// The AppKit half of the macOS backend: NSEvent in, pardes_* out, one
// CoreGraphics pass per frame back.
//
// This file keeps no model of the screen. The core owns the grid and hands it
// over whole through src/macos/pardes.h, so everything here is translation, and
// the only state worth holding is the font metrics — which are expensive to
// measure and never change.
//
// Every C constant below is wrapped in an explicit conversion (UInt16(...),
// UInt32(...)) rather than used bare. A macro's imported Swift type is decided
// by the importer, not by us, and this file should not have an opinion about it.

import AppKit
import CoreText

protocol PardesViewDelegate: AnyObject {
    func pardesViewDidResize(_ view: PardesView)
    func pardesViewRequestsPaste(_ view: PardesView)
}

// Matches bg_default/fg_default in src/gui/gui.zig and DEFAULT_FG/DEFAULT_BG in
// src/web/app.mjs. Three shells render the same core; if these drift, comparing
// a screenshot across backends stops meaning anything.
private let defaultFG: UInt32 = 0xCC_CC_CC
private let defaultBG: UInt32 = 0x12_12_12

private let inputNotification = Notification.Name("pardesDidInput")

// UNVERIFIED: kCTFontAttributeName bridged through NSAttributedString.Key. It is
// the same string as .font, but spelling the CoreText key means the value stays
// a CTFont instead of being bridged to NSFont on the way in.
private let fontAttribute = NSAttributedString.Key(kCTFontAttributeName as String)

// The named sixteen, then xterm's 6x6x6 cube, then the 24-step grey ramp. These
// sixteen are app.mjs's, not gui.zig's: gui.zig borrows ghostty's palette
// because it already links it, and the two disagree on the base colors.
private let ansi16: [UInt32] = [
    0x00_00_00, 0xCC_00_00, 0x4E_9A_06, 0xC4_A0_00,
    0x34_65_A4, 0x75_50_7B, 0x06_98_9A, 0xD3_D7_CF,
    0x55_57_53, 0xEF_29_29, 0x8A_E2_34, 0xFC_E9_4F,
    0x72_9F_CF, 0xAD_7F_A8, 0x34_E2_E2, 0xEE_EE_EC,
]

private func paletteColor(_ index: UInt8) -> UInt32 {
    if index < 16 { return ansi16[Int(index)] }
    if index >= 232 {
        let grey = UInt32(8 + (Int(index) - 232) * 10)
        return grey << 16 | grey << 8 | grey
    }
    let n = Int(index) - 16
    func level(_ part: Int) -> UInt32 { part == 0 ? 0 : UInt32(55 + part * 40) }
    return level(n / 36) << 16 | level(n / 6 % 6) << 8 | level(n % 6)
}

private func decodeColor(_ encoded: UInt32, _ fallback: UInt32) -> UInt32 {
    if encoded == UInt32(PARDES_COLOR_DEFAULT) { return fallback }
    if encoded & UInt32(PARDES_COLOR_TAG_MASK) == UInt32(PARDES_COLOR_INDEXED) {
        return paletteColor(UInt8(encoded & 0xFF))
    }
    return encoded & UInt32(PARDES_COLOR_RGB_MASK)
}

/// `block` means the filled cursor sits on this cell.
private func resolve(
    _ cell: pardes_cell_s,
    block: Bool
) -> (fg: UInt32, bg: UInt32, alpha: CGFloat, visible: Bool) {
    // The core never painted this cell, which is most of the screen most of the
    // time, so this branch is the one that has to stay cheap.
    if cell.flags & UInt8(PARDES_CELL_DEFAULT) != 0 {
        return block ? (defaultBG, defaultFG, 1, false) : (defaultFG, defaultBG, 1, false)
    }
    var fg = decodeColor(cell.fg, defaultFG)
    var bg = decodeColor(cell.bg, defaultBG)
    // The block cursor is a second reverse, so a cell that is already reversed
    // cancels back to normal underneath it. Same rule as emitInstance in
    // src/gui/gui.zig; the two must not drift.
    var reverse = block
    if cell.attrs & UInt16(PARDES_ATTR_REVERSE) != 0 { reverse = !reverse }
    if reverse { swap(&fg, &bg) }
    // ponytail: PARDES_ATTR_BLINK is decoded into nothing. Honouring it costs a
    // timer plus a repaint budget for a bit nothing in pardes emits today; drive
    // setNeedsDisplay from an NSTimer here when something does.
    let visible = cell.attrs & UInt16(PARDES_ATTR_INVISIBLE) == 0 && cell.len > 0
    // The other shells scale the channels by 6/10. Over a dark background alpha
    // lands in the same place and costs one blend instead of three multiplies.
    let alpha: CGFloat = cell.attrs & UInt16(PARDES_ATTR_DIM) != 0 ? 0.6 : 1
    return (fg, bg, alpha, visible)
}

