import type { SupabaseClient } from '@supabase/supabase-js'
import type { AiChatTurn } from '@/lib/ai'

/**
 * Thread persistence for the single-call chat console (/chat).
 *
 * The console answers in one call via answerAssistantQuestion (no tool loop,
 * no streaming: runs on a local model). But the founder wants the /chat
 * sidebar and "resume a thread" to keep working, so each console turn is
 * written to the SAME durable tables the streaming runtime uses:
 * agent_conversations + agent_messages. That way old and new threads live in
 * one list and one schema.
 *
 * Content is stored as the canonical Anthropic content array
 * ([{ type: 'text', text }]) so normalizeStoredMessages() renders these rows
 * identically to run-turn's, and the BFL append-only audit invariant on
 * agent_messages holds (no UPDATE/DELETE policy exists on that table).
 *
 * Only the general.help intent uses this path. Tool-loop intents
 * (categorization, invoice draft, supplier review) still go through
 * run-turn.ts because they stage operations and need the tool loop.
 */

/** The only intent the single-call console persists under. */
export const CHAT_INTENT_ID = 'general.help'

// How much of a thread the model sees on each turn. Bounded because every
// resumed turn replays it: a long-lived thread must not grow the prompt
// without limit, and a local model may have a small context window. The
// newest turns win; the tail that fits is what the model gets.
export const HISTORY_MAX_MESSAGES = 16
export const HISTORY_MAX_CHARS = 10_000
// One turn is clamped too so a single pasted wall of text cannot eat the
// whole budget on its own.
const HISTORY_MAX_TURN_CHARS = 3_000

// The sidebar caches a one-line preview per row; the title is the sidebar
// label. Both are bounded so a long first question can't bloat the row.
const PREVIEW_MAX = 200
const TITLE_MAX = 80

/** Truncate on a whole-grapheme boundary is overkill here; a hard slice with an ellipsis is fine for a preview. */
function clamp(text: string, max: number): string {
  const t = text.trim().replace(/\s+/g, ' ')
  if (t.length <= max) return t
  return `${t.slice(0, max - 1).trimEnd()}…`
}

function textBlocks(text: string): { type: 'text'; text: string }[] {
  return [{ type: 'text', text }]
}

export type ResolveConversationResult =
  | { ok: true; conversationId: string; created: boolean }
  // The client passed a conversation id that isn't this user's general.help
  // thread in this company. Same outcome as "doesn't exist": a 404, never a
  // 403 that would confirm someone else's id is real.
  | { ok: false; reason: 'not_found' }

/**
 * Resolve the conversation to append this turn to.
 *
 * With no id, create a fresh general.help conversation titled from the first
 * question. With an id, verify ownership the same way /api/agent/invoke does:
 * RLS on agent_conversations is COMPANY-scoped, so a colleague's thread would
 * otherwise load; the user_id + company_id + intent_id checks close that.
 */
export async function resolveChatConversation(
  supabase: SupabaseClient,
  userId: string,
  companyId: string,
  conversationId: string | null | undefined,
  firstQuestion: string,
  contextRef?: string | null,
): Promise<ResolveConversationResult> {
  if (conversationId) {
    const { data: conv } = await supabase
      .from('agent_conversations')
      .select('id, user_id, company_id, intent_id')
      .eq('id', conversationId)
      .maybeSingle()
    if (
      !conv ||
      conv.user_id !== userId ||
      conv.company_id !== companyId ||
      conv.intent_id !== CHAT_INTENT_ID
    ) {
      return { ok: false, reason: 'not_found' }
    }
    return { ok: true, conversationId: conv.id as string, created: false }
  }

  const { data: created, error } = await supabase
    .from('agent_conversations')
    .insert({
      company_id: companyId,
      user_id: userId,
      intent_id: CHAT_INTENT_ID,
      context_ref: contextRef ?? null,
      title: clamp(firstQuestion, TITLE_MAX) || 'Fråga din assistent',
    })
    .select('id')
    .single()
  if (error || !created) throw error ?? new Error('Failed to create conversation')
  return { ok: true, conversationId: created.id as string, created: true }
}

