//! Low-level Postgres CRUD + filter-query builder over the `docs`
//! table (migration 0013). Stays storage-only; authorization, event
//! emission, and empty-collection validation live one layer up in
//! `DocsServiceImpl`.
//!
//! The `find` SQL builder is the security-critical surface. **Every
//! field-path segment and every comparison value is bound as a
//! `$N` parameter — never interpolated into the SQL string.** The base
//! `WHERE app_id = $1 AND collection = $2` clause is fixed and
//! prepended to every query so cross-app isolation can't be widened by
//! any operator. See `sql_starts_with_app_collection_predicate`
//! assertion in tests for the load-bearing guarantee.

use async_trait::async_trait;
use base64::engine::general_purpose::URL_SAFE_NO_PAD;
use base64::Engine as _;
use chrono::{DateTime, Utc};
use picloud_shared::{AppId, DocId, DocRow, DocsListPage};
use serde_json::Value;
use sqlx::postgres::PgRow;
use sqlx::{PgPool, Postgres, QueryBuilder, Row};
use uuid::Uuid;

use crate::docs_filter::{ComparisonOp, DocsFilter, SortDir};

#[derive(Debug, thiserror::Error)]
pub enum DocsRepoError {
    #[error("database error: {0}")]
    Db(#[from] sqlx::Error),

    #[error("invalid pagination cursor")]
    InvalidCursor,
}

/// Repo surface. The trait is exposed so the service unit tests can
/// substitute an in-memory backing without spinning up Postgres.
#[async_trait]
pub trait DocsRepo: Send + Sync {
    /// Create a new doc with a server-generated UUID. Returns the
    /// fully-materialised `DocRow` so the caller has timestamps too
    /// (no separate select-back round-trip).
    async fn create(
        &self,
        app_id: AppId,
        collection: &str,
        data: Value,
    ) -> Result<DocRow, DocsRepoError>;

    async fn get(
        &self,
        app_id: AppId,
        collection: &str,
        id: DocId,
    ) -> Result<Option<DocRow>, DocsRepoError>;

    /// Filter-based query. The parsed `DocsFilter` ensures every
    /// field-path segment and operator value is bound as a parameter.
    async fn find(
        &self,
        app_id: AppId,
        collection: &str,
        filter: &DocsFilter,
    ) -> Result<Vec<DocRow>, DocsRepoError>;

    /// Full document replace. Returns `Some(previous_data)` on
    /// success, `None` if no doc matched (the service maps that to
    /// `DocsError::NotFound`). The prev value is the input to the
    /// emitted update event's `old_payload`.
    async fn update(
        &self,
        app_id: AppId,
        collection: &str,
        id: DocId,
        data: Value,
    ) -> Result<Option<Value>, DocsRepoError>;

    /// Returns the deleted doc's data if it existed, `None` if no
    /// such doc. The caller converts `Some` → `Ok(true)` for the SDK's
    /// was-present return; the `Value` feeds the delete event's
    /// `old_payload`.
    async fn delete(
        &self,
        app_id: AppId,
        collection: &str,
        id: DocId,
    ) -> Result<Option<Value>, DocsRepoError>;

    async fn list(
        &self,
        app_id: AppId,
        collection: &str,
        cursor: Option<&str>,
        limit: u32,
    ) -> Result<DocsListPage, DocsRepoError>;
}

pub struct PostgresDocsRepo {
    pool: PgPool,
}

impl PostgresDocsRepo {
    #[must_use]
    pub fn new(pool: PgPool) -> Self {
        Self { pool }
    }
}

/// Hard ceiling on `list` page size — mirrors KV's `KV_LIST_MAX_LIMIT`.
/// Scripts that pass anything larger get silently clamped.
const DOCS_LIST_MAX_LIMIT: u32 = 1_000;
const DOCS_LIST_DEFAULT_LIMIT: u32 = 100;

