import type { AgentMessage } from "@mariozechner/pi-agent-core";
import type { ExtensionAPI, ExtensionContext, FileOperations } from "@mariozechner/pi-coding-agent";
import { estimateTokens, generateSummary } from "@mariozechner/pi-coding-agent";

import { DEFAULT_CONTEXT_TOKENS } from "../defaults.js";

const BASE_CHUNK_RATIO = 0.4;
const MIN_CHUNK_RATIO = 0.15;
const SAFETY_MARGIN = 1.2; // 20% buffer for estimateTokens() inaccuracy
const FALLBACK_SUMMARY =
  "Summary unavailable due to context limits. Older messages were truncated.";
const TURN_PREFIX_INSTRUCTIONS =
  "This summary covers the prefix of a split turn. Focus on the original request," +
  " early progress, and any details needed to understand the retained suffix.";
const MAX_TOOL_FAILURES = 8;
const MAX_TOOL_FAILURE_CHARS = 240;

function isAbortError(err: unknown): boolean {
  if (!err || typeof err !== "object") return false;
  const name = "name" in err ? String(err.name) : "";
  if (name === "AbortError") return true;
  const message =
    "message" in err && typeof err.message === "string" ? err.message.toLowerCase() : "";
  return message.includes("aborted");
}

type ToolFailure = {
  toolCallId: string;
  toolName: string;
  summary: string;
  meta?: string;
};

function normalizeFailureText(text: string): string {
  return text.replace(/\s+/g, " ").trim();
}

function truncateFailureText(text: string, maxChars: number): string {
  if (text.length <= maxChars) return text;
  return `${text.slice(0, Math.max(0, maxChars - 3))}...`;
}

function formatToolFailureMeta(details: unknown): string | undefined {
  if (!details || typeof details !== "object") return undefined;
  const record = details as Record<string, unknown>;
  const status = typeof record.status === "string" ? record.status : undefined;
  const exitCode =
    typeof record.exitCode === "number" && Number.isFinite(record.exitCode)
      ? record.exitCode
      : undefined;
  const parts: string[] = [];
  if (status) parts.push(`status=${status}`);
  if (exitCode !== undefined) parts.push(`exitCode=${exitCode}`);
  return parts.length > 0 ? parts.join(" ") : undefined;
}

function extractToolResultText(content: unknown): string {
  if (!Array.isArray(content)) return "";
  const parts: string[] = [];
  for (const block of content) {
    if (!block || typeof block !== "object") continue;
    const rec = block as { type?: unknown; text?: unknown };
    if (rec.type === "text" && typeof rec.text === "string") {
      parts.push(rec.text);
    }
  }
  return parts.join("\n");
}

function collectToolFailures(messages: AgentMessage[]): ToolFailure[] {
  const failures: ToolFailure[] = [];
  const seen = new Set<string>();

  for (const message of messages) {
    if (!message || typeof message !== "object") continue;
    const role = (message as { role?: unknown }).role;
    if (role !== "toolResult") continue;
    const toolResult = message as {
      toolCallId?: unknown;
      toolName?: unknown;
      content?: unknown;
      details?: unknown;
      isError?: unknown;
    };
    if (toolResult.isError !== true) continue;
    const toolCallId = typeof toolResult.toolCallId === "string" ? toolResult.toolCallId : "";
    if (!toolCallId || seen.has(toolCallId)) continue;
    seen.add(toolCallId);

    const toolName =
      typeof toolResult.toolName === "string" && toolResult.toolName.trim()
        ? toolResult.toolName
        : "tool";
    const rawText = extractToolResultText(toolResult.content);
    const meta = formatToolFailureMeta(toolResult.details);
    const normalized = normalizeFailureText(rawText);
    const summary = truncateFailureText(
      normalized || (meta ? "failed" : "failed (no output)"),
      MAX_TOOL_FAILURE_CHARS,
    );
    failures.push({ toolCallId, toolName, summary, meta });
  }

  return failures;
}

function formatToolFailuresSection(failures: ToolFailure[]): string {
  if (failures.length === 0) return "";
  const lines = failures.slice(0, MAX_TOOL_FAILURES).map((failure) => {
    const meta = failure.meta ? ` (${failure.meta})` : "";
    return `- ${failure.toolName}${meta}: ${failure.summary}`;
  });
  if (failures.length > MAX_TOOL_FAILURES) {
    lines.push(`- ...and ${failures.length - MAX_TOOL_FAILURES} more`);
  }
  return `\n\n## Tool Failures\n${lines.join("\n")}`;
}

function computeFileLists(fileOps: FileOperations): {
  readFiles: string[];
  modifiedFiles: string[];
} {
  const modified = new Set([...fileOps.edited, ...fileOps.written]);
  const readFiles = [...fileOps.read].filter((f) => !modified.has(f)).sort();
  const modifiedFiles = [...modified].sort();
  return { readFiles, modifiedFiles };
}

