import Foundation

/// The IME owns its marked text until commit. Compare its committed native
/// result to the exact source string it began with, using scalar-safe UTF-16.
@MainActor enum DocumentComposition {
    static func replacement(before: String, after: String) -> (NSRange, String)? {
        let old = Array(before.unicodeScalars), new = Array(after.unicodeScalars)
        var prefix = 0
        while prefix < min(old.count, new.count), old[prefix] == new[prefix] { prefix += 1 }
        var suffix = 0
        while suffix < min(old.count, new.count) - prefix, old[old.count - suffix - 1] == new[new.count - suffix - 1] { suffix += 1 }
        guard prefix != old.count || prefix != new.count else { return nil }
        func units(_ values: ArraySlice<Unicode.Scalar>) -> Int { values.reduce(0) { $0 + ($1.value > 0xffff ? 2 : 1) } }
        let range = NSRange(location: units(old[..<prefix]), length: units(old[prefix..<(old.count - suffix)]))
        return (range, String(String.UnicodeScalarView(new[prefix..<(new.count - suffix)])))
    }
}
#if os(macOS)
import AppKit
final class DocsTextView: DocsPagedTextView {
    var action: ((String) -> Bool)?
    var canAction: ((String) -> Bool)?
    var ruleCommand: (([String: JSONValue]) -> Bool)?
    var lastInputRule: DocumentInputRules.Plan?
    var clipboardEdit: (([JSONValue]?, NSRange, String) -> Bool)?
    var compositionChanged: ((Bool) -> Void)?
    var compositionCommitted: ((NSAttributedString, String) -> Bool)?
    private var original: NSAttributedString?
    var isComposing: Bool { original != nil }
    @objc func undo(_ sender: Any?) { _ = action?("undo") }
    @objc func redo(_ sender: Any?) { _ = action?("redo") }
    override func validateMenuItem(_ menuItem: NSMenuItem) -> Bool {
        if menuItem.action == #selector(undo(_:)) { return canAction?("undo") == true }
        if menuItem.action == #selector(redo(_:)) { return canAction?("redo") == true }
        return super.validateMenuItem(menuItem)
    }
    override func performKeyEquivalent(with event: NSEvent) -> Bool {
        let flags = event.modifierFlags
        if let key = event.charactersIgnoringModifiers,
           let name = DocumentKeyboardBindings.action(key: key, command: flags.contains(.command), shift: flags.contains(.shift), option: flags.contains(.option), control: flags.contains(.control)) {
            _ = action?(name); return true
        }
        return super.performKeyEquivalent(with: event)
    }
    override func insertTab(_ sender: Any?) { _ = action?("indent") }
    override func insertBacktab(_ sender: Any?) { _ = action?("outdent") }
    override func insertLineBreak(_ sender: Any?) { _ = action?("hard-break") }
    override func deleteBackward(_ sender: Any?) {
        if !revertInputRule() { super.deleteBackward(sender) }
    }
    override func copy(_ sender: Any?) {
        lastInputRule = nil
        let range = selectedRange()
        guard range.length > 0 else { return }
        _ = DocsRichClipboard.write(attributedString().attributedSubstring(from: range))
    }
    override func cut(_ sender: Any?) {
        lastInputRule = nil
        let range = selectedRange()
        guard isEditable, !isComposing, range.length > 0,
              DocsRichClipboard.write(attributedString().attributedSubstring(from: range)),
              clipboardEdit?(nil, range, "") == true else { return }
        textStorage?.replaceCharacters(in: range, with: "")
        setSelectedRange(NSRange(location: range.location, length: 0)); didChangeText()
    }
    override func paste(_ sender: Any?) {
        lastInputRule = nil
        guard isEditable, !isComposing else { return }
        guard let blocks = DocsRichClipboard.read() else { super.pasteAsPlainText(sender); return }
        let range = selectedRange()
        guard let replacement = DocumentClipboardInsertion.attributed(blocks: blocks, in: attributedString(), range: range),
              clipboardEdit?(blocks, range, replacement.string) == true else { return }
        textStorage?.replaceCharacters(in: range, with: replacement)
        setSelectedRange(NSRange(location: range.location + replacement.length, length: 0)); didChangeText()
    }
    override func setMarkedText(_ string: Any, selectedRange: NSRange, replacementRange: NSRange) {
        if original == nil { original = NSAttributedString(attributedString: attributedString()); compositionChanged?(true) }
        super.setMarkedText(string, selectedRange: selectedRange, replacementRange: replacementRange)
    }
    override func unmarkText() { super.unmarkText(); finishComposition() }
    override func insertText(_ insertString: Any, replacementRange: NSRange) {
        let composing = isComposing
        let range = replacementRange.location == NSNotFound ? selectedRange() : replacementRange
        if !composing, let text = insertString as? String, interceptInput(text, range: range) { return }
        super.insertText(insertString, replacementRange: replacementRange)
        if composing && !hasMarkedText() { finishComposition() }
    }
    private func finishComposition() {
        guard let original else { return }
        if compositionCommitted?(original, string) == false { textStorage?.setAttributedString(original) }
        self.original = nil; compositionChanged?(false)
    }
}
#else
import UIKit
final class DocsTextView: DocsPagedTextView {
    var action: ((String) -> Bool)?
