/** Package-owned durable plan-mode invariants. @module @deepseek-ai/dsh-plan-mode/invariant */

import type { Context } from 'cordis'
import type { Session, SessionEvent } from '@deepseek-ai/dsh-session'
import type { InvariantFailure, InvariantInstaller } from '@deepseek-ai/dsh-invariants'

const PACKAGE_NAME = '@deepseek-ai/dsh-plan-mode'

/** Cordis companion plugin name. */
export const name = 'plan-mode-invariant'
/** Service required before the companion can reserve package ownership. */
export const inject = ['invariants']

/** Validate one `plan/mode` event before it reaches the durable log. */
function validateEvent(openTurn: number | null, event: SessionEvent, fail: InvariantFailure): void {
  if (event.type !== 'plan/mode') return
  if (openTurn === null) fail('plan/mode appended outside any open turn')
  const active = (event.data as { active?: unknown }).active
  if (typeof active !== 'boolean') {
    fail(`plan/mode carries invalid active state ${JSON.stringify(active)}; expected a boolean`)
  }
}

/* jscpd:ignore-start -- package companions share replay and dispatch plumbing */
/** Install validation for loaded and newly appended plan-mode state. */
const install: InvariantInstaller = Object.assign((ctx: Context, fail: InvariantFailure) => {
  const traces = new WeakMap<Session, number | null>()
  const seed = (session: Session): number | null => {
    let openTurn: number | null = null
    traces.set(session, openTurn)
    for (const event of session.events) {
      if (event.type === 'turn/start') openTurn = event.data.turn
      else if (event.type === 'turn/end') openTurn = null
      validateEvent(openTurn, event, fail)
      traces.set(session, openTurn)
    }
    return openTurn
  }
  const traceFor = (session: Session): number | null => traces.get(session) ?? seed(session)

  for (const session of ctx.sessions.list()) seed(session)
  ctx.on('session/created', (session) => { seed(session) }, { global: true })
  ctx.on('session/event', (session, event) => {
    if (event.type === 'turn/start') traces.set(session, event.data.turn)
    else if (event.type === 'turn/end') traces.set(session, null)
  }, { global: true })
  ctx.on('internal/dispatch', (_mode, eventName, args) => {
    if (eventName !== 'session/event') return
    const [session, event] = args as [Session, SessionEvent]
    validateEvent(traceFor(session), event, fail)
  }, { global: true })
}, { inject: ['sessions'] })
/* jscpd:ignore-end */

/**
 * Register the plan-mode invariant companion.
 * @param ctx - Cordis context carrying the invariant service.
 * @returns the installed registration's disposer after setup succeeds.
 */
export const apply = (ctx: Context): Promise<() => void> =>
  Promise.resolve(ctx.invariants.register(PACKAGE_NAME, install))