/**
 * Non-production focused-call diagnostics harness.
 *
 * Makes an independent request to the configured Ollama server with the
 * same prompt, captures raw response text and completion metadata before
 * delegating recovery/parse to an inline implementation (recoverJson) that
 * mirrors the production helper's behavior.
 *
 * Callers must handle the returned diagnostics object or any thrown
 * DiagnosticError to capture what the focused path would have seen.
 */

const DETECTION_CACHE = new Map();

/**
 * Inline JSON recovery — mirrors the production recoverJson in lib/llm/provider.js
 * without importing it (recoverJson is not exported).
 */
function recoverJson(raw) {
  if (typeof raw !== "string") return raw;
  const trimmed = raw.trim();
  
  if (trimmed.length === 0) throw new SyntaxError("Model produced empty output");
  
  try {
    return JSON.parse(trimmed);
  } catch { /* Not directly parseable */ }

  let result = trimmed;
  
  let braceDepth = 0;
  let bracketDepth = 0;
  let inString = false;
  let escaped = false;
  
  for (let i = 0; i < result.length; i++) {
    const ch = result[i];
    
    if (escaped) { escaped = false; continue; }
    if (ch === '\\') { escaped = true; continue; }
    if (ch === '"') { inString = !inString; continue; }
    if (inString) continue;
    if (ch === '{') braceDepth++;
    else if (ch === '}') braceDepth--;
    else if (ch === '[') bracketDepth++;
    else if (ch === ']') bracketDepth--;
  }

  const closingBrackets = [];
  for (let i = 0; i < bracketDepth; i++) closingBrackets.push(']');
  for (let i = 0; i < braceDepth; i++) closingBrackets.push('}');
  
  if (closingBrackets.length > 0) {
    const closed = result + closingBrackets.reverse().join('');
    try { return JSON.parse(closed); } catch { /* still broken */ }
  }

  const lastOpen = Math.max(result.lastIndexOf('{'), result.lastIndexOf('['));
  if (lastOpen >= 0) {
    try { return JSON.parse(result.slice(lastOpen)); } catch { /* nothing works */ }
  }

  throw new SyntaxError("Model output could not be parsed as JSON: " + result.slice(0, 300) + "...");
}

/**
 * Throw a tagged error that preserves captured diagnostics for failure
 * artifact writing without any production code modification.
 */
class DiagnosticError extends Error {
  constructor(message, cause) {
    super(message, { cause });
    this.name = "DiagnosticError";
    this.focusedDiagnostics = null;
  }
}

/**
 * Detect whether /api/chat is available for a given baseUrl.
 */
async function detectChatSupport(baseUrl) {
  if (DETECTION_CACHE.has(baseUrl)) return DETECTION_CACHE.get(baseUrl);

  try {
    const res = await fetch(`${baseUrl}/api/chat`, {
      method: "POST",
      headers: { "Content-Type": "application/json" },
      body: JSON.stringify({
        model: "dummy-check",
        messages: [{ role: "user", content: "test" }],
        stream: false,
      }),
    });

    let chatSupported;
    if (res.ok) { await res.body?.consume(); chatSupported = true; }
    else if (res.status === 405 || res.status === 501) { await res.body?.consume(); chatSupported = false; }
    else { await res.body?.consume(); chatSupported = false; }

    DETECTION_CACHE.set(baseUrl, chatSupported);
    return chatSupported;
  } catch {
    DETECTION_CACHE.set(baseUrl, false);
    return false;
  }
}

/**
 * Make one focused request that captures all observable diagnostics
 * before delegating recovery/parse back to the caller.
 *
 * @param {object} params
 * @param {string} params.baseUrl
 * @param {string} params.modelName
 * @param {string} params.prompt
 * @returns {{ diagnostics: object, error?: DiagnosticError | null, parsedResult: unknown }}
 */
export async function runFocusedDiagnostic({ baseUrl, modelName, prompt }) {
  const diagnostics = {
    rawResponseText: null,
    rawResponseCharacterCount: null,
    done: null,
    doneReason: null,
    promptEvalCount: null,
    evalCount: null,
    modelElapsedMs: null,
    apiUsed: null,
  };

  const startedAt = Date.now();

  let chatSupported = false;
  try { chatSupported = await detectChatSupport(baseUrl); } catch { /* use default */ }

  let rawResponse = null;
  let fullResponseData = null;
  let apiUsed = null;

  // ---- Try /api/chat (same path as production) ----
  if (chatSupported) {
    try {
      const controller = new AbortController();
      const timeout = setTimeout(() => controller.abort(), 60000);

      const res = await fetch(`${baseUrl}/api/chat`, {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({
          model: modelName,
          messages: [{ role: "user", content: prompt }],
          stream: false,
          format: "json",
        }),
        signal: controller.signal,
      });

      clearTimeout(timeout);

      if (res.ok) {
        fullResponseData = await res.json();
        rawResponse = typeof fullResponseData.message?.content === "string"
          ? fullResponseData.message.content
          : JSON.stringify(fullResponseData.message?.content ?? null);
        apiUsed = "/api/chat";
      } else {
        await res.body?.consume();
      }
    } catch (e) {
      if (!e.message?.includes("abort")) { /* non-fatal */ }
    }
  }