    var canAction: ((String) -> Bool)?
    var ruleCommand: (([String: JSONValue]) -> Bool)?
    var lastInputRule: DocumentInputRules.Plan?
    var clipboardEdit: (([JSONValue]?, NSRange, String) -> Bool)?
    var compositionChanged: ((Bool) -> Void)?
    var compositionCommitted: ((NSAttributedString, String) -> Bool)?
    private var original: NSAttributedString?
    var isComposing: Bool { original != nil }
    override var undoManager: UndoManager? { nil }
    override var keyCommands: [UIKeyCommand]? {
        DocumentKeyboardBindings.all.map { binding in
            let command = UIKeyCommand(input: binding.key, modifierFlags: (binding.command ? UIKeyModifierFlags.command : []).union(binding.shift ? .shift : []), action: #selector(handleKey(_:)))
            command.wantsPriorityOverSystemBehavior = true
            return command
        }
    }
    @objc private func handleKey(_ key: UIKeyCommand) {
        guard let input = key.input,
              let name = DocumentKeyboardBindings.action(key: input, command: key.modifierFlags.contains(.command), shift: key.modifierFlags.contains(.shift), option: key.modifierFlags.contains(.alternate), control: key.modifierFlags.contains(.control)) else { return }
        _ = action?(name)
    }
    override func deleteBackward() {
        if !revertInputRule() { super.deleteBackward() }
    }
    override func copy(_ sender: Any?) {
        lastInputRule = nil
        guard selectedRange.length > 0 else { return }
        _ = DocsRichClipboard.write(attributedText.attributedSubstring(from: selectedRange))
    }
    override func cut(_ sender: Any?) {
        lastInputRule = nil
        let range = selectedRange
        guard isEditable, !isComposing, range.length > 0,
              DocsRichClipboard.write(attributedText.attributedSubstring(from: range)),
              clipboardEdit?(nil, range, "") == true else { return }
        textStorage.replaceCharacters(in: range, with: "")
        selectedRange = NSRange(location: range.location, length: 0)
        delegate?.textViewDidChange?(self)
    }
    override func paste(_ sender: Any?) {
        lastInputRule = nil
        guard isEditable, !isComposing else { return }
        guard let blocks = DocsRichClipboard.read() else { super.paste(sender); return }
        let range = selectedRange
        guard let replacement = DocumentClipboardInsertion.attributed(blocks: blocks, in: attributedText, range: range),
              clipboardEdit?(blocks, range, replacement.string) == true else { return }
        textStorage.replaceCharacters(in: range, with: replacement)
        selectedRange = NSRange(location: range.location + replacement.length, length: 0)
        delegate?.textViewDidChange?(self)
    }
    override func setMarkedText(_ markedText: String?, selectedRange: NSRange) {
        if original == nil { original = NSAttributedString(attributedString: attributedText); compositionChanged?(true) }
        super.setMarkedText(markedText, selectedRange: selectedRange)
    }
    override func unmarkText() { super.unmarkText(); finishComposition() }
    override func insertText(_ text: String) {
        let composing = isComposing
        if !composing, interceptInput(text, range: selectedRange) { return }
        super.insertText(text)
        if composing && markedTextRange == nil { finishComposition() }
    }
    private func finishComposition() {
        guard let original else { return }
        if compositionCommitted?(original, text) == false { attributedText = original }
        self.original = nil; compositionChanged?(false)
    }
}
#endif