/**
 * Agent turn service — the core adaptive turn loop. Mirrors
 * `apps/application/src/agent/turn_service.rs`.
 */
import {
  type ChatMessage,
  type StreamEvent,
  type ToolCall,
  type ToolDef,
  type JsonValue,
  systemMessage,
  userMessage,
  assistantMessage,
  toolResultMessage,
  sanitizeToolArguments,
} from "@zesdex/domain";
import {
  type AgentTurnParams,
  type TurnEventSink,
  mainAgentPromptWithProjectContext,
  compactionPrompt,
  errorRecoveryNote,
} from "@zesdex/agent";
import type { ProviderService } from "./ports.ts";
import type { ToolExecutor } from "./index.ts";

/* -------------------------------------------------------------------------- */
/*  Constants (mirrors Rust)                                                  */
/* -------------------------------------------------------------------------- */

const MAX_TURN_ITERATIONS = 50;
const MAX_CONSECUTIVE_TOOL_ERRORS = 3;
const MAX_TOTAL_TOOL_ERRORS = 8;
const TOOL_OUTPUT_MAX_CHARS = 12_000;
const AUTO_COMPACT_CHARS = 60_000;
const MAX_PARALLEL_TOOLS = 8;
const PROJECT_CONTEXT_MAX_CHARS = 12_000;
const RULE_FILENAMES = ["AGENTS.md", "agent.md", "CLAUDE.md", "claude.md", ".cursorrules", ".zesdexrules"];
const COMPACT_KEEP_TAIL = 6;

/** Whether the output string denotes a tool error. */
function isErrorOutput(output: string): boolean {
  return output.startsWith("Error:");
}

/** Truncate a long tool output, preserving the head + truncation marker. */
export function truncateToolOutput(output: string): string {
  if (output.length <= TOOL_OUTPUT_MAX_CHARS) return output;
  const head = output.slice(0, TOOL_OUTPUT_MAX_CHARS);
  return `${head}\n...[truncated ${output.length - TOOL_OUTPUT_MAX_CHARS} chars]`;
}

/** Pick a `max_tokens` budget based on the user's request length. */
export function adaptiveMaxTokens(requestLen: number): number {
  if (requestLen <= 80) return 800;
  if (requestLen <= 400) return 1600;
  return 4096;
}

/** Sum character length of message content as a context-size proxy. */
export function conversationChars(messages: ChatMessage[]): number {
  return messages.reduce((acc, m) => acc + (m.content?.length ?? 0), 0);
}

/** Best-effort build of project context from convention rule files. */
export function buildProjectContext(root: string): string {
  let ctx = "";
  for (const file of RULE_FILENAMES) {
    try {
      const content = requireNodeFsReadFile(root, file);
      ctx += `\n### ${file}\n\`\`\`\n${content.trim()}\n\`\`\``;
    } catch {
      /* file missing — skip */
    }
  }
  const context = ctx.trim();
  if (context.length <= PROJECT_CONTEXT_MAX_CHARS) return context;
  return `${context.slice(0, PROJECT_CONTEXT_MAX_CHARS)}\n...[project context truncated]`;
}

/** Read a repo rule file synchronously (Bun-compatible). */
function requireNodeFsReadFile(root: string, file: string): string {
  const fs = require("node:fs");
  return fs.readFileSync(`${root}/${file}`, "utf8");
}

/* -------------------------------------------------------------------------- */
/*  ErrorTracker                                                              */
/* -------------------------------------------------------------------------- */

/** Track repeated tool-call errors so the loop can recover. */
export class ErrorTracker {
  consecutive = 0;
  total = 0;
  lastTool: string | null = null;
  lastError = "";

  record(toolName: string, error: string, messages: ChatMessage[]): void {
    if (this.lastTool === toolName) {
      this.consecutive += 1;
    } else {
      this.consecutive = 1;
    }
    this.lastTool = toolName;
    this.lastError = error;
    this.total += 1;

    const sysNoteInContext = messages.some((m) => m.content?.includes("[System note]"));
    if (this.consecutive >= MAX_CONSECUTIVE_TOOL_ERRORS && !sysNoteInContext) {
      messages.push(systemMessage(errorRecoveryNote(toolName, error)));
    }
  }

  shouldStop(): boolean {
    return this.consecutive >= MAX_CONSECUTIVE_TOOL_ERRORS * 2 || this.total >= MAX_TOTAL_TOOL_ERRORS;
  }
}

