package github

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"net/http"
	"net/url"

	"gitea.weiker.me/rodin/review-bot/vcs"
)

const (
	// reviewsPerPage is the number of reviews to fetch per API page.
	reviewsPerPage = 100
	// maxReviewPages is the maximum number of pages to paginate through
	// when listing reviews. Acts as a safeguard against infinite pagination.
	maxReviewPages = 100
)

// ErrCannotDeleteSubmittedReview is returned when DeleteReview is called on
// a review that has already been submitted (APPROVED, REQUEST_CHANGES, COMMENT).
// GitHub only allows deletion of PENDING reviews. Callers that need to replace
// a submitted review should use DismissReview instead.
var ErrCannotDeleteSubmittedReview = errors.New("cannot delete submitted review: use DismissReview instead")

// ErrConflictingCommitIDs is returned when PostReview receives comments with
// differing non-empty CommitIDs. The GitHub API accepts only a single commit_id
// per review submission; callers must ensure all comments target the same commit.
var ErrConflictingCommitIDs = errors.New("comments contain conflicting commit IDs: all must target the same commit")

// postReviewRequest is the GitHub API request body for creating a review.
type postReviewRequest struct {
	CommitID string               `json:"commit_id,omitempty"`
	Body     string               `json:"body"`
	Event    string               `json:"event"`
	Comments []reviewCommentEntry `json:"comments,omitempty"`
}

// reviewCommentEntry is a single inline comment in a review creation request.
type reviewCommentEntry struct {
	Path     string `json:"path"`
	Position int    `json:"position"`
	Body     string `json:"body"`
}

// reviewResponse is the GitHub API response for a review.
type reviewResponse struct {
	ID       int64  `json:"id"`
	Body     string `json:"body"`
	State    string `json:"state"`
	CommitID string `json:"commit_id"`
	User     struct {
		Login string `json:"login"`
	} `json:"user"`
}

// dismissReviewRequest is the GitHub API request body for dismissing a review.
type dismissReviewRequest struct {
	Message string `json:"message"`
	Event   string `json:"event"`
}

// userResponse is the GitHub API response for the authenticated user.
type userResponse struct {
	Login string `json:"login"`
}

// translateGitHubReviewState translates a GitHub API review state to the
// canonical vcs.Review.State value.
func translateGitHubReviewState(state string) string {
	switch state {
	case "CHANGES_REQUESTED":
		return "REQUEST_CHANGES"
	case "COMMENTED":
		return "COMMENT"
	default:
		// States like APPROVED, DISMISSED, and PENDING pass through unchanged
		// as they already match the canonical vcs representation. PENDING appears
		// on draft reviews that have not yet been submitted via the GitHub UI or API.
		return state
	}
}

// PostReview submits a review on a pull request.
//
// The vcs.ReviewEvent constants (ReviewEventApprove, ReviewEventRequestChanges,
// ReviewEventComment) have string values that match GitHub's wire-format event
// strings (APPROVE, REQUEST_CHANGES, COMMENT), so Event is cast directly to
// string without translation.
//
// ReviewComment.Position maps directly to the GitHub API position field.
// When req.Comments is empty, the payload omits the comments field entirely
// (via the omitempty tag on postReviewRequest.Comments).
//
// The GitHub API accepts a single commit_id per review submission. PostReview
// uses req.CommitID as the primary commit anchor. If req.CommitID is empty,
// it falls back to extracting from the first comment with a non-empty CommitID.
// If any subsequent comment specifies a different CommitID, PostReview returns
// ErrConflictingCommitIDs. Comments with an empty CommitID are allowed and
// inherit the review-level value.
func (c *Client) PostReview(ctx context.Context, owner, repo string, number int, req vcs.ReviewRequest) (*vcs.Review, error) {
	reqURL := fmt.Sprintf("%s/repos/%s/%s/pulls/%d/reviews",
		c.baseURL, url.PathEscape(owner), url.PathEscape(repo), number)

	payload := postReviewRequest{
		Body:     req.Body,
		Event:    string(req.Event),
		CommitID: req.CommitID,
	}

	// Build the payload in one pass. The GitHub API accepts a single commit_id
	// per review. req.CommitID is the primary source; if empty, we extract from
	// the first comment that supplies one. Reject if any comment disagrees with
	// the resolved commit_id.
	for _, comment := range req.Comments {
		if comment.CommitID != "" {
			if payload.CommitID == "" { // only reachable when req.CommitID is empty
				payload.CommitID = comment.CommitID
			} else if payload.CommitID != comment.CommitID {
				return nil, ErrConflictingCommitIDs
			}
			// else: matching SHA is a no-op by design
		}
		payload.Comments = append(payload.Comments, reviewCommentEntry{
			Path:     comment.Path,
			Position: comment.Position,
			Body:     comment.Body,
		})
	}

	body, err := c.doJSONRequest(ctx, http.MethodPost, reqURL, payload)
	if err != nil {
		return nil, fmt.Errorf("post review: %w", err)
	}

	var resp reviewResponse
	if err := json.Unmarshal(body, &resp); err != nil {
		return nil, fmt.Errorf("parse review response: %w", err)
	}

	return &vcs.Review{
		ID:       resp.ID,
		Body:     resp.Body,
		User:     vcs.UserInfo{Login: resp.User.Login},
		State:    translateGitHubReviewState(resp.State),
		CommitID: resp.CommitID,
	}, nil
}

