// Draws pardes.app's icon at build time and hands the result to iconutil.
//
// It is generated instead of committed because the mark IS the palette: the
// body is defaultBG, the tag bar and the block cursor are entries out of the
// same ansi16 table src/macos/Sources/PardesView.swift paints cells with. A
// checked-in .icns is a binary blob that stops matching the app the first time
// one of those colours moves, silently, with nothing in a diff to catch it.
//
// src/macos/build-app.sh compiles this file alone into a temporary binary and
// runs it with the bundle's Contents/Resources as argv[1]; Info.plist's
// CFBundleIconFile names the pardes.icns that comes out. Compiled alone is also
// what makes top-level code legal here: one file, one module, its own binary.
//
// Byte-identical output for byte-identical input is a requirement, not a
// nicety — an icns that churns on every build is a bundle that churns on every
// build, and Launch Services notices. Hence a pinned sRGB colour space, integer
// geometry, and nothing read from the clock or the environment.

import CoreGraphics
import Foundation
import ImageIO
import UniformTypeIdentifiers

/// Every failure path lands here. A build that ships the generic blank-page
/// icon looks like an app nobody finished, so half-drawn is worse than absent
/// and the script has `set -e` waiting for the exit code.
func die(_ message: String) -> Never {
    fputs("icon.swift: \(message)\n", stderr)
    exit(1)
}

struct RGB {
    let red: CGFloat
    let green: CGFloat
    let blue: CGFloat

    init(_ hex: UInt32) {
        red = CGFloat((hex >> 16) & 0xFF) / 255
        green = CGFloat((hex >> 8) & 0xFF) / 255
        blue = CGFloat(hex & 0xFF) / 255
    }

    func components(_ alpha: CGFloat) -> [CGFloat] { [red, green, blue, alpha] }
}

// Straight out of PardesView.swift. If those move these move, because the icon
// is a picture of the running program and a stale picture is worse than none:
// it looks deliberate.
let bodyTop = RGB(0x12_12_12)      // defaultBG
let bodyBottom = RGB(0x0A_0A_0A)   // defaultBG, shaded
let tagBar = RGB(0x34_65_A4)       // ansi16[4], the muted blue
let text = RGB(0xCC_CC_CC)         // defaultFG
let cursor = RGB(0xFC_E9_4F)       // ansi16[11], bright yellow

// Apple's icon grid rather than the whole square: the artwork is a rounded
// square floating in a transparent margin, 824 of 1024 with a 185.4 corner
// radius in the template — 80.47% of the canvas, and 22.37% of the SQUARE, not
// of the canvas, which would over-round it by a quarter. Filling the canvas
// edge to edge is the loudest tell that an app was not built on a Mac.
let squareFraction: CGFloat = 0.8047
let cornerFraction: CGFloat = 0.2237

// The composition, as fractions of the body square. It has to survive being
// twelve pixels across, so it is four bands and nothing else: the full-width
// tag bar, a dim line for the pane that does not hold the keyboard, a gutter
// wide enough to read as the boundary between panes, then the focused pane's
// line with the block cursor parked at its end. Three shapes under the bar is
// the entire budget; a fourth is grey mush at 16 pixels.
let tagHeight: CGFloat = 0.165
let sidePad: CGFloat = 0.145
let lineHeight: CGFloat = 0.085
let dimLineTop: CGFloat = 0.355
let dimLineWidth: CGFloat = 0.505
let dimLineAlpha: CGFloat = 0.52
let liveLineTop: CGFloat = 0.645
let liveLineWidth: CGFloat = 0.300
let liveLineAlpha: CGFloat = 0.72
let cursorLeft: CGFloat = 0.515
// A cell, not a square: a block cursor covers a whole character box, so it is
// wider than the gap before it and well over twice the height of the ink it
// sits on. The exact numbers are also the ones that survive rounding — 0.205
// of a twelve-pixel body spans 2.46 pixels, which lands on two rows wherever
// the top edge falls, whereas anything near 0.155 collapses to one row for
// half the possible alignments and the block turns into a dash.
let cursorWidth: CGFloat = 0.130
let cursorHeight: CGFloat = 0.205

