package gitea

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"io"
	"net/http"
	"net/url"
	"strconv"
	"strings"

	"go.maximumdirect.net/releasekit/internal/artifact"
)

type AssetState string

const (
	AssetMatching     AssetState = "matching"
	AssetMissing      AssetState = "missing"
	AssetConflicting  AssetState = "conflicting"
	AssetUnverifiable AssetState = "unverifiable"
)

type RemoteAsset struct {
	ID          int64
	Filename    string
	Size        int64
	DownloadURL string
}

type AssetInspection struct {
	Expected artifact.ExpectedAsset
	State    AssetState
	Existing []RemoteAsset
	Err      error
}

type Inspection struct {
	Assets    []AssetInspection
	Unrelated []RemoteAsset
}

type assetResponse struct {
	ID                 int64  `json:"id"`
	Name               string `json:"name"`
	Size               int64  `json:"size"`
	BrowserDownloadURL string `json:"browser_download_url"`
}

// InspectAssets lists the release's attachments and compares every declared
// asset by streamed SHA-256 content. It does not create or modify remote data.
func (c Client) InspectAssets(ctx context.Context, destination Destination, releaseID int64, expected []artifact.ExpectedAsset) (Inspection, error) {
	if releaseID <= 0 {
		return Inspection{}, failure(FailureInvalid, "inspect release assets", 0, errors.New("release ID must be positive"))
	}
	if strings.TrimSpace(destination.Token) == "" {
		return Inspection{}, failure(FailureInvalid, "inspect release assets", 0, errors.New("Gitea token is required"))
	}
	base, err := parseBaseURL(destination.BaseURL)
	if err != nil {
		return Inspection{}, failure(FailureInvalid, "validate destination", 0, err)
	}
	if strings.TrimSpace(destination.Owner) == "" || strings.ContainsAny(destination.Owner, "/\\") || strings.TrimSpace(destination.Repository) == "" || strings.ContainsAny(destination.Repository, "/\\") {
		return Inspection{}, failure(FailureInvalid, "inspect release assets", 0, errors.New("Gitea owner and repository must be path segments"))
	}
	if err := artifact.ValidateExpectedAssets(expected); err != nil {
		return Inspection{}, failure(FailureInvalid, "inspect release assets", 0, err)
	}
	apiRoot := strings.TrimRight(base.String(), "/") + "/api/v1/repos/" + url.PathEscape(destination.Owner) + "/" + url.PathEscape(destination.Repository)
	listed, err := c.listAssets(ctx, c.httpClient(), destination.Token, releaseID, apiRoot)
	if err != nil {
		return Inspection{}, err
	}
	remoteByName := make(map[string][]RemoteAsset, len(listed))
	for _, item := range listed {
		remoteByName[item.Filename] = append(remoteByName[item.Filename], item)
	}
	inspection := Inspection{Assets: make([]AssetInspection, 0, len(expected))}
	declared := make(map[string]struct{}, len(expected))
	for _, item := range expected {
		declared[item.Filename] = struct{}{}
		matches := remoteByName[item.Filename]
		observation := AssetInspection{Expected: item, Existing: matches}
		switch len(matches) {
		case 0:
			observation.State = AssetMissing
		case 1:
			remoteHash, _, err := c.downloadHash(ctx, c.httpClient(), base, destination.Token, matches[0].DownloadURL)
			if err != nil {
				observation.State = AssetUnverifiable
				observation.Err = err
			} else if remoteHash == item.SHA256 {
				observation.State = AssetMatching
			} else {
				observation.State = AssetConflicting
			}
		default:
			observation.State = AssetConflicting
		}
		inspection.Assets = append(inspection.Assets, observation)
	}
	for _, item := range listed {
		if _, expected := declared[item.Filename]; !expected {
			inspection.Unrelated = append(inspection.Unrelated, item)
		}
	}
	return inspection, nil
}

