//! Programmer mode evaluator for Tally.
//!
//! All operations use exact integer arithmetic (u128 storage), with results masked
//! to the configured width. No floating-point involved. The bitwise operators, the
//! shifts and the rotations live in `bitwise.zig`, which standard mode shares; what
//! is here is the wrapping arithmetic and the walk over the tree.

const std = @import("std");
const Allocator = std.mem.Allocator;
const ast = @import("ast.zig");
const Expr = ast.Expr;
const BinaryOp = ast.BinaryOp;
const Integer = @import("Integer.zig");
const BitWidth = Integer.BitWidth;
const Signedness = Integer.Signedness;
const Parser = @import("Parser.zig");
const bitwise = @import("bitwise.zig");
const number_mod = @import("number.zig");
const Number = number_mod.Number;

/// What programmer-mode evaluation can fail with: the parse, the fixed-width
/// operators, its own arithmetic and name errors, and the exact parse of a decimal
/// literal (`number_mod.Error`), since that is how a literal becomes a value here.
pub const Error = error{
    DivisionByZero,
    DomainError,
    InvalidNumber,
    InvalidOperandType,
    Overflow,
    UnknownFunction,
    UnknownVariable,
} || Parser.Error || bitwise.Error || number_mod.Error;

/// What programmer mode needs to know: the integer type to compute in, and one
/// display preference that does not affect arithmetic.
pub const Config = struct {
    width: BitWidth = .bits64,
    signedness: Signedness = .signed,
    /// Byte order for the HEX and ASCII rows only. Defaults to big-endian so the
    /// HEX row reads as the number itself (matching DEC/OCT/BIN); the little-endian
    /// view (x86 memory layout) is available via the toggle.
    display_endian: std.builtin.Endian = .big,

    /// A value of the configured integer type. Every literal and every result goes
    /// through here, so the width and signedness are attached once rather than
    /// tracked alongside a bare pattern.
    pub fn value(self: Config, raw: u128) Integer {
        return .{ .raw = raw & self.width.mask(), .width = self.width, .signedness = self.signedness };
    }
};

/// Evaluate an AST in programmer mode, producing an exact integer result.
///
/// The allocator is for parsing decimal literals, which go through the exact tier so
/// that `3.99` truncates the value the user wrote rather than an f64's approximation
/// of it. Nothing else here allocates.
///
/// There used to be a `pub fn evalProgrammer` in front of this that forwarded to it
/// and nothing else. Its only caller was `evalProgrammerString` below, in this file,
/// so the parser-facing entry point was public API with no consumer.
fn evalExpr(allocator: Allocator, config: Config, expr: *const Expr) Error!Integer {
    switch (expr.*) {
        .number => |n| return literalToInteger(allocator, config, n),
        .string_literal => |text| {
            // Pack ASCII bytes into integer.
            // Big-endian packing: first char -> most significant used byte.
            const max_bytes = @as(usize, config.width.bits()) / 8;
            if (text.len > max_bytes) return Error.Overflow;
            var result: u128 = 0;
            for (text) |byte| {
                if (byte > 0x7F) return Error.InvalidNumber;
                result = (result << 8) | byte;
            }
            return config.value(result);
        },
        .variable => {
            return Error.UnknownVariable;
        },
        .assignment => {
            return Error.InvalidOperandType;
        },
        .unary => |u| {
            const operand = try evalExpr(allocator, config, u.operand);
            return switch (u.op) {
                .negate => bitwise.negate(operand),
                .bitwise_not => bitwise.not(operand),
            };
        },
        .binary => |b| {
            const left = try evalExpr(allocator, config, b.left);
            const right = try evalExpr(allocator, config, b.right);
            return evalBinaryOp(b.op, left, right);
        },
        .call => {
            // No function calls in programmer mode
            return Error.UnknownFunction;
        },
    }
}

