package main

import (
	"bufio"
	"bytes"
	"os"
)

var commentPrefix = []byte("--")
var requirementPrefix = []byte("requires:")

// Removes the provided prefix from the byte slice and removes
// any spaces leading or trailing the resulting slice.
//
// If the prefix is not present, nothing is removed except
// the leading and trailing spaces.
func cutPrefixAndTrim(b []byte, prefix []byte) []byte {
	withoutPrefix, _ := bytes.CutPrefix(b, prefix)
	return bytes.TrimSpace(withoutPrefix)
}

func StripComments(sql []byte) []byte {
	scanner := bufio.NewScanner(bytes.NewReader(sql))

	sqlWithoutComments := []byte{}

	for scanner.Scan() {
		currentBytes := scanner.Bytes()

		if !bytes.HasPrefix(currentBytes, commentPrefix) {
			sqlWithoutComments = append(sqlWithoutComments, currentBytes...)
			sqlWithoutComments = append(sqlWithoutComments, []byte("\n")...)
		}
	}

	totalLength := len(sqlWithoutComments)

	if totalLength > 0 {
		return sqlWithoutComments[:totalLength-1]
	}
	return sqlWithoutComments
}

// Extracts any migration headers present in the migration source file.
// Headers are left in comments of the form:
// -- <header-name>: ...
// Anything else than the known headers is ignored.
func gatherMigrationHeaders(migrationFile *os.File) MigrationHeaders {
	scanner := bufio.NewScanner(migrationFile)

	requirements := []string{}

	for scanner.Scan() {
		currentBytes := scanner.Bytes()

		if !bytes.HasPrefix(currentBytes, commentPrefix) {
			continue
		}

		commentBytes := cutPrefixAndTrim(currentBytes, commentPrefix)

		if bytes.HasPrefix(commentBytes, requirementPrefix) {
			reqName := cutPrefixAndTrim(commentBytes, requirementPrefix)
			requirements = append(requirements, string(reqName))
		}
	}

	return MigrationHeaders{Requirements: requirements}
}