// Copyright (c) 2026 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
// vtest build: macos
//
// Bit-equality pin for s174: `build_fn_bodies_from_flat` (flat-cursor port)
// must build the same SSA bodies as the legacy `build_fn_bodies`. The flat
// port walks one file's top-level stmts via FileCursor and reads FnDecl
// signatures, filters, params, and body statements directly from cursors.
// Non-FnDecl stmts (ModuleStmt, StructDecl, EnumDecl, ConstDecl, etc.) are
// never decoded.
module ssa

import v2.ast
import v2.types

fn make_build_fn_bodies_fixture() []ast.File {
    return [
        ast.File{
            name:  'main.v'
            mod:   'main'
            stmts: [
                ast.Stmt(ast.ModuleStmt{
                    name: 'main'
                }),
                ast.Stmt(ast.FnDecl{
                    name:  'answer'
                    typ:   ast.FnType{
                        return_type: ast.Expr(ast.Ident{
                            name: 'int'
                        })
                    }
                    stmts: [
                        ast.Stmt(ast.ReturnStmt{
                            exprs: [
                                ast.Expr(ast.BasicLiteral{
                                    kind:  .number
                                    value: '42'
                                }),
                            ]
                        }),
                    ]
                }),
                ast.Stmt(ast.FnDecl{
                    name: 'noop'
                    typ:  ast.FnType{}
                }),
            ]
        },
    ]
}

// build_fn_bodies_from_flat on a file with no fns must not build any
// function bodies — same as build_fn_bodies.
fn test_build_fn_bodies_from_flat_no_fns_matches_legacy() {
    files := [
        ast.File{
            name:  'empty.v'
            mod:   'main'
            stmts: [ast.Stmt(ast.ModuleStmt{
                name: 'main'
            })]
        },
    ]
    flat := ast.flatten_files(files)

    env := types.Environment.new()

    mut mod_legacy := Module.new('bfb_empty_legacy')
    mut b_legacy := Builder.new_with_env(mod_legacy, env)
    b_legacy.build_fn_bodies(files[0])

    mut mod_flat := Module.new('bfb_empty_flat')
    mut b_flat := Builder.new_with_env(mod_flat, env)
    b_flat.build_fn_bodies_from_flat(flat.file_cursor(0))

    // Neither path built any function bodies.
    assert mod_legacy.funcs.len == mod_flat.funcs.len
    assert mod_legacy.blocks.len == mod_flat.blocks.len
    assert mod_legacy.instrs.len == mod_flat.instrs.len
}

// build_fn_bodies_from_flat on a file with two FnDecls (answer + noop) must
// build identical SSA bodies — same number of funcs, blocks, and instrs.
fn test_build_fn_bodies_from_flat_matches_legacy_for_two_fns() {
    files := make_build_fn_bodies_fixture()
    flat := ast.flatten_files(files)

    env := types.Environment.new()

    mut mod_legacy := Module.new('bfb_two_legacy')
    mut b_legacy := Builder.new_with_env(mod_legacy, env)
    // build_fn requires fn_index populated (register_fn_signatures runs in
    // Phase 3 before Phase 4 in legacy build_all).
    b_legacy.register_fn_signatures(files[0])
    b_legacy.build_fn_bodies(files[0])

    mut mod_flat := Module.new('bfb_two_flat')
    mut b_flat := Builder.new_with_env(mod_flat, env)
    b_flat.register_fn_signatures_from_flat(flat.file_cursor(0))
    b_flat.build_fn_bodies_from_flat(flat.file_cursor(0))

    // Both paths registered + built 2 fns.
    assert mod_legacy.funcs.len == mod_flat.funcs.len
    assert mod_legacy.funcs.len == 2
    // Same number of basic blocks on both paths (identical control flow).
    assert mod_legacy.blocks.len == mod_flat.blocks.len
    // Same number of instructions emitted (return 42 + return void).
    assert mod_legacy.instrs.len == mod_flat.instrs.len
    // Same number of SSA values.
    assert mod_legacy.values.len == mod_flat.values.len
}