package agent

import (
	"bytes"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"strings"
)

// APIError is a non-2xx response from the Gitea API. It carries the status code
// so callers can react to specific failures (e.g. tolerate a 404 for a commit
// whose branch was deleted after a merge) instead of parsing error strings.
type APIError struct {
	Method     string
	Path       string
	StatusCode int
	Body       string
}

func (e *APIError) Error() string {
	return fmt.Sprintf("gitea %s %s: HTTP %d: %s", e.Method, e.Path, e.StatusCode, e.Body)
}

// isNotFound reports whether err is a Gitea 404.
func isNotFound(err error) bool {
	var apiErr *APIError
	return errors.As(err, &apiErr) && apiErr.StatusCode == http.StatusNotFound
}

// GiteaClient talks to the Gitea REST API as the agent user.
type GiteaClient struct {
	BaseURL string
	Token   string
	HTTP    *http.Client
}

// NewGiteaClient builds a client from the configured base URL and a Vault-minted
// token.
func NewGiteaClient(token string) *GiteaClient {
	return &GiteaClient{BaseURL: GiteaURL(), Token: token, HTTP: httpClient}
}

func (c *GiteaClient) do(method, path string, body any, out any) error {
	var reader io.Reader
	if body != nil {
		b, err := json.Marshal(body)
		if err != nil {
			return err
		}
		reader = bytes.NewReader(b)
	}
	url := strings.TrimRight(c.BaseURL, "/") + path
	req, err := http.NewRequest(method, url, reader)
	if err != nil {
		return err
	}
	req.Header.Set("Authorization", "token "+c.Token)
	req.Header.Set("Accept", "application/json")
	if body != nil {
		req.Header.Set("Content-Type", "application/json")
	}

	resp, err := c.HTTP.Do(req)
	if err != nil {
		return err
	}
	defer func() { _ = resp.Body.Close() }()
	data, _ := io.ReadAll(resp.Body)
	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
		return &APIError{Method: method, Path: path, StatusCode: resp.StatusCode, Body: strings.TrimSpace(string(data))}
	}
	if out != nil && len(data) > 0 {
		if err := json.Unmarshal(data, out); err != nil {
			return fmt.Errorf("gitea %s %s: decoding response: %w", method, path, err)
		}
	}
	return nil
}

// User is the subset of the Gitea user object we care about.
type User struct {
	Login string `json:"login"`
	ID    int64  `json:"id"`
}

// Whoami returns the authenticated user (GET /api/v1/user).
func (c *GiteaClient) Whoami() (User, error) {
	var u User
	err := c.do(http.MethodGet, "/api/v1/user", nil, &u)
	return u, err
}

// PullRequest is the subset of Gitea's PR object we track.
type PullRequest struct {
	Number    int    `json:"number"`
	State     string `json:"state"`
	Title     string `json:"title"`
	Merged    bool   `json:"merged"`
	Mergeable bool   `json:"mergeable"`
	HTMLURL   string `json:"html_url"`
	Head      struct {
		Sha string `json:"sha"`
	} `json:"head"`
}

// CreatePROptions are the fields for opening a PR.
type CreatePROptions struct {
	Base  string `json:"base"`
	Head  string `json:"head"`
	Title string `json:"title"`
	Body  string `json:"body"`
}

// CreatePR opens a pull request (POST /api/v1/repos/{owner}/{repo}/pulls).
func (c *GiteaClient) CreatePR(repoPath string, opts CreatePROptions) (PullRequest, error) {
	var pr PullRequest
	err := c.do(http.MethodPost, "/api/v1/repos/"+repoPath+"/pulls", opts, &pr)
	return pr, err
}

// GetPR fetches a single pull request.
func (c *GiteaClient) GetPR(repoPath string, number int) (PullRequest, error) {
	var pr PullRequest
	err := c.do(http.MethodGet, fmt.Sprintf("/api/v1/repos/%s/pulls/%d", repoPath, number), nil, &pr)
	return pr, err
}

// Comment is the subset of an issue comment we track.
type Comment struct {
	ID   int64  `json:"id"`
	User User   `json:"user"`
	Body string `json:"body"`
}

// CreateComment posts a comment on the PR's issue thread
// (POST /api/v1/repos/{owner}/{repo}/issues/{n}/comments).
func (c *GiteaClient) CreateComment(repoPath string, number int, body string) (Comment, error) {
	var cm Comment
	payload := map[string]string{"body": body}
	err := c.do(http.MethodPost, fmt.Sprintf("/api/v1/repos/%s/issues/%d/comments", repoPath, number), payload, &cm)
	return cm, err
}

// ListComments lists the PR's issue comments.
func (c *GiteaClient) ListComments(repoPath string, number int) ([]Comment, error) {
	var out []Comment
	err := c.do(http.MethodGet, fmt.Sprintf("/api/v1/repos/%s/issues/%d/comments", repoPath, number), nil, &out)
	return out, err
}

// CombinedStatus is the combined commit status for a ref.
type CombinedStatus struct {
	State string `json:"state"`
}

// CommitStatus returns the combined CI status for a commit SHA
// (GET /api/v1/repos/{owner}/{repo}/commits/{sha}/status). An empty ref yields
// an empty state without an API call.
func (c *GiteaClient) CommitStatus(repoPath, sha string) (string, error) {
	if sha == "" {
		return "", nil
	}
	var cs CombinedStatus
	err := c.do(http.MethodGet, fmt.Sprintf("/api/v1/repos/%s/commits/%s/status", repoPath, sha), nil, &cs)
	return cs.State, err
}