function formatFileOperations(readFiles: string[], modifiedFiles: string[]): string {
  const sections: string[] = [];
  if (readFiles.length > 0) {
    sections.push(`<read-files>\n${readFiles.join("\n")}\n</read-files>`);
  }
  if (modifiedFiles.length > 0) {
    sections.push(`<modified-files>\n${modifiedFiles.join("\n")}\n</modified-files>`);
  }
  if (sections.length === 0) return "";
  return `\n\n${sections.join("\n\n")}`;
}

function chunkMessages(messages: AgentMessage[], maxTokens: number): AgentMessage[][] {
  if (messages.length === 0) return [];

  const chunks: AgentMessage[][] = [];
  let currentChunk: AgentMessage[] = [];
  let currentTokens = 0;

  for (const message of messages) {
    const messageTokens = estimateTokens(message);
    if (currentChunk.length > 0 && currentTokens + messageTokens > maxTokens) {
      chunks.push(currentChunk);
      currentChunk = [];
      currentTokens = 0;
    }

    currentChunk.push(message);
    currentTokens += messageTokens;

    if (messageTokens > maxTokens) {
      // Split oversized messages to avoid unbounded chunk growth.
      chunks.push(currentChunk);
      currentChunk = [];
      currentTokens = 0;
    }
  }

  if (currentChunk.length > 0) {
    chunks.push(currentChunk);
  }

  return chunks;
}

/**
 * Compute adaptive chunk ratio based on average message size.
 * When messages are large, we use smaller chunks to avoid exceeding model limits.
 */
function computeAdaptiveChunkRatio(messages: AgentMessage[], contextWindow: number): number {
  if (messages.length === 0) return BASE_CHUNK_RATIO;

  const totalTokens = messages.reduce((sum, m) => sum + estimateTokens(m), 0);
  const avgTokens = totalTokens / messages.length;

  // Apply safety margin to account for estimation inaccuracy
  const safeAvgTokens = avgTokens * SAFETY_MARGIN;
  const avgRatio = safeAvgTokens / contextWindow;

  // If average message is > 10% of context, reduce chunk ratio
  if (avgRatio > 0.1) {
    const reduction = Math.min(avgRatio * 2, BASE_CHUNK_RATIO - MIN_CHUNK_RATIO);
    return Math.max(MIN_CHUNK_RATIO, BASE_CHUNK_RATIO - reduction);
  }

  return BASE_CHUNK_RATIO;
}

/**
 * Check if a single message is too large to summarize.
 * If single message > 50% of context, it can't be summarized safely.
 */
function isOversizedForSummary(msg: AgentMessage, contextWindow: number): boolean {
  const tokens = estimateTokens(msg) * SAFETY_MARGIN;
  return tokens > contextWindow * 0.5;
}

async function summarizeChunks(params: {
  messages: AgentMessage[];
  model: NonNullable<ExtensionContext["model"]>;
  apiKey: string;
  signal: AbortSignal;
  reserveTokens: number;
  maxChunkTokens: number;
  customInstructions?: string;
  previousSummary?: string;
}): Promise<string> {
  if (params.messages.length === 0) {
    return params.previousSummary ?? "No prior history.";
  }

  const chunks = chunkMessages(params.messages, params.maxChunkTokens);
  let summary = params.previousSummary;

  for (const chunk of chunks) {
    summary = await generateSummary(
      chunk,
      params.model,
      params.reserveTokens,
      params.apiKey,
      params.signal,
      params.customInstructions,
      summary,
    );
  }

  return summary ?? "No prior history.";
}

/**
 * Summarize with progressive fallback for handling oversized messages.
 * If full summarization fails, tries partial summarization excluding oversized messages.
 */
async function summarizeWithFallback(params: {
  messages: AgentMessage[];
  model: NonNullable<ExtensionContext["model"]>;
  apiKey: string;
  signal: AbortSignal;
  reserveTokens: number;
  maxChunkTokens: number;
  contextWindow: number;
  customInstructions?: string;
  previousSummary?: string;
}): Promise<string> {
  const { messages, contextWindow } = params;

  if (messages.length === 0) {
    return params.previousSummary ?? "No prior history.";
  }

  // Try full summarization first
  try {
    return await summarizeChunks(params);
  } catch (fullError) {
    if (params.signal.aborted || isAbortError(fullError)) {
      throw fullError;
    }
    console.warn(
      `Full summarization failed, trying partial: ${
        fullError instanceof Error ? fullError.message : String(fullError)
      }`,
    );
  }