/* -------------------------------------------------------------------------- */
/*  Tool execution                                                            */
/* -------------------------------------------------------------------------- */

/** Execute one tool call, push events, return the result string. */
async function executeToolCall(
  executor: ToolExecutor,
  sink: TurnEventSink,
  tc: ToolCall,
): Promise<string> {
  const name = tc.function.name;
  const args = sanitizeToolArguments(tc.function.arguments);

  let output: string;
  try {
    output = await executor.execute(name, args as JsonValue);
  } catch (e) {
    output = `Error: ${(e as Error).message}`;
  }

  const isError = isErrorOutput(output);
  const truncated = truncateToolOutput(output);

  sink.push({
    kind: "tool_result",
    tool_call_id: tc.id,
    tool_name: name,
    output: truncated,
    is_error: isError,
    path: null,
  });

  return truncated;
}

/** Execute a batch of read-only tool calls concurrently (bounded) in original order. */
async function executeToolCallsInParallel(
  executor: ToolExecutor,
  sink: TurnEventSink,
  toolCalls: ToolCall[],
): Promise<string[]> {
  // Simple bounded concurrency preserving input order.
  const results: string[] = new Array(toolCalls.length);
  let next = 0;

  async function worker() {
    while (true) {
      const idx = next++;
      if (idx >= toolCalls.length) return;
      results[idx] = await executeToolCall(executor, sink, toolCalls[idx]!);
    }
  }

  const workers = Array.from({ length: Math.min(MAX_PARALLEL_TOOLS, toolCalls.length) }, () => worker());
  await Promise.all(workers);
  return results;
}

/* -------------------------------------------------------------------------- */
/*  Compaction                                                                */
/* -------------------------------------------------------------------------- */

/**
 * Compact oversized conversation history using AI summarisation. At most once
 * per turn. Keeps the last COMPACT_KEEP_TAIL messages.
 */
export async function compactMessagesWithAi(
  messages: ChatMessage[],
  provider: ProviderService,
): Promise<void> {
  if (messages.length <= COMPACT_KEEP_TAIL + 2) return;

  const splitIdx = messages.length - COMPACT_KEEP_TAIL;
  const evicted = messages.splice(0, splitIdx);

  const summaryPrompt: ChatMessage[] = [systemMessage(compactionPrompt()), ...evicted, userMessage("Please summarise our previous conversation above for context continuity.")];

  try {
    const { message } = await provider.chat(summaryPrompt, undefined, 1024, 0.3);
    const summaryText = message.content ?? "Previous context summarised.";
    messages.unshift(systemMessage(`[AI Summary of Previous Conversation]\n${summaryText.trim()}`));
  } catch {
    messages.unshift(systemMessage("[Earlier conversation messages compacted to save context window]"));
  }
}

/* -------------------------------------------------------------------------- */
/*  AgentTurnServiceImpl                                                      */
/* -------------------------------------------------------------------------- */

/** Service implementation for executing an agent turn asynchronously. */
export class AgentTurnServiceImpl {
  private provider: ProviderService;
  private toolExecutor: ToolExecutor;
  private toolDefs: ToolDef[];

  constructor(provider: ProviderService, toolExecutor: ToolExecutor, toolDefs: ToolDef[]) {
    this.provider = provider;
    this.toolExecutor = toolExecutor;
    this.toolDefs = toolDefs;
  }

  /** Emit a TurnEvent onto the sink (no-op if the sink is missing). */
  private push(sink: TurnEventSink, event: Parameters<TurnEventSink["push"]>[0]): void {
    sink.push(event);
  }

  /** Execute a single LLM stream call, forwarding tokens and checking abort. */
  private async callLlm(
    messages: ChatMessage[],
    abort: AbortController,
    sink: TurnEventSink,
    maxTokens: number,
    temperature: number,
  ): Promise<{ message: ChatMessage; usage: [number, number] | null }> {
    const onEvent = (event: StreamEvent): boolean => {
      if (abort.signal.aborted) return false;
      if (event.kind === "token") this.push(sink, { kind: "stream_token", content: event.content });
      else if (event.kind === "reasoning") this.push(sink, { kind: "stream_reasoning", content: event.content });
      return true;
    };

    try {
      return await this.provider.chatStream(messages, this.toolDefs, maxTokens, temperature, onEvent, abort.signal);
    } catch (e) {
      throw new Error(`LLM error: ${(e as Error).message}`);
    }
  }

