import ByreAPI
import SwiftUI

typealias Participant = Components.Schemas.Participant
typealias MergeFacts = Components.Schemas.MergeFacts

@MainActor
private var mergeDrafts: [String: String] = [:]

private let maxTitle = 72

typealias Leave = @MainActor (@escaping @MainActor () -> Void) -> Void

struct MergeWarning {
    let text: String
    var open: (@MainActor () -> Void)?
    var detail = ""
}

@MainActor
@Observable
final class MergeModel {
    let taskId: String
    let target: String
    let keepOpen: Bool
    let parentTitle: String?
    let original: String
    var title: String
    var editing = false
    var toParent: Bool
    @ObservationIgnored var leave: Leave = { _ in }

    init(taskId: String, target: String, keepOpen: Bool, parentTitle: String?, title: String) {
        self.taskId = taskId
        self.target = target
        self.keepOpen = keepOpen
        self.parentTitle = parentTitle
        original = title
        self.title = title
        toParent = parentTitle != nil
    }

    var valid: Bool {
        toParent || !trimmed(title).isEmpty
    }

    var sentTitle: String {
        editing ? title : original
    }
}

@MainActor
func confirmMerge(_ taskId: String, _ store: Store, _ overlays: Overlays, keepOpen: Bool = false) async {
    guard let task = store.findTask(taskId), task.status == .active else {
        return
    }
    if store.taskBusy(taskId) {
        overlays.showAlert("Agent is mid-turn; merge when it's idle")
        return
    }
    if task.mergeQueuedAt != nil {
        overlays.showAlert("Merge already held behind another merge in this project")
        return
    }
    if task.mergingIntoParent {
        overlays.showAlert("Already waiting for the parent task's agent to merge this subtask")
        return
    }
    let target = store.projects.first { $0.id == task.projectId }?.defaultBranch ?? "the default branch"
    if task.mergeFacts.unmergedCommits == 0 && task.mergeFacts.unmergedFiles == 0 {
        overlays.showAlert("Nothing to merge: no commits or uncommitted files differ from \(target)")
        return
    }
    let parent = task.workflowStage == nil ? task.parentTaskId.flatMap { store.findTask($0) } : nil
    let title = mergeDrafts[taskId] ?? task.mergeTitle
    mergeDrafts[taskId] = nil
    let model = MergeModel(taskId: taskId, target: target, keepOpen: keepOpen, parentTitle: !keepOpen && parent?.status == .active ? parent?.name : nil, title: title)
    model.leave = { [weak model] go in
        if let model {
            mergeDrafts[taskId] = model.sentTitle
        }
        overlays.answerModal("cancel")
        go()
    }
    let content = MergeContent(model: model)
    let choice = await overlays.showModal(content, keepOpen
        ? [ModalButton(label: "Cancel", value: "cancel"), ModalButton(label: "Merge & continue", value: "now", primary: true)]
        : store.findTask(taskId)?.mergeFacts.reviewRunning == true
        ? [
            ModalButton(label: "Cancel", value: "cancel"),
            ModalButton(label: "Merge & complete now", value: "now"),
            ModalButton(label: "Merge & complete after review", value: "after", primary: true, help: "Merge once the running review finishes with no findings"),
        ]
        : [ModalButton(label: "Cancel", value: "cancel"), ModalButton(label: "Merge & complete", value: "now", primary: true)],
        inPane: true, canSubmit: { model.valid })
    if choice != "now" && choice != "after" {
        return
    }
    let afterReview = choice == "after"
    let body: Operations.MergeTask.Input.Body.JsonPayload = model.toParent
        ? .init(target: .parent, afterReview: afterReview ? true : nil)
        : .init(mergeTitle: model.sentTitle, afterReview: afterReview ? true : nil, keepOpen: keepOpen ? true : nil)
    do {
        _ = try await store.api.client.mergeTask(path: .init(taskId: taskId), body: .json(body)).accepted
    } catch {
        overlays.showAlert(errorText(error))
    }
}

@MainActor
private func reviewWarnings(_ taskId: String, _ f: MergeFacts, _ store: Store, _ leave: @escaping Leave) -> [MergeWarning] {
    if f.reviewSnapshot == 0 {
        return [MergeWarning(text: "These changes haven't been reviewed")]
    }
    var items: [MergeWarning] = []
    let open: @MainActor () -> Void = {
        leave {
            store.jumpTo(taskId, .review(f.reviewSnapshot))
        }
    }
    if f.reviewCount == 0 {
        items.append(MergeWarning(text: "The latest snapshot hasn't been reviewed", open: open))
    }
    if f.reviewRunning {
        items.append(MergeWarning(text: "The review of the latest snapshot is still running", open: open))
    }
    if f.reviewFailed {
        items.append(MergeWarning(text: "The review of the latest snapshot failed", open: open))
    }
    if f.reviewFindings > 0 {
        items.append(MergeWarning(text: "The review of the latest snapshot has \(f.reviewFindings) open finding\(f.reviewFindings == 1 ? "" : "s")", open: open))
    }
    if f.unreviewedChanges {
        items.append(MergeWarning(text: "Changes since the last snapshot haven't been reviewed"))
    }
    return items
}

private func coAuthorsLabel(_ coAuthors: [Participant]) -> String {
    let missing = coAuthors.filter { $0.gitName.isEmpty || $0.gitEmail.isEmpty }.count
    return "\(coAuthors.count) co-author\(coAuthors.count == 1 ? "" : "s")\(missing > 0 ? " (\(missing) without git identity)" : "")"
}

