// Package gitea implements the internal Gitea REST operations used by delivery.
package gitea

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

type FailureKind string

const (
	FailureInvalid      FailureKind = "invalid_request"
	FailureNotFound     FailureKind = "not_found"
	FailureUnauthorized FailureKind = "unauthorized"
	FailureConflict     FailureKind = "conflict"
	FailureMalformed    FailureKind = "malformed_response"
	FailureUnverifiable FailureKind = "unverifiable"
	FailureTransport    FailureKind = "transport"
	FailureRejected     FailureKind = "rejected"
	FailureUnknown      FailureKind = "unknown"
)

// Failure describes how a Gitea operation failed. StatusCode is zero when no
// HTTP response was received.
type Failure struct {
	Kind       FailureKind
	Operation  string
	StatusCode int
	Err        error
}

func (f *Failure) Error() string {
	if f.StatusCode != 0 {
		return fmt.Sprintf("gitea %s: %s (HTTP %d)", f.Operation, f.Kind, f.StatusCode)
	}
	if f.Err != nil {
		return fmt.Sprintf("gitea %s: %s: %v", f.Operation, f.Kind, f.Err)
	}
	return fmt.Sprintf("gitea %s: %s", f.Operation, f.Kind)
}

func (f *Failure) Unwrap() error { return f.Err }

type Destination struct {
	BaseURL    string
	Owner      string
	Repository string
	Token      string
}

type Request struct {
	Destination Destination
	Tag         string
	Commit      string
	Note        string
}

type Release struct {
	ID         int64
	URL        string
	TagName    string
	Title      string
	Body       string
	Draft      bool
	Prerelease bool
}

type Result struct {
	Release        Release
	Created        bool
	WriteAttempted bool // a create request was issued, including reconciled creates.
}

type Client struct {
	HTTPClient *http.Client
}

type tagResponse struct {
	Commit struct {
		SHA string `json:"sha"`
	} `json:"commit"`
}

type releaseResponse struct {
	ID              int64  `json:"id"`
	HTMLURL         string `json:"html_url"`
	TagName         string `json:"tag_name"`
	TargetCommitish string `json:"target_commitish"`
	Name            string `json:"name"`
	Body            string `json:"body"`
	Draft           bool   `json:"draft"`
	Prerelease      bool   `json:"prerelease"`
}

type createReleaseRequest struct {
	TagName         string `json:"tag_name"`
	TargetCommitish string `json:"target_commitish"`
	Name            string `json:"name"`
	Body            string `json:"body"`
	Draft           bool   `json:"draft"`
	Prerelease      bool   `json:"prerelease"`
}

// EnsureRelease verifies the hosted tag and finds or creates its stable release
// page. It never edits a release that already exists.
func (c Client) EnsureRelease(ctx context.Context, request Request) (Result, error) {
	if err := validateRequest(request); err != nil {
		return Result{}, err
	}
	base, err := parseBaseURL(request.Destination.BaseURL)
	if err != nil {
		return Result{}, failure(FailureInvalid, "validate destination", 0, err)
	}
	client := c.httpClient()
	apiRoot := strings.TrimRight(base.String(), "/") + "/api/v1/repos/" + url.PathEscape(request.Destination.Owner) + "/" + url.PathEscape(request.Destination.Repository)
	tagURL := apiRoot + "/tags/" + url.PathEscape(request.Tag)

	var tag tagResponse
	if err := c.getJSON(ctx, client, request.Destination.Token, "get hosted tag", tagURL, &tag); err != nil {
		return Result{}, err
	}
	if tag.Commit.SHA != request.Commit {
		return Result{}, failure(FailureConflict, "verify hosted tag", 0, fmt.Errorf("tag %q targets %q, want %q", request.Tag, tag.Commit.SHA, request.Commit))
	}

	releaseURL := apiRoot + "/releases/tags/" + url.PathEscape(request.Tag)
	existing, status, err := c.getRelease(ctx, client, request.Destination.Token, releaseURL)
	if err == nil {
		return acceptExisting(existing, request)
	}
	if status != http.StatusNotFound {
		return Result{}, err
	}

	title := noteTitle(request.Note)
	body, err := json.Marshal(createReleaseRequest{
		TagName: request.Tag, TargetCommitish: request.Commit,
		Name: title, Body: request.Note,
	})
	if err != nil {
		return Result{}, failure(FailureInvalid, "encode release", 0, err)
	}
	created, postStatus, postErr := c.postRelease(ctx, client, request.Destination.Token, apiRoot+"/releases", body)
	if postErr == nil {
		result, verifyErr := acceptCreated(created, request)
		if verifyErr == nil {
			result.WriteAttempted = true
			return result, nil
		}
		postErr = verifyErr
	}
	if !shouldReconcileWrite(postStatus, postErr) {
		return Result{}, postErr
	}

