import Foundation
let data = try! Data(contentsOf: URL(fileURLWithPath: "shot.bmp"))
// BMP header parsing
let pixOff = data.withUnsafeBytes { $0.load(fromByteOffset: 10, as: UInt32.self) }
let w = Int(data.withUnsafeBytes { $0.load(fromByteOffset: 18, as: Int32.self) })
let hRaw = Int(data.withUnsafeBytes { $0.load(fromByteOffset: 22, as: Int32.self) }); let h = abs(hRaw)
let bpp = data.withUnsafeBytes { $0.load(fromByteOffset: 28, as: UInt16.self) }
let B = Int(bpp)/8; let rowBytes = (B * w + 3) & ~3
print("bmp \(w)x\(h) bpp=\(bpp) pixOff=\(pixOff)")
var minX = w, minY = h, maxX = 0, maxY = 0, count = 0
var rows: [Int] = Array(repeating: 0, count: h)
for y in 0..<h {
    let rowStart = Int(pixOff) + (hRaw > 0 ? (h - 1 - y) : y) * rowBytes
    for x in 0..<w {
        let i = rowStart + x * B
        let b = data[i], g = data[i+1], r = data[i+2]
        let ri = Int(r), gi = Int(g), bi = Int(b)
        // blue button detection
        if bi > 120 && bi > ri + 30 && bi > gi + 15 && ri < 160 {
            count += 1; rows[y] += 1
            if x < minX { minX = x }; if x > maxX { maxX = x }
            if y < minY { minY = y }; if y > maxY { maxY = y }
        }
    }
}
print("bluePixels=\(count) bbox=(\(minX),\(minY))-(\(maxX),\(maxY))")
// row profile to separate blobs
var bands: [(Int,Int,Int)] = []
var start = -1
for y in 0..<h {
    if rows[y] > 20 && start < 0 { start = y }
    if (rows[y] <= 20 || y == h-1) && start >= 0 { bands.append((start, y, (start...y).map{rows[$0]}.max()!)); start = -1 }
}
for bd in bands { print("band y=\(bd.0)-\(bd.1) maxRowPx=\(bd.2)") }