller to record.
   * @throws when the preset is unknown or its composition is unusable.
   */
  async mount(agentCtx: Context, id?: string): Promise<AgentPreset> {
    const agentKey = scopeOf(agentCtx)
    if (agentKey === undefined) {
      throw new Error('agent-presets: refusing to compose an unscoped context; the scope key is what joins an agent to its preset')
    }
    const preset = await this.resolve(id)
    const standing = await this.ensureStanding(preset)
    setScopeParent(agentKey, standing.key)
    return preset
  }

  /**
   * One agent's instance of a service its preset mounted.
   *
   * A preset publishes services behind `isolate` realms, which are invisible
   * outside the group that declares them — including to the host. This is how a
   * caller holding the agent reads one anyway: a request that is ABOUT a
   * session but arrives from outside it, which is every browser RPC.
   *
   * Read addressing only. A host row that `inject`s a service cannot use this,
   * because injection resolves before any session exists and has no agent to
   * key by; such a service belongs on the host plane instead.
   * @param agent - the agent whose composition to look inside.
   * @param name - the service name as the preset's rows resolve it.
   * @returns the agent's instance, or undefined when its preset mounts none.
   */
  serviceFor<K extends string & keyof Context>(agent: { ctx: Context }, name: K): Context[K] | undefined {
    return serviceForAgent(this.ctx, agent, name)
  }

  /**
   * Re-link one agent to a different preset's standing composition.
   *
   * Only valid while the agent has produced nothing: swapping tools mid
   * conversation would leave logged tool calls the new composition cannot
   * make. The CALLER owns that check — this method does not read session
   * history.
   *
   * The swap is a parent re-link, not an unmount: standing mounts are shared
   * and permanent, so the old composition stays for its other agents and the
   * new one is ensured BEFORE the link moves. An unknown or unusable preset
   * therefore throws with the agent exactly as it was — there is no torn-down
   * state to restore.
   * @param agentCtx - the agent's scope context.
   * @param id - the preset to compose the agent from instead.
   * @returns the preset now installed.
   * @throws when the preset is unknown or its composition is unusable.
   */
  async recompose(agentCtx: Context, id: string): Promise<AgentPreset> {
    const agentKey = scopeOf(agentCtx)
    if (agentKey === undefined) {
      throw new Error('agent-presets: refusing to recompose an unscoped context')
    }
    const preset = await this.resolve(id)
    const standing = await this.ensureStanding(preset)
    setScopeParent(agentKey, standing.key)
    return preset
  }

  /**
   * The standing scope key of one preset, for a host reader with no agent.
   *
   * A cold transcript read resolves tool presenters against the composition
   * the session recorded, and the standing mount makes that possible without
   * resuming anything: ensuring the mount composes plugins but starts no
   * agent, no session, and no turn.
   * @param id - the preset id, or `undefined` for {@link defaultId}.
   * @returns the standing scope key readers pass as a registry view scope.
   * @throws when the preset is unknown or its composition is unusable.
   */
  async standingKeyFor(id?: string): Promise<ScopeKey> {
    const preset = await this.resolve(id)
    return (await this.ensureStanding(preset)).key
  }

  /** Resolve (or create, single-flight) the standing mount of one preset. */
  private ensureStanding(preset: AgentPreset): Promise<StandingMount> {
    const pending = this.standing.get(preset.id)
    if (pending !== undefined) return pending
    const created = (async (): Promise<StandingMount> => {
      const key: ScopeKey = { agentPreset: preset.id }
      const scope = createScope(this.selfCtx, key)
      try {
        await mountPreset(scope.ctx, preset)
      } catch (error) {
        this.standing.delete(preset.id)
        await scope.dispose()
        throw error
      }
      return { key, scope }
    })()
    this.standing.set(preset.id, created)
    return created
  }
}

/** One preset's standing composition. */
interface StandingMount {
  /** Scope key agents are parented to; also the mount's registration scope. */
  readonly key: ScopeKey
  /** Disposal boundary; held for whole-tree teardown, never per-session. */
  readonly scope: Scope
}

export default AgentPresets