	// A conflict or interrupted server response may have followed a successful
	// create. One lookup resolves only a page with the exact selected content.
	retry, retryStatus, retryErr := c.getRelease(ctx, client, request.Destination.Token, releaseURL)
	if retryErr == nil {
		result, matchErr := acceptExisting(retry, request)
		if matchErr == nil {
			result.WriteAttempted = true
			return result, nil
		}
		return Result{}, failure(FailureConflict, "resolve release creation", postStatus, matchErr)
	}
	if retryStatus == http.StatusNotFound {
		if postStatus == http.StatusConflict {
			return Result{}, failure(FailureConflict, "create release", postStatus, postErr)
		}
		return Result{}, failure(FailureUnknown, "resolve release creation", postStatus, postErr)
	}
	return Result{}, failure(FailureUnknown, "resolve release creation", postStatus, errors.Join(postErr, retryErr))
}

func shouldReconcileWrite(status int, err error) bool {
	if status == http.StatusConflict || status >= 500 || errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
		return true
	}
	var failure *Failure
	return errors.As(err, &failure) && (failure.Kind == FailureTransport || failure.Kind == FailureMalformed)
}

func (c Client) getRelease(ctx context.Context, client *http.Client, token, endpoint string) (Release, int, error) {
	request, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
	if err != nil {
		return Release{}, 0, failure(FailureInvalid, "find release", 0, err)
	}
	request.Header.Set("Authorization", "token "+token)
	request.Header.Set("Accept", "application/json")
	response, err := client.Do(request)
	if err != nil {
		return Release{}, 0, failure(FailureTransport, "find release", 0, err)
	}
	defer response.Body.Close()
	if response.StatusCode == http.StatusNotFound {
		return Release{}, response.StatusCode, failure(FailureNotFound, "find release", response.StatusCode, nil)
	}
	if response.StatusCode < 200 || response.StatusCode >= 300 {
		return Release{}, response.StatusCode, responseFailure("find release", response.StatusCode)
	}
	var decoded releaseResponse
	if err := decodeJSON(response.Body, &decoded); err != nil {
		return Release{}, response.StatusCode, failure(FailureMalformed, "decode release", response.StatusCode, err)
	}
	return decoded.Release(), response.StatusCode, nil
}

func (c Client) getJSON(ctx context.Context, client *http.Client, token, operation, endpoint string, destination any) error {
	request, err := http.NewRequestWithContext(ctx, http.MethodGet, endpoint, nil)
	if err != nil {
		return failure(FailureInvalid, operation, 0, err)
	}
	request.Header.Set("Authorization", "token "+token)
	request.Header.Set("Accept", "application/json")
	response, err := client.Do(request)
	if err != nil {
		return failure(FailureTransport, operation, 0, err)
	}
	defer response.Body.Close()
	if response.StatusCode < 200 || response.StatusCode >= 300 {
		return responseFailure(operation, response.StatusCode)
	}
	if err := decodeJSON(response.Body, destination); err != nil {
		return failure(FailureMalformed, operation, response.StatusCode, err)
	}
	return nil
}

func (c Client) postRelease(ctx context.Context, client *http.Client, token, endpoint string, body []byte) (Release, int, error) {
	request, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(body))
	if err != nil {
		return Release{}, 0, failure(FailureInvalid, "create release", 0, err)
	}
	request.Header.Set("Authorization", "token "+token)
	request.Header.Set("Accept", "application/json")
	request.Header.Set("Content-Type", "application/json")
	response, err := client.Do(request)
	if err != nil {
		return Release{}, 0, failure(FailureTransport, "create release", 0, err)
	}
	defer response.Body.Close()
	if response.StatusCode < 200 || response.StatusCode >= 300 {
		return Release{}, response.StatusCode, responseFailure("create release", response.StatusCode)
	}
	var decoded releaseResponse
	if err := decodeJSON(response.Body, &decoded); err != nil {
		return Release{}, response.StatusCode, failure(FailureMalformed, "decode created release", response.StatusCode, err)
	}
	return decoded.Release(), response.StatusCode, nil
}