private func advance(_ font: CTFont, _ character: UniChar) -> CGFloat {
    var input = character
    var glyph = CGGlyph(0)
    guard CTFontGetGlyphsForCharacters(font, &input, &glyph, 1) else { return 0 }
    var size = CGSize.zero
    CTFontGetAdvancesForGlyphs(font, .horizontal, &glyph, &size, 1)
    return size.width
}

private func modifiers(_ flags: NSEvent.ModifierFlags) -> UInt32 {
    var mods: UInt32 = 0
    if flags.contains(.control) { mods |= UInt32(PARDES_MOD_CTRL) }
    if flags.contains(.option) { mods |= UInt32(PARDES_MOD_ALT) }
    if flags.contains(.shift) { mods |= UInt32(PARDES_MOD_SHIFT) }
    return mods
}

final class PardesView: NSView {
    let cellWidth: CGFloat
    let cellHeight: CGFloat
    weak var delegate: PardesViewDelegate?

    private let regular: CTFont
    private let bold: CTFont
    private let italic: CTFont
    private let boldItalic: CTFont
    private let ascent: CGFloat
    private let ruleThickness: CGFloat
    private let underlineOffset: CGFloat
    private var reportedCols: UInt16 = 0
    private var reportedRows: UInt16 = 0

    init(fontSize: CGFloat) {
        let system = NSFont.monospacedSystemFont(ofSize: fontSize, weight: .regular)
        var face = CTFontCreateWithName(system.fontName as CFString, fontSize, nil)
        // The whole layout is a fixed grid, so a proportional face is not a
        // cosmetic problem, it is a broken screen. Resolving the system monospace
        // font by name is a lookup that can miss; "M" and "i" disagreeing on
        // advance is the cheapest possible proof that it did.
        let em = advance(face, 0x4D)
        if em <= 0 || abs(em - advance(face, 0x69)) > 0.01 {
            face = CTFontCreateWithName("Menlo" as CFString, fontSize, nil)
        }

        // UNVERIFIED: CTFontSymbolicTraits member spelling (.traitBold/.traitItalic).
        // A face with no italic cut returns nil here, hence the fallback to `face`.
        func variant(_ traits: CTFontSymbolicTraits) -> CTFont {
            CTFontCreateCopyWithSymbolicTraits(face, fontSize, nil, traits, traits) ?? face
        }
        regular = face
        bold = variant(.traitBold)
        italic = variant(.traitItalic)
        boldItalic = variant([.traitBold, .traitItalic])

        cellWidth = max(1, advance(face, 0x4D))
        ascent = CTFontGetAscent(face)
        cellHeight = max(1, (ascent + CTFontGetDescent(face) + CTFontGetLeading(face)).rounded(.up))
        ruleThickness = max(1, CTFontGetUnderlineThickness(face))
        underlineOffset = CTFontGetUnderlinePosition(face)

        // 80x24 only so the window has a size to open at; the AppDelegate reads
        // gridSize back and boots the core with whatever it actually got.
        super.init(frame: NSRect(x: 0, y: 0, width: cellWidth * 80, height: cellHeight * 24))
    }

    required init?(coder: NSCoder) { fatalError("PardesView is built in code, not a nib") }

    // Row 0 at the top, so the drawing arithmetic reads like the grid it is.
    override var isFlipped: Bool { true }
    override var isOpaque: Bool { true }
    override var acceptsFirstResponder: Bool { true }

    var gridSize: (cols: UInt16, rows: UInt16) {
        let cols = min(max((bounds.width / cellWidth).rounded(.down), 1), CGFloat(UInt16.max))
        let rows = min(max((bounds.height / cellHeight).rounded(.down), 1), CGFloat(UInt16.max))
        return (UInt16(cols), UInt16(rows))
    }

