// This file is part of Moonfire NVR, a security camera network video recorder.
// Copyright (C) 2020 The Moonfire NVR Authors; see AUTHORS and LICENSE.txt.
// SPDX-License-Identifier: GPL-v3.0-or-later WITH GPL-3.0-linking-exception.

//! Comparison of actual and expected on-disk schema.
//! This is used as part of the `moonfire-nvr check` database integrity checking
//! and for tests of `moonfire-nvr upgrade`.

use base::Error;
use rusqlite::params;
use std::fmt::Write;

#[derive(Debug, PartialEq)]
struct Column {
    cid: u32,
    name: String,
    type_: String,
    notnull: bool,
    dflt_value: rusqlite::types::Value,
    pk: u32,
}

impl std::fmt::Display for Column {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{self:?}")
    }
}

#[derive(Debug, Eq, PartialEq)]
struct Index {
    seq: u32,
    name: String,
    unique: bool,
    origin: String,
    partial: bool,
}

impl std::fmt::Display for Index {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{self:?}")
    }
}

#[derive(Debug, Eq, PartialEq)]
struct IndexColumn {
    seqno: u32,
    cid: u32,
    name: String,
}

impl std::fmt::Display for IndexColumn {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{self:?}")
    }
}

/// If `slice1` and `slice2` differ, return differences in roughly unified diff form.
fn diff_slices<T: std::fmt::Display + PartialEq>(
    name1: &str,
    slice1: &[T],
    name2: &str,
    slice2: &[T],
) -> Option<String> {
    let mut diff = format!("--- {name1}\n+++ {name2}\n");
    let mut changed = false;
    for item in diff::slice(slice1, slice2) {
        match item {
            diff::Result::Left(i) => {
                changed = true;
                writeln!(&mut diff, "-{i}")
            }
            diff::Result::Both(i, _) => writeln!(&mut diff, " {i}"),
            diff::Result::Right(i) => {
                changed = true;
                writeln!(&mut diff, "+{i}")
            }
        }
        .unwrap();
    }
    if !changed {
        return None;
    }
    Some(diff)
}

/// Returns a sorted vec of table names in the given connection.
fn get_tables(c: &rusqlite::Connection) -> Result<Vec<String>, rusqlite::Error> {
    c.prepare(
        r#"
        select
            name
        from
            sqlite_master
        where
            type = 'table' and
            name not like 'sqlite_%'
        order by name
        "#,
    )?
    .query_map(params![], |r| r.get(0))?
    .collect()
}

/// Returns a vec of columns in the given table.
fn get_table_columns(
    c: &rusqlite::Connection,
    table: &str,
) -> Result<Vec<Column>, rusqlite::Error> {
    // Note that placeholders aren't allowed for these pragmas. Just assume sane table names
    // (no escaping). "select * from pragma_..." syntax would be nicer but requires SQLite
    // 3.16.0 (2017-01-02). Ubuntu 16.04 Xenial (still used on Travis CI) has an older SQLite.
    c.prepare(&format!("pragma table_info(\"{table}\")"))?
        .query_map(params![], |r| {
            Ok(Column {
                cid: r.get(0)?,
                name: r.get(1)?,
                type_: r.get(2)?,
                notnull: r.get(3)?,
                dflt_value: r.get(4)?,
                pk: r.get(5)?,
            })
        })?
        .collect()
}

/// Returns a vec of indices associated with the given table.
fn get_indices(c: &rusqlite::Connection, table: &str) -> Result<Vec<Index>, rusqlite::Error> {
    // See note at get_tables_columns about placeholders.
    c.prepare(&format!("pragma index_list(\"{table}\")"))?
        .query_map(params![], |r| {
            Ok(Index {
                seq: r.get(0)?,
                name: r.get(1)?,
                unique: r.get(2)?,
                origin: r.get(3)?,
                partial: r.get(4)?,
            })
        })?
        .collect()
}

/// Returns a vec of all the columns in the given index.
fn get_index_columns(
    c: &rusqlite::Connection,
    index: &str,
) -> Result<Vec<IndexColumn>, rusqlite::Error> {
    // See note at get_tables_columns about placeholders.
    c.prepare(&format!("pragma index_info(\"{index}\")"))?
        .query_map(params![], |r| {
            Ok(IndexColumn {
                seqno: r.get(0)?,
                cid: r.get(1)?,
                name: r.get(2)?,
            })
        })?
        .collect()
}

pub fn get_diffs(
    n1: &str,
    c1: &rusqlite::Connection,
    n2: &str,
    c2: &rusqlite::Connection,
) -> Result<Option<String>, Error> {
    let mut diffs = String::new();

    // Compare table list.
    let tables1 = get_tables(c1)?;
    let tables2 = get_tables(c2)?;
    if let Some(diff) = diff_slices(n1, &tables1[..], n2, &tables2[..]) {
        write!(&mut diffs, "table list mismatch, {n1} vs {n2}:\n{diff}")
            .expect("write to String shouldn't fail");
    }

    // Compare columns and indices for each table.
    for t in &tables1 {
        let columns1 = get_table_columns(c1, t)?;
        let columns2 = get_table_columns(c2, t)?;
        if let Some(diff) = diff_slices(n1, &columns1[..], n2, &columns2[..]) {
            write!(&mut diffs, "table {t:?} column, {n1} vs {n2}:\n{diff}")
                .expect("write to String shouldn't fail");
        }

        let mut indices1 = get_indices(c1, t)?;
        let mut indices2 = get_indices(c2, t)?;
        indices1.sort_by(|a, b| a.name.cmp(&b.name));
        indices2.sort_by(|a, b| a.name.cmp(&b.name));
        if let Some(diff) = diff_slices(n1, &indices1[..], n2, &indices2[..]) {
            write!(&mut diffs, "table {t:?} indices, {n1} vs {n2}:\n{diff}")
                .expect("write to String shouldn't fail");
        }

        for i in &indices1 {
            let ic1 = get_index_columns(c1, &i.name)?;
            let ic2 = get_index_columns(c2, &i.name)?;
            if let Some(diff) = diff_slices(n1, &ic1[..], n2, &ic2[..]) {
                write!(
                    &mut diffs,
                    "table {t:?} index {i:?} columns {n1} vs {n2}:\n{diff}"
                )
                .expect("write to String shouldn't fail");
            }
        }
    }

    Ok(if diffs.is_empty() { None } else { Some(diffs) })
}