  // ---- Fallback to /api/generate (production-compatible path) ----
  if (rawResponse == null || rawResponse === "") {
    try {
      const controller = new AbortController();
      const timeout = setTimeout(() => controller.abort(), 300000);

      apiUsed = "/api/generate";

      const res = await fetch(`${baseUrl}/api/generate`, {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({
          model: modelName,
          prompt,
          stream: false,
        }),
        signal: controller.signal,
      });

      clearTimeout(timeout);

      if (!res.ok) {
        const text = await res.text().catch(() => "");
        throw new Error(`/api/generate returned ${res.status}: ${text.slice(0, 500)}`);
      }

      fullResponseData = await res.json();

      rawResponse = typeof fullResponseData.response === "string"
        ? fullResponseData.response
        : JSON.stringify(fullResponseData);
    } catch (e) {
      // Preserve abort/timeout — these are legitimate signal-based failures
      if (e.name === "AbortError" || e.message?.includes("aborted")) {
        throw e;
      }
      if (apiUsed === "/api/generate") {
        throw new Error(
          `Ollama /api/generate request timed out after 5 minutes.\n\n` +
          `This usually means:\n` +
          `1. The model is loading into memory for the first time (cold start)\n` +
          `2. Your hardware is slow for this model size\n` +
          `3. Ollama server is overloaded\n\n` +
          `Try:\n` +
          `- Run the request again after ~1 minute (model may be cached now)\n` +
          `- Use a smaller model (e.g., llama3.1 instead of llama3.1:70b)\n` +
          `- Check Ollama logs: \`ollama serve\``
        );
      }
      throw e;
    }
  }

  diagnostics.rawResponseText = rawResponse;
  diagnostics.rawResponseCharacterCount = rawResponse?.length ?? 0;
  diagnostics.apiUsed = apiUsed || "none";
  diagnostics.modelElapsedMs = Date.now() - startedAt;

  // Completion metadata (available in fullResponseData for both /api/chat and /api/generate)
  if (fullResponseData != null) {
    diagnostics.done = fullResponseData.done ?? null;
    diagnostics.doneReason = fullResponseData.done_reason ?? null;
    diagnostics.promptEvalCount = fullResponseData.prompt_eval_count ?? null;
    diagnostics.evalCount = fullResponseData.eval_count ?? null;
  }

  // ---- Error path: signal parse failure ----
  if (rawResponse == null || rawResponse === "") {
    let diagInfo = "";
    if (fullResponseData) {
      const keys = Object.keys(fullResponseData);
      diagInfo += "Keys in response: " + keys.join(", ") + "\n";
      for (const key of keys) {
        const val = fullResponseData[key];
        if (typeof val === "string") {
          diagInfo += `  ${key}: "${val.slice(0, 200)}"\n`;
        } else if (typeof val === "object" && val != null) {
          try { diagInfo += `  ${key}: ${JSON.stringify(val).slice(0, 300)}\n`; } catch { diagInfo += `  ${key}: [object]\n`; }
        } else {
          diagInfo += `  ${key}: ${String(val)}\n`;
        }
      }
    }

    const err = new DiagnosticError(
      "Model produced empty output.\n\n" +
      "API used: " + (apiUsed || "none") + "\n" +
      "/api/chat supported: " + chatSupported + "\n" +
      "Full server response:\n" + (diagInfo || "(none)\n") +
      "\nPossible causes:\n" +
      "- Check 'ollama list' — make sure the model name matches exactly\n" +
      "- The model may be corrupted. Try: ollama pull " + modelName + "\n" +
      "- This Ollama version does not support format:json — relying on prompt instructions only\n" +
      "- If your model is very small (e.g., tinyllama, phi), try a larger one like llama3.1"
    );
    err.focusedDiagnostics = structuredClone(diagnostics);
    throw err;
  }

  // ---- Recovery / parse delegation to inline implementation ----
  let parsedResult = null;
  let recoveryError = null;
  try {
    parsedResult = recoverJson(rawResponse);
  } catch (e) {
    if (e instanceof SyntaxError) {
      recoveryError = new DiagnosticError(
        "Model returned output that could not be parsed as valid JSON.\n\n" +
        "API used: " + (apiUsed || "none") + "\n" +
        "/api/chat supported: " + chatSupported + "\n" +
        "Raw model output:\n" + rawResponse.slice(0, 1000) + (rawResponse.length > 1000 ? "\n...(truncated)" : "") +
        "\n\nPossible causes:\n" +
        "- This Ollama version does not support format:json\n" +
        "- Try a larger model (llama3.1, mistral-large) which follows JSON instructions better\n" +
        "- Shorten your scenario to under 500 words\n" +
        "- Consider upgrading Ollama: https://ollama.com/download"
      );
      recoveryError.focusedDiagnostics = structuredClone(diagnostics);
    }
    // Propagate non-SyntaxError without wrapping
    if (!(e instanceof SyntaxError)) throw e;
  }

  return { diagnostics, parsedResult, error: recoveryError };
}

// ---- Named export for static analysis verification ----
export function _getDetectionCache() { return DETECTION_CACHE; }