/** Append the user's question as a persisted turn (append-only). */
export async function persistUserTurn(
  supabase: SupabaseClient,
  conversationId: string,
  question: string,
): Promise<void> {
  const { error } = await supabase.from('agent_messages').insert({
    conversation_id: conversationId,
    role: 'user',
    content: textBlocks(question),
  })
  if (error) throw error
}

/**
 * Append the assistant's answer and roll the conversation row forward so the
 * sidebar shows this thread at the top with a fresh preview. run-turn updates
 * the same two columns on every assistant turn; we mirror that exactly.
 */
export async function persistAssistantTurn(
  supabase: SupabaseClient,
  conversationId: string,
  answer: string,
): Promise<void> {
  const { error: msgErr } = await supabase.from('agent_messages').insert({
    conversation_id: conversationId,
    role: 'assistant',
    content: textBlocks(answer),
  })
  if (msgErr) throw msgErr

  // Best-effort: a failed roll-forward only mis-sorts the sidebar row, it does
  // not lose the answer (already persisted above). Do not fail the request on it.
  await supabase
    .from('agent_conversations')
    .update({
      last_message_at: new Date().toISOString(),
      last_message_preview: clamp(answer, PREVIEW_MAX),
    })
    .eq('id', conversationId)
}

/** Plain text of a stored Anthropic-shaped content array; empty for tool-only rows. */
function textOfContent(content: unknown): string {
  if (typeof content === 'string') return content.trim()
  if (!Array.isArray(content)) return ''
  return content
    .filter(
      (b): b is { type: 'text'; text: string } =>
        !!b && typeof b === 'object' && (b as { type?: unknown }).type === 'text' && typeof (b as { text?: unknown }).text === 'string',
    )
    .map((b) => b.text)
    .join('\n')
    .trim()
}

function clampTurn(text: string): string {
  if (text.length <= HISTORY_MAX_TURN_CHARS) return text
  return `${text.slice(0, HISTORY_MAX_TURN_CHARS).trimEnd()}…`
}

/**
 * The earlier turns of a thread, as the model should see them.
 *
 * This is what makes a resumed thread a conversation rather than a series of
 * unrelated questions: without it every turn was answered blind, so a
 * follow-up ("och förra månaden?") got "vad syftar du på?". Only the
 * conversation's own rows are read (the caller has already proven ownership
 * via resolveChatConversation).
 *
 * Shape rules, so both AI adapters can send the result as-is:
 *   - text only: tool_use / tool_result rows from the old streaming runtime
 *     carry no prose, and hidden rows are prompt-template scaffolding, never
 *     something the user said; both are dropped.
 *   - alternating, starting with a user turn: consecutive same-role turns are
 *     merged (a question whose answer failed sits next to its retry), and a
 *     leading assistant turn (its question fell off the window) is dropped.
 *   - bounded: newest HISTORY_MAX_MESSAGES rows, then trimmed from the oldest
 *     end until the text fits HISTORY_MAX_CHARS.
 */
export async function loadChatHistory(
  supabase: SupabaseClient,
  conversationId: string,
): Promise<AiChatTurn[]> {
  const { data, error } = await supabase
    .from('agent_messages')
    .select('role, content, hidden, created_at')
    .eq('conversation_id', conversationId)
    .order('created_at', { ascending: false })
    .order('id', { ascending: false })
    .limit(HISTORY_MAX_MESSAGES)
  if (error) throw error

  const rows = (data ?? []) as { role: string; content: unknown; hidden?: boolean | null }[]
  const turns: AiChatTurn[] = []
  // Oldest first from here on.
  for (const row of rows.slice().reverse()) {
    if (row.hidden) continue
    if (row.role !== 'user' && row.role !== 'assistant') continue
    const text = textOfContent(row.content)
    if (!text) continue
    const clamped = clampTurn(text)
    const last = turns[turns.length - 1]
    if (last && last.role === row.role) {
      last.text = clampTurn(`${last.text}\n\n${clamped}`)
    } else {
      turns.push({ role: row.role, text: clamped })
    }
  }

  // Trim from the oldest end until the total fits, then make sure what is
  // left opens with the user.
  let total = turns.reduce((n, t) => n + t.text.length, 0)
  while (turns.length > 0 && total > HISTORY_MAX_CHARS) {
    total -= turns[0].text.length
    turns.shift()
  }
  while (turns.length > 0 && turns[0].role !== 'user') turns.shift()
  return turns
}