/// A literal as a value of the configured integer type.
///
/// A non-decimal literal is a bit pattern and converts directly. A decimal literal
/// is a number, so it is parsed exactly and then truncated toward zero: programmer
/// mode computes on integers, and `3.99` means 3.
///
/// The truncation used to run through an f64, which cost precision on the way in
/// (`1e30` arrived as 1000000000000000019884624838656) and needed range guards
/// because `@intFromFloat` on an out-of-range value is illegal behaviour: `tally -p
/// '1e40'` aborted the process before those guards existed. Parsing exactly removes
/// both problems, since a value too wide for the width is simply `Overflow`.
fn literalToInteger(allocator: Allocator, config: Config, n: ast.Expr.Number) Error!Integer {
    if (n.base != .decimal) return config.value(try n.base.parseDigits(n.text));

    var parsed = try Number.parse(allocator, n.text);
    defer parsed.deinit();
    // Literals are never negative here: unary minus is its own operator.
    var whole = try Number.floor(allocator, parsed);
    defer whole.deinit();
    return config.value(whole.asExactInt(u128) orelse return Error.Overflow);
}

/// Evaluate a binary operation on two values of the configured type.
///
/// The bitwise operators, shifts and rotations are not here: they live in
/// `bitwise.zig`, which standard mode uses too, so the two modes cannot drift
/// apart again. What remains is the arithmetic, which genuinely differs between the
/// modes: it wraps at the width here and is exact rational arithmetic there.
fn evalBinaryOp(op: BinaryOp, left_in: Integer, right_in: Integer) Error!Integer {
    const mask = left_in.width.mask();
    const left = left_in.unsignedValue();
    const right = right_in.unsignedValue();

    const raw: u128 = switch (op) {
        .add => left +% right,
        .sub => left -% right,
        .mul => left *% right,
        .div => blk: {
            if (right == 0) return Error.DivisionByZero;
            break :blk left / right;
        },
        .mod => blk: {
            if (right == 0) return Error.DivisionByZero;
            break :blk left % right;
        },
        .pow => blk: {
            // Integer exponentiation
            var base = left;
            var exp = right;
            var acc: u128 = 1;
            while (exp > 0) : (exp >>= 1) {
                if (exp & 1 != 0) acc = (acc *% base) & mask;
                base = (base *% base) & mask;
            }
            break :blk acc;
        },
        // The fixed-width operators, in the shared implementation. `inline else`
        // resolves the operator at comptime, so an operator added to `BinaryOp`
        // that `bitwise.fromBinaryOp` does not know is a compile error here.
        inline else => |fixed_op| return try bitwise.apply(
            comptime bitwise.fromBinaryOp(fixed_op).?,
            left_in,
            right_in,
        ),
    };

    return left_in.withRaw(raw);
}

/// High-level: parse and evaluate a string in programmer mode.
pub fn evalProgrammerString(allocator: Allocator, source: []const u8, config: Config) Error!Integer {
    var p = Parser.init(allocator, source);
    const expr = try p.parse();
    // Same ownership rule as evalStringInfo: the tree is ours to release, and the
    // returned Integer does not borrow from it.
    defer Parser.freeExpr(allocator, expr);
    return evalExpr(allocator, config, expr);
}

// -- Tests --

const testing = std.testing;

fn testProg(source: []const u8) !Integer {
    return testProgWith(source, .{});
}

/// Tests care about the width and signedness, never about the display byte order,
/// so they pass a partial config.
fn testProgWith(source: []const u8, config: Config) !Integer {
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer _ = arena.deinit();
    return evalProgrammerString(arena.allocator(), source, config);
}

test "prog: simple number" {
    const result = try testProg("42");
    try testing.expectEqual(@as(u128, 42), result.unsignedValue());
}

test "prog: hex number" {
    const result = try testProg("0xFF");
    try testing.expectEqual(@as(u128, 255), result.unsignedValue());
}

test "prog: binary number" {
    const result = try testProg("0b1010");
    try testing.expectEqual(@as(u128, 10), result.unsignedValue());
}

test "prog: addition" {
    const result = try testProg("10 + 20");
    try testing.expectEqual(@as(u128, 30), result.unsignedValue());
}

test "prog: subtraction wrapping" {
    // 5 - 10 in 8-bit unsigned wraps
    const result = try testProgWith("5 - 10", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 251), result.unsignedValue()); // 256 - 5
    try testing.expectEqual(@as(i128, -5), result.signedValue());
}

