import SwiftUI

// MARK: - CardWindowView

/// The card window's content: **two full-height, independently scrolling columns** — a wide body
/// column leading, a narrow attributes sidebar trailing (05-card-window.md ▸ Composition).
///
/// ### What this milestone builds, and what it deliberately does not
///
/// The *shell*: the two columns, their scrolling, the sidebar's fixed width, and the read-only
/// renderings of what the loader already knows — the card's title, its created/modified line, and
/// its body as plain text. Everything that reads or writes beyond that is later work and is marked
/// where it lands:
///
/// - the title as an editable field (commit on Return / focus loss, Escape abandons),
/// - the body's Preview/Edit pairing and the raw-source outlet,
/// - the sidebar's five sections, which are section *headers* here and nothing more.
///
/// The placeholders are structural rather than apologetic: the sidebar's inventory and its order are
/// settled (05 ▸ The attributes sidebar), so the shell states them and the sections fill in
/// underneath without the composition moving.
///
/// ### The width rule, in one line
///
/// The sidebar has a fixed width from `CardWindowMetrics`; the body column takes `.infinity`. That
/// is the whole of "the window's resize flex goes to the body" — no split view, no stored divider
/// position, nothing for a drag to disagree with.
struct CardWindowView: View {

    let card: Card

    /// The body font's point size, read once per body evaluation: every measurement in this view —
    /// the sidebar's width, both gutters, the vertical rhythm — is derived from it, so they scale
    /// together when the system text size changes.
    private var bodyPointSize: CGFloat { CardWindowMetrics.bodyPointSize }

    var body: some View {
        HStack(spacing: 0) {
            bodyColumn
                .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .topLeading)

            Divider()

            sidebar
                // Fixed, and the one place it comes from.
                .frame(width: CardWindowMetrics.sidebarWidth(bodyPointSize: bodyPointSize))
                .frame(maxHeight: .infinity, alignment: .top)
                .background(.background.secondary)
        }
    }

    // MARK: - Body column

    /// Title, the quiet created/modified line, then the body — 05's top-to-bottom order.
    private var bodyColumn: some View {
        ScrollView(.vertical) {
            VStack(alignment: .leading, spacing: bodyPointSize * 0.75) {
                // m6-card-body: the title *field* — large and borderless, committing to frontmatter
                // on Return or focus loss, clearing to remove the `title` key, Escape abandoning to
                // the on-disk title. Read-only here; the placeholder rendering is already final.
                Text(card.title.value ?? "Untitled")
                    .font(.largeTitle)
                    // "Untitled" is a rendering, never a value (03-board-ui.md § Card face) — the
                    // same secondary treatment the face gives it.
                    .foregroundStyle(card.title.value == nil ? .secondary : .primary)
                    .textSelection(.enabled)

                if let dateLine {
                    Text(dateLine)
                        .font(.caption)
                        .foregroundStyle(.secondary)
                        .textSelection(.enabled)
                }

                // m6-card-body: Preview/Edit proper — a rendered preview with live task-list
                // checkboxes, and a syntax-highlighted raw editor behind ⌘E. Plain selectable text
                // until then: honest about being unrendered rather than half-rendering Markdown.
                if !card.body.isEmpty {
                    Text(card.body)
                        .font(.body)
                        .textSelection(.enabled)
                        .frame(maxWidth: .infinity, alignment: .leading)
                }
            }
            .frame(maxWidth: .infinity, alignment: .leading)
            .padding(CardWindowMetrics.gutter(bodyPointSize: bodyPointSize))
        }
    }

    /// "Created ⟨date⟩ · Modified ⟨date⟩ · by ⟨modified-by⟩", **omitting whichever keys are absent**
    /// (05 ▸ Composition) — the whole line disappears when the card carries none of the three.
    ///
    /// The "by" segment renders only with the self-reported provenance stamp present
    /// (01-storage-format.md), which is the point of showing it at all: provenance made visible where
    /// git history may not exist.
    private var dateLine: String? {
        var parts: [String] = []
        if let created = card.created.value {
            parts.append("Created \(Self.dateText(created))")
        }
        if let modified = card.modified.value {
            parts.append("Modified \(Self.dateText(modified))")
        }
        if let by = card.modifiedBy.value, !by.isEmpty {
            parts.append("by \(by)")
        }
        return parts.isEmpty ? nil : parts.joined(separator: " · ")
    }

    private static func dateText(_ date: Date) -> String {
        date.formatted(date: .abbreviated, time: .shortened)
    }

    // MARK: - Attributes sidebar

    /// The sidebar's sections, **in 05's settled order**, as headers over empty space.
    ///
    /// Two of them are conditional once they have content — Details appears only when the card
    /// carries unknown frontmatter keys, and History is absent on boards without app-managed git —
    /// and the shell shows them unconditionally because it has neither the key inventory nor a git
    /// mode to consult yet. That is the one place these placeholders are not yet the final
    /// composition, and it resolves when the sections do.
    private var sidebar: some View {
        ScrollView(.vertical) {
            VStack(alignment: .leading, spacing: bodyPointSize * 1.25) {
                // m6-card-attachments: every top-level file of `attachments/`, compact rows with a
                // QuickLook thumbnail, keyboard-navigable.
                section("Attachments")
                // m6-card-sidebar: the embedded style editor — the same component the board popover
                // and Style… already host (`StyleEditor`).
                section("Style")
                // m6-card-sidebar: read-only key/value rows for every unknown frontmatter key, in
                // file order.
                section("Details")
                // m7-git: the card's commit trail, read-only; absent on mode none / repo-nested.
                section("History")
                // m6-card-sidebar: Delete (tombstones, the window then dismisses itself) and Reveal
                // in Finder.
                section("Actions")
            }
            .frame(maxWidth: .infinity, alignment: .leading)
            .padding(CardWindowMetrics.gutter(bodyPointSize: bodyPointSize))
        }
    }

    /// A stacked small-caps header over the space its section will occupy (05: "Stacked sections
    /// under small-caps headers").
    private func section(_ title: String) -> some View {
        VStack(alignment: .leading, spacing: 4) {
            Text(title)
                .font(.caption.weight(.semibold))
                .textCase(.uppercase)
                .foregroundStyle(.secondary)
            Divider()
        }
        .frame(maxWidth: .infinity, alignment: .leading)
        .accessibilityElement(children: .combine)
    }
}