import type { TranscriptItem } from "./agentSessionTypes";

export type TranscriptTurnSegment =
  | { kind: "item"; item: TranscriptItem }
  | { kind: "setup"; items: Extract<TranscriptItem, { type: "lifecycle" }>[] }
  | {
      kind: "prompt";
      user: Extract<TranscriptItem, { type: "message" }>;
      context: Extract<TranscriptItem, { type: "metadata" }> | null;
      setup: Extract<TranscriptItem, { type: "lifecycle" }>[];
    };

export type TranscriptDisplayBlock =
  | { kind: "single"; item: TranscriptItem }
  | { kind: "turn"; turnId: string; segments: TranscriptTurnSegment[] };

function isUserPrompt(
  item: TranscriptItem,
): item is Extract<TranscriptItem, { type: "message" }> {
  return (
    item.type === "message" &&
    item.role === "user" &&
    item.acpSource === "session/prompt:user"
  );
}

function isPromptContext(
  item: TranscriptItem,
): item is Extract<TranscriptItem, { type: "metadata" }> {
  return (
    item.type === "metadata" && item.acpSource === "session/prompt:context"
  );
}

function isSetupLifecycle(
  item: TranscriptItem,
): item is Extract<TranscriptItem, { type: "lifecycle" }> {
  return (
    item.type === "lifecycle" &&
    (item.acpSource === "turn_started" || item.acpSource === "session_resolved")
  );
}

function isErrorLifecycle(
  item: TranscriptItem,
): item is Extract<TranscriptItem, { type: "lifecycle" }> {
  return (
    item.type === "lifecycle" && item.title.toLowerCase().includes("error")
  );
}

type TurnBucket = {
  turnId: string;
  items: TranscriptItem[];
};

function classifyTurnItems(items: TranscriptItem[]): TranscriptTurnSegment[] {
  const userPrompt = items.find(isUserPrompt) ?? null;
  const setupLifecycle = items.filter(isSetupLifecycle);
  const promptContext = items.find(isPromptContext) ?? null;
  const consumed = new Set<TranscriptItem>();

  if (userPrompt) consumed.add(userPrompt);
  for (const item of setupLifecycle) consumed.add(item);
  if (promptContext) consumed.add(promptContext);

  const activity = items.filter((item) => !consumed.has(item));

  if (!userPrompt) {
    return items.map((item) => ({ kind: "item", item }));
  }

  const segments: TranscriptTurnSegment[] = [
    {
      kind: "prompt",
      user: userPrompt,
      context: promptContext,
      setup: setupLifecycle,
    },
  ];

  for (const item of activity) {
    if (isErrorLifecycle(item)) {
      segments.push({ kind: "item", item });
      continue;
    }
    if (isSetupLifecycle(item)) {
      continue;
    }
    segments.push({ kind: "item", item });
  }

  return segments;
}

/**
 * Build presentation-only display blocks from normalized transcript items.
 * Raw observer order is preserved in the source items; this only reorders
 * within a turn for user-facing narrative flow.
 */
export function buildTranscriptDisplayBlocks(
  items: TranscriptItem[],
): TranscriptDisplayBlock[] {
  const blocks: TranscriptDisplayBlock[] = [];
  const turnBuckets = new Map<string, TurnBucket>();
  const displayOrder: Array<
    { kind: "single"; item: TranscriptItem } | { kind: "turn"; turnId: string }
  > = [];

  for (const item of items) {
    const turnId = item.turnId;
    if (!turnId) {
      displayOrder.push({ kind: "single", item });
      continue;
    }

    let bucket = turnBuckets.get(turnId);
    if (!bucket) {
      bucket = { turnId, items: [] };
      turnBuckets.set(turnId, bucket);
      displayOrder.push({ kind: "turn", turnId });
    }
    bucket.items.push(item);
  }

  for (const entry of displayOrder) {
    if (entry.kind === "single") {
      blocks.push({ kind: "single", item: entry.item });
      continue;
    }

    const bucket = turnBuckets.get(entry.turnId);
    if (!bucket || bucket.items.length === 0) {
      continue;
    }

    blocks.push({
      kind: "turn",
      turnId: entry.turnId,
      segments: classifyTurnItems(bucket.items),
    });
  }

  return blocks;
}

/** Flatten display blocks back to items for testing display order. */
export function flattenDisplayBlocks(
  blocks: TranscriptDisplayBlock[],
): TranscriptItem[] {
  const result: TranscriptItem[] = [];

  for (const block of blocks) {
    if (block.kind === "single") {
      result.push(block.item);
      continue;
    }

    for (const segment of block.segments) {
      if (segment.kind === "item") {
        result.push(segment.item);
      } else if (segment.kind === "prompt") {
        result.push(segment.user);
        result.push(...segment.setup);
        if (segment.context) {
          result.push(segment.context);
        }
      } else {
        result.push(...segment.items);
      }
    }
  }

  return result;
}

/** Human-readable labels for a collapsed turn setup row. */
export function formatTurnSetupLabel(
  items: Extract<TranscriptItem, { type: "lifecycle" }>[],
): string {
  const labels = items.map((item) => item.title);
  return labels.join(" · ");
}

/** Earliest timestamp among setup lifecycle items. */
export function turnSetupTimestamp(
  items: Extract<TranscriptItem, { type: "lifecycle" }>[],
): string | null {
  if (items.length === 0) return null;
  return items.reduce(
    (earliest, item) =>
      Date.parse(item.timestamp) < Date.parse(earliest)
        ? item.timestamp
        : earliest,
    items[0].timestamp,
  );
}

/** Optional detail text from setup lifecycle items (e.g. trigger count). */
export function turnSetupDetail(
  items: Extract<TranscriptItem, { type: "lifecycle" }>[],
): string | null {
  const details = items
    .map((item) => item.text.trim())
    .filter((text) => text.length > 0);
  if (details.length === 0) return null;
  return details.join(" ");
}