  // Fallback 1: Summarize only small messages, note oversized ones
  const smallMessages: AgentMessage[] = [];
  const oversizedNotes: string[] = [];

  for (const msg of messages) {
    if (isOversizedForSummary(msg, contextWindow)) {
      const role = (msg as { role?: string }).role ?? "message";
      const tokens = estimateTokens(msg);
      oversizedNotes.push(
        `[Large ${role} (~${Math.round(tokens / 1000)}K tokens) omitted from summary]`,
      );
    } else {
      smallMessages.push(msg);
    }
  }

  if (smallMessages.length > 0) {
    try {
      const partialSummary = await summarizeChunks({
        ...params,
        messages: smallMessages,
      });
      const notes = oversizedNotes.length > 0 ? `\n\n${oversizedNotes.join("\n")}` : "";
      return partialSummary + notes;
    } catch (partialError) {
      if (params.signal.aborted || isAbortError(partialError)) {
        throw partialError;
      }
      console.warn(
        `Partial summarization also failed: ${
          partialError instanceof Error ? partialError.message : String(partialError)
        }`,
      );
    }
  }

  // Final fallback: Just note what was there
  return (
    `Context contained ${messages.length} messages (${oversizedNotes.length} oversized). ` +
    `Summary unavailable due to size limits.`
  );
}

export default function compactionSafeguardExtension(api: ExtensionAPI): void {
  api.on("session_before_compact", async (event, ctx) => {
    const { preparation, customInstructions, signal } = event;
    const { readFiles, modifiedFiles } = computeFileLists(preparation.fileOps);
    const fileOpsSummary = formatFileOperations(readFiles, modifiedFiles);
    const toolFailures = collectToolFailures([
      ...preparation.messagesToSummarize,
      ...preparation.turnPrefixMessages,
    ]);
    const toolFailureSection = formatToolFailuresSection(toolFailures);
    const fallbackSummary = `${FALLBACK_SUMMARY}${toolFailureSection}${fileOpsSummary}`;

    const model = ctx.model;
    if (!model) {
      return {
        compaction: {
          summary: fallbackSummary,
          firstKeptEntryId: preparation.firstKeptEntryId,
          tokensBefore: preparation.tokensBefore,
          details: { readFiles, modifiedFiles },
        },
      };
    }

    const apiKey = await ctx.modelRegistry.getApiKey(model);
    if (!apiKey) {
      return {
        compaction: {
          summary: fallbackSummary,
          firstKeptEntryId: preparation.firstKeptEntryId,
          tokensBefore: preparation.tokensBefore,
          details: { readFiles, modifiedFiles },
        },
      };
    }

    try {
      const contextWindowTokens = Math.max(
        1,
        Math.floor(model.contextWindow ?? DEFAULT_CONTEXT_TOKENS),
      );

      // Use adaptive chunk ratio based on message sizes
      const allMessages = [...preparation.messagesToSummarize, ...preparation.turnPrefixMessages];
      const adaptiveRatio = computeAdaptiveChunkRatio(allMessages, contextWindowTokens);
      const maxChunkTokens = Math.max(1, Math.floor(contextWindowTokens * adaptiveRatio));
      const reserveTokens = Math.max(1, Math.floor(preparation.settings.reserveTokens));

      const historySummary = await summarizeWithFallback({
        messages: preparation.messagesToSummarize,
        model,
        apiKey,
        signal,
        reserveTokens,
        maxChunkTokens,
        contextWindow: contextWindowTokens,
        customInstructions,
        previousSummary: preparation.previousSummary,
      });

      let summary = historySummary;
      if (preparation.isSplitTurn && preparation.turnPrefixMessages.length > 0) {
        const prefixSummary = await summarizeWithFallback({
          messages: preparation.turnPrefixMessages,
          model,
          apiKey,
          signal,
          reserveTokens,
          maxChunkTokens,
          contextWindow: contextWindowTokens,
          customInstructions: TURN_PREFIX_INSTRUCTIONS,
        });
        summary = `${historySummary}\n\n---\n\n**Turn Context (split turn):**\n\n${prefixSummary}`;
      }

      summary += toolFailureSection;
      summary += fileOpsSummary;

      return {
        compaction: {
          summary,
          firstKeptEntryId: preparation.firstKeptEntryId,
          tokensBefore: preparation.tokensBefore,
          details: { readFiles, modifiedFiles },
        },
      };
    } catch (error) {
      console.warn(
        `Compaction summarization failed; truncating history: ${
          error instanceof Error ? error.message : String(error)
        }`,
      );
      return {
        compaction: {
          summary: fallbackSummary,
          firstKeptEntryId: preparation.firstKeptEntryId,
          tokensBefore: preparation.tokensBefore,
          details: { readFiles, modifiedFiles },
        },
      };
    }
  });
}

export const __testing = {
  collectToolFailures,
  formatToolFailuresSection,
  computeAdaptiveChunkRatio,
  isOversizedForSummary,
  BASE_CHUNK_RATIO,
  MIN_CHUNK_RATIO,
  SAFETY_MARGIN,
} as const;