package github

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"net/url"

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

// pullRequestResponse is the GitHub API response for a pull request.
type pullRequestResponse struct {
	Number int    `json:"number"`
	Title  string `json:"title"`
	Body   string `json:"body"`
	Head   struct {
		SHA string `json:"sha"`
		Ref string `json:"ref"`
	} `json:"head"`
	Base struct {
		Ref string `json:"ref"`
	} `json:"base"`
}

// changedFileResponse is the GitHub API response for a changed file in a PR.
type changedFileResponse struct {
	Filename string `json:"filename"`
	Status   string `json:"status"`
	Patch    string `json:"patch"`
}

// commitStatusResponse is the GitHub combined status API response.
type commitStatusResponse struct {
	State    string `json:"state"`
	Statuses []struct {
		Context     string `json:"context"`
		State       string `json:"state"`
		Description string `json:"description"`
		TargetURL   string `json:"target_url"`
	} `json:"statuses"`
}

// checkRunsResponse is the GitHub check runs API response.
type checkRunsResponse struct {
	CheckRuns []struct {
		Name       string  `json:"name"`
		Conclusion *string `json:"conclusion"`
		Status     string  `json:"status"`
		HTMLURL    string  `json:"html_url"`
	} `json:"check_runs"`
}

// GetPullRequest fetches PR metadata.
func (c *Client) GetPullRequest(ctx context.Context, owner, repo string, number int) (*vcs.PullRequest, error) {
	reqURL := fmt.Sprintf("%s/repos/%s/%s/pulls/%d", c.baseURL, url.PathEscape(owner), url.PathEscape(repo), number)
	body, err := c.doGet(ctx, reqURL)
	if err != nil {
		return nil, fmt.Errorf("fetch PR: %w", err)
	}
	var resp pullRequestResponse
	if err := json.Unmarshal(body, &resp); err != nil {
		return nil, fmt.Errorf("parse PR JSON: %w", err)
	}
	return &vcs.PullRequest{
		Number: resp.Number,
		Title:  resp.Title,
		Body:   resp.Body,
		Head:   vcs.HeadRef{SHA: resp.Head.SHA, Ref: resp.Head.Ref},
		Base:   vcs.BaseRef{Ref: resp.Base.Ref},
	}, nil
}

// GetPullRequestDiff fetches the unified diff for a PR.
// Uses Accept: application/vnd.github.diff to get raw diff text.
func (c *Client) GetPullRequestDiff(ctx context.Context, owner, repo string, number int) (string, error) {
	reqURL := fmt.Sprintf("%s/repos/%s/%s/pulls/%d", c.baseURL, url.PathEscape(owner), url.PathEscape(repo), number)
	body, err := c.doRequest(ctx, http.MethodGet, reqURL, "application/vnd.github.diff")
	if err != nil {
		return "", fmt.Errorf("fetch diff: %w", err)
	}
	return string(body), nil
}

// maxPages is the upper bound on pagination loops to prevent unbounded iteration
// in case the server returns a full page indefinitely.
const maxPages = 100

// GetPullRequestFiles fetches the list of files changed in a PR.
// Paginates through all pages (100 per page) to collect all files.
// Returns nil (not an empty slice) when the PR has no changed files.
// Callers can safely range over or check len() on a nil slice.
func (c *Client) GetPullRequestFiles(ctx context.Context, owner, repo string, number int) ([]vcs.ChangedFile, error) {
	var allFiles []vcs.ChangedFile

	for page := 1; page <= maxPages; page++ {
		reqURL := fmt.Sprintf("%s/repos/%s/%s/pulls/%d/files?per_page=100&page=%d",
			c.baseURL, url.PathEscape(owner), url.PathEscape(repo), number, page)
		body, err := c.doGet(ctx, reqURL)
		if err != nil {
			return nil, fmt.Errorf("fetch PR files page %d: %w", page, err)
		}
		var files []changedFileResponse
		if err := json.Unmarshal(body, &files); err != nil {
			return nil, fmt.Errorf("parse PR files JSON: %w", err)
		}
		if len(files) == 0 {
			break
		}
		for _, f := range files {
			allFiles = append(allFiles, vcs.ChangedFile{
				Filename: f.Filename,
				Status:   f.Status,
				Patch:    f.Patch,
			})
		}
		if len(files) < 100 {
			break
		}
	}