#[async_trait]
impl DocsRepo for PostgresDocsRepo {
    async fn create(
        &self,
        app_id: AppId,
        collection: &str,
        data: Value,
    ) -> Result<DocRow, DocsRepoError> {
        let id = Uuid::new_v4();
        let row: (DateTime<Utc>, DateTime<Utc>) = sqlx::query_as(
            "INSERT INTO docs (app_id, collection, id, data) \
             VALUES ($1, $2, $3, $4) \
             RETURNING created_at, updated_at",
        )
        .bind(app_id.into_inner())
        .bind(collection)
        .bind(id)
        .bind(&data)
        .fetch_one(&self.pool)
        .await?;
        Ok(DocRow {
            id,
            data,
            created_at: row.0,
            updated_at: row.1,
        })
    }

    async fn get(
        &self,
        app_id: AppId,
        collection: &str,
        id: DocId,
    ) -> Result<Option<DocRow>, DocsRepoError> {
        let row: Option<(Value, DateTime<Utc>, DateTime<Utc>)> = sqlx::query_as(
            "SELECT data, created_at, updated_at FROM docs \
             WHERE app_id = $1 AND collection = $2 AND id = $3",
        )
        .bind(app_id.into_inner())
        .bind(collection)
        .bind(id)
        .fetch_optional(&self.pool)
        .await?;
        Ok(row.map(|(data, created_at, updated_at)| DocRow {
            id,
            data,
            created_at,
            updated_at,
        }))
    }

    async fn find(
        &self,
        app_id: AppId,
        collection: &str,
        filter: &DocsFilter,
    ) -> Result<Vec<DocRow>, DocsRepoError> {
        let mut qb = build_find_query(app_id, collection, filter);
        let rows = qb.build().fetch_all(&self.pool).await?;
        rows.into_iter().map(row_to_doc).collect()
    }

    async fn update(
        &self,
        app_id: AppId,
        collection: &str,
        id: DocId,
        data: Value,
    ) -> Result<Option<Value>, DocsRepoError> {
        // Same CTE shape as KV's set ([kv_repo.rs:101-132]): SELECT the
        // previous data before the UPDATE so the service can emit
        // `prev_data` in the update ServiceEvent. Single statement, no
        // explicit transaction. Inherits KV's last-writer-wins race
        // under concurrent writers; documented as a known limitation
        // for v1.1.2.
        let row: Option<(Option<Value>,)> = sqlx::query_as(
            "WITH prev AS ( \
                SELECT data FROM docs \
                WHERE app_id = $1 AND collection = $2 AND id = $3 \
             ), \
             updated AS ( \
                UPDATE docs SET data = $4, updated_at = NOW() \
                WHERE app_id = $1 AND collection = $2 AND id = $3 \
                RETURNING 1 \
             ) \
             SELECT (SELECT data FROM prev) FROM updated",
        )
        .bind(app_id.into_inner())
        .bind(collection)
        .bind(id)
        .bind(&data)
        .fetch_optional(&self.pool)
        .await?;
        // `row` is None when the UPDATE matched no rows (missing doc);
        // Some((Some(prev),)) on success. `data` is JSONB NOT NULL so
        // the inner Option is always Some when prev exists.
        Ok(row.and_then(|(v,)| v))
    }

    async fn delete(
        &self,
        app_id: AppId,
        collection: &str,
        id: DocId,
    ) -> Result<Option<Value>, DocsRepoError> {
        let row: Option<(Value,)> = sqlx::query_as(
            "DELETE FROM docs \
             WHERE app_id = $1 AND collection = $2 AND id = $3 \
             RETURNING data",
        )
        .bind(app_id.into_inner())
        .bind(collection)
        .bind(id)
        .fetch_optional(&self.pool)
        .await?;
        Ok(row.map(|(v,)| v))
    }

