function readWriteConfig()

in patcher/patcher.js [661:753]
75 lines of code
28 McCabe index (conditional complexity)

function readWriteConfig(buf, patch) {
    let patchPtr = null
    let origData = []
    let cfgLen = 0
    let isUF2 = false
    if (read32(buf, 0) == UF2_MAGIC_START0) {
        isUF2 = true
        log("detected UF2 file")
    } else {
        let stackBase = read32(buf, 0)
        if ((stackBase & 0xff000003) == 0x20000000 &&
            (read32(buf, 4) & 1) == 1) {
            log("detected BIN file")
        } else {
            let str = bufToString(buf)
            if (str.indexOf("/* CF2 START") >= 0) {
                log("detected CF2 header file")
                let rr = patchHFile(str, patch)
                console.log(rr.data)
                return patch ? stringToBuf(rr.patched) : rr.data
            } else {
                err("unknown file format")
            }
        }
    }
    if (patch)
        patch.push(0, 0)
    for (let off = 0; off < buf.length; off += 512) {
        let start = 0
        let payloadLen = 512
        let addr = off

        if (isUF2) {
            start = 32
            if (read32(buf, off) != UF2_MAGIC_START0 ||
                read32(buf, off + 4) != UF2_MAGIC_START1) {
                err("invalid data at " + off)
            }
            payloadLen = read32(buf, off + 16)
            addr = read32(buf, off + 12) - 32
        }

        for (let i = start; i < start + payloadLen; i += 4) {
            if (read32(buf, off + i) == CFG_MAGIC0 &&
                read32(buf, off + i + 4) == CFG_MAGIC1) {
                let addrS = "0x" + (addr + i).toString(16)
                if (patchPtr === null) {
                    log(`Found CFG DATA at ${addrS}`)
                    patchPtr = -4
                } else {
                    log(`Skipping second CFG DATA at ${addrS}`)
                }
            }

            if (patchPtr !== null) {
                if (patchPtr == -2) {
                    cfgLen = read32(buf, off + i)
                    if (patch)
                        write32(buf, off + i, (patch.length >> 1) - 1)
                }

                if (patchPtr >= 0) {
                    if (origData.length < cfgLen * 2 + 40)
                        origData.push(read32(buf, off + i))
                    if (patch) {
                        if (patchPtr < patch.length) {
                            write32(buf, off + i, patch[patchPtr])
                        }
                    }
                }
                patchPtr++
            }
        }
    }

    let len0 = cfgLen * 2
    origData.push(0, 0)
    while (origData[len0])
        len0 += 2
    origData = origData.slice(0, len0 + 2)
    if (len0 != cfgLen * 2)
        log("size information incorrect; continuing anyway")

    if (origData.length == 0)
        err("config data not found")
    if (patch && patchPtr < patch.length)
        err("no space for config data")
    let tail = origData.slice(origData.length - 2)
    if (tail.some(x => x != 0))
        err("config data not zero terminated: " + tail.join(","))
    origData = origData.slice(0, origData.length - 2)
    return patch ? buf : origData
}