/** Package-owned tool-pipeline invariants. @module @deepseek-ai/dsh-tools/invariant */

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

const PACKAGE_NAME = '@deepseek-ai/dsh-tools'

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

type ToolStage = 'pre' | 'execute' | 'post'

/** Validate the immutable final execution/result snapshot. */
function validateResult(
  exec: Readonly<ToolExecution>,
  result: Readonly<ToolExecutionResult>,
  fail: InvariantFailure,
): void {
  if (!Object.isFrozen(exec)) fail('tools/result execution must be frozen before publication')
  if (!Object.isFrozen(result) || !Object.isFrozen(result.content)) {
    fail('tools/result outcome and content must be frozen before publication')
  }
  if (exec.name.length === 0 || String(exec.callId).length === 0) {
    fail('tools/result execution must carry non-empty name and callId')
  }
}

/** Install monotonic pipeline, final-snapshot, and code-dispatch enclosure checks. */
const install: InvariantInstaller = Object.assign((ctx: Context, fail: InvariantFailure) => {
  const stages = new WeakMap<object, ToolStage>()
  const openTurns = new WeakMap<Session, number | null>()
  const seed = (session: Session): number | null => {
    let openTurn: number | null = null
    for (const event of session.events) {
      if (event.type === 'turn/start') openTurn = event.data.turn
      else if (event.type === 'turn/end') openTurn = null
      else if ((event.type === 'tool/code-dispatch-start' || event.type === 'tool/code-dispatch')
        && openTurn === null) {
        fail(`${event.type} appended outside any open turn`)
      }
    }
    openTurns.set(session, openTurn)
    return openTurn
  }
  const openTurnFor = (session: Session): number | null => openTurns.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') openTurns.set(session, event.data.turn)
    else if (event.type === 'turn/end') openTurns.set(session, null)
  }, { global: true })
  ctx.on('internal/dispatch', (_mode, eventName, args) => {
    if (eventName === 'session/event') {
      const [session, event] = args as [Session, SessionEvent]
      if ((event.type === 'tool/code-dispatch-start' || event.type === 'tool/code-dispatch')
        && openTurnFor(session) === null) {
        fail(`${event.type} appended outside any open turn`)
      }
      return
    }
    if (eventName === 'tools/pre-execute') {
      const exec = args[0] as ToolExecution
      if (stages.has(exec)) fail('tools/pre-execute repeated for one execution')
      stages.set(exec, 'pre')
      return
    }
    if (eventName === 'tools/execute') {
      const exec = args[0] as ToolExecution
      if (stages.get(exec) !== 'pre') fail('tools/execute must follow tools/pre-execute')
      stages.set(exec, 'execute')
      return
    }
    if (eventName === 'tools/post-execute') {
      const exec = args[0] as ToolExecution
      const previous = stages.get(exec)
      if (previous !== 'pre' && previous !== 'execute') {
        fail('tools/post-execute must follow tools/pre-execute or tools/execute')
      }
      stages.set(exec, 'post')
      return
    }
    if (eventName !== 'tools/result') return
    const [exec, result] = args as [Readonly<ToolExecution>, Readonly<ToolExecutionResult>]
    validateResult(exec, result, fail)
    stages.delete(exec)
  }, { global: true })
}, { inject: ['sessions'] })

/**
 * Register the tools 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))