use std::collections::HashMap;

use git::facade::GitContext;
use globset::{Glob, GlobSet, GlobSetBuilder};
use models::pull_request::{pull_request_review, pull_request_reviewer, pull_requests};
use sea_orm::{ColumnTrait, EntityTrait, PaginatorTrait, QueryFilter, QueryOrder};
use serde::{Deserialize, Serialize};
use uuid::Uuid;

use crate::errors::PullError;
use crate::services::changes::PullSummaryDto;
use crate::services::service::PullService;

const SIGNED_CHECK_CAP: usize = 50;

#[derive(Debug, Clone, Serialize, Deserialize, utoipa::ToSchema)]
pub struct MergeGateDto {
    pub allowed: bool,
    pub reasons: Vec<String>,
    pub protected: bool,
    pub required_approvals: i32,
    pub approvals: i32,
    pub change_requests: i32,
    pub outdated: bool,
    pub bypassed: bool,
}

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ReviewVerdict {
    Approved,
    ChangesRequested,
    Commented,
}

fn build_glob_set(raw: &str) -> Result<Option<GlobSet>, PullError> {
    let mut builder = GlobSetBuilder::new();
    let mut count = 0usize;
    for line in raw.split([',', '\n']) {
        let trimmed = line.trim();
        if trimmed.is_empty() {
            continue;
        }
        let pattern = if trimmed.contains('/') {
            trimmed.to_string()
        } else {
            format!("**/{trimmed}")
        };
        builder.add(
            Glob::new(&pattern)
                .map_err(|e| PullError::Internal(format!("invalid glob `{pattern}`: {e}")))?,
        );
        count += 1;
    }
    if count == 0 {
        return Ok(None);
    }
    builder
        .build()
        .map(Some)
        .map_err(|e| PullError::Internal(format!("invalid glob set: {e}")))
}

impl PullService {
    /// 每位审阅者在 PR 上的最新一次非草稿评审结论。
    pub async fn latest_verdicts(
        &self,
        pull_id: Uuid,
        head_sha: &str,
        dismiss_stale: bool,
    ) -> Result<HashMap<i64, ReviewVerdict>, PullError> {
        let mut select = pull_request_review::Entity::find()
            .filter(pull_request_review::Column::PullRequestId.eq(pull_id))
            .filter(
                pull_request_review::Column::State
                    .ne(models::pull_request::pull_request_review::ReviewState::Pending),
            )
            .order_by_asc(pull_request_review::Column::CreatedAt);
        if dismiss_stale {
            select = select.filter(pull_request_review::Column::CommitSha.eq(head_sha));
        }
        let rows = select.all(self.db_read()).await?;
        let mut out: HashMap<i64, ReviewVerdict> = HashMap::new();
        for row in rows {
            let verdict = match row.state {
                models::pull_request::pull_request_review::ReviewState::Approved => {
                    ReviewVerdict::Approved
                }
                models::pull_request::pull_request_review::ReviewState::ChangesRequested => {
                    ReviewVerdict::ChangesRequested
                }
                _ => ReviewVerdict::Commented,
            };
            out.insert(row.user_id, verdict);
        }
        Ok(out)
    }

    /// 待处理（未满足）的审阅请求人数。
    pub async fn pending_requests(&self, pull_id: Uuid) -> Result<i32, PullError> {
        Ok(pull_request_reviewer::Entity::find()
            .filter(pull_request_reviewer::Column::PullRequestId.eq(pull_id))
            .filter(pull_request_reviewer::Column::Required.eq(true))
            .filter(
                pull_request_reviewer::Column::State
                    .eq(models::pull_request::pull_request_reviewer::ReviewerState::Requested),
            )
            .count(self.db_read())
            .await? as i32)
    }

    pub async fn merge_gate(
        &self,
        ctx: &GitContext,
        pull: &pull_requests::Model,
        caller: i64,
        admin: bool,
        summary: &PullSummaryDto,
    ) -> Result<MergeGateDto, PullError> {
        let policy = self
            .git
            .merge_requirements(ctx, &pull.base_branch, caller)
            .await?;
        let outdated = summary.commits_behind > 0;
        let Some(policy) = policy else {
            return Ok(MergeGateDto {
                allowed: true,
                reasons: Vec::new(),
                protected: false,
                required_approvals: 0,
                approvals: 0,
                change_requests: 0,
                outdated,
                bypassed: false,
            });
        };
        let required = policy.required_approvals;
        let dismiss_stale = policy.dismiss_stale_approvals;
        let bypassed = admin || policy.whitelist_bypass;
        let mut reasons: Vec<String> = Vec::new();

