export function parseS3Uri()

in packages/core/src/shared/clients/s3.ts [705:784]
65 lines of code
16 McCabe index (conditional complexity)

export function parseS3Uri(uri: string): [region: string, bucket: string, key: string] {
    const endpointPattern = /^(.+\.)?s3[.-]([a-z0-9-]+)\./
    const defaultRegion = 'us-east-1' // Default region for URI parsing, if region is not found
    const parsedUri = url.parse(uri)
    let bucket: string | undefined = undefined
    let region: string = defaultRegion
    let key: string | undefined = undefined

    if (parsedUri.protocol === 's3:') {
        bucket = parsedUri.host ?? undefined
        if (!bucket) {
            throw new Error(`Invalid S3 URI: no bucket: ${uri}`)
        }
        if (!parsedUri.pathname || parsedUri.pathname.length <= 1) {
            // s3://bucket or s3://bucket/
            key = undefined
        } else {
            // s3://bucket/key
            // Remove the leading '/'.
            key = parsedUri.pathname.substring(1)
        }
        if (key !== undefined) {
            key = decodeURIComponent(key)
        }
        return [region, bucket, key!]
    }

    if (!parsedUri.host) {
        throw new Error(`Invalid S3 URI: no hostname: ${uri}`)
    }

    const matches = parsedUri.host.match(endpointPattern)
    if (!matches) {
        throw new Error(`Invalid S3 URI: hostname does not appear to be a valid S3 endpoint: ${uri}`)
    }

    const prefix = matches[1]
    if (!prefix) {
        if (parsedUri.pathname === '/') {
            bucket = undefined
            key = undefined
        } else {
            const index = parsedUri.pathname!.indexOf('/', 1)
            if (index === -1) {
                // https://s3.amazonaws.com/bucket
                bucket = parsedUri.pathname!.substring(1) ?? undefined
                key = undefined
            } else if (index === parsedUri.pathname!.length - 1) {
                // https://s3.amazonaws.com/bucket/
                bucket = parsedUri.pathname!.substring(1, index)
                key = undefined
            } else {
                // https://s3.amazonaws.com/bucket/key
                bucket = parsedUri.pathname!.substring(1, index)
                key = parsedUri.pathname!.substring(index + 1)
            }
        }
    } else {
        // Remove the trailing '.' from the prefix to get the bucket.
        bucket = prefix.substring(0, prefix.length - 1)

        if (!parsedUri.pathname || parsedUri.pathname === '/') {
            key = undefined
        } else {
            // Remove the leading '/'.
            key = parsedUri.pathname.substring(1)
        }
    }

    if (matches[2] !== 'amazonaws') {
        region = matches[2]
    } else {
        region = defaultRegion
    }

    if (key !== undefined) {
        key = decodeURIComponent(key)
    }
    return [region, bucket!, key!]
}