import SwiftUI

/// Bewegungsverlauf: wer hat wann was ein- und ausgelagert.
///
/// Dieselbe Ansicht dient dem Gesamtverlauf und dem Verlauf eines einzelnen
/// Artikels - der Unterschied ist nur `productId`.
struct HistoryView: View {
    @EnvironmentObject private var display: DisplaySettings

    var productId: Int?

    @State private var movements: [Movement] = []
    @State private var limit = 100
    @State private var busy = true
    @State private var error: String?

    var body: some View {
        List {
            if let error {
                Section { Text(error).foregroundStyle(.red).font(.callout) }
            }

            ForEach(tage, id: \.key) { tag in
                Section(display.formatDay(tag.eintraege[0].createdAt)) {
                    ForEach(tag.eintraege) { movement in
                        MovementRow(movement: movement, showProduct: productId == nil)
                    }
                }
            }

            if movements.isEmpty && !busy {
                Text("Noch keine Bewegungen.").foregroundStyle(.secondary)
            }

            // Nachladen erst anbieten, wenn die aktuelle Menge auch voll ist.
            if movements.count >= limit {
                Button("Mehr laden") {
                    limit += 100
                    Task { await load() }
                }
            }
        }
        .navigationTitle("Verlauf")
        .navigationBarTitleDisplayMode(.inline)
        .refreshable { await load() }
        .task { await load() }
    }

    private struct Tag {
        let key: String
        let eintraege: [Movement]
    }

    /// Nach Tagen gruppiert, neueste zuerst. Die API liefert bereits sortiert,
    /// deshalb reicht es, der Reihe nach zu sammeln.
    private var tage: [Tag] {
        var result: [Tag] = []
        for movement in movements {
            let key = DisplaySettings.dayKey(movement.createdAt)
            if let last = result.last, last.key == key {
                result[result.count - 1] = Tag(key: key, eintraege: last.eintraege + [movement])
            } else {
                result.append(Tag(key: key, eintraege: [movement]))
            }
        }
        return result
    }

    private func load() async {
        busy = true
        defer { busy = false }
        do {
            movements = try await APIClient.shared.movements(limit: limit, productId: productId)
            error = nil
        } catch {
            self.error = error.localizedDescription
        }
    }
}

struct MovementRow: View {
    @EnvironmentObject private var display: DisplaySettings

    let movement: Movement
    var showProduct = true

    var body: some View {
        HStack(spacing: 12) {
            Image(systemName: movement.isIncoming ? "arrow.down.circle.fill" : "arrow.up.circle.fill")
                .font(.title3)
                .foregroundStyle(movement.isIncoming ? Color.green : Color.orange)
            VStack(alignment: .leading, spacing: 2) {
                if showProduct {
                    Text(movement.productName)
                }
                Text(menge)
                    .font(showProduct ? .caption : .body)
                    .foregroundStyle(showProduct ? .secondary : .primary)
                if let note = movement.note, !note.isEmpty {
                    Text(note).font(.caption2).foregroundStyle(.secondary)
                }
            }
            Spacer()
            VStack(alignment: .trailing, spacing: 2) {
                Text(display.formatTime(movement.createdAt))
                    .font(.caption).foregroundStyle(.secondary)
                if let user = movement.username, !user.isEmpty {
                    Text(user).font(.caption2).foregroundStyle(.tertiary)
                }
            }
        }
    }

    /// Vorzeichen macht die Richtung auch ohne Farbe lesbar.
    private var menge: String {
        let zeichen = movement.isIncoming ? "+" : "−"
        return zeichen + display.amountText(movement.quantity,
                                            packageSize: movement.packageSize,
                                            baseUnit: movement.baseUnit)
    }
}