use std::time::Duration;

use futures_util::stream::TryStreamExt;
use serde::Deserialize;
use serde_json::{Value, json};
use tokio::io::AsyncReadExt;
use tokio_util::io::StreamReader;
use tracing::{instrument, warn};

use crate::{
    bot::{ReviewResult, ReviewSeverity, ReviewSide},
    consts::MAX_DIFF_SIZE,
    errors::AppError,
};

/// Page size requested when listing the files of a pull request.
const FILE_PAGE_SIZE: u64 = 50;

/// Maximum number of pages fetched for a pull request file list.
const MAX_FILE_PAGES: u64 = 10;

#[derive(Clone)]
pub struct GiteaAPI {
    base_url: String,
    token: String,
    client: reqwest::Client,
}

impl GiteaAPI {
    pub fn new(base_url: &str, token: &str, timeout: u64) -> anyhow::Result<Self> {
        let mut default_headers = reqwest::header::HeaderMap::new();
        default_headers.insert(
            reqwest::header::HeaderName::from_static("authorization"),
            reqwest::header::HeaderValue::from_str(&format!("Bearer {}", token))?,
        );

        Ok(Self {
            base_url: String::from(base_url),
            token: String::from(token),
            client: reqwest::Client::builder()
                .timeout(Duration::from_secs(timeout))
                .default_headers(default_headers)
                .build()?,
        })
    }

    /// API token used to authenticate against Gitea.
    pub fn token(&self) -> &str {
        &self.token
    }

    #[instrument(skip(self))]
    pub async fn get_authorized_user(&self) -> anyhow::Result<User> {
        let url = format!("{}/api/v1/user", self.base_url);
        let res = self.client.get(url).send().await?;

        if !res.status().is_success() {
            return Err(anyhow::anyhow!(
                "Failed to get authorized user: {}",
                res.status()
            ));
        }

        res.json::<User>().await.map_err(anyhow::Error::from)
    }

    #[instrument(skip(self))]
    pub async fn comment(
        &self,
        body: &str,
        full_name: &str,
        index: u64,
    ) -> anyhow::Result<Comment> {
        let url = format!(
            "{}/api/v1/repos/{}/issues/{}/comments",
            self.base_url, full_name, index
        );

        let res = self
            .client
            .post(url)
            .json(&json!({
                "body": body
            }))
            .send()
            .await?;

        if !res.status().is_success() {
            return Err(anyhow::anyhow!("Failed to comment: {}", res.status()));
        }

        res.json::<Comment>().await.map_err(anyhow::Error::from)
    }

    #[instrument(skip(self))]
    pub async fn edit_comment(
        &self,
        body: &str,
        full_name: &str,
        comment_id: u64,
    ) -> anyhow::Result<()> {
        let url = format!(
            "{}/api/v1/repos/{}/issues/comments/{}",
            self.base_url, full_name, comment_id
        );

        let res = self
            .client
            .patch(url)
            .json(&json!({
                "body": body
            }))
            .send()
            .await?;

        if !res.status().is_success() {
            return Err(anyhow::anyhow!("Failed to comment: {}", res.status()));
        }

        Ok(())
    }

    #[instrument(skip(self))]
    pub async fn delete_comment(&self, full_name: &str, comment_id: u64) -> anyhow::Result<()> {
        let url = format!(
            "{}/api/v1/repos/{}/issues/comments/{}",
            self.base_url, full_name, comment_id
        );

        let res = self.client.delete(url).send().await?;

        if !res.status().is_success() {
            return Err(anyhow::anyhow!(
                "Failed to delete comment: {}",
                res.status()
            ));
        }

        Ok(())
    }

    /// Raw unified diff of a pull request.
    ///
    /// The API endpoint is used rather than the `diff_url` carried by the
    /// webhook: that one points at a web route, which is session authenticated
    /// and therefore does not serve private repositories to an API token.
    #[instrument(skip(self))]
    pub async fn pull_request_diff(&self, full_name: &str, index: u64) -> anyhow::Result<String> {
        let url = format!(
            "{}/api/v1/repos/{}/pulls/{}.diff",
            self.base_url, full_name, index
        );

        let res = self.client.get(url).send().await?;

        if !res.status().is_success() {
            return Err(anyhow::anyhow!(
                "Failed to download pull request diff: {}",
                res.status()
            ));
        }

        read_capped(res).await
    }

    /// Files changed by a pull request, with their exact path and status.
    #[instrument(skip(self))]
    pub async fn pull_request_files(
        &self,
        full_name: &str,
        index: u64,
    ) -> anyhow::Result<Vec<PullRequestFile>> {
        let mut files = Vec::new();

        for page in 1..=MAX_FILE_PAGES {
            let url = format!(
                "{}/api/v1/repos/{}/pulls/{}/files?limit={FILE_PAGE_SIZE}&page={page}",
                self.base_url, full_name, index
            );

            let res = self.client.get(url).send().await?;

            if !res.status().is_success() {
                return Err(anyhow::anyhow!(
                    "Failed to list pull request files: {}",
                    res.status()
                ));
            }

            let page_files = res.json::<Vec<PullRequestFile>>().await?;