func (c Client) listAssets(ctx context.Context, client *http.Client, token string, releaseID int64, apiRoot string) ([]RemoteAsset, error) {
	if releaseID <= 0 {
		return nil, failure(FailureInvalid, "list release assets", 0, errors.New("release ID must be positive"))
	}
	assetsURL := apiRoot + "/releases/" + strconv.FormatInt(releaseID, 10) + "/assets"
	var listed []assetResponse
	if err := c.getJSON(ctx, client, token, "list release assets", assetsURL, &listed); err != nil {
		return nil, err
	}
	if listed == nil {
		return nil, failure(FailureMalformed, "decode release assets", http.StatusOK, errors.New("attachment response must be a JSON array"))
	}
	assets := make([]RemoteAsset, 0, len(listed))
	for _, item := range listed {
		if item.ID <= 0 || item.Name == "" || item.Size < 0 {
			return nil, failure(FailureMalformed, "decode release assets", http.StatusOK, errors.New("attachment entry is missing its ID, name, or size"))
		}
		assets = append(assets, RemoteAsset{ID: item.ID, Filename: item.Name, Size: item.Size, DownloadURL: item.BrowserDownloadURL})
	}
	return assets, nil
}

func (c Client) downloadHash(ctx context.Context, client *http.Client, base *url.URL, token, rawURL string) (string, int64, error) {
	stream, err := c.openAsset(ctx, client, base, token, rawURL)
	if err != nil {
		return "", 0, err
	}
	defer stream.Close()
	hasher := sha256.New()
	size, err := io.Copy(hasher, stream)
	if err != nil {
		return "", size, failure(FailureUnverifiable, "read release asset", 0, err)
	}
	return hex.EncodeToString(hasher.Sum(nil)), size, nil
}

func (c Client) openAsset(ctx context.Context, client *http.Client, base *url.URL, token, rawURL string) (io.ReadCloser, error) {
	if strings.TrimSpace(rawURL) == "" {
		return nil, failure(FailureUnverifiable, "download release asset", 0, errors.New("attachment has no download URL"))
	}
	assetURL, err := base.Parse(rawURL)
	if err != nil || assetURL.User != nil {
		return nil, failure(FailureUnverifiable, "download release asset", 0, errors.New("invalid attachment URL"))
	}
	assetURL.Fragment = ""
	visited := make(map[string]struct{})
	for {
		key := assetURL.String()
		if _, exists := visited[key]; exists {
			return nil, failure(FailureUnverifiable, "download release asset", 0, errors.New("asset redirect loop"))
		}
		visited[key] = struct{}{}
		request, err := http.NewRequestWithContext(ctx, http.MethodGet, key, nil)
		if err != nil {
			return nil, failure(FailureUnverifiable, "download release asset", 0, err)
		}
		if sameOrigin(base, assetURL) {
			request.Header.Set("Authorization", "token "+token)
		}
		request.Header.Set("Accept", "application/octet-stream")
		response, err := client.Do(request)
		if err != nil {
			return nil, failure(FailureUnverifiable, "download release asset", 0, err)
		}
		if isRedirect(response.StatusCode) {
			location, locationErr := response.Location()
			_ = response.Body.Close()
			if locationErr != nil || location.User != nil {
				return nil, failure(FailureUnverifiable, "redirect release asset", response.StatusCode, errors.New("invalid attachment redirect"))
			}
			location.Fragment = ""
			assetURL = location
			continue
		}
		if response.StatusCode < 200 || response.StatusCode >= 300 {
			_ = response.Body.Close()
			return nil, responseFailure("download release asset", response.StatusCode)
		}
		return response.Body, nil
	}
}

func sameOrigin(base, target *url.URL) bool {
	if target == nil || target.User != nil || target.Host == "" {
		return false
	}
	return strings.EqualFold(base.Scheme, target.Scheme) && strings.EqualFold(base.Hostname(), target.Hostname()) && effectivePort(base) == effectivePort(target)
}

func effectivePort(parsed *url.URL) string {
	if port := parsed.Port(); port != "" {
		return port
	}
	if strings.EqualFold(parsed.Scheme, "https") {
		return "443"
	}
	return "80"
}

func isRedirect(status int) bool {
	switch status {
	case http.StatusMovedPermanently, http.StatusFound, http.StatusSeeOther, http.StatusTemporaryRedirect, http.StatusPermanentRedirect:
		return true
	default:
		return false
	}
}