// Package repospec validates a new-repo request and renders the terraform-git
// repository config file it becomes.
package repospec

import (
	"fmt"
	"regexp"
	"sort"
	"strings"
)

// ConfigDir is the terraform-git tree that owns repository definitions.
const ConfigDir = "config/git.unkin.net/unkin/repository"

// nameRE is the DNS-label-ish shape a repository name must take: it becomes a
// branch name, a container image name and a k8s object name downstream.
var nameRE = regexp.MustCompile(`^[a-z0-9]([a-z0-9-]*[a-z0-9])?$`)

// maxNameLen keeps generated Job names (prefix + name + suffix) inside the 63
// character limit k8s applies to object names.
const maxNameLen = 40

// Request is a submitted new-repo request.
type Request struct {
	Name         string   `json:"name"`
	Description  string   `json:"description"`
	Woodpecker   bool     `json:"woodpecker"`
	StatusChecks []string `json:"status_checks"`
}

// FieldErrors maps a request field to why it was rejected.
type FieldErrors map[string]string

func (f FieldErrors) Error() string {
	keys := make([]string, 0, len(f))
	for k := range f {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	parts := make([]string, 0, len(keys))
	for _, k := range keys {
		parts = append(parts, k+": "+f[k])
	}
	return strings.Join(parts, "; ")
}

// Normalize trims incidental whitespace and drops blank status check lines. The
// UI submits the check list as a textarea, so blank lines are routine.
func (r Request) Normalize() Request {
	r.Name = strings.TrimSpace(r.Name)
	r.Description = strings.TrimSpace(r.Description)
	checks := make([]string, 0, len(r.StatusChecks))
	seen := map[string]bool{}
	for _, c := range r.StatusChecks {
		c = strings.TrimSpace(c)
		if c == "" || seen[c] {
			continue
		}
		seen[c] = true
		checks = append(checks, c)
	}
	r.StatusChecks = checks
	return r
}

// Validate checks a normalized request, returning nil or a FieldErrors naming
// every problem at once so the form can show them together.
func (r Request) Validate() error {
	errs := FieldErrors{}
	switch {
	case r.Name == "":
		errs["name"] = "required"
	case len(r.Name) > maxNameLen:
		errs["name"] = fmt.Sprintf("must be at most %d characters", maxNameLen)
	case !nameRE.MatchString(r.Name):
		errs["name"] = "must be lowercase letters, digits and dashes, starting and ending alphanumeric"
	}
	if r.Description == "" {
		errs["description"] = "required"
	}
	if len(r.StatusChecks) == 0 {
		errs["status_checks"] = "at least one status check context is required"
	}
	for _, c := range r.StatusChecks {
		if strings.ContainsAny(c, "\n\"") {
			errs["status_checks"] = "must not contain quotes or newlines"
			break
		}
	}
	if len(errs) == 0 {
		return nil
	}
	return errs
}

// ConfigPath is the repository config file a request writes.
func (r Request) ConfigPath() string { return ConfigDir + "/" + r.Name + ".yaml" }

// BranchName is the terraform-git branch the PR job pushes.
func (r Request) BranchName() string { return "repospawner/" + r.Name }

// RenderYAML produces the terraform-git repository config. Everything except
// the description and the status check contexts is fixed estate policy: public,
// main-default, squash-merged, branch-deleted, and a protected main only the
// Owners team can merge into with benvin as the approver.
func (r Request) RenderYAML() string {
	var b strings.Builder
	fmt.Fprintf(&b, "description: %s\n", quote(r.Description))
	b.WriteString("private: false\n")
	b.WriteString("default_branch: \"main\"\n")
	b.WriteString("default_delete_branch_after_merge: true\n")
	b.WriteString("default_merge_style: \"squash\"\n")
	b.WriteString("branch_protection:\n")
	b.WriteString("  - rule_name: \"main\"\n")
	b.WriteString("    merge_whitelist_teams:\n")
	b.WriteString("      - \"Owners\"\n")
	b.WriteString("    enable_push: false\n")
	b.WriteString("    status_check_contexts:\n")
	for _, c := range r.StatusChecks {
		fmt.Fprintf(&b, "      - %s\n", quote(c))
	}
	b.WriteString("    approval_whitelist_users:\n")
	b.WriteString("      - \"benvin\"\n")
	return b.String()
}

// quote emits a double-quoted YAML scalar, escaping the two characters that
// can break out of one.
func quote(s string) string {
	s = strings.ReplaceAll(s, `\`, `\\`)
	s = strings.ReplaceAll(s, `"`, `\"`)
	return `"` + s + `"`
}