import Foundation
import SuggestionModel
import Workspace

public struct FilespaceSuggestionSnapshot: Equatable {
    public var linesHash: Int
    public var cursorPosition: CursorPosition

    public init(linesHash: Int, cursorPosition: CursorPosition) {
        self.linesHash = linesHash
        self.cursorPosition = cursorPosition
    }
}

public struct FilespaceSuggestionSnapshotKey: FilespacePropertyKey {
    public static func createDefaultValue()
        -> FilespaceSuggestionSnapshot { .init(linesHash: -1, cursorPosition: .outOfScope) }
}

public extension FilespacePropertyValues {
    @WorkspaceActor
    var suggestionSourceSnapshot: FilespaceSuggestionSnapshot {
        get { self[FilespaceSuggestionSnapshotKey.self] }
        set { self[FilespaceSuggestionSnapshotKey.self] = newValue }
    }
}

public extension Filespace {
    @WorkspaceActor
    func resetSnapshot() {
        // swiftformat:disable redundantSelf
        self.suggestionSourceSnapshot = FilespaceSuggestionSnapshotKey.createDefaultValue()
        // swiftformat:enable all
    }

    /// Validate the suggestion is still valid.
    /// - Parameters:
    ///    - lines: lines of the file
    ///    - cursorPosition: cursor position
    /// - Returns: `true` if the suggestion is still valid
    @WorkspaceActor
    func validateSuggestions(lines: [String], cursorPosition: CursorPosition) -> Bool {
        guard let presentingSuggestion else { return false }

        // cursor has moved to another line
        if cursorPosition.line != presentingSuggestion.position.line {
            reset()
            resetSnapshot()
            return false
        }

        // the cursor position is valid
        guard cursorPosition.line >= 0, cursorPosition.line < lines.count else {
            reset()
            resetSnapshot()
            return false
        }

        let editingLine = lines[cursorPosition.line].dropLast(1) // dropping \n
        let suggestionLines = presentingSuggestion.text.split(separator: "\n")
        let suggestionFirstLine = suggestionLines.first ?? ""
        
        /// For example:
        /// ```
        /// ABCD012     // typed text
        ///     ^
        ///     0123456 // suggestion range 4-11, generated after `ABCD`
        /// ```
        /// The suggestion should contain `012`, aka, the suggestion that is typed.
        ///
        /// Another case is that the suggestion may contain the whole line.
        /// /// ```
        /// ABCD012     // typed text
        /// ----^
        /// ABCD0123456 // suggestion range 0-11, generated after `ABCD`
        /// The suggestion should contain `ABCD012`, aka, the suggestion that is typed.
        /// ```
        let typedSuggestion = {
            let startIndex = editingLine.index(
                editingLine.startIndex,
                offsetBy: presentingSuggestion.range.start.character,
                limitedBy: editingLine.endIndex
            ) ?? editingLine.startIndex
            
            let endIndex = editingLine.index(
                editingLine.startIndex,
                offsetBy: cursorPosition.character,
                limitedBy: editingLine.endIndex
            ) ?? editingLine.endIndex
            
            if endIndex > startIndex {
                return editingLine[startIndex..<endIndex]
            }
            
            return ""
        }()

        // the line content doesn't match the suggestion
        if cursorPosition.character > 0,
           !suggestionFirstLine.hasPrefix(typedSuggestion)
        {
            reset()
            resetSnapshot()
            return false
        }

        // finished typing the whole suggestion when the suggestion has only one line
        if typedSuggestion.hasPrefix(suggestionFirstLine), suggestionLines.count <= 1 {
            reset()
            resetSnapshot()
            return false
        }

        // undo to a state before the suggestion was generated
        if editingLine.count < presentingSuggestion.position.character {
            reset()
            resetSnapshot()
            return false
        }

        return true
    }
}