// ListReviews retrieves all reviews for a pull request with pagination.
// GitHub review states are translated to canonical vcs values.
func (c *Client) ListReviews(ctx context.Context, owner, repo string, number int) ([]vcs.Review, error) {
	perPage := reviewsPerPage
	if c.reviewPageSize > 0 {
		perPage = c.reviewPageSize
	}
	maxPages := maxReviewPages
	if c.reviewMaxPages > 0 {
		maxPages = c.reviewMaxPages
	}

	var allReviews []vcs.Review
	truncated := false

	for page := 1; page <= maxPages; page++ {
		reqURL := fmt.Sprintf("%s/repos/%s/%s/pulls/%d/reviews?per_page=%d&page=%d",
			c.baseURL, url.PathEscape(owner), url.PathEscape(repo), number, perPage, page)

		body, err := c.doGet(ctx, reqURL)
		if err != nil {
			return nil, fmt.Errorf("list reviews page %d: %w", page, err)
		}

		var responses []reviewResponse
		if err := json.Unmarshal(body, &responses); err != nil {
			return nil, fmt.Errorf("parse reviews response: %w", err)
		}

		if len(responses) == 0 {
			break
		}

		for _, r := range responses {
			allReviews = append(allReviews, vcs.Review{
				ID:       r.ID,
				Body:     r.Body,
				User:     vcs.UserInfo{Login: r.User.Login},
				State:    translateGitHubReviewState(r.State),
				CommitID: r.CommitID,
			})
		}

		if len(responses) < perPage {
			break
		}

		// Truncation detection: this runs on the final allowed iteration
		// (page == maxPages) only when the page was full (the len < perPage
		// early-break above didn't fire). A full final page means additional
		// reviews likely exist beyond our pagination limit.
		if page == maxPages {
			truncated = true
		}
	}

	if truncated {
		slog.Warn("ListReviews hit page limit; results may be truncated",
			"owner", owner, "repo", repo, "pr", number,
			"maxPages", maxPages, "reviewsFetched", len(allReviews))
	}

	return allReviews, nil
}

// DeleteReview deletes a pull request review.
// Only PENDING reviews can be deleted; attempting to delete a submitted review
// (APPROVED, CHANGES_REQUESTED, or COMMENTED per GitHub API naming) returns
// ErrCannotDeleteSubmittedReview.
func (c *Client) DeleteReview(ctx context.Context, owner, repo string, number int, reviewID int64) error {
	reqURL := fmt.Sprintf("%s/repos/%s/%s/pulls/%d/reviews/%d",
		c.baseURL, url.PathEscape(owner), url.PathEscape(repo), number, reviewID)

	// nil body: the GitHub DELETE endpoint for reviews requires no request body.
	_, err := c.doRequestWithBody(ctx, http.MethodDelete, reqURL, nil)
	if err != nil {
		var apiErr *APIError
		if errors.As(err, &apiErr) && apiErr.StatusCode == 422 {
			return fmt.Errorf("delete review: %w", ErrCannotDeleteSubmittedReview)
		}
		return fmt.Errorf("delete review: %w", err)
	}
	return nil
}

// DismissReview dismisses a submitted review on a pull request.
// This is the correct way to "remove" a submitted review (APPROVED, REQUEST_CHANGES).
// GitHub does not allow deleting submitted reviews — they must be dismissed.
func (c *Client) DismissReview(ctx context.Context, owner, repo string, number int, reviewID int64, message string) error {
	reqURL := fmt.Sprintf("%s/repos/%s/%s/pulls/%d/reviews/%d/dismissals",
		c.baseURL, url.PathEscape(owner), url.PathEscape(repo), number, reviewID)

	payload := dismissReviewRequest{
		Message: message,
		// Event is required by the GitHub API for dismissal requests, even though
		// "DISMISS" is the only valid value for this endpoint.
		Event: "DISMISS",
	}

	_, err := c.doJSONRequest(ctx, http.MethodPut, reqURL, payload)
	if err != nil {
		return fmt.Errorf("dismiss review: %w", err)
	}
	return nil
}

// SupersedeReviews marks prior reviews as superseded by dismissing them.
// This implements vcs.ReviewSuperseder for the GitHub adapter.
// The baseURL and sentinel parameters are unused for GitHub (dismissal is the mechanism).
func (c *Client) SupersedeReviews(ctx context.Context, owner, repo string, prNumber int, oldReviews []vcs.Review, newReviewID int64, _, _ string) error {
	var errs []error
	for _, old := range oldReviews {
		if err := c.DismissReview(ctx, owner, repo, prNumber, old.ID, "Superseded by new review"); err != nil {
			errs = append(errs, fmt.Errorf("dismiss review %d: %w", old.ID, err))
		}
	}
	return errors.Join(errs...)
}

// GetAuthenticatedUser returns the login name of the authenticated user.
func (c *Client) GetAuthenticatedUser(ctx context.Context) (string, error) {
	reqURL := fmt.Sprintf("%s/user", c.baseURL)
	body, err := c.doGet(ctx, reqURL)
	if err != nil {
		return "", fmt.Errorf("get authenticated user: %w", err)
	}
	var resp userResponse
	if err := json.Unmarshal(body, &resp); err != nil {
		return "", fmt.Errorf("parse user response: %w", err)
	}
	return resp.Login, nil
}