// Package gitea is the small slice of the Gitea API repospawner needs: does a
// repository config file already exist, open a pull request, and follow that
// pull request to its merge.
package gitea

import (
	"bytes"
	"context"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strconv"
	"strings"
	"time"
)

// TokenFunc supplies a Gitea token. force asks for a freshly minted one, which
// the client requests exactly once per call after a 401.
type TokenFunc func(ctx context.Context, force bool) (string, error)

// Client talks to one Gitea instance.
type Client struct {
	BaseURL string
	Token   TokenFunc
	HTTP    *http.Client
}

// New builds a Client with a bounded HTTP client.
func New(baseURL string, token TokenFunc) *Client {
	return &Client{
		BaseURL: strings.TrimSuffix(baseURL, "/"),
		Token:   token,
		HTTP:    &http.Client{Timeout: 30 * time.Second},
	}
}

// Repo is the subset of a repository record repospawner uses. ID is the forge
// remote id Woodpecker enablement needs.
type Repo struct {
	ID       int64  `json:"id"`
	FullName string `json:"full_name"`
}

// PullRequest is the subset of a pull request record repospawner uses.
type PullRequest struct {
	Number  int    `json:"number"`
	HTMLURL string `json:"html_url"`
	State   string `json:"state"`
	Merged  bool   `json:"merged"`
}

// Repo fetches a repository by "owner/name".
func (c *Client) Repo(ctx context.Context, repo string) (Repo, error) {
	var out Repo
	err := c.do(ctx, http.MethodGet, "/api/v1/repos/"+repo, nil, &out)
	return out, err
}

// FileExists reports whether path exists on ref in repo. A 404 is the answer
// "no", not an error; anything else is an error, so a broken forge can never be
// mistaken for a free name.
func (c *Client) FileExists(ctx context.Context, repo, path, ref string) (bool, error) {
	ep := "/api/v1/repos/" + repo + "/contents/" + escapePath(path)
	if ref != "" {
		ep += "?ref=" + url.QueryEscape(ref)
	}
	err := c.do(ctx, http.MethodGet, ep, nil, nil)
	var se *StatusError
	if errors.As(err, &se) && se.Status == http.StatusNotFound {
		return false, nil
	}
	if err != nil {
		return false, err
	}
	return true, nil
}

// CreateBranch branches newBranch off oldRef. An existing branch is not an
// error: a retried Job must be able to finish what its predecessor started.
func (c *Client) CreateBranch(ctx context.Context, repo, newBranch, oldRef string) error {
	payload := map[string]string{"new_branch_name": newBranch, "old_ref_name": oldRef}
	err := c.do(ctx, http.MethodPost, "/api/v1/repos/"+repo+"/branches", payload, nil)
	var se *StatusError
	if errors.As(err, &se) && se.Status == http.StatusConflict {
		return nil
	}
	return err
}

// CreateFile writes a new file on branch. content is raw bytes; Gitea wants it
// base64-encoded.
func (c *Client) CreateFile(ctx context.Context, repo, path, branch, message string, content []byte) error {
	payload := map[string]string{
		"branch":  branch,
		"content": base64.StdEncoding.EncodeToString(content),
		"message": message,
	}
	return c.do(ctx, http.MethodPost, "/api/v1/repos/"+repo+"/contents/"+escapePath(path), payload, nil)
}

// CreatePullRequest opens a pull request from head into base.
func (c *Client) CreatePullRequest(ctx context.Context, repo, head, base, title, body string) (PullRequest, error) {
	payload := map[string]string{"head": head, "base": base, "title": title, "body": body}
	var out PullRequest
	err := c.do(ctx, http.MethodPost, "/api/v1/repos/"+repo+"/pulls", payload, &out)
	return out, err
}

// PullRequest fetches one pull request by index.
func (c *Client) PullRequest(ctx context.Context, repo string, number int) (PullRequest, error) {
	var out PullRequest
	err := c.do(ctx, http.MethodGet, "/api/v1/repos/"+repo+"/pulls/"+strconv.Itoa(number), nil, &out)
	return out, err
}

// StatusError carries a non-2xx response.
type StatusError struct {
	Status int
	Method string
	Path   string
	Body   string
}

func (e *StatusError) Error() string {
	msg := fmt.Sprintf("gitea %s %s: status %d", e.Method, e.Path, e.Status)
	if e.Body != "" {
		msg += ": " + e.Body
	}
	return msg
}

// do issues one API call, retrying exactly once with a freshly minted token
// when the forge answers 401 — dynamic Gitea credentials expire after about an
// hour and the watch job outlives that.
func (c *Client) do(ctx context.Context, method, path string, in, out any) error {
	var body []byte
	if in != nil {
		var err error
		if body, err = json.Marshal(in); err != nil {
			return err
		}
	}
	resp, err := c.attempt(ctx, method, path, body, false)
	if err != nil {
		return err
	}
	if resp.StatusCode == http.StatusUnauthorized {
		_ = resp.Body.Close()
		if resp, err = c.attempt(ctx, method, path, body, true); err != nil {
			return err
		}
	}
	defer func() { _ = resp.Body.Close() }()

	if resp.StatusCode < 200 || resp.StatusCode > 299 {
		snippet, _ := io.ReadAll(io.LimitReader(resp.Body, 512))
		return &StatusError{Status: resp.StatusCode, Method: method, Path: path, Body: strings.TrimSpace(string(snippet))}
	}
	if out == nil {
		_, _ = io.Copy(io.Discard, resp.Body)
		return nil
	}
	return json.NewDecoder(resp.Body).Decode(out)
}

func (c *Client) attempt(ctx context.Context, method, path string, body []byte, force bool) (*http.Response, error) {
	var reader io.Reader
	if body != nil {
		reader = bytes.NewReader(body)
	}
	req, err := http.NewRequestWithContext(ctx, method, c.BaseURL+path, reader)
	if err != nil {
		return nil, err
	}
	req.Header.Set("Accept", "application/json")
	if body != nil {
		req.Header.Set("Content-Type", "application/json")
	}
	if c.Token != nil {
		token, err := c.Token(ctx, force)
		if err != nil {
			return nil, err
		}
		if token != "" {
			req.Header.Set("Authorization", "token "+token)
		}
	}
	client := c.HTTP
	if client == nil {
		client = http.DefaultClient
	}
	return client.Do(req)
}

// escapePath percent-escapes each path segment so a config path survives the
// contents API without collapsing its separators.
func escapePath(p string) string {
	parts := strings.Split(strings.TrimPrefix(p, "/"), "/")
	for i, s := range parts {
		parts[i] = url.PathEscape(s)
	}
	return strings.Join(parts, "/")
}