private func mergeTrailers(_ coAuthors: [Participant]) -> String {
    var lines: [String] = []
    let credited = coAuthors.filter { !$0.gitName.isEmpty && !$0.gitEmail.isEmpty }
    let missing = coAuthors.filter { $0.gitName.isEmpty || $0.gitEmail.isEmpty }
    if !credited.isEmpty {
        lines.append("Co-authored-by:")
        lines += credited.map { "  \($0.gitName) <\($0.gitEmail)>" }
    }
    if !missing.isEmpty {
        if !lines.isEmpty {
            lines.append("")
        }
        lines.append("No git identity, so no trailer:")
        lines += missing.map { "  \($0.displayName) (\($0.login))" }
    }
    return lines.joined(separator: "\n")
}

private struct MergeContent: View {
    @Bindable var model: MergeModel
    @Environment(Store.self) private var store
    @FocusState private var focused: Bool

    var body: some View {
        let taskId = model.taskId
        let leave = model.leave
        let facts = store.findTask(taskId)?.mergeFacts
        let coAuthors = facts?.participants.filter { $0.login != store.me?.login } ?? []
        let questions = store.inbox.filter { $0.taskId == taskId }.count
        var warnings = facts.map { reviewWarnings(taskId, $0, store, leave) } ?? []
        if questions > 0 {
            warnings.append(MergeWarning(text: questions == 1 ? "The agent's open question will be dismissed" : "The agent's \(questions) open questions will be dismissed", open: {
                leave {
                    store.showQuestion(taskId)
                }
            }))
        }
        return VStack(alignment: .leading, spacing: 0) {
            if let parentTitle = model.parentTitle {
                VStack(alignment: .leading, spacing: 8) {
                    option(true, "Into \(parentTitle)", "Its agent merges this subtask's branch into the parent's branch; the subtask closes once it has.")
                    option(false, "Into \(model.target)", "Squashed into one commit on the default branch and pushed, like any task.")
                }
                .padding(.bottom, 16)
            }
            if !model.toParent {
                Text(model.keepOpen ? "Merge the work so far into \(model.target), keeping the task open, as:" : "Merge into \(model.target) as:")
                    .foregroundStyle(Palette.muted)
                    .padding(.bottom, 4)
                titleRow
                    .padding(.bottom, 16)
            }
            if !warnings.isEmpty {
                VStack(alignment: .leading, spacing: 2) {
                    ForEach(Array(warnings.enumerated()), id: \.offset) { _, w in
                        warningRow(w)
                    }
                }
                .foregroundStyle(Palette.warn)
                .padding(.bottom, 16)
            }
            if !model.toParent && !coAuthors.isEmpty {
                DetailsBox(boxed: false) {
                    Text(coAuthorsLabel(coAuthors))
                        .foregroundStyle(Palette.muted)
                } content: {
                    ModalText(text: mergeTrailers(coAuthors))
                        .padding(.top, 8)
                }
                .padding(.bottom, 16)
            }
        }
        .frame(maxWidth: .infinity, alignment: .leading)
    }

    @ViewBuilder
    private var titleRow: some View {
        if model.editing {
            TextField("", text: Binding(get: { model.title }, set: { model.title = String($0.prefix(maxTitle)) }))
                .modifier(FieldStyle(focused: focused))
                .focused($focused)
                .accessibilityLabel("Commit title")
                .onAppear {
                    focused = true
                }
        } else {
            HStack(alignment: .firstTextBaseline, spacing: 8) {
                Text(model.title)
                    .font(Fonts.font(13, weight: 700))
                    .textSelection(.enabled)
                    .fixedSize(horizontal: false, vertical: true)
                    .frame(maxWidth: .infinity, alignment: .leading)
                Button("✎") {
                    model.editing = true
                }
                .buttonStyle(.plain)
                .foregroundStyle(Palette.muted)
                .padding(.horizontal, 6)
                .help("Edit the commit title")
                .accessibilityLabel("Edit the commit title")
            }
        }
    }

    private func option(_ value: Bool, _ label: String, _ hint: String) -> some View {
        Button {
            model.toParent = value
        } label: {
            HStack(alignment: .firstTextBaseline, spacing: 8) {
                Image(systemName: model.toParent == value ? "largecircle.fill.circle" : "circle")
                    .foregroundStyle(model.toParent == value ? Palette.accent : Palette.muted)
                VStack(alignment: .leading, spacing: 0) {
                    Text(label)
                    Text(hint)
                        .font(Fonts.font(12))
                        .foregroundStyle(Palette.muted)
                        .fixedSize(horizontal: false, vertical: true)
                }
            }
            .contentShape(Rectangle())
        }
        .buttonStyle(.plain)
    }

    @ViewBuilder
    private func warningRow(_ w: MergeWarning) -> some View {
        if let open = w.open {
            HStack(alignment: .firstTextBaseline, spacing: 0) {
                Text("⚠ ")
                Button(action: open) {
                    Text(w.text)
                        .underline()
                        .multilineTextAlignment(.leading)
                        .fixedSize(horizontal: false, vertical: true)
                }
                .buttonStyle(.plain)
            }
        } else {
            Text("⚠ \(w.text)")
                .fixedSize(horizontal: false, vertical: true)
                .help(w.detail)
        }
    }
}

@MainActor
func confirmDiscard(_ task: ByreTask, _ store: Store, _ overlays: Overlays) async {
    if !(await overlays.showConfirm(["Discard \"\(task.name)\"?"], action: "Discard", danger: true, inPane: true)) {
        return
    }
    do {
        _ = try await store.api.client.discardTask(path: .init(taskId: task.id)).accepted
        try await store.setFocus(taskId: .some(nil))
    } catch {
        overlays.showAlert(errorText(error))
    }
}