func (c Client) httpClient() *http.Client {
	client := http.DefaultClient
	if c.HTTPClient != nil {
		clientCopy := *c.HTTPClient
		clientCopy.CheckRedirect = func(*http.Request, []*http.Request) error { return http.ErrUseLastResponse }
		return &clientCopy
	}
	clientCopy := *client
	clientCopy.CheckRedirect = func(*http.Request, []*http.Request) error { return http.ErrUseLastResponse }
	return &clientCopy
}

func validateRequest(request Request) error {
	if strings.TrimSpace(request.Tag) == "" {
		return failure(FailureInvalid, "validate request", 0, errors.New("full release tag is required"))
	}
	if !validObjectID(request.Commit) {
		return failure(FailureInvalid, "validate request", 0, errors.New("source commit must be a lowercase Git object ID"))
	}
	if strings.TrimSpace(request.Destination.Owner) == "" || strings.ContainsAny(request.Destination.Owner, "/\\") {
		return failure(FailureInvalid, "validate request", 0, errors.New("Gitea owner is required as one path segment"))
	}
	if strings.TrimSpace(request.Destination.Repository) == "" || strings.ContainsAny(request.Destination.Repository, "/\\") {
		return failure(FailureInvalid, "validate request", 0, errors.New("Gitea repository is required as one path segment"))
	}
	if strings.TrimSpace(request.Destination.Token) == "" {
		return failure(FailureInvalid, "validate request", 0, errors.New("Gitea token is required"))
	}
	if noteTitle(request.Note) == "" {
		return failure(FailureInvalid, "validate request", 0, errors.New("release note must begin with a level-one heading"))
	}
	return nil
}

func parseBaseURL(raw string) (*url.URL, error) {
	parsed, err := url.Parse(raw)
	if err != nil {
		return nil, err
	}
	if (parsed.Scheme != "http" && parsed.Scheme != "https") || parsed.Host == "" || parsed.User != nil || parsed.RawQuery != "" || parsed.Fragment != "" {
		return nil, errors.New("base URL must be an absolute HTTP(S) origin or path without credentials, query, or fragment")
	}
	return parsed, nil
}

func acceptExisting(release Release, request Request) (Result, error) {
	if release.TagName != request.Tag || release.Body != request.Note || release.Draft || release.Prerelease {
		return Result{}, failure(FailureConflict, "verify existing release", 0, errors.New("existing release does not match the committed note and stable tag"))
	}
	return Result{Release: release}, nil
}

func acceptCreated(release Release, request Request) (Result, error) {
	if release.ID <= 0 || release.TagName != request.Tag || release.Body != request.Note || release.Title != noteTitle(request.Note) || release.Draft || release.Prerelease {
		return Result{}, failure(FailureMalformed, "verify created release", 0, errors.New("created release response does not match the requested stable release"))
	}
	return Result{Release: release, Created: true}, nil
}

func (response releaseResponse) Release() Release {
	return Release{ID: response.ID, URL: response.HTMLURL, TagName: response.TagName, Title: response.Name, Body: response.Body, Draft: response.Draft, Prerelease: response.Prerelease}
}

func noteTitle(note string) string {
	first := strings.SplitN(note, "\n", 2)[0]
	if !strings.HasPrefix(first, "# ") {
		return ""
	}
	return strings.TrimSpace(strings.TrimPrefix(first, "# "))
}

func validObjectID(value string) bool {
	if len(value) != 40 && len(value) != 64 {
		return false
	}
	for _, r := range value {
		if !(r >= '0' && r <= '9') && !(r >= 'a' && r <= 'f') {
			return false
		}
	}
	return true
}

func responseFailure(operation string, status int) error {
	kind := FailureRejected
	switch status {
	case http.StatusUnauthorized, http.StatusForbidden:
		kind = FailureUnauthorized
	case http.StatusConflict:
		kind = FailureConflict
	case http.StatusNotFound:
		kind = FailureNotFound
	}
	return failure(kind, operation, status, nil)
}

func failure(kind FailureKind, operation string, status int, err error) error {
	return &Failure{Kind: kind, Operation: operation, StatusCode: status, Err: err}
}

func decodeJSON(reader io.Reader, destination any) error {
	decoder := json.NewDecoder(reader)
	if err := decoder.Decode(destination); err != nil {
		return err
	}
	var trailing any
	if err := decoder.Decode(&trailing); !errors.Is(err, io.EOF) {
		if err == nil {
			return errors.New("response contains multiple JSON values")
		}
		return err
	}
	return nil
}