FindPanelViewModel+Find.swift

//
//  FindPanelViewModel+Find.swift
//  CodeEditSourceEditor
//
//  Created by Khan Winter on 4/18/25.
//

import Foundation

extension FindPanelViewModel {
    // MARK: - Find

    /// Performs a find operation on the find target and updates both the ``findMatches`` array and the emphasis
    /// manager's emphases.
    func find() {
        // Don't find if target isn't ready or the query is empty
        guard let target = target, !findText.isEmpty else {
            self.findMatches = []
            return
        }

        // Set case sensitivity based on matchCase property
        var findOptions: NSRegularExpression.Options = matchCase ? [] : [.caseInsensitive]

        // Add multiline options for regular expressions
        if findMethod == .regularExpression {
            findOptions.insert(.dotMatchesLineSeparators)
            findOptions.insert(.anchorsMatchLines)
        }

        let pattern: String

        switch findMethod {
        case .contains:
            // Simple substring match, escape special characters
            pattern = NSRegularExpression.escapedPattern(for: findText)

        case .matchesWord:
            // Match whole words only using word boundaries
            pattern = "\\b" + NSRegularExpression.escapedPattern(for: findText) + "\\b"

        case .startsWith:
            // Match at the start of a line or after a word boundary
            pattern = "(?:^|\\b)" + NSRegularExpression.escapedPattern(for: findText)

        case .endsWith:
            // Match at the end of a line or before a word boundary
            pattern = NSRegularExpression.escapedPattern(for: findText) + "(?:$|\\b)"

        case .regularExpression:
            // Use the pattern directly without additional escaping
            pattern = findText
        }

        guard let regex = try? NSRegularExpression(pattern: pattern, options: findOptions) else {
            self.findMatches = []
            self.currentFindMatchIndex = 0
            return
        }

        let text = target.textView.string
        let nsText = text as NSString
        let range = NSRange(location: 0, length: nsText.length)
        let matches = regex.matches(in: text, range: range)

        self.findMatches = matches.map(\.range)

        // Find the nearest match to the current cursor position
        currentFindMatchIndex = getNearestEmphasisIndex(matchRanges: findMatches) ?? 0

        // Only add emphasis layers if the find panel is focused
        if isFocused {
            addMatchEmphases(flashCurrent: false)
        }
    }

    // MARK: - Get Nearest Emphasis Index

    private func getNearestEmphasisIndex(matchRanges: [NSRange]) -> Int? {
        // order the array as follows
        // Found: 1 -> 2 -> 3 -> 4
        // Cursor:       |
        // Result: 3 -> 4 -> 1 -> 2
        guard let cursorPosition = target?.cursorPositions.first else { return nil }
        let start = cursorPosition.range.location

        var left = 0
        var right = matchRanges.count - 1
        var bestIndex = -1
        var bestDiff = Int.max  // Stores the closest difference

        while left <= right {
            let mid = left + (right - left) / 2
            let midStart = matchRanges[mid].location
            let diff = abs(midStart - start)

            // If it's an exact match, return immediately
            if diff == 0 {
                return mid
            }

            // If this is the closest so far, update the best index
            if diff < bestDiff {
                bestDiff = diff
                bestIndex = mid
            }

            // Move left or right based on the cursor position
            if midStart < start {
                left = mid + 1
            } else {
                right = mid - 1
            }
        }

        return bestIndex >= 0 ? bestIndex : nil
    }

}