test "prog: multiplication" {
    const result = try testProg("6 * 7");
    try testing.expectEqual(@as(u128, 42), result.unsignedValue());
}

test "prog: multiplication overflow 8-bit" {
    const result = try testProgWith("200 * 2", .{ .width = .bits8 });
    // 400 & 0xFF = 144
    try testing.expectEqual(@as(u128, 144), result.unsignedValue());
}

test "prog: division" {
    const result = try testProg("100 / 4");
    try testing.expectEqual(@as(u128, 25), result.unsignedValue());
}

test "prog: division by zero" {
    const result = testProg("10 / 0");
    try testing.expectError(Error.DivisionByZero, result);
}

test "prog: modulo" {
    const result = try testProg("10 % 3");
    try testing.expectEqual(@as(u128, 1), result.unsignedValue());
}

test "prog: power" {
    const result = try testProg("2 ** 10");
    try testing.expectEqual(@as(u128, 1024), result.unsignedValue());
}

test "prog: bitwise AND" {
    const result = try testProg("0xFF & 0x0F");
    try testing.expectEqual(@as(u128, 0x0F), result.unsignedValue());
}

test "prog: bitwise OR" {
    const result = try testProg("0xF0 | 0x0F");
    try testing.expectEqual(@as(u128, 0xFF), result.unsignedValue());
}

test "prog: bitwise XOR" {
    const result = try testProg("0xFF xor 0x0F");
    try testing.expectEqual(@as(u128, 0xF0), result.unsignedValue());
}

test "prog: caret is power not XOR" {
    // 0x2 ^ 0x3 = 2^3 = 8 (power), NOT 1 (XOR)
    const result = try testProg("0x2 ^ 0x3");
    try testing.expectEqual(@as(u128, 8), result.unsignedValue());
}

test "prog: and/or/not keywords" {
    const a = try testProg("0xFF and 0x0F");
    try testing.expectEqual(@as(u128, 0x0F), a.unsignedValue());
    const o = try testProg("0xF0 or 0x0F");
    try testing.expectEqual(@as(u128, 0xFF), o.unsignedValue());
    const n = try testProgWith("not 0x0F", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0xF0), n.unsignedValue());
}

test "prog: bitwise NOT 8-bit" {
    const result = try testProgWith("~0x0F", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0xF0), result.unsignedValue());
}

test "prog: bitwise NOT 16-bit" {
    const result = try testProgWith("~0x00FF", .{ .width = .bits16 });
    try testing.expectEqual(@as(u128, 0xFF00), result.unsignedValue());
}

test "prog: bitwise NOT 32-bit" {
    const result = try testProgWith("~0", .{ .width = .bits32 });
    try testing.expectEqual(@as(u128, 0xFFFF_FFFF), result.unsignedValue());
}

test "prog: shift left" {
    const result = try testProg("1 << 8");
    try testing.expectEqual(@as(u128, 256), result.unsignedValue());
}

test "prog: shift left past the width shifts everything out" {
    // The distance used to be clamped to width - 1, so this gave 128.
    const result = try testProgWith("1 << 8", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0), result.unsignedValue());

    // One less than the width still keeps the bit.
    const edge = try testProgWith("1 << 7", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 128), edge.unsignedValue());
}

test "prog: logical shift right" {
    const result = try testProgWith("0x80 >>> 4", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0x08), result.unsignedValue());
}

test "prog: arithmetic shift right (sign bit preserved)" {
    // 0x80 in 8-bit is -128; >> 1 should give 0xC0 (-64)
    const result = try testProgWith("0x80 >> 1", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0xC0), result.unsignedValue());
    try testing.expectEqual(@as(i128, -64), result.signedValue());
}

test "prog: arithmetic shift right (positive)" {
    // 0x40 in 8-bit is positive; >> 1 should give 0x20
    const result = try testProgWith("0x40 >> 1", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0x20), result.unsignedValue());
}

test "prog: rotate left 8-bit" {
    // 0x81 rol 1 in 8-bit: bit 7 wraps to bit 0 -> 0x03
    const result = try testProgWith("0x81 rol 1", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0x03), result.unsignedValue());
}