        let verdicts = if required > 0 || policy.block_on_change_requested_reviews {
            self.latest_verdicts(pull.id, &summary.head_sha, dismiss_stale)
                .await?
        } else {
            HashMap::new()
        };
        let approvals = verdicts
            .values()
            .filter(|verdict| **verdict == ReviewVerdict::Approved)
            .count() as i32;
        let change_requests = verdicts
            .values()
            .filter(|verdict| **verdict == ReviewVerdict::ChangesRequested)
            .count() as i32;

        if !bypassed {
            if required > 0 && approvals < required {
                reasons.push(format!(
                    "{required} approval(s) required, {approvals} granted on the current head commit"
                ));
            }
            if change_requests > 0 && policy.block_on_rejected_reviews {
                reasons.push(format!("change requested by {change_requests} reviewer(s)"));
            }
            if change_requests > 0 && policy.block_on_change_requested_reviews {
                reasons.push(format!(
                    "unaddressed change request from {change_requests} reviewer(s)"
                ));
            }
            if outdated && policy.block_on_outdated_branch {
                reasons.push(
                    "base branch has new commits; sync the branch before merging".to_string(),
                );
            }
            if policy.require_signed_commits {
                let commits = self
                    .git
                    .merge_commits(
                        ctx,
                        &format!("refs/heads/{}", pull.base_branch),
                        &summary.head_sha,
                    )
                    .await?;
                if commits.len() > SIGNED_CHECK_CAP {
                    return Err(PullError::Conflict(format!(
                        "pull request carries more than {SIGNED_CHECK_CAP} commits; the commit signature policy cannot be verified"
                    )));
                }
                for commit in &commits {
                    let verify = self
                        .git
                        .signature_verify_commit(ctx, commit.sha.clone())
                        .await?;
                    if !verify.signed || !verify.valid {
                        reasons.push(format!("commit {} is not validly signed", commit.sha));
                        break;
                    }
                }
            }

            let required_contexts = &policy.required_status_contexts;
            if !required_contexts.is_empty() {
                let statuses = self
                    .git
                    .list_commit_statuses(ctx, summary.head_sha.clone())
                    .await?;
                for context in required_contexts {
                    let state = statuses
                        .iter()
                        .find(|status| status.context == *context)
                        .map(|status| status.state);
                    match state {
                        Some(git::facade::CommitStatusDtoState::Success) => {}
                        Some(other) => reasons.push(format!(
                            "required check `{context}` is {}",
                            match other {
                                git::facade::CommitStatusDtoState::Pending => "pending",
                                git::facade::CommitStatusDtoState::Failure => "failed",
                                git::facade::CommitStatusDtoState::Error => "errored",
                                git::facade::CommitStatusDtoState::Success => "successful",
                            }
                        )),
                        None => {
                            reasons.push(format!("required check `{context}` has not reported yet"))
                        }
                    }
                }
            }

            let protected_raw = &policy.protected_file_patterns;
            let unprotected_raw = &policy.unprotected_file_patterns;
            if !protected_raw.trim().is_empty() || !unprotected_raw.trim().is_empty() {
                let from = summary
                    .merge_base
                    .clone()
                    .unwrap_or_else(|| summary.base_sha.clone());
                let changed = self
                    .git
                    .diff_files_changed_between(ctx, from, summary.head_sha.clone())
                    .await?;
                let protected = build_glob_set(protected_raw)?;
                let unprotected = build_glob_set(unprotected_raw)?;
                let blocked: Vec<String> = changed
                    .into_iter()
                    .filter(|path| {
                        let hit = protected.as_ref().is_some_and(|set| set.is_match(path));
                        let exempt = unprotected.as_ref().is_some_and(|set| set.is_match(path));
                        hit && !exempt
                    })
                    .collect();
                if !blocked.is_empty() {
                    reasons.push(format!(
                        "protected file(s) changed without whitelist permission: {}",
                        blocked.join(", ")
                    ));
                }
            }
        }

        Ok(MergeGateDto {
            allowed: reasons.is_empty(),
            reasons,
            protected: true,
            required_approvals: required,
            approvals,
            change_requests,
            outdated,
            bypassed,
        })
    }
}