    async fn list(
        &self,
        app_id: AppId,
        collection: &str,
        cursor: Option<&str>,
        limit: u32,
    ) -> Result<DocsListPage, DocsRepoError> {
        let limit = if limit == 0 {
            DOCS_LIST_DEFAULT_LIMIT
        } else {
            limit.min(DOCS_LIST_MAX_LIMIT)
        };

        let last_id = match cursor {
            Some(c) => Some(decode_cursor(c)?),
            None => None,
        };

        let take = i64::from(limit) + 1;
        let rows: Vec<(Uuid, Value, DateTime<Utc>, DateTime<Utc>)> = sqlx::query_as(
            "SELECT id, data, created_at, updated_at FROM docs \
             WHERE app_id = $1 AND collection = $2 \
               AND ($3::uuid IS NULL OR id > $3) \
             ORDER BY id ASC \
             LIMIT $4",
        )
        .bind(app_id.into_inner())
        .bind(collection)
        .bind(last_id)
        .bind(take)
        .fetch_all(&self.pool)
        .await?;

        let mut docs: Vec<DocRow> = rows
            .into_iter()
            .map(|(id, data, created_at, updated_at)| DocRow {
                id,
                data,
                created_at,
                updated_at,
            })
            .collect();
        let next_cursor = if docs.len() > limit as usize {
            docs.truncate(limit as usize);
            docs.last().map(|d| encode_cursor(&d.id))
        } else {
            None
        };

        Ok(DocsListPage { docs, next_cursor })
    }
}

fn row_to_doc(row: PgRow) -> Result<DocRow, DocsRepoError> {
    Ok(DocRow {
        id: row.try_get("id")?,
        data: row.try_get("data")?,
        created_at: row.try_get("created_at")?,
        updated_at: row.try_get("updated_at")?,
    })
}

fn encode_cursor(last_id: &Uuid) -> String {
    URL_SAFE_NO_PAD.encode(last_id.as_bytes())
}

fn decode_cursor(cursor: &str) -> Result<Uuid, DocsRepoError> {
    let bytes = URL_SAFE_NO_PAD
        .decode(cursor)
        .map_err(|_| DocsRepoError::InvalidCursor)?;
    let arr: [u8; 16] = bytes
        .as_slice()
        .try_into()
        .map_err(|_| DocsRepoError::InvalidCursor)?;
    Ok(Uuid::from_bytes(arr))
}

// ----------------------------------------------------------------------------
// SQL builder — the load-bearing security surface.
//
// Every field-path segment + every comparison value goes through
// `QueryBuilder::push_bind`, which appends `$N` to the SQL string and
// binds the value as a parameter. The only literal strings appended to
// the SQL are: hardcoded SQL fragments (SELECT/WHERE/AND/etc.) and
// hardcoded operator strings ("=", "IS DISTINCT FROM", ">", "ASC", …).
// **No user input ever lands in the SQL text unparameterized.**
// ----------------------------------------------------------------------------

fn build_find_query<'a>(
    app_id: AppId,
    collection: &'a str,
    filter: &'a DocsFilter,
) -> QueryBuilder<'a, Postgres> {
    let mut qb =
        QueryBuilder::new("SELECT id, data, created_at, updated_at FROM docs WHERE app_id = ");
    qb.push_bind(app_id.into_inner());
    qb.push(" AND collection = ");
    qb.push_bind(collection);

    for cond in &filter.conditions {
        qb.push(" AND ");
        emit_condition(&mut qb, cond);
    }

    qb.push(" ORDER BY ");
    if let Some(sort) = &filter.sort {
        push_jsonb_path(&mut qb, sort.path.segments());
        qb.push(match sort.direction {
            SortDir::Asc => " ASC",
            SortDir::Desc => " DESC",
        });
        qb.push(", id ASC");
    } else {
        qb.push("id ASC");
    }