/// sRGB in the bitmap and sRGB in every colour put into it. `setFillColor(red:
/// green:blue:alpha:)` speaks DeviceRGB, which is a colour match on the way in,
/// and #121212 would stop being #121212.
func sRGB() -> CGColorSpace {
    guard let space = CGColorSpace(name: CGColorSpace.sRGB) else { die("sRGB colour space unavailable") }
    return space
}

func cgColor(_ rgb: RGB, alpha: CGFloat = 1) -> CGColor {
    guard let color = CGColor(colorSpace: sRGB(), components: rgb.components(alpha)) else {
        die("CGColor from sRGB components failed")
    }
    return color
}

/// Whole device pixels, or the 16pt render turns each one-pixel bar into two
/// rows of half-lit grey and the whole mark goes soft. Rounding the edges
/// rather than the size is what keeps the gaps between bands even.
func snap(_ rect: CGRect) -> CGRect {
    let left = rect.minX.rounded()
    let top = rect.minY.rounded()
    return CGRect(
        x: left, y: top,
        width: max(1, rect.maxX.rounded() - left),
        height: max(1, rect.maxY.rounded() - top))
}

func renderIcon(pixels: Int) -> CGImage {
    guard
        let ctx = CGContext(
            data: nil, width: pixels, height: pixels,
            bitsPerComponent: 8, bytesPerRow: 0, space: sRGB(),
            bitmapInfo: CGImageAlphaInfo.premultipliedLast.rawValue)
    else { die("CGContext \(pixels)x\(pixels) failed") }

    // Top-left origin, so the constants above read in the order the picture
    // does. The scale stays ±1, which is what lets snap() round in user space.
    ctx.translateBy(x: 0, y: CGFloat(pixels))
    ctx.scaleBy(x: 1, y: -1)

    // Round the MARGIN and derive the square from it. Rounding the square
    // instead leaves an odd remainder to split, and at 16 pixels the artwork
    // lands a pixel off centre. At 1024 this is Apple's 100/824/100 exactly.
    let canvas = CGFloat(pixels)
    let inset = (canvas * (1 - squareFraction) / 2).rounded()
    let side = canvas - 2 * inset
    let body = CGRect(x: inset, y: inset, width: side, height: side)
    let corner = side * cornerFraction

    ctx.saveGState()
    ctx.addPath(CGPath(roundedRect: body, cornerWidth: corner, cornerHeight: corner, transform: nil))
    ctx.clip()

    // The only gradient in the icon, and it earns its place: a flat near-black
    // square reads as a hole punched in the Dock rather than as an object.
    let stops = bodyTop.components(1) + bodyBottom.components(1)
    let locations: [CGFloat] = [0, 1]
    guard
        let gradient = CGGradient(
            colorSpace: sRGB(), colorComponents: stops, locations: locations, count: 2)
    else { die("CGGradient failed") }
    ctx.drawLinearGradient(
        gradient,
        start: CGPoint(x: body.midX, y: body.minY),
        end: CGPoint(x: body.midX, y: body.maxY),
        options: [])

    // Full bleed, and still inside the clip so its top corners round with the
    // body. src/pardes.zig fills row 0 across the whole width the same way;
    // that strip is the silhouette of an acme screen and it is the one thing
    // that has to survive being two pixels tall.
    ctx.setFillColor(cgColor(tagBar))
    ctx.fill(
        CGRect(
            x: body.minX, y: body.minY,
            width: side, height: max(1, (side * tagHeight).rounded())))
    ctx.restoreGState()

