package forge

import (
	"context"
	"fmt"
	"net/url"
	"strings"

	"code.gitea.io/sdk/gitea"
)

// Gitea is a Provider backed by a Gitea/Forgejo instance. It also decides which
// repos it serves: only those whose remote host matches its base URL.
type Gitea struct {
	host   string
	client *gitea.Client
}

// NewGitea builds a Gitea provider from a base URL and token. It returns
// (nil, nil) when not configured (either value empty) so forge features simply
// stay absent (§8.4 graceful degradation).
func NewGitea(baseURL, token string) (*Gitea, error) {
	baseURL = strings.TrimRight(strings.TrimSpace(baseURL), "/")
	token = strings.TrimSpace(token)
	if baseURL == "" || token == "" {
		return nil, nil
	}
	u, err := url.Parse(baseURL)
	if err != nil || u.Hostname() == "" {
		return nil, fmt.Errorf("invalid GITEA_URL %q", baseURL)
	}
	c, err := gitea.NewClient(baseURL, gitea.SetToken(token))
	if err != nil {
		return nil, err
	}
	return &Gitea{host: u.Hostname(), client: c}, nil
}

// Handles reports whether a remote host is this Gitea instance.
func (g *Gitea) Handles(host string) bool {
	return strings.EqualFold(host, g.host)
}

// ListPullRequests lists the open PRs of owner/repo.
func (g *Gitea) ListPullRequests(_ context.Context, owner, repo string) ([]PullRequest, error) {
	prs, _, err := g.client.ListRepoPullRequests(owner, repo, gitea.ListPullRequestsOptions{State: gitea.StateOpen})
	if err != nil {
		return nil, err
	}
	out := make([]PullRequest, 0, len(prs))
	for _, p := range prs {
		out = append(out, toPR(p))
	}
	return out, nil
}

// MergeAndCleanup merges the PR and deletes its head branch (when the head is in
// the same repo — never a fork's branch). Callers MUST have confirmed with the
// user first (§1.4).
func (g *Gitea) MergeAndCleanup(_ context.Context, owner, repo string, number int64, method MergeMethod) (MergeResult, error) {
	pr, _, err := g.client.GetPullRequest(owner, repo, number)
	if err != nil {
		return MergeResult{}, err
	}
	branch := ""
	if pr.Head != nil {
		branch = pr.Head.Ref
	}
	sameRepo := pr.Head != nil && pr.Base != nil && pr.Head.RepoID == pr.Base.RepoID
	del := sameRepo && branch != ""

	merged, _, err := g.client.MergePullRequest(owner, repo, number, gitea.MergePullRequestOption{
		Style:                  toStyle(method),
		DeleteBranchAfterMerge: &del,
	})
	if err != nil {
		return MergeResult{}, err
	}

	res := MergeResult{Number: number, Merged: merged, Branch: branch, BranchDeleted: del && merged}
	// Best-effort fallback in case the merge option didn't delete the branch
	// (older Gitea). Ignore the error — the branch may already be gone.
	if merged && del {
		_, _, _ = g.client.DeleteRepoBranch(owner, repo, branch)
	}
	return res, nil
}

func toPR(p *gitea.PullRequest) PullRequest {
	pr := PullRequest{
		Number:    p.Index,
		Title:     p.Title,
		Draft:     p.Draft,
		Mergeable: p.Mergeable,
		URL:       p.HTMLURL,
	}
	if p.Poster != nil {
		pr.Author = p.Poster.UserName
	}
	if p.Head != nil {
		pr.Head = p.Head.Ref
	}
	if p.Base != nil {
		pr.Base = p.Base.Ref
	}
	if p.Head != nil && p.Base != nil {
		pr.SameRepo = p.Head.RepoID == p.Base.RepoID
	}
	return pr
}

func toStyle(m MergeMethod) gitea.MergeStyle {
	switch m {
	case MergeMerge:
		return gitea.MergeStyleMerge
	case MergeRebase:
		return gitea.MergeStyleRebase
	default:
		return gitea.MergeStyleSquash
	}
}