    let limit = filter
        .limit
        .map_or(DOCS_LIST_MAX_LIMIT, |l| l.min(DOCS_LIST_MAX_LIMIT));
    qb.push(" LIMIT ");
    qb.push_bind(i64::from(limit));

    qb
}

fn emit_condition<'a>(
    qb: &mut QueryBuilder<'a, Postgres>,
    cond: &'a crate::docs_filter::FieldCondition,
) {
    push_jsonb_path(qb, cond.path.segments());
    match cond.op {
        ComparisonOp::Eq => {
            if cond.value.is_null() {
                qb.push(" IS NULL");
            } else {
                qb.push(" = ");
                qb.push_bind(value_to_text(&cond.value));
            }
        }
        ComparisonOp::Ne => {
            // IS DISTINCT FROM correctly handles NULL on either side
            // (would otherwise silently exclude rows with missing
            // paths). Holds for the literal-NULL case too.
            if cond.value.is_null() {
                qb.push(" IS NOT NULL");
            } else {
                qb.push(" IS DISTINCT FROM ");
                qb.push_bind(value_to_text(&cond.value));
            }
        }
        ComparisonOp::Gt => {
            qb.push(" > ");
            qb.push_bind(value_to_text(&cond.value));
        }
        ComparisonOp::Gte => {
            qb.push(" >= ");
            qb.push_bind(value_to_text(&cond.value));
        }
        ComparisonOp::Lt => {
            qb.push(" < ");
            qb.push_bind(value_to_text(&cond.value));
        }
        ComparisonOp::Lte => {
            qb.push(" <= ");
            qb.push_bind(value_to_text(&cond.value));
        }
        ComparisonOp::In => {
            qb.push(" = ANY(");
            let texts: Vec<Option<String>> = cond
                .value
                .as_array()
                .map(|arr| arr.iter().map(value_to_text).collect())
                .unwrap_or_default();
            qb.push_bind(texts);
            qb.push(")");
        }
    }
}

/// Append `jsonb_extract_path_text(data, $N1, $N2, …)` with each
/// segment bound as a separate text parameter. Variadic path lengths
/// (1–5) all flow through this single helper.
fn push_jsonb_path<'a>(qb: &mut QueryBuilder<'a, Postgres>, segments: &'a [String]) {
    qb.push("jsonb_extract_path_text(data");
    for seg in segments {
        qb.push(", ");
        qb.push_bind(seg.as_str());
    }
    qb.push(")");
}

/// JSON scalar → TEXT for binding. `Value::Null` is preserved as
/// `None` so the binding lands as SQL NULL (handled specially above for
/// `Eq` / `Ne`). Arrays + objects serialize to compact JSON; the user
/// is comparing against the JSONB text rendering, which is consistent
/// with `jsonb_extract_path_text`'s output for those types.
fn value_to_text(v: &Value) -> Option<String> {
    match v {
        Value::Null => None,
        Value::String(s) => Some(s.clone()),
        Value::Bool(b) => Some(b.to_string()),
        Value::Number(n) => Some(n.to_string()),
        Value::Array(_) | Value::Object(_) => Some(v.to_string()),
    }
}

// ----------------------------------------------------------------------------
// SQL-shape guardrail tests — pure (no DB) so they run in the default
// test suite. These are the highest-stakes tests in the release: they
// pin the cross-app isolation invariant at the SQL level.
// ----------------------------------------------------------------------------

#[cfg(test)]
mod sql_shape_tests {
    use super::*;
    use crate::docs_filter::parse_filter;
    use serde_json::json;

    fn sql_for(filter_json: serde_json::Value) -> String {
        let filter = parse_filter(&filter_json).unwrap();
        let qb = build_find_query(AppId::new(), "users", &filter);
        qb.sql().to_string()
    }