    // MARK: - drawing

    override func draw(_ dirtyRect: NSRect) {
        guard let ctx = NSGraphicsContext.current?.cgContext else { return }
        // ponytail: dirtyRect is ignored. pardes_frame() re-renders the whole grid
        // whatever we do, so clipping would save fills and nothing else. Narrow
        // the row loops to the dirty band if that ever shows up in a profile.
        let count = pardes_frame()
        let cols = Int(pardes_frame_cols())
        let rows = Int(pardes_frame_rows())
        fill(ctx, bounds, defaultBG, 1)
        guard cols > 0, rows > 0, Int(count) == cols * rows, let cells = pardes_frame_cells() else { return }

        // -1 when hidden, which never matches a real cell, so hidden and "bar, so
        // not a block" collapse into the same comparison.
        let bar = pardes_cursor_bar()
        let blockX = bar ? -1 : Int(pardes_cursor_x())
        let blockY = bar ? -1 : Int(pardes_cursor_y())

        // Background first, batched into runs of equal color. A full redraw is
        // 80x24 cells at the low end and per-cell fills are exactly what makes
        // that feel slow. Antialiasing is off because touching rects share an
        // edge, and blending that edge twice draws a visible seam.
        ctx.setShouldAntialias(false)
        for row in 0..<rows {
            let base = row * cols
            let y = CGFloat(row) * cellHeight
            var start = 0
            var color = resolve(cells[base], block: blockY == row && blockX == 0).bg
            for col in 1...cols {
                // A real color is 24 bits, so .max is a sentinel that cannot
                // compare equal and therefore always flushes the last run.
                let next: UInt32 = col == cols
                    ? .max
                    : resolve(cells[base + col], block: blockY == row && blockX == col).bg
                if next == color { continue }
                fill(ctx, CGRect(x: CGFloat(start) * cellWidth, y: y,
                                 width: CGFloat(col - start) * cellWidth, height: cellHeight),
                     color, 1)
                start = col
                color = next
            }
        }

        // CTFontDrawGlyphs lays glyph outlines out with +y up, and isFlipped hands
        // us a y-down CTM, so drawing text directly in view space renders every
        // line mirrored. Un-flip once for the whole glyph pass and convert each
        // baseline into it rather than fighting the text matrix per cell.
        ctx.setShouldAntialias(true)
        ctx.saveGState()
        ctx.textMatrix = .identity
        ctx.translateBy(x: 0, y: bounds.height)
        ctx.scaleBy(x: 1, y: -1)
        let height = bounds.height
        for row in 0..<rows {
            let base = row * cols
            let baseline = height - (CGFloat(row) * cellHeight + ascent)
            for col in 0..<cols {
                let cell = cells[base + col]
                if cell.flags & UInt8(PARDES_CELL_DEFAULT) != 0 { continue }
                let style = resolve(cell, block: blockY == row && blockX == col)
                drawCell(ctx, cell, style, x: CGFloat(col) * cellWidth, baseline: baseline)
            }
        }
        ctx.restoreGState()

        if bar {
            let x = Int(pardes_cursor_x()), y = Int(pardes_cursor_y())
            if x >= 0, y >= 0, x < cols, y < rows {
                // gui.zig paints U+258F here. A rect is the same picture without
                // asking the font for a glyph it may not carry.
                let fg = resolve(cells[y * cols + x], block: false).fg
                fill(ctx, CGRect(x: CGFloat(x) * cellWidth, y: CGFloat(y) * cellHeight,
                                 width: max(1, cellWidth / 8), height: cellHeight), fg, 1)
            }
        }
    }

