package mentions

import (
	"sort"
	"strings"
	"unicode"

	"git.gobha.me/xcaliber/chat-switchboard/models"
)

// Mention represents a parsed @mention token in message content.
type Mention struct {
	Raw      string              // "@claude-3-opus" as written (includes @)
	Name     string              // "claude-3-opus" (normalized, no @)
	Start    int                 // byte offset in message content
	End      int                 // byte offset end (exclusive)
	Resolved *models.ChannelModel // nil if unresolved
}

// Parse extracts @mentions from message content and resolves them
// against the channel's model roster.
//
// Rules:
//   - @ followed by one or more non-whitespace characters
//   - Greedy: @claude-3-opus-20240229 matches the full token
//   - Resolution: case-insensitive match against display_name with
//     hyphens/spaces normalized (e.g. "claude 3 opus" matches "Claude-3-Opus")
//   - Longest-match-first when display names overlap
//   - Unresolved mentions are included with Resolved = nil
//   - @ must be at start of content or preceded by whitespace
func Parse(content string, roster []models.ChannelModel) []Mention {
	if len(roster) == 0 || !strings.Contains(content, "@") {
		return nil
	}

	// Build lookup: normalized display_name → *ChannelModel
	// Sort roster by display_name length descending for longest-match-first
	type entry struct {
		normalized string
		model      models.ChannelModel
	}
	entries := make([]entry, 0, len(roster))
	for _, cm := range roster {
		if cm.DisplayName == "" {
			continue
		}
		entries = append(entries, entry{
			normalized: normalize(cm.DisplayName),
			model:      cm,
		})
	}
	sort.Slice(entries, func(i, j int) bool {
		return len(entries[i].normalized) > len(entries[j].normalized)
	})

	// Extract @tokens
	var mentions []Mention
	i := 0
	for i < len(content) {
		if content[i] != '@' {
			i++
			continue
		}

		// @ must be at start or preceded by whitespace
		if i > 0 && !unicode.IsSpace(rune(content[i-1])) {
			i++
			continue
		}

		// Extract the token after @
		start := i
		i++ // skip @
		tokenStart := i
		for i < len(content) && !unicode.IsSpace(rune(content[i])) {
			i++
		}

		if i == tokenStart {
			continue // bare @ with no token
		}

		// Strip trailing punctuation (commas, periods, etc.)
		tokenEnd := i
		for tokenEnd > tokenStart && isMentionTrailingPunct(content[tokenEnd-1]) {
			tokenEnd--
		}
		if tokenEnd == tokenStart {
			continue // all punctuation
		}

		raw := content[start:tokenEnd]
		name := content[tokenStart:tokenEnd]
		normalizedName := normalize(name)

		// Try to resolve against roster (longest match first)
		var resolved *models.ChannelModel
		for idx := range entries {
			if normalizedName == entries[idx].normalized {
				cm := entries[idx].model
				resolved = &cm
				break
			}
		}

		mentions = append(mentions, Mention{
			Raw:      raw,
			Name:     name,
			Start:    start,
			End:      tokenEnd,
			Resolved: resolved,
		})
	}

	return mentions
}

// ResolvedModels returns deduplicated resolved models from parsed mentions.
// Returns nil if no mentions resolved.
func ResolvedModels(mentions []Mention) []models.ChannelModel {
	if len(mentions) == 0 {
		return nil
	}

	seen := make(map[string]bool)
	var result []models.ChannelModel
	for _, m := range mentions {
		if m.Resolved != nil && !seen[m.Resolved.ID] {
			seen[m.Resolved.ID] = true
			result = append(result, *m.Resolved)
		}
	}
	return result
}

// isMentionTrailingPunct returns true for punctuation that commonly
// follows an @mention but isn't part of the name.
func isMentionTrailingPunct(b byte) bool {
	switch b {
	case ',', '.', '!', '?', ':', ';', ')', ']', '}':
		return true
	}
	return false
}

// normalize converts a display name to a canonical form for matching:
// lowercase, hyphens → spaces collapsed, trimmed.
func normalize(s string) string {
	s = strings.ToLower(s)
	s = strings.ReplaceAll(s, "-", " ")
	s = strings.ReplaceAll(s, "_", " ")
	// Collapse multiple spaces
	fields := strings.Fields(s)
	return strings.Join(fields, " ")
}