    /// **Load-bearing**: every generated SELECT begins
    /// `WHERE app_id = $1 AND collection = $2`. The app_id parameter
    /// is the cross-app isolation gate. No user-supplied filter
    /// fragment can ever appear before these clauses.
    #[test]
    fn every_query_starts_with_app_id_and_collection_predicate() {
        let cases = vec![
            json!({}),
            json!({ "tier": "gold" }),
            json!({ "created_at": { "$gt": "2026-01-01" } }),
            json!({ "tier": { "$in": ["gold", "platinum"] } }),
            json!({ "tier": "gold", "status": "active" }),
            json!({ "$sort": { "created_at": -1 }, "$limit": 5 }),
            json!({ "tier": "gold", "$sort": { "created_at": 1 } }),
            json!({ "deleted_at": { "$ne": null } }),
        ];
        for case in cases {
            let sql = sql_for(case.clone());
            assert!(
                sql.starts_with(
                    "SELECT id, data, created_at, updated_at FROM docs WHERE app_id = $1 AND collection = $2"
                ),
                "filter {case} produced SQL: {sql}"
            );
        }
    }

    /// Every comparison value lands as a `$N` placeholder — there
    /// should be NO double-quoted string literal in the SQL after the
    /// fixed prefix. (This guards against an accidental `format!`
    /// regression.)
    #[test]
    fn no_user_string_literal_in_sql() {
        let sql = sql_for(json!({ "tier": "gold; DROP TABLE docs;--" }));
        assert!(!sql.contains("gold"), "value leaked into SQL string: {sql}");
        assert!(!sql.contains("DROP"), "value leaked into SQL string: {sql}");
    }

    /// Field-path segments also bind as parameters. A user passing a
    /// path that looks like SQL keywords doesn't change the structure.
    #[test]
    fn no_user_path_literal_in_sql() {
        let sql = sql_for(json!({ "drop_table_users": "v" }));
        assert!(
            !sql.contains("drop_table_users"),
            "path leaked into SQL string: {sql}"
        );
    }

    #[test]
    fn empty_filter_sql_has_no_extra_conditions() {
        let sql = sql_for(json!({}));
        // After the fixed prefix, only ORDER BY + LIMIT — no `AND`s.
        let suffix = sql
            .trim_start_matches(
                "SELECT id, data, created_at, updated_at FROM docs WHERE app_id = $1 AND collection = $2",
            )
            .trim();
        assert!(
            suffix.starts_with("ORDER BY"),
            "expected ORDER BY immediately after base WHERE; got: {suffix}"
        );
    }

    #[test]
    fn eq_with_null_emits_is_null() {
        let sql = sql_for(json!({ "x": null }));
        assert!(sql.contains("IS NULL"), "sql: {sql}");
    }

    #[test]
    fn ne_with_null_emits_is_not_null() {
        let sql = sql_for(json!({ "x": { "$ne": null } }));
        assert!(sql.contains("IS NOT NULL"), "sql: {sql}");
    }

    #[test]
    fn ne_with_value_uses_is_distinct_from() {
        // IS DISTINCT FROM, NOT <> — see ComparisonOp::Ne comment.
        let sql = sql_for(json!({ "x": { "$ne": "v" } }));
        assert!(sql.contains("IS DISTINCT FROM"), "sql: {sql}");
        assert!(!sql.contains(" <> "), "sql: {sql}");
    }

    #[test]
    fn in_emits_any_array() {
        let sql = sql_for(json!({ "x": { "$in": ["a", "b"] } }));
        assert!(sql.contains("= ANY"), "sql: {sql}");
    }

    #[test]
    fn sort_appends_tiebreaker_id_asc() {
        let sql = sql_for(json!({ "$sort": { "created_at": -1 } }));
        assert!(sql.contains("DESC, id ASC"), "sql: {sql}");
    }

    #[test]
    fn jsonb_extract_path_used_for_field_access() {
        let sql = sql_for(json!({ "user.email": "a@b" }));
        assert!(sql.contains("jsonb_extract_path_text(data"), "sql: {sql}");
    }
}