            // The instance may cap the page size below the requested one, so a
            // short page is not the end of the list: an empty one is.
            if page_files.is_empty() {
                return Ok(files);
            }

            files.extend(page_files);
        }

        warn!(files = files.len(), "Pull request file list was truncated");

        Ok(files)
    }

    #[instrument(skip(self, review_result))]
    pub async fn post_pull_request_review(
        &self,
        review_result: &ReviewResult,
        final_comment: &str,
        full_name: &str,
        index: u64,
    ) -> anyhow::Result<()> {
        let url = format!(
            "{}/api/v1/repos/{}/pulls/{}/reviews",
            self.base_url, full_name, index
        );

        let comments = review_result
            .reviews
            .iter()
            .filter_map(|review| {
                let line = review.line?;
                let path = review.filename.clone();
                let severity = review
                    .severity
                    .unwrap_or(ReviewSeverity::Maintainability)
                    .label();
                let body = format!("**[{severity}]** {}", review.message);

                // A line removed by the pull request only exists in the old
                // version of the file, so it is anchored with `old_position`.
                Some(match review.side {
                    Some(ReviewSide::Removed) => json!({
                        "path": path,
                        "old_position": line,
                        "body": body
                    }),
                    _ => json!({
                        "path": path,
                        "new_position": line,
                        "body": body
                    }),
                })
            })
            .collect::<Vec<_>>();

        let res = self
            .client
            .post(url)
            .json(&json!({
                "event": "COMMENT",
                "body": final_comment,
                "comments": comments
            }))
            .send()
            .await?;

        if !res.status().is_success() {
            return Err(anyhow::anyhow!("Failed to post review: {}", res.status()));
        }

        Ok(())
    }
}

/// Reads a response body, refusing to buffer more than [`MAX_DIFF_SIZE`].
async fn read_capped(response: reqwest::Response) -> anyhow::Result<String> {
    let stream = response.bytes_stream().map_err(std::io::Error::other);

    let mut buf = Vec::with_capacity(MAX_DIFF_SIZE);
    StreamReader::new(stream)
        .take((MAX_DIFF_SIZE + 1) as u64)
        .read_to_end(&mut buf)
        .await?;

    if buf.len() > MAX_DIFF_SIZE {
        anyhow::bail!("Pull request diff exceeds the maximum allowed size of 1 MiB");
    }

    Ok(String::from_utf8_lossy(&buf).into_owned())
}

#[derive(Debug)]
pub enum WebhookType {
    Review(ReviewPayload),
}

impl WebhookType {
    pub fn event_id(&self) -> u64 {
        match self {
            WebhookType::Review(payload) => payload.comment.id,
        }
    }

    pub fn event_type_str(&self) -> &'static str {
        match self {
            WebhookType::Review(_) => "review",
        }
    }
}

#[derive(Deserialize, Debug)]
pub struct ReviewPayload {
    pub action: String,
    pub pull_request: PullRequest,
    pub repository: Repository,
    pub comment: Comment,
}

#[derive(Deserialize, Debug)]
pub struct PullRequest {
    pub number: u64,
    pub title: String,
}

#[derive(Deserialize, Debug)]
pub struct Comment {
    pub id: u64,
    pub body: String,
}

#[derive(Deserialize, Debug)]
pub struct User {
    pub login: String,
}

#[derive(Deserialize, Debug)]
pub struct Repository {
    pub full_name: String,
    pub clone_url: String,
}

/// A file changed by a pull request, as reported by the API.
#[derive(Deserialize, Debug)]
pub struct PullRequestFile {
    /// Path of the file in the new version of the repository.
    pub filename: String,
    /// Previous path, for a renamed file.
    #[serde(default)]
    pub previous_filename: Option<String>,
    /// `added`, `modified`, `deleted`, `renamed`…
    pub status: String,
}

impl WebhookType {
    pub fn from_event(event: &str, bot_name: &str, json: Value) -> Result<Self, AppError> {
        let wb = match event {
            "pull_request_comment" => Ok(WebhookType::Review(serde_json::from_value(json)?)),
            _ => Err(AppError::UnknownEventErr),
        }?;

        let action = match &wb {
            WebhookType::Review(review_payload) => &review_payload.action,
        };

        if action != "created" {
            return Err(AppError::InvalidActionErr);
        }

        let pr_body = match &wb {
            WebhookType::Review(review_payload) => &review_payload.comment.body,
        };

        if !pr_body.starts_with(&format!("@{}", bot_name)) {
            return Err(AppError::UnauthorizedUserErr);
        }

        Ok(wb)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use serde_json::json;