    private func drawCell(
        _ ctx: CGContext,
        _ cell: pardes_cell_s,
        _ style: (fg: UInt32, bg: UInt32, alpha: CGFloat, visible: Bool),
        x: CGFloat,
        baseline: CGFloat
    ) {
        // Rules before the glyph, and independent of it: an underlined space is a
        // real thing and so is an underlined invisible cell.
        let underline = Int(cell.attrs >> PARDES_ATTR_UL_SHIFT) & 7
        if underline != Int(PARDES_UL_OFF) {
            let y = baseline + underlineOffset
            fill(ctx, CGRect(x: x, y: y, width: cellWidth, height: ruleThickness), style.fg, style.alpha)
            // ponytail: curly, dotted and dashed all come out solid; only double
            // earns its second rule. ctx.setLineDash for two of them and a sine
            // path for the third is the upgrade, once anyone notices.
            if underline == Int(PARDES_UL_DOUBLE) {
                fill(ctx, CGRect(x: x, y: y - ruleThickness * 2, width: cellWidth, height: ruleThickness),
                     style.fg, style.alpha)
            }
        }
        if cell.attrs & UInt16(PARDES_ATTR_STRIKETHROUGH) != 0 {
            fill(ctx, CGRect(x: x, y: baseline + ascent * 0.3, width: cellWidth, height: ruleThickness),
                 style.fg, style.alpha)
        }
        guard style.visible else { return }

        // UNVERIFIED: withUnsafeBytes over an imported C fixed-size array, which
        // Swift models as an 8-tuple. String(decoding:) substitutes U+FFFD rather
        // than trapping, and the core has shipped invalid UTF-8 through here
        // before — the renderer must not be the thing that dies over it. prefix
        // clamps, so a bogus len cannot walk off the eight bytes either.
        let text = withUnsafeBytes(of: cell.text) { raw in
            String(decoding: raw.prefix(Int(cell.len)), as: UTF8.self)
        }
        guard !text.isEmpty, text != " " else { return }

        let heavy = cell.attrs & UInt16(PARDES_ATTR_BOLD) != 0
        let slanted = cell.attrs & UInt16(PARDES_ATTR_ITALIC) != 0
        let font = heavy ? (slanted ? boldItalic : bold) : (slanted ? italic : regular)
        setFill(ctx, style.fg, style.alpha)

        // ponytail: no glyph cache — a cmap lookup per cell, and a whole CTLine
        // for anything that is not one BMP scalar the face covers. A
        // [UnicodeScalar: CGGlyph] map, then an atlas, is the upgrade path when a
        // full redraw shows up in Instruments.
        let units = text.utf16
        if units.count == 1, var character = units.first {
            var glyph = CGGlyph(0)
            if CTFontGetGlyphsForCharacters(font, &character, &glyph, 1) {
                var position = CGPoint(x: x, y: baseline)
                CTFontDrawGlyphs(font, &glyph, &position, 1, ctx)
                return
            }
        }
        // Emoji, combining marks and anything the face is missing: CTLine finds a
        // fallback font. The position is set explicitly per cell — this is a fixed
        // grid, and letting CoreText advance across a row would drift off it.
        let attributed = NSAttributedString(string: text, attributes: [fontAttribute: font])
        ctx.textPosition = CGPoint(x: x, y: baseline)
        CTLineDraw(CTLineCreateWithAttributedString(attributed as CFAttributedString), ctx)
    }

    private func setFill(_ ctx: CGContext, _ rgb: UInt32, _ alpha: CGFloat) {
        ctx.setFillColor(red: CGFloat((rgb >> 16) & 0xFF) / 255,
                         green: CGFloat((rgb >> 8) & 0xFF) / 255,
                         blue: CGFloat(rgb & 0xFF) / 255,
                         alpha: alpha)
    }

    private func fill(_ ctx: CGContext, _ rect: CGRect, _ rgb: UInt32, _ alpha: CGFloat) {
        setFill(ctx, rgb, alpha)
        ctx.fill(rect)
    }

