import type { ChatMessage, DocIndex } from "../chatTools";
import type {
    AssistantRoutingContextV2,
    AssistantSurface,
    FocusedDocumentExcerpt,
} from "./types";
import type { RequestedAssistantMode } from "./requestedMode";
import { detectMutationIntentHint } from "./mutationHint";

export const CONTEXT_RECENT_MESSAGE_MAX = 2;
export const CONTEXT_RECENT_MESSAGE_CHAR_LIMIT = 800;
export const CONTEXT_LATEST_MESSAGE_CHAR_LIMIT = 12_000;
export const CONTEXT_FOCUSED_EXCERPT_CHAR_LIMIT = 4_000;

function truncate(value: string, max: number): string {
    if (value.length <= max) return value;
    return value.slice(0, max);
}

function fileTypeFor(filename: string, known?: string): string | null {
    if (known && typeof known === "string") return known;
    const lower = (filename || "").toLowerCase();
    const ext = lower.slice(lower.lastIndexOf(".") + 1);
    if (!ext || ext === lower) return null;
    return ext;
}

function isEditable(fileType: string | null): boolean {
    return fileType === "docx";
}

interface ContextDocInput {
    documentId: string;
    filename: string;
}

/**
 * Build the bounded, sanitized routing context. Contains only metadata safe to
 * send to a read-only router model: latest user message, at most two recent
 * conversation messages (truncated), filenames/file types/editable flags, and
 * optionally a focused excerpt the user pasted/quoted or selected in the UI.
 *
 * Never includes: signed URLs, storage paths, database rows, comments, full
 * document bodies, tool results, or secrets.
 */
export function buildAssistantRoutingContext(params: {
    surface: AssistantSurface;
    requestedMode: RequestedAssistantMode;
    messages: ChatMessage[];
    docIndex: DocIndex;
    displayedDocument?: ContextDocInput | null;
    attachedDocuments?: ContextDocInput[];
    projectDocumentCount?: number;
    selectedWorkflow?: { workflowId: string; title: string } | null;
    focusedDocumentExcerpt?: FocusedDocumentExcerpt | null;
    confirmationPresented?: boolean;
}): AssistantRoutingContextV2 {
    const {
        surface,
        requestedMode,
        messages,
        docIndex,
        displayedDocument = null,
        attachedDocuments = [],
        projectDocumentCount = 0,
        selectedWorkflow = null,
        focusedDocumentExcerpt = null,
        confirmationPresented = false,
    } = params;

    // Latest user message only.
    const latestUser =
        [...messages].reverse().find((m) => m.role === "user") ?? null;
    const latestUserMessage = truncate(
        latestUser?.content ?? "",
        CONTEXT_LATEST_MESSAGE_CHAR_LIMIT,
    );

    // At most two recent conversation messages for reference resolution.
    const recentConversation: AssistantRoutingContextV2["recentConversation"] = [];
    const trimmed = messages.slice(-CONTEXT_RECENT_MESSAGE_MAX - 1);
    for (const m of trimmed) {
        if (m.role !== "user" && m.role !== "assistant") continue;
        recentConversation.push({
            role: m.role,
            content: truncate(m.content ?? "", CONTEXT_RECENT_MESSAGE_CHAR_LIMIT),
        });
        if (recentConversation.length >= CONTEXT_RECENT_MESSAGE_MAX) break;
    }

    function resolveDoc(input: ContextDocInput) {
        const entry = docIndex[input.documentId];
        const filename = entry?.filename ?? input.filename;
        const fileType = fileTypeFor(filename, entry?.file_type);
        return {
            documentId: input.documentId,
            filename,
            fileType,
            editable: isEditable(fileType),
            revisionId: entry?.version_id ?? null,
        };
    }

    const displayedDocumentResolved = displayedDocument
        ? resolveDoc(displayedDocument)
        : null;

    const attachedDocumentsResolved = attachedDocuments.map(resolveDoc);

    // Focused excerpt only when pasted/quoted by the user or selected in UI,
    // capped, never scanned from a document body.
    let focused: FocusedDocumentExcerpt | null = null;
    if (focusedDocumentExcerpt && focusedDocumentExcerpt.text) {
        focused = {
            documentId: focusedDocumentExcerpt.documentId,
            text: truncate(
                focusedDocumentExcerpt.text,
                CONTEXT_FOCUSED_EXCERPT_CHAR_LIMIT,
            ),
            source: focusedDocumentExcerpt.source,
        };
    }

    return {
        schemaVersion: 2,
        surface,
        requestedMode,
        currentDate: new Date().toISOString().slice(0, 10),
        latestUserMessage,
        recentConversation,
        displayedDocument: displayedDocumentResolved,
        attachedDocuments: attachedDocumentsResolved,
        projectDocumentCount,
        selectedWorkflow,
        focusedDocumentExcerpt: focused,
        mutationIntentHint: detectMutationIntentHint(latestUserMessage),
        confirmationPresented,
    };
}