test "prog: rotate right 8-bit" {
    // 0x81 ror 1 in 8-bit: bit 0 wraps to bit 7 -> 0xC0
    const result = try testProgWith("0x81 ror 1", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0xC0), result.unsignedValue());
}

test "prog: negation two's complement" {
    const result = try testProgWith("-1", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0xFF), result.unsignedValue());
    try testing.expectEqual(@as(i128, -1), result.signedValue());
}

test "prog: negation 16-bit" {
    const result = try testProgWith("-42", .{ .width = .bits16 });
    try testing.expectEqual(@as(i128, -42), result.signedValue());
}

test "prog: complex expression" {
    // (0xFF & 0x0F) | (1 << 4) = 0x0F | 0x10 = 0x1F
    const result = try testProg("(0xFF & 0x0F) | (1 << 4)");
    try testing.expectEqual(@as(u128, 0x1F), result.unsignedValue());
}

test "prog: precedence AND before OR" {
    // 0xF0 | 0xFF & 0x0F = 0xF0 | (0xFF & 0x0F) = 0xF0 | 0x0F = 0xFF
    const result = try testProg("0xF0 | 0xFF & 0x0F");
    try testing.expectEqual(@as(u128, 0xFF), result.unsignedValue());
}

test "prog: chained shifts" {
    const result = try testProg("1 << 4 << 2");
    // Left-associative: (1 << 4) << 2 = 16 << 2 = 64
    try testing.expectEqual(@as(u128, 64), result.unsignedValue());
}

test "prog: mask applied to input" {
    // 0x1FF in 8-bit mode should be masked to 0xFF
    const result = try testProgWith("0x1FF", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0xFF), result.unsignedValue());
}

test "prog: 32-bit operations" {
    const result = try testProgWith("0xFFFF_FFFF + 1", .{ .width = .bits32 });
    try testing.expectEqual(@as(u128, 0), result.unsignedValue());
}

test "prog: 64-bit max" {
    const result = try testProgWith("~0", .{ .width = .bits64 });
    try testing.expectEqual(@as(u128, 0xFFFF_FFFF_FFFF_FFFF), result.unsignedValue());
}

test "prog: negative float input" {
    // -5.0 as a float in programmer mode should become two's complement
    const result = try testProgWith("-5", .{ .width = .bits8 });
    try testing.expectEqual(@as(i128, -5), result.signedValue());
}

test "prog: variable reference errors" {
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer _ = arena.deinit();
    const result = evalProgrammerString(arena.allocator(), "x", .{});
    try testing.expectError(Error.UnknownVariable, result);
}

test "prog: assignment errors" {
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer _ = arena.deinit();
    const result = evalProgrammerString(arena.allocator(), "X = 5", .{});
    try testing.expectError(Error.InvalidOperandType, result);
}

test "prog: function call errors" {
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer _ = arena.deinit();
    const result = evalProgrammerString(arena.allocator(), "sin(1)", .{});
    try testing.expectError(Error.UnknownFunction, result);
}

test "prog: ASCII literal single char" {
    const result = try testProg("'A'");
    try testing.expectEqual(@as(u128, 0x41), result.unsignedValue());
}

test "prog: ASCII literal multi char" {
    const result = try testProg("'ELF'");
    try testing.expectEqual(@as(u128, 0x454C46), result.unsignedValue());
}

test "prog: ASCII literal full word" {
    const result = try testProg("'ascii'");
    try testing.expectEqual(@as(u128, 0x6173636969), result.unsignedValue());
}

test "prog: ASCII literal in expression" {
    const result = try testProg("'A' | 0x20");
    // 0x41 | 0x20 = 0x61 = 'a'
    try testing.expectEqual(@as(u128, 0x61), result.unsignedValue());
}

test "prog: ASCII literal overflow 8-bit" {
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    defer _ = arena.deinit();
    const result = evalProgrammerString(arena.allocator(), "'AB'", .{ .width = .bits8 });
    try testing.expectError(Error.Overflow, result);
}

test "prog: float literal truncates to integer" {
    // Programmer mode computes on integers, so a fractional literal truncates.
    const result = try testProg("3.14");
    try testing.expectEqual(@as(u128, 3), result.unsignedValue());
}

