import type { GenerateOptions, StreamChunk } from '@deepseek-ai/dsh-llm'
import { LlmAdapter } from '@deepseek-ai/dsh-llm'

/** Helpers to write scripted responses tersely. */
export function textResponse(text: string): StreamChunk[] {
  return [
    { type: 'block-start', index: 0, blockType: 'text' },
    ...[...text].map((char): StreamChunk => ({ type: 'text-delta', index: 0, text: char })),
    { type: 'block-end', index: 0, block: { type: 'text', text } },
    { type: 'usage', usage: { inputTokens: 10, outputTokens: text.length } },
    { type: 'finish', reason: { kind: 'stop' } },
  ]
}

export function toolCallResponse(callId: string, name: string, args: object, text?: string): StreamChunk[] {
  const argumentsJson = JSON.stringify(args)
  const chunks: StreamChunk[] = []
  let index = 0
  if (text) {
    chunks.push(
      { type: 'block-start', index, blockType: 'text' },
      { type: 'text-delta', index, text },
      { type: 'block-end', index, block: { type: 'text', text } },
    )
    index += 1
  }
  chunks.push(
    { type: 'block-start', index, blockType: 'tool-call' },
    { type: 'tool-call-delta', index, id: callId, name, argumentsDelta: argumentsJson.slice(0, 5) },
    { type: 'tool-call-delta', index, id: callId, argumentsDelta: argumentsJson.slice(5) },
    {
      type: 'block-end',
      index,
      block: { type: 'tool-call', id: callId, name, arguments: argumentsJson },
    },
    { type: 'usage', usage: { inputTokens: 10, outputTokens: 5 } },
    { type: 'finish', reason: { kind: 'tool-calls' } },
  )
  return chunks
}

/**
 * Mock adapter driven by a script: each model call consumes the next entry.
 * Records every request it receives for assertions. An entry may be a
 * function to compute chunks from the request, or a 'hang' marker that
 * streams one chunk then waits until aborted.
 */
export class MockAdapter extends LlmAdapter {
  requests: GenerateOptions[] = []

  constructor(private script: (StreamChunk[] | ((options: GenerateOptions) => StreamChunk[]) | 'hang')[]) {
    super()
  }

  async * stream(options: GenerateOptions): AsyncIterable<StreamChunk> {
    this.requests.push(options)
    const entry = this.script.shift()
    if (!entry) throw new Error('MockAdapter: script exhausted')
    if (entry === 'hang') {
      yield { type: 'block-start', index: 0, blockType: 'text' }
      yield { type: 'text-delta', index: 0, text: 'partial' }
      await new Promise<void>((_resolve, reject) => {
        if (options.signal?.aborted) return reject(new Error('aborted'))
        options.signal?.addEventListener('abort', () => reject(new Error('aborted')), { once: true })
      })
      return
    }
    const chunks = typeof entry === 'function' ? entry(options) : entry
    for (const chunk of chunks) {
      if (options.signal?.aborted) throw new Error('aborted')
      yield chunk
    }
  }
}