  /** Auto-compact history in place if it exceeds the threshold. */
  private async autoCompactIfNeeded(messages: ChatMessage[]): Promise<void> {
    if (conversationChars(messages) <= AUTO_COMPACT_CHARS) return;
    const sys = messages[0];
    if (!sys) return;
    const rest = messages.splice(1);
    const before = rest.length;
    try {
      await compactMessagesWithAi(rest, this.provider);
    } catch (e) {
      console.warn(`auto-compact failed (non-fatal): ${(e as Error).message}`);
    }
    messages.length = 0;
    messages.push(sys, ...rest);
    console.info(`auto-compacted history: ${before} messages -> ${rest.length}`);
  }

  /** Run the full agent turn loop. */
  async runTurn(params: AgentTurnParams): Promise<void> {
    const sink = params.turn_events;
    const abort = params.abort;
    const { in_flight } = params;

    // Insert system prompt at index 0 with repo conventions loaded.
    const projectContext = buildProjectContext(params.workspace_roots[0] ?? ".");
    const systemPrompt = mainAgentPromptWithProjectContext(projectContext);
    params.messages.unshift(systemMessage(systemPrompt));
    const originalCount = params.messages.length;

    // Estimate request complexity from the last user message.
    const last = params.messages[params.messages.length - 1];
    const requestLen = last?.content?.length ?? 0;

    const errors = new ErrorTracker();
    let sawToolCalls = false;

    for (let iteration = 0; iteration < MAX_TURN_ITERATIONS; iteration++) {
      // Check abort flag.
      if (abort.signal.aborted) {
        this.push(sink, { kind: "system_note", systemKind: "info", message: "Turn aborted by user" });
        break;
      }

      if (errors.shouldStop()) {
        this.push(sink, { kind: "system_note", systemKind: "warn", message: "Stopping: repeated tool errors without progress" });
        break;
      }

      // Auto-compact oversized history before the LLM call.
      await this.autoCompactIfNeeded(params.messages);

      // Adaptive generation parameters.
      const maxTokens = adaptiveMaxTokens(requestLen);
      const temperature = sawToolCalls ? 0.2 : 0.7;

      this.push(sink, { kind: "stream_start" });

      let result;
      try {
        result = await this.callLlm(params.messages, abort, sink, maxTokens, temperature);
      } catch (e) {
        const msg = (e as Error).message;
        console.warn(msg);
        this.push(sink, { kind: "error", message: msg });
        break;
      }

      const { message: assistantMsg, usage } = result;
      const content = assistantMsg.content ?? "";
      const toolCalls = assistantMsg.tool_calls ?? [];

      this.push(sink, { kind: "stream_done", message: assistantMsg });
      if (usage) this.push(sink, { kind: "usage", tokens_in: usage[0], tokens_out: usage[1] });

      // No tool calls → assistant is done.
      if (toolCalls.length === 0) {
        params.messages.push(assistantMessage(content));
        break;
      }

      sawToolCalls = true;
      params.messages.push(assistantMsg);

      // Execute tool calls — parallel when all read-only, else sequential.
      const isParallelSafe = (tc: ToolCall): boolean =>
        typeof this.toolExecutor.isParallelSafe === "function"
          ? this.toolExecutor.isParallelSafe(tc.function.name)
          : false;
      const parallel = toolCalls.length > 1 && toolCalls.every(isParallelSafe);

      const outputs = parallel
        ? await executeToolCallsInParallel(this.toolExecutor, sink, toolCalls)
        : await (async () => {
            const seq: string[] = [];
            for (const tc of toolCalls) seq.push(await executeToolCall(this.toolExecutor, sink, tc));
            return seq;
          })();

      for (let i = 0; i < toolCalls.length; i++) {
        const tc = toolCalls[i]!;
        const output = outputs[i]!;
        if (isErrorOutput(output)) errors.record(tc.function.name, output, params.messages);
        params.messages.push(toolResultMessage(tc.id, output));
      }
    }

    // Remove the synthetic sys_msg before emitting to the transcript.
    const compacted = params.messages.splice(originalCount - 1);
    this.push(sink, { kind: "compacted", messages: compacted });
    this.push(sink, { kind: "done" });
    in_flight.value = false;
  }
}