/**
 * Serialize harness vocabulary (`GenerateOptions`, `Message[]`) into the
 * DeepSeek chat-completions request body.
 *
 * Block-type mapping (core types handled explicitly; merge-extensible unions
 * mean plugin-added block types exist — they are skipped, never errors):
 *
 * - user `text` → string content (joined)
 * - assistant `text` → `content`; `reasoning` → `reasoning_content`, but
 *   ONLY on assistant messages that carry tool calls (the official passback
 *   rule for thinking mode — required there, ignored elsewhere, so we save
 *   the tokens elsewhere); `tool-call` → `tool_calls[]`
 * - `tool-result` → its own `{role: 'tool'}` message (text flattened)
 * - `image` → skipped (MVP limitation, documented in the README)
 *
 * @module dsh-llm-deepseek/serialize
 */

import { LlmError } from '@deepseek-ai/dsh-llm'
import type { ContentBlock, GenerateOptions, Message } from '@deepseek-ai/dsh-llm'
import type { WireMessage, WireRequest, WireTool } from './types.ts'

/** Adapter-level request defaults (from plugin config). */
export interface RequestDefaults {
  thinking?: 'enabled' | 'disabled' | undefined
  reasoningEffort?: 'high' | 'max' | undefined
}

/** Join the text blocks of a message (used for user/tool-result content). */
function flattenText(blocks: ContentBlock[]): string {
  return blocks
    .filter(block => block.type === 'text')
    .map(block => block.text)
    .join('')
}

/** Serialize one assistant message (text + reasoning + tool calls). */
function serializeAssistant(message: Message): WireMessage {
  const text = flattenText(message.content)
  const reasoning = message.content
    .filter(block => block.type === 'reasoning')
    .map(block => block.text)
    .join('')
  const toolCalls = message.content
    .filter(block => block.type === 'tool-call')
    .map(block => ({
      id: block.id,
      type: 'function' as const,
      function: { name: block.name, arguments: block.arguments },
    }))

  return {
    role: 'assistant',
    // Tool-call turns send "" rather than null: the live API answers both,
    // but the official samples replay message.content verbatim (which is ""
    // for pure tool-call responses) and some gateways reject null outright.
    content: text.length > 0 ? text : toolCalls.length > 0 ? '' : null,
    // Official passback rule (guides/thinking_mode.mdx): reasoning_content
    // must return on tool-call turns; it is ignored on plain turns, so we
    // drop it there to save tokens.
    ...toolCalls.length > 0 && reasoning.length > 0 ? { reasoning_content: reasoning } : {},
    ...toolCalls.length > 0 ? { tool_calls: toolCalls } : {},
  }
}

/**
 * Serialize the conversation. `tool-result` blocks become standalone
 * `{role: 'tool'}` messages; the harness puts each tool result in its own
 * user-role message, so a mixed user message contributes its text first and
 * its tool results as separate wire messages after.
 */
export function serializeMessages(messages: Message[]): WireMessage[] {
  const wire: WireMessage[] = []
  for (const message of messages) {
    if (message.role === 'system') {
      wire.push({ role: 'system', content: flattenText(message.content) })
      continue
    }
    if (message.role === 'assistant') {
      wire.push(serializeAssistant(message))
      continue
    }
    // user role: tool results ride in user messages in the harness
    // vocabulary, but DeepSeek wants them as role:'tool' messages.
    const toolResults = message.content.filter(block => block.type === 'tool-result')
    const text = flattenText(message.content)
    if (text.length > 0 || toolResults.length === 0) {
      wire.push({ role: 'user', content: text })
    }
    for (const result of toolResults) {
      wire.push({
        role: 'tool',
        tool_call_id: result.toolCallId,
        // Empty tool output still needs SOME content on the wire.
        content: flattenText(result.content) || '(no output)',
      })
    }
  }
  return wire
}

/**
 * Build the full wire request. Throws `LlmError('UNSUPPORTED')` for
 * `prefill` (DeepSeek's chat-prefix completion is a Beta feature on a
 * different base URL — see README).
 */
export function serializeRequest(options: GenerateOptions, defaults: RequestDefaults = {}): WireRequest {
  if (options.prefill !== undefined) {
    throw new LlmError(
      'prefill is not supported by the DeepSeek adapter (Beta chat-prefix completion is future work)',
      'UNSUPPORTED',
    )
  }

  const messages: WireMessage[] = []
  if (options.system !== undefined) {
    messages.push({ role: 'system', content: options.system })
  }
  messages.push(...serializeMessages(options.messages))

  const tools: WireTool[] | undefined = options.tools?.map(tool => ({
    type: 'function',
    function: {
      name: tool.name,
      description: tool.description,
      parameters: tool.parameters,
      // strict is officially supported (Beta); pass the tool author's choice.
      ...tool.strict !== undefined ? { strict: tool.strict } : {},
    },
  }))

  return {
    model: options.model,
    messages,
    stream: true,
    stream_options: { include_usage: true },
    ...defaults.thinking !== undefined ? { thinking: { type: defaults.thinking } } : {},
    ...defaults.reasoningEffort !== undefined ? { reasoning_effort: defaults.reasoningEffort } : {},
    ...tools !== undefined && tools.length > 0 ? { tools } : {},
    ...options.temperature !== undefined ? { temperature: options.temperature } : {},
    ...options.maxTokens !== undefined ? { max_tokens: options.maxTokens } : {},
    ...options.stop !== undefined ? { stop: options.stop } : {},
  }
}