    // Two panes. The gap between the lines is deliberately the widest space in
    // the icon: it is the pane boundary, and proximity is the only way to say
    // so without spending the fourth shape on a divider.
    let leftEdge = body.minX + side * sidePad
    ctx.setFillColor(cgColor(text, alpha: dimLineAlpha))
    ctx.fill(
        snap(
            CGRect(
                x: leftEdge, y: body.minY + side * dimLineTop,
                width: side * dimLineWidth, height: side * lineHeight)))

    ctx.setFillColor(cgColor(text, alpha: liveLineAlpha))
    ctx.fill(
        snap(
            CGRect(
                x: leftEdge, y: body.minY + side * liveLineTop,
                width: side * liveLineWidth, height: side * lineHeight)))

    // Centred on the line it follows and taller than it, the way a block cursor
    // covers a whole cell rather than the ink in it. Full-strength yellow
    // against the blue is what tells you at a glance which pane has focus.
    let cursorTop = liveLineTop + (lineHeight - cursorHeight) / 2
    ctx.setFillColor(cgColor(cursor))
    ctx.fill(
        snap(
            CGRect(
                x: body.minX + side * cursorLeft, y: body.minY + side * cursorTop,
                width: side * cursorWidth, height: side * cursorHeight)))

    guard let image = ctx.makeImage() else { die("CGContext.makeImage failed at \(pixels)") }
    return image
}

func writePNG(_ image: CGImage, to url: URL) {
    guard
        let sink = CGImageDestinationCreateWithURL(
            url as CFURL, UTType.png.identifier as CFString, 1, nil)
    else { die("cannot open \(url.path) for writing") }
    CGImageDestinationAddImage(sink, image, nil)
    guard CGImageDestinationFinalize(sink) else { die("encoding \(url.lastPathComponent) failed") }
}

// The ten names iconutil demands, spelled out rather than derived: the set is
// fixed by the tool, and a loop that generated them would be a loop to read
// before believing the list. 32, 256 and 512 appear twice under two names and
// are simply drawn twice — a third of a megapixel, against the clarity of not
// caching anything in a build tool.
let variants: [(name: String, pixels: Int)] = [
    ("icon_16x16.png", 16),
    ("icon_16x16@2x.png", 32),
    ("icon_32x32.png", 32),
    ("icon_32x32@2x.png", 64),
    ("icon_128x128.png", 128),
    ("icon_128x128@2x.png", 256),
    ("icon_256x256.png", 256),
    ("icon_256x256@2x.png", 512),
    ("icon_512x512.png", 512),
    ("icon_512x512@2x.png", 1024),
]

let arguments = CommandLine.arguments
guard arguments.count == 2 else {
    die("usage: \(URL(fileURLWithPath: arguments.first ?? "icon").lastPathComponent) <output-directory>")
}

let files = FileManager.default
let outputDir = URL(fileURLWithPath: arguments[1], isDirectory: true)
let output = outputDir.appendingPathComponent("pardes.icns")

// A fixed scratch path, cleared before use rather than a unique one: a run that
// died half way leaves a partial iconset behind, and iconutil would happily
// fold the stale sizes into the next icns without a word.
let scratch = files.temporaryDirectory.appendingPathComponent("pardes-icon", isDirectory: true)
let iconset = scratch.appendingPathComponent("pardes.iconset", isDirectory: true)

try? files.removeItem(at: scratch)
do {
    try files.createDirectory(at: iconset, withIntermediateDirectories: true)
    try files.createDirectory(at: outputDir, withIntermediateDirectories: true)
} catch {
    die("cannot create \(iconset.path): \(error.localizedDescription)")
}

for variant in variants {
    writePNG(renderIcon(pixels: variant.pixels), to: iconset.appendingPathComponent(variant.name))
}

let iconutil = Process()
iconutil.executableURL = URL(fileURLWithPath: "/usr/bin/iconutil")
iconutil.arguments = ["-c", "icns", "-o", output.path, iconset.path]
do {
    try iconutil.run()
} catch {
    die("cannot run /usr/bin/iconutil: \(error.localizedDescription)")
}
iconutil.waitUntilExit()
guard iconutil.terminationStatus == 0 else {
    die("iconutil exited \(iconutil.terminationStatus) over \(iconset.path)")
}

try? files.removeItem(at: scratch)