    #[test]
    fn test_from_event_valid_pull_request_comment() {
        let json = json!({
            "action": "created",
            "pull_request": {
                "id": 42,
                "diff_url": "https://mydiff.fr",
                "number": 1,
                "title": "My PR"
            },
            "repository": {
                "full_name": "owner/repo",
                "clone_url": "https://github.com/owner/repo.git"
            },
            "comment": {
                "id": 7,
                "body": "@test_bot LGTM",
                "user": {
                    "id": 100,
                    "login": "test_user"
                }
            }
        });

        let result = WebhookType::from_event("pull_request_comment", "test_bot", json);
        assert!(result.is_ok());

        match result.unwrap() {
            WebhookType::Review(payload) => {
                assert_eq!(payload.action, "created");
                assert_eq!(payload.comment.id, 7);
                assert_eq!(payload.comment.body, "@test_bot LGTM");
            }
        }
    }

    #[test]
    fn test_from_event_unknown_event() {
        let json = json!({});
        let result = WebhookType::from_event("push", "test_bot", json);
        assert!(result.is_err());

        match result.unwrap_err() {
            AppError::UnknownEventErr => {}
            _ => panic!("expected UnknownEventErr"),
        }
    }

    #[test]
    fn test_from_event_malformed_json() {
        let json = json!({
            "action": "created"
            // pull_request and comment are missing
        });

        let result = WebhookType::from_event("pull_request_comment", "test_bot", json);
        assert!(result.is_err());

        match result.unwrap_err() {
            AppError::BadJsonStructErr(_) => {}
            _ => panic!("expected BadJsonStructErr"),
        }
    }

    #[test]
    fn test_from_event_rejects_non_created_action() {
        let json = json!({
            "action": "edited",
            "pull_request": {
                "id": 1,
                "diff_url": "https://mydiff.fr",
                "number": 1,
                "title": "My PR"
            },
            "repository": {
                "full_name": "owner/repo",
                "clone_url": "https://github.com/owner/repo.git"
            },
            "comment": {
                "id": 1,
                "body": "@test_bot body",
                "user": {
                    "id": 1,
                    "login": "test_user"
                }
            }
        });

        let result = WebhookType::from_event("pull_request_comment", "test_bot", json);
        assert!(result.is_err());

        match result.unwrap_err() {
            AppError::InvalidActionErr => {}
            _ => panic!("expected InvalidActionErr"),
        }
    }

    #[test]
    fn test_deserialize_review_payload() {
        let json = json!({
            "action": "created",
            "pull_request": {
                "id": 99,
                "diff_url": "https://mydiff.fr",
                "number": 5,
                "title": "My PR"
            },
            "repository": {
                "full_name": "owner/repo",
                "clone_url": "https://github.com/owner/repo.git"
            },
            "comment": {
                "id": 12,
                "body": "Needs work",
                "user": {
                    "id": 200,
                    "login": "test_user"
                }
            }
        });

        let payload: ReviewPayload = serde_json::from_value(json).unwrap();
        assert_eq!(payload.action, "created");
        assert_eq!(payload.comment.id, 12);
        assert_eq!(payload.comment.body, "Needs work");
        assert_eq!(
            payload.repository.clone_url,
            "https://github.com/owner/repo.git"
        );
    }

    #[test]
    fn test_from_event_empty_json() {
        let result = WebhookType::from_event("pull_request_comment", "test_bot", json!({}));
        assert!(result.is_err());
        assert!(matches!(result.unwrap_err(), AppError::BadJsonStructErr(_)));
    }

    #[test]
    fn test_from_event_rejects_wrong_bot_name() {
        let json = json!({
            "action": "created",
            "pull_request": {
                "id": 1,
                "diff_url": "https://mydiff.fr",
                "number": 1,
                "title": "My PR"
            },
            "repository": {
                "full_name": "owner/repo",
                "clone_url": "https://github.com/owner/repo.git"
            },
            "comment": {
                "id": 1,
                "body": "@other_bot do something",
                "user": {
                    "id": 1,
                    "login": "test_user"
                }
            }
        });

        let result = WebhookType::from_event("pull_request_comment", "test_bot", json);
        assert!(matches!(result.unwrap_err(), AppError::UnauthorizedUserErr));
    }

    #[test]
    fn test_from_event_rejects_no_bot_prefix() {
        let json = json!({
            "action": "created",
            "pull_request": {
                "id": 1,
                "diff_url": "https://mydiff.fr",
                "number": 1,
                "title": "My PR"
            },
            "repository": {
                "full_name": "owner/repo",
                "clone_url": "https://github.com/owner/repo.git"
            },
            "comment": {
                "id": 1,
                "body": "just a comment without bot mention",
                "user": {
                    "id": 1,
                    "login": "test_user"
                }
            }
        });

        let result = WebhookType::from_event("pull_request_comment", "test_bot", json);
        assert!(matches!(result.unwrap_err(), AppError::UnauthorizedUserErr));
    }
}