    // MARK: - keyboard

    override func keyDown(with event: NSEvent) {
        let flags = event.modifierFlags
        // The ABI has no super bit, so a Command chord cannot be expressed at all.
        // Cmd-V is the paste the delegate owns; every other one is swallowed
        // rather than delivered as the bare keystroke the core would insert.
        if flags.contains(.command) {
            if event.charactersIgnoringModifiers?.lowercased() == "v" {
                delegate?.pardesViewRequestsPaste(self)
            }
            return
        }

        let control = flags.contains(.control)
        let option = flags.contains(.option)
        // With ctrl or option down, `characters` is already the composed result —
        // Ctrl-A is U+0001, Option-A is "å". The core wants the base key and no
        // text, which is what app.mjs does with the same two bits.
        let composed = (control || option ? event.charactersIgnoringModifiers : event.characters) ?? ""
        guard let scalar = composed.unicodeScalars.first else { return }

        var codepoint = scalar.value
        // 0xF700..0xF8FF is AppKit's private-use block for function keys. The nine
        // the core names get translated; the rest (F1-F12, Insert, the keypad) are
        // dropped, because passing one through paints a stray glyph.
        // These constants come from an unnamed C enum, so which width Swift picks
        // for them is not something this file should depend on: wrapping each in
        // UInt32() compiles whether they import as Int, Int32 or UInt32.
        if scalar.value >= 0xF700 && scalar.value <= 0xF8FF {
            switch scalar.value {
            case UInt32(NSUpArrowFunctionKey): codepoint = UInt32(PARDES_KEY_UP)
            case UInt32(NSDownArrowFunctionKey): codepoint = UInt32(PARDES_KEY_DOWN)
            case UInt32(NSLeftArrowFunctionKey): codepoint = UInt32(PARDES_KEY_LEFT)
            case UInt32(NSRightArrowFunctionKey): codepoint = UInt32(PARDES_KEY_RIGHT)
            case UInt32(NSHomeFunctionKey): codepoint = UInt32(PARDES_KEY_HOME)
            case UInt32(NSEndFunctionKey): codepoint = UInt32(PARDES_KEY_END)
            case UInt32(NSPageUpFunctionKey): codepoint = UInt32(PARDES_KEY_PAGE_UP)
            case UInt32(NSPageDownFunctionKey): codepoint = UInt32(PARDES_KEY_PAGE_DOWN)
            case UInt32(NSDeleteFunctionKey): codepoint = UInt32(PARDES_KEY_DELETE)
            default: return
            }
        }

        // Enter, Tab, Escape and Backspace already arrive as the ASCII controls the
        // header names. Two keys do not: the keypad's Enter is U+0003 and Shift-Tab
        // is U+0019, neither of which is in the function-key block above, so without
        // this both reach the core as a control it has no binding for and do
        // nothing. The browser shell resolves them from the DOM key name and this
        // is what keeps the two hosts saying the same thing.
        if codepoint == 0x03 { codepoint = UInt32(PARDES_KEY_ENTER) }
        if codepoint == 0x19 { codepoint = UInt32(PARDES_KEY_TAB) }

        // A control character is functional, and functional keys must not also
        // carry text.
        let functional = codepoint < 0x20 || codepoint == 0x7F || codepoint >= 0xF0000
        let text = functional || control || option ? "" : composed
        // The pointer is borrowed for the call and nowhere else, which is the only
        // thing the header promises about it.
        text.withCString { pardes_key(codepoint, $0, text.utf8.count, modifiers(flags)) }
        NotificationCenter.default.post(name: inputNotification, object: self)
    }

    // MARK: - mouse

    override func mouseDown(with event: NSEvent) { send(PARDES_MOUSE_LEFT, PARDES_MOUSE_PRESS, event) }
    override func mouseUp(with event: NSEvent) { send(PARDES_MOUSE_LEFT, PARDES_MOUSE_RELEASE, event) }
    override func mouseDragged(with event: NSEvent) { send(PARDES_MOUSE_LEFT, PARDES_MOUSE_DRAG, event) }
    override func rightMouseDown(with event: NSEvent) { send(PARDES_MOUSE_RIGHT, PARDES_MOUSE_PRESS, event) }
    override func rightMouseUp(with event: NSEvent) { send(PARDES_MOUSE_RIGHT, PARDES_MOUSE_RELEASE, event) }
    override func rightMouseDragged(with event: NSEvent) { send(PARDES_MOUSE_RIGHT, PARDES_MOUSE_DRAG, event) }
    // otherMouse covers button 2 and up. acme's vocabulary stops at three, so
    // every one of them lands on middle rather than being invented into a fourth.
    override func otherMouseDown(with event: NSEvent) { send(PARDES_MOUSE_MIDDLE, PARDES_MOUSE_PRESS, event) }
    override func otherMouseUp(with event: NSEvent) { send(PARDES_MOUSE_MIDDLE, PARDES_MOUSE_RELEASE, event) }
    override func otherMouseDragged(with event: NSEvent) { send(PARDES_MOUSE_MIDDLE, PARDES_MOUSE_DRAG, event) }
    override func mouseMoved(with event: NSEvent) { send(PARDES_MOUSE_NONE, PARDES_MOUSE_MOTION, event) }