	return allFiles, nil
}

// GetFileContentAtRef fetches a file at a specific ref from a repo.
// If ref is empty, the query parameter is omitted (uses default branch).
//
// Note: dot-segments ("." and "..") in the path are silently removed to
// prevent path traversal. This means a path like "foo/../bar" resolves
// to "foo/bar" rather than "bar".
func (c *Client) GetFileContentAtRef(ctx context.Context, owner, repo, path, ref string) (string, error) {
	reqURL := fmt.Sprintf("%s/repos/%s/%s/contents/%s",
		c.baseURL, url.PathEscape(owner), url.PathEscape(repo), escapePath(path))
	if ref != "" {
		reqURL += "?ref=" + url.QueryEscape(ref)
	}
	body, err := c.doGet(ctx, reqURL)
	if err != nil {
		return "", fmt.Errorf("fetch file %s: %w", path, err)
	}
	var resp struct {
		Content  string `json:"content"`
		Encoding string `json:"encoding"`
	}
	if err := json.Unmarshal(body, &resp); err != nil {
		return "", fmt.Errorf("parse file content JSON: %w", err)
	}
	if resp.Encoding != "base64" {
		return "", fmt.Errorf("unexpected encoding %q for file %s", resp.Encoding, path)
	}
	decoded, err := decodeBase64Content(resp.Content)
	if err != nil {
		return "", fmt.Errorf("decode base64 content for %s: %w", path, err)
	}
	return decoded, nil
}

// GetCommitStatuses fetches both commit statuses and check runs for a SHA,
// merging them into a unified []vcs.CommitStatus slice.
// Returns nil (not an empty slice) when there are no statuses or check runs.
// If the commit statuses endpoint fails (e.g. 404 for an unknown SHA), the
// function returns immediately without attempting the check-runs endpoint.
func (c *Client) GetCommitStatuses(ctx context.Context, owner, repo, sha string) ([]vcs.CommitStatus, error) {
	var result []vcs.CommitStatus

	// Fetch commit statuses
	statusURL := fmt.Sprintf("%s/repos/%s/%s/commits/%s/status",
		c.baseURL, url.PathEscape(owner), url.PathEscape(repo), url.PathEscape(sha))
	statusBody, err := c.doGet(ctx, statusURL)
	if err != nil {
		return nil, fmt.Errorf("fetch commit statuses: %w", err)
	}
	var statusResp commitStatusResponse
	if err := json.Unmarshal(statusBody, &statusResp); err != nil {
		return nil, fmt.Errorf("parse commit statuses JSON: %w", err)
	}
	for _, s := range statusResp.Statuses {
		result = append(result, vcs.CommitStatus{
			Context:     s.Context,
			Status:      s.State,
			Description: s.Description,
			TargetURL:   s.TargetURL,
		})
	}

	// Fetch check runs (paginated)
	for checkPage := 1; checkPage <= maxPages; checkPage++ {
		checkURL := fmt.Sprintf("%s/repos/%s/%s/commits/%s/check-runs?per_page=100&page=%d",
			c.baseURL, url.PathEscape(owner), url.PathEscape(repo), url.PathEscape(sha), checkPage)
		checkBody, err := c.doGet(ctx, checkURL)
		if err != nil {
			return nil, fmt.Errorf("fetch check runs page %d: %w", checkPage, err)
		}
		var checkResp checkRunsResponse
		if err := json.Unmarshal(checkBody, &checkResp); err != nil {
			return nil, fmt.Errorf("parse check runs JSON: %w", err)
		}
		for _, cr := range checkResp.CheckRuns {
			result = append(result, vcs.CommitStatus{
				Context:     cr.Name,
				Status:      mapCheckRunStatus(cr.Conclusion),
				Description: derefString(cr.Conclusion),
				TargetURL:   cr.HTMLURL,
			})
		}
		if len(checkResp.CheckRuns) < 100 {
			break
		}
	}

	return result, nil
}

// mapCheckRunStatus maps a check run conclusion to a vcs.CommitStatus status string.
// Conclusion alone determines the mapped state: nil conclusion means the run is
// still in progress (pending), regardless of the status field value.
func mapCheckRunStatus(conclusion *string) string {
	if conclusion == nil {
		// Still running or queued
		return "pending"
	}
	switch *conclusion {
	case "success":
		return "success"
	case "failure", "action_required", "timed_out":
		return "failure"
	case "cancelled", "skipped", "neutral":
		return "success" // non-blocking
	case "stale", "waiting":
		return "pending"
	default:
		return "pending"
	}
}

// derefString safely dereferences a string pointer, returning empty string if nil.
func derefString(s *string) string {
	if s == nil {
		return ""
	}
	return *s
}