import Foundation
import SstCore

public struct HistoryEntry: Codable, Equatable, Identifiable, Sendable {
    public var id: UUID
    public var date: Date
    public var duration: TimeInterval
    public var rawText: String
    public var finalText: String
    public var corrections: [AppliedCorrection]

    public init(
        id: UUID = UUID(), date: Date, duration: TimeInterval,
        rawText: String, finalText: String, corrections: [AppliedCorrection] = []
    ) {
        self.id = id
        self.date = date
        self.duration = duration
        self.rawText = rawText
        self.finalText = finalText
        self.corrections = corrections
    }

    public init(result: DictationResult) {
        self.init(
            date: result.date, duration: result.duration, rawText: result.rawText,
            finalText: result.finalText, corrections: result.corrections)
    }
}

/// Newest first, stored as one JSON file; saves are debounced.
@MainActor
public final class HistoryStore {
    public enum LoadOutcome: Equatable {
        case empty
        case loaded
        case recoveredCorrupt(backup: URL)
        /// The file exists but cannot be read; it is left alone and nothing is written over it.
        case unreadable(String)
    }

    private struct Document: Codable {
        var version: Int
        var entries: [HistoryEntry]
    }

    public private(set) var entries: [HistoryEntry] = []
    public private(set) var lastError: String?
    public var onChange: (() -> Void)?

    private let fileURL: URL
    private var readOnly = false
    private var saveTask: Task<Void, Never>?

    public init(fileURL: URL) {
        self.fileURL = fileURL
    }

    private static func makeEncoder() -> JSONEncoder {
        let encoder = JSONEncoder()
        encoder.dateEncodingStrategy = .iso8601
        encoder.outputFormatting = [.prettyPrinted, .sortedKeys]
        return encoder
    }

    private static func makeDecoder() -> JSONDecoder {
        let decoder = JSONDecoder()
        decoder.dateDecodingStrategy = .iso8601
        return decoder
    }

    @discardableResult
    public func load() -> LoadOutcome {
        let data: Data
        do {
            data = try Data(contentsOf: fileURL)
        } catch {
            if !FileManager.default.fileExists(atPath: fileURL.path) {
                entries = []
                onChange?()
                return .empty
            }
            readOnly = true
            lastError = error.localizedDescription
            return .unreadable(error.localizedDescription)
        }
        do {
            entries = try Self.makeDecoder().decode(Document.self, from: data).entries
            onChange?()
            return .loaded
        } catch {
            let stamp = ISO8601DateFormatter().string(from: Date()).replacingOccurrences(of: ":", with: "-")
            let backup = fileURL.deletingLastPathComponent().appending(path: "history.corrupt-\(stamp).json")
            try? FileManager.default.moveItem(at: fileURL, to: backup)
            entries = []
            onChange?()
            return .recoveredCorrupt(backup: backup)
        }
    }

    public func add(_ entry: HistoryEntry) {
        entries.insert(entry, at: 0)
        changed()
    }

    public func remove(id: UUID) {
        entries.removeAll { $0.id == id }
        changed()
    }

    /// Replaces the final text of an entry. The highlighted corrections no longer match an edited text, so they are dropped.
    public func updateText(id: UUID, to text: String) {
        guard let index = entries.firstIndex(where: { $0.id == id }), entries[index].finalText != text else { return }
        entries[index].finalText = text
        entries[index].corrections = []
        changed()
    }

    public func removeAll() {
        entries = []
        changed()
    }

    /// Writes immediately (also call this when the app quits).
    public func flush() {
        saveTask?.cancel()
        saveTask = nil
        guard !readOnly else { return }
        do {
            try FileManager.default.createDirectory(
                at: fileURL.deletingLastPathComponent(), withIntermediateDirectories: true)
            let data = try Self.makeEncoder().encode(Document(version: 1, entries: entries))
            try data.write(to: fileURL, options: .atomic)
            lastError = nil
        } catch {
            lastError = error.localizedDescription
        }
    }

    private func changed() {
        onChange?()
        saveTask?.cancel()
        saveTask = Task { [weak self] in
            try? await Task.sleep(for: .milliseconds(300))
            guard !Task.isCancelled else { return }
            self?.flush()
        }
    }
}

public enum HistorySearch {
    static func fold(_ text: String) -> String {
        text.folding(options: [.caseInsensitive, .diacriticInsensitive], locale: nil)
    }

    /// Every query word must occur in the final or the original text (case- and diacritic-insensitive).
    public static func filter(_ entries: [HistoryEntry], query: String) -> [HistoryEntry] {
        let words = fold(query).split(whereSeparator: \.isWhitespace).map(String.init)
        guard !words.isEmpty else { return entries }
        return entries.filter { entry in
            let haystack = fold(entry.finalText + " " + entry.rawText)
            return words.allSatisfy { haystack.contains($0) }
        }
    }
}

public struct HistoryDay: Identifiable, Equatable, Sendable {
    public let day: Date
    public let entries: [HistoryEntry]
    public var id: Date { day }
}

public enum HistoryGrouping {
    /// Groups newest-first entries by calendar day, keeping their order.
    public static func byDay(_ entries: [HistoryEntry], calendar: Calendar = .current) -> [HistoryDay] {
        var days: [HistoryDay] = []
        for entry in entries {
            let start = calendar.startOfDay(for: entry.date)
            if let last = days.last, last.day == start {
                days[days.count - 1] = HistoryDay(day: start, entries: last.entries + [entry])
            } else {
                days.append(HistoryDay(day: start, entries: [entry]))
            }
        }
        return days
    }
}