sqlstr 0.1.0

Sql string builder
Documentation 
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use alloc::string::String;
use core::convert::Infallible;

use crate::format_num::format_u32_base10;

pub trait ArgumentBuffer<T> {
    type Error;

    /// Push a new argument into the buffer
    fn push(&mut self, value: T) -> Result<(), Self::Error>;

    /// Returns the number of arguments pushed into `Self`
    fn count(&self) -> u32;
}

pub trait WriteSql<Arg> {
    fn push_expr<T>(&mut self, operand: SqlExpr<'_, T>) -> Result<(), Arg::Error>
    where
        Arg: ArgumentBuffer<T>;

    fn push_value<T>(&mut self, value: T) -> Result<(), Arg::Error>
    where
        Arg: ArgumentBuffer<T>;

    fn push_cmd(&mut self, expr: &str);

    fn as_command(&self) -> &str;
}

/// SQL Fragment
#[cfg_attr(any(feature = "fmt", test, debug_assertions), derive(Debug))]
#[derive(Clone, PartialEq, Eq, PartialOrd, Ord)]
pub enum SqlExpr<'ex, T> {
    /// Value of a sql command argument.
    Value(T),
    /// Expression of a sql command.
    Expr(&'ex str),
}

pub const fn sqlexpr<T>(expr: &str) -> SqlExpr<'_, T> {
    SqlExpr::Expr(expr)
}

pub const fn sqlvalue<T>(expr: T) -> SqlExpr<'static, T> {
    SqlExpr::Value(expr)
}

#[cfg_attr(any(feature = "fmt", test, debug_assertions), derive(Debug))]
#[derive(Clone, Default, PartialEq, Eq)]
pub struct SqlCommand<Arg> {
    pub command: String,
    pub arguments: Arg,
}

impl<Arg> SqlCommand<Arg> {
    pub const fn new(command: String, arguments: Arg) -> Self {
        Self { command, arguments }
    }

    pub fn push_expr<T>(&mut self, operand: SqlExpr<'_, T>) -> Result<(), Arg::Error>
    where
        Arg: ArgumentBuffer<T>,
    {
        match operand {
            SqlExpr::Value(val) => self.push_value(val)?,
            SqlExpr::Expr(expr) => self.command.push_str(expr),
        }
        Ok(())
    }

    pub fn push_value<T>(&mut self, value: T) -> Result<(), Arg::Error>
    where
        Arg: ArgumentBuffer<T>,
    {
        self.arguments.push(value)?;
        let mut buf = [0; 10];
        self.command.push('$');
        self.command
            .push_str(format_u32_base10(self.arguments.count(), &mut buf));
        Ok(())
    }

    pub fn push_cmd(&mut self, expr: &str) {
        self.command.push_str(expr);
    }

    pub fn as_command(&self) -> &str {
        self.command.as_str()
    }
}

impl<Arg> WriteSql<Arg> for SqlCommand<Arg> {
    fn push_expr<T>(&mut self, operand: SqlExpr<'_, T>) -> Result<(), Arg::Error>
    where
        Arg: ArgumentBuffer<T>,
    {
        SqlCommand::push_expr(self, operand)
    }

    fn push_value<T>(&mut self, val: T) -> Result<(), <Arg>::Error>
    where
        Arg: ArgumentBuffer<T>,
    {
        SqlCommand::push_value(self, val)
    }

    fn push_cmd(&mut self, expr: &str) {
        SqlCommand::push_cmd(self, expr)
    }

    fn as_command(&self) -> &str {
        self.command.as_str()
    }
}

/// Void argument buffer
///
/// This [ArgumentBuffer] does not hold any argument written.
#[cfg_attr(any(feature = "fmt", test, debug_assertions), derive(Debug))]
#[derive(Default, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub struct Void(u32);

impl Void {
    pub const fn new() -> Self {
        Self(0)
    }

    pub const fn with_count(count: u32) -> Self {
        Self(count)
    }

    pub const fn count(&self) -> u32 {
        self.0
    }
}

impl<T> ArgumentBuffer<T> for Void {
    type Error = Infallible;

    fn push(&mut self, _: T) -> Result<(), Self::Error> {
        self.0 += 1;
        Ok(())
    }

    fn count(&self) -> u32 {
        self.0
    }
}