test "prog: arithmetic shift right past the width leaves the sign fill" {
    // 0xFF in 8-bit is -1; shifting a negative value all the way out leaves every
    // bit set, which is still -1. The distance used to be clamped to width - 1,
    // which reached the same answer here for the wrong reason.
    const result = try testProgWith("0xFF >> 20", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0xFF), result.unsignedValue());
    try testing.expectEqual(@as(i128, -1), result.signedValue());
}

test "prog: logical shift right past the width shifts everything out" {
    // Used to clamp the distance to 7 and give 1.
    const result = try testProgWith("0xFF >>> 20", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0), result.unsignedValue());

    // One less than the width still keeps the bottom bit.
    const edge = try testProgWith("0xFF >>> 7", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 1), edge.unsignedValue());
}

test "prog: arithmetic shift right past the width, positive value" {
    // 0x40 in 8-bit is positive, so the fill is zeros and everything shifts out.
    const result = try testProgWith("0x40 >> 20", .{ .width = .bits8 });
    try testing.expectEqual(@as(u128, 0), result.unsignedValue());
}

test "no leak: evalProgrammerString releases the parsed tree" {
    // testing.allocator rather than an arena, so a retained AST fails the test.
    const config: Config = .{};
    const good = [_][]const u8{ "0xFF and 0x0F", "1 << 8", "not 0", "0b1010 xor 0b0101", "5 rol 2" };
    for (good) |source| {
        _ = try evalProgrammerString(std.testing.allocator, source, config);
    }

    const bad = [_][]const u8{ "0xFF and", "1 <<", "(1 | 2" };
    for (bad) |source| {
        _ = evalProgrammerString(std.testing.allocator, source, config) catch continue;
        return error.TestUnexpectedResult;
    }
}

test "programmer mode: a decimal literal truncates exactly, and past the width overflows" {
    const config: Config = .{};
    // `tally -p '1e40'` used to abort the process: `@intFromFloat` on a value past
    // u128 is illegal behaviour. There is no float on this path any more, so a
    // literal too wide for the pattern is simply an overflow.
    try std.testing.expectError(
        Error.Overflow,
        evalProgrammerString(std.testing.allocator, "1e40", config),
    );
    try std.testing.expectError(
        Error.Overflow,
        evalProgrammerString(std.testing.allocator, "1e100", config),
    );
    // 10^400 is a 401-digit integer, which the exact tier parses without complaint
    // and no width can hold. It used to report DomainError, because the f64
    // projection of it was infinity.
    try std.testing.expectError(
        Error.Overflow,
        evalProgrammerString(std.testing.allocator, "1e400", config),
    );

    // Fractional literals still truncate toward zero: programmer mode computes on
    // integers.
    const small = try evalProgrammerString(std.testing.allocator, "3.99", config);
    try std.testing.expectEqual(@as(u128, 3), small.unsignedValue());

    // And the truncation is of the value written, not of an f64 of it. Through the
    // old float path this arrived as 1000000000000000019884624838656.
    const exact = try evalProgrammerString(std.testing.allocator, "1e30", .{ .width = .bits128 });
    try std.testing.expectEqual(@as(u128, 1_000_000_000_000_000_000_000_000_000_000), exact.unsignedValue());
}

test "programmer mode: the full width is reachable from every base" {
    // Open item 11: the tokenizer's `int_value` was a u64, so a literal wider than
    // 64 bits was "invalid number" in a mode whose widest type is 128 bits.
    const config: Config = .{ .width = .bits128, .signedness = .unsigned };
    const cases = [_][]const u8{
        "0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF",
        "340282366920938463463374607431768211455",
        "0o3777777777777777777777777777777777777777777",
    };
    for (cases) |source| {
        const result = try evalProgrammerString(std.testing.allocator, source, config);
        try std.testing.expectEqual(std.math.maxInt(u128), result.unsignedValue());
    }

    const seventeen_nibbles = try evalProgrammerString(std.testing.allocator, "0x1FFFFFFFFFFFFFFFF", config);
    try std.testing.expectEqual(@as(u128, 0x1FFFFFFFFFFFFFFFF), seventeen_nibbles.unsignedValue());
}