    override func scrollWheel(with event: NSEvent) {
        guard let at = cell(for: event) else { return }
        if event.hasPreciseScrollingDeltas {
            // The core scrolls a row at a time, so libpardes accumulates the
            // sub-row travel and spends it as wheel presses — which is why the
            // cell has to travel with the delta.
            pardes_scroll(Float(-event.scrollingDeltaY / cellHeight), at.col, at.row)
        } else if event.scrollingDeltaY != 0 {
            // AppKit's sign is the opposite of the DOM's: positive deltaY means the
            // content moved down, which is a scroll back through history.
            let button = event.scrollingDeltaY > 0 ? PARDES_MOUSE_WHEEL_UP : PARDES_MOUSE_WHEEL_DOWN
            pardes_mouse(button, PARDES_MOUSE_PRESS, at.col, at.row, modifiers(event.modifierFlags))
        } else {
            return
        }
        NotificationCenter.default.post(name: inputNotification, object: self)
    }

    private func send(_ button: pardes_mouse_button_e, _ kind: pardes_mouse_kind_e, _ event: NSEvent) {
        guard let at = cell(for: event) else { return }
        pardes_mouse(button, kind, at.col, at.row, modifiers(event.modifierFlags))
        NotificationCenter.default.post(name: inputNotification, object: self)
    }

    private func cell(for event: NSEvent) -> (col: UInt16, row: UInt16)? {
        // Clamp against the frame the core last rendered, not against our own
        // metrics: a window that has been resized but not yet ticked would
        // otherwise report a column the core has no cell for. Before the first
        // frame there is no grid to point at and the event is meaningless.
        let cols = Int(pardes_frame_cols())
        let rows = Int(pardes_frame_rows())
        guard cols > 0, rows > 0 else { return nil }
        let point = convert(event.locationInWindow, from: nil)
        let col = min(max(Int(point.x / cellWidth), 0), cols - 1)
        let row = min(max(Int(point.y / cellHeight), 0), rows - 1)
        return (UInt16(col), UInt16(row))
    }

    // MARK: - geometry

    override func updateTrackingAreas() {
        super.updateTrackingAreas()
        for area in trackingAreas { removeTrackingArea(area) }
        // .inVisibleRect keeps the area correct across resizes on its own, which
        // is why the rect argument can be anything.
        addTrackingArea(NSTrackingArea(rect: .zero,
                                       options: [.mouseMoved, .inVisibleRect, .activeInKeyWindow],
                                       owner: self,
                                       userInfo: nil))
    }

    override func setFrameSize(_ newSize: NSSize) {
        super.setFrameSize(newSize)
        // AppKit resizes a view many times over one drag and almost all of those
        // land inside the same cell. Only a changed grid is news, and the core
        // reflows every pty on a resize, so the no-ops are not free.
        let grid = gridSize
        guard grid.cols != reportedCols || grid.rows != reportedRows else { return }
        reportedCols = grid.cols
        reportedRows = grid.rows
        delegate?.pardesViewDidResize(self)
    }

    // Dragging the window between a Retina display and a 1x one changes the
    // backing scale without moving a single bound, so setFrameSize above never
    // fires and the physical cell metrics the core uses to place PDF pages stay
    // at the old scale forever. This is the only notification of it. (Ghostty
    // hooks the same one, and additionally re-fires from the window's
    // didChangeScreen notification, which AppKit does not always pair with it.)
    override func viewDidChangeBackingProperties() {
        super.viewDidChangeBackingProperties()
        delegate?.pardesViewDidResize(self)
    }
}

// ponytail: no NSTextInputClient, so dead keys and IME composition never reach
// the core — keyDown reads `characters` and that is the whole story. Adopting
// the protocol and routing through interpretKeyEvents is the upgrade when
// someone needs to type Japanese.