import UIKit
import Runestone

@MainActor
final class CompletionController: ObservableObject {
    @Published var items:     [CompletionItem] = []
    @Published var isVisible: Bool = false
    @Published var anchorRect: CGRect = .zero

    private weak var textView: Runestone.TextView?
    private let lspClient: LSPClient
    private var debounceTask: Task<Void, Never>?
    private var lastId = 0
    private let autoTriggers: Set<Character> = [".", "(", ","]

    init(lspClient: LSPClient) { self.lspClient = lspClient }

    func attach(to tv: Runestone.TextView) { self.textView = tv }

    func textDidChange(in tv: Runestone.TextView, filePath: String) {
        let sel = tv.selectedRange
        guard sel.location > 0 else { dismiss(); return }
        let text = tv.text as NSString
        let c = text.character(at: sel.location - 1)
        let shouldTrigger = Unicode.Scalar(c).map { autoTriggers.contains(Character($0)) } ?? false

        if shouldTrigger {
            requestCompletions(tv: tv, filePath: filePath)
        } else if isVisible {
            debounceTask?.cancel()
            debounceTask = Task { [weak self] in
                try? await Task.sleep(for: .milliseconds(200))
                guard !Task.isCancelled else { return }
                self?.requestCompletions(tv: tv, filePath: filePath)
            }
        }
    }

    func requestManual(tv: Runestone.TextView, filePath: String) {
        requestCompletions(tv: tv, filePath: filePath)
    }

    func dismiss() { debounceTask?.cancel(); items = []; isVisible = false }

    func insert(_ item: CompletionItem, into tv: Runestone.TextView) {
        let sel = tv.selectedRange
        let text      = tv.text as NSString
        let wordRange = text.rangeOfCurrentWord(at: sel.location)
        let insertText = item.insertText ?? item.label
        tv.replace(wordRange, withText: insertText)
        if insertText.hasSuffix("()") {
            let loc = tv.selectedRange.location > 0 ? tv.selectedRange.location - 1 : 0
            tv.selectedRange = NSRange(location: loc, length: 0)
        }
        dismiss()
    }

    private func requestCompletions(tv: Runestone.TextView, filePath: String) {
        let sel = tv.selectedRange
        guard let loc = tv.textLocation(at: sel.location) else { return }
        // caretRect(for:) on Runestone.TextView takes UITextPosition, not Int.
        // Approximate anchor position from font metrics for the completion popover.
        let font       = tv.theme.font
        let lineHeight = ceil(font.lineHeight * tv.lineHeightMultiplier)
        let approxY    = CGFloat(loc.lineNumber) * lineHeight
                         + tv.textContainerInset.top
                         - tv.contentOffset.y
        anchorRect = CGRect(x: 0, y: approxY, width: 0, height: lineHeight)
        lastId += 1; let id = lastId
        Task { [weak self] in
            guard let self else { return }
            let results = await lspClient.requestCompletions(filePath: filePath, line: loc.lineNumber + 1, column: loc.column + 1)
            guard self.lastId == id else { return }
            if results.isEmpty { self.dismiss() } else { self.items = results; self.isVisible = true }
        }
    }
}

private extension NSString {
    func rangeOfCurrentWord(at location: Int) -> NSRange {
        let wordChars = CharacterSet.alphanumerics.union(CharacterSet(charactersIn: "_"))
        var start = location
        while start > 0, let scalar = Unicode.Scalar(character(at: start - 1)), wordChars.contains(scalar) { start -= 1 }
        return NSRange(location: start, length: location - start)
    }
}