package main

import "strings"

// bufferedMsg is one prior room message the bot retained for context.
type bufferedMsg struct {
	sender string
	body   string
	isBot  bool
}

// buildContext assembles the provider-neutral message list under the owner's
// minimisation rule ("trigger + bot replies only", §6/F8):
//
//   - GROUP rooms: send ONLY the bot's own prior replies (assistant turns) plus
//     the single triggering message (user turn). Other participants' messages and
//     display names never reach the model — the third-party-consent mitigation.
//   - 1:1 rooms: there are no third parties, so the peer's recent turns are
//     included too for coherence. Still no display names (pseudo "user").
//
// `history` is the recent room window EXCLUDING the trigger; `triggerBody` is the
// message that addressed the bot. Bodies are stripped of reply-fallback quotes so
// quoted third-party text doesn't leak.
func buildContext(system string, history []bufferedMsg, isDM bool, triggerBody string, maxEvents, maxTokens int) []Message {
	msgs := []Message{{Role: "system", Content: system}}

	// Keep at most the last maxEvents history items.
	if len(history) > maxEvents {
		history = history[len(history)-maxEvents:]
	}
	for _, h := range history {
		body := stripReplyFallback(h.body)
		if body == "" {
			continue
		}
		if h.isBot {
			msgs = append(msgs, Message{Role: "assistant", Content: body})
			continue
		}
		if isDM {
			msgs = append(msgs, Message{Role: "user", Content: body})
		}
		// group + non-bot history → dropped (privacy minimisation)
	}

	msgs = append(msgs, Message{Role: "user", Content: stripReplyFallback(triggerBody)})
	return truncateToTokens(msgs, maxTokens)
}

// routerContextMaxRunes caps each line fed to the classifier/rewrite so a long buffered
// turn can't blow the router's token budget; ~200 runes is plenty to resolve a follow-up.
const routerContextMaxRunes = 200

// routerContext returns the privacy-minimised conversation window the Layer-1 classifier
// and the follow-up rewrite read, drawn ONLY from the already-minimised `msgs` (a strict
// subset of what the final Grok call sees — no new privacy surface, §6):
//
//   - DM: the last ≤2 bot (assistant) turns plus the interleaved/final user turns, so a
//     bare follow-up like "2024 года" carries the prior film name into search_query.
//   - GROUP: ONLY the final user line. The per-(room,thread) buffer interleaves different
//     members' topics (it is keyed by room+thread, not sender), so resolving a follow-up
//     against prior turns could ground a confidently-wrong answer about the WRONG subject.
//
// Formatted "BOT: …\nUSER: …", each line truncated to routerContextMaxRunes. Empty when
// there is nothing to send.
func routerContext(msgs []Message, isDM bool) string {
	conv := msgs
	if len(conv) > 0 && conv[0].Role == "system" {
		conv = conv[1:]
	}
	if len(conv) == 0 {
		return ""
	}
	start := len(conv) - 1 // group default: only the final user line
	if isDM {
		// Walk back to include up to the 2 most recent assistant turns before the trigger.
		const maxAssistant = 2
		seen := 0
		for i := len(conv) - 1; i >= 0; i-- {
			start = i
			if conv[i].Role == "assistant" {
				if seen++; seen >= maxAssistant {
					break
				}
			}
		}
	}
	var b strings.Builder
	for _, m := range conv[start:] {
		text := strings.TrimSpace(m.Content)
		if text == "" {
			continue
		}
		if r := []rune(text); len(r) > routerContextMaxRunes {
			text = string(r[:routerContextMaxRunes])
		}
		label := "USER"
		if m.Role == "assistant" {
			label = "BOT"
		}
		b.WriteString(label)
		b.WriteString(": ")
		b.WriteString(text)
		b.WriteByte('\n')
	}
	return strings.TrimRight(b.String(), "\n")
}

// estimateTokens is a cheap upper-ish heuristic (~4 chars/token + per-message
// overhead). Used only to bound request size, not for billing (billing reads the
// API's returned usage).
func estimateTokens(s string) int {
	return len([]rune(s))/4 + 4
}

// truncateToTokens drops the oldest non-system, non-final messages until the
// estimate fits maxTokens. The system prompt (index 0) and the final user
// trigger are always preserved.
func truncateToTokens(msgs []Message, maxTokens int) []Message {
	total := 0
	for _, m := range msgs {
		total += estimateTokens(m.Content)
	}
	// Drop from index 1 upward (after system), never the last (trigger).
	for total > maxTokens && len(msgs) > 2 {
		total -= estimateTokens(msgs[1].Content)
		msgs = append(msgs[:1], msgs[2:]...)
	}
	return msgs
}

// stripReplyFallback removes the Matrix rich-reply fallback: leading lines that
// start with "> " (the quoted parent) followed by a blank separator line. This
// keeps quoted third-party text out of xAI and de-noises the prompt.
func stripReplyFallback(body string) string {
	if !strings.HasPrefix(body, "> ") {
		return strings.TrimSpace(body)
	}
	lines := strings.Split(body, "\n")
	i := 0
	for i < len(lines) && strings.HasPrefix(lines[i], ">") {
		i++
	}
	for i < len(lines) && strings.TrimSpace(lines[i]) == "" {
		i++
	}
	return strings.TrimSpace(strings.Join(lines[i:], "\n"))
}