package golang

import "strings"

// Parse takes a diff of a .bzl file defining go_repository rules and returns
// the list of impacted go libraries (e.g., @com_github_foo_bar//...)
func Parse(diff []string) []string {
	names := []string{}
	for i, line := range diff {
		// removal will come first in diff, so search for that
		if strings.Contains(line, "-        sum") && checkDiffPair(diff, i) {
			// work our way backwards until we reach the first line with a name in it
			names = append(names, "@"+findName(diff, i)+"//...")
		}
	}

	return names
}

// check forward to find matching + line in diff, otherwise the
// go_repository is being removed and we can ignore it
func checkDiffPair(diff []string, index int) bool {
	var pairSum = "+        sum"
	// check both +1 and +2 forward because version might not be changed when
	// the sum is
	return strings.Contains(diff[index+1], pairSum) || strings.Contains(diff[index+2], pairSum)
}

func findName(diff []string, index int) string {
	for !isNameLine(diff[index]) {
		// if it isnt the line with the name on it, decrease index by one
		// to continue working backwards
		index = index - 1
	}
	// we have found the name line, read name and return it
	return readName(diff[index])
}

// determines if a given line in a go_repository file contains the name
func isNameLine(line string) bool {
	return strings.HasPrefix(strings.TrimSpace(line), "name = ")
}

// reads the name of a bazel repository from a line in the .bzl file
func readName(line string) string {
	// there should only be two quotes on a single line, so our desired value
	// will always be the second element:
	//          name = "com_github_pmezard_go_difflib